Latitude gradient changes on herbaceous biomass and leaf N and P stoichiometry characteristics in Loess Plateau

【Objective】 Plant biomass can give an index to the trends of plant growth conditions and the change of natural environment, stoichiometry can reflect the plant nutrient content and using strategy. Our objective was to examine changes of herbaceous biomass and leaf N and P stoichiometry characteristics along latitudinal gradient in Loess Plateau, and 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. 【Methods】 We investigated the herbaceous biomass and leaf N and P contents, and compared the herbaceous biomass amounts of different vegetation zones along the latitudinal gradient in Loess Plateau in Shanxi Province, including Fu County, Ganquan County, Ansai County, Jingbian County and Hengshan County and Yuyang District. One-way analysis and regression analysis were conducted to find main constraints of plant nutrition elements and to examine overall patterns of response of the herbaceous biomass, leaf N and P stoichiometry to latitude. 【Results】 Across the 35.95-38.36N latitude gradient, the range of herbaceous biomass amounts of different vegetation zones in Loess Plateau is from 9.10 to 27.59 g/m2, and the arithmetic mean is 19.45 g/m2 and the coefficient of variation is 30.3%. The herbaceous biomass amounts in the four different vegetation zones are in order of grass zone ＞forest-grass zone ＞forest zone ＞grass-desert zone, and with the increase of latitude, the herbaceous biomass amounts are first increased and then decreased. The leaf N and P stoichiometry characteristics are primarily from 18.08 to 33.17 mg/g for N, from 1.07 to 1.7 mg/g for P and from 15.4-21.6 for the N/P ratio, the arithmetic means are 25.79 mg/g, 1.37 mg/g and 18.71, separately, and the variation coefficients are 17.1%, 13.9% and 9.94% in which the leaf N content is the greatest and the N/P ratio is the lowest. The leaf N and P are closely correlated, and leaf N and P significantly increases with latitude increasing, but the N/P ratios is not. The leaf N content in Loess Plateau is higher than the global average level and the leaf P content in Loess Plateau is lower than the global average level, consequently leading to a higher N/P ratio in Loess Plateau. 【Conclusions】 There is a certain correlation between the herbaceous biomass and latitude, however, that is not a simple linear correlation, and the change of herbaceous biomass is also related with species composition of the vegetation zones. There are obvious correlations between leaf N and P and latitude, while the relationship between the N/P ratio and latitude is not significant. These results demonstrate that the plants are under P limitation in Loess Plateau.