Bustamante Mauricio, Verdejo Valentina, Zúñiga Catalina, Espinosa Fernanda, Orlando Julieta, Carú Margarita
Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile Santiago, Chile.
Front Microbiol. 2012 Aug 8;3:282. doi: 10.3389/fmicb.2012.00282. eCollection 2012.
Water availability is the main limiting factor in arid soils; however, few studies have examined the effects of drying and rewetting on nitrifiers from these environments. The effect of water availability on the diversity of ammonia-oxidizing bacteria (AOB) and archaea (AOA) from a semiarid soil of the Chilean sclerophyllous matorral was determined by microcosm assays. The addition of water every 14 days to reach 60% of the WHC significantly increased nitrate content in rewetted soil microcosms (p < 0.001). This stimulation of net nitrification by water addition was inhibited by acetylene addition at 100 Pa. The composition of AOA and AOB assemblages from the soils microcosms was determined by clone sequencing of amoA genes (A-amoA and B-amoA, respectively), and the 16S rRNA genes specific for β-proteobacteria (beta-amo). Sequencing of beta-amo genes has revealed representatives of Nitrosomonas and Nitrosospira while B-amoA clones consisted only of Nitrosospira sequences. Furthermore, all clones from the archaeal amoA gene library (A-amoA) were related to "mesophilic Crenarchaeota" sequences (actually, reclassified as the phylum Thaumarchaeota). The effect of water availability on both microbial assemblages structure was determined by T-RFLP profiles using the genetic markers amoA for archaea, and beta-amo for bacteria. While AOA showed fluctuations in some T-RFs, AOB structure remained unchanged by water pulses. The relative abundance of AOA and AOB was estimated by the Most Probable Number coupled to Polymerase Chain Reaction (MPN-PCR) assay. AOB was the predominant guild in this soil and higher soil water content did not affect their abundance, in contrast to AOA, which slightly increased under these conditions. Therefore, these results suggest that water addition to these semiarid soil microcosms could favor archaeal contribution to ammonium oxidation.
水分有效性是干旱土壤中的主要限制因素；然而，很少有研究考察干燥和再湿润对这些环境中硝化细菌的影响。通过微观试验确定了水分有效性对智利硬叶灌丛半干旱土壤中氨氧化细菌（AOB）和古菌（AOA）多样性的影响。每14天添加水分以使土壤达到田间持水量的60%，显著增加了再湿润土壤微观环境中的硝酸盐含量（p < 0.001）。在100 Pa下添加乙炔可抑制因加水而对净硝化作用的这种刺激。通过对amoA基因（分别为A-amoA和B-amoA）以及β-变形菌特异性的16S rRNA基因（beta-amo）进行克隆测序，确定了土壤微观环境中AOA和AOB群落的组成。beta-amo基因测序揭示了亚硝化单胞菌属和亚硝化螺菌属的代表，而B-amoA克隆仅由亚硝化螺菌属序列组成。此外，来自古菌amoA基因文库（A-amoA）的所有克隆均与“嗜温泉古菌”序列相关（实际上，已重新分类为泉古菌门）。利用古菌的amoA基因标记和细菌的beta-amo基因标记，通过末端限制性片段长度多态性（T-RFLP）图谱确定了水分有效性对两种微生物群落结构的影响。虽然AOA在一些末端限制性片段（T-RF）中表现出波动，但AOB结构并未因水分脉冲而改变。通过与聚合酶链反应（MPN-PCR）分析相结合的最可能数法估计了AOA和AOB的相对丰度。AOB是该土壤中的主要类群，与AOA不同，较高的土壤含水量并不影响其丰度，而AOA在这些条件下略有增加。因此，这些结果表明，向这些半干旱土壤微观环境中加水可能有利于古菌对铵氧化的贡献。
