Plant tissue nitrogen: Traits: Biomass Allocation Trends in Old Field in Relation to Gradients of Succesional Age and Soil Nitrogen

The objective of this experiment is to assess biomass allocation trends in the field in relation to gradients of successional age and soil nitrogen. This objective was approached in three ways: A) 37 old fields of various ages were surveyed for above and below ground biomass, soil N, and light penetration. Five strips (1m x 10cm) were clipped in each field for above ground biomass (sorted to grasses and forbs; then sorted to leaf and stem), and 3 root cores (down to 30cm) taken per strip (rinsed, dried and weighed). Two light measurements and one pooled (3 cores) soil N sample (for available and total N) were taken per strip. B) 35 abundant species of known successional status were harvested from the field (usually 15 individuals per species), including roots contained in a core 20x30cm, dried, sorted to stem, leaf, and root, and weighed. These data can be combined with the old field survey results (E014) to estimate successional trends in allocation. C) Root cores will be taken from microplots in fields A, B, C, and D, all treatments. This will be an estimate of root biomass to be combined with the above ground samples (E001) to assess root-shoot trends in response to manipulation of soil N in fields of different age.本实验旨在评估野外生物量分配（biomass allocation）格局与演替年龄（successional age）梯度及土壤氮素（soil nitrogen）的相关性。本研究目标通过三种途径实现： A）对37个不同发育年限的撂荒地（old fields）开展调查，测定其地上生物量（above ground biomass）、地下生物量（below ground biomass）、土壤氮含量以及光照穿透率（light penetration）。每个撂荒地内设置5条样带（1m×10cm），采集地上生物量样品（先划分为草本与阔叶杂草，再进一步分为叶片与茎秆组分）；每条样带采集3个深度达30cm的根芯（root cores），经冲洗、烘干后称重。每条样带进行2次光照测定，并采集1份由3个根芯土壤混合而成的土样，用于分析有效氮（available N）与全氮（total N）含量。 B）从野外采集35个已知演替地位的常见物种（每个物种通常采集15个个体），采用20×30cm的根芯采集其根系，样品经烘干后划分为茎、叶、根组分并称重。该数据集可与撂荒地调查结果（E014）结合，以估算生物量分配的演替趋势。 C）将从地块A、B、C、D的微样地中采集根芯，覆盖所有处理组。本次采样所得数据将用于估算根系生物量，并与地上生物量样品（E001）结合，以评估不同演替年龄地块在土壤氮素调控下的地下-地上生物量分配趋势。