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Review of literature
2. Review of literature
2.1. Growth parameters
Eucalyptus species are not consistent in their growth and the variation is considerable
depending upon the conditions under which they are grown. Therefore depending upon the site,
selection of species and their provenances the actual yields have varied considerably.
Phanuel Oballa et al., (2005) studied the growth performance of different Eucalyptus
clones and the seedlings and reported that, all the clones performed equally well at this site as
compared to the local landraces, clone GC14 had a height of 17.15 m while the local landraces E.
camaldulensis and E. tereticornis had the lowest height of 11.99 m and 11.58 m respectively. In
the case of DBH, there were significant differences in DBH in year three at p < 0.001. The best
performing clones and species at this site are GC15, GC581, GC14 and GC642. E. camaldulensis
and E. tereticornis did not perform well at this site, as they are more adapted to low and warmer
sites.
The varied growth trends in the different sites showed a strong environment-by-clone interaction,
an observation supported by Wamalwa et al., (2007).
Balozi Kirongo et al., (2010) reported that, the potential of Eucalyptus clones to
outperform local Eucalyptus species. However, the trial results for the local Eucalyptus species
recorded the mean height of 18.40 m (i.e. E. camaldulensis, E. tereticornis and E.urophylla)
were much poorer especially for E. urophylla with a mean height of 12.05 m compared to clones
in height and girth parameters.
Height of Eucalyptus differed significantly among different Eucalyptus species. E. hybrid
recorded significantly higher height (11.25 m) followed by E. grandis (10.90 m) and E.
tereticornis (10.35 m). Lowest height was recorded in E. pelleta (9.10 m). Height increment was
significantly higher in E. hybrid followed by E. tereticornis and E. grandis throughout the
growing season. The maximum height increments of 2.36 and 2.18 m were observed during 2005
in E. teriticornis and E. hybrid respectively. E. hybrid recorded significantly higher DBH (20.18
cm) followed by E. tereticornis (18.60 cm) and lowest diameter was observed in E. pelleta
(12.14 cm) and the clone selected from Dandeli (10.86 cm). Current annual increment in dbh was
significantly higher in E. tereticornis and E. hybrid and lowest was observed in E. pelleta. Mean
annual increment in DBH was significantly higher in E. tereticornis (2.33 cm) and E. hybrid
(2.52 cm) as compared to the clone selected from Dandeli (1.36 cm) (Patil et al., 2012).
Similarly significant differences in different Eucalyptus species have been reported by
various workers. Lal (2005) conducted a study to assess the comparative growth performance of
various Eucalyptus species. Kumar and Bangawa (2006) observed significant differences for
growth attributes among seven species of Eucalyptus species. Maximum MAI for diameter at
breast height was recorded in E. tereticornis and E. hybrid.
Patil et al., (2012) revealed that, among the Eucalyptus species maximum variation was
observed in E. tereticornis for all the characters under this study. Significantly higher values
were observed in current annual increment of total height, clear bole height and diameter
increment in E. tereticornis and E. hybrid. These results are in confirmation with results of
Gomes and Correia (1995) and Kumar and Bangarwa (2006).
Significant differences were observed between G×N hybrid clones in both growth and
snow tolerance. The top-performing clones significantly outperformed both pure species controls
in terms of growth and snow tolerance. Early results indicate that G×N hybrids may be better
suited to high-potential, mid-altitude sites exposed to light snow risk than the currently
recommended pure species (Iain Thompson, 2013).
Evaluation of Provenances of E. camaldulensis and clones of E. camaldulensis and E.
tereticornis at contrasting sites in Southern India by Varghese et al., (2008) revealed that,
interaction of provenance performance with site was significant. Within-provenance individual-
tree heritabilities for height and diameter at breast height (dbh) were low at the three individual
sites, ranging from 0.08 ± 0.05 to 0.19 ± 0.05 for height and 0.10 ± 0.05 to 0.19 ± 0.04 for dbh.
Across-site heritabilities, 0.07 ± 0.02 for both height and dbh, were lower than those at
individual sites.
Wei Zhongmian et al., (2009) evaluated the growth comparison of eight year old
Eucalyptus clones (Eucalyptus urophylla × E. grandis clones 3229, 30-1 and E. urophylla clone
U6) and revealed that, Eucalyptus clones showed high growth rate during the first three years.
There were significant differences amongst the 3 Eucalyptus clones in plant height, diameter and
volume growth. These indexes were positively correlated with the increasing age. Clone 3229
showed best growth followed by 30-1, while the U6 grew worst.
2.2. Biomass and Productivity
The general term ‘productivity’ may be considered as the rate of net primary production. Mean
annual net primary productivity is obtained by averaging the biomass over the age of the stand. The
production by a plant community is the reflection of its capacity to assimilate solar energy under some set
of environmental conditions.
Wood production varies substantially with resource availability, and the variation in
wood production can result from several mechanisms: increased photosynthesis, and changes in
partitioning of photosynthesis to wood production, belowground flux, foliage production or
respiration.
Different plant communities have different rates of biomass production, based on their efficiency.
High producing forest plantations in Europe generally attain a biomass of approximately 350X103 kg ha
-1
at about 50 years of age.
Vijay Rawat and Negi (2004) reported that, Eucalyptus plantations raised from seed
origin, produced the biomass range from 11.9 t ha-1
in three year old plantation to 146 t ha-1
than
in 9 year old plantation in moist regions. In dry tropical region it varied from 5.65 t ha-1
in 5 year
plantation to 135.5 t ha-1
in 9 year old plantation. In dry tropical regions biomass accumulation
was more in cooler areas as compared to warmer areas. Where water is not the limiting factor,
comparatively higher mean annual temperature of around 25 °C seems to produce higher
biomass. A higher share of leaf biomass was observed in dry region. Prabhakar (1998) reported
that, under eight year rotation, the mean annual growth of Eucalyptus per hectare, is about 8
cubic metres (cu. m.), though has been known to reach as much as 40 cu. m, while for
indigenous trees, the average is 0.50 cu. m.
Very short rotation (2 to 6 years) clonal eucalypt plantations are producing very high
volumes (40-80 m3 ha
-1 yr
-1), MAIs of 60 m
3 ha
-1 yr
-1 have been reported in Brazil (Laércio
Couto et al., 2011). E. grandis has an MAI range from about 20-47 m3 ha
-1 yr
-1, with optimum
rotation of 7-10 years in Uganda (Dennis Alder et al., 2003). Reyna Perez-Sandoval et al.,
(2012) reported that mean annual increments (MAI) of E. urophylla and E. grandis were
comparable to other regions of the world reaching 49 m3
ha−1
yr−1
across a range of low to high
soil fertility gradient (15 to 80 m3 ha
−1 yr
−1) in Mexico.
Overall biomass produced by the Eucalyptus was 2-8 folds higher than native species
while water use [transpiration] was 2-3 folds. Translating this into transpiration coefficient (TC)
and WUE, Eucalyptus growth performance was better than native species. Data showed that
Eucalyptus was very efficient water users with TC of 739 L kg-1
as compared to Acacia, Albizzia,
and Azadirachta which used 1042 L, 872 L and 1951 L of water to produce one kg of biomass
(Din Muhammad Zahid et al., 2010). It was reported by Kallarackal and Somen, (1997) that
under low relative humidity and without supply of nutrients the TC becomes higher.
Eucalyptus shows a broad productivity response depending on species, clones and soils
factors (Onyekwelu et al., 2011). Eucalyptus sp. has some of the highest net primary productivity
rates up to 49 m3
ha–1
yr–1
. Mean annual increments of clone plantations of Eucalyptus sp. with
no fertilization, with fertilization and fertilization combined with irrigation are 33, 46 and 62 m3
ha–1
yr–1
, respectively (Stape et al., 2010).
Eucalyptus hybrids plantations (E. urophylla × E. grandis) in South America recorded
productivity ranging from 15 - 60 m3
ha–1
yr–1
. Rodríguez et al., (2009) reported MAI in
plantations of E. nitens in Chile ranging from 47 to 52 m3
ha–1
yr–1
. Under intensive management
practices, genetic improvement and high productivity sites, Eucalyptus Clonal Forestry
Plantation (CFP) produced 60 m3
ha–1
yr–1
in MAI (Stape et al., 2010).
Eucalyptus plantations in Brazil in 1970 typically grew at rates of about 15 m3 ha
-1 yr
-1.
Over the next 35 years, intensive research and improved operations tripled the average yields
across almost 4 million ha, through improved silviculture (site preparation, fertilization and
control of leaf cutting ants and weeds), improved seed selection, and the development of clonal
propagation (Queiroz and Barrichelo, 2008).
The relationship between soil texture and soil water is key factor to consider in the
establishment of forest plantations of Eucalyptus in South-east Mexico. Aluminum saturation is
not negatively related to the productivity of E. urophylla but a negative relationship was seen for
E. grandis. Soil phosphorus availability showed positive correlation with the productivity of E.
urophylla but not with that of E. grandis (Stape et al., 2010). Jose Luiz Stape et al., (2010)
revealed that, Eucalyptus plantations yields 33 m3 ha
-1 yr
-1 under rainfed conditions and about 62
m3
ha-1
yr-1
under irrigated conditions in Brazil.
Herwitz and Gutterman (1990) revealed that, Eucalyptus salubris was considered to have
the most efficient water use, with highest annual productivity (1169 kg ha-1
) and lowest
transpiration rates. Eucalyptus torquata was slightly less efficient than E. salubris. E.
woodwardii was comparable in terms of productivity, but transpired at much higher rates.
Eucalyptus socialis and E. grossa were the least efficient in water use, with significantly lower
annual productivity (<660 kg ha-1
).
Singh and Toky (1995) revealed that, Leucaena leucocephala showed fairly high net primary
productivity (33 t ha−1
yr−1
) closely followed by E. tereticornis (29 t ha−1
yr−1
) and the standing
biomass after 4 years was 112 t ha−1
in L. leucocephala, 96 t ha−1
in E. tereticornis and 52 t ha−1
in
A. nilotica. Prasad et al., (2011) reported that, marketable biomass productivity was higher with
Leucaena (95 Mg ha−1
) in comparison to Eucalyptus (87 Mg ha−1
).
Comparative production of Acacia auriculiformis and C. equisetifolia was studied by
Kushalapa (1987) in high rainfall areas of Karnataka, and the study revealed that above ground
biomass (AGB) of C. equisetifolia was 108.3 t ha-1
at the age of 9 years. Jayaraman et al., (1992)
reported that C. equisetifolia plantations growing in the West Coast areas of Kerala are highly
productive and can produce biomass of 190 t ha-1
at the age of 4.5 years. Swaminath (1988)
studied the response of fast growing forest species grown for biomass production under irrigation
and found that, C. equisetifolia produced biomass of 26.97 t ha-1
yr-1
under irrigated condition
compared to 17.95 t ha-1
yr-1
under normal. Biomass production in accordance with different
spacing was also reported in Tectona grandis by Adams (1993) and in Leucaena leucocephala
by Mishra et al., (1986).
Eucalyptus is the dominant hardwood planted and the mean annual increment of managed
forests has increased from 12 m3 ha
−1 year
-1 in the 1960s to 20–60 m
3 ha
−1 yr
-1 as a result of
improved genetics and silviculture (Santana et al., 2000). Hunter (2001) reported that, two
Eucalyptus species had a total dry weight averaging 45.3 t ha-1
while the Dalbergia had an
average dry weight of only 7.6 tonnes. There were no interactions between species and
treatments. Irrigation increased dry weight linearly across treatments and by 74% in the highest
irrigation rate. The two eucalyptus had accumulated a stem volume of 60 m3
ha-1
at a rate of 20
m3 ha
−1 yr
-1.
Stand parameters indicate that soils in the study area can potentially reach high levels of
mean annual increment (MAI) with values from 23 to 49 m3
ha–1
yr–1
. This productivity falls in
the range of that of some eucalyptus hybrids plantations (E. urophylla × E. grandis) in South
America with MAI from 15 - 60 m3
ha–1
yr–1
. Rodríguez et al., (2009) reported MAI in
plantations of E. nitens in Chile ranging from 47 to 52 m3
ha–1
yr–1
. Under intensive management
practices, genetic improvement and high productivity sites, Eucalyptus CFP produced 60 m3
ha–1
yr–1
in MAI (Stape et al., 2010).
Piare Lal (2006) evaluated different Eucalyptus clones (E. camaldulensis, E. tereticornis
and E. hybrid) for yield and productivity in Punjab and reported that, the most productive clones
(2070, 285, 316, 288, 498, 286 and 2045) in clonal testing area (CTA-1) were ranging with MAI
from 24 to 30 m3
ha-1
yr-1
at 4 years age. The most productive clones (413, 407, 285, 290, 105 and
72) in CTA-2 were ranging with MAI 30-36 m3
ha-1
yr-1
. The clone 413 performed significantly
superior among all other clones at 4 years of age.
George (1986) concluded that the organic matter and exchangeable potassium are
depleted in the soil under Eucalyptus plantation than in wood lands, but no difference in calcium
and magnesium was observed. Hopmans et al., (1990) studied the Growth, biomass production
and nutrient accumulation by seven tree species irrigated with municipal effluent and reported
that, Height and diameter growth varied significantly between species. At the age of four years,
mean dominant height of E. grandis, E. saligna and Populus deltoides × P. nigra ranged from
14.3 to 15.0 m compared with 6.6 to 9.8 m for Casuarina cunninghamiana, E. camaldulensis, P.
deltoides and Pinus radiata. Wood production of the faster-growing species (E. grandis and E.
saligna) was approximately 130 m3 ha
−1 or around 32 m
3 ha
−1 year
−1 over a 4-year period. This
was nearly three-fold the production of the other native species and twice that of P. radiata.
Volume growth of P. deltoides × P. nigra (85 m3 ha
−1) was significantly greater than that of P.
deltoides (42 m3 ha
−1).
2.3. Biomass distribution
Mineral capital and its distribution within wood land ecosystems changes as a result of
the balance between the various factors, both internal and external, affecting the circulation of
chemical elements.
Fabio et al., (1995) revealed that, the proportion of the below ground biomass relative to
the total tree biomass and the root/shoot ratio were higher in C at early growth periods. The
average aboveground biomass of E. globulus increased with age from 79.23 t ha-1
at 6 years to
112.04 t ha-1
at 9 years. This increase of biomass was allocated to stem-wood and stem-bark.
Stem-wood was the major component and its biomass was comprised between 69% and 77% of
total aboveground biomass (Cole and Rapp, 1980).
Biomass partitioning to the bole was high in case of Leucaena ranged from 83% in 2.5-5
cm diameter at breast height (DBH) trees to 89% in 12.5-15 cm DBH trees and in eucalyptus
clones the corresponding values were 71% in 2.5-5 cm DBH trees and 83% in 12.5-15 cm DBH
trees (Prasad et al., 2011).
Allocation to the bole-wood in E. urophylla changed from 46 to 36%, in E.
camaldulensis from 37 to 32%, and E. pellita from 31–34% at 3x1.5 vs. 4x3 m spacing,
respectively. Allocation to the root system in E. urophylla changed from 23–30%, in E.
camaldulensis from 34–45%, and E. pellita from 37–33% at 3x1.5 vs. 4x3 m spacing,
respectively (Alberto L. Bernardo et al., 1998). Poggiani and Couto (1983) revealed that the
Biomass distribution in the E. grandis plantation recorded that, among the components of the
stand is about 9% leaves, 7% limbs and 83% stems. However nutrients content in the stand
biomass are about 37% in the leaves, 10% in the limbs and 53% in the stems.
Sara Bastien-Henri et al., (2010) studied the biomass distribution among tropical tree
species grown under differing regional climates and the results showed that, 18 species
accumulated greater total biomass at the humid site than at the dry site over a two-year period.
Species-specific biomass partitioning among leaves, branches and trunks was observed.
2.4. Physiological Parameters
2.4.1. Photosynthesis
Plant productivity is ultimately dependent on the rate of photosynthesis, but it is well
known that it is the amount rather than the activity of the photosynthetic tissues that usually
determines plant productivity.
Gratani et al., (1998) studied the relationship between the photosynthetic activity and
chlorophyll content in Oak trees and found that, discordances between chlorophyll content and
PN over the year influenced the regression analysis, which although positive did not show very
high correlation coefficients (r = 0.7). The high Chl (a+b) content during most of the year
indicated that the photosynthetic apparatus remained basically intact also during stress periods.
Enhanced transpiration and stomatal conductance were beneficial to the photosynthesis
for higher productivity. According to Novak et al., (2005) reliable estimates of plant
transpiration rates are essential to predict the water flow and crop growth and thus, the rate of
transpiration depends on various properties of the continuum soil-plant-atmosphere.
Novriyanti et al., (2012) reported that, relative to the Eucalyptus, Acacias had lower leaf
net photosynthetic nitrogen use efficiency, higher water use efficiency, higher LMA and higher
leaf nitrogen per unit area.
Morphological and physiological parameters which correlate with growth rate were
sought as early indicators of field performance. The physiological basis of vigorous growth of
faster-growing genotypes has been correlated with gibberellin levels water use efficiency and, in
some studies, net photosynthesis (i.e., photosynthesis minus respiration). However, correlations
between morphological and physiological parameters and growth in the field are often poor. The
influence of plant water status and growth rate appears to have received little study. However,
the authors revealed that, faster growing hybrids had a greater ability to limit transpirational
water loss compared with slower-growing clones, resulting in a higher water use efficiency – i.e.,
they fixed more carbon in photosynthesis per unit of water transpired. (Blake and Yeatman,
1989).
2.4.2. Stomatal conductance
The stomata are not only the entry route for gas exchanges for CO2, but also the outflow
of water in vapor form, from the inside to the outside of the leaf. In order to absorb CO2 from the
outside, the plant inexorably loses water and when this loss decreases, it also restricts the intake
of CO2. This interdependence was recognized long ago and numerically expressed by the ratio
between total assimilation and water consumption.
It is often assumed that species with high WUE would be favoured in dry environments,
but there may be a physiological cost for this. Models of stomatal conductance (gs) are based on
coupling between gs and CO2 assimilation (Anet), and it is often assumed that the slope of this
relationship (‘g1’) is constant across species. A decrease in stomatal conductance causes a
proportionally larger decrease in transpiration than in carbon assimilation, with the net result of a
higher WUE.
The maintenance of high WUE, by maintaining stomata partially closed, also decreases
the rate of carbon assimilation, thus reducing growth (De Lucia and Heckathorn, 1989).
Therefore, the main role of this stomatal response may be related to the control of water loss,
rather in the sense of preventing tissue damage so as to maximise carbon assimilation in the
prevailing circumstances than in the sense of conserving water (Grace, 1993).
The efficiency of water use (WUE) represents the ability that vegetation has to absorb
carbon while limiting water loss through the stomata. Stomatal control or a reduction in leaf area
will almost certainly lead to a significant reduction in productivity. Differences among clones in
transpiration were related to differences in leaf area under optimum conditions. Because yield is
correlated with transpiration and the relationship between transpiration and leaf area confirms the
importance of early leaf development for maximizing productivity (Turner and Jones, 1980).
The authors also found that Eucalyptus have efficient stomatal control on transpiration
during the dry season. The decline in WUEi, results from a reduction in stomatal conductance,
which affects more the photosynthetic rate than the rate of leaf transpiration.
Roberts and Rosier (1993) used evaporation from leaf replicas of E. camaldulensis and E.
tereticornis to estimate gb for individual leaves ranging from 0.8 to 2.6 mol m-2
s-1
at low (0.5 m
s-1
) and high (4 m s-1
) wind speeds, respectively. These values were consistently higher than
those for gs, which reached a maximum value of 700 m mol m-2
s-1
in early-morning conditions
during the monsoon period. Values of gs were substantially lower than this later in the day and at
other times in the year.
Based on measurements made with E. grandis leaves, Leuning (1995) showed that a
hyperbolic relationship best explained the response of gs to air saturation deficit (D), though it is
often described by an exponential decay function. The slopes of exponential functions in E.
globulus and E. nitens (-0.63) and E. grandis (-0.61 in summer) were commensurate with 50 and
90% reductions in gs at D = 1:1 and 3.7 kPa, respectively, an indication that gs can be quite
sensitive to D in some Eucalyptus species. Stomatal conductance in E. grandis was less sensitive
to D in summer (slope -0.30) but a 50% reduction in gs was still observed at D = 2:3 kPa (Dye
and Olbrich, 1993).
2.4.3. Transpiration
According to Novak et al., (2005) reliable estimates of plant transpiration rates are
essential to predict the water flow and crop growth and thus, the rate of transpiration depends on
various properties of the continuum soil-plant-atmosphere.
Pilar Pita and Rose Pardos (2001) studied the transpiration, tissue water relations,
changes in leaf size and specific leaf area in rooted cuttings of selected clones of E. globulus and
found that there was a significant clone x treatment interactions in transpiration.
Hybrids of E. urophylla x E. grandis and E. urophylla x E. tereticornis, with high
photosynthesis and transpiration rate grew faster than E. urophylla x E. camalduensis and E.
urophylla (Zhaohua Lu et al., 2001).
Terry Blake and Eddie Bevilacqua (1990) reported that, clonal differences were observed
in physiological parameters, with cv. 79 and cv. 33 having significantly higher gwv, T, and Pn
compared to cv. 93.
Prabhakar (1998) stated that the transpiration of Eucalyptus is high under conditions of
high soil moisture, termed ‘luxury consumption’, and under conditions of water stress, stomatal
closure occurs, which restricts water loss from the plant. Greenwood et al., (1985) measured and
compared transpiration from two species of Eucalyptus, and grassland, and annual average
transpiration rates were found to be 2700 mm and 390 mm respectively. However, another study
indicated that plantations of E. tereticornis and E. camaldulensis use no greater quantity of water
than degraded indigenous forest on adjacent sites.
Mana Gharun et al., (2013) studied the canopy transpiration in the E. radiate and E.
goniocalyx and revealed that, there was a stronger relationship between average daily
transpiration (0.71 mm day−1
) and daily minimum relative humidity (R2 = 0.71), than between
average daily transpiration and daily maximum temperature (R2 = 0.65).
Din Muhammad Zahid and Aamir Nawaz (2007) found significant variation between two
species was observed for WUE and transpiration coefficient (TC). WUE and TC of Shisham
were 0.89 and 7.94 g L-1
as compared to that of Eucalyptus, which were 0.93 and 4.06 g L-1
,
respectively. However, evaporation losses were higher (0.99 g L-1
) for shisham than for
Eucalyptus (0.84 g L-1
).
Water consumption by one year old Eucalyptus (149.27 L) was almost twice that of by
Albizia (82.84 L) and more than three times that of by Acacia (58.30 L), and Azadirachta (51.57
L). Significant variation between the species was observed for biomass produced. When this was
translated into water use efficiency, it was found as 0.32 g L-1
, 0.48 g L-1
, 0.16 g L-1
and 0.77 g
L-1
while transpiration coefficient was 1042 L kg-1
, 872 L kg-1
, 1951 L kg-1
and 739 L kg-1
for
Acacia, Albizzia, Azadirachta and Eucalyptus respectively. It is important to control evaporation
losses (44-69% of total irrigation) which may be much higher than transpiration (Zahid et al.,
2010).
Dunn and Connor (1993) measured sap flow in E. regnans trees of different ages and
estimated maximum transpiration rates of 1.9 and 0.8 mm per day for 50- and 230-year-old trees,
respectively. In annual terms, this amounted to a difference of 383 mm, which would be
observed as an increase in water yield. Sap velocity was the same in trees of different ages and
the decline in transpiration with increasing age was attributed to decreases in sapwood
conducting area, and thus leaf area (Hatton et al., 1995) of the older stands.
Zahid et al., (2010) reported that the transpiration efficiency (g L-1
) alternatively called
Aboveground Net Primary Productivity ANPP (kg m-3
) of Acacia, Albizzia, Azadirachta and
Eucalyptus was 0.63, 0.51, 0.13 and 0.68 respectively. Stoneman et al., (1996) reported a quite
high ANPP (3.21 kg m-3
) of E. tereticornis plantation with added nitrogen fertilizer in tropical
soils having high fertility and high rainfall.
2.5. Water Use Efficiency:
Water Use Efficiency (WUE) is an indicator of the relationship between the amount of
water required for a particular purpose and the amount of water used or delivered. WUE is
traditionally defined as the ratio of dry matter accumulation to water consumption over a season.
The term "water use efficiency" originates in the economic concept of productivity. Water use
efficiency studies are very limited in tree species and particularly at the level of clones. This is
one of the important physiological parameters for ranking the clones for better water use
efficiency and higher productivity under varied site conditions. Water productivity might be
measured by the volume of water taken into a plant to produce a unit of the output. In general,
the lower the resource input requirement per unit, the higher the efficiency.
Increasing WUE could theoretically affect plant growth. When water is limited, plants
that use a finite water supply more efficient would grow more rapidly, in this case, high WUE
would positively affect plant productivity. Another way to increase WUE is to close stomata
partially, thus restricting photosynthesis relative to plants whose stomata are fully open, this
strategy would result in a negative correlation between WUE and plant productivity (Richards
and Condon, 1993).
Reduced water use, which is reflected in higher WUE, is generally achieved by plant
traits and environmental responses that reduce yield potential. Improved WUE on the basis of
reduced water use is expressed in improved yield under water-limited conditions only when there
is need to balance crop water use against a limited and known soil moisture reserve. However,
under most dry land situations where crops depend on unpredictable seasonal rainfall, the
maximization of soil moisture use is a crucial component of drought resistance (avoidance),
which is generally expressed in lower WUE.
The strength and direction of the relationship between water-use efficiency and plant
performance can illustrate interspecific differences in drought tolerance strategies, ranging from
stress tolerance to stress avoidance (Aranda et al., 2012; Chaves et al., 2002 and Nicotra et al.,
2010) for a more complete discussion of tree responses to drought). Stress tolerance is associated
with higher water use efficiency, lower photosynthetic rates, slower growth, and higher survival,
while stress avoidance is associated with lower water-use efficiency, higher photosynthetic rates,
faster growth, and lower survival (Chaves et al., 2002).
Plant water-use efficiency, the amount of water used per carbon gain, explicitly links
plant performance with water availability. At the leaf level, intrinsic water-use efficiency is
expressed as the balance between photosynthetic carbon fixation (A) and stomatal conductance
(gs), which is correlated with the ratio of intercellular to ambient CO2 partial pressures (Ci/Ca) in
C3 plants. Therefore, time-integrated, intrinsic water-use efficiency can be inferred using stable
carbon isotope ratios (d13
C) of plant tissues given its inverse linear relationship with Ci/Ca,
whereby high water use efficiency is indicated by less negative d13
C and low Ci/Ca and vice
versa (Dawson et al. 2002; Farquhar et al., 1982; Farquhar and Richards, 1984).
Water use efficiency varies significantly among Eucalyptus clones (for the same age and
site). Evidence of this was presented by Olbrich et al., (1993) who found significant clonal
differences in WUE between four E. grandis clones growing on a high quality site. In a lysimeter
study, Le Roux et al., (1996) investigated variation in WUE among six Eucalyptus clones up to
the age of 16 months and found significant clonal variation in WUE as well as patterns of growth
allocation to roots, stems, branches, and leaves.
Stape et al., (2004) concluded that water use efficiency of Eucalyptus species was 3.8 kg
m-3
in irrigated plots in wet year and 1.8 kg m-3
in control during normal year (low rainfall).
The amount of water use by Eucalyptus plantation is a relevant ecological question
worldwide. Eucalyptus actually appears to be more efficient in water use than other ‘useful’
native trees. The study showed that Eucalyptus consumed 0.48 litres of water to produce a gram
of wood, compared to 0.55, 0.77, 0.50 and 0.88 litre per gram for siris, shisham, jamun and kanji
respectively (Prabhakar, 1998). Chaturvedi et al., (1988) reported that of ten species tested for
water consumption, E. tereticornis was found to be the most efficient in biomass production per
litre of water consumed, but also found to consume most water overall, given its high
productivity.
Pryor (1976) stated that Eucalyptus has ‘an ability to extract water from the soil even
though soil moisture tension is higher than that at which more mesophytic plants can extract
water.
Productivity of fast-growing species, such as poplars, is highly dependent on water
availability (Tschaplinski et al., 1994). Inter- and intraspecific differences in WUE, defined as
the ratio between plant biomass accumulation and plant transpiration, have been reported
(Condon et al., 2002). Inter-genotypic variability in WUE is mainly controlled by diversity in
stomatal conductance, whereas a positive relationship indicates that WUE is controlled mainly
by photosynthetic capacity (Farquhar et al., 1989).
Debbie Le Roux et al., (1996) reported that water use efficiencies differed significantly
between Eucalyptus clones. Chunying Yin (2005) found that there were significant inter-specific
differences in early growth, dry matter allocation, and WUE between two sympatric Populus
species under well-watered and water-stressed treatments.
In nature, the WUE is influenced not only by water, but also by climatic conditions
(Tonello and Filho, 2013). Similar situations were reported by several authors in different
cultures, including several genera of Eucalyptus sp (Whitehead and Beadle, 2004 and Poni et al.,
2009).
Poni et al., (2009) clearly showed that regardless of the stress level in the soil, the
intrinsic WUE tends to increase with increasing VPD, while instantaneous WUE usually shows
an opposite tendency.
Studies conducted at the Institute of Forest Genetics and Tree Breeding, Coimbatore
revealed considerable variation with respect to physiological parameters including water use
efficiency in 33 Casuarina equisetifolia clones (Kannan, et al., 2007). Water use efficiency
studies have been conducted especially in Eucalyptus species at Kerala Forest Research Institute
(Kallarackal and Somen, 1997).
2.6. Carbon isotope discrimination
WUE is defined in agronomic terms as the ratio of dry matter production to water use
(Boyer, 1996) or, in physiological terms, as the ratio between the rate of carbon fixed and the
rate of water transpired. Farquhar and Richards (1984) described the relationship between WUE
and carbon isotope discrimination in C3 plants. The discrimination against the heavier carbon
isotope, 13
C (d13
C), is calculated as the 13
C/12
C ratio in plant material relative to the value of the
same ratio in the air assimilated by plants. Carbon isotope discrimination has been proposed by
several authors as an indirect selection criterion for yield under drought (Condon et al., 2002). It
has been shown that d13
C is related to WUE in wheat genotypes (Farquhar and Richards,1984).
Thus, the smaller the CO2 partial pressure inside the plant in comparison to the partial pressure in
the atmosphere, the less the plants discriminate between the two isotopes (d13
C more positive)
and the greater the WUE (Ehlers and Goss, 2003). This theory is corroborated by a large volume
of literature (Wright et al., 1988; Hall et al., 1992) but also contradicted by other authors (Austin
et al., 1990; Ngugi et al., 1996). Moreover, except for the studies published by Johnson and
Tieszen (1994) and Ray et al. (2004), there are no clear data for this WUE/d13
C relationship in
alfalfa genotypes.
The isotopic ratio of 13
C to 12
C in plant tissue is less than the isotopic ratio of 13
C to 12
C
in the atmosphere, indicating that plants discriminate against 13
C during photosynthesis.
Variation in discrimination against 13
C during photosynthesis is due to both stomatal limitations
and enzymatic processes. Theoretical and empirical studies have demonstrated that carbon
isotope discrimination is highly correlated with plant water use efficiency. Analysis of carbon
isotope discrimination has conceptual and practical advantages over measuring water use
efficiency by instantaneous measurements of gas exchange or whole-plant harvests. Carbon
isotope discrimination provides an integrated measure of water-use efficiency.
The isotopic ratio of 13
C to 12
C in C3 plants (d13
C) varies mainly due to discrimination
during diffusion and enzymatic processes. The rate of diffusion of 13
CO2 across the stomatal pore
is lower than that of 12
CO2 by a factor of 4.4%. Additionally, there is an isotope effect caused by
the preference of ribulose bisphosphate carboxylase (Rubisco) for 12
CO2 over 13
CO2 (by a factor
of ~27‰). In both cases, the processes discriminate against the heavier isotope, 13
C (Farquhar et
al. 1989). Based on the work of Farquhar the linkage between discrimination against 13
C during
photosynthesis and water use efficiency may be demonstrated by the following relationships.
The stable isotope ratio (d13
C) is expressed as the 13
C/12
C ratio relative to a standard (Pee Dee
Belemnite) (Craig, 1957). The resulting d13
C value may be used to estimate isotope
discrimination (D) as:
D= (da – dp)/(1+ dp).
Where dp is the isotopic composition of the plant material and da is that of the air (assumed to be
8%). As CO2 assimilation (A) increases or stomatal conductance (gs) decreases, intercellar
CO2 decreases resulting in decreased discrimination against 13
C. The relationship between Ci and
D is represented by the model of Farquhar et al., (1982).
Carbon isotope discrimination has several conceptual and logistical advantages to
screening for drought tolerance based on TE or WUEi. Carbon isotope discrimination
integrates ci/ca over the time the sampled tissue was formed. In contrast, WUEi measured by gas
exchange provides ‘snapshots’ of A/g or A/E and may not be representative of overall WUE.
Measurements of D are much less time and labor intensive than calculation of whole plant water
use and dry weight data needed to calculate TE.
This water use efficiency will be measured in directly through the ‘Stable Isotope Mass
Spectrophotometer’ based on the carbon isotope discrimination expressed as stable isotope ratio
(d13
C) which is the ratio of 13
C to 12
C. Water and nutrient supplies are the main abiotic factors
affecting plantation growth in the tropics (Fisher and Binkley, 2000) and evaluation of these
supplies is important for zoning plantation potential and for establishing silvicultural methods for
site preparation, fertilization and control of competition. Rapid forest growth rates are generally
coupled with the high use of site resources, which raises questions regarding both the ecological
impacts of plantations and the sustainability of wood production (Wang et al., 1991; Lima,
1993).
Recently the relationships between d13
C and dry mass accumulation and WUE have
been explored in woody shrub and tree species. Negative correlations between d13
C of leaf tissue
and tree height were demonstrated in 13-month old commercial clones of E. grandis, implying
that more water-use-efficient trees were more productive (Bond and Stock, 1990).
Similarly, growing season WUE and d13
C were positively correlated in western larch and
E. globulus seedlings (Zhang and Marshall 1993, Osório and Pereira 1994). Genetic variation in
WUE and d13
C was also reported for both tree and shrub species (Hubick and Gibson 1993,
Zhang and Marshall 1993, Donovan and Ehleringer, 1994). Although clonal variation in d13
C
was shown in a study of four-year-old clones of Eucalyptus grandis (Olbrich et al., 1993), a poor
relationship was found between d13
C and WUE in the production of harvestable stems (i.e., the
water cost of wood production) suggesting that the relationship between d13
C and WUE in leaves
may change when scaling up to stems, shoots and whole trees.
Variation in allocation patterns in trees could result in simultaneous changes in
harvestable stem coupled with changes in WUE. Individuals allocating a high proportion of dry
mass to stems could have a high WUE when expressed on harvestable stem basis but have a low
WUE at the whole-plant level. A strong correlation between isotope discrimination and water use
efficiency has been reported for numerous crop and tree species. Greenwood and Beresford
(1979) reported that, considerable variation exists in WUE between species at different sites in
Australia. Kallarackal and Soman (1997) reported that, the relation between the net
photosynthesis and stomatal conductance was almost linear in six Eucalyptus species and better
water use efficiency was recorded in E. urophylla, E. camaldulensis, E. brassiana and E. pellita
compared to E. degulpta and E. tereticornis.
2.7. Nutrient in the standing biomass:
Mineral capital and its distribution within wood land ecosystems changes as result of the
balance between the various factors, both external and internal, affecting the circulation of
chemical elements. The buildup of the plant mass results in a progressive accumulation of
minerals which are effectively removed from the active circulatory systems. Brans et al., (2000)
reported that, in mature plantations of Eucalyptus globulus (6-18 years old), the total quantities
of P, K, Ca and Mg in tree biomass were higher than available quantities of P, K, Ca and Mg in
the soil.
Nutrient concentrations varied considerably among tree components and according to
position within the tree canopy. Nitrogen, P and K concentrations were highest in foliage
whereas Mg and Ca concentrations were highest in stem-bark. The high Ca concentration in bark
(28.21 mg g-1
) is similar to that reported for other Eucalyptus species (Spangenberg et al., 1996).
Stem-wood had the lowest concentrations of all those nutrients for other Eucalyptus species
reported for different forest species. Nitrogen and P concentrations in foliage decreased from the
top to the bottom of the canopy and this variation may be attributed to the withdrawal of these
elements, as has been reported for several Eucalyptus species (Attiwill and Leeper, 1987).
George and Varghese (1990) reported that, in Eucalyptus globulus, the contribution of
bgb to total biomass was 18 per cent and the accumulation of various nutrients ranged from 22 to
28 %. Similar observation was also reported by Negi et al., (1990) in Tectona grandis.
Harvesting of Eucalyptus wood would cause an export of about 224 kg ha-1
of N, 19 kg
ha-1
of P, 106 kg ha-1
of K and 110 kg ha-1
of Ca. These quantities represent 43% of N, 39% of P,
49% of K and 24% of Ca contained in aboveground tree biomass in Brazil (José Leonardo de
Moraes Gonçalves et al., 1998).
Qureshi et al., (1967) reported that in C. equisetifolia, the needles contain highest (1.95
per cent) concentration of Ca and lowest of P (0.16 per cent). Wang et al., (1991) revealed that
in C. equisetifolia, concentration of most nutrients followed the order, leaves > bark > small
branches > wood of stem.
During growth and development of trees, nutrients will be accumulated in biomass
components. Malhotra et al., (1987) reported that in Pinus patula plantations, maximum amount
of nutrients are accumulated in needles in younger stands but as the stand matures, accumulation
occurs in the boles. Similar observation was also reported by Tandon et al., (1996) in Eucalyptus
hybrid and Negi and Tandon (1997) in Populus elliotii. Wang et al., (1991) reported that in C.
equisetifolia, among various nutrients, Ca accumulated maximum (940 kg ha-1
) and P the
minimum (119 kg ha-1
) at age of 5.5 years.
Verma et al., (1987) revealed that, in C. equisetifolia, nutrient accumulation in agb
increases with increase in age. Increasing trend of nutrient contents with plantations age was
largely in the order of N > K > Ca > Mg > P (Kadeba, 1991). Similar observation in the
accumulation of nutrients with stand age was also reported by Pande et al., (1987) in Eucalyptus
hybrid; Tandon et al., (1988) in Eucalyptus grandis and Singh (1994) in Cryptomeria japoica.
Negi et al., (1990) reported that in Gmelina arborea, BGB accumulates 32% of N, 44%
of P, 13% of Ca and 25% of Mg and accumulation of K exceeds the total accumulation of K in
agb.
After 3-year growth, E. globulus stands irrigated with effluent accumulated 72 oven dry
t/ha of above-ground total biomass with a total of 651 kg N, 55 kg P, 393 kg K, 251 kg Ca, 35 kg
Mg and 67 kg Mn. Effluent irrigation increased the accumulation of biomass, N, P, K and Mn,
but tended to reduce the leaf area index and leaf biomass, and decreased the accumulation of Ca
and Mg (Guo et al., 2002).
Xue (1996) also reported that in Cunninghamia lanceolata, among different nutrients, Ca
constituted highest concentration (0.07 per cent to 1.37 per cent) and P the least (0.005 to 0.08
per cent). Similar observation in C. equisetifolia was reported by Verma et al., (1987) and
Jamaludheen (1994) and George (1985) in Eucalyptus hybrid.
Nutrient concentration varies considerably with age. Queshi et al., (1967) and Vadiraj
(1993) reported that in Casuarina equisetifolia, there was a general increase in nutrient
percentage in aerial components with increase in stand age. Singh (1994) made similar
observation in Cryptomeria japonica and by Singh (1982) in Pinus patula. Concentration of
certain nutrients shows a definite trend with increase in age. Ovington and Madgwick (1959)
reported that in Betula verrucosa, Mg concentration in the needle increases with age. Wright and
Will (1958) reported that Scots and Crosican pine growing on sand dunes exhibited decreasing
pattern of some nutrients with age.
2.8. Nutrient use efficiency
The annual increment in above-ground biomass, and the corresponding nutrient content
of eucalypt plantations growing in nine different sites, were evaluated by Santana et al., (2000)
and reported that, the nutrient content in the stem was highest in the most productive sites,
showing a close relationship with biomass production. At three of the sites, the amount of
nutrients in the stem decreased in the order nitrogen > calcium > potassium > magnesium > and
phosphorus. However, calcium exceeded nitrogen at the other six sites. Nutrient use efficiency
(NUE) for stem and above-ground biomass production was significantly different among sites.
On average, the values of NUE for both stem and above-ground biomass decreased in the order
phosphorus > magnesium > potassium > nitrogen > calcium. Although bark constitutes only 10%
of the above-ground dry matter, it contains large amounts of nutrients (73% of the calcium in the
stem, 65% of the magnesium, 46% of the phosphorus, 41% of the potassium, and 24% of the
nitrogen).
Anthony A. Kimaro et al., (2007) studied the above ground use efficiency for N (P =
0.0035), P (P < 0.0001), K (P < 0.0001), Ca (P = 0.001), and Mg (P = 0.0081) varied
significantly among the tree species. In general, A. crassicarpa was the most efficient for all
nutrients except for N and Mg, exemplifying that this species produced the highest above ground
biomass at lowest nutrient ‘‘costs’’. Its K-use efficiency was four times higher than that of G.
sepium while P-use efficiency was three times as high as that of A. nilotica. Similar results were
also observed for nutrient use efficiency based on wood production. Overall, nutrient use
efficiency of wood was consistently higher than that of whole-tree biomass except for K, Ca, and
Mg in A. polyacantha, and for P and Ca in A. nilotica.
Although some fluxes of nutrients have been studied intensively (mainly litter fall and
nutrient content of the trees), studies quantifying the dynamics of the main fluxes of the
biological cycle of nutrients during stand development are scarce for Eucalyptus plantations
(Bargali et al., 1992; Goncalves et al., 1997; Parrotta, 1999). For a production of 92 t ha-1
ligneous aerial dry matter of 7 year old Eucalyptus stand, immobilization in the ligneous
components of the trees amounted to 235 kg ha-1
of N, 47 kg ha-1
of P, 59 kg ha-1
of K, 68 kg ha-1
of Ca and 49 kg ha-1
of Mg (Jean Paul Laclau et al., 2003).
Also reported that nutrient return of 159 kg N ha-1
yr-1
, 9 kg P ha-1
yr-1
, 28 kg K ha-1
yr-1
,
125 kg Ca ha-1
yr-1
and 22 kg Mg ha-1
yr-1
under the 3 year rotation of three Eucalyptus short
rotation forest species.
Nutrient concentration controls the biochemical as well as biogeochemical cycles.
Bargali et al., (1992), George and Verghese (1991) and Lodhiyal (1990) have reported that leaf
contains highest concentration of nutrients in eucalypt, teak and poplar plantations, respectively.
Present investigation agrees to these reports only to the extent that only nitrogen concentration is
highest in the leaves while phosphorus is highest in roots. However, magnitude of concentration
of N and P is 1.51% and 0.16%, respectively. This is comparable to the reports of George and
Verghese (1991) where N and P concentration is 1.60% and 0.11%, respectively.
Final output of nutrient cycling is standing state of nutrients that has been defined as
quantity of nutrient storage at a given time in a unit area. Standing state of nutrients increased
with increase in age of the plantation and at the age of thirty years teak stored 586.6 kg/ha N and
208.8 kg/ha P. This kind of age versus storage relationship was also found in poplar (Bargali et
al., 1992) and Eucalyptus (Lodhiyal, 1990) in the same locality.
Magnitude of primary productivity is directly proportional to nutrient uptake. Since
annual productivity was not affected by the age of stands nutrient uptake also did not show any
relationship between uptake amount and age. At the age of 30 years gross uptake of N and P was
107.73 and 20.20 kg-1
ha-1
yr-1
, respectively. This report is well within the range of uptake (87-
256 kg-1
ha-1
yr-1
for N and 4-134 kg-1
ha-1
yr-1
for P) in different forest types and plantations.
However, quantum of uptake for both N and P towards the lower range shows comparatively less
nutrient demanding nature of the species.
The nitrogen use efficiencies were 181, 211 and 191 g of tree aboveground dry matter
produced per g of N supplied by uptake and retranslocation in the sapling, pole stage and mature
stands, respectively. Field vegetation was more efficient in nitrogen use than trees. Stand
belowground/aboveground and fine root/coarse root biomass ratios decreased with tree age. With
only slightly higher fine root biomass, almost three times more nitrogen had to be taken-up from
soil for biomass production in the mature stand than in the sapling stand. Retranslocation
supplied 17–42% of the annual N, P and K requirements for tree aboveground biomass
production. Precipitation and throughfall were important in transferring K and Mg, and also N in
the sapling stand. Litter fall was an important pathway for N, Ca, Mg and micro nutrients,
especially in the oldest stands (Heljä-Sisko Helmisaari, 1995).
2.9. Role of Leaf Potassium in Water Use Efficiency
Adequate amounts of K can enhance the total dry mass accumulation of crop plants under
drought stress in comparison to lower K concentrations (Egilla et al., 2001). This finding might
be attributable to stomatal regulation by K+ and corresponding higher rates of photosynthesis
(Marschner, 2012). Furthermore, K is also essential for the translocation of photoassimilates in
root growth. Root growth promotion by increased appropriate K supply under K-deficient soil
was found to increase the root surface that was exposed to soil as a result of increased root water
uptake (Romheld and Lindhauer, 2010). Lindhauer (1985) reported that fine K nutrition not only
increased plant total dry mass and leaf area, but also improved the water retention in plant tissues
under drought stress.
Potassium plays a crucial role in turgor regulation within the guard cells during stomatal
movement. As stomatal closure is preceded by a rapid release of K+ from the guard cells into the
leaf apoplast, it is reasonable to think that stomata would be difficult to remain open under K-
deficient conditions. Some studies also stated that K deficiency may induce stomatal closure and
inhibit photosynthetic rates in several crop plants (Jin et al., 2011; Tomemori et al., 2002).
Conversely, many studies suggest that K had no effect on stomatal conductance and
photosynthetic rates under well-watered conditions, but K starvation could favor stomatal
opening and promote transpiration, compared with K sufficiency in several plants under drought
stress. Furthermore, photosynthetic rate was decreased under drought stress in K-deficient plants.
During drought stress, the stomata cannot function properly in K+-deficient plants,
resulting in greater water loss. Drought stress did not decrease water use efficiency (WUE),
whereas it did increase WUE by rapid stomata closing during water deficit. Adequate levels of K
nutrition enhanced plant drought resistance, water relations, WUE and plant growth under
drought conditions (Egilla et al., 2005).
Hsiao and Lauchli (1986) observed substantial variation in stomatal responses to
variation in K+ availability in different species and concluded that although stomatal conductance
was lower under low K+ levels this may occur only at an advanced stage of K deficiency.
2.10. Specific Leaf Weight
Specific Leaf Weight (dry matter per unit leaf area-SLW) showed that all genotypes were
decreased under drought stress conditions, as pointed out by Vanaja et al., (2011). Specific leaf
weight was shown to be a valuable index for comparing photosynthesis by various parts of a tree
canopy over a season or throughout an entire year. Mean annual photosynthetic rate in five
separate portions of a spruce canopy was directly proportional to observed differences in specific
leaf weight (r2 = 0.99). Annual carbon uptake was a function of total foliage biomass (r
2 = 0.96).
When foliage biomass at each crown segment was adjusted for differences in specific leaf
weight, reflecting differences in photosynthetic rates, the predictive equation further improved C
(r2 = 0.99). Specific leaf weight is recommended as an index for comparing the relative effects of
various silvicultural treatments on photosynthesis (Oren Ram, 1984).
Specific leaf weight was shown to be positively correlated to transpiration efficiency in
peanuts and in other species. The reason for this relationship is not clear, but could be due to the
association of thicker leaves with higher photosynthetic capacity (Brown and Byrd, 1996).