DISSERTATION RESEARCH: Limits to proteolytic enzyme production and activity in temperate forest soils

温带林木从大气中吸收二氧化碳并将其并入活组织的能力受到土壤中氮(N)有效性的限制。控制土壤中氮素有效性的过程仍然存在很大的不确定性。土壤微生物通过酶的释放将氮从土壤中的有机物质中释放出来。这项研究将集中在一类酶-蛋白水解酶，它将蛋白质分解成氨基酸，可被植物和微生物用作氮的来源。这项研究的目标是测试一种新的蛋白水解酶生产和活性的概念模型。该模型将经济理论应用于蛋白水解酶的活性，因为它检验了这样的假设：(1)树根以碳的形式提供能量，以补贴土壤微生物生产蛋白水解酶，以及(2)微生物对蛋白水解酶生产的投资取决于土壤中N的有效性。这些假说将在整个生长季节得到检验，因此会对温度和蛋白质底物可获得性的季节性变化做出反应。这些分析将在一系列综合的野外和实验室实验中进行。这项研究将促进对调节土壤中N素有效性的过程的基本理解，从而促进森林生产力以及它们隔离大气二氧化碳浓度上升的能力。这是一项潜在的变革性研究，通过详细分析控制蛋白水解酶生产的过程以及这一大类酶对全球变化的反应，包括气温上升和地下植物碳分配的变化。博士生和他的导师将继续针对大波士顿马萨诸塞州地区的K-12学校开展实质性的教育和推广活动，其中许多学校服务于代表性不足的群体。

The ability of temperate forest trees to take up carbon dioxide from the atmosphere and incorporate it in their living tissues is limited by the availability of nitrogen (N) in soils. There remain significant uncertainties in the processes that control N availability in soils. Soil microorganisms release N from organic material in the soil through the release of enzymes. This study will focus on one class of enzymes, proteolytic enzymes, which break down proteins into amino acids that can be used by plants and microbes as a source of N. The goal of this research is to test a new conceptual model for proteolytic enzyme production and activity. This model applies economic theory to proteolytic enzyme activity in that it tests the hypothesis that (1) tree roots provide energy in the form of carbon to subsidize the production of proteolytic enzymes by soil microbes, and (2) microbial investment in the production of proteolytic enzymes depends on the availability of N in the soil. These hypotheses will be tested through the growing season and therefore in response to seasonal variations in temperature and protein-substrate availability. These analyses will be conducted in a series of integrated field and laboratory experiments.This research will advance fundamental understanding of the processes that regulate N availability in the soil and hence the productivity of forests as well as their ability to sequester rising concentrations of atmospheric carbon dioxide. This is potentially transformative research through its detailed analysis of the processes controlling the production of proteolytic enzymes and the response of this large class of enzymes to global changes, including rising temperatures and changes in belowground plant carbon allocation. The doctoral candidate and his advisor will continue their substantial educational and outreach activities targeting K-12 schools in the greater Boston MA area, many of which serve underrepresented groups.