Hillslope geodiversity shapes ammonia-oxidizing communities and other microbial regulators in a semi-arid shrubland

The determinants and consequences of drought-related shrub mortality were studied for over a decade, as a model for desertification processes, in a semi-arid long-term ecological research station. Recent studies have shown that geodiversity is an important spatial predictor of plant viability under extreme drought conditions. Homogeneous hillslopes, with a deep soil profile and lack of stoniness, could not support shrubs under long term drought conditions due to low water storage in their soil. Conversely, heterogeneous hillslopes, with shallow soil profiles and high stoniness, supported shrub communities under similar conditions, due to the comparatively greater soil-water content. In the current study, we investigated the effect of hillslope geodiversity on the soil microbial diversity. Using DNA metabarcoding, we found small but consistent differences in the microbial community compositions of the homogeneous and heterogeneous hillslopes; more ammonia oxidizing and reducing-sugar degrading bacteria are found in the homogeneous hillslopes, possibly dwindling the ammonia supply to shrubs. Additionally, based on functional metagenomic reconstruction, we suggest that homogeneous hillslopes have lower superoxide and antibiotics production, leading to reduced protection against pathogens. In fungi, we observed an increase in possible pathogens, at the expense of lichen forming fungi. Lichens are considered to support soil-water by slowly releasing intercepted raindrops. In conclusion, we show that not only plant-diversity but also microbial-diversity is shaped by geodiversity, and that the community shift in homogeneous hillslopes may further promote shrub mortality in this drought-prone, water limited ecosystem. HIGHLIGHTSO_LIHomogeneous hillslopes reduce soil water storage and increase aeration. C_LIO_LIAmmonia oxidizers and reducing-sugar degraders dwindle ammonia supply for plants. C_LIO_LIHomogenous hillslopes do not support moisture providing lichens. C_LIO_LIReduced antibiotics and superoxide secretion capacitate pathogens. C_LIO_LIGeodiversity facilitates microbial regulation during drought. C_LI GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=87 SRC="FIGDIR/small/434393v2_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@1503208org.highwire.dtl.DTLVardef@4c589org.highwire.dtl.DTLVardef@144d17dorg.highwire.dtl.DTLVardef@1159040_HPS_FORMAT_FIGEXP M_FIG C_FIG