[C, N, P, K Stoichiometric Characteristic of Leaves, Root and Soil in Different Abandoned Years in Loess Plateau].

The research of plant ecological stoichiometry characteristics, nutrients distribution and their changes is of great significance to explain the response and adaptation of plants to environmental change. Leaves, root and soil from eight different abandoned years in Yanhe River basin were selected to study the content, characteristic ratio and distribution of carbon ( C) , nitrogen (N) , phosphorus (P), potassium (K). The results showed that the C, N, P, K contents of plant leaves were 444.21, 22.34, 1.49, 14.66 mg · g⁻¹ respectively, the C/N, C/P, C/K, N/P ratios of plant leaves were 21.86, 424.72, 39.82, 20.27 respectively; the C, N, P, K contents of root were 285.16, 5.79, 0.27, 6.07 mg · g⁻¹ respectively, the C/N, C/P, C/K, N/P ratios of root were .60. 56, 1019.33, 46.55, 21.36 respectively; the C, N, P, K contents of soil were 2.28, 0.18, 0.28, 4.33 mg · g⁻¹ respectively, the C/N, C/P, C/K, N/P ratios of soil were 16.43, 8.40, 0.54, 0.66 respectively. During the abandoned year of 1-35, C content of leaves increased, N content increased and then declined, P content declined overall, K content declined and then increased. The C/N, C/P, C/K, N/P ratios of plant leaves showed a rising trend overall. The changing pattern of root was different from that of leaves. Along with the increasing rehabilitation age, C and N contents of soil increased, P content changed as arc-sin function, K content changed as parabola, C/N decreased, C/P, C/K, N/P increased. With the increase of Abandoned Years, the ratio of C, P, K contents in leaves and root decreased, the ratio of C, N, P contents in leaves and soil decreased, the ratio of C, N contents in root and soil decreased. Corresponding relationship and its intension between different abandoned years and plant nutrient limit status and its allocation pattern were different.

[Impact of micro-landform on grassland plant comniunity structure and function in the hilly Loess Plateau region, China].

In order to analyze the impact of micro-landform on grassland plant community structure and function, species composition, aboveground and belowground biomass, and annual fine root production at different slope aspects (sunny slope and shady slope) and different slope positions (top, upper, middle and lower) were investigated in the hilly Loess Plateau region. The results showed that grassland communities were mainly composed of plants species belonging to Compositae, Poaceae and Leguminosae. The aboveground and belowground biomass and annual fine root production of community were 164.12 g · m⁻², 1044.87 g · m⁻² and 731.77 g · m⁻² · a⁻¹, respectively. Aboveground biomass, belowground biomass and annual fine root production of community were in the order of shady slope > sunny slope > top slope. In shady slope, the biomass of community under different positions were in the order of lower > middle > upper > top, but it exhibited different orders in the sunny slope compared with shady slope. Fine root mainly concentrated in the 0-20 cm top soil layer and decreased with soil depth. The average turnover time of root was 0.75 a⁻¹ and changed with soil layers and micro-landform.