NSF Postdoctoral Fellowship in Biology FY 2012

干燥土壤中的气态氮通量：存活的微生物控制氮排放吗？土壤气态氮（N）的排放通常不考虑在生态系统的N收支，大概是因为在梅西奇网站，水文N损失平衡N输入。 然而，在旱地环境中，大量的N通过气体途径输出，但控制通量的机制知之甚少。 特别是，微生物控制干燥土壤中的氮排放吗？ 土壤复湿是否在增强非生物过程的同时阻碍了微生物活动？ 奇怪的是，生物控制的N排放似乎在土壤干燥过程中加强，并在土壤复湿过程中变得不那么重要。 由于旱地地区约占陆地面积的1/3，占土壤NO排放量的25%，了解什么过程控制氮损失是至关重要的营养收支和模拟氮污染。 本研究旨在通过评估两种广泛持有的范式来改变对N循环的理解：1）在干旱土壤中，氮素的生物循环并不重要，2）氮素的排放在氮素的年收支中并不重要。培训的目的是拓宽土壤碳氮循环的知识，学习涡度相关的应用，更广泛的影响包括土地管理应用，以确定通过植被类型转换和野火发生率增加受氮污染影响的生态系统中的氮临界负荷。 这项研究还将用于促进代表性不足的群体参与科学和数学，通过PUENTE计划，塞奇威克保护区的“户外教室”和Scienceline（一个与K-12学生合作的科学家网站）提供课程计划。

Gaseous nitrogen fluxes in dry soils: are surviving microbes controlling nitrogen emissions?Soil gaseous nitrogen (N) emissions are not typically considered in ecosystem N budgets, presumably because in mesic sites, hydrologic N losses balance N inputs. However, in dryland environments, significant amounts of N are exported through gaseous pathways, yet the mechanisms controlling fluxes are poorly understood. In particular, are microbes controlling N emissions in dry soil? Does soil rewetting hinder microbial activity while enhancing abiotic processes? Paradoxically, biological control of N emissions appears to intensify during soil drying and becomes less important during soil rewetting. Because dryland regions comprise about 1/3 of the land surface and account for 25% of soil NO emissions, understanding what processes control N losses is critical for developing nutrient budgets and modeling N pollution. This research seeks to transform understanding of N cycling by evaluating two widely held paradigms: 1) that in dry soil, biological cycling of N is unimportant and 2) that N emissions are not significant in annual N budgets.The training objectives are to broaden knowledge in soil C and N cycling, learn the application of eddy covariance, develop a method for measuring the isotopic composition of oxygen in NO. Broader impacts include land management applications to establish N critical loads in ecosystems impacted by N pollution through vegetation type conversions and increased incidence of wildfires. This research will also be used to foster participation of underrepresented groups in science and mathematics by delivering lesson plans through the PUENTE program, the "Outdoor Classroom" at Sedgwick Reserve, and Scienceline, a website that partners scientists with K-12 students.