Final Project Report Elvenia J. Slosson Endowment Fund for Ornamental …slosson.ucdavis.edu/newsletters/Young_200628970.pdf · 2007-01-19 · using grasses from the Mediterranean

Final Project Report Elvenia J. Slosson Endowment Fund for Ornamental Horticulture Project Title: Perennial grasses: adaptations to drought stress and responses to soil

moisture manipulations Principal Investigators: Truman Young, Jeffrey Clary, Warren Roberts, Richard Evans & Kurt Vaughn Department of Environmental Horticulture (Plant Sciences) & University Arboretum University of California One Shields Ave Davis, CA 95616, USA Robert Savé, Carmen Biel, Felicidad de Herralde & Xavier Aranda Departament d’ Horticultura Ambiental Institut de Recerca i Tecnologia Agroalimentaries 08348 Cabrils Barcelona, Spain

PROJECT SUMMARY: Both native California grasses and grasses from dry regions of the Mediterranean Basin have great potential for use in gardens, landscaping and revegetation projects where low maintenance input is desired. With increasing interest and investment in these species comes a need for better understanding of their physiological strategies, tolerances, and vulnerabilities. We propose a physiological survey of a suite of native perennial grass species of interest to horticultural and restoration practitioners, with emphasis on responses to summer drought stress. Additionally, we will compare the species with a suite of analogous grass species from similar ecological settings of the Mediterranean Basin, looking at their horticultural potential as well as their potential to invade surrounding natural habitats. We hope to identify any physiological strategies that seem unique to California natives and their implications for successful establishment and maintenance of these species in varied settings, and to make recommendations as to the appropriateness of using grasses from the Mediterranean Basin in gardens of the western United States. INTRODUCTION Native California grasses are now finding their places in a range of horticultural settings, including gardens, landscaping and revegetation projects, as well as in large-scale ecological restoration of native plant communities. Other perennial grasses, especially those from similar Mediterranean climate regions, can also be attractive choices for low-input garden settings, especially in xeriscape gardens and non –irrigated landscape restorations (Feldman et al. 1997; Sachs and Shaw 1993). With this new interest and investment in these species comes a need for better understanding of their physiological and ecological

strategies, tolerances, and vulnerabilities. We carried out a physiological survey of a suite of native perennial grass species of interest to horticultural and restoration practitioners, with special emphasis on responses to summer drought stress. Additionally, we compared the species with a suite of analogous grass species from similar ecological settings of the Mediterranean Basin, looking at their horticulture potential as well as their potential for invasion into surrounding natural habitats. We sought to identify any physiological strategies that seem unique to California natives and their implications for successful establishment and maintenance of these species in varied settings, and to make recommendations as to the appropriateness of using grasses from the Mediterranean Basin in western gardens. Our study examined adult perennial grass plants of horticultural interest currently growing in garden/landscaping settings, such as the UC Davis Arboretum and the IRTA-Cabrils Research Center, and new plants grown from seed under controlled conditions. We measured a full range of physiological parameters using standard techniques, focusing on those with strong links to plant water relations and competitiveness for water capture and use. Additionally, we measured grass responses to drought and irrigation events. We hope our results will help us refine our application of resources, like supplemental water, fertilizer, and pesticide, to maximize aesthetic or ecological success while minimizing inputs. Current interest in native grasses in California is driven in part by their relative rarity in the natural landscape. Perennial bunchgrasses were apparently once dominant over a vast area of California, especially grassland and woodland areas such as those surrounding the Central Valley (Crampton 1974, Heady 1988), but these native species have been replaced almost entirely by annual grasses of Mediterranean Basis origin. Restoration attempts have been frequently hindered by competition from non-native annual species (Bartolome & Gemmill 1981, Brown & Rice, 2000, Lulow 2006). Even some introduced perennial grasses appear better able to establish than natives under California conditions (Bugg et al. 1997, Williamson & Harrison 2002). However, by refining planting methods and targeting competing species for control, grassland restoration and revegetation efforts are becoming more successful. Furthermore, these bunchgrass species are increasingly being incorporated into other types of landscape plantings, especially where climatic conditions favor xeriscaping. Though California native grasses and Mediterranean grasses (specifically from Spain) are both adapted to “Mediterranean” climates, the typical California summer is long and completely rainless, while most of Spain experiences at least a small amount of summer rainfall and a rainy season that begins by late September (Figure 1). These differing ecological contexts may lead to different strategies for water capture and use between the two groups of species, as well as different requirements for satisfactory growth in a landscaping setting. In preliminary results (from a small number of species) from field and greenhouse experiments carried out by our working group, we have observed patterns consistent with this idea. For example, we have documented that California perennial grasses may invest less in leaves, but relatively more in first-year seed production than their Mediterranean counterparts. Also, somewhat counter-intuitively, we have documented that California grasses may exhibit less resistance to hydraulic flow through roots that

Mediterranean ones (Clary et al. 2004, Clary et al. unpublished data); this implies that California species may in some respects be less conservative in their use of soil water, perhaps because they have more fixed mechanisms of later drought avoidance, consistent with phenological patterns of dormancy that Jackson and Roy (1986) reported in California grasses. Similarly, we have observed higher survival of California species after extreme drought stress, but less ability to take advantage of summer rain or irrigation events than their Mediterranean counterparts. In roadside plantings and xeric gardens, weedy competitors of bunchgrasses can be well controlled and pose relatively few problems, so maintaining high survivorship and esthetic qualities in the native plants takes on great importance. In restoration or revegetation settings, competition with exotic annuals is of overwhelming importance to successful establishment and growth of these bunchgrasses. In both cases, a better understanding of the physiological mechanisms that grasses use to cope with summer drought will help us target application of resources, like supplemental water, to give native grasses an establishment and growth advantage. The main objective of this work was to examine relationships among leaf, root and water use characteristics of several species of grasses - currently or potentially useful for ornamental applications - and their habitats, using standardized methods to obtain ecophysiological information for these species and their functional relationships by means of simple and objective methods. The work proposed here is designed to a direct impact on garden and landscape restoration management, because it can provide objective information about plant development under resource-limited conditions, consequently helping to minimize inputs of irrigation, fertilization and pesticides. This research will provide a basis for further study of gardening and restoration of xeric landscapes, where initial success with plant establishment is critical. We made basic comparisons between grasses, such as their relative competitiveness for water at the root level, the interactions of form and function in canopies and root systems, and the functional convergence or divergence among species of California and Spanish xeric landscapes. In addition to their value for gardens, the results are of value to the maintenance or restoration of biodiversity on disturbed sites. Many restoration projects fail because of difficulties in establishing desired vegetation in xeric sites, often because of a lack of horticultural understanding. This research can increase our insights into the ecophysiological and technological tools that could improve the general ornamental quality of bunchgrasses in xeric gardens and restored landscapes in Mediterranean climates. On a more theoretical level, we these results address a central question facing restoration practitioners in California grasslands: are California native grasses now relatively rare in natural systems because they are inherently poor competitors, especially when faced with new invaders? Although invasions of non-native perennials into California grasslands suggests that Mediterranean species may be more competitive under California conditions than California perennials, our studies of the perennial grasses suggest different but apparently effective physiological strategies in California species.

METHODS California species Nassella pulchra (Np) Nassella lepida (Nl) Elymus elymoides (Ee) Elymus glaucus (Eg) Melica californica (Mc) Koeleria macrantha (Km) Festuca californica (Fc) Festuca idahoensis (Fi) Muhlenbergia rigens (Mr) Leymus triticoides (Lt) Bouteloua gracilis (Bg)

Mediterranean species Stipa gigantea (Sg) Stipa tenacissima (St) Brachypodium phoenicoides (Bp) Brachypodium retusum (Br) Dactylis gomerata (Dg) Plus: Cynodon dactylon (Cn)

Table 1. Bunchgrass species used for comparative survey of ecophysiological parameters. Our experimental work consisted of two components, the first using existing plants in gardens and landscape settings, such as the Arboretum of UC Davis and the Cabrils Research Center (assisted by the Institut Botanic de Barcelona). We selected grass species of current or potential horticultural interest (Table 1). On different subsets of these species, we measured ecophysiological parameters on leaves growing under similar environmental and plant developmental conditions of the garden setting, including specific leaf weight, cuticular transpiration rate, fractal index (leaf perimeter/leaf area), relative water content at turgor loss point, and minimum relative water content (after 24 h of dehydration on a laboratory bench) (Savé et al. 2003). Water Use Efficiency will also be measured in the same samples by means of a Waltz Portable gas exchange system. The second component involved growing plants of a subset of these same species together from seed in a common garden on the UC Davis Campus, and in containers at the IRTA-Cabrils laboratories. Using plants of the same age grown under the same environmental conditions allowed direct comparisons of the species’ physiological characteristics. We analyzed the response of basic physiological parameters to at least two watering treatments with the same total water delivered of the growing season, but distributed as: A) the average pattern of rainfall in the Central Valley of California, and B) the average pattern of rainfall in Barcelona (Figure 1). These treatments should allowed us to compare the plasticity of the species with regards to summer photosynthetic capacity and any fixed dormancy responses, and to examine their capacity to capture water from summer irrigation or rainfall events (Roy et al. 1987, Clary et al. 2004). Furthermore, from the container-grown bunchgrasses we excavated intact roots for analyses of root hydraulic, osmotic and morphological characteristics (Hendry and Grime 1993; Reigosa 2001). All of these parameters were related to the ecological origin of the studied species, as well as their implications for grasses in the restoration or landscaping setting. In addition, we examined the competitive ability of Nassella pulchra in the face of and invasive Mediterranean

annual (Bromus hordeaceus) and a native Californian annual grass (Vulpia microstachys) under these two watering regimes WORK CALENDAR Summer 2005: Physiological characterization of grasses growing in irrigated garden settings in Davis. Collection of seed for establishment of new plants. Fall 2005: Planting in common garden of full suite of California and Mediterranean grasses in Davies. Maintenance of common garden (weed control). Establishment and maintenance of container plants in Cabrils. Winter 2005: Maintenance of common garden (weed control). Spring/Summer 2006: Application of irrigation regimes, weed control. Physiological characterization of irrigated and non-irrigated grasses from garden. Excavation and physiological characterization of roots from containers. RESULTS Experiments in Cabrils Competitiveness between perennials and annuals grasses submitted to different Mediterranean rainfall regime: California and Catalonia”. The first objective of this essay was to study the response of a California perennial grass grown with two annual species, one from California and the other from Catalonia. The second objective was to compare the effect of two different rainfall patterns (California and Catalonia patterns, Figure 1) in this response. The perennial species was Nassella pulchra from Winters, California. The annual species were Bromus hordeaceus from Catalonia and Vulpia microstachys from California. The seeds were sown in October 26 (Nassella and Bromus) and November 9 (Vulpia) 2004 in 1 m2 and 0.45 m of depth plots. The soil was sandy. Species combinations: We carried out a "substitution competition experiment", keeping the total numbers of plants constant across treatments. The species treatment was plots with mono-specific composition of three species and the combinations of the three species summarized as: 1) Nassella pulchra (25 plants/m2)

2) Bromus hordeaceus (25 plants/m2) 3) Vulpia microstachys (25 plants/m2) 4) Nassella pulchra (13 plants/m2) + Bromus hordeaceus (12 plants/m2) 5) Nassella pulchra (13 plants/m2) + Vulpia microstachys (12 plants/m2) 6) Bromus hordeaceus (13 plants/m2) + Vulpia microstachys (12 plants/m2) There were three replicates of each of these six combinations. Irrigation treatments: Rainfall was simulated by drip irrigation system with 25 emitters/plot. The total rainfall was 580 mm/year but distributed as Winters (California) rainfall or Cabrils (Catalonia) rainfall (Figure 1). Each week we applied one quarter of the designated monthly rainfall.

Figure 1. Winters (CAL) and Cabrils (MED) rainfall distribution.

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Photograph 1. Picture examples taken in March 2005 We measured 1) plant cover by zenithal digital pictures, b) number of flowering spikes and seeds, c) leaf and spike height, and d) recovery after summer drought. Germination and growth of Nassella were initially enhanced by the presence of annual grasses (Figure 2 and 4). Later in the spring, Bromus reduced the number of active leaves in Nasella (Figure 2C). Surprisingly, Nassella performed better in the fall in plots that had annual grasses in the spring, which were now all dead. One possibility is that these the litter from these dead annual plants provided shade, mulch and high water availability to Nassella, promoting higher green biomass when it is living in mixed treatments than alone. The other possibility is that this is an expression of the lower density of Nassella plants (less intraspecific competition) in these treatments. Tiller leaf height and spike height were not different between rainfall regime and species combination treatments for each species (Figure 3). Nassella cover closely paralleled the watering regime (Figure 4). The plants in the California regime virtually shutting down during the summer months without water, whereas in the Mediterranean regime, growth continued through the summer. This is in contrast to field situations in California, where supplemental water does not appear to stimulate growth in mative perennial grasses (J. Clary, unpublished data). Nassella cover was strongly affected by reduced competition with annuals (Figure 4). In June and November 2005 Mediterranean rainfall had a positive and significant effect in soil cover. In March 2006 there weren’t differences between species combination and rainfall regime.

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Figure 3. Taller leaf height and spike height of Nassella, Bromus and Vulpia species grown in combination and submitted to two water rainfalls.

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Figure 4. Cover by plants of Nassella growing alone (A), with Bromus (B) and with Vulpia (C). (Average of three plots ±s.e.).

Competition strongly affected sexual reproduction (Figure 5). The number of spikes were significantly higher in Nassella when it grown alone and with Vulpia than when it grown with Bromus. These effects were consistent across rainfall regimes.

Figure 5. Number of spikes and seeds per plant in the first year of Nassella growing alone (A), with Bromus and with Vulpia in Californian (CAL) and Mediterranean (MED) rainfall regime. (Average of three plots ±s.e.).

Spike production in second year was significantly higher in all combinations than first one (note the change in scale in Figure 6). Unlike the first year, however, there were no significant differences between competition treatments, although there was a tendency for plants in the Mediterranean regime to have higher preproduction than those in the California regime.

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Figure 6. Number of spikes and seeds per plant 2nd year of Nassella growing alone, with Bromus and with Vulpia in Californian (CAL) and Mediterranean (MED) rainfall regime (average of 3 plots ±s.e.).

In June 2006 (in the second year) plants of Nassella were removed from the soil and leaves and roots were sampled. Biomass distribution between leaves spikes and roots

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Figure 7. Biomass distribution of Nassella plants grown alone, with Bromus and with Vulpia plants in Californian (CAL) and Mediterranean (MED) rainfall regime. Water drought cycle During 27 June and 12 July 2006 a water drought cycle was applied to four species, two Spanish species (Brachipodium phoenicoides and Stipa gigantea) and two Californian species (Nassella pulchra and Koeleria macrantha). Plants were sown in March 2006 and grown in container with peat:perlite (2:1 v:v) and daily irrigated with tap water without fertilization. This experimental cycle of drought /rewatering showed strong differences (Figure 8). Drought stress was associated with large reductions in relative water content and stomatal conductance, but not in photosynthesis and chlorophyll fluorescence, which suggests a high drought resistance of studied species.

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Fig. 8 Measured parameters during water stres cycle A) Soil water content B) Leaf Relative Water Content. C) Photosynthetic rate. D) Stomatal conductance. E) Yield. UC Davis Arboretum experiment At UC Davis Arboretum in June 2006 we studied several parameters in 13 grass species. Water loss curves were done and cuticular transpiration rates (TRc, Fig. 9A), relative water content at turgor loss point (RWCtlp, Fig 9B) and minimum relative water content (RWCmin, Fig. 9C) were calculated. There were significant differences among species for the three parameters. The lowest value of TRc was obtained in Stipa gigantea, the only European species included in this study.

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Figure 1. Water loss parameters in leaves of 13 species of grasses. A) Cuticular transpiration rate (TRC [g H2O·g-1 DW·min-1]) B) Relative water content at turgor loss point (RWCtlp [%]) C) Minimum relative water content after 4 hours (RWCmin [%]). All the results are mean of n=5. Vertical bars represent S.E. Different letters over columns for each parameter represent significant differences among species (Duncan’s Multiple Range Test (P<0.05).

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Figure 1. Water loss parameters in leaves of 13 species of grasses. A) Cuticular transpiration rate (TRC [g H2O·g-1 DW·min-1]) B) Relative water content at turgor loss point (RWCtlp [%]) C) Minimum relative water content after 4 hours (RWCmin [%]). All the results are mean of n=5. Vertical bars represent S.E. Different letters over columns for each parameter represent significant differences among species (Duncan’s Multiple Range Test (P<0.05).

Fig. 9

Leaf morphological parameters also showed significant differences among species. (Fig 10). Three species, Fc, Sg and Mr, have SLW values over 10, for which they can be considered as sclerophyllous species. The lowest value corresponded to Lt.

Carbon stable isotopes were analyzed. Species showed significant differences in both isotopic composition (Fig 11A) and WUE (Fig 11B). The lower d13C (approx. -15 ‰) and higher WUE (approx. 70 mmol CO2·mol-1 H2O) of Mr and Bg showed indicates that these two species have C4 type of photosynthetic metabolism, whereas the rest of species have C3 metabolism. In C3 species, values around -30‰ indicate high stomatal conductance and consequently low stress conditions.

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Figure 2. Leaf morphologicalparameters of 13 species of grasses. A) Specific leaf weight (SLW [mg DW·cm-2]) B) Leaf Perimeter to Leaf Area ratio (Per/Area [cm-1]). All the results are mean of n=5. Vertical bars represent S.E. Different letters over columns for each parameter represent significant differences among species (Duncan’s Multiple Range Test (P < 0.05).

A

a

bb

c


0

2

4

6

8

10

12

14

16


Species

SLW

(mg·

cm-2)

B

a

b

ccdcde

de dee ee

fff

0

2

4

6

8

10

12

14


Species

Per/A

rea

(cm

-1)

A

a

bb

c


0

2

4

6

8

10

12

14

16


Species

SLW

(mg·

cm-2)

B

a

b

ccdcde

de dee ee

fff

0

2

4

6

8

10

12

14


Species

Per/A

rea

(cm

-1)

Figure 2. Leaf morphologicalparameters of 13 species of grasses. A) Specific leaf weight (SLW [mg DW·cm-2]) B) Leaf Perimeter to Leaf Area ratio (Per/Area [cm-1]). All the results are mean of n=5. Vertical bars represent S.E. Different letters over columns for each parameter represent significant differences among species (Duncan’s Multiple Range Test (P < 0.05).

A

j

cf d

i j gk h e i

b a

-35

-30

-25

-20

-15

-10

-5

0Cn Eg Fc Fi Km Lt Mc Nl Np Ps Sg Bg Mr

Species

δ13

C (%

o)

B

i

ce e

ab

d df gg h h

0

10

20

30

40

50

60

70

80


Species

WU

E ( µ

mol

CO

2·mol

-1H 2

O)

Figure 3. Leaf isotope analyses of 13 species of grasses. A) Isotopic composition (δ13CSLW [‰]) B) Water use efficiency (WUE [µmol CO2·mol-1 H2O]). All the results are mean of n=3. Vertical bars represent S.E. Different letters over columns for each parameter represent significant differences among species (Duncan’s Multiple Range Test (P < 0.05).

A

j

cf d

i j gk h e i

b a

-35

-30

-25

-20

-15

-10

-5

0Cn Eg Fc Fi Km Lt Mc Nl Np Ps Sg Bg Mr

Species

δ13

C (%

o)

B

i

ce e

ab

d df gg h h

0

10

20

30

40

50

60

70

80


Species

WU

E ( µ

mol

CO

2·mol

-1H 2

O)

Figure 3. Leaf isotope analyses of 13 species of grasses. A) Isotopic composition (δ13CSLW [‰]) B) Water use efficiency (WUE [µmol CO2·mol-1 H2O]). All the results are mean of n=3. Vertical bars represent S.E. Different letters over columns for each parameter represent significant differences among species (Duncan’s Multiple Range Test (P < 0.05).

Fig. 10

Fig. 11

All these parameters showed some relationship between each other, even though they were not significant. Higher values of SLW promoted lower TRc, higher RWCtlp and higher WUE, which is also reflected in the relationship between TRc and WUE and RWCtlp and WUE. RWCmin was negatively affected by TRC. (Fig 12).

Cn

EgFc

Fi

Km

Mr

Sg

LtPs Bg

Mc

Np

Nl

y = -0.1973x + 7.5188R2 = 0.0862 n.s.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0.0 5.0 10.0 15.0

SLW (mg·cm-2)

TRc

(mg

H 2O

·g-1

DW

·min

-1)

Mr

Sg

FcBgCnNp Fi

Ps

McNl

Lt

KmEg

y = 0.6886x + 60.856R2 = 0.0390 n.s.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

0.0 5.0 10.0 15.0

SLW (mg·cm-2)

RW

Ctlp

(%)

BgMr

SgFcFi

EgPs

NlLt Km

Cn

Mc Np

y = 2.483x + 2.162R2 = 0.1428 n.s

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

0.0 5.0 10.0 15.0SLW (mg·cm-2)

WU

E ( µm

ol C

O2·m

ol H

2O)

SgCn

Np

NlLtKm

FcMc

Eg

PsFi

BgMr

y = -0.2423x + 11.736R2 = 0.0225 n.s.

y = -10.519x + 141.13R2 = 1 n.s.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

0.0 5.0 10.0 15.0TRc (mg H2O·g-1 DW·min-1)

WU

E ( µm

ol C

O2·m

ol H

2O)

BgMr

Eg

Ps Fi

NlKmSg

McLt

NpFcCn

y = 0.7298x - 28.9259

R2 = 0.1500 n.s.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

0.0 20.0 40.0 60.0 80.0 100.0

RWCtlp (%)

WU

E ( µm

ol C

O2·m

ol H

2O)

CnBg

Fc

MrPsMc

Eg KmNl

LtFi

SgNp

y = -3.8428x + 54.356R2 = 0.2214 n.s.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

0.0 5.0 10.0 15.0

TRc (mg H2O·g-1 DW·min-1)

RW

Cm

in(%

)

A B

C D

E F

Figure 4. Relationships between different parameters for 13 grasses species.A) Specific leaf weight (SLW [mg·cm-2]) vs. Cuticular transpiration rate (TRC [g H2O·g-1 DW·min-1]); B) Specific leaf weight (SLW [mg·cm-2]) vs. Relative water content at turgor loss point (RWCtlp [%]); C) Specific leaf weight (SLW [mg·cm-2]) vs. Water use efficiency (WUE [µmol CO2·mol-1 H2O]). D) Cuticular transpiration rate (TRC [g H2O·g-1 DW·min-1]) vs. Water use efficiency (WUE [µmol CO2·mol-1 H2O]). E) Relative water content at turgor loss point (RWCtlp [%]) vs. Water use efficiency (WUE [µmol CO2·mol-1 H2O]). F) Cuticular transpiration rate (TRC [g H2O·g-1 DW·min-1]) vs. Minimum relative water content a (RWCmin[%]) Each point represents the mean of n=3 or 5 for each species.

Cn

EgFc

Fi

Km

Mr

Sg

LtPs Bg

Mc

Np

Nl

y = -0.1973x + 7.5188R2 = 0.0862 n.s.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0.0 5.0 10.0 15.0

SLW (mg·cm-2)

TRc

(mg

H 2O

·g-1

DW

·min

-1)

Mr

Sg

FcBgCnNp Fi

Ps

McNl

Lt

KmEg

y = 0.6886x + 60.856R2 = 0.0390 n.s.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

0.0 5.0 10.0 15.0

SLW (mg·cm-2)

RW

Ctlp

(%)

BgMr

SgFcFi

EgPs

NlLt Km

Cn

Mc Np

y = 2.483x + 2.162R2 = 0.1428 n.s

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

0.0 5.0 10.0 15.0SLW (mg·cm-2)

WU

E ( µm

ol C

O2·m

ol H

2O)

SgCn

Np

NlLtKm

FcMc

Eg

PsFi

BgMr

y = -0.2423x + 11.736R2 = 0.0225 n.s.

y = -10.519x + 141.13R2 = 1 n.s.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

0.0 5.0 10.0 15.0TRc (mg H2O·g-1 DW·min-1)

WU

E ( µm

ol C

O2·m

ol H

2O)

BgMr

Eg

Ps Fi

NlKmSg

McLt

NpFcCn

y = 0.7298x - 28.9259

R2 = 0.1500 n.s.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

0.0 20.0 40.0 60.0 80.0 100.0

RWCtlp (%)

WU

E ( µm

ol C

O2·m

ol H

2O)

CnBg

Fc

MrPsMc

Eg KmNl

LtFi

SgNp

y = -3.8428x + 54.356R2 = 0.2214 n.s.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

0.0 5.0 10.0 15.0


RW

Cm

in(%

)

A B

C D

E F

Cn

EgFc

Fi

Km

Mr

Sg

LtPs Bg

Mc

Np

Nl

y = -0.1973x + 7.5188R2 = 0.0862 n.s.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0.0 5.0 10.0 15.0

SLW (mg·cm-2)

TRc

(mg

H 2O

·g-1

DW

·min

-1)

Mr

Sg

FcBgCnNp Fi

Ps

McNl

Lt

KmEg

y = 0.6886x + 60.856R2 = 0.0390 n.s.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

0.0 5.0 10.0 15.0

SLW (mg·cm-2)

RW

Ctlp

(%)

Mr

Sg

FcBgCnNp Fi

Ps

McNl

Lt

KmEg

y = 0.6886x + 60.856R2 = 0.0390 n.s.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

0.0 5.0 10.0 15.0

SLW (mg·cm-2)

RW

Ctlp

(%)

BgMr

SgFcFi

EgPs

NlLt Km

Cn

Mc Np

y = 2.483x + 2.162R2 = 0.1428 n.s

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

0.0 5.0 10.0 15.0SLW (mg·cm-2)

WU

E ( µm

ol C

O2·m

ol H

2O)

SgCn

Np

NlLtKm

FcMc

Eg

PsFi

BgMr

y = -0.2423x + 11.736R2 = 0.0225 n.s.

y = -10.519x + 141.13R2 = 1 n.s.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

0.0 5.0 10.0 15.0TRc (mg H2O·g-1 DW·min-1)

WU

E ( µm

ol C

O2·m

ol H

2O)

BgMr

Eg

Ps Fi

NlKmSg

McLt

NpFcCn

y = 0.7298x - 28.9259

R2 = 0.1500 n.s.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

0.0 20.0 40.0 60.0 80.0 100.0

RWCtlp (%)

WU

E ( µm

ol C

O2·m

ol H

2O)

CnBg

Fc

MrPsMc

Eg KmNl

LtFi

SgNp

y = -3.8428x + 54.356R2 = 0.2214 n.s.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

0.0 5.0 10.0 15.0


RW

Cm

in(%

)

CnBg

Fc

MrPsMc

Eg KmNl

LtFi

SgNp

y = -3.8428x + 54.356R2 = 0.2214 n.s.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

0.0 5.0 10.0 15.0


RW

Cm

in(%

)

A B

C D

E F

Figure 4. Relationships between different parameters for 13 grasses species.A) Specific leaf weight (SLW [mg·cm-2]) vs. Cuticular transpiration rate (TRC [g H2O·g-1 DW·min-1]); B) Specific leaf weight (SLW [mg·cm-2]) vs. Relative water content at turgor loss point (RWCtlp [%]); C) Specific leaf weight (SLW [mg·cm-2]) vs. Water use efficiency (WUE [µmol CO2·mol-1 H2O]). D) Cuticular transpiration rate (TRC [g H2O·g-1 DW·min-1]) vs. Water use efficiency (WUE [µmol CO2·mol-1 H2O]). E) Relative water content at turgor loss point (RWCtlp [%]) vs. Water use efficiency (WUE [µmol CO2·mol-1 H2O]). F) Cuticular transpiration rate (TRC [g H2O·g-1 DW·min-1]) vs. Minimum relative water content a (RWCmin[%]) Each point represents the mean of n=3 or 5 for each species.

Fig. 12.

Catalonia (IRTA) experiment Root hydraulic resistance was measured for both California and Spanish grasses at IRTA in Catalonia in June 2006 (Fig. 13). Water loss curves were done and cuticular transpiration rates (TRc, Fig 14), relative water content at turgor loss point (RWCtlp, Fig 15) and minimum relative water content (RWCmin, Fig 16) were calculated. There were significant differences among species for the three parameters. The relationship among these three factors are shown in Figures 17A,B and C.

Root hydraulic resistance

0.242 0.288 0.260

1.909

0.3650.045 0.015 0.015

0.461 0.3410.083

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Bra

chyp

odiu

mph

oeni

coid

es

Brac

hipo

retu

sum

Dact

ylis

glom

erat

a

Stip

ate

naci

ssim

a

Stip

agi

gant

ea

Elym

usel

ymoi

des

Koe

leria

mac

rant

ha

Mel

ica

calif

orni

ca

Nass

ella

pulc

hra

Nass

ella

cern

ua

Cyno

don

dact

ilon

Species

Root

hyd

raul

ic r

esis

tanc

e (M

Pa.s

.cm

-

1 )x10

6

Fig. 13. Root hydraulic resistance in Spanish (first five spp.) and Californian (second five spp.) grasses, and Cynodon dactylon (a broadly naturalized African grass)

Cuticular transpiration

0

1

2

3

4

5

6

7

8

Brachypodiumphoenicoides

Brachypodiumretusum

Dactilisglomerata

Stipa gigantea Stipatenacissima

TRc

(mg.

g DW

-1.m

in-1

)

Figure 14. Cuticular transpiration in Spanish grasses.

RWCtlp

0102030405060708090

100


Brachypodiumretusum

Dactilisglomerata


RW

Ctlp

(%)

Figure 15. RWCtlp in Spanish grasses.

RWCminimum

0

10

20

30

40

50

60


Brachypodiumretusum

Dactilisglomerata


RW

Cmin

imum

(%)

Fig. 16. RWC minimum in Spanish grasses.

y = -2.06x + 20.45R2 = 0.66

0

2

4

6

8

10

12

14

16

18

0 2 4 6 8

Trc (mg.g DW-1.min-1)

SLW

(mg.

cm-2)

Bp

St

Sg

Br

Dg

y = -1.65x + 94.96R2 = 0.34

0

1020

30

4050

60

70

8090

100

0 5 10 15 20

SLW (mg.cm-2)

RW

Ctlp

(%)

Bp

Sg

St

Br

Dg

y = -1.49x + 34.34R2 = 0.03

0

10

20

30

40

50

60

0 2 4 6 8

Trc (mg.g DW-1.min-1)

RW

C m

in (%

)

Dg

Br

St

Bp

Sg

Figure 17 A,B,C, relationships among physiological traits in Spanish grasses.

DISCUSSION Competition experiment This was the first study of how rainfall regime affects the perfomance of California and Mediterranean grasses, alone and in a competitive setting. We were able to show that the very dry Californian summers did reduce plant growth, but that this difference was "recovered" during the rest of the year. Both native Californian annual grass (Vulpia microstachys) and an invasive Mediterranean grass (Bromus hordeaceus) decreased the growth and reproduction of the Californian perennial Nassella pulchra, but the Mediterranean grass was significantly more competitive. This may help explain the success of Mediterranean grasses tin supplanting natives in California, especially in the Central Valley. In the California watering regime in particular, these two annual species had a "legacy effect"—in the fall after they grew and died, Nassella in those plots that had these annuals in the previous season grew faster. One possibility is that this is an expression of the lower density of Nassella plants (less intraspecific competition) in these treatments. The other possibility is that the litter from these dead annual plants provided shade, mulch and high water availability to Nassella, promoting higher green biomass when it is living in mixed treatments than alone. This second possibility is particularly intriguing, should be explored further. Physiological studies Our present reveal large interspecific specific differences among grasses in a variety of physiological response related to drought stress, but he recurring theme of our physiological studies is that all of the Californian and Mediterranean grasses species we tested should considerable drought tolerance, both in their relatively conservative growth patterns, and in their ability to rebound for short-term drought stress. One particular pattern of interest was the tendency of the Californian grasses to be less conservative in several aspects of their growth: higher reproduction, lower specific leaf areas, water use efficiency, and hydraulic resistance. We hypothesize that this is due to the fact that rather than trying to grow though the summer (when Mediterranean sites still receive some rainfall) these species have evolve to go more fuller dormant (not unlike annuals) in the more severe California winters. This may allow them to be less conservative during their more predictably wet winter growing season. Implications for Horticulture and Restoration All of the species we tested are appropriate in gardening and/or landscape restoration because they can provide relatively fast and regular growth with only moderate amounts of water, can survive low water in the summer, and can also be source of seeds and consequently new propagules. In general, all could be considered drought-resistant, despite specific differences in avoidance or tolerance mechanisms. Vigorous growth even under the adverse weather conditions characteristic of Mediterranean climate provide appropriate ecophysiological adapations for xeriscape and peri-urban landscape restorations, because these permit vegetation at low maintenance

cost, above all, at low water and nutrient requirements (Savé et al 1999; Serrano et al 2005; Galmés et al 2006). In spite of these postive points, our research revealed significant competitive suppression by invasives, which could become exacerbated under conditions predicted by global climate change models. For example, new summer characteristics of Mediterranean areas of Spain are likely to be more severe than now because rainfall rate would be reduced in 20% and period without rain would be longer. In these new scenario, the use of species from America could be a potential problem because they are apparently better adapted to these drier summers, and could potentially become invasive, supplanting native Spanish grasses, in a pattern similar to, but in the opposite direction to direction what has happened in the past in California with invasive European grasses (Savé and Evans 2006; Huddleston and Young. 2004, Lulow 2006). Another point that should be take in consideration is the potential competition between grasses and ornamental woody species, because in early stages of garden development the water absorption and water use efficiency is much better in grasses than in young trees or shrubs, and consequently the ornamental value of new garden or landscape restoration could be compromised (Clary et al 2004, Garcia- Navarro et al .2004; Young and Chan 1998; Young and Evans 2005). Under both present and potential new future environmental conditions in Mediterranean climate biomes, grasses are and will be an appropriate source of plant material for ornamental and restoration uses because they provide soil stabilization, low cost of maintenance, important source of food for an important number of animal species, and interesting ornamental value because their morphological and phenological characteristics provide a changing landscape throughout the year.

LITERATURE CITED Bartolome JW & B Gemmill. 1981. The ecological status of Stipa pulchra (Poacea) in

California. Madrono 28:172-184. Brown, CS & KJ Rice. 2000. The mark of Zorro: Effects of the exotic annual grass

Vulpia myuros on California native perennial grasses. Restoration Ecology 8:10-17.

Bugg, RL, CS Brown & JH Anderson. 1997. Restoring native perennial grasses to rural roadsides in the Sacramento Valley of California: establishment and evaluation. Restoration Ecology 5:214-225.

Clary, J, R Save, C Biel and F de Herralde. 2004. Water relations in competitive interactions of Mediterranean grasses and shrubs. Annals of Applied Biology 144:149-155.

Crampton, B. 1974. Grasses in California. University of California Press, Berkeley. Farquhar G.D., Ehleringer J.R and Hubick K.T. (1989) Carbon isotope discrimination

and photosynthesis. Annual Review of Plant Physiology and Plant Molecular Biology, 40:503-537

Farquhar G.D. and Richards R.A. (1984) Isotopic composition of plant carbon correlates with water-use efficiency of wheat genotypes. Australian Journal of Plant Physiology, 11:539-552.

Feldman, W.R., Carter, S.A. and Stone, K.W. 1997. Water requirements of arid-adapted groundcover and sub-shrub species for landscape use in Arizona. Desert plants: 18-24.

Galmés, J., Medrano, H., Savé, R. and Flexas, J. 2006. Ecophysiological responses to water stress and recovery in Mediterranean plants with different growth forms and leaf habits. I. Water relations and stomatal conductance. Plant and Soil DOI 10.1007/s11104-006-9148-6

García-Navarro, M.C., Evans, R.Y. & Savé, R. 2004. Estimation of relative water use among ornamental landscape species. Scientia Horticulturae 99:163-174.

Hendry, G.A.F. & Grime J.P. 1993. Methods in Comparative Plant Ecology. Chapman & Hall. London.

Huddleston, R.T & T.P. Young. 2004. Spacing and competition between planted grass plugs and pre-existing perennial grasses. Restoration Ecology 12:546-551

Jackson, L.E. and J. Roy. 1986. Growth patterns of Mediterranean annual and perennial grasses under simulated rainfall regimes of southern France and California. Acta Oecologia 7:191-212.

Lulow, M.E. 2006. Invasion by non-native annual grasses: The importance of species biomass, composition, and time among California native grasses of the Central Valley. Restoration Ecology 14:616-626.

Reigosa Roger, M.J. 2001. Handbook of Plant Physiology Techniques. Kluwer Academic Publishers. Dordrecht.

Shachs, R.M. and Shaw, D.A. 1993. Avoidance of Drought injury and minimum irrigation in a Mediterranean climate: The requirement for acclimatized (hardened) plants. J. of Arboriculture 19(2): 99-105.

Savé, R., Terradas, J. and Castell, C. 1999. Gas exchange and water relations. An ecophysiological approach to plant response to environment. In Ecology of Mediterranean Evergreen Oak Forests. Ecological Series. Springer-Verlag.

Savé, R., Biel, C., De Herralde, F., Garcia-Navarro, C., Roberts, W., & Evans, R.Y. 2003. Some ecophysiological characteristics of leaves of sixteen Quercus species.. Proc. Symp. Optimization of Water use by plants in the Mediterranean. March 2003. Mallorca. Spain

Savé, R. & Evans, R.Y. 2006. L’ecofisiologia com a base I eina per a l’optimització de la producció agroforestal sota un clima mediterrani. Temes de Recerca I Innovació. 4C: 5 -6.

Serrano, L., Peñuelas, J., Ogaya, R. And Savé, R. 2005. Tissue-water relations of two co-occurring evergreen Mediterranean species in response to seasonal and experimental drought conditions. J- Plant Res. 118: 263-269.

Williamson, J & S Harrison. 2002. Biotic and abiotic limits to the spread of exotic revegetation species. Ecological Applications 12:40-51.

Young, T.P. & R.Y. Evans. 2005. Effects of containers and irrigation regimes on initial seedling survival and growth in Valley Oak (Quercus lobata). Native Plants Journal, in press.

Young, T.P. & F. Chan. 1998. Establishment of deergrass (Muhlenbergia rigens) at a restoration site, and its prospects for woody plant suppression in transmission rights of way. Grasslands 8(3):3-10.

Nassella grown without competition

June-05

January-05

CAL

MED

November-05 May-05 March-05

2

Nassella grown with Vulpia

June-05

January-05

CAL

MED


3

Nasella grown March 06

Nassella alone

CAL

MED

Nassella + Vulpia Nassella + Bromus

4

Nassella grown with Bromus

June-05

January-05

CAL

MED


Documents

Final Project Report Elvenia J. Slosson Endowment Fund for Ornamental …slosson.ucdavis.edu/newsletters/Young_200628970.pdf · 2007-01-19 · using grasses from the Mediterranean