Characterizing soil microbial diversity under the three dominate state changes in dryland systems

Background/Question/Methods

In the Chihuahua Desert of the American Southwest, degradation of our drylands results in the conversion of the historical perennial grasslands to woody shrubs which can lead to soil erosion, loss of biodiversity, and loss of soil nutrients and carbon. Climate change induced droughts have further facilitated shrub growth and has led to more frequent state transitions. Researchers have found that state transitions are not permanent and can be reversed, but success in restoring historic grasses remains limited. To better achieve restoration goals in dryland systems, more knowledge is needed on how microbial communities vary under different global change pressures and the specific microbial taxa that interact with dryland plant species. Duneland Restoration Project (DuRP) sites at the JRN LTER is a monitoring system established in 2017 that focuses on three alternative states including black gramma dominated sites (the reference historical perennial grassland state); shrub invaded grassland (recovering state); and dune lands (mesquite shrub dominated, unrecovered state). In each plot, I collected 4 replicates from 2 regions: bulk and rhizosphere. For each soil sample totaling about 228, DNA was extracted to assess the bacterial and fungal microbial diversity and community structure using 16S and ITS primers respectively.

Results/Conclusions

We were able to compare microbial community measurements to both plant diversity and soil nutrients. Plant cover was higher on black gramma sites followed by mesquite invaded sites and then on dune sites. At the same time, we found that carbon, nitrogen, and carbon to nitrogen ratios are significantly lower in dune sites than in shrub invaded and black gramma sites. There was no significant difference in bulk density among the sites. In addition, there were no significant differences in maximum carbonate storage. The infiltration rate was significantly different between mesquite and dune which is thought to be driven by grass and bare cover. With an increase in aggregate stability, dune sites were seen to be significantly different in comparison to mesquite invaded sites and black gramma sites. Neither bacterial nor fungal diversity and structure correlated with plant cover or biomass. Instead, overall soil properties were a better predictor of microbial structure. While microbial diversity was higher in soil samples from grass plots, rhizosphere diversity did not significantly differ between the plots. Our research suggests that there are microbial rhizosphere hotspots even in the dune sites and this may be important for grass establishment and ecological restoration.