Search

Determining the abundance of N isotope (δ15N) in natural environments is a simple but powerful method for providing integrated information on the N cycling dynamics and status in an ecosystem under exogenous N inputs. However, whether the input of different N compounds could differently impact plant growth and their 15N signatures remains unclear. Here, the response of 15N signatures and growth of three dominant plants (Leymus chinensis, Carex duriuscula, and Thermopsis lanceolata) to the addition of three N compounds (NH4HCO3, urea, and NH4NO3) at multiple N addition rates were assessed in a meadow steppe in Inner Mongolia. The three plants showed different initial foliar δ15N values because of differences in their N acquisition strategies. Particularly, T. lanceolata (N2‐fixing species) showed significantly lower 15N signatures than L. chinensis (associated with arbuscular mycorrhizal fungi [AMF]) and C. duriuscula (associated with AMF). Moreover, the foliar δ15N of all three species increased with increasing N addition rates, with a sharp increase above an N addition rate of ~10 g N m−2 year−1. Foliar δ15N values were significantly higher when NH4HCO3 and urea were added than when NH4NO3 was added, suggesting that adding weakly acidifying N compounds could result in a more open N cycle. Overall, our results imply that assessing the N transformation processes in the context of increasing global N deposition necessitates the consideration of N deposition rates, forms of the deposited N compounds, and N utilization strategies of the co‐existing plant species in the ecosystem. [ABSTRACT FROM AUTHOR]

Photographs of the Transformation of the Social-Ecological Rangeland System in Ujimqin Grasslands, Inner Mongolia, China Across the world, rangeland systems have been transformed from a less-exploited preindustrial status to intensive exploitation, often leading to long-term livestock population booms, overgrazing, and rangeland degradation. Modern houses and sufficient forage protected livestock from severe climate events and density dependence of food competition, but indirectly caused grassland degradation. [Extracted from the article]

Across the world, social‐ecological rangeland systems have been transformed from a preindustrial extensive status to intensive exploitation, often leading to long‐term livestock population booms, overgrazing, and rangeland degradation. To understand the regulatory mechanisms involved in such historical social‐ecological transformations, we collected population data on the native sheep of the last nomadic county in the Inner Mongolia Autonomous Region (1961–2005). We detected changes in internal feedbacks (e.g., density‐dependent effects) and external disturbance (e.g., winter harshness, rainfall, harvest) between the extensive and intensive management periods using regression models of sheep population growth rate and counterfactual analyses. We found that, in the extensive period, sheep populations were regulated during harsh winters by climate, while they were regulated during mild winters by negative density dependence. In the intensive period, the negative feedback of density dependence was removed through the provision of additional forage and shelter, and only winter climate and growing season rainfall regulated sheep populations. Counterfactual analyses also confirmed the irreplaceable role of density‐dependence in maintaining a sustainable rangeland ecosystem. Although herders attempted to adapt to the removal of negative feedbacks by improving livestock harvest, overgrazing and grassland degradation remain a challenge in this system. We conclude that internal feedbacks within social‐ecological systems should be carefully anticipated and accounted for when managing rangelands for sustainability. [ABSTRACT FROM AUTHOR]

Higher ecosystem nitrogen (N) inputs resulting from human activities often suppress soil microbial biomass and respiration, thereby altering biogeochemical cycling. Soil acidification and carbon (C) limitation may drive these microbial responses, yet their relative importance remains elusive, which limits our understanding of the longer term effects of increasing N inputs. In a field experiment with continuous N addition at seven different rates from 0 to 50 g N m−2 year−1 over 6 years in a temperate grassland of Inner Mongolia, China, we examined the responses of soil microbial biomass and respiration to changes in soil acidity and C availability by adding lime and/or glucose to soil samples. Soil microbial biomass and respiration did only weakly respond to increasing soil pH, but increased strongly in response to higher C availability with increasing N addition rates. Soil net N immobilization increased in response to glucose addition, and soil microbial biomass increased at higher rates than microbial respiration along the gradient of previous N addition rates, both suggesting increasingly reinforced microbial C limitation with increasing N addition. Our results provide clear evidence for strong N‐induced microbial C limitation, but only little support for soil acidity effects within the initial pH range of 4.73–7.86 covered by our study. Field data support this conclusion by showing reduced plant C allocation belowground in response to N addition, resulting in soil microbial C starvation over the long term. In conclusion, soil microbial biomass and respiration under N addition were strongly dependent on C availability, most likely originating from plant belowground C inputs, and was much less affected by changes in soil pH. Our data help clarify a long‐standing debate about how increasing N input rates affect soil microbial biomass and respiration, and improve the mechanistic understanding of the linkages between ecosystem N enrichment and C cycling. [ABSTRACT FROM AUTHOR]

China is currently implementing the “separating three property rights” (STPR) reform to consolidate rural land. This reform divides rural land property rights into three components: nontradable ownership, nontradable contractual rights and tradable land use rights. The STPR reform adopts the rental of grassland use rights, a market-oriented approach, as the main arrangement for grassland consolidation. However, this arrangement may undermine the cornerstones of grassland restoration, which are the security of grassland property and payments for ecosystem services (PES) policies. As an alternative to the market-oriented approach, cooperatives are also encouraged to consolidate grassland use rights. We used a natural experiment approach to systematically examine how two different land consolidation arrangements affected key grassland ecosystem services in Inner Mongolia. In rented grasslands, all ecosystem services except provisioning services degenerated severely. Traded grassland use rights were perceived as insecure, which led to predatory land use by tenants. In contrast, cooperative-managed grasslands showed no serious degradation in ecosystem services. However, these cooperatives limited their group size by chief kinship to avoid the free-rider problem; thus, they are unlikely to become a primary channel of grassland consolidation. Because PES policy subsidies are still allocated to grassland contractors rather than to tenants, these policies are irrelevant to the conservation of rented grasslands. Based on our analysis, we suggest several ways to improve this new rural land property reform to avoid a major wave of grassland degradation in China. [ABSTRACT FROM AUTHOR]

Context: Understanding the causes and consequences of land use and land cover change in drylands is crucial for global sustainability. Inner Mongolia consists of arid and semiarid ecosystems of global importance. Objectives: Our main goal was twofold: to review the patterns and drivers of land use and land cover change in Inner Mongolia, and to discuss ecological impacts and strategies for promoting landscape and regional sustainability. Methods: We took an interdisciplinary and retrospective approach, based on historical records and remote sensing data. Results: Inner Mongolia has evolved from an ocean to a forested region and then to a dryland area in the past millions of years. As a cradle of Chinese civilization, Inner Mongolia has experienced a series of land transitions from localized primitive agriculture that occurred in prehistoric times to broad-scale nomadic pastoralism that lasted for a few 1000 years, and to sedentary pastoralism with increasing agriculture and urbanization since the 1960s. The general land use pattern has long been shaped by the interactions between nomadic pastoralism and agrarian culture. The major drivers of land use and land cover change include: climate, demography, socioeconomic structures, institutional changes, and technological innovations. Conclusions: The landscapes of Inner Mongolia have evolved historically through several phases, and the profound and unsustainable landscape transformations during the past 50 years have been driven primarily by land use policies. Strategies based on landscape sustainability science are needed to curb ecosystem degradation and promote sustainability in the region. [ABSTRACT FROM AUTHOR]

Context: Spatial heterogeneity is ubiquitous in ecological systems, and has important effects on biological diversity and ecological processes. Objectives: Does spatial heterogeneity affect the relationship between biodiversity and ecosystem functioning (BEF)? To help address this question, this study investigated how the spatial patterns of key BEF variables changed before and after the biodiversity removal during a BEF experiment in China. Methods: Our analysis was based on data from the Inner Mongolia grassland removal experiment (IMGRE) which was conducted in the Xilingol Steppe, Inner Mongolia, China. We quantified the spatial patterns of key variables of BEF, and examined the spatial relationships among these variables, using biodiversity indices and spatial statistical methods (autocorrelation and semivariance analysis). Results: Our results show that the variables of BEF in the Inner Mongolian grassland had various spatial patterns, most of which were spatially correlated to each other. Removal treatments had significant effects on these spatial structures and correlations. These effects were diverse in terms of both their kinds and magnitudes because of different removal protocols and treatments. Conclusions: The differences in spatial patterns of plant and soil variables and their correlations before and after the biodiversity manipulation do not necessarily imply that the results from BEF experiments like IMGRE are invalid, but they do suggest that the possible effects of spatial heterogeneity on the BEF relationship should be further scrutinized in future studies. [ABSTRACT FROM AUTHOR]