Molybdenum threshold for ecosystem scale alternative vanadium nitrogenase activity in boreal forests
Molybdenum threshold for ecosystem scale alternative vanadium nitrogenase activity in boreal forests
复制标题
DOI：
10.1073/pnas.1913314116
复制
发表时间：
2019-12-03
影响因子：
11.1
通讯作者：
Zhang, Xinning
中科院分区：
文献类型：
--
作者：
Darnajoux, Romain;Magain, Nicolas;Zhang, Xinning
生物固氮（BNF）的微生物与隐花植物覆盖，如cyanolichens和brabrites，是一个主要来源的固定氮在原始，高纬度生态系统。在陆地上，钼（Mo）的低可用性已被证明是限制生物固氮的最常见形式的固氮酶（Nase），它需要钼在其活性位点。钒（V）和铁只有Nases已被认为是可行的替代品，以对抗钼限制生物固氮，然而，现场数据支持这一长期存在的假设一直缺乏。在这里，我们阐明钒固氮酶（V-Nase）的贡献，生物固氮蓝藻横跨600公里的纬度样带在北美东部的北方森林。检测到广泛的V-Nase活性（类似于总生物固氮率的15-50%），大多数活性出现在样带的北方部分。我们观察到在20周的生长季节的V-Nase贡献增加了3倍。通过包括V-Nase对生物固氮的贡献，蓝地衣新氮输入的估计增加了30%。我们发现，在V为基础的生物固氮的变异性是密切相关的钼的可用性，我们确定了钼阈值类似于250 ng.g（地衣）（-1）的V为基础的生物固氮的发病。我们的研究结果提供了令人信服的生态系统规模的证据使用的V-Nase作为替代酶，有助于生物固氮时，钼是有限的。鉴于广泛的发现陆地钼限制，包括富碳环寒带，全球变化最迅速，额外的考虑V为基础的生物固氮需要在实验和模拟研究的陆地地球化学。
Biological nitrogen fixation (BNF) by microorganisms associated with cryptogamic covers, such as cyanolichens and bryophytes, is a primary source of fixed nitrogen in pristine, high-latitude ecosystems. On land, low molybdenum (Mo) availability has been shown to limit BNF by the most common form of nitrogenase (Nase), which requires Mo in its active site. Vanadium (V) and iron-only Nases have been suggested as viable alternatives to countering Mo limitation of BNF; however, field data supporting this long-standing hypothesis have been lacking. Here, we elucidate the contribution of vanadium nitrogenase (V-Nase) to BNF by cyanolichens across a 600-km latitudinal transect in eastern boreal forests of North America. Widespread V-Nase activity was detected (similar to 15-50% of total BNF rates), with most of the activity found in the northern part of the transect. We observed a 3-fold increase of V-Nase contribution during the 20-wk growing season. By including the contribution of V-Nase to BNF, estimates of new N input by cyanolichens increase by up to 30%. We find that variability in V-based BNF is strongly related to Mo availability, and we identify a Mo threshold of similar to 250 ng.g(lichen)(-1) for the onset of V-based BNF. Our results provide compelling ecosystem-scale evidence for the use of the V-Nase as a surrogate enzyme that contributes to BNF when Mo is limiting. Given widespread findings of terrestrial Mo limitation, including the carbon-rich circumboreal belt where global change is most rapid, additional consideration of V-based BNF is required in experimental and modeling studies of terrestrial biogeochemistry.