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Abstract
Natural scrublands in semi-arid deserts are increasingly being converted into fields. This results in losses of characteristic flora and fauna, and may also affect microbial diversity. In the present study, the long-term effect (50 years) of such a transition on soil bacterial communities was explored at two sites typical of semi-arid deserts. Comparisons were made between soil samples from alfalfa fields and the adjacent scrublands by two complementary methods based on 16S rRNA gene fragments amplified from total community DNA. Denaturing gradient gel electrophoresis (DGGE) analyses revealed significant effects of the transition on community composition of Bacteria, Actinobacteria, Alpha- and Betaproteobacteria at both sites. PhyloChip hybridization analysis uncovered that the transition negatively affected taxa such as Acidobacteria, Chloroflexi, Acidimicrobiales, Rubrobacterales, Deltaproteobacteria and Clostridia, while Alpha-, Beta- and Gammaproteobacteria, Bacteroidetes and Actinobacteria increased in abundance. Redundancy analysis suggested that the community composition of phyla responding to agricultural use (except for Spirochaetes) correlated with soil parameters that were significantly different between the agricultural and scrubland soil. The arable soils were lower in organic matter and phosphate concentration, and higher in salinity. The variation in the bacterial community composition was higher in soils from scrubland than from agriculture, as revealed by DGGE and PhyloChip analyses, suggesting reduced beta diversity due to agricultural practices. The long-term use for agriculture resulted in profound changes in the bacterial community and physicochemical characteristics of former scrublands, which may irreversibly affect the natural soil ecosystem.
Highlights
Converting natural land into arable soils results in losses to the landscapes characterized by a typical indigenous flora and fauna
To compare the bacterial community in soils under different land use, 16S rRNA gene fragments of bacteria, Alphaproteobacteria, Betaproteobacteria and Actinobacteria PCR-products amplified from total community DNA of alfalfa or adjacent scrubland soils sampled at two sites were analyzed by Denaturing gradient gel electrophoresis (DGGE) (Figures S1, S2, S3, S4)
For bacteria including all bacterial subgroups analyzed, Box-Whisker plots revealed that the variability of the bacterial community compositions among replicates was generally lower for alfalfa soils than the scrubland soil, except for Betaproteobacteria at site 2 (Figure 1)
Summary
Converting natural land into arable soils results in losses to the landscapes characterized by a typical indigenous flora and fauna. The ecological consequences of such transitions have been addressed in several studies focusing on land degradation [1,2,3], losses of macrobiodiversity [4,5], nutrient exhaustion in soils [3], sustainability [6,7] and restoration [8]. Soil microorganisms, including protozoa, fungi, bacteria and archaea, are essential for the proper functioning and sustainability of ecosystems [9,10,11]. The influence of land use and management on soil microorganisms was addressed in several recent studies [16,17]. The information acquired is still not sufficient as a systematic identification of taxa responding to the transition in land use was not done.The studies investigated soils from various geographic sites in Australia, The Netherlands, and Brazil [16] a comparison of the results might be difficult due to the differences in the experimental designs and the resolution level of the methods used
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