Bioscience Division, Los Alamos National Laboratory Los Alamos, NM, USA.
Front Microbiol. 2012 Oct 11;3:358. doi: 10.3389/fmicb.2012.00358. eCollection 2012.
Biological soil crusts (biocrusts), which supply significant amounts of fixed nitrogen into terrestrial ecosystems worldwide (∼33 Tg y(-1)), are likely to respond to changes in temperature and precipitation associated with climate change. Using nifH gene-based surveys, we explored variation in the diazotrophic community of biocrusts of the Colorado Plateau, USA in response to season (autumn vs. spring), as well as field manipulations that increased the frequency of small volume precipitation events and year-round soil temperature. Abundance of nifH genes in biocrusts ranged from 3 × 10(6) to 1 × 10(8) g(-1) soil, and nifH from heterocystous cyanobacteria closely related to Scytonema hyalinum, Spirirestis rafaelensis, and Nostoc commune comprised >98% of the total. Although there was no apparent seasonal effect on total nifH gene abundance in the biocrusts, T-RFLP analysis revealed a strong seasonal pattern in nifH composition. SpirirestisnifH abundance was estimated to oscillate 1 to >2 orders of magnitude between autumn (low) and spring (high). A year-round increase of soil temperature (2-3°C) had little effect on the diazotroph community structure over 2 years. Altered summer precipitation had little impact on diazotroph community structure over the first 1.5 years of the study, when natural background patterns across years and seasons superseded any treatment effects. However, after the second summer of treatments, nifH abundance was 2.6-fold lower in biocrusts receiving altered precipitation. Heterocystous cyanobacteria were apparently more resilient to altered precipitation than other cyanobacteria. The results demonstrate that diazotrophic community composition of biocrusts in this semi-arid grassland undergoes strong seasonal shifts and that the abundance of its dominant members decreased in response to more frequent, small volume precipitation events.
生物土壤结皮（biocrusts）在全球范围内为陆地生态系统提供了大量的固定氮（约 33Tg y(-1)），它们可能会对气候变化导致的温度和降水变化做出响应。本研究利用 nifH 基因调查，探究了美国科罗拉多高原生物土壤结皮的固氮生物群落变化，分别为季节变化（秋季与春季）以及田间处理（增加小体积降水事件频率和全年土壤温度）。生物土壤结皮中 nifH 基因的丰度范围为 3×10(6)至 1×10(8) g(-1)土壤，其中与 Scytonema hyalinum、Spirirestis rafaelensis 和 Nostoc commune 密切相关的异形胞蓝细菌 nifH 占总量的>98%。尽管生物土壤结皮中总 nifH 基因丰度没有明显的季节性变化，但 T-RFLP 分析显示 nifH 组成具有很强的季节性模式。SpirirestisnifH 的丰度估计在秋季（低）和春季（高）之间波动 1 到>2 个数量级。经过 2 年的研究，全年土壤温度升高（2-3°C）对固氮生物群落结构几乎没有影响。在研究的头 1.5 年中，改变夏季降水对固氮生物群落结构的影响较小，当时多年和季节性的自然背景模式超过了任何处理效应。然而，在处理的第二个夏季后，接受改变降水的生物土壤结皮中的 nifH 丰度降低了 2.6 倍。异形胞蓝细菌显然比其他蓝细菌更能耐受改变的降水。结果表明，这种半干旱草原生物土壤结皮的固氮生物群落组成经历了强烈的季节性变化，其主要成员的丰度在应对更频繁、小体积降水事件时会减少。
