Effect of Water Potential and Temperature on the Germination of Four Species of African Savanna Trees

The germination responses of seeds from the African tree speciesColophospermum mopane, Combretum apiculatum, Acacia tortilisand Acacia karroo under varying regimes of temperature and waterstress (induced by incubation in PEG 8000) are reported Withthe exception of Combretum (at –0.14 and –0.29 MPa)and Colophospermum (at –0.29 MPa), incubation in PEG decreasedthe maximum achieved germination percentage (90–100% forall species), but did not extend the germination lag (exceptin Combretum) or affect the time required to reach maximum germinationCombretum and Colophospermum were found to germinate under thewidest range of temperatures and water potentials, for example,as strongly negative as –1.0 MPa at 20 and 30 °C,respectively These seeds also showed greater or equivalent hypocotylelongation in PEG solutions creating potentials of –0.14,–0.29 or –0.51 MPa when compared with seeds germinatedin water, indicating an additional stress adaptation Acaciaspecies showed progressive reduction in germination rates andradicle elongation in response to decreasing water potentialExperiments giving pre-imbibition treatments in water priorto transfer to PEG solutions showed that both Acacia speciesgerminated at approximately 90% if given such pre-treatmentand less than 10% if transferred directly to PEG It is concludedthat the most stress-adapted species studied are Colophospermummopane and Combretum apiculatum, a finding generally correlatedwith the growth habit of these trees Colophospermum mopane, Combretum apiculatum, Acacia tortilis, Acacia karroo, germination, water stress, Zimbabwe     

Effect of Water Deficit on Accumulation of Dry Matter, Carbon and Nitrogen in the Kernel of Wheat Genotypes Differing in Yield Stability

Water stress effects on accumulation of dry matter, carbon andnitrogen in grains were analysed in varieties and species ofwheat differing in yield stability. Variable water environmentswere generated using a line source sprinkler system. Althoughlarge fluctuations occurred in the water potentials of the flagleaf and ear, grain growth remained relatively buffered undermoisture stress. Developing grains were at a lower moisturelevel throughout grain growth in plants subjected to moisturestress relative to the unstressed plants. Carbon content decreasedmore than the nitrogen content in the stressed grains of thespecies and varieties. Reduction in the duration of grain growthand the rate of dry weight accumulation induced by water stresswas more prominent in T. aestivum var. C306 and T. sphaerococcum.Grain yield was reduced significantly under water stress, themaximum being in the high yielding cultivar HD2329. Both grainnumber and grain weight were reduced in response to stress,the extent of reduction being different in different genotypes.Copyright1994, 1999 Academic Press Water deficit, yield stability, C and N accumulation, heat degree days     

Comparison of Osmotic Adjustment Responses to Water and Temperature Stresses in Spring Wheat and Sudangrass

This study explores the mechanisms of osmotic adjustment bycomparing the growth of spring wheat and sudangrass, which exhibitdifferent degrees of osmotic adjustment, under soil water andtemperature stresses. Leaf water potential ( ₁), osmotic potential(), and rate of leaf area growth of spring wheat and sudangrassseedlings were measured at combinations of five soil water potentials,from -0·03 to -0·25 MPa, and six root temperatures,from 14 to 36°C. Spring wheat exhibit little osmotic adjustment.The leaf osmotic potential was not affected by either soil wateror root temperature stress. Osmotic potential of sudangrassdecreased in parallel with the decreasing leaf water potentialas a result of osmotic adjustment. As soil water potential decreasedfrom -0·03 to -0·25 MPa, the rates of growth andphotosynthesis of spring wheat both decreased by about 30%.For sudangrass with the same range of soil water potential,the photosynthesis rate decreased by only 10% while the leafarea growth rate decreased by 49%. We introduce a dimensionlessindex (R) to quantify the degree to which environmental stressesalter the balance between production of photosynthates and theiruse for growth. The index, R, is equal to 1 when stress reducesgrowth and photosynthesis by the same degree, i.e. the balancebetween production and consumption of photosynthate is not disturbed.R is smaller than 1 when growth is reduced more than photosynthesis.R was equal to 1 for spring wheat where there was no osmoticadjustment. For sudangrass, R decreased from 1 to 0·25as osmotic potential decreased from -1·10 to -1·63MPa. These findings lead to the hypothesis that osmotic adjustmentcould result from an imbalance between production, consumptionand translocation of photosynthates under stressed conditions.Copyright1993, 1999 Academic Press Osmotic adjustment, water stress, root temperature     

More than 400 million years of evolution and some plants still can't make it on their own: plant stress tolerance via fungal symbiosis

All plants in natural ecosystems are thought to be symbioticwith mycorrhizal and/or endophytic fungi. Collectively, thesefungi express different symbiotic lifestyles ranging from parasitismto mutualism. Analysis of Colletotrichum species indicates thatindividual isolates can express either parasitic or mutualisticlifestyles depending on the host genotype colonized. The endophytecolonization pattern and lifestyle expression indicate thatplants can be discerned as either disease, non-disease, or non-hosts.Fitness benefits conferred by fungi expressing mutualistic lifestylesinclude biotic and abiotic stress tolerance, growth enhancement,and increased reproductive success. Analysis of plant–endophyteassociations in high stress habitats revealed that at leastsome fungal endophytes confer habitat-specific stress toleranceto host plants. Without the habitat-adapted fungal endophytes,the plants are unable to survive in their native habitats. Moreover,the endophytes have a broad host range encompassing both monocotsand eudicots, and confer habitat-specific stress tolerance toboth plant groups. Key words: Colletotrichum, fungal endophytes, stress tolerance, symbiosis, symbiotic lifestyle Received 19 June 2007; Revised 25 November 2007 Accepted 30 November 2007     

Biomass and Pigment Production in Three Isolates of Azolla I. Response to Water Stress

Two isolates of Azolla Lam. from Colombia, South America, andone from the USA (Florida) were selected for characterizationof their growth potentials in certain defined stress environments.These isolates were Amazonian (RAR) and Atlantic coastal (M-3)specimens of Azolla caroliniana Willd and a Floridian variety(LA) of Azolla filiculoides Lam. Osmotic stress (from polyethylene glycol-amended media) andosmotic/salt stress (from seawater-amended media) were the chosendeterminants in these trials. Their effects on growth responseswere monitored. Initial growth rates of LA and M-3 were stimulatedat 1 and 5 ppt seawater salts, relative to growth under controlconditions. RAR, however, was generally the most stable isolatein the experiments with seawater-induced ionic stress. LA wasmost stable in its biomass growth in experiments with polyethyleneglycol 6000, but chlorophyll accumulation data were again leastaffected in RAR. LA survived the longest of the three isolatesat a water potential of approximately —10 bars with eitherseawater (13 ppt salts) or polyethylene glycol (26 per cent).The latter amendment was usually more inhibitory to acetylenereduction rates in RAR and consistently more inhibitory in LA.RAR was tentatively judged by its reactions to water stressto be the superior isolate of the three. Azolla caroliniana Willd., Azolla filiculoides Lam., biomass and chlorophyll accumulation, acetylene reduction, osmotic/salt stress     

Inhibition of photosynthesis in olive trees (Olea europaea L.) during water stress and rewatering

The effect of high levels of natural light on leaf photosynthesisin olive trees (Olea europaea L. var. Coratina), grown in potsoutdoors in the summer and subjected to water, stress, was studied.Net photosynthetic rates reached maximum values early in themorning in both control and stressed plants and subsequentlydeclined gradually. This inactivation of photosynthetic activitywas accompanied by changes in the fluorescence characteristicsof the upper intact leaf surface. The maximum fluorescence yield(Fp) and the ratio Fv/Fp decreased at midday especially in water-stressedplants, but the initial fluorescence (Fo) rose to a maximumvalue at midday and declined again in the afternoon. In controlplants the values of maximum fluorescence Fp and the ratio Fv/Fpincreased again in the afternoon and had recovered almost completelyby 8 p.m. as the leaf water potential recovered. In stressedplants this diurnal recovery was not complete, so that the photosyntheticrates and the ratio Fv/Fp declined gradually during the developmentof water stress. These results indicate that in olive treessubjected to severe water stress the non-stomatal componentof photosynthesis was affected and perhaps a light-dependentinactivation of the primary photochemistry associated with photosystemII (PSII) occurred. Four to five days after rewatering severelystressed plants, the predawn leaf water potential, net photosyntheticrates and chlorophyll fluorescence indices recovered only partially. Key words: Olea europaea, photosynthesis, water stress, chlorophyll a fluorescence, inhibition of photosynthesis     

Maize lateral root developmental plasticity induced by mild water stress. I: Genotypic variation across a high‐resolution series of water potentials

Lateral root developmental plasticity induced by mild water stress was examined across a high‐resolution series of growth media water potentials (Ψ_w) in two genotypes of maize. The suitability of several media for imposing near‐stable Ψ_w treatments on transpiring plants over prolonged growth periods was assessed. Genotypic differences specific to responses of lateral root growth from the primary root system occurred between cultivars FR697 and B73 over a narrow series of water stress treatments ranging in Ψ_w from ?0.25 to ?0.40 MPa. In FR697, both the average length and number of first‐order lateral roots were substantially enhanced at a Ψ_w of ?0.25 MPa compared with well‐watered controls. These effects were separated spatially, occurring primarily in the upper and lower regions of the axial root, respectively. Furthermore, first‐order lateral roots progressively increased in diameter with increasing water stress, resulting in a maximum 2.3‐fold increase in root volume at a Ψ_w of ?0.40 MPa. In B73, in contrast, the length, diameter, nor number of lateral roots was increased in any of the water stress treatments. The genotype‐specific responses observed over this narrow range of Ψ_w demonstrate the necessity of high‐resolution studies at mild stress levels for characterization of lateral root developmental plasticity.     

Ecophysiological Mechanisms used by Aster kantoensis, an Endangered Species, to Withstand High Light and Heat Stresses of its Gravelly Floodplain Habitat

Aster kantoensis Kitam., an endangered plant species of thefamily Compositae, is a local endemic to the gravelly floodplainsof a few rivers in central Japan. The successful growth of A.kantoensis is mainly restricted to sparsely vegetated siteswhere, due to lack of continuous vegetation, high radiant energyinput results in stressful conditions with excessive light andheat. To reveal the ecophysiological characteristics which enablethe species to cope with such environmental stresses, we measuredleaf temperature, shoot architecture and photosynthetic andtranspirational responses together with the microclimate ofthe natural habitat. Even under sunny summer conditions, theleaf temperature of A. kantoensis was much lower (35–39°C)than the soil surface temperature (max. 60°C). The relationshipbetween leaf position (height from the ground) and leaf temperatureshowed that the caulescent rosette form of A. kantoensis helpsavoid leaf overheating. Moreover, in situ gas exchange measurementsrevealed that the high transpirational capacity (as high as10 mmol H₂O m^-2s^-1) was effective in controlling leaf temperature,as long as the soil water supply was not severely limited. Sinceit has effective mechanisms to avoid the multiple stresses indigenousto its gravelly floodplain habitat, A. kantoensis can maintaina high photosynthetic rate (up to 30 µmol CO₂m^-2s^-1) withoutany midday depression under sunny summer conditions. Copyright2000 Annals of Botany Company Aster kantoensis Kitam., gravelly floodplain, high light stress, leaf temperature, photosynthesis, shoot architecture, transpiration     

Phylogenetic Relationships of Empetraceae, Epacridaceae, Ericaceae, Monotropaceae, and Pyrolaceae: Evidence from Nuclear Ribosomal 18s Sequence Data

Recent studies of phylogenetic relationships have indicatedthat the traditional recognition of Epacridaceae and Empetraceaeas distinct from Ericaceae should be reevaluated. These studiesused morphological data and nucleotide sequence from the chloroplastencodedrbc L (rubisco, large subunit) gene. They indicated thatEricaceae as presently recognized are paraphyletic and shouldinclude Epacridaceae and Empetraceae, as well as Pyrolaceaeand Monotropaceae. A study of nuclear ribosomal 18s gene sequenceswas undertaken to test the hypothesis that Epacridaceae forma monophyletic derived group out of Ericaceae. The problematictaxaPrionotesandLebetanthuswere included because these taxahave been alternatively placed in Ericaceae and Epacridaceae.Representatives of the herbaceous (Pyrolaceae) and mycoparasitictaxa (non-chlorophyllous, Monotropaceae) were also includedin the study. Taxa that represented lineages peripherally relatedto Ericaceae and Epacridaceae were included in order to developa better understanding of the relationships and limits of Ericales.Parsimony analyses of 18s sequences and a combined analysisof 18s+rbcL sequences were performed. Results of these analysesindicate strong support for the recognition of a monophyleticEricaceae that includes Empetraceae, Epacridaceae, Pyrolaceae,and Monotropaceae. nr18s; Empetraceae; Epacridaceae; Ericaceae; Monotropaceae; Pyrolaceae; rbc L     

Effects of Temperature and Water Potential on Germination, Radicle Elongation and Emergence of Mungbean

Controlled environment experiments were performed to determinethe effects of temperature and water potential on germination,radicle elongation and emergence of mungbean (Vigna radiata(L.) Wilczek cv. IPB-M79-17-79). The effects of a range of constant temperatures (15–45°C) and water potentials (0 to –2.2 MPa) on germinationand radicle elongation rates were studied using an osmoticumtechnique, in which seeds were held against a semi-permeablemembrane sac containing a polyethylene glycol solution. Linearrelationships were established between median germination time(Gt₅₀) and water potential at different temperatures, and betweenreciprocal Gt₅₀ (germination rate) and temperature at differentwater potentials. Germination occurred at potentials as lowas –2.2 MPa at favourable temperatures (30–40 °C),but was fastest at 40 °C when water was not limiting, withan estimated base temperature (T_b) of about 10 °C. Subsequentradicle elongation, however, was restricted to a slightly narrowertemperature range and was fastest at 35 °C. The conceptof thermal time was used to develop an equation to model thecombined effects of water potential and temperature on germination.Predictions made using this model were compared with the actualgermination obtained in a related series of experiments in columnsof soil. Some differences observed suggested the additionalimportance of the seed/soil/water contact zone in influencingseed germination in soil. Seedling emergence appeared to reflectfurther the radicle elongation results by occurring within anarrower range of temperatures and water potentials than germination.Emergence had an estimated T_b of 12.6 °C and was fastestat 35 °C. A soil matric potential of not less than about–0.5 MPa at sowing was required to obtain 50% or moreseedling emergence. Key words: Germination, temperature, water potential     

Nitrogen and Phosphorus Nutrition in Mycorrhizal Epacridaceae of South-west Australia

Xylem transport of nitrogen and phosphorus was examined in maturemycorrhizal plants of 41 species in 15 genera of Epacridaceaein native habitat in south-west Australia. Glutamine was theprincipal nitrogenous solute of xylem of all but four species.In the latter species, arginine or asparagine predominated.Nitrate and ammonium comprised minor fractions of xylem (tracheal)sap N, except in two species in which nitrate contributed overhalf of the N. Ratios of total-N:phosphate-P in xylem sap variedwidely (mean 67±18, range 0.2–495) between speciesand habitats. Plants ofCroninia kingiana (syn.Leucopogon kingeanus)from the one habitat showed higher levels of N and P in xylemearly than late in the mycorrhizal season, but there was noconsistent evidence of higher N and P levels from upper thandeeper parts of their root systems. Study of juvenile populationsof four species of epacrids indicated that substantial fractionsof the yearly increment of N, P and dry matter was accumulatedduring the three summer months when infected mycorrhizal hairroots were absent. Glasshouse culture of mycorrhizal plantsof Epacridaceae in habitat soil enriched with decomposed andleached double (¹³C,¹⁵N)-labelled dry matter of wheat showedsubstantial labelling of shoots with¹⁵N but not with¹³C. Plantsfed similarly treated¹⁵N-labelled root residues of maize acquired¹⁵Nbut failed to generate ¹³C values different from those of controlplants. Possible avenues of mycorrhizal and non-mycorrhizalnutrition of Epacridaceae are discussed. amino acids; mycorrhizal nutrition; xylem transport; south-west Australia; Epacridaceae; nitrogen; phosphorus     

The Structure and Fungal Associates of Mycorrhizas in Leucopogon parviflorus (Andr.) Lindl.

Mycorrhizal root systems ofLeucopogon parviflorus (Andr.) Lindl.were collected from wild populations at three sites on the coastof New South Wales, Australia and examined by light and electronmicroscopy. The structure of the hair roots is typical of thefamily, there being an epidermal layer in which ericoid mycorrhizasare formed, two cortical layers (an exodermis and endodermis)and a very small stele. The colour, size and coil structureof the fungal symbionts indicate that there were at least twodifferent fungi that consistently formed ericoid mycorrhizalstructures at these sites. Transmission electron microscopyof the endophytes showed only ascomycete fungi. Plants fromtwo of the populations were used for fungal isolations. Fungiwere isolated by incubating surface sterilized hair-root piecesin a solution of bovine serum albumin with penicillin and streptomycin.Twenty-one different culture types were obtained, four of whichwere common to both sites. Two of the common culture types weredark, sterile, slow-growing cultures similar to the ericoidendophyteHymenoscyphus ericae(Read) Korf & Kernan. Leucopogon parviflorus ; bearded heath; Epacridaceae; Ericaceae; mycorrhiza; ultrastructure; endophytes; callose     

Adaptive Growth Responses to Osmotic Stress of Hypocotyl Sections of Vigna unguiculata: Roles of the Xylem Proton Pump and IAA

The growth responses to osmotic stress of hypocotyl sectionsof Vigna unguiculata were studied by the xylem perfusion method.Hypocotyl sections shrank upon exposure to osmotic stress. Sectionsshowed no adaptive responses to osmotic stress when they werein an IAA-depleted condition as a result of perfusion with solutionsthat lacked IAA for 3–4 h. The correlation between thegrowth rate and the membrane potential of the xylem/symplastboundary (V^px) was very limited in the absence of IAA. By contrast,hypocotyl sections showed distinct adaptive responses to osmoticstress after perfusion with solutions that contained 10 µMIAA. In the presence of IAA, V^px increased in the negative directionand growth resumed in spite of the osmotic stress. The growthrate was closely correlated with the xylem membrane potential.Hyper-polarization of the membranes of the xylem/symplast boundaryalways preceded the recovery of growth under osmotic stress.It appears that IAA is essential for the adaptive recovery ofgrowth under osmotic stress and, moreover, that the xylem protonpump plays an indispensable role in modulating the growth ofhypocotyl sections. This result confirms prediction of an earliersimulation study using the apoplast canal model [Katou and Furumoto(1986) Protoplasma 133: 174, Katou and Enomoto (1991) PlantCell Physiol. 32: 343]. (Received June 27, 1996; Accepted October 28, 1996)     

Cytoevolution, Phylogeny and Taxonomy in Epacridaceae

Chromosome numbers in Epacridaceae were collated from variousauthors and superimposed on to recent cladograms for the family.The results strongly indicate that reduction in chromosome numberoccurs with evolutionary advancement. Thus Epacridaceae, incommon with ‘Ericaceaesens. strict .’ and ‘Vacciniaceaesens.strict. ’, has evolved from a primitive karyotype of atleastx =12 and probablyx =13. This conclusion dispels earlierpaleopolyploid models based on a primitivex =6 in the family.Other aspects of cytoevolution, such as chromosome number asa generic character especially in cytologically advanced generaof the Styphelieae, are discussed. Cytoevolution; cladistic models; primitive character states for chromosome number; dysploid falls; cytotaxonomy; Epacridaceae; Richeoideae; Epacridoideae; Epacrideae; Styphelieae; Ericaceae     

Sagebrush (Artemisia tridentata Nutt.) roots maintain nutrient uptake capacity under water stress

Phosphorus and nitrogen uptake capacities were assessed during36–58 d drying cycles to determine whether the abilityof sagebrush (Artemisia tridentata Nutt.) to absorb these nutrientschanged as the roots were subjected to increasing levels ofwater stress. Water was withheld from mature plants in large(6 I) containers and the uptake capacity of excised roots insolution was determined as soil water potentials decreased from–0.03 MPa to –5.0 MPa. Phosphorus uptake rates of excised roots at given substrateconcentrations increased as preharvest soil water potentialsdecreased to –5.0 MPa. V_max and K_m also increased as soilwater potentials declined. Declining soil water potentials depressednitrogen uptake at set substrate concentrations, but uptakecapacity, calculated as the sum V_max for both NH⁺₄+NO^–₃,did not change significantly with drying. The sum V_max correlatedwith root nitrogen concentration. Root uptake capacity for nitrogen and phosphorus was extremelystable under severe water stress in this aridland shrub. Maintenanceof uptake capacity, coupled with a previously demonstrated abilityto conduct hydraulic lift, may enable A. tridentata better tomaintain nitrogen and phosphorus uptake as soil water availabilitydeclines. These mechanisms may be important in the ability ofA. tridentata to maintain growth, complete reproduction, andgain an advantage against competitors late in the season whenthe soil layers with higher nutrient availability are dry. Key words: Kinetics, nitrogen, phosphorus, roots, water stress     

The Relationship between Stem Diameter and Water Potentials in Stems of Young Cabbage Plants

Continuous measurements were made of stem shrinkage, stem waterpotential (₃) and transpiration rate (T) in young, pot-growncabbage plants subjected to cycling evaporative demands. Sequencesof increasing evaporative demands induced increases in T anddecreases in both ₃ and stem diameter and conversely, wheneverevaporative demand decreased, T declined and ₃ and stem diameterrose. Over short periods, stem water potentials and stem shrinkagewere virtually parallel even when rapid oscillations were induced.Over longer periods the effects of growth were important comparedwith those of water stress on stem diameter when the moisturecontent of the soil was high. Growth, however, ceased when theplant was subjected to relatively mild water stress (₃ = –0.4MPa). Stem diameters, after correction for growth, were linearlyrelated to plant water potential. The results suggest that stemshrinkage and only a few calibration measurements might be usedto provide continuous estimates of water potentials in fieldcrops. Key words: Cabbage, Stem diameter, Stem water potential     

The Use of Coleoptile Responses to Water Stress to Differentiate Wheat Genotypes for Osmoregulation, Growth and Yield

Differences in osmoregulation between genotypes of wheat (Triticumaestivum L.) were identified by measuring responses of coleoptilesto water stress. Seeds were germinated in Petri dishes on germinationpads. Water stress was applied when coleoptiles were 1 cm longby either adding polyethylene glycol 6000 (20% w/w) or by removingthe lids of the dishes and allowing the pads to dry by evaporationfor a period of 2 d, or from the beginning of germination byvarying the amount of water in the germination pads. Measurementsof the water and osmotic potentials of shoots and roots (usingthermocouple psychrometers) were used to estimate turgor pressures.Wheat genotypes showed the same segregation for shoot and rootlengths and turgor pressures as they had done in previous studiesfor flag-leaf osmoregulation and yield. It was concluded thatobservations of the responses of coleoptile length to waterstress could be used in plant-breeding applications to identifydifferences in osmoregulation between genotypes of wheat. Triticum aestivum, osmoregulation, turgor maintenance, coleoptile growth, root, selection criterion     

Molecular diversity within and between ericoid endophytes from the Ericaceae and Epacridaceae

This study investigated the relationships between ericoid mycorrhizal endophytes of the Ericaceae (Northern Hemisphere) and the Epacridaceae (Australia). Over 200 fungi were isolated from the roots of two species of Epacridaceae from Victoria, Australia. The isolates were divided into 12 groups by morphology on quarter-strength potato dextrose agar. All were slow-growing and most were dematiaceous, but groups varied from white through pink to dark olive. The ITS1–5.8S–ITS2 ribosomal DNA was amplified and sequenced from eight isolates, forming typical ericoid mycorrhizal morphology in Epacris impressa and one nonmycorrhizal isolate. Sequences were compared, by using similarities and maximum-parsimony analysis, with those of Hymenoscyphus ericae (Leotiales) and Oidiodendron species (Hyphomycetes), the most common endophytes of the Ericaceae. Maximum-parsimony analysis produced four clusters: (1) all Oidiodendron species (at least 90% similarity); (2) all five Victorian dark grey-olive isolates (at least 96% similarity); (3) one Victorian isolate and Cistella grevillei (88% similarity); (4) two light-coloured Victorian isolates and H. ericae (81% similarity). This suggests that these isolates from the Epacridaceae do not belong to the same species as those forming ericoid mycorrhiza in the Ericaceae.     

Effects of Increasing Water Stress on Simulated Swards of Festuca arundinacea Schreb under Wind Tunnel Conditions

The effects of increasing water stress on water relations, leafconductance, leaf extension and leaf rolling of Festuca arundinaceain sward (I m²) were investigated under wind tunnel conditions.The plants were grown in a container 60 cm deep and the experimentwas conducted over a 36 d period. Upon cessation of watering(day 11), leaf extension and conductance were affected. Within8 d, the onset of leaf rolling helped to reduce transpirationand to maintain leaf water potential. Nocturnal recovery of turgor potential helped in maintainingleaf extension at a moderate level and in the final 5 d waterand osmotic potentials dropped sharply as leaf rolling becamemore acute and leaf extension stopped. The grass combines various morphological and physiological mechanismsto prevent water losses and maintain growth. Festuca arundinacea, tall fescue, wind tunnel, water stress, water potential, osmotic potential, conductance, leaf rolling, leaf extension     

Utilisation of organic nitrogen and phosphorus sources by mycorrhizal endophytes of Woollsia pungens (Cav.) F. Muell. (Epacridaceae)

 The ability of four ericoid mycorrhizal endophytes isolated from roots of Woollsia pungens (Cav.) F. Muell. (Epacridaceae) to utilise organic forms of nitrogen and phosphorus during growth in axenic culture was assessed. All isolates were able to utilise glutamine, arginine and bovine serum albumin (BSA), along with NH₄ ⁺ or NO₃ ^–, in most cases yielding at least as much biomass as the ericoid mycorrhizal endophyte Hymenoscyphus ericae (Read) Korf & Kernan. All isolated endophytes were able to utilise BSA, arginine and glutamine as sole sources of N and C. With the exception of a single isolate (C40), which showed little growth on glutamine, biomass yields on glutamine as the sole N and C source was significantly greater for all isolates than on either of the other two organic N sources. Two isolates from W. pungens (C40 and A43) utilised DNA and sodium inositol hexaphosphate as sole P sources, in each case yielding significantly more biomass than H. ericae. The results suggest that mycorrhizal endophytes from epacrid plant hosts and those from ericaceous hosts have similar abilities to utilise organic forms of N and P. Accepted: 4 September 1998