Differential effects of two species of arbuscular mycorrhizaon the growth and water relations of Spartium junceumand Anthyllis cytisoides

Marta Busquets & Cinta Calvet & Amelia Camprubí &Victoria Estaún

Received: 17 June 2010 /Accepted: 19 October 2010 /Published online: 15 November 2010# Springer Science+Business Media B.V. 2010

Abstract Anthyllis cytisoides and Spartium junceum are twoleguminous shrubs native of semiarid mediterranean areas,often used in revegetation strategies. Mycorrhization of bothshrubs with Glomus intraradices BEG 72 enhanced bothplants growth and water relations under drought stress. Rootcolonization achieved by Glomus mosseae was lower thanthe level achieved by G. intraradices in both plants studied,and the effects of the inoculation with G. mosseae BEG 116were less positive than those observed for G. intraradices.Before the onset of the drought stress period the specific leafweight (SLW) of S. junceum plants inoculated with G.mosseae was lower than the SLW of control and G.intraradices plants. At the end of the stress period, after15 days of withholding water, the relative water content of S.junceum twigs was lower for G. mosseae inoculated plantsand higher for G. intraradices inoculated plants, compared tocontrol, non-inoculated plants. At the end of the recoveryperiod, 15 days after the reestablishment of watering, therewere no differences between inoculation treatments on theparameters related to the plants water status. Anthylliscytisoides plants inoculated with G. intraradices had lowerleaf osmotic potential, more leaves, and higher chlorophyllcontent (measured as SPAD values). Anthyllis cytisoidesplants responded to drought defoliating, but defoliationwas lower for the plants inoculated with G. intraradices.At the end of the drought, the leaf osmotic potential waslowest for G. intraradices plants as was the relative water

content (RWC) whilst Glomus mosseae inoculated plantshad the highest RWC, SLWand osmotic potential values. Atthe end of the recovery period, all plants recuperated theosmotic potential values measured at the pre-stress period. Inour experiments, G. intraradices BEG 72 was found to besuperior to G. mosseae BEG 116, this difference could beattributed to the origin of the fungus, native from aMediterranean area, compared to G. mosseae (BEG116)isolated from the UK.

Keywords Relative water content (RWC) . Specific leafweight (SLW) . SPAD chlorophyll meter measurements .

Osmotic potential . Drought .Glomus mosseae .Glomusintraradices

1 Introduction

In semi–arid environments the establishment of a plantcover is the most important step in the restoration ofdegraded areas, to avoid further degradation and desertifi-cation. In this aspect leguminous shrubs are importantcomponents of re-vegetation processes in the Mediterra-nean because they are well adapted to the prevailingedaphoclimatic conditions of the area. The MediterraneanBasin’s climate combines cool or cold and wet winters, andlong, hot and dry summers. Summer drought is of variableduration, but frequent periods of drought can occur at anytime of the year (Vallejo et al. 2006). The anthropogenicpressure over the land in the Mediterranean basin hascaused the loss of the original vegetation (Puigdefábregasand Mendizabal 1998) with a higher risk of soil erosionand desertification. As a result of these conditions, soilsare shallow and low in nutrients (Yaalon 1997), othercharacteristics include low organic matter content (Aranda

Submitted to the special issue ‘The Potential of exploitingMycorrhizal associations in semi arid regions’.

M. Busquets :C. Calvet :A. Camprubí :V. Estaún (*)IRTA,Carretera de Cabrils Km 2 08348 Cabrils,Barcelona, Spaine-mail: victoria.estaun@irta.es

Symbiosis (2010) 52:95–101DOI 10.1007/s13199-010-0097-8

and Oyonarte 2005) and low levels of microbial activity(Bastida et al. 2007). Additionally in this region theirregular rain with high summer temperatures generateepisodes of drought that hold back the spontaneousrevegetation of many of these areas. It is well establishedthat the reclamation of degraded ecosystems should userecognized succession trajectories to improve the degradedecosystem structure and function (Walker and del Moral2008). The use of known reference systems, such as theoriginal vegetation exploiting the potential of native specieswill increase the ecosystem resilience, especially in relationto drought events and a gradual drift to hotter and drierclimates (Pausas 2004). Shrubs are pioneer plants whichhelp the survival of tree seedlings and therefore can speedup the spontaneous (or human-mediated) succession(Gómez-Aparicio et al. 2004). Evergreen sclerophyllousand drought deciduous shrubs are both key components ofthe Mediterranean vegetation of arid and semi-arid environ-ments and both life strategies are considered adaptations todrought (Freitas and Billib 1997). In the Mediterraneanregion wild legume shrubs comprise a group of woodyFaboideae (Genista, Spartium, Cytisus, Anthyllis andothers), able to colonise poor and arid soils. Woodylegumes are important species of the sparse shrub land thatis often associated with the primary stages of succession ofanthropogenically degraded lands (López-Pintor et al.2006). The establishment of the tripartite symbiosis withrhizobia and mycorrhizal fungi in the roots of these shrubsfacilitates the plant’s nutrition and represents a net influx ofnitrogen into the ecosystem (Cardinale et al. 2010). Twowoody legumes were chosen for this study: an evergreensclerophyllous shrub, Spartium junceum L., and a droughtdeciduous legume shrub Anthyllis cytisoides L., bothcommon in the Spanish Mediterranean region and oftenused in rehabilitated arid Mediterranean areas. Spanishbroom (S. junceum) is a perennial, evergreen legume shrubthat can reach six to ten feet tall. It is the only species of thegenera and is the most drought resistant of the broomsfamily. It is found in areas with full sun and limited waterand it can grow in poor, rocky soils. A. cytisoides is foundon limestone soils. In nature both A. cytisoides (López-Sánchez et al. 1992) and S. junceum (Maremmani et al.2003) present the arbuscular mycorrhizal (AM) symbiosis.As microsymbiont propagules might be scarce in disturbedenvironments (Estaún et al. 2008), inoculation of wildlegume plantlets with selected fungi prior to their estab-lishment in a degraded area should improve both plantgrowth and soil quality (Rillig and Mummey 2006).Mycorrhizal effects on plant water relations are not asconsistent as those on P acquisition and host growth,however there is no doubt that AM fungi can modify hostwater relations (Augé 2001). Mycorrhiza have been shownto influence, among other water related parameters, the leaf

osmotic pressure and also the relative water content (RWC)(Subramanian et al. 1995; Subramanian and Charest 1999);these influences might be circumstance and also symbiontspecific.

The objective of this work was to evaluate the response oftwo type-specific woody legumes, an evergreen sclerophyllousshrub and a drought deciduous shrub to the inoculation withtwo different arbuscular mycorrhizal fungi (AMF) isolates.Both shrubs are commonly used in restoration strategies andthe aim of the study was to assess how two differentmycorrhizal fungi isolates might influence plant developmentand the plant’s response to a short drought period.

2 Materials and methods

Spartium junceum seeds and Anthyllis cytisoides seeds werecollected from the wild in the region of El Maresme(Northern Catalunya, Spain). After collection, vital seeds,those that were not attacked by insects, or looked damagedin any other way, were kept in the dark at 4°C. Spartiumjunceum seeds were immersed in concentrated sulphuricacid for 60 min, rinsed with running water and immersed inwater for 1 h before planting. Anthyllis cytisoides seedswere immersed in concentrated sulphuric acid for 24 h,rinsed with tap water and then left immersed in water foranother hour before planting.

Seeds of both plants were sown in sterilised sandy soil(1 h at 120°C, repeated twice with a 24 h interval). Fortyfive days after the emergence, when plants had two trueleaves they were transplanted to a pasteurized potting mix(soil: quartz sand : sphagnum peat) in 5 L pots. Attransplant one third of the plants were inoculated withGlomus intraradices Schenck & Smith (BEG 72); Glomusmosseae Nicolson & Gerdemann; Gerdemann & Trappe(BEG 116) or non inoculated. The roots of plants left overon the seedling tray were stained to confirm the non-establishment of the arbuscular mycorrhizal symbiosisbefore transplant and inoculation.

Inocula for arbuscular mycorrhizal fungi were producedin leek (Allium porrum L.) pot plants grown in sterilizedsand. The number of spores was assessed for each fungalinoculum before being used in the experiments. Sporenumbers for each batch were counted in a 50 g of the mixedsoil inoculum sample after wet sieving and decanting(Daniels and Skipper 1982) and shredding the roots in ablender to recover intraradical spores. The resultingconcentration of mycorrhizal propagules was approximately1,000 spores/10 g of soil inoculum and 80 sporocarps/10 gof soil inoculum for G. intraradices BEG 72 and G.mosseae BEG 116 respectively. The inoculation was doneby placing 20 g of the soil inoculum directly under theplantlet roots.

96 M. Busquets et al.

All plants were also inoculated with Rhizobium strainsthat were isolated from corresponding wild plants. Bacteriawere grown on a yeast manitol specific media. Plants wereinoculated (1 ml plant-1) at a concentration of about109 CFUml-1 after germination. At transplant all plantshad nodules, and a second inoculum dose was added onemonth after transplant. No attempt was made to identify theRhizobium strains.

Plants were grown for 4 months under greenhouseconditions. Plant growth was monitored by measuring thefollowing parameters: plant height, stem diameter, and forA. cytisoides the two maximum values of crown and basaldiameters (cm), which are perpendicular to each other, werealso measured to calculate the canopy volume. There were40 plants per treatment.

The 1st week of September, after 4 months growth, 10plants of each species per treatment were harvested andbiomass allocation and plant water relation parameterswere determined (pre-stress measurements). Irrigationwas withheld for 15 days (stress period) in all plants.At the end of this period 10 plants per treatment wereharvested and plant water relations were determined (endof drought measurements). Then, all the plants were re-irrigated to run-off, and subsequently, as needed for15 days when the water relation parameters weremeasured again (end of recovery measurements).

2.1 Measurements

Plants were separated into leaf blades, leaf sheaths+stem,and roots and plant parts were dried at 65°C to constantweight. The area of leaf blades of A. cytisoides wasdetermined using a digital leaf area meter (Delta T Ltd,Cambridge, UK). The area of the leaves of S. junceumplants, due to their morphology, was only measured tocalculate the specific leave weight (SLW) in the droughtexperiment, using 10 leaves per treatment. The relativechlorophyll (a+b) content of the leaves was determinedusing a portable chlorophyllmeter (SPAD-502, Minolta,Japan). SPAD chlorophyll meter readings have been shownto have a direct linear relationship to extracted leafchlorophyll (Yadava 1986) and are also related leaf nitrogenconcentration (Bullock and Anderson 1998). The followingallometric parameters were calculated: root:shoot ratio, leafweight ratio (LWR; leaf dry weight per plant dry weight),shoot : plant ratio (SWR), root : plant ratio (RWR). Leafwater related parameters were calculated before withholdingthe water, at the end of the drought period and at the end of therecovery period. Leaf osmotic potential was measured for A.cytisoides on 10 leaves per treatment, the leaves were frozenin liquid nitrogen and osmotic potential (Ψo) was measuredafter thawing the samples and extracting the sap, using aWescor 5500 vapour pressure osmometer, the specific leaf

weight (SLW; leaf dry weight per leaf area) was calculatedfor both plant species. Pressure-volume curves were calcu-lated for fully expanded leaves or in the case of S. junceum,due to the morphology of the plant, small twigs, taken fromthe middle of the plant. Leaves (in the case of S. junceumtwigs) were excised pre-dawn, placed in plastic bags, andallowed to reach full turgor by dipping in distilled water for24 h in darkness at 4°C. The re-saturated leaves (twigs) wereweighed using an analytical balance (± 0.1 mg precision),placed into the pressure chamber (lined with damp filterpaper) and slowly pressurized (0.025 MPas-1) until thebalance pressure was reached (when the leaf sap appearsthrough the cut petiole (stem) protruding from the chamber).Once depressurized, the leaves (twigs) were repeatedlyweighed and their balance pressures determined over thefull range of the pressure gauge. Leaves were finally dried at65°C to determine their dry weights. The curves were drawnusing a type II transformation (Tyree and Richter 1982) tocalculate the RWC (relative water content).

To evaluate arbuscular mycorrhizal root colonisation aroot subsample from 5 plants per treatment was taken andafter clearing and staining (Koske and Gemma 1989)analyzed using the grid intersect method (Giovanetti andMosse 1980). The number of nodules was counted in fiveroot systems for each plant species and treatment.

The statistics design was an ANOVA with threetreatment levels for the inoculation factor.

3 Results

Glomus intraradices and G. mosseae stimulated plantgrowth of both A. cytisoides and S. junceum (Tables 1 and2). Glomus intraradices produced a more positive responsethan G. mosseae in plant height, stem diameter and plantdry weight of S. junceum, (Table 1) although G. mosseaeplants were better than control non inoculated plants forthese parameters. When considering the allometric parame-ters measured, only the relation between the leaves and theplant dry weight was significantly different between controland inoculated plants. Control plants had a higher leafweight ratio (LWR) than inoculated plants with either fungi.Anthyllis cytisoides (Table 2) plants inoculated with G.intraradices were taller, had a thicker stem diameter and ahigher dry weight, than control and G. mosseae inoculatedplants. Glomus mosseae plants were only better than controlplants when considering plant height. The allometricparameters measured showed that non-inoculated A. cyti-soides plants had a higher root/shoot weight ratio thaninoculated plants. In both plant species, G. mosseae achievedlower levels of root colonisation, when compared to G.intraradices, although the amount of inocula used per plantwas more than enough to establish the symbiosis. The

Differential effects of two species of arbuscular mycorrhiza 97

number of Rhizobium nodules was significantly higher for S.junceum mycorrhizal plants while in A. cytisoides thedifferences observed were not significant.

At the end of the pre-stress period the specific leafweight (SLW) of S. junceum plants inoculated with G.mosseae (Table 3) was lower than the SLW of control andG. intraradices plants. At the end of the stress period, after15 days of withholding water, the relative water content ofS. junceum twigs was lowest for G. mosseae inoculatedplants and highest for G. intraradices inoculated plants. Atthe end of the recovery period, 15 days after the reestablish-ment of watering, there were no differences betweeninoculation treatments on the parameters evaluating the plantswater status (RWC and SLW). In the case of A. cytisoides theparameters measured (Table 4) showed a positive influenceof G. intraradices on some of the plants water relations atthe pre-stress period. Glomus intraradices inoculated plantshad more leaves, and lower leaf osmotic potential. TheSPAD values were higher for the mycorrhizal plants and G.intraradices plants had 3 times more leaves than non-inoculated control and G. mosseae plants. At the end of thestress period, after 15 days of withholding water, the numberof leaves was reduced in all treatments, however G.intraradices plants still had significantly more leaves thanthe other A. cytisoides plants, the leaf osmotic potential was

lowest for G. intraradices plants as was the relative watercontent (RWC). Glomus mosseae inoculated plants had thehighest RWC, SLW and osmotic potential values. The SPADvalues were significantly lower for both AMF inoculationtreatments. At the end of the recovery period, despite asevere defoliation in all treatments, G. intraradices plantsstill had more leaves than the other treatments, and the SPADvalues were recovered. All plants recuperated the osmoticpotential values measured at the pre-stress period, althoughG. intraradices inoculated plants had a higher osmoticpotential than G. mosseae plants. The values of SLW andRWC remained significantly lower for G. intraradicesinoculated plants.

4 Discussion

Perennial leguminous shrubs are in some Mediterraneanmarginal lands the most important vegetation, interspersedwith bare areas or grass (Puigdefábregas and Mendizabal1998). The expansion of the shrub land in agriculturallyabandoned areas represents an intermediate state of oldfield successions (Haase et al. 1997). Due to climatic andalso land use changes water is becoming a scarcer resourcein many areas of the Mediterranean, particularly of Spain

Non-inoculated G. mosseae G. intraradices

Plant height (cm) 23.43 c 45.10 b 76.98 a

Stem diameter (mm) 1.87 c 2.54 b 3.05 a

Plant dry weight (g) 0.443 b 1.195 b 3.009 a

LWR (leaf weight ratio) 0.165 a 0.062 b 0.057 b

SWR (shoot weight ratio) 0.624 0.711 0.725

RWR (root weight ratio) 0.264 0.228 0.218

Root/shoot weight ratio 0.409 0.305 0.409

Rhizobium nodules (per gram plant roots) 1.5 b 4.02 a 3.25 a

AM root colonisation (%) 0 33 b 76 a

Table 1 Spartium junceum plantdevelopment and biomass parti-tioning after 4 months growth ingreenhouse conditions

Data are means of 10 replicates(non destructive measures: plantheight and stem diameter 40replicates)

Letters in the same row indicatedifferences at p≤0.05

Non-inoculated G. mosseae G. intraradices

Plant height (cm) 18.46 b 23.12 a 24.74 a

Stem diameter (mm) 1.73 b 1.85 ab 1.98 a

Canopy volumen (cm3) 17.18 c 32.51 b 55.52 a

Plant dry weight (g) 8.803 b 8.976 b 10.488 a

Leaf area (cm2) 18 ab 16 b 22 a

LWR (leaf weight ratio) 0.323 0.381 0.389

SWR (shoot weight ratio) 0.169 0.177 0.198

RWR (root weight ratio) 0.508 0.442 0.413

Root/shoot weight ratio 1.351 a 0.868 b 0.741 b

Rhizobium nodules (per gram plant roots) 6.857 3.571 5.429

AM root colonisation (%) 0 14 b 43 a

Table 2 Anthyllis cytisoidesplant development and biomasspartitioning after 4 monthsgrowth in greenhouse conditions

Data are means of 10 replicates(non destructive measures: plantheight and stem diameter 40replicates)

Leaf area data are leaf meanvalues for 10 plants. Letters inthe same row indicate differencesat p≤0.05

98 M. Busquets et al.

(Archer et al. 2002). These shrub lands effectively increaseground cover and favor the rain water infiltration decreasingthe rainfall run off, with the net effect of reducing soilerosion. Perennial leguminous shrubs have been shown to bemycorrhizal (Maremmani et al. 2003), and to respondpositively to AM inoculation when assessing plant growth.Our results confirm the findings of Requena et al. (1996) inA. cytisoides, where the inoculation with G. intraradices wasbetter at increasing plant development than the inoculationwith G. mosseae. Spartium junceum has also been shown tobenefit from mycorrhizal inoculation, (Quatrini et al. 2002)in a greenhouse experiment and in a landfill restorationproject. Quatrini et al. (2002) studied plants inoculated withAMF and Rhizobia in contrast to plants that were inoculatedwith neither Rhizobium nor AMF. In our study all plantswere inoculated with Rhizobium, and we found thatmycorrhiza inoculation increased the number of nodules inS. junceum roots. When assessing the effect of mycorrhizal

inoculation on plant growth we found two different levels ofresponse, G. mosseae increased plant growth compared tocontrol, however G. intraradices was better than G. mosseae.The sequence: control ≤ G. mosseae ≤ G. intraradices wasmaintained in all the parameters measured, showing aspecific functional response of the symbiosis between S.junceum and G. intraradices. The AM fungus G. intra-radices BEG 72 was isolated from an area cultivated withcitrus trees in the south of Catalunya (Camprubí and Calvet1996) where drought episodes are common, therefore thisisolate might be particularly suited to establish the symbiosiswith plants that are native of similar edaphoclimatic areas, suchas S. junceum and A. cytisoides. Requena et al. 1997 alsofound that an indigenous fungus Glomus coronatum wasbetter than a culture collection G. intraradices at increasingA. cytisoides growth. Inoculation with Glomus versiformeincreased the number of leaves in tangerine (Citrus tangerine)under well watered and also under stressed conditions (Wu

Table 4 Anthyllis cytisoides water relations parameters. Measures were done before withholding the water, at the end of the stress period, and theend of the recovery period

Relative watercontent (%) (RWC)

Specific leafweight (SLW)

Osmoticpotential (MPa)

Chlorophyll(SPAD)

NºLeaves

Control 78.87 8.92 b -1.48 a 50.10 b 12.52 b

Pre-stressed G. mosseae 75.87 9.41 a -1.60 a 60.10 a 18.89 b

G. intraradices 75.45 9.36 a -1.81 b 59.33 a 43.29 a

Control 35.32 ab 8.29 b -4.80 b 53.64 a 8.4 b

End of drought G. mosseae 39.74 a 9.17 a -4.49 a 47.68 b 14.70 b

G. intraradices 32.36 b 8.68 ab -5.22 c 47.10 b 30.10 a

Control 77.92 ab 8.42 a -1.78 ab 35.37 c 8.00 b

End of recovery G. mosseae 78.44 a 8.22 a -1.96 b 45.02 b 7.50 b

G. intraradices 74.64 b 5.94 b -1.68 a 54.17 a 16.60 a

Data are means of 10 replicates

Letters in the same subsection indicate differences at p≤0.05

Table 3 Spartium junceum water relation parameters. Measures were done before withholding the water, at the end of the stress period and at theend of the recovery period

Relative water content (%) (RWC) Specific leaf weight (SLW) Chlorophyll (SPAD)

Control 58.34 9.21 a 50.55

Pre-stressed G. mosseae 66.36 7.76 b 50.21

G. intraradices 64.79 10.51 a 52.93

Control 48.43 b 8.44 54.48

End of drought G. mosseae 31.96 c 9.61 52.62

G. intraradices 52.65 a 7.04 53.53

Control 78.15 8.16 47.29

End of recovery G. mosseae 86.57 7.73 45.25

G. intraradices 81.57 8.65 45.11

Data are means of 10 replicates

Letters in the same subsection indicate differences at p≤0.05

Differential effects of two species of arbuscular mycorrhiza 99

and Xia 2006); in our experiment A. cytisoides inoculatedwith G. intraradices had more leaves in all measurements,although the plants responded to drought defoliating, con-firming previous results (Haase et al. 2000; Archer et al.2002) that describe the shrub as drought deciduous. At theend of the drought episode, control plants retained morechlorophyll, and mycorrhizal plants were more yellow, thesituation was reversed at the end of the recovery period whencontrol plants had the least chlorophyll, and plants inoculatedwith G. intraradices had almost pre-stress measurements ofSPAD. In Rosmarinus officinalis subjected to drought thechlorophyll content of leaves was reduced by up to 85%during the drought with an increase in the de-epoxidationstate of the xanthophyll cycle which conferred protectionagainst irreversible damage to the photosystem under a severedrought stress, enabling the recovery of the plants after theautumn rains (Munné-Bosch and Alegre 2009). In ourexperiment the early onset of the xantophyll cycle shownby theG. intraradices plants might explain the quick recoveryof the chlorophyll once the irrigation is re-established. Lowerleaf osmotic potentials have been associated to plants adaptedto growing on xeric sites (Gebre et al. 1998; Liu et al. 2003),A. cytisoides shows low water potential values, even whenwell watered and the symbiosis lowers the values measured atthe pre-stress phase and also at the end of the stress period.The low relative water content (RWC) measures and therelatively high specific leaf weight (SLW) show that A.cytisoides possess typical xeric characteristics such as thickleaves, also enhanced by the establishment of the symbiosis.It has been shown for Fragaria virginiana (O’Neill 1983)that osmotic adjustments are dependent on leaf age, with thehighest capacity for adjustment in the intermediate ageleaves; old leaves senesce and promote the osmotic adjust-ment of the rest. In our experiment, at the end of the recoveryperiod the SLW of plants inoculated with G. intraradices hada higher SLW than the other treatments, inoculated with G.mosseae and non mycorrhizal control, and their osmoticpotential was higher than the values observed at the pre-stressperiod for the same treatment. This could be the result of thesenescence of older leaves followed by the severe defoliationobserved during the drought stress. Most of the leaves thatremained in the G. intraradices plants might be young,explaining the values both of SLW, of osmotic pressure andof SPAD observed. The data found for A. cytisoides showthat the plant has a double system of drought tolerance, itdefoliates thus avoiding drought but also lowers the osmoticpotential of the leaves thus increasing its intrinsic droughtresistance. At the pre-stress measurements S. junceum waterrelation parameters were not significantly changed bythe symbiosis, except for the specific leaf weight (SLW) thatwas higher for G. intraradices plants, whilst A. cytisoidesSLW was higher for plants inoculated with both fungiassayed. Similar results were found for Erythrina variegata

(Manoharan et al. 2010) confirming that mycorrhization canfavour the adaptation to xeric environments. At the end of thedrought period the relative water content of plants inoculatedwith G. intraradices was higher that the RWC of control andof G. mosseae plants. Soya bean plants were also shown tohave an increased RWC due to mycorrhization (Aliasgharzadet al. 2006) at all soil moisture levels. In that case both fungiassayed, G. mosseae and Glomus etunicatum gave similarresults; in our experiment G. intraradices was significantlybetter than G. mosseae at improving the plant response todrought stress. At the end of the recovery period, waterrelation parameters in S. junceum were not significantlydifferent among treatments.

Both plants, indigenous legumes from semi arid Medi-terranean shrub lands, are often used in revegetationstrategies (Requena et al. 2001; Preti and Giadrossich2009). The use of mycorrhiza inoculated plants canenhance plant growth and also improve the response todrought, thus increasing the possibilities of survival andgrowth of these plants in an arid environment. The selectionof the fungal inoculum is decisive as not all the AM fungielicit the same response. In these experiments, G. intra-radices BEG 72 was found to be superior to G. mosseaeBEG 116, this difference could be attributed to the origin ofthe fungus, a native isolate from a Mediterranean area,compared to G. mosseae (BEG 116) isolated from the UK.These results confirm that the use of mycorrhizal inocula-tion should be included as a standard practice in revegeta-tion programs (Estaún et al. 2008), specially in degradedsemi arid soils where the AMF might be in low numbersand unable to establish an effective symbiosis.

Acknowledgements This work has been partly funded by theSpanish Ministry of Science (MICINN) grants CGL2006-05648/BOS and INIA RTA2007-00039.

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