Orlando Julieta, Carú Margarita, Pommerenke Bianca, Braker Gesche
Department of Ecological Sciences, Faculty of Sciences, University of Chile Santiago, Chile.
Front Microbiol. 2012 Apr 5;3:101. doi: 10.3389/fmicb.2012.00101. eCollection 2012.
The Chilean sclerophyllous matorral is a Mediterranean semiarid ecosystem affected by erosion, with low soil fertility, and limited by nitrogen. However, limitation of resources is even more severe for desert soils such as from the Atacama Desert, one of the most extreme arid deserts on Earth. Topsoil organic matter, nitrogen and moisture content were significantly higher in the semiarid soil compared to the desert soil. Although the most significant loss of biologically preferred nitrogen from terrestrial ecosystems occurs via denitrification, virtually nothing is known on the activity and composition of denitrifier communities thriving in arid soils. In this study we explored denitrifier communities from two soils with profoundly distinct edaphic factors. While denitrification activity in the desert soil was below detection limit, the semiarid soil sustained denitrification activity. To elucidate the genetic potential of the soils to sustain denitrification processes we performed community analysis of denitrifiers based on nitrite reductase (nirK and nirS) genes as functional marker genes for this physiological group. Presence of nirK-type denitrifiers in both soils was demonstrated but failure to amplify nirS from the desert soil suggests very low abundance of nirS-type denitrifiers shedding light on the lack of denitrification activity. Phylogenetic analysis showed a very low diversity of nirK with only three distinct genotypes in the desert soil which conditions presumably exert a high selection pressure. While nirK diversity was also limited to only few, albeit distinct genotypes, the semiarid matorral soil showed a surprisingly broad genetic variability of the nirS gene. The Chilean matorral is a shrub land plant community which form vegetational patches stabilizing the soil and increasing its nitrogen and carbon content. These islands of fertility may sustain the development and activity of the overall microbial community and of denitrifiers in particular.
智利硬叶灌丛是一种受侵蚀影响的地中海半干旱生态系统，土壤肥力低，受氮限制。然而，对于像地球上最极端的干旱沙漠之一阿塔卡马沙漠的沙漠土壤来说，资源限制更为严重。与沙漠土壤相比，半干旱土壤的表土有机质、氮和水分含量显著更高。虽然陆地生态系统中生物偏好的氮的最大损失是通过反硝化作用发生的，但对于在干旱土壤中蓬勃生长的反硝化菌群落的活性和组成几乎一无所知。在本研究中，我们探索了来自两种具有截然不同土壤因子的土壤中的反硝化菌群落。虽然沙漠土壤中的反硝化活性低于检测限，但半干旱土壤维持着反硝化活性。为了阐明土壤维持反硝化过程的遗传潜力，我们基于亚硝酸还原酶（nirK和nirS）基因对反硝化菌进行了群落分析，这些基因是该生理组的功能标记基因。在两种土壤中都证实了nirK型反硝化菌的存在，但未能从沙漠土壤中扩增出nirS，这表明nirS型反硝化菌的丰度非常低，这也解释了反硝化活性缺乏的原因。系统发育分析表明，nirK的多样性非常低，沙漠土壤中只有三种不同的基因型，这种条件可能施加了很高的选择压力。虽然nirK的多样性也仅限于少数几个不同的基因型，但半干旱灌丛林土壤中nirS基因显示出惊人的广泛遗传变异性。智利灌丛林是一个灌木地植物群落，形成植被斑块，稳定土壤并增加其氮和碳含量。这些肥沃的岛屿可能维持整个微生物群落尤其是反硝化菌的发育和活性。
