Characteristic Of Herbage Biomass And Ecological Stoichiometry With Abandoned Years In Loess Plateau

Due to natural and human factors, natural vegetation damage, water and soil erosion, ecological environment deterioration had threatened sustainable development of ecological environment and agriculture in loess hilly region. To deal with this science and technology issues, exchanging plantation to nature implemented, herbaceous vegetation communities were widely distributed and play an important role in in soil and water conservation and ecological restoration because of its biological characteristics. Ecological stoichiometry applied to study the growth conditions and limiting condition of herbaceous communities. Variation regularity of species diversity, biomass and annual fine root production analyzed along the abandoned years（1a, 5a, 10 a, 15 a, 20 a, 25 a, 30 a, 35a） in Yanhe basin, based on herb community survey, biomass and root production calculation, and Experimental measurement and calculation for leaf, root and soil stoichiometry.（1） Species diversity improved when abandoned years increased, with community succession, after 15 years abandoned, species diversity reduced and then changed in a periodic and fluctuating way. The average value of community biomass was 765 g·m-2, root biomass was 462 g·m-2, account for 82%, root production was 1071 g?m-2?a-1, reduced with soil depth. The range of annual fine root turnover rates was between 1.10³.77 a-1, average value was 2.01 a-1,the average value in 0²0、20⁵0、50⁸0、80¹00 cm soil depth respectively were 1.20、2.67、5.26、6.51 a-1, increased with soil depth and decreased with abandon time.（2） The range of soil organic content, available nitrogen phosphorus and potassium respectively were 2.86⁴.90 mg·g^-1, 159²03 mg·kg^-1, 15.4¹7.2 mg·kg^-1, 119¹61 mg·kg^-1; average value respectively were 3.93 mg·g^-1, 182 mg·kg^-1, 16.0mg·kg^-1, 134 mg·kg^-1;Coefficient variation were 0.179, 0.082, 0.038, 0.110. Soil organic content increased with abandon time.（3） C, N, P, K content of plant leaves were 439.35, 23.95, 1.60, 14.30mg?g^-1 separately, the C/N, C/P, C/K, N/P of plant leaves were 24.35, 397.23, 41.83, 21.40 separately; the C, N, P, K content of root were 285.16, 5.79, 0.27, 6.07mg?g^-1 separately, the C/N, C/P, C/K, N/P of root were 60.56, 1019.33, 46.55, 21.36 separately; the C, N, P, K content of soil were 2.28, 0.18, 0.28, 4.33mg?g^-1 separately, the C/N, C/P, C/K, N/P of soil were 16.43, 8.40, 0.54, 0.66 separately.（4）Allocation proportion of C, N, P, K in leaf, root and soil exist different variability along the time gradient. The value of leaf divide root, leaf divide and root divide mostly decreased.（5） Response degree of aboveground biomass, root production, root turnover rates, N, P content of leaf and root to addition of nitrogenous and phosphate fertilizer stronger than addition of nitrogenous fertilizer. Along the time gradient, root production increased with abandon years, whether with fertilization or not; response degree of root nitrogen content to fertilization, both of nitrogen and nitrogen + phosphorus increased firstly and decreased later. Soil nitrogen and phosphorus content increased differently with nitrogen and nitrogen + phosphorus fertilization; N/P ratio in soil changed little between fertilization or unfertilized.