Biomass Components and Environmental Controls in Ningxia Grasslands

Grassland plays an important role in the global carbon cycle and climate regulation. However, there are still large uncertainties in grassland carbon pool and also its role in global carbon cycle due to the lack of measured grassland biomass at regional scale or global scale with a unified survey method, particular for below-ground biomass. The present study, based on a total of 44 grassland sampling plots with 220 quadrats across Ningxia, investigated the characteristics of above-ground biomass (AGB), below-ground biomass (BGB), litter biomass (LB), total biomass (TB) and root:shoot ratios (R:S) for six predominantly grassland types, and their relationships with climatic factors. AGB, BGB, LB and TB varied markedly across different grassland types, the median value ranging from 28.2-692.6 g m(-2) for AGB, 130.4-2036.6 g m(-2) for BGB, 9.2-82.3 g m(-2) for LB, and 168.0-2681.3 g m(-2) for TB. R:S showed less variation with median values from 3.2 to 5.3 (excluding marshy meadow). The different grassland types showed similar patterns of biomass allocation, with more than 70% BOB for all types. There is evidence of strong positive effects associated with mean annual precipitation (MAP) and negative effects associated with mean annual temperature (MAT) on AGB, BGB, and LB, although both factors have the opposite effect on R:S.</p

Carbon Storage Dynamics in Alfalfa (Medicago sativa) Fields in the Hilly-Gully Region of the Loess Plateau, China

Alfalfa (Medicago sativa) has been widely employed in the dryland region of the Loess Plateau, China to improve soil and water conservation and to develop livestock production. Our objective was to study the dynamics of plant and soil organic carbon (SOC) pools following the conversion of sloping farmland to alfalfa fields over a period of 30 years. The succession gradient is composed of seven differently aged alfalfa fields (0, 5, 9, 13, 16, 23, 30 years). The results show that soil C storage (0-100cm) dynamics were consistent with belowground biomass storage with increased planting years, but C storage always increased with the number of planting years in the 0-5cm soil layer. Planted perennial alfalfa resulted in a decline in soil C storage in the 0-100cm soil depth in the early period (nine years). During the late succession stage of alfalfa (13 years) soil C storage tends to recover, and after 16 years, storage values again dropped. However, it had recovered by 30 years at which time alfalfa productivity was very low. Vegetation C storage was mainly decided by the belowground biomass and ecosystem C storage dynamics was consistent with soil C storage. Vegetation biomass, root/shoot ratio, SOC, soil total nitrogen, and total phosphorus were the main factors affecting C storage in the entire alfalfa field ecosystem. The results suggest that C storage in vegetation is directly related to plant productivity, C storage in the soil throughout the entire alfalfa field ecosystem was not only related to plant productivity, but also to SOC and soil nutrients.</p

Soil organic carbon storage capacity positively related to forest succession on the Loess Plateau, China

Land-use change resulting from natural restoration probably enhances the carbon sequestration capacity of terrestrial ecosystems. To explore those factors which foster changes in the soil carbon pool in forest restoration, a study comparing soil organic carbon at different vegetation succession stages along a 150-year chronosequence was conducted in the Ziwuling forest region located in the central part of the Loess Plateau, China. It showed that in long-term (-150 yr) secondary forest succession the soil organic carbon storage (Cs), soil organic carbon (SOC), total nitrogen (TN), and C/N ratio all increased rapidly and tended to be at their highest at roughly the 50-year restoration mark. From this point onward the values gradually stabilized indicating that the SOC and the TN accumulated mainly in the early restoration stages. The Cs was significantly and positively correlated with the SOC, the TN, and the C/N ratio (P &lt; 0.01). The Cs in the soil was higher in the upper rather than the lower soil layers. However, the increments of the Cs mainly changed in the lower soil layers. Soil water storage was not the key factor influencing the Cs. The results suggested that changes to the Cs were the result of the accumulation of the SOC and the TN during forest succession and this capacity has shown to be positively related to forest succession on the Loess Plateau, China.</p