US Geological Survey, Southwest Biological Science Center, Moab, UT 84532, USA.
Oecologia. 2010 Oct;164(2):521-31. doi: 10.1007/s00442-010-1649-6. Epub 2010 May 9.
The role of biodiversity in ecosystem function receives substantial attention, yet despite the diversity and functional relevance of microorganisms, relationships between microbial community structure and ecosystem processes remain largely unknown. We used tropical rain forest fertilization plots to directly compare the relative abundance, composition and diversity of free-living nitrogen (N)-fixer communities to in situ leaf litter N fixation rates. N fixation rates varied greatly within the landscape, and 'hotspots' of high N fixation activity were observed in both control and phosphorus (P)-fertilized plots. Compared with zones of average activity, the N fixation 'hotspots' in unfertilized plots were characterized by marked differences in N-fixer community composition and had substantially higher overall diversity. P additions increased the efficiency of N-fixer communities, resulting in elevated rates of fixation per nifH gene. Furthermore, P fertilization increased N fixation rates and N-fixer abundance, eliminated a highly novel group of N-fixers, and increased N-fixer diversity. Yet the relationships between diversity and function were not simple, and coupling rate measurements to indicators of community structure revealed a biological dynamism not apparent from process measurements alone. Taken together, these data suggest that the rain forest litter layer maintains high N fixation rates and unique N-fixing organisms and that, as observed in plant community ecology, structural shifts in N-fixing communities may partially explain significant differences in system-scale N fixation rates.
生物多样性在生态系统功能中的作用受到了广泛关注，但尽管微生物具有多样性和功能相关性，微生物群落结构与生态系统过程之间的关系在很大程度上仍然未知。我们使用热带雨林施肥实验地来直接比较自由生活固氮菌群落的相对丰度、组成和多样性与原地凋落物氮固定速率之间的关系。氮固定速率在景观内差异很大，在对照和磷施肥实验地中都观察到了高氮固定活性的“热点”。与平均活性区相比，未施肥实验地中的氮固定“热点”在固氮菌群落组成上存在明显差异，整体多样性也大大提高。磷的添加增加了固氮菌群落的效率，导致每 nifH 基因固定的速率升高。此外，磷施肥增加了氮固定速率和固氮菌丰度，消除了一群高度新颖的固氮菌，并增加了固氮菌多样性。然而，多样性和功能之间的关系并不简单，将速率测量与群落结构指标相结合，揭示了仅通过过程测量不明显的生物动态。总之，这些数据表明，雨林凋落物层维持着高的氮固定速率和独特的固氮生物，而且，与植物群落生态学中的观察结果一样，固氮菌群落的结构变化可能部分解释了系统尺度氮固定速率的显著差异。
