Cumulative nitrogen enrichment alters the drivers of grassland overyielding

Effects of plant diversity on grassland productivity, or overyielding, are found to be robust to nutrient enrichment. However, the impact of cumulative nitrogen (N) addition (total N added over time) on overyielding and its drivers are underexplored. Synthesizing data from 15 multi-year grassland biodiversity experiments with N addition, we found that N addition decreases complementarity effects and increases selection effects proportionately, resulting in no overall change in overyielding regardless of N addition rate. However, we observed a convex relationship between overyielding and cumulative N addition, driven by a shift from complementarity to selection effects. This shift suggests diminishing positive interactions and an increasing contribution of a few dominant species with increasing N accumulation. Recognizing the importance of cumulative N addition is vital for understanding its impacts on grassland overyielding, contributing essential insights for biodiversity conservation and ecosystem resilience in the face of increasing N deposition

Rainfall pulses mediate long‐term plant community compositional dynamics in a semi‐arid rangeland

Semi-arid rangelands, comprising more than 40% of the Earth's land surface, provide critical ecosystem services. Worldwide, these ecosystems are experiencing rapid degradation due to overgrazing and precipitation changes. However, how plants respond to these interacting factors remains relatively unexplored, and precisely which and how rainfall factors determine plant community dynamics in rangelands has not been well developed. We used a long-term (1953-2018) dataset from semi-arid rangeland to investigate coupled effects of grazing intensity and rainfall intensity (the total amount of precipitation) on different groups of plant cover (herbaceous, woody and cacti plants) using linear mixed-effects models, redundancy analysis and structural equation models. We examined how rainfall intensity influenced plant cover dynamics according to pulse size (intensity over time) categories, which we analysed at three scales: yearly, within the wet season only (June-September) and within the dry season only (October-May). Plant community cover showed a humpbacked trend in the last six decades, mostly through changes in woody plants. Although both grazing intensity and rainfall presented similar humpbacked trends with plant community cover, our models demonstrated that the reduction of plant cover from the 1990s has been mainly caused by a decrease of rainfall rather than grazing intensity, particularly due to profound reductions of the intensity of relatively small rainfall pulses (e.g. 5.1-15 mm/day) during the dry season. Specifically, these small rainfall pulses can increase plant cover of all subgroups of woody and herbaceous species, thereby increasing plant community cover. Moreover, rainfall pulses during the wet season had negative effects on herbaceous species and positive effects on woody plants. These results suggest a phenological niche partitioning between woody plants and herbaceous in subtropical rangelands. Synthesis and applications. Our results show how critical seasonal rainfall pulses are for regulating plant community compositional dynamics, which has significant implications for rangeland management and our ability to adapt and mitigate amplified climate influences in semi-arid ecosystems.12 month embargo; published 28 October 2020This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Foliar Nutrient Content Mediates Grazing Effects on Species Dominance and Plant Community Biomass

Grazing-induced changes in plant community structure can be altered by the biogeochemical regime of the ecosystem. However, responses of community structure (e.g., changes in biomass, canopy height, and stand density) to grazing-induced changes in foliar nutrient content—whether species-specific or species group-specific (dominant vs. subordinate)—are still poorly studied. We conducted a grazing experiment with four sheep stocking rates in the typical steppe of Inner Mongolia, China. We identified the dominant (Leymus chinensis and Stipa grandis) and subordinate species (Anemarrhena asphodeloides and Cleistogenes squarrosa) and examined grazing-induced changes in the relative abundance and foliar carbon (C), nitrogen (N), and phosphorus (P) contents of these species. We explored subsequent consequences on the mechanisms driving grazing-induced succession in grasslands using structural equation models (SEMs). Aboveground biomass and relative abundance increased for S. grandis, decreased for L. chinensis and A. asphodeloides in response to grazing, but did not change for C. squarrosa. Higher grazing intensity increased foliar N and P contents of subordinate species, whereas no changes occurred with increasing grazing intensity for dominant species. SEMs confirmed that the dominants were homeostatic in response to grazing while the subordinates were more flexible and adjusted foliar nutrient content to grazing intensity. Moreover, SEMs indicated that the relative abundance of species was mediated by foliar C content of both groups, whereas community biomass was dependent on foliar N and P content for the dominants but only foliar P content for the subordinates. Our findings highlight that grazing-induced shifts in plant dominance is species specific rather than group specific (dominant vs. subordinate) and that foliar nutrient content has a key role in mediating plant community compositions and biomass under grazing-managed succession.National Key Research and Development Program of China [2016YFC0500503]; "Dynamics of Coupled Natural and Human Systems (CNH)" Program of the NSFNational Science Foundation (NSF)NSF - Directorate for Biological Sciences (BIO) [1313761]24 month embargo; published online: 1 November 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Structural equation modeling

Structural equation modeling of grazing and drought to predict community structure and biodiversity & ecosystem function by regulating the plant functional groups

Grazing-induced biodiversity loss impairs grassland ecosystem stability at multiple scales

Livestock grazing is a major driver shaping grassland biodiversity, functioning and stability. Whether grazing impacts on grassland ecosystems are scale-dependent remains unclear. Here, we conducted a sheep-grazing experiment in a temperate grassland to test grazing effects on the temporal stability of productivity across scales. We found that grazing increased species stability but substantially decreased local community stability due to reduced asynchronous dynamics among species within communities. The negative effect of grazing on local community stability propagated to reduce stability at larger spatial scales. By decreasing biodiversity both within and across communities, grazing reduced biological insurance effects and hence the upscaling of stability from species to communities and further to larger spatial scales. Our study provides the first evidence for the scale dependence of grazing effects on grassland stability through biodiversity. We suggest that ecosystem management should strive to maintain biodiversity across scales to achieve sustainability of grassland ecosystem functions and services

Grazing-induced biodiversity loss impairs grassland ecosystem stability at multiple scales

Livestock grazing is a major driver shaping grassland biodiversity, functioning and stability. Whether grazing impacts on grassland ecosystems are scale-dependent remains unclear. Here, we conducted a sheep-grazing experiment in a temperate grassland to test grazing effects on the temporal stability of productivity across scales. We found that grazing increased species stability but substantially decreased local community stability due to reduced asynchronous dynamics among species within communities. The negative effect of grazing on local community stability propagated to reduce stability at larger spatial scales. By decreasing biodiversity both within and across communities, grazing reduced biological insurance effects and hence the upscaling of stability from species to communities and further to larger spatial scales. Our study provides the first evidence for the scale dependence of grazing effects on grassland stability through biodiversity. We suggest that ecosystem management should strive to maintain biodiversity across scales to achieve sustainability of grassland ecosystem functions and services

Community structure

Results of Tukey's test of plant species richness, stand density, and canopy height in different experimental treatments (Mean ± SD)

The relative abundance of PFGs

Results of Tukey's test of the relative abundance (Mean ± SD) of PFGs in different experimental treatments

Biodiversity and ecosystem function

Results of Tukey's test of plant species diversity, functional diversity, and aboveground biomass in different experimental treatments (Mean ± SD)