Combined effects between temporal heterogeneity of water supply,nutrient level,and population density on biomass of four broadly distributed herbaceous species

Temporal heterogeneity of water supply affects grassland community productivity and it can interact with nutrient level and intraspecific competition. To understand community responses, the responses of individual species to water heterogeneity must be evaluated while considering the interactions of this heterogeneity with nutrient levels and population density. We compared responses of four herbaceous species grown in monocultures to various combinations of water heterogeneity, nutrient level, and population density: two grasses (Cynodon dactylon and Lolium perenne), a forb (Artemisia princeps), and a legume (Trifolium repens). Treatment effects on shoot and root biomass were analyzed. In all four species, shoot biomass was larger under homogeneous than under heterogeneous water supply. Shoot responses of L. perenne tended to be greater at high nutrient levels. Although root biomass was also larger under homogeneous water supply, effects of water heterogeneity on root biomass were not significant in the grasses. Trifolium repens showed marked root responses, particularly at high population density. Although greater shoot and root growth under homogeneous water supply appears to be a general trend among herbaceous species, our results suggested differences among species could be found in the degree of response to water heterogeneity and its interactions with nutrient level and intraspecific competition.     

The interactive effects of elevated CO<Subscript>2</Subscript>, temperature and initial size on growth and competition between a native C<Subscript>3</Subscript> and an invasive C<Subscript>3</Subscript> grass

A controlled environment experiment was conducted to determine the impact of enhanced carbon dioxide and temperature on competition between the C₃ grasses Austrodanthonia eriantha and Vulpia myuros. Plants were grown in mixtures and monocultures to compare the responses both with and without an interspecific competitor. Temperature and CO₂ were set at current levels (350 ppm CO₂; 20 °C day and 10 °C night temperature), in factorial combination with enhanced levels (700 ppm CO₂; 23 °C day and 13 °C night temperature). To examine the potential impact of initial seedling size on competition under elevated CO₂ and temperature, the two species were combined in mixtures of differing initial sizes. Above-ground growth of all plants was enhanced by increased CO₂ and temperature alone, however the combined temperature and CO₂ treatment showed a sub-additive effect, where growth was less than expected based on the responses to each factor independently. Austrodanthonia in mixture with Vulpia plants of the same initial size experienced a 27 reduction in growth. Austrodanthonia grown in the presence of an initially larger Vulpia plant experienced a 58 reduction in growth. When the Vulpia plant was initially smaller than Austrodanthonia, growth of the Austrodanthonia was reduced by 16%. The growth of Vulpia appeared to be largely unaffected by the presence of Austrodanthonia. Variation in the CO₂ and temperature environment did not affect the pattern of these interspecific interactions, although there was some evidence to suggest that the degree of suppression of Austrodanthonia by Vulpia was less under elevated CO₂. These results do not support the initial advantage hypothesis, as Vulpia was always able to suppress Austrodanthonia, regardless of the initial relative sizes of the competitors. Furthermore, the lack of an effect of changing the CO₂ or temperature environment on the direction of interspecific competition suggests that the competitiveness of the invasive Vulpia will be minimally affected by changes in atmospheric CO₂ concentration or temperature.     

Population Interactions and the Determinants of Population Size

Abstract The flux of individuals within populations is dependent upon six controlling processes: the intrinsic rate of increase of the plant, intraspecific competition for resources, interspecific competition, natural enemies, mutualisms and refuge effects such as the immigration of seeds from other populations. Although population interactions are generally believed to play a major role in determining the flux of individuals within populations, little attempt has been made to quantify the strength of these interactions and their role in the dynamics of populations. In this paper we examine the role of competition, herbivory and mutualistic interactions in determining the dynamics of a range of annual plant species. Firstly, it is shown that the dynamics of three weed species ( Bromus sterilis, Galium aparine, Papaver rhoeas ) in an experimental community in an arable cropping system of winter wheat are determined primarily by the rapid population growth of B. sterilis . Interactions between the species play a minor part in the dynamics of the system. Secondly, it is shown that current levels of grazing by overwintering populations of brent geese have a minor impact on the abundance of Salicornia europaea , but that increased grazing has the potential to reduce abundance and increase the instability of S. europaea populations. This is a consequence of the aggregative response of the geese, which results in an increasing proportion of the seeds of S. europaea being eaten as plant density increases. Thirdly, it is shown that there is a complex interaction between root pathogenic and arbuscular mycorrhizal fungi in natural field populations of Vulpia ciliata and that the benefit of mycorrhizal fungi to the plant is in providing protection against pathogens.     

Decomposition of litter produced under elevated CO2: Dependence on plant species and nutrient supply

We investigated the effect of CO₂ concentration and soilnutrient availability during growth on the subsequent decomposition andnitrogen (N) release from litter of four annual grasses that differ inresource requirements and native habitat. Vulpia microstachys isa native grass found on California serpentine soils, whereas Avenafatua, Bromus hordaceus, and Lolium multiflorum areintroduced grasses restricted to more fertile sandstone soils (Hobbs & Mooney 1991). Growth in elevated CO₂ altered litter C:N ratio,decomposition, and N release, but the direction and magnitude of thechanges differed among plant species and nutrient treatments. ElevatedCO₂ had relatively modest effects on C:N ratio of litter,increasing this ratio in Lolium roots (and shoots at high nutrients),but decreasing C:N ratio in Avena shoots. Growth of plants underelevated CO₂ decreased the decomposition rate of Vulpialitter, but increased decomposition of Avena litter from the high-nutrient treatment. The impact of elevated CO₂ on N loss fromlitter also differed among species, with Vulpia litter from high-CO₂ plants releasing N more slowly than ambient-CO₂litter, whereas growth under elevated CO₂ caused increased Nloss from Avena litter. CO₂ effects on N release in Lolium and Bromus depended on the nutrient regime in whichplants were grown. There was no overall relationship between litter C:Nratio and decomposition rate or N release across species and treatments.Based on our study and the literature, we conclude that the effects ofelevated CO₂ on decomposition and N release from litter arehighly species-specific. These results do not support the hypothesis thatCO₂ effects on litter quality consistently lead to decreasednutrient availability in nutrient-limited ecosystems exposed to elevatedCO₂.     

Growth, fecundity and competitive ability of transgenic Trifolium subterraneum subsp. subterraneum cv. Leura expressing a sunflower seed albumin gene

Ecological risk assessment is an important step in the production and commercialisation of transgenic plants. To date, however, most risk assessment studies have been performed on crop plants, and few have considered the ecological consequences associated with genetic modification of pasture species. In this study we compared the growth, yield, population dynamics and competitive ability of transgenic Trifolium subterraneum subsp. subterraneum cv. Leura (subclover) expressing a nutritive sunflower seed albumin (ssa) gene with the equivalent non-transgenic commercial line in a glasshouse competition trial. Plants were grown in low-fertility soil typical of unimproved native southeastern Australian grasslands. We measured survivorship, seed production rate, seed germination rate, seed weight, dry weight yield and the intrinsic rate of population increase (lambda) of plants grown in mixtures and monocultures over a range of densities (250 to 2000 plants m(-2)), and also determined intragenotypic and intergenotypic competition coefficients for each line. There were no significant differences between transgenic and non-transgenic plants in any of the measured variables except survivorship; transgenic plants had a significantly lower survival rate than non-transgenic plants when grown at high densities (p<0.01). However, density-dependent effects were observed for all measured variables, and in all models plant density affected the response variables more than the presence of the transgene. Based on these results, we conclude that the ssa gene construct appears to confer no advantage to transgenic T. s. subterraneum cv. Leura growing in mixed or pure swards under the fertility and density regimes examined in the trial. Our data also suggest that transgenic subterranean clover expressing the ssa gene is unlikely to exhibit a competitive advantage over associated non-transgenic commercial cultivars when grown in dense swards in low-fertility pastures.     

Competition between Australian native and introduced grasses along a nutrient gradient

Abstract Seven grass species were grown in monocultures and in multispecies mixtures along a gradient of total nutrient levels that ranged from 1/64 to 16× the normal level of nutrient solution. The seven grasses represented three ecological groups: (i) three perennial species native to Australia (Themeda triandra, Poa labillardieri and Danthonia carphoides); (ii) two introduced annuals (Vulpia bromoides and Hordeum leporinum); and (iii) two introduced perennials (Lolium perenne and Dactylis glomerata). We hypothesized that the native grasses would prove less competitive when grown at increased nutrient levels than those introduced from Europe. Results supported the hypothesis. The native species were unable to compete in mixtures even at the lowest nutrient level, where T. triandra was the most productive species in monoculture. Lolium perenne and Dactylis glomerata dominated mixtures at intermediate nutrient levels. The responses of the annual introduced grasses differed in that Vulpia bromoides showed an optimum at intermediate nutrient levels in both monoculture and in mixtures, whereas Hordeum leporinum dominated at the highest nutrient levels in mixture but was suppressed by V. bromoides, L. perenne and D. glomerata at intermediate levels. The results are discussed in terms of predicting species responses in mixtures from their performance in monocultures as well as in terms of previous observations on the sequential changes in botanical composition of south‐eastern Australian grasslands after 150 years of continuous grazing by sheep.     

Plant species diversity and composition of experimental grasslands affect genetic differentiation of Lolium perenne populations

Contrasting hypotheses exist about the relationship between plant species diversity and genetic diversity. However, experimental data of species diversity effects on genetic differentiation among populations are lacking. To address this, Lolium perenne was sown with an equal number of seeds in 78 experimental grasslands (Jena Experiment) varying in species richness (1, 2, 4, 8 to 16) and functional group richness and composition (1-4; grasses, legumes, small herbs, tall herbs). Population sizes were determined 4years after sowing, and single-nucleotide polymorphism (SNP) DNA markers based on bulk samples of up to 100 individuals per population were applied. Genetic distances between the field populations and the initially sown seed population increased with sown species richness. The degree of genetic differentiation from the original seed population was largely explained by actual population sizes, which suggests that genetic drift was the main driver of differentiation. Weak relationships among relative allele frequencies and species diversity or actual population sizes, and a positive correlation between actual population sizes and expected heterozygosity also supported the role of genetic drift. Functional composition had additional effects on genetic differentiation of L. perenne populations, indicating a selection because of genotype-specific interactions with other species. Our study supports that genetic diversity is likely to be lower in plant communities with a higher number of interspecific competitors. Negative effects of species richness on population sizes may increase the probability of genetic drift, and selection because of genotype-specific interactions depending on species and genotypic community composition may modulate this relationship.     

The effects of herbivory on neighbor interactions along a coastal marsh gradient

Many current theories of community function are based on the assumption that disturbances such as herbivory act to reduce the importance of neighbor interactions among plants. In this study, we examined the effects of herbivory (primarily by nutria, Myocastor coypus) on neighbor interactions between three dominant grasses in three coastal marsh communities, fresh, oligohaline, and mesohaline. The grasses studied were Panicum virgatum, Spartina patens, and Spartina alterniflora, which are dominant species in the fresh, oligohaline, and mesohaline marshes, respectively. Additive mixtures and monocultures of transplants were used in conjunction with exclosure fences to determine the impact of herbivory on neighbor interactions in the different marsh types. Herbivory had a strong effect on all three species and was important in all three marshes. In the absence of herbivores, the impact of neighbors was significant for two of the species (Panicum virgatum and Spartina patens) and varied considerably between environments, with competition intensifying for Panicum virgatum and decreasing for Spartina patens with increasing salinity. Indications of positive neighbor effects (mutualisms) were observed for both of these species, though in contrasting habitats and to differing degrees. In the presence of herbivores, however, competitive and positive effects were eliminated. Overall, then, it was observed that in this case, intense herbivory was able to override other biotic interactions such as competition and mutualism, which were not detectable in the presence of herbivores.     

Abiotic constraints on the competitive ability of exotic and native grasses in a Pacific Northwest prairie

In prairie ecosystems, abiotic constraints on competition can structure plant communities; however, the extent to which competition between native and exotic plant species is constrained by environmental factors is still debated. The objective of our study was to use paired field and greenhouse experiments to evaluate the competitive dynamics between two native (Danthonia californica and Deschampsia cespitosa) and two exotic (Schedonorus arundinaceus and Lolium multiflorum) grass species under varying nutrient and moisture conditions in an upland prairie in the Willamette Valley, Oregon. We hypothesized the two invasive, exotic grasses would be more competitive under high-nutrient, moderate-moisture conditions, resulting in the displacement of native grasses from these environments. In the field, the experimental reduction of competition resulted in shorter, wider plants, but only the annual grass, Lolium multiflorum, produced more aboveground biomass when competition was reduced. In the greenhouse, the two exotic grasses produced more total biomass than the two native grasses. Competitive hierarchies were influenced by nutrient and/or moisture treatments for the two exotic grasses, but not for the two native grasses. L. multiflorum dominated competitive interactions with all other grasses across treatments. In general, S. arundinaceus dominated when in competition with native grasses, and D. cespitosa produced the most biomass in monoculture or under interspecific competition with the other native grass, D. californica. D. californica, D. cespitosa, and S. arundinaceus all produced more biomass in high-moisture, high-nutrient environments, and D. cespitosa, L. multiflorum, and S. arundinaceus allocated more biomass belowground in the low nutrient treatment. Taken together, these experiments suggest the competitive superiority of the exotic grasses, especially L. multiflorum, but, contrary to our hypothesis, the native grasses were not preferentially excluded from nutrient-rich, moderately wet environments. Laurel Pfeifer-Meister and Esther M. Cole contributed equally to this work.     

The shifting balance of facilitation and competition affects the outcome of intra- and interspecific interactions over the life history of California grassland annuals

Trait-based resource competition in plants, wherein more similar plants compete more strongly for resources, is a foundation of niche-based explanations for the maintenance of diversity in plant communities. Alternatively, neutral theory predicts that community diversity can be maintained despite equivalent resource requirements among species. We examined interactions at three life history stages (germination, survival, and juvenile-adult growth) for three native and three exotic California annual species in a glasshouse experiment. We varied plant density and species composition in small pots, with pots planted with either intraspecific seeds or in a three species mix of intra- and interspecific neighbors. We saw a range of facilitative, neutral, and competitive interactions that varied significantly by species, rather than by native or exotic status. There were more competitive interactions at the emergence and juvenile-adult growth stages and more facilitative interactions for survival. Consequently, the relative strength of competition in intraspecific versus mixed-species communities depended on whether we considered only the juvenile-adult growth stage or the entire life history of the interacting plants. Using traditional analysis of juvenile-adult growth only, all species showed negative density-dependent interactions for final biomass production. However, when the net effect of plant interactions from seed to adult was considered, which is a prediction of population growth, two native species ceased to show negative density dependence, and the difference between intraspecific and mixed-species competition was only significant for one exotic species. Results were consistent with predictions of neutral, rather than niche, theory for five of six species.     

Conversion of native terrestrial ecosystems in Hawai‘i to novel grazing systems: a review

The remote oceanic islands of Hawai‘i exemplify the transformative effects that non-native herbivorous mammals can bring to isolated terrestrial ecosystems. We reviewed published literature containing systematically collected, analyzed, and peer-reviewed original data specifically addressing direct effects of non-native hoofed mammals (ungulates) on terrestrial ecosystems, and indirect effects and interactions on ecosystem processes in Hawai‘i. The effects of ungulates on native vegetation and ecosystems were addressed in 58 original studies and mostly showed strong short-term regeneration of dominant native trees and understory ferns after ungulate removal, but unassisted recovery was dependent on the extent of previous degradation. Ungulates were associated with herbivory, bark-stripping, disturbance by hoof action, soil erosion, enhanced nutrient cycling from the interaction of herbivory and grasses, and increased pyrogenicity and competition between native plants and pasture grasses. No studies demonstrated that ungulates benefitted native ecosystems except in short-term fire-risk reduction. However, non-native plants became problematic and continued to proliferate after release from herbivory, including at least 11 species of non-native pasture grasses that had become established prior to ungulate removal. Competition from non-native grasses inhibited native species regeneration where degradation was extensive. These processes have created novel grazing systems which, in some cases, have irreversibly altered Hawaii’s terrestrial ecology. Non-native plant control and outplanting of rarer native species will be necessary for recovery where degradation has been extensive. Lack of unassisted recovery in some locations should not be construed as a reason to not attempt restoration of other ecosystems.     

损伤冷蒿挥发性有机化合物(VOCs)成分分析及其对牧草根系生长发育的影响

采用GC-MS测定损伤冷蒿VOCs的主要成分,并通过生物测定的方法研究损伤冷蒿VOCs对牧草幼苗根系生长发育的影响。结果表明:损伤冷蒿释放30种VOCs,包含萜烯类、醇类、酯类、醛类和酮类等5类化合物,其中相对含量高于1%的化合物共占VOCs总量的97.37%,桉树脑含量最高(22.43%)。损伤冷蒿释放的VOCs极显著(P0.01)的抑制草木樨、苏丹草、披碱草和冰草幼根的伸长,以及苏丹草侧根与冰草须根的发育,抑制率分别为51.55%、55.34%、37.57%、48.68%、93.04%和25.00%;同时也极显著抑制4种牧草幼根生物量的积累(P0.01)。损伤冷蒿VOCs影响牧草根部中柱组织结构的分化,使草木樨中柱内木质部、韧皮部与形成层不能正常分化;苏丹草、披碱草和冰草的凯氏带发育不完整。由此可见,损伤冷蒿VOCs对牧草根系生长发育具有明显的抑制作用。     

Genetic identity affects performance of species in grasslands of different plant diversity: an experiment with Lolium perenne cultivars

Background and Aims

Recent biodiversity research has focused on ecosystem processes, but less is known about responses of populations of individual plant species to changing community diversity and implications of genetic variation within species. To address these issues, effects of plant community diversity on the performance of different cultivars of Lolium perenne were analysed.

Methods

Populations of 15 genetic cultivars of Lolium perenne were established in experimental grasslands varying in richness of species (from 1 to 60) and functional groups (from 1 to 4). Population sizes, mean size of individual plants, biomass of individual shoots and seed production were measured in the first and second growing season after establishment.

Key Results

Population sizes of all cultivars decreased with increasing community species richness. Plant individuals formed fewer shoots with a lower shoot mass in more species-rich plant communities. A large proportion of variation in plant size and relative population growth was attributable to effects of community species and functional group richness, but the inclusion of cultivar identity explained additional 4–7 % of variation. Cultivar identity explained most variation (28–51 %) at the shoot level (biomass of individual tillers and reproductive shoots, seed production, heading stage). Coefficients of variation of the measured variables across plant communities were larger in cultivars with a lower average performance, indicating that this variation was predominantly due to passive growth reductions and not a consequence of larger adaptive plastic responses. No single cultivar performed best in all communities.

Conclusions

The decreasing performance of Lolium perenne in plant communities of increasing species richness suggests a regulation of competitive interactions by species diversity. Genetic variation within species provides a base for larger phenotypic variation and may affect competitive ability. However, heterogeneous biotic environments (= plant communities of different species composition) are important for the maintenance of intra-specific genetic variation.Key words: Biodiversity, competition, genetic variation, growth reduction, Lolium perenne, phenotypic plasticity, species richness     

The host-plant relationships of apterous virginoparae of the grass aphid Metopolophiurn festucae cerealium

Metopolophium festucae cerealium has at various times caused damage to both grass and cereal crops. Despite this, little work has been done on the relative susceptibility of different grass and cereal cultivars to this aphid. The present work showed that for the cultivars examined the most common ley pasture species (Lolium perenne and Lolium multiflorum) exhibited relatively low levels of antibiotic resistance to M. f. cerealium and that wheat is more susceptible than any of the grass species tested. This enigma, in view of the aphid's low pest status on wheat, is discussed. The resistance in the grasses was greater at the stem elongation stages than at the seedling stage but the ranking was consistent between growth stages. M. f. cerealium exhibited a preference for feeding on emerging and senescing leaves of 10-wk-old grass but on wheat it distributed itself evenly between all available green leaves.     

The Enemy of My Enemy Hypothesis: Why Coexisting with Grasses May Be an Adaptive Strategy for Savanna Trees

Savannas are characterized by the coexistence of trees and flammable grasses. Yet, tree–grass coexistence has been labeled as paradoxical—how do these two functional groups coexist over such an extensive area, despite being generally predisposed to excluding each other? For instance, many trees develop dense canopies that limit grass growth, and many grasses facilitate frequent/intense fires, increasing tree mortality. This study revisits tree–grass coexistence with a model of hierarchical competition between pyrogenic grasses, “forest trees” adapted to closed-canopy competition, and “savanna trees” that are inferior competitors in closed-canopy communities, but more resistant to fire. The assumptions of this model are supported by empirical observations, including a systematic review of savanna and forest tree community composition reported here. In general, the model simulations show that when savanna trees exert weaker competitive effects on grasses, a self-reinforcing grass community is maintained, which limits forest tree expansion while still allowing savanna trees to persist (albeit as a subdominant to grasses). When savanna trees exert strong competitive effects on grasses, savanna trees cover increases initially, but as grasses decline their inhibitory effect on forest trees weakens, allowing forest trees to expand and exclude grasses and savanna trees. Rather than paradoxical, these results suggest that having weaker competitive effects on grasses may be advantageous for savanna trees, leading to greater long-term abundance and stability. We label this the “enemy of my enemy hypothesis,” which might apply to species coexistence in communities defined by hierarchical competition or with species capable of generating strong ecological feedbacks.     

The Mark of Zorro: Effects of the Exotic Annual Grass Vulpia myuros on California Native Perennial Grasses

Native perennial grasses were once common in California prairies that are now dominated by annual grasses introduced from Europe. Competition from exotics may be a principal impediment to reestablishment of native perennial grasses. Introduced annual grasses, such as Vulpia myuros (zorro fescue), are often included with native perennial species in revegetation seed mixtures used in California. To examine the potential suppressive effect of this graminoid, we evaluated the growth and performance of a mixture of California native perennial grasses and resident weeds when grown with varying densities of V. myuros. The annual fescue exhibited a strongly plastic growth response to plant density, producing similar amounts of above‐ground biomass at all seeding densities. Perennial grass seedling survival and above‐ ground biomass decreased and individuals became thinner (i.e., reduced weight‐to‐height ratio) with increasing V. myuros seeding density. V. myuros also significantly suppressed above‐ground biomass and densities of weeds and had a more negative effect on weed densities than on native perennial grass densities. Biomass of native grasses and weeds was not differentially affected by increasing densities of V. myuros. Overall, because V. myuros significantly reduced the survival and performance of the mixture of native perennial grasses and this effect increased with increasing V. myuros density, we conclude that including this exotic annual in native seed mixtures is counterproductive to restoration efforts.     

The impact of environmental variability and species composition on the stability of experimental microbial populations and communities

Understanding how environmental fluctuations affect the stability of populations and communities is complex, for example, because direct effects of environmental variability on populations may be modified and propagated across communities by species interactions. One way to explore and further understand these complexities is via a factorial manipulation of community composition and environmental conditions. Using laboratory based aquatic microcosms we manipulated environmental fluctuation by creating two environments; one with variable light and one with constant light. Within these environments, community composition was manipulated by constructing communities from all possible combinations of three species that vary in their reliance on light for growth (an autotroph: a diatom completely reliant on light, a heterotroph: a Paramecium species not reliant on light, and a mixotroph: a Paramecium species somewhat reliant on light). Community composition was predicted to affect populations and communities by introducing and altering competitive interactions between species and affecting the degree of niche differentiation between species. We found that population stability was predominantly influenced by an interaction between community composition and environmental variability, whereby the effect of environmental variability synergistically combined with effects of community composition to reduce population stability. Covariance of populations was determined by an interaction between community composition and environmental variability, though this did not result from the effect of niche differentiation between species. Species interactions drove correlations between population biomass and the environment which otherwise did not exist. Our results demonstrate the complex and interrelated effects of abiotic and biotic factors on population and community stability, and suggest the need to consider aspects of community composition when predicting the impact of environmental fluctuations.     

Soil microbial and chemical responses to foliar Epichloë fungal infection in Lolium perenne,Hordeum brevisubulatum and Achnatherum inebrians

We tested whether the host species identity in grass-Epichloë symbioses affected soil chemical and microbial properties. We grew endophyte infected (E+) and endophyte free (E−) Lolium perenne, Hordeum brevisubulatum and Achnatherum inebrians for 18 months in field plots. In E+ soil of all three grasses, available phosphorus was lower whereas total soil nitrogen was higher. Endophyte effects on soil pH, microbial biomass nitrogen, total carbon and organic carbon as well as bacteria and fungi abundance were host species dependent. Ammonia oxidizing bacteria abundance was higher in E+ soils for all species. Bacterial community composition of E+ and E− soils were different only for Lolium perenne with soil pH being the key factor. Fungal community composition of E+ and E− soils was not different for the three grasses. This study confirmed that the effects of foliar Epichloë infection on belowground properties depended on host species identity.     

Fine-scale community and genetic structure are tightly linked in species-rich grasslands

Recent evidence indicates that grassland community structure and species diversity are influenced by genetic variation within species. We review what is known regarding the impact of intraspecific diversity on grassland community structure, using an ancient limestone pasture as a focal example. Two genotype-dependent effects appear to modify community structure in this system. First, the abundance of individual constituent species can depend upon the combined influence of direct genetic effects stemming from individuals within the population. Second, the outcome of localized interspecific interactions occurring within the community can depend on the genotypes of participating individuals (indicating indirect genetic effects). Only genotypic interactions are thought to be capable of allowing the long-term coexistence of both genotypes and species. We discuss the implications of these effects for the maintenance of diversity in grasslands. Next, we present new observations indicating that losses of genotypic diversity from each of two species can be predicted by the abundance of other coexisting species within experimental grassland communities. These results suggest genotype-specific responses to abundance in other coexisting species. We conclude that both direct and indirect genetic effects are likely to shape community structure and species coexistence in grasslands, implying tight linkage between fine-scale genetic and community structure.     

Phylogeny of the festucoid grasses of subtribe Loliinae and allies (Poeae, Pooideae) inferred from ITS and trnL-F sequences

Analyses of ribosomal ITS and chloroplast trnL-F sequences provide phylogenetic reconstruction for the festucoids (Poeae: Loliinae), a group of temperate grasses with morphological and molecular affinities to the large genus Festuca. Parsimony and Bayesian analyses of the combined ITS/trnL-F dataset show Loliinae to be monophyletic but unresolved for a weakly supported clade of 'broad-leaved Festuca,' a well-supported clade of 'fine-leaved Festuca,' and Castellia. The first group includes subgenera Schenodorus, Drymanthele, Leucopoa, and Subulatae, and sections Subbulbosae, Scariosa, and Pseudoscariosa of Festuca, plus Lolium and Micropyropsis. The second group includes sections Festuca, Aulaxyper, Eskia, and Amphigenes of Festuca, plus Vulpia, Ctenopsis, Psilurus, Wangenheimia, Cutandia, Narduroides, and Micropyrum. Subtribes Dactylidinae and Cynosurinae/Parapholiinae are sister clades and are the closest relatives of Loliinae. Vulpia is polyphyletic within the 'fine-leaved' fescues as revealed by the two genome analyses. Lolium is resolved as monophyletic in the ITS and combined analyses, but unresolved in the trnL-F based tree. Conflict between the ITS and the trnL-F trees in the placement of several taxa suggests the possibility of past reticulation events, although lineage sorting and possible ITS paralogy cannot be ruled out.