State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, Yangling, China.
Department of Forest Resources, University of Minnesota, St. Paul, MN, USA.
Glob Chang Biol. 2017 Nov;23(11):4717-4727. doi: 10.1111/gcb.13757. Epub 2017 Jun 2.
Species richness (SR) and functional group richness (FGR) are often confounded in both observational and experimental field studies of biodiversity and ecosystem function. This precludes discernment of their separate influences on ecosystem processes, including nitrogen (N) cycling, and how those influences might be moderated by global change factors. In a 17-year field study of grassland species, we used two full factorial experiments to independently vary SR (one or four species, with FGR = 1) and FGR (1-4 groups, with SR = 4) to assess SR and FGR effects on ecosystem N cycling and its response to elevated carbon dioxide (CO ) and N addition. We hypothesized that increased plant diversity (either SR or FGR) and elevated CO would enhance plant N pools because of greater plant N uptake, but decrease soil N cycling rates because of greater soil carbon inputs and microbial N immobilization. In partial support of these hypotheses, increasing SR or FGR (holding the other constant) enhanced total plant N pools and decreased soil nitrate pools, largely through higher root biomass, and increasing FGR strongly reduced mineralization rates, because of lower root N concentrations. In contrast, increasing SR (holding FGR constant and despite increasing total plant C and N pools) did not alter root N concentrations or net N mineralization rates. Elevated CO had minimal effects on plant and soil N metrics and their responses to plant diversity, whereas enriched N increased plant and soil N pools, but not soil N fluxes. These results show that functional diversity had additional effects on both plant N pools and rates of soil N cycling that were independent of those of species richness.
物种丰富度（SR）和功能群丰富度（FGR）在生物多样性和生态系统功能的观测和实验野外研究中经常混淆。这使得人们无法辨别它们对生态系统过程（包括氮（N）循环）的单独影响，以及这些影响可能如何被全球变化因素所调节。在一项为期 17 年的草原物种野外研究中，我们使用两个完全因子实验来独立地改变 SR（一个或四个物种，FGR=1）和 FGR（1-4 个组，SR=4），以评估 SR 和 FGR 对生态系统 N 循环及其对升高的二氧化碳（CO）和 N 添加的响应的影响。我们假设，增加植物多样性（无论是 SR 还是 FGR）和升高的 CO 都会由于植物 N 吸收的增加而增强植物 N 库，但由于土壤碳输入和微生物 N 固定化的增加而降低土壤 N 循环速率。在一定程度上支持这些假设，增加 SR 或 FGR（保持另一个不变）增强了总植物 N 库，并降低了土壤硝酸盐库，主要是通过更高的根生物量，并且增加 FGR 强烈降低了矿化率，因为根 N 浓度较低。相比之下，增加 SR（保持 FGR 不变，尽管总植物 C 和 N 库增加）并没有改变根 N 浓度或净 N 矿化率。升高的 CO 对植物和土壤 N 指标及其对植物多样性的响应几乎没有影响，而富化的 N 增加了植物和土壤 N 库，但没有增加土壤 N 通量。这些结果表明，功能多样性对植物 N 库和土壤 N 循环速率具有独立于物种丰富度的额外影响。
