Herbaceous Community Biomass And Leaf Stoichiometry Characteristics In Loess Plateau

Plant biomass can give an index to the trends of plant growth conditions and the change of natural environment, plant leaf stoichiometry can reflect the plant nutrient content and using strategy. We regarded the herbaceous biomass and plant leaf stoichiometry as the research objects, and investigated the herbaceous community above-ground and below-ground biomass, leaf and soil C, N and P content in Loess Plateau in Shaanxi Province, including Ganquan County, Ansai County, Yanan County, Jingbian County and Hengshan County. One-way analysis and regression analysis were conducted to examine the effects of different environmental factors on herbaceous community above-ground and below-ground biomass and their ratio, leaf C, N and P stoichiometry characteristics in Loess Plateau, in order to provide references for the prediction of plant growth and development prospect in Loess Plateau, soil nutrient status of the ecosystem and constraints of plant nutrition elements. The results showed that(1)The Shannon index, Margalef index and Pielou index, these three indexes of different vegetation zones were different: forest zone had the maximum value, however, grass-desert had the minimum value, meanwhile, forest-grass zone and grass zone changed alternately. The three indexes of herbaceous species diversity showed a single-peak distribution pattern.(2)Across the 35.95°~38.36°N latitude gradient, the range of herbaceousa community aboveground、belowground、below/aboveground and total biomass amounts in Loess Plateau are from 54.6 to 204.32 g/m2, from 78.88 to 829.64 g/m2, from 0.93 to 4.49 and from 133.48 to 1015.72 g/m2; the coefficient of variation are 30.3%, 49%, 37.8% and 40.2%。There was not a simple linear relationship between the herbaceous community aboveground, belowground and total biomass and the latitude, but, with the increasing latitude, these three biomass increased firstly and then decreased. For the ratio of below/ aboveground biomass, with the latitudinal changing there appeared two high peak: the transition from forest zone to forest-grass zone and from grass zone to grass-desert zone, the two turning point were 36.55° N and 37.03° N. The leaf C, N and P stoichiometry characteristics are primarily from 336.95 to 477.38 mg/g for C, from 18.08 to 33.17 mg/g for N, from 1.07 to 1.7 mg/g for P, the arithmetic means are 442.9 mg/g, 25.79 mg/g, 1.37 mg/g, separately, and the variation coefficients are 11.9%,17.4% and 13.3%. There were obvious correlation between leaf C, N, P and the latitude, leaf C, C/N ratio and C/P ratio significantly decreased with the increasing latitude, while leaf N and P significantly increased with the increasing latitude. The relationship between N/P ratio and latitude was not significant.(3)There was a similar relationship between the herbaceous community aboveground, belowground and total biomass and the mean annual temperature(MAT) and the mean annual precipitation(MAP): with the increasing of MAT and MAP, these three biomass showed a trend of decrease firstly and then increase. While the below/ aboveground biomass almost showed the increasing trend all the time, but the regression relationship with MAT and MAP was not significant. There was also a similar relationship between the leaf C, N, P and MAT and MAP, the leaf C, C/N ratio and C/P ratio significantly increased with the increasing of MAT and MAP, in contrast, the leaf N and P decreased, the relationship between N/P ratio and MAT and MAP was not significant.(4)There were significant correlation between different soil layers of C, N, P content, C/N, C/P ratio and the herbaceous community plant aboveground, belowground, below/ aboveground and total biomass except N/P ratio. Leaf C, C/N and C/P ratios were correlated to soil organic C, soil total N and soil total P in all soil layers, leaf N and P were correlated to soil organic C and soil total N, while leaf N/P ratio was not correlated to soil organic C, soil total N and soil total P.