Species In Semi-arid Grasslands Research Articles

Contrasting Effects of Grazing in Shaping the Seasonal Trajectory of Foliar Fungal Endophyte Communities on Two Semiarid Grassland Species.

Fungal endophytes are harboured in the leaves of every individual plant host and contribute to plant health, leaf senescence, and early decomposition. In grasslands, fungal endophytes and their hosts often coexist with large herbivores. However, the influence of grazing by large herbivores on foliar fungal endophyte communities remains largely unexplored. We conducted a long-term (18 yr) grazing experiment to explore the effects of grazing on the community composition and diversity of the foliar fungal endophytes of two perennial grassland species (i.e., Artemisia capillaris and Stipa bungeana) across one growing season. Grazing significantly increased the mean fungal alpha diversity of A. capillaris in the early season. In contrast, grazing significantly reduced the mean fungal alpha diversity of endophytic fungi of S. bungeana in the late season. Grazing, growing season, and their interactions concurrently structured the community composition of the foliar fungal endophytes of both plant species. However, growing season consistently outperformed grazing and environmental factors in shaping the community composition and diversity of both plant species. Overall, our findings demonstrate that the foliar endophytic fungal community diversity and composition differed in response to grazing between A. capillaris and S. bungeana during one growing season. The focus on this difference will enhance our understanding of grazing's impact on ecological systems and improve land management practices in grazing regions. This variation in the effects of leaf nutrients and plant community characteristics on foliar endophytic fungal community diversity and composition may have a pronounced impact on plant health and plant-fungal interactions.

Phosphorus Availability Mediates Grazing Impacts on Resorption and Allocation of Foliar Nitrogen and Phosphorus by Dominant Species in Semiarid Grasslands

Phosphorus Availability Mediates Grazing Impacts on Resorption and Allocation of Foliar Nitrogen and Phosphorus by Dominant Species in Semiarid Grasslands

Drought Eliminates the Difference in Root Trait Plasticity and Mycorrhizal Responsiveness of Two Semiarid Grassland Species with Contrasting Root System.

Root traits and arbuscular mycorrhizal (AM) fungi are important in determining the access of plants to soil resources. However, whether plants with different root systems (i.e., taproot vs. fibrous-root) exhibit different root trait plasticity and mycorrhizal responsiveness under drought remains largely unexplored. Tap-rooted Lespedeza davurica and fibrous-rooted Stipa bungeana were grown in monocultures in sterilized and live soils, followed by a drought treatment. Biomass, root traits, root colonization by AM fungi, and nutrient availability were evaluated. Drought decreased biomass and root diameter but increased the root:shoot ratio (RSR), specific root length (SRL), soil NO3--N, and available P for the two species. Under control and drought conditions, soil sterilization significantly increased the RSR, SRL, and soil NO3--N for L. davurica, but this only occurs under drought condition for S. bungeana. Soil sterilization significantly reduced AM fungal root colonization of both species, but drought significantly increased it in live soil. In water-abundant conditions, tap-rooted L. davurica may depend more on AM fungi than fibrous-rooted S. bungeana; however, under drought conditions, AM fungi are of equal importance in favoring both plant species to forage soil resources. These findings provide new insights for understanding the resource utilization strategies under climate change.

Interactions between soil water and plant community during vegetation succession in the restored grasslands on the Loess Plateau of China

AbstractPlant–soil water relations are important for understanding the development of plant communities, especially in arid and semiarid areas. However, the interactions between vegetation characteristics and soil water dynamics in the restored grasslands along succession chronosequence were limitedly understood. In this study, we measured the functional traits of dominant species, plant community characteristics and soil water dynamics in grasslands restored for 5, 15, and 30 years (RG5, RG15 and RG30, respectively), and investigated the linkage between plant traits and soil water at the community/plot scale. The results showed that soil water content was high at RG5, while soil water storage increment at RG5 was low. With soil water content highest at RG5 (16.25%), decreased at RG15 (14.81%), and then recovered in some degree at RG30 (15.2%), dominant plant species changed from pioneer species Artemisia capillaries to perennial legume Lespedesa davurica with high specific leaf area, and finally to perennial forb Stipa bungeana with low specific leaf area and low shoot/root ratio. Plant community characteristics including aboveground biomass, vegetation coverage, species diversity all increased with restoration and reached the highest value at RG15 or RG30. Aboveground biomass of perennial grass, as well as species richness showed a significantly positive relationship with soil water recharge and soil water storage increment at deeper layers (10–120 cm and 40–120 cm). Species diversity had positive correlations with soil water content in 0–10 cm layer, a negative correlation with soil water storage increment in 0–10 cm layer and no correlation in 10–20 cm layer. Our findings suggested that changes in soil water content might enhance perennial grass species in semiarid grasslands, and time lag also existed in the plant–soil water interactions.

Soil moisture and species richness interactively affect multiple ecosystem functions in a microcosm experiment of simulated shrub encroached grasslands

Understanding relationships between biodiversity and ecosystem functions (BEF) and the way in which ecosystem functions respond to changing climatic conditions or community composition is useful for predicting ecological consequences of global changes. However, how soil moisture condition, plant species richness interactively affect ecosystem functions in shrub-encroached grasslands is poorly understood. We conducted a soil moisture × species richness microcosm experiment using semi-arid grassland species with a N-fixing shrub Caragana microphylla Lam. as the dominant species to evaluate how soil moisture and plant species richness affected ecosystem functions directly or indirectly via regulating community functional structure, such as community-weighted mean values (CWM) and functional dispersion (FDis). Soil moisture and species richness interactively affected soil functions (soil C-, N-, P cycles and soil multifunctionality), with greater species richness buffering the adverse effects of soil drought. Soil moisture and species richness showed opposite effects on FDis but similar effects on CWM. FDis mediated the indirect effect of soil moisture and species richness on ecosystem functions, while CWM only mediated the indirect effect of soil moisture. More specifically, both soil moisture and plant species richness were negatively associated with soil P cycle, and the CWMPC1 contributed by traits related to resource-conservative strategy was positively associated with soil N cycle. Species richness showed a positive direct effect on total shoot biomass, which was mainly contributed by the complementarity effect of neighbor species richness. This study provides strong empirical support of how biomass and soil nutrient cycles respond to the changes of soil moisture and plant species richness in C. microphylla shrub-encroached grasslands, and insights on the mechanisms underlying the interactive effects of soil condition and community species composition on multiple ecosystem functions in N-fixing shrub encroached grasslands in semi-arid grassland regions.

Drought in maternal environment boosts offspring performance in a subordinate annual grass

Drought can induce shifts in plant species or functional group abundances, which may favor coexisting subordinate species at the expense of previous dominants. Within-generation and transgenerational phenotypic plasticity can be important mechanisms to shape species responses to drought. Although a handful of studies have already investigated transgenerational plasticity in the context of drought, they provided variable results, and usually focused on species that currently dominate communities.We performed pot experiments with Secale sylvestre, a typical subordinate species in semiarid grasslands of Central Hungary. We tested if this annual grass shows reduced growth or reproduction in response to drought, and whether drought in the maternal environment affects offspring performance.For both maternal and offspring generations, plant height, shoot biomass, flowering onset, and seed number showed no within-generation plasticity in response to drought, and drought only decreased the seed mass of mother plants. In contrast, we found strong transgenerational effects on the overall performance of progenies, which changed with offspring age. At an early life stage, shoots were shorter for the offspring of drought-treated mothers than for the progenies of control mothers. This difference turned in the opposite direction later, and tiller number was also greater for the offspring of drought-treated mothers. Furthermore, the offspring of drought-treated mothers had over two-times higher adult shoot biomass and seed production compared to the offspring of control mothers. These beneficial transgenerational effects may help S. sylvestre to gain dominance in sand grasslands following dry years that decrease the abundance of perennial grasses, a vegetation change often observed in these grasslands after droughts.Our study provides the first evidence for positive transgenerational plasticity in response to drought for a subordinate species, which may be adaptive when the suppression of dominant species in the offspring environment is predictable from drought in the maternal environment.

Direct effects of nitrogen addition on seed germination of eight semi-arid grassland species.

Seed germination plays an important role in mediating plant species composition of grassland communities under nitrogen (N) enrichment. Shifts of plant community structure with N‐enhanced deposition in terrestrial ecosystems have occurred globally. Despite numerous studies about the effects of enhanced N deposition on mature plant communities, few studies have focused on seed germination. Using a laboratory experiment, we report the effects of five N concentrations, including 0, 5, 10, 20, and 40 mM N (NH4NO3) on seed germination of eight semi‐arid grassland species. Results showed that low N concentrations (5‐ and 20‐mM N) promoted mean final germination proportion of all eight species by 4.4% and 6.4%, but high concentrations (40 mM N) had no effect. The mean germination rate was decreased 2.1% and 5.1% by higher N concentration (20‐ and 40‐mM N) levels, but germination start time showed the opposite trend, delayed by 0.7, 0.9, and 1.8 d for the 10, 20, and 40 mM N treatments. Final germination proportion, mean germination rate, and germination start time were significantly different among species in response to N concentration treatments. The final germination proportion of Allium tenuissimum and Chenopodium glaucum were suppressed by increased N concentration, whereas it increased for Potentilla bifurca, Plantago asiatica, and Setaria viridis. Our findings provide novel insights into N deposition‐induced species loss based on seed germination factors in semi‐arid grassland communities.

Native Seedling Colonization on Stockpiled Mine Soils Is Constrained by Site Conditions and Competition with Exotic Species

Sites disturbed through mining practices can be challenging to restore with native vegetation, as the path of ecological succession is often unknown and hard to predict. We conducted an establishment study that explored restoration strategies to increase native vegetation on a newly formed stockpile of soil at New Gold’s New Afton Mine in British Columbia, Canada. Establishment of native species in semi-arid grasslands is often constrained by seed and seedling microsite limitations, so treatments were imposed to assist in reducing these limitations. We established a fully factorial design with a native seed treatment (seeded and unseeded) and four soil preparations: raking, hydroseed slurry, a combination of raking and hydroseed slurry, and no preparation. Raking assisted in increasing total seedling establishment, regardless of whether the site was seeded or not. Raking and seeding increased the number of native seedlings and resulted in the greatest species richness, suggesting that native seedling establishment is primarily seed-limited, but that microclimate is also important for the establishment of some native seeds. We found that exotic species were able to capitalize on the disturbance and outcompeted the native species, but reducing seed-limitations by sowing more native seeds and increasing available microclimates by raking or tilling may increase native species’ success at the establishment phase.

Variation and heritability of morphological and physiological traits among Leymus chinensis genotypes under different environmental conditions

Intraspecific trait variation and heritability in different environmental conditions not only suggest a potential for an evolutionary response but also have important ecological consequences at the population, community, and ecosystem levels. However, the contribution of quantitative trait variation within a grassland species to evolutionary responses or ecological consequences is seldom documented. Leymus chinensis is an important dominant species in semi-arid grasslands of China, which has seriously suffered from drought and high temperature stresses in recent decades. In the present study, we measured variation and heritability of 10 quantitative traits, namely the number of tillers, maximum shoot height, number of rhizomes, maximum rhizome length, rhizome mass, aboveground mass, root mass, maximum net photosynthetic rate (Pmax), specific leaf area (SLA), and leaf length to leaf width ratio (LL/LW), for 10 genotypes of L. chinensis under one non-stress (Ck) condition and three environmental stress conditions (i.e., drought (Dr), high temperature (Ht), and both drought and high temperature (DrHt)). Result indicated that (1) the interaction of genotype and environmental condition (G×E) was significant for 6 traits but not significant for the other 4 traits as shown by two-way analysis of variance (ANOVA), suggesting that different selection forces were placed for different traits on the factors dominating phenotypic responses to different environmental conditions. Moreover, these significant G×E effects on traits indicated significantly different phenotypic adaptive responses among L. chinensis genotypes to different environmental conditions. Additionally, individuals could be grouped according to environmental condition rather than genotype as shown by canonical discriminant analysis, indicating that environmental condition played a more important role in affecting phenotypic variation than genotype; (2) by one-way ANOVA, significant differences among L. chinensis genotypes were found in all 10 traits under Ck and Dr conditions, in 8 traits under DrHt condition and only in 4 traits under Ht condition; and (3) all 10 traits showed relatively low or non-measurable broad-sense heritability (H2) under stress conditions. However, the lowest H2 value for most traits did not occur under DrHt condition, which supported the hypothesis of 'unfavorable conditions have unpredictable effects' rather than 'unfavorable conditions decrease heritability'. Results from our experiment might aid to improve predictions on the potential impacts of climate changes on L. chinensis and eventually species conservation and ecosystem restoration.

Predicting root biomass for semiarid grassland species of the southern Chihuahuan Desert

Most of carbon in grasslands comes from underground biomass, particularly in arid grassland ecosystems. However, estimation of root biomass in these ecosystems has been poorly studied. In this study was analyzed the correlation between above ground plant variables and root biomass to develop statistical models for reliable root biomass estimations. Twenty-six plant species were collected within grazing-excluded grasslands. Linear, exponential and logarithmic regression models were performed for each species and for the whole data set to determine the variables that best predicted root biomass. Only Frankenia gypsophila and Dalea gypsophila showed root/shoot ratio (RSR) higher than one. Enneapogon desvauxii and Atriplex acantocarpha had a RSR close to one. Eight species showed statistical significance in at least one of the correlation analyses but only Tiquilia canescens, Bouteloua gracilis, Machaerantera pinnatifida, Lesquerella fendleri, and Atriplex acanthocarpa had both statistical significance and acceptable coefficient of determination (r2 ≥0.50). Using the Marquardt exponential method, 14 out of 15 studied species showed a high determination coefficient and statistical significance. This method was adequate (r2=0.853) to estimate root biomass for the whole set of plants from plant height and crown diameter.

Responses of litter decomposition and nutrient release rate to water and nitrogen addition differed among three plant species dominated in a semi-arid grassland

Precipitation and nitrogen (N) deposition are predicted to increase in northern China. The present paper aimed to better understand how different dominant species in semi-arid grasslands in this region vary in their litter decomposition and nutrient release responses to increases in precipitation and N deposition. Above-ground litter of three dominant species (two grasses, Agropyron cristatum and Stipa krylovii, and one forb, Artemisia frigida) was collected from areas without experimental treatments in a semi-arid grassland in Inner Mongolia. Litter decomposition was studied over three years to determine the effects of water and N addition on litter decomposition rate and nutrient dynamics. Litter mass loss and nutrient release were faster for the forb species than for the two grasses during decomposition. Both water and N addition increased litter mass loss of the grass A. cristatum, while the treatments showed no impacts on that of the forb A. frigida. Supplemental N had time-dependent, positive effects on litter mass loss of the grass S. krylovii. During the three-year decomposition study, the release of N from litter was inhibited by N addition for the three species, and it was promoted by water addition for the two grasses. Across all treatments, N and potassium (K) were released from the litter of all three species, whereas calcium (Ca) was accumulated. Phosphorus (P) and magnesium (Mg) were released from the forb litter but accumulated in the grass litter after three years of decomposition. Our findings revealed that the litter decomposition response to water and N supplementation differed among dominant plant species in a semi-arid grassland, indicating that changes in dominant plant species induced by projected increases in precipitation and N deposition are likely to affect litter decomposition, nutrient cycling, and further biogeochemical cycles in this grassland. The asynchronous nutrient release of different species’ litter found in the present study highlights the complexity of nutrient replenishment from litter decomposition in the temperate steppe under scenarios of enhancing precipitation and N deposition.

Plant traits, stoichiometry and microbes as drivers of decomposition in the rhizosphere in a temperate grassland

Summary It is becoming increasingly clear that plant roots can impact the decomposition of existing soil C in the rhizosphere. Studies under controlled conditions suggest this impact may be plant species dependent, but whether this is the case in natural conditions or what factors underlie this variation is mostly unknown. With a novel field‐based isotopic approach combining 13C‐enriched glucose and 5‐bromo‐2‐deoxyuridine additions, we compared in situ C decomposition of added labile C and native soil C (priming) among eight semi‐arid grassland species’ rhizospheres to investigate the factors driving inter‐species variation. We examined the influence of several rhizosphere factors related to soil chemistry, microbial activity, microbial community, microbial stoichiometry, plant chemistry and root morphology. Plant species generated distinct microbial and chemical rhizosphere environments, which translated into differences in the direction, magnitude and temporal dynamics of the soil C priming. Soil C decomposition was positively related to soil C/P and soil N/P (via its influence on the bacterial community), which in turn were positively related to plant N/P. Plant C/N was also a significant factor via its negative influence on soil N/P. In contrast, the main direct predictors of labile C decomposition were microbial biomass, microbial C/N and the C‐degrading enzymes, which in turn were linked to root morphology and C chemistry. Synthesis. Within this community, plant species’ rhizospheres can vary in their susceptibility to C loss in response to changes in C availability. Soil stoichiometry, driven by plant chemical traits, appeared to be the strongest driver of priming. Our study suggests that shifts in plant communities involving increases in N relative to P have the greatest potential to lead to C loss. We provide evidence of root morphology and C chemistry as drivers of labile C processing in soil, a novel empirical contribution to our understanding of the role of plant traits below‐ground. The contrasting regulation of different pools of soil C suggests observations of the regulation of simple C compounds should not be extrapolated to the whole C pool. Our findings provide support for rhizosphere‐driven mechanisms by which shifts in plant community composition could have implications on the ecosystem‐level C balance.

Planning agriculture based on landuse responses of threatened semiarid grassland species in India

Balancing biodiversity conservation and rural food security is a pressing challenge for developing countries, with tropical agro-grasslands facing particularly high human dependence and species’ endangerment. We explored the potential influences of agricultural growth and allocation of multiple landuses on the status of two threatened species inhabiting semiarid agro-grasslands of India. Sampling 1km2 cells for flagship lesser florican Sypheotides indica and 0.03ha plots for spiny-tailed lizard Saara hardwickii, we modeled species’ abundances with land-cover, vegetation structure, and disturbances using N-mixture (florican) and poisson (lizard) models. Florican abundance responded unimodally to herbaceous biomass (grassland proportion×ground-vegetation height), wherein, numbers peaked at optimally large combinations of grassland proportion (0.5–1) and ground-vegetation height (35–65cm). Whereas, lizard abundance was positively influenced by grassland occurrence and ground-vegetation<50cm cover but negatively influenced by cropland occurrence. Livestock grazing promoted short vegetation over tall vegetation, partially hindering florican but facilitating lizard. Such inter-specific differences in landuse response invoked multi-criteria planning based on surrogates of ecologically distinct species-groups. Fitting our models to simulated landuse scenarios, we demonstrated that managing florican habitats as grassland interspersed with croplands and pastures spared rotationally provided optimal results at low production-level. However, projected agricultural growth would cause considerable declines of florican (>30%) and lizard (>20%) populations. To prevent this, remaining florican occupied agro-grasslands should be secured as Community/Conservation reserves so that further landuse conversions can be legally restricted. Simultaneously, government schemes like food provisioning to small farmers through public distribution system could be harnessed to compensate for production deficit within/adjoining reserves.

Effects of ENSO-linked climate and vegetation on population dynamics of sympatric rodent species in semiarid grasslands of Inner Mongolia, China

El Niño Southern Oscillation (ENSO) linked climate has been known to be associated with several rodent species, but its effects on rodent community at both spatial and temporal scales are not well studied. In this study, we investigated the possible causal chain relating ENSO, precipitation, temperature, and vegetation index (normalized difference vegetation index, NDVI) to rodent abundance for 14 sympatric rodent species in 21 counties of semiarid grasslands in Inner Mongolia, China, from 1982 to 2006. We found that both precipitation and temperature showed a generally direct positive effect on rodent abundance in many species in the current year, but indirect effects that operate through NDVI in the current or following year could have a reverse effect on abundance. We described one ENSO-linked precipitation bottom-up chain and three ENSO-linked temperature bottom-up chains. These observed bottom-up links reveal that in El Niño years, or 1 year after La Niña years, or 2 years after El Niño years, ENSO-driven climate or vegetation factors tend to increase population abundances of many sympatric rodent species in this region. We also found time-lag effects and the life-history strategy (i.e., functional groups of hibernating behavior, activity rhythm, or food habits) also contribute to the observed complicated effects of SOI on precipitation, temperature, NDVI, and ultimately rodent abundance.

Water limitation and plant inter-specific competition reduce rhizosphere-induced C decomposition and plant N uptake

Plants can affect soil organic matter decomposition and mineralization through litter inputs, but also more directly through root-microbial interactions (rhizosphere effects). Depending on resource availability and plant species identity, these rhizosphere effects can be positive or negative. To date, studies of rhizosphere effects have been limited to plant species grown individually. It is unclear how belowground resources and inter-specific interactions among plants may influence rhizosphere effects on soil C decomposition and plant N uptake. In this study, we tested the simple and interactive effects of plant diversity and water availability on rhizosphere-mediated soil C decomposition and plant N uptake. The study was conducted in the greenhouse with five semi-arid grassland species (monocultures and mixtures of all five species) and two water levels (15 and 20% gravimetric soil moisture content). We hypothesized that microbial decomposition and N release would be less in the low compared to high water treatment and less in mixtures compared to monocultures. Rhizosphere effects on soil C decomposition were both positive and negative among the five species when grown in monoculture, although negative effects prevailed by the end of the experiment. When grown in mixture, rhizosphere effects reduced soil C decomposition and plant N uptake compared to monocultures, but only at the low-water level. Our results suggest that when water availability is low, plant species complementarity and selection effects on water and N use can decrease soil C decomposition through rhizosphere effects. Although complementarity and selection effects can increase plant N uptake efficiency, plant N uptake in the mixtures was still lower than expected, most likely because rhizosphere effects reduced N supply in the mixtures more than in the monocultures. Our results indicate that rhizosphere effects on C and N cycling depend on water availability and inter-specific plant interactions. Negative rhizosphere effects on soil C decomposition and N supply in mixtures relative to monocultures of the component species could ultimately increase soil C storage and possibly influence how plant communities in semi-arid grasslands respond to global climate change.

Microbially mediated CH4 consumption and N2O emission is affected by elevated CO2, soil water content, and composition of semi-arid grassland species

Elevated CO2 affects plant productivity, but also water availability and plant species composition in semi-arid grasslands, thereby potentially causing complex effects on CH4 consumption and N2O emission. We studied the effects of atmospheric CO2 concentration (400 vs 780 μL L−1), water content (15 vs 20% gravimetric soil moisture), and composition of semi-arid grassland species (perennial grasses Bouteloua gracilis, Hesperostipa comata, and Pascopyrum smithii; sub-shrub Artemisia frigida; invasive forb Linaria dalmatica grown in monoculture and all five species together) on CH4 consumption and N2O emission in a full factorial greenhouse experiment. We used a unique method where we measured microbial effects on CH4 consumption and N2O emission in isolation from effects of gas diffusivity. Microbially mediated CH4 consumption was significantly higher under elevated CO2 (by 20%), but was not affected by soil water content or plant species composition. Microbially mediated N2O emission was not significantly affected by elevated CO2, but was significantly higher with high water content (by 67%) and differed significantly among species. Treatment effects on CH4 consumption and N2O emission often could not be explained simply by differences in soil moisture, suggesting that treatment-induced changes in other soil and microbial properties played a role in causing these effects.

NATURAL HISTORY OF THE MASSASAUGA, SISTRURUS CATENATUS EDWARDSII, IN SOUTHEASTERN COLORADO

A BSTRACT Studies of natural history are important for determining baseline information, particularly for species that might be threatened or endangered. We collected 254 (141M:94F:19UNK) massasauga, Sistrurus catenatus edwardsii, from May 1995 through October 1996. The average snoutvent length (SVL 6 SD) for adult males (355 6 45 mm) was not significantly different than the SVL of adult females (364 6 24 mm). Habitat descriptions indicate that the massasauga in Colorado is a semi-arid grassland species that utilizes areas of relatively open shortgrass prairie. Massasaugas were active between 14 and 308C, with an average ambient temperature during activity of 22.1 6 2.58C. The time of observed activity shifted through the season, with primarily diurnal activity during the cooler months (April and late September to October) and primarily early evening activity during the hotter months (May through August). Massasaugas in Colorado gave birth to litters of 5 to 7 young between late August and late September, and reproduction appeared to be biennial. Populations of S. c. edwardsii in Colorado are scattered but population size appeared to be relatively large based on number of captures and low recapture rates, particularly in Lincoln County. However, due to habitat loss and fragmentation resulting from agricultural expansion, these populations might become increasingly threatened in the future.

The quantification of grazing capacity from grazing — and production values for forage species in semi-arid grasslands of southern Africa

The relation between rangeland condition and grazing capacity was determined along a degradation gradient. In studying agronomic values of forage species, the average production per tuft was combined with its grazing preferences, to link grazing values for species in the semi-arid grasslands of southern Africa. A production index, based on mean mass per tuft, was first compiled for species. Preference utilisation ratio of species was estimated for each of cattle and sheep, from the proportion of each species found in the diet relative to the proportion of the species found in the forage on offer. A microhistological technique was applied to oesophageal fistula samples to determine the proportion of each species found in the diet. Grazing values and grazing index were determined from the production and preference utilisation ratio of species. Where grazing values of species were determined subjectively in the past, in this study species were objectively classified based on estimated grazing values. Meaningful relationships between rangeland condition and grazing capacity were determined, along a degradation gradient, with the long-term coefficient of forecasting more than 75%. The financial implication with respect to sustainable animal production and rangeland condition variation was also calculated.

Stomatal Characteristics, Conductance Ratios, and Drought-Induced Leaf Modifications of Semiarid Grassland Species

Stomatal Characteristics, Conductance Ratios, and Drought-Induced Leaf Modifications of Semiarid Grassland Species

Stomatal characteristics, conductance ratios, and drought‐induced leaf modifications of semiarid grassland species

Seventeen greenhouse‐grown grasses from the Nebraska Sandhills region were surveyed for foliar stomatal density and distribution, closed guard cell lengths, open stomatal apertures, and surface characteristics (using scanning electron microscopy), surface conductance (using a steady‐state porometer), and drought‐induced leaf modifications. Leaves of C3 species exhibited a proclivity toward being amphistomatic or hyperstomatic, while C4 species tended to be more hypostomatic. Leaf modification, when it occurred, resulted in the enshrouding of the adaxial surface. Conductance data showed functional amphistomaty in most species, revealing differential functioning of adaxial and abaxial stomata. Conductance patterns were not closely related to stomatal aperture per unit area leaf surface or to stomatal distribution patterns. Lowered adaxial: abaxial conductance ratios, increased stomatal density, reduced stomatal size, and less drought‐induced leaf modification were seen in C4 grasses as compared with C3 grasses. C3 range and C3 meadow species did not differ in conductance ratios, density ratios, or stomatal size, although meadow species exhibited much greater drought‐induced leaf modification. Postulations involving correlation of adaxial: abaxial conductance ratios to stomatal distribution patterns, and assumptions of stomatal distribution based upon habitat and/or photosynthetic pathway may be erroneous. These characteristics may be of limited usefulness as morphological indicators in the search for drought‐tolerant ecotypes of prairie grasses.