Scale-dependent patterns and mechanisms of grazing-induced biodiversity loss: evidence from a field manipulation experiment in semiarid steppe

Although many studies have demonstrated that grazing may increase or decrease plant diversity of grasslands at small scales, few studies have examined the patterns and mechanisms of grazing effects on biodiversity across multiple scales. Our study tested the scale dependence of grazing effects on plant diversity based a 7-year grazing manipulation experiment with seven levels of grazing intensity (0-9 sheep ha(-1)) in a typical steppe of the Inner Mongolia grassland. Species area relationships (SARs) were used to analyze the scale dependence of species loss. SAR decomposition approaches were followed to examine the contribution of four potential mechanisms to changes in the slope of SARs, including species aggregation, overall species richness, total number of individuals, and species abundance distribution. The proportional species loss increased with sampling area (4-1024 m(2)), which was evidenced by decreasing intercepts and slopes of SARs with grazing. Reduction in the slope of SARs was mainly caused by changes in overall species richness and species abundance distribution, with the relative minor effect of changes in number of individuals. The negative effect of grazing on overall species richness was mainly attributed to the loss of grazing-sensitive rare species from species pool. Compared with flat systems, plant diversity in slope systems was more sensitive to grazing at low intensities. However, the responses of plant diversity to grazing tended to converge between the flat and slope systems at high levels of grazing intensity. Our study has important implications for adaptive ecosystem management and biodiversity conservation in arid and semiarid grasslands

Data from: Testing the scaling effects and mechanisms of N-induced biodiversity loss: evidence from a decade-long grassland experiment

Although extensive studies demonstrate that nitrogen (N) enrichment frequently reduces plant diversity within small quadrats (0.5 –4 m2), only a few studies have evaluated N effects on biodiversity across different spatial scales. We conducted the first experimental test of the scale dependence of N effects on species richness from a 10-year N treatment (1.75- 28 g N m−2 yr−1) in a typical steppe. We used species area relationship (SAR) to analyze the scale dependence of species loss with power model S = cAz (S is species number, A is area, c is intercept, and z is slope). Absolute species loss decreased at sampling area > 8 m2. Proportional species loss (compared to control) decreased and critical threshold (Ncrit) for biodiversity losses increased with sampling areas. These scale dependences were quantified as increasing slope (z-value) of SAR with N addition. Through SAR decomposition, we found that this overall positive effect was in response to positive effects of changes to the species abundance distribution over negative effects of overall species richness losses. Synthesis. As nitrogen (N) enrichment typically occurs at scales much larger than individual plots, understanding how N enrichment affects the scaling patterns of biodiversity is necessary for biodiversity conservation and ecosystem management in response to anthropogenic N deposition

Testing the scaling effects and mechanisms of N-induced biodiversity loss: evidence from a decade-long grassland experiment

Although extensive studies demonstrate that nitrogen (N) enrichment frequently reduces plant diversity within small quadrats (0.5-4m(2)), only a few studies have evaluated N effects on biodiversity across different spatial scales. We conducted the first experimental test of the scale dependence of N effects on species richness from a 10-year N treatment (1.75-28gNm(-2)year(-1)) in a typical steppe. We used species-area relationship (SAR) to analyse the scale dependence of species loss with power model S=cA(z) (S is species number, A is area, c is intercept, and z is slope). Absolute species loss decreased at sampling area > 8m(2). Proportional species loss (compared to control) decreased and critical threshold (N-crit) for biodiversity losses increased with sampling areas. These scale dependences were quantified as increasing slope (z-value) of SAR with N addition. Through SAR decomposition, we found that this overall positive effect was in response to positive effects of changes to the species abundance distribution over negative effects of overall species richness losses.Synthesis. As nitrogen (N) enrichment typically occurs at scales much larger than individual plots, understanding how N enrichment affects the scaling patterns of biodiversity is necessary for biodiversity conservation and ecosystem management in response to anthropogenic N deposition

Optimization of Saccharomyces boulardii production in solid-state fermentation with response surface methodology

Saccharomyces boulardii preparations are promising probiotics and clinical agents for animals and humans. This work focused on optimizing the nutritional conditions for the production of S. boulardii in solid-state fermentation by using classical and statistical methods. In single-factor experiments, the S. boulardii production was significantly increased by the addition of glucoamylase and the optimal carbon and nitrogen sources were found to be soluble starch and NH4Cl, respectively. The effects of the glucoamylase, soluble starch and NH4Cl on S. boulardii production were evaluated by a three-level three-factor Box–Behnken design and response surface methodology (RSM). The maximal yeast count (4.50 ×109CFU/g) was obtained under the optimized conditions (198 U/g glucoamylase, 2.37% soluble starch and 0.9% NH4Cl), which was in a good agreement with the predicted value of the model. This study has provided useful information on how to improve the accumulation of yeast cells by RSM

Species richness

Species richness was the average of number of species at each sampling area in each 5m × 5m plot. The N addition rates are 0.00, 1.75, 5.25, 10.50, 17.50, and 28.00 g N m-2 yr-1, respectively

Species abundance

Species abundance was the number of individuals for each species in each 5m × 5m plot. The N addition rates are 0.00, 1.75, 5.25, 10.50, 17.50, and 28.00 g N m-2 yr-1, respectively