Nitrate Assimilation under Elevated CO2 and Leaf N2O Emissions

PI发现，高二氧化碳水平干扰了小麦植株利用硝酸盐肥料作为氮源的能力。如果这是一种普遍现象，它将为其他几个尚未解决的问题提供机制上的解释，包括(A)为什么高二氧化碳水平对光合作用的刺激随着时间的推移而下降，(B)为什么高二氧化碳水平抑制植物呼吸，以及(C)为什么氮的可用性决定生态系统对二氧化碳浓度增加的反应。PIS还发现，小麦叶片排放大量一氧化二氮，这是一种温室气体，其影响大约是二氧化碳的250倍，有助于高层大气中臭氧的降解。采购经理人指数的初步结果显示，叶片一氧化二氮的排放量可能占全球一氧化二氮排放量的12%。拟议的研究将调查一系列植物类型的二氧化碳抑制硝酸盐同化和叶片一氧化二氮排放，以确定它们是否普遍存在。它将评估这种抑制背后的一些可能的机制。它将评估几种可能的一氧化二氮排放来源的重要性，包括地上部硝酸盐同化、根部硝酸盐同化和根部周围微生物的产生。它将通过与正在进行的一项研究合作，在实地评估这些现象，该研究正在检查墨西哥雅基河谷麦田的土壤一氧化二氮排放。这项研究的结果将是深远的，为植物对二氧化碳升高的反应以及植物排放温室气体的机制提供基本信息。

The PIs have found that high carbon dioxide levels interfere with the ability of wheat plants to use nitrate fertilizer as a nitrogen source. Were this a general phenomenon, it would offer a mechanistic explanation for several other unresolved issues including (a) why the stimulation of photosynthesis by high carbon dioxide levels declines over time, (b) why high carbon dioxide levels inhibit plant respiration, and (c) why nitrogen availability determines ecosystem response to carbon dioxide enrichment. The PIs have also discovered that wheat leaves emit significant amounts of nitrous oxide, a greenhouse gas that has an effect approximately 250 times greater than carbon dioxide and that contributes to ozone degradation in the upper atmosphere. The PIs preliminary results indicate that leaf nitrous oxide emissions could account for as much as 12% of the nitrous oxide generated worldwide.The proposed research will survey a range of plant types for carbon dioxide inhibition of nitrate assimilation and leaf nitrous oxide emissions to determine whether they are common occurrences. It will evaluate some of the possible mechanisms behind this inhibition. It will assess the importance of several possible sources of nitrous oxide emissions including shoot nitrate assimilation, root nitrate assimilation, and production by microbes around the root. It will evaluate these phenomena in the field through a collaboration with an ongoing study that is examining soil nitrous oxide emissions from wheat fields in the Yaqui Valley of Mexico. The results of this research will be far-reaching, providing fundamental information on the mechanisms responsible for plant responses to elevated carbon dioxide as well as for greenhouse gas emissions from plants.