The Abundance of Microbial Functional Genes in Grassy Woodlands Is Influenced More by Soil Nutrient Enrichment than by Recent Weed Invasion or Livestock Exclusion
The Abundance of Microbial Functional Genes in Grassy Woodlands Is Influenced More by Soil Nutrient Enrichment than by Recent Weed Invasion or Livestock Exclusion
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DOI：
10.1128/aem.03054-09
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发表时间：
2010-08-01
影响因子：
4.4
通讯作者：
Wakelin, Steven A.
中科院分区：
文献类型：
--
作者：
Lindsay, Elizabeth A.;Colloff, Matthew J.;Wakelin, Steven A.
不同的土壤微生物群落参与氮循环，这些微生物可以受到土地管理措施和杂草入侵的影响。我们调查了20个有牲畜放牧历史的林地，最近从10个地点排除了牲畜。我们调查了土壤养分是否较低时，放牧被排除在外，外来草占主导地位的林下植物。其次，利用实时定量PCR，我们调查了微生物氮功能基因（NFG）丰度是否改变土壤养分富集，牲畜排斥，和外来草入侵。目标基因是chiA（分解-氨化）、nifH（固氮）、nirK和narG（反硝化）以及细菌amoA（硝化）。林地土壤富含磷和氮相比，参考条件网站，但土壤养分不低于牲畜排除。放牧林地土壤总氮与nifH呈负相关，表明地上部的草食动物减少了地下部的固氮能力。外来草占主导地位的林地有较高的硝酸盐，narG，和nirK比那些占主导地位的本地草。我们推测，反硝化潜力的增加是由于土壤硝酸盐的增加，而不是植物成分的变化。总体而言，土壤物理化学解释更多的变化，NFG丰度比牲畜的存在或植物入侵，特别是对于chiA和细菌amoA，所有五个NFG丰度和总氮或硝酸盐之间的显着关系。所有被调查的林地都有人为干扰和营养化的历史，土壤养分水平和NFG的丰度可能与长期的土地管理实践有关。
A diverse soil microbial community is involved in nitrogen cycling, and these microbes can be affected by land management practices and weed invasion. We surveyed 20 woodlands with a history of livestock grazing, with livestock recently excluded from 10 sites. We investigated whether soil nutrients were lower when grazing was excluded and higher when exotic grasses dominated the understory. Second, using quantitative real-time PCR, we investigated whether microbial nitrogen functional gene (NFG) abundance was altered with soil nutrient enrichment, livestock exclusion, and exotic grass invasion. The target genes were chiA (decomposition-ammonification), nifH (nitrogen fixation), nirK and narG (denitrification), and bacterial amoA (nitrification). Woodland soils were enriched in phosphorus and nitrogen compared to reference condition sites, but soil nutrients were not lower following livestock exclusion. Total nitrogen and nifH were negatively correlated in grazed woodlands, suggesting that aboveground herbivory reduces the capacity for belowground nitrogen fixation. Woodlands dominated by exotic grasses had higher levels of nitrate, narG, and nirK than those dominated by native grasses. We hypothesize that the increase in potential for denitrification was due to increases in soil nitrate, rather than changes in plant composition. Overall, soil physicochemistry explained more variation in NFG abundance than livestock presence or plant invasion, particularly for chiA and bacterial amoA, with significant relationships between the abundance of all five NFGs and total nitrogen or nitrate. All woodlands investigated had a history of anthropogenic disturbance and nutrification, and soil nutrient levels and the abundance of NFGs are likely to be related to long-term land management practices.