Abstract
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.
Highlights
Cycles of drought-rewetting are common in most terrestrial ecosystems, but they are pronounced in arid and semiarid environments mainly with seasonal rainfall (Fierer and Schimel, 2002)
Net nitrification occurred in rewetted microcosms throughout the incubation period, in which the nitrate content was above five times higher than in the non-treated samples (w/t) (p < 0.001)
The aim of this study was to evaluate the effect of periodic rewetting of semiarid soil microcosms from the Chilean sclerophyllous matorral on nitrification and on ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) communities structure
Summary
Cycles of drought-rewetting are common in most terrestrial ecosystems, but they are pronounced in arid and semiarid environments mainly with seasonal rainfall (Fierer and Schimel, 2002). In the Andean foothills some fragments of matorral are composed mainly by Colletia hystrix These shrubs are considered pioneer species that contribute to primary plant successions stabilizing the soil and increasing its nitrogen content (Silvester et al, 1985) because of their ability to form root nodules with Frankia, a N2-fixing actinomycete (Carú, 1993; Carú et al, 2003). This semiarid soil sustained denitrification activity and showed a broad genetic variability of denitrifiers (Orlando et al, 2012). Other major players in the nitrogen cycle are nitrifiers, archaea and/or bacteria, which have not been studied in this particular environment and have generally been addressed in some arid environments only
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