Zhang Tonghui

Biomass allocation response of species with different life history strategies to nitrogen and water addition in sandy grassland in Inner Mongolia

Biomass allocation response of species with different life history strategies to nitrogen and water addition in sandy grassland in Inner Mongolia MAO Wei, LI Yu-Lin, CUI Duo, ZHAO Xue-Yong, ZHANG Tong-Hui, and LI Yu-Qiang Naiman Desertification Research Station, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China; and Center for Earth System Science, Tsinghua University, Beijing 100084, China

Comparison of soil physico-chemical properties under different land-use and cover types in northeastern China's Horqin Sandy Land

The Horqin Sandy Land of northeastern China was originally a grassland with plenty of water and lush vegetation dominated by palatable grass species along with sparsely scattered woody species. However, it has experienced severe desertification in recent decades due to its fragile ecology together with inappropriate human activities. Currently, the landscape of the Horqin Sandy Land is dominated by irrigated croplands and sand dunes with different degrees of vegetation cover, as the region has become the most important part of the semiarid agro-pastoral ecotone of northern China. In this study, we compared soil physical and chemical properties under different land-use and cover types (irrigated cropland, rainfed cropland, sandy grassland, fixed dunes, and mobile dunes) . We found that soil particle size distribution; organic C, total N, and total mineral element, microelement, and available microelement and nutrient contents; pH; CEC; and bulk density differed significantly among the land-use and cover types. In general, soil quality was highest in the cropland, intermediate in the sandy grassland, and lowest in the dunes. The most important soil quality attribute, soil organic carbon (SOC) storage, decreased in the following order: irrigated cropland (5, 699 g/m 2 ) ＞ sandy grassland (3, 390 g/m 2 ) ＞ rainfed cropland (2, 411 g/m 2 ) ＞ fixed dunes (821 g/m 2 ) ＞ mobile dunes (463 g/m 2 ) . SOC was significantly positively correlated with a large proportion of the other soil physico-chemical parameters. Our results suggest that the key issue in restoration of the degraded soils will be to increase SOC storage, which would also create a high potential for sequestering soil C in desertified areas of the Horqin Sandy Land.

Seasonal changes in the relationship between species richness and community biomass in grassland under grazing and exclosure, Horqin Sandy Land, northern China

This study carried out an analysis of seasonal changes in relationships between vegetation cover,plant density,species richness and above-ground biomass in grassland under grazing and exclosure in Horqin Sandy Land.Results showed that in grassland being grazed and fenced,vegetation cover,richness and biomass were lower in April than those in August,while plant density showed a reverse trend.Vegetation cover over the season was higher in fenced grassland than that in grazed grassland;biomass in June and August was higher in fenced grassland than that in grazed grassland,while plant density in April and June and was lower in fenced grassland than that in grazed grassland.In fenced grassland,the relationship between species richness and biomass was significantly negative in August(p0.01);in grazed grassland,the relationship between plant density and biomass was significantly positive in the April(p0.01) and was significantly negative in August(p0.01).The relationship between plant density and total biomass for dominant species varied with seasonal changes under grazing and exclosure.In grassland under grazing,the relationship between plant density of Cleistogenes squarrosa and biomass was significantly positive in April(p0.01) and was significantly negative in August(p0.01);the relationship between plant density of Artemisia scoparia or Setaria viridis and biomass was significantly negative in August(p0.01);the relationship between plant density of Salsola collina and biomass was significantly positive in April and June(p0.01).In fenced grassland,the relationship between plant density of Lesredeza davurica or Salsola collina and biomass was significantly positive in August(p0.01).These results suggest that long-term grazing,seasonal changes and their interaction significantly influence vegetation cover,plant density and biomass in grassland(p0.05).Long-term grazing also affects the seasonal changes of plant density and biomass of dominant species,which further affects the seasonal relationship between plant density and biomass in grassland.Species competition in fenced grassland results in the seasonal changes of relationship between species richness and biomass.

Closure properties of mixture degradation model

Recorded lifetime data, which give the information about the time-to-failure of system units, play a very important role in assessing the system reliability. In this paper, we obtained some closure properties of IFR, IFRA and NBU life distribution classes based on mixture degradation model. In addition, we proved the closure properties of some stochastic orders based on this model.