RUI: Microbial Assimilation of Nitrate in Disturbed and Undisturbed Forest Ecosystems

彻底了解控制硝酸盐池大小的因素对于最大限度地减少氮损失、地下水硝酸盐污染和微量氮气产生等不良过程至关重要。利用最近开发的15N同位素稀释技术，可以测量相对未受干扰土壤中的总N转化速率，这些研究人员提供了证据，证明硝酸盐的微生物同化是三个森林生态系统中无机N循环的重要组成部分。尽管在森林土壤中，硝酸盐的微生物同化通常被认为是微不足道的，但他们认为，从这项研究和其他研究中有足够的证据表明，硝酸盐的微生物同化可能是硝酸盐池大小的主要调节因素。该项目将检查沿两个样带（俄勒冈州和新墨西哥州）的森林地点，并确定碳和氮供应的异质性对同化率的影响；温度和湿度对无机氮总同化速率和产量的影响；负责硝酸盐同化的特定微生物种群；以及植物作为碳源和氮竞争对手的角色。这项研究将为建立基于过程的模型提供必要的信息，这些模型预测了干扰对N循环的影响，并预测了在全球气候变化期间，随着生态系统中C和N输入的变化，潜在的反馈回路将会发展。

A thorough understanding of the factors controlling nitrate pool sizes is critical to minimizing such undesirable processes as nitrogen loss, nitrate pollution of ground water, and trace N-gas production. Using recently developed 15N isotopic dilution techniques that allow measurement of gross N-transformation rates in relatively undisturbed soil, these investigators have provided evidence that microbial assimilation of nitrate is a significant component in the inorganic N cycle of three forest ecosystems. Although microbial assimilation of nitrate has generally been discounted as being insignificant in forest soils, they believe that there is sufficient evidence from this and other studies to indicate that microbial assimilation of nitrate may be a primary regulator of nitrate pool sizes. This project will examine forest sites along two transects (in Oregon and New Mexico) and determine the effect of heterogeneity in carbon and nitrogen supply on assimilation rates; the influence of temperature and moisture on gross rates of inorganic N assimilation and production; the specific microbial populations responsible for nitrate assimilation; and the role of plants as sources of carbon versus competitors for nitrogen. This study will provide information that is necessary for the formulation of process-based models predicting the impacts of disturbance on N cycling as well predicting potential feedback loops that will develop as C and N inputs to ecosystems shift during global climate change.