Interactions In Grasslands Research Articles

Plant-soil interactions in grasslands of the Mongolian Plateau under global change

Plant-soil interactions in grasslands of the Mongolian Plateau under global change

Allelopathy and Allelochemicals in Grasslands and Forests

Plants can produce and release allelochemicals to interfere with the establishment and growth of conspecific and interspecific plants. Such allelopathy is an important mediator among plant species in natural and managed ecosystems. This review focuses on allelopathy and allelochemicals in grasslands and forests. Allelopathy drives plant invasion, exacerbates grassland degradation and contributes to natural forest regeneration. Furthermore, autotoxicity (intraspecific allelopathy) frequently occurs in pastures and tree plantations. Various specialized metabolites, including phenolics, terpenoids and nitrogen-containing compounds from herbaceous and woody species are responsible for allelopathy in grasslands and forests. Terpenoids with a diversity of metabolites are qualitative allelochemicals occurring in annual grasslands, while phenolics with a few specialized metabolites are quantitative allelochemicals occurring in perennial forests. Importantly, allelochemicals mediate below-ground ecological interactions and plant–soil feedback, subsequently affecting the biodiversity, productivity and sustainability of grasslands and forests. Interestingly, allelopathic plants can discriminate the identity of neighbors via signaling chemicals, adjusting the production of allelochemicals. Therefore, allelochemicals and signaling chemicals synergistically interact to regulate interspecific and intraspecific interactions in grasslands and forests. Allelopathy and allelochemicals in grasslands and forests have provided fascinating insights into plant–plant interactions and their consequences for biodiversity, productivity and sustainability, contributing to our understanding of terrestrial ecosystems and global changes.

Litter manipulation enhances plant community heterogeneity via distinct mechanisms: The role of distribution patterns of plant functional composition and niche breadth variability

Plant litter can greatly alter community compositional dynamics and variability of intraspecific interactions in grasslands, and thus the overall ecosystem structure and functions. However, whether plant activity can be driven by plant litter to modify plant community heterogeneity remains poorly explored. We investigate the responses of plant community heterogeneity to litter addition as well as their associated mechanisms. Here we conducted a three-year field experiment in a Tibetan alpine meadow to explore the effects of multiple plant litter addition (five mass levels and three species) on plant communities. We found that the effect of litter manipulation on plant community heterogeneity was mainly driven by litter mass rather than litter species. Higher litter mass manipulation significantly enhanced plant community heterogeneity, which was mainly determined by the niche breadth of forbs and the distribution patterns of functional composition rather than plant diversity. Our findings provide significant insights for understanding the effects of plant litter on grassland ecosystem dynamics to maintain the structure and function of ecosystems. Furthermore, this study suggests that reasonable management practices (e.g., moderate grazing in non−growing seasons) may be pivotal in achieving sustainability of grassland systems through plant litter dynamics.

Warming effects on grassland productivity depend on plant diversity

AbstractAimClimate warming and biodiversity loss both alter plant productivity, yet we lack an understanding of how biodiversity regulates the responses of ecosystems to warming. In this study, we examine how plant diversity regulates the responses of grassland productivity to experimental warming using meta‐analytic techniques.LocationGlobal.Major taxa studiedGrassland ecosystems.MethodsOur meta‐analysis is based on warming responses of 40 different plant communities obtained from 20 independent studies on grasslands across five continents.ResultsOur results show that plant diversity and its responses to warming were the most important factors regulating the warming effects on plant productivity, among all the factors considered (plant diversity, climate and experimental settings). Specifically, warming increased plant productivity when plant diversity (indicated by effective number of species) in grasslands was lower than 10, whereas warming decreased plant productivity when plant diversity was greater than 10. Moreover, the structural equation modelling showed that the magnitude of warming enhanced plant productivity by increasing the performance of dominant plant species in grasslands of diversity lower than 10. The negative effects of warming on productivity in grasslands with plant diversity greater than 10 were partly explained by diversity‐induced decline in plant dominance.Main conclusionsOur findings suggest that the positive or negative effect of warming on grassland productivity depends on how biodiverse a grassland is. This may mainly be due to differences in how warming may affect plant dominance and subsequent shifts in interspecific interactions in grasslands of different plant diversity levels.

Elucidating plant-pollinator interactions in South Brazilian grasslands: What do we know and where are we going?

Grassland ecosystems present patterns of plant-pollinator interactions that may be linked to habitat heterogeneity, plant composition and disturbances. Most studies about plant-pollinator interactions in the Neotropics were conducted in forest, savanna-like, or Andean vegetation. However, the current increase in the number of studies about interactions in grassland vegetation promises a better understanding of the pollination ecology of these landscapes. In this systematic review, we summarised information from 24 articles about plant-pollinator interactions in South Brazilian grasslands. We highlighted patterns of plant-pollinator interactions, indicating their particularities compared to other grassland communities in South America. Bees are important pollinators of many plant species in these grasslands and most plants are visited by more than one group of pollinators. Among the plant species visited by a single pollinator group, most were visited by bees. However, many types of pollinators, plant species, habitats, and regions have, thus far, received little sampling effort. Pollination by groups other than bees, such as nocturnal pollinators, flies, beetles, and birds, is particularly understudied. The information provided in this review summarizes data that could be used to foster more detailed pollination studies to understand the diversification and maintenance of grassland floras of South Brazil.

Soil acidification reduces the effects of short-term nutrient enrichment on plant and soil biota and their interactions in grasslands.

Soil nitrogen (N) and phosphorus (P) contents, and soil acidification have greatly increased in grassland ecosystems due to increased industrial and agricultural activities. As major environmental and economic concerns worldwide, nutrient enrichment and soil acidification can lead to substantial changes in the diversity and structure of plant and soil communities. Although the separate effects of N and P enrichment on soil food webs have been assessed across different ecosystems, the combined effects of N and P enrichment on multiple trophic levels in soil food webs have not been studied in semiarid grasslands experiencing soil acidification. Here we conducted a short-term N and P enrichment experiment in non-acidified and acidified soil in a semiarid grassland on the Mongolian Plateau. We found that net primary productivity was not affected by N or P enrichment alone in either non-acidified or acidified soil, but was increased by combined N and P enrichment in both non-acidified and acidified soil. Nutrient enrichment decreased the biomass of most microbial groups in non-acidified soil (the decrease tended to be greatest with combined N and P enrichment) but not in acidified soil, and did not affect most soil nematode variables in non-acidified or acidified soil. Nutrient enrichment also changed plant and microbial community structure in non-acidified but not in acidified soil, and had no effect on nematode community structure in non-acidified or acidified soil. These results indicate that the responses to short-term nutrient enrichment were weaker for higher trophic groups (nematodes) than for lower trophic groups (microorganisms) and primary producers (plants). The findings increase our understanding of the effects of nutrient enrichment on multiple trophic levels of soil food webs, and highlight that soil acidification, as an anthropogenic stressor, reduced the responses of plants and soil food webs to nutrient enrichment and weakened plant-soil interactions.

Living With Locusts: Connecting Soil Nitrogen, Locust Outbreaks, Livelihoods, and Livestock Markets

Coupled human and natural systems (CHANS) are systems of feedback linking people and ecosystems. A feature of CHANS is that this ecological feedback connects people across time and space. Failing to account for these dynamic links results in intertemporal and spatial externalities, reaping benefits in the present but imposing costs on future and distant people, such as occurs with overgrazing. Recent findings about locust–nutrient dynamics create new opportunities to address spatiodynamic ecosystem externalities and develop new sustainable strategies to understand and manage locust outbreaks. These findings in northeast China demonstrate that excessive livestock grazing promotes locust outbreaks in an unexpected way: by lowering plant nitrogen content due to soil degradation. We use these human–locust–livestock–nutrient interactions in grasslands to illustrate CHANS concepts. Such empirical discoveries provide opportunities to address externalities such as locust outbreaks, but society’s ability to act may be limited by preexisting institutional arrangements.

The effects of large herbivore grazing on meadow steppe plant and insect diversity

Summary The interactions between adjacent trophic levels are essential for ecosystem functioning and stability. Grazing by domestic herbivores is an essential interaction in grasslands, but little information is available on the nature of relationship between plant and insect diversity under grazing by large herbivores. We examined the effects of large herbivores on the relationship between plant and insect diversity with five grazing treatments (control, cattle, goat, sheep and a mixture of the three grazing types) across three plant diversity levels (low: 4–5 species, intermediate: 8–9 species and high: 15–17 species) in a meadow steppe. We found that the grazing treatments did not significantly affect plant species richness, but reduced plant biomass, plant height and cover. Grazers affected variation in plant height differently at different plant diversity levels, and this variation increased at the low plant diversity level and decreased at the high plant diversity level after grazing. A similar pattern was observed for insect species richness: grazing had a positive impact at the low plant diversity level, but had a negative impact at the high plant diversity level. In the absence of grazing, insect species richness was positively associated with plant species richness, but it decreased with increasing plant diversity in the grazing treatments. This was attributed to strong responses of insect species richness to plant height heterogeneity under grazing by large herbivores, implying that plant structural heterogeneity is more important than plant diversity in influencing insect diversity in grazed grasslands. Synthesis and applications. Grazing by large herbivores may reverse the positive relationship between plant diversity and insect diversity by modifying plant structural heterogeneity. Therefore, the spatial heterogeneity of vegetation structure should be given more attention in future work on plant–insect interactions. This study further highlights the importance of using large herbivore grazing in management actions, not only to maintain diversity but also to mediate trophic interactions in grasslands.

Soil arthropods beneficially rather than detrimentally impact plant performance in experimental grassland systems of different diversity

Abstract Impacts of belowground insecticide application on plant performance and changes in plant community structure almost uniformly have been ascribed to reduced belowground herbivory, although recent studies reported distinct side effects on detritivore soil animals, particularly on Collembola. Consequently, it remains controversial if the resulting soil feedbacks on plants are due to alterations in arthropod herbivory or to changes in the activity of detritivores. We investigated the impacts of the application of a commonly used belowground insecticide (chlorpyrifos) on soil animals and soil feedbacks on model plant species representing two main plant functional groups of grassland communities, the grass Lolium perenne and the forb Centaurea jacea . Insecticide application decreased soil insect herbivore densities considerably. However, also Collembola densities and diversity decreased markedly due to insecticide application and this was most pronounced in Entomobryidae, Isotomidae, Hypogastruridae, and Sminthuridae. While densities of other detritivore taxa were not affected or even increased (Oribatida) in insecticide subplots, that of predators mostly decreased. Both model plant species built considerably more biomass in control subplots than in insecticide subplots irrespective of characteristics of the resident plant community. This suggests that soil feedbacks on plants were not due to belowground herbivory and highlights the significance of alternative mechanisms responsible for insecticide-mediated soil feedbacks on plants. The deterioration of model plant species’ performances in insecticide subplots most likely was due to decreased densities of Collembola resulting in the deceleration of nutrient cycling and plant nutrition. The results suggest that it is oversimplistic to only ascribe insecticide-mediated soil feedbacks on plants to belowground herbivores. The results further indicate that in the present study the impact of arthropod detritivores on plant productivity was more important than that of belowground herbivores. This emphasizes that plant–soil arthropod interactions in grassland might be based on both facilitative and antagonistic interrelationships.

Nutrient Limitations of Carbon Uptake: From Leaves to Landscapes in a California Rangeland Ecosystem

Nutrient controls of ecosystem pattern and process have been widely studied at the Jasper Ridge Biological Preserve, a well-studied California rangeland ecosystem. Here we review these studies, from leaf to landscape scales, with the intention of developing a deeper understanding of carbon (C)–nutrient interactions in such an ecosystem. At the leaf scale, several studies conducted on diverse plant species have revealed a strong positive relationship between leaf nitrogen (N) concentrations and maximal rates of photosynthesis. This relationship, which has subsequently been observed globally, can be explained by the nutritional requirements of photosynthetic machinery. Consistent with this local physiological constraint, N availability has been shown to limit carbon uptake of California rangeland ecosystems. In some cases phosphorus (P; and N plus P) limits productivity, too—particularly in serpentine soils, pointing to the importance of parent material in regulating CO 2 uptake at landscape scales. Nutrient dynamics are also affected by herbivory , which seems to accelerate N and P cycles over the short term (years), but may lead to nutrient limitation of plant production over the longer term (decades). Simulated global change experiments at Jasper Ridge have also provided insight into C–nutrient interactions in grasslands. In particular, several field-based experiments have shown that CO 2 doubling does not necessarily simulate productivity of California grasslands; rather, the strength and sign of net primary productivity (NPP) responses to CO 2 doubling varies across years and conditions. Although simulated N deposition stimulates NPP, N plus CO 2 combinations do not necessarily increase productivity beyond N treatments singly. Poorly understood feedbacks between plants, microbes , and P availability may underlie variation in the response of California grasslands to increasing atmospheric CO 2 concentrations. We conclude that interactions between C, N, and P appear especially vital in shaping plant productivity patterns in California rangelands and the capacity of this ecosystem to store additional C in the future. Los controles ejercidos por los nutrientes sobre los patrones y procesos del ecosistema han sido ampliamente estudiados en la Reserva Biológica de Jasper Ridge, un ecosistema de pastizales naturales de California que ha sido bien estudiado. Aquí hacemos una revisión de dichos trabajos desde la hoja de una planta hasta la escala de paisaje, con la intención de desarrollar una compresión más profunda de las interacciones Carbono (C)-nutrientes de dicho ecosistema. A la escala de una hoja varios trabajos realizados en varias especies vegetales han revelado una fuerte correlación positiva entre la concentración de nitrógeno (N) y las tasas máximas de fotosíntesis. Esta relación, que subsecuentemente ha sido observada a nivel global, puede ser explicada por las necesidades nutritivas de la maquinaria fotosintética. En consonancia con esta restricción fisiológica local, se ha comprobado que la disponibilidad de N limita la captura de carbono de los ecosistemas de pastizales naturales de California. En algunos casos el fósforo (P) (y N más P) también limita la productividad – particularmente en suelos de serpentina, subrayando la importancia del material originario en la regulación de la captura de carbono a escalas de paisaje. La dinámica de nutrientes también es afectada por la herbivoría, que aparentemente acelera los ciclos de N y P en el corto plazo (años), pero podría resultar en una limitación de nutrientes para la producción vegetal en el más largo plazo (décadas). Experimentos realizados en Jasper Ridge simulando cambio global también han proporcionado una comprensión más profunda de las interacciones C-nutrientes en pastizales. En particular, varios experimentos de campo han demostrado que la duplicación de la concentración actual de CO 2 de la atmósfera no necesariamente estimula la producción de los pastizales de California; más bien, la intensidad y el sentido de las respuestas en PPN a la duplicación de la concentración de CO 2 varía con los años y las condiciones ambientales. Mientras que la deposición simulada de N estimula la PPN, la combinación de N más CO 2 no necesariamente incrementa la producción más allá de la adición de N solamente. Los procesos de retroalimentación pobremente comprendidos que vinculan a las plantas, los microbios, y la disponibilidad de P podrían ser responsables de la variación en la respuesta de los pastizales de California a incrementos en la concentración de CO 2 atmosférico. Concluimos que las interacciones entre C, N y P aparentan ser particularmente vitales en la conformación de los patrones de productividad de los pastizales naturales de California y la capacidad de este ecosistema de almacenar C adicional en el futuro.

Lack of relationship between below‐ground competition and allocation to roots in 10 grassland species

Summary A field experiment in a native grassland in Central Alberta, Canada, tested whether plants alter relative allocation to roots vs. shoots in response to below‐ground competition, and whether the mass of a species’ root system accounts for interspecific differences in below‐ground competitive response. Seedlings of each of 10 native species were transplanted into the naturally occurring vegetation in the field at the start of the growing season. Root interactions between the target plants and their neighbours were manipulated through the use of PVC root exclusion tubes, with target plants grown with or without potential root interactions with their neighbours. Neighbour shoots were also tied back, forcing any target–neighbour interactions to be below ground. Below‐ground competition generally reduced plant growth, with its relative magnitude varying among species. An allometric analysis indicated that competition below ground did not result in an increase in the relative biomass allocated to roots for any of the 10 target species. This is counter to the growth‐balance hypothesis (and optimal foraging theory). Below‐ground competition did increase root : shoot ratios, but this was due to reduced plant size (small plants have larger root : shoot ratios), rather than adaptive plasticity. A species’ below‐ground competitive ability was not related to its root system size. Although this finding is counter to commonly made assumptions, it is supported by other work demonstrating below‐ground competition to be generally size‐symmetric. Despite the majority of plant–plant interactions in grasslands being below ground, our understanding of plant competition above ground is significantly more robust. Several wide‐spread assumptions regarding below‐ground competition are suspect, and more multispecies studies such as this are required to provide a fuller picture of how plants respond to, and compete for, soil resources.

Complex interactions between plant diversity, succession and elevated CO 2

Considerable optimism and a certain disdain for all things past are distinctive characteristics of quickly developing fields of science. This is true of research into plant responses to elevated atmospheric CO2 and on biodiversity effects on ecosystem processes, two areas of research that have tended to ignore both each other and some fundamental community processes that are well understood within the framework of traditional plant ecology. Highly simplistic experimental arrangements and strong responses to treatments – sometimes leading to dramatic projections to the real world – were characteristics of early studies in these areas.Recently, there has been an increased interest in moving into more realistic growth conditions and plant assemblages, based on accumulating evidence that responses of natural systems tend to be strongly influenced by resource conditions, plant traits and interactions, and might involve complex positive and negative feedbacks. The new article by Pascal Niklaus and colleagues1xA long-term field study on biodiversity x elevated CO2 interactions in grassland. Niklaus, P.A. et al. Ecol. Monogr. 2001; 71: 341–356See all References1 is a rare example of this new research trend.Together with Reich et al.2xPlant diversity enhances ecosystem responses to elevated CO2 and nitrogen deposition. Reich, P.B. et al. Nature. 2001; 410: 809–812Crossref | PubMed | Scopus (320)See all References2, Niklaus et al.1xA long-term field study on biodiversity x elevated CO2 interactions in grassland. Niklaus, P.A. et al. Ecol. Monogr. 2001; 71: 341–356See all References1 are one of the first to show bi-directional interactive effects of elevated CO2 and plant diversity on plant community productivity. The authors tested whether the ecosystem responses to elevated CO2 changed when specific sets of species were lost from nutrient-poor calcareous grasslands. They set up a five-year field experiment in northwestern Switzerland, constructing communities composed of five, 12 and 31 plant species assembled from the native species pool, and submitting them to either ambient or elevated atmospheric CO2.As reported elsewhere2xPlant diversity enhances ecosystem responses to elevated CO2 and nitrogen deposition. Reich, P.B. et al. Nature. 2001; 410: 809–812Crossref | PubMed | Scopus (320)See all References2, Niklaus et al. found that diversity influenced plant-community response to CO2 enrichment. Elevated CO2 increased biomass production only in communities with the highest number of species. Interestingly, as recently established communities, the assemblages underwent compositional changes during the experiment. Following a classic secondary succession process, there was a gradual replacement of fast-growing short-lived species by slower-growing conservative species. At different successional stages, increased biomass production by elevated CO2 in more diverse communities was due to the presence of responsive species that were absent in species-poorer communities, and these responsive species were different at different successional stages. This suggests that, although response to elevated CO2 is more dependent on plant species traits than on species number, a rich species pool might be important to maintain high productivity under changing environmental conditions.CO2 enrichment also affected biodiversity. Elevated CO2 altered succession by reducing species extinction and increasing coexistence between early- and late-successional species. The fact that elevated CO2 might slow down secondary succession is relevant in a world where disturbance makes early-successional communities increasingly common.The findings of Niklaus et al. might be bad news for those wishing to obtain simple principles to predict the future. Species composition is unlikely to be just a passive response variable in the face of global change. Self-feeding, nonlinear processes can occur, with different communities having different responses to CO2 enrichment, and elevated CO2 affecting the composition of these communities. However, this article shows how fruitful it can be to integrate CO2 and biodiversity research in long-term studies, and combine cutting-edge enquiry with good old-fashioned natural history.

Elevated CO 2and water supply interactions in grasslands: a pastures and rangelands management perspective

Water is a key variable driving the composition and productivity of pastures and rangelands, and many of the ecosystems in these grasslands are highly sensitive to changes in water supply. The possibility that elevated CO2 concentrations may alter plant water relations is therefore particularly relevant to pastures and rangelands, and may have important consequences for grassland ecosystem function, water use, carbon storage and nutrient cycling. The planning of effective research to better understand these changes requires attention to both: (i) gaps in knowledge about CO2 and water interactions, and (ii) knowledge of how precisely the effects of CO2 must be understood in relation to other factors, in order to predict changes in grassland structure and production. A recent microcosm experiment illustrates that non‐linear effects of CO2 and water stress could perturb primary production by triggering changes in grassland community composition. The magnitudes of the effects of CO2 on key grassland ecosystems remain to be precisely determined through ecosystem‐level experiments. A simplified simulation of the impact of different levels of productivity change in a water‐limited Australian rangeland system was conducted by varying effects of CO2 on radiation and water use efficiency. The results indicate that direct effects of CO2 may be moderated at the enterprise scale by accompanying changes in adaptive management by farmers. We conclude that future research should aim to construct quantitative relationships and identify thresholds of response for different grassland systems. The sensitivity of these systems to management (such as grazing pressure) should also be considered when developing integrated predictions of future effects of CO2 on water supply to grassland ecosystems.

Plant-Animal Interactions in a Continuously Grazed Mixture. II. The Role of Differences in the Physiology of Plant Growth and of Selective Grazing on the Performance and Stability of Species in a Mixture

SUMMARY (1) A physiologically based mechanistic model of the dynamic interaction between plants and animals is used to consider the role of differences in growth rate between plant species, and of selective grazing by animals, in the stability of plant species in a continuously grazed mixture, and so the long-term consequences of different intensities of grazing on the composition of the sward and diet. (2) The model provides a means to apply a detailed account of plant physiology in controlling the availability of food resources (prey) in analyses of predator-prey interactions in grassland. (3) The model confirms that mixtures are intrinsically unstable. In the absence of a mechanism in either species to escape grazing, one which possesses a physiological advantage is shown progressively to dominate the mixture. Where the advantage is a simple one, the mixture tends to a monoculture of that species at all intensities of grazing. But, where the advantaged species is also the preferred species, the intensity of grazing is shown to determine which species dominates the mixture. (4) The model suggests that stable mixtures may arise when either species can escape grazing to some extent. Under these circumstances, the otherwise advantaged species takes the brunt of variations in the intensity of grazing. (5) The model is used to consider the sustainability of differences in composition between the diet and sward. At high intensities of grazing, the composition of the diet is shown to be more a reflection of differences in growth rate between plant species than of the preferences of grazing animals. It is also shown that, because of its adverse impact on vegetation dynamics, the long-term consequence of a preference for one species in the diet is that there may be less of that species in the diet (both as a proportion and as an amount) than if there had been less preference for it or a preference against it. The implications of these analyses for the biological interpretation of field data are discussed.