Grazing exclusion significantly improves grassland ecosystem C and N pools in a desert steppe of Northwest China

Grazing exclusion is often implemented as an effective management practice to increase the sustainability of grassland ecosystems. However, it remains unclear if grazing exclusion can improve ecosystem services related to carbon (C) and nitrogen (N) sequestration in grassland ecosystems. We investigated the effects of 11 years of grazing exclusion on plant biomass and diversity, soil properties (pH, soil water content (SWC), bulk density (BD), soil organic carbon (SOC), total nitrogen (TN),.and C/N ratio), and the C and N stocks of plants and soils in a desert grassland of Northwest China. Grazing exclusion improved plant aboveground biomass and diversity, as well as SWC, SOC, and TN contents, but lowered the belowground biomass, root/shoot ratio, pH, and BD. Moreover, grazing exclusion strongly influenced the C and N stocks of the ecosystem, and the annual mearbecosystem C and N sequestration rates were 0.47 and 0.09 Mg ha(-1) yr(-1), respectively, over 11 years of grazing exclusion. Soil C stocks were most dynamic in the top 30 cm of the soil, and N stocks mainly changed in the top 20 cm after grazing exclusion. Our results indicated that grazing exclusion is an effective measurement on improving the ecosystem C and N pools in desert steppe of Northwest China. (C) 2015 Elsevier B.V. All rights reserved

Characteristics and Driving Factors of Precipitation-Use Efficiency across Diverse Grasslands in Chinese Loess Plateau

Understanding the characteristics of the precipitation-use efficiency (PUE) of grassland ecosystems and its drivers is critical for predicting how ecosystem functions will respond to future climate change. In this study, we investigated several covarying biotic and abiotic factors (e.g., biomass, coverage, diversity, precipitation, temperature, and humid index (HI)) of 81 sites across a broad natural grassland gradient in the Loess Plateau of China to determine how PUE changes along a precipitation gradient and to assess the effects of biotic and abiotic factors on PUE. Our results showed that HI, below-ground biomass (BGB), vegetation coverage, and species diversity were the most important biotic factors in controlling PUE. HI had a higher positive indirect effect on PUE mainly through its influence on community characteristics. Our results suggest that precipitation and community characteristics are both important for the precipitation-use efficiency of natural grasslands across the arid and semiarid areas of the Loess Plateau. Additionally, improving the vegetation structure and increasing species diversity can help enhance the adaptability of grassland ecosystems to climate change

Dynamics of ecosystem carbon stocks during vegetation restoration on the Loess Plateau of China

In the last few decades, the Loess Plateau had experienced an extensive vegetation restoration to reduce soil erosion and to improve the degraded ecosystems. However, the dynamics of ecosystem carbon stocks with vegetation restoration in this region are poorly understood. This study examined the changes of carbon stocks in mineral soil (0-100 cm), plant biomass and the ecosystem (plant and soil) following vegetation restoration with different models and ages. Our results indicated that cultivated land returned to native vegetation (natural restoration) or artificial forest increased ecosystem carbon sequestration. Tree plantation sequestered more carbon than natural vegetation succession over decades scale due to the rapid increase in biomass carbon pool. Restoration ages had different effects on the dynamics of biomass and soil carbon stocks. Biomass carbon stocks increased with vegetation restoration age, while the dynamics of soil carbon stocks were affected by sampling depth. Ecosystem carbon stocks consistently increased after tree plantation regardless of the soil depth; but an initial decrease and then increase trend was observed in natural restoration chronosequences with the soil sampling depth of 0-100 cm. Moreover, there was a time lag of about 15-30 years between biomass production and soil carbon sequestration in 0-100 cm, which indicated a long-term effect of vegetation restoration on deeper soil carbon sequestration

Response of the Meltwater Erosion to Runoff Energy Consumption on Loessal Slopes

Soil properties are influenced by freeze-thaw, which in turn influences soil erosion. Despite this, only a few studies have investigated the impacts on soil hydrodynamic processes. The objective of this study was to evaluate the impact of soil freezing conditions on runoff, its energy consumption, and soil erosion. A total of 27 laboratory-concentrated meltwater flow experiments were performed to investigate the soil erosion rate, the runoff energy consumption, and the relationship between the soil erosion rate and runoff energy consumption by concentrated flow under combinations of three flow rates (1, 2, and 4 L/min) and three soil conditions (unfrozen, shallow-thawed, and frozen). The individual and combined effects of soil condition, flow rate, and runoff energy consumption on the soil erosion rate were analyzed. For the same flow rate, the shallow-thawed and frozen slope produced mean values of 3.08 and 4.53 times the average soil erosion rates compared to the unfrozen slope, respectively. The number of rills in the unfrozen soil slope were 4, 3, and 2 under the flow rate of 1, 2, and 4 L/min, respectively. The number of rills in the thawed-shallow and frozen soil slope were all 1 under the flow rate of 1, 2, and 4 L/min. The rill displayed disconnected distribution patterns on the unfrozen slope, but a connected rill occurred on the shallow-thawed and frozen slopes. The average rill width on unfrozen, thawed-shallow, and frozen soil slopes increased by 1.87 cm, 4.38 cm, and 1.68 cm as the flow rate increased from 1 L/min to 4 L/min. There was no significant difference in the rill length on the frozen slope under different flow rates (p > 0.05). The runoff energy consumption ranged from unfrozen > shallow-thawed > frozen slopes at the same flow rate. The soil erosion rate had a linear relationship with runoff energy consumption. The spatial distribution of the runoff energy implied that soil erosion was mainly sourced from the unfrozen down slope, shallow-thawed upper slope, and frozen full slope

Has “Grain for Green” threaten food security on the Loess Plateau of China?

There is debating over the question of whether the large-scale ‘Grain for Green’ program on the Loess Plateau of China threatens regional food security. Self-sufficiency index and cropland pressure index were used to assess food security on the Loess Plateau after the implementation of revegetation program. The results showed that the ‘Grain for Green’ program initially had a considerable impact on regional food security, where grain yield fell from 1999 to 2001, resulting in a lower grain self-sufficiency and increased farmland stress. Subsequently, grain yield in this region increased due to the elevated agricultural material input and increased construction of terraces and check dams. The grain self-sufficiency index would have increased to 96.55% if there were improvements to the agricultural conditions, such as fertilization and irrigation, which would have resulted in an increase in the crop yield per unit of 20%. However, the grain self-sufficiency increased to 105.25% via the construction of terraces and check dams. Thus, the government should further expand the ‘Grain for Green’ program in coordination with improvements to the agricultural production conditions and the construction of terraces and check dams on the Loess Plateau