The biogeochemical cycles of carbon (C), nitrogen (N) and phosphorus (P) are interlinked by primary production, respiration and decomposition in terrestrial ecosystems. It has been suggested that the C, N and P cycles could become uncoupled under rapid climate change because of the different degrees of control exerted on the supply of these elements by biological and geochemical processes. Climatic controls on biogeochemical cycles are particularly relevant in arid, semi-arid and dry sub-humid ecosystems (drylands) because their biological activity is mainly driven by water availability. The increase in aridity predicted for the twenty-first century in many drylands worldwide may therefore threaten the balance between these cycles, differentially affecting the availability of essential nutrients. Here we evaluate how aridity affects the balance between C, N and P in soils collected from 224 dryland sites from all continents except Antarctica. We find a negative effect of aridity on the concentration of soil organic C and total N, but a positive effect on the concentration of inorganic P. Aridity is negatively related to plant cover, which may favour the dominance of physical processes such as rock weathering, a major source of P to ecosystems, over biological processes that provide more C and N, such as litter decomposition. Our findings suggest that any predicted increase in aridity with climate change will probably reduce the concentrations of N and C in global drylands, but increase that of P. These changes would uncouple the C, N and P cycles in drylands and could negatively affect the provision of key services provided by these ecosystems.

Increasing plant diversity can increase ecosystem functioning, stability, and services in both natural and managed grasslands, but the effects of herbivore diversity, and especially of livestock diversity, remain underexplored. Given that managed grazing is the most extensive land use worldwide, and that land managers can readily change livestock diversity, we experimentally tested how livestock diversification (sheep, cattle, or both) influenced multidiversity (the diversity of plants, insects, soil microbes, and nematodes) and ecosystem multifunctionality (including plant biomass production, plant leaf N and P, above-ground insect abundance, nutrient cycling, soil C stocks, water regulation, and plant–microbe symbiosis) in the world’s largest remaining grassland. We also considered the potential dependence of ecosystem multifunctionality on multidiversity. We found that livestock diversification substantially increased ecosystem multifunctionality by increasing multidiversity. The link between multidiversity and ecosystem multifunctionality was always stronger than the link between single diversity components and functions. Our work provides insights into the importance of multitrophic diversity to maintain multifunctionality in managed ecosystems and suggests that diversifying livestock could promote both multidiversity and ecosystem multifunctionality in an increasingly managed world.

Global environmental changes are altering ecosystem stability, sometimes by altering biodiversity. For example, by driving grassland plant species loss, nitrogen (N) addition can reduce ecosystem stability. In other cases, however, N addition may alter productivity and ecosystem stability, by increasing the dominance of particularly productive or stable species. We examined how N addition affected plant diversity, productivity and the temporal stability of productivity in an 8‐year grassland experiment. We found that N addition enhanced productivity and decreased ecosystem stability throughout the experimental period, even though it reduced species richness in the first 4 years, but increased richness during the subsequent years. During the early years, N addition decreased ecosystem stability by synchronizing species fluctuations and population stability of the dominant species. During later years, N addition did not increase stability, even though it increased species richness; instead, N addition continued to decrease ecosystem stability by decreasing species dominance and stability of the dominant species, without changing the identity of the dominant species. Synthesis. Our results indicate that N addition decreased ecosystem stability via mechanisms that were both dependent and independent of plant diversity, and that the mechanisms involved shifted over time. N addition impacted on ecosystem functioning through species richness and the effects on species dominance and the stability of most dominant species, highlighting the join effect of multiple biotic drivers in regulating ecosystem stability.

Close spatial relationships between plant species are often important for defense against herbivory. The associational plant defense may have important implications for plant community structure, species diversity, and species coexistence. An increasing number of studies have focused on associational plant defense against herbivory at the scale of the individual plant and its nearest neighbors. However, the average neighborhood effects between plant species at the scale of whole plant communities have received almost no attention. The aims of this study were to determine patterns of spatial relationship between different plant species that can provide effective defense against herbivory. We conducted a manipulative experiment using sheep and three native plant species with different palatability. Consumption of palatable plants by herbivores was largest when the three plant species were isolated in three patches and independent of each other. A homogenous and spatially equal neighbor relationship between the three species did not reduce the risk of herbivory of palatable species compared to isolation of these species, but it reduced the total intake of all plant species. The palatable species was subject to less herbivory in a complex spatial neighborhood of several plant species. High complexity of spatial neighborhood resulted in herbivores passively reducing selectivity, thereby reducing the probability of damage to palatable species in the community, or making inaccurate judgments in foraging selectivity between and within patches, thereby reducing the vulnerability of palatable plants and even the whole plant community. We conclude that compelling herbivores to passively reduce the magnitude of foraging selectivity by establishing spatially complex neighborhoods between plant species is a compromise and optimal spatial strategy by plants to defend themselves again herbivory. This may contribute not only to maintenance of plant species diversity but also to a stable coexistence between herbivores and plants in grassland ecosystems.

BackgroundPlants and herbivores can evolve beneficial interactions. Growth factors found in animal saliva are probably key factors underlying plant compensatory responses to herbivory. However, there is still a lack of knowledge about how animal saliva interacts with herbivory intensities and how saliva can mobilize photosynthate reserves in damaged plants.Methodology/Principal FindingsThe study examined compensatory responses to herbivory and sheep saliva addition for the grass species Leymus chinensis in three experiments over three years. The first two experiments were conducted in a factorial design with clipping (four levels in 2006 and five in 2007) and two saliva treatment levels. The third experiment examined the mobilization and allocation of stored carbohydrates following clipping and saliva addition treatments. Animal saliva significantly increased tiller number, number of buds, and biomass, however, there was no effect on height. Furthermore, saliva effects were dependent on herbivory intensities, associated with meristem distribution within perennial grass. Animal saliva was found to accelerate hydrolyzation of fructans and accumulation of glucose and fructose.Conclusions/SignificanceThe results demonstrated a link between saliva and the mobilization of carbohydrates following herbivory, which is an important advance in our understanding of the evolution of plant responses to herbivory. Herbivory intensity dependence of the effects of saliva stresses the significance of optimal grazing management.