Effect of Rainfall-Induced Soil Geochemistry Dynamics on Grassland Soil Microbial Communities

Abstract

gIn Mediterranean-type grassland ecosystems, the timing of rainfall events controls biogeochemical cycles, as well as the phenology and productivity of plants and animals. Here, we investigate the effect of short-term (days) soil environmental conditions on microbial community structure and composition during a natural wetting and drying cycle. Soil samples were collected from a meadow in Northern California at four time points after the first two rainfall events of the rainy season. We used 16S rRNA microarrays (PhyloChip) to track changes in bacterial and archaeal community composition. Microbial communities at time points 1 and 3 were significantly different than communities at time points 2 and 4. Based on ordination analysis, the available carbon, soil moisture, and temperature explained most of the variation in community structure. For the first time, a complementary and more comprehensive approach using linear regression and generalized logical networks were used to identify linear and nonlinear associations among environmental variables and with the relative abundance of subfamilies. Changes in soil moisture and available carbon were correlated with the relative abundance of many phyla. Only the phylum Actinobacteria showed a lineage-specific relationship to soil moisture but not to carbon or nitrogen. The results indicate that the use of a high taxonomic rank in correlations with nutritional indicators might obscure divergent subfamily-level responses to environmental parameters. An important implication of this research is that there is short-term variation in microbial community composition driven in part by rainfall fluctuation that may not be evident in long-term studies with coarser time resolution.

Response of soil CO2 efflux to precipitation manipulation in a semiarid grassland

“…This seasonality of SCE and CO 2 emission was likely due mainly to changes in root and microbial respiration, which are determined by the seasonal patterns of soil temperature and moisture, consistent with the findings of other studies (Boone et al, 1998;Luo et al, 2001;Wan et al, 2007). Changes in precipitation can directly influence plant growth and root and microbial respiration by altering the availability of soil water (Rodríguez-Iturbe and Porporato, 2005;Wan et al, 2007;Cruz-Martínez et al, 2012). The effects of soil-water availability on SCE are particularly strong and important in arid and semiarid ecosystems that are limited by the availability of precipitation or soil water (Austin et al, 2004).…”

“…Precipitation most directly affects soil moisture, which is a key driver of biological processes and plays a prominent role in terrestrial ecosystems by affecting plant productivity and soil processes (Ehrenfeld et al, 2005;Rodríguez-Iturbe and Porporato, 2005;Cruz-Martínez et al, 2012), which in turn modulate the impacts of other drivers of global change such as elevated atmospheric CO 2 levels, temperature, and nitrogen deposition (Wan et al, 2007;Jia et al, 2012). The responses of ecosystem processes to variations in soil moisture due to changes in precipitation have thus become the focus of current ecological and environmental research.…”

Loss of deep roots limits biogenic agents of soil development that are only partially restored by decades of forest regeneration

“…ANOVA was used to test for any influence of land use on the four modelled parameter estimates generated for each soil profile. Though a wealth of information is contained in environmental molecular data (Cruz-Martinez et al, 2012;Evans and Wallenstein, 2014), we focused on using genomic data as indices of months if not years (Carini et al, 2016) of dominant soil biogeochemical environments, and whether they exhibited variation with depth and land use history. First, Good's coverage and rarefaction analysis were used to assess our DNA extraction and sequencing procedures.…”

Assessment of Soil Microbial Communities in Carotenoid-Biofortified Rice Ecosystem

“…The rice rhizosphere soil's microbial community density was found to be similar between the two rice for each time period except an increase in the soil bacterial population density in August. An increase in temperature during August is suspected to have caused this increase, with factors such as available carbon, soil humidity and temperature being expected to explain most of the change (Cruz-Martínez et al, 2012). The result of this study indicated no significant difference between the microorganism population density of PAC and Nakdong except the March and August soil, which is consistent with reports from other studies such as there being no difference in culturable bacteria, fungi, protozoa, nematodes and earthworms numbers between Cry1Ab transgenic Bt-maize and non-Bt maize (Saxena and Stotzky, 2001b), as well as the number of bacteria, fungi and protozoa being unaffected whether a soil was treated with refined Cry1Ab and Cry1Ac protein or not (Donegan et al, 1995).…”