Griffith Jocelyn C, Lee William G, Orlovich David A, Summerfield Tina C
Department of Botany, University of Otago, Dunedin, New Zealand.
Landcare Research, Dunedin, New Zealand.
PLoS One. 2017 Jun 28;12(6):e0179652. doi: 10.1371/journal.pone.0179652. eCollection 2017.
The cultivation of grasslands can modify both bacterial community structure and impact on nutrient cycling as well as the productivity and diversity of plant communities. In this study, two pristine New Zealand grassland sites dominated by indigenous tall tussocks (Chionochloa pallens or C. teretifolia) were examined to investigate the extent and predictability of variation of the bacterial community. The contribution of free-living bacteria to biological nitrogen fixation is predicted to be ecologically significant in these soils; therefore, the diazotrophic community was also examined. The C. teretifolia site had N-poor and poorly-drained peaty soils, and the C. pallens had N-rich and well-drained fertile soils. These soils also differ in the proportion of organic carbon (C), Olsen phosphorus (P) and soil pH. The nutrient-rich soils showed increased relative abundances of some copiotrophic bacterial taxa (including members of the Proteobacteria, Bacteroidetes and Firmicutes phyla). Other copiotrophs, Actinobacteria and the oliogotrophic Acidobacteria showed increased relative abundance in nutrient-poor soils. Greater diversity based on 16S rRNA gene sequences and the Tax4Fun prediction of enhanced spore formation associated with nutrient-rich soils could indicate increased resilience of the bacterial community. The two sites had distinct diazotrophic communities with higher diversity in C. teretifolia soils that had less available nitrate and ammonium, potentially indicating increased resilience of the diazotroph community at this site. The C. teretifolia soils had more 16S rRNA gene and nifH copies per g soil than the nutrient rich site. However, the proportion of the bacterial community that was diazotrophic was similar in the two soils. We suggest that edaphic and vegetation factors are contributing to major differences in the composition and diversity of total bacterial and diazotrophic communities at these sites. We predict the differences in the communities at the two sites will result in different responses to environmental change.
草地开垦会改变细菌群落结构，影响养分循环以及植物群落的生产力和多样性。在本研究中，对两个以本土高草丛（苍白绒毛草或圆柱绒毛草）为主的原始新西兰草地进行了调查，以研究细菌群落变异的程度和可预测性。预计在这些土壤中，自由生活细菌对生物固氮的贡献具有重要生态意义；因此，还对固氮群落进行了研究。圆柱绒毛草生长的地点土壤氮含量低且排水不良，为泥炭土，而苍白绒毛草生长的地点土壤氮含量高且排水良好，为肥沃土壤。这些土壤在有机碳（C）、 Olsen 磷（P）比例和土壤pH值方面也存在差异。养分丰富的土壤中，一些富营养型细菌类群（包括变形菌门、拟杆菌门和厚壁菌门的成员）的相对丰度增加。其他富营养菌、放线菌和贫营养嗜酸菌在养分贫瘠的土壤中相对丰度增加。基于16S rRNA基因序列的更高多样性以及与养分丰富土壤相关的孢子形成增强的Tax4Fun预测可能表明细菌群落的恢复力增强。两个地点具有不同的固氮群落，圆柱绒毛草生长的土壤中固氮群落多样性更高，该土壤中可利用的硝酸盐和铵较少，这可能表明该地点固氮菌群落的恢复力增强。每克圆柱绒毛草生长的土壤中16S rRNA基因和nifH拷贝数比养分丰富的地点更多。然而，两个土壤中固氮细菌群落的比例相似。我们认为土壤和植被因素导致了这些地点总细菌和固氮细菌群落组成和多样性的主要差异。我们预测两个地点群落的差异将导致对环境变化的不同反应。
