ABSTRACT
Based on the date from chemical analysis of 10,785 botanical and 1489 edaphic samples, the amount of nutrients accumulated in soil layer (0-60 cm) of sharptooth oak stands, the total biomass of the stands and their contents of accumulated nutrients, and the amount of litter and its contents of accumulated nutrients in southern slope of Mt. Qinling were calculated. To a certain extent, the biomass and the nutrient accumulation of the stands were increased with stand densities and stand ages from thin to high or from young to old, similar to the utilization efficiency of the stands to soil nutrient elements and the trunk canopy ratio. The tree composition of the stands much more influenced nutrient accumulation contents than the biomass. The more broad-leaved tree of species composition, the higher nutrient accumulation contents of stands. In the same region biomass and its nutrient contents of the stands with similar site factors and stand factors had not remarkably difference among different forest-types, but had a difference among various forest types and species composition. In different region, biomass and its nutrient contents of the stands with similar site factors and stand factors had a difference with the sequence of south slope > north slope, middle section > east section or west section. The utilization efficiency of soil nutrient elements by the stands was decreased from lower to higher elevation, from the south to north slope, from middle to east and west section.
Subject(s)
Trees/metabolism , Environment , Soil/analysisABSTRACT
Abstract The modification of nitrogen isotopic signals during particle sedimentation in the sea is of great interest for the use of sedimentary δ(15)N-values as a paleoceanographic tool. The effect of organic matter degradation on such modification was studied by analyzing nitrogen, hydrolyzable amino acids (THAA) and δ(15)N-values in a suit of marine settling particles collected from the Bay of Bengal, Indian Ocean, by using time-series sediment traps, and in underlying sediments. The flux of settling particles showed temporal variations which are related to the monsoons, the major climatic feature of this marine region. During high flux periods settling particles are enriched in nitrogenous material that is less degraded and exhibit higher δ(15)N-values than particles showing characteristics of degradation. At the sediment surface more than 95% of the settling particulate nitrogen is lost and the δ(15)N-values of the residual sedimentary nitrogen are higher than those of settling particles. The observed increase is interpreted to be due to fractionation during degradation of organic matter.
