Seasonality drives microbiome composition and nitrogen cycling in soil below biocrusts

Authors: NEVINS, CLAYTON - University Of Florida; INGLETT, PATRICK - University Of Florida; Reardon, Catherine - Kate; STRAUSS, SARAH - University Of Florida

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2022
Publication Date: 1/20/2022
Publication URL: https://handle.nal.usda.gov/10113/7629670
Citation: Nevins, C.J., Inglett, P.W., Reardon, C.L., Strauss, S.L. 2022. Seasonality drives microbiome composition and nitrogen cycling in soil below biocrusts. Soil Biology and Biochemistry. 166. Article 108551. https://doi.org/10.1016/j.soilbio.2022.108551.
DOI: https://doi.org/10.1016/j.soilbio.2022.108551

Interpretive Summary: Biological soil crusts (biocrusts) are naturally formed mats of macro- and microscopic organisms, including moss, algae, fungi, cyanobacteria, and archaea, that have the potential to fix nitrogen, cycle nutrients, and influence the soil moisture. Biocrusts are commonly on the upper millimeters of dryland soils and have been discovered in agricultural systems. In citrus production, year-round N availability is vital, with vegetative flushes in the spring and fall and fruit development in the fall and winter. Due to the N demand and natural formation of biocrusts in citrus, we investigated the influence of biocrusts on soil moisture content, N cycling, and microbiome composition in the root zone of a sandy soil citrus orchard (Florida, USA). Subsurface soil samples were collected from 0.4 to 2 inches below the soil surface at eight different dates over a one-year period. Soils were collected below both biocrusts and the nearby bare soil. Samples were analyzed for moisture content, inorganic and microbial N pools, and potential ammonia oxidation activity which is the first step of nitrification. Biocrust presence and sampling date significantly impacted the soil moisture and soluble and microbial N pools. Soil moisture and inorganic N were greater below biocrusts compared to below bare soil controls during the dry season from fruit set through harvest. Microbial biomass N and potential ammonia oxidation activity were also higher in September and November during fruit set. Throughout these periods, the microbiome of the soil below biocrusts had a greater abundance of bacteria and fungi capable of carrying out nitrification. Overall, these results indicate that the presence of biocrusts promote increased moisture, N concentrations, and relative abundances of microbiota with the capacity cycle N in the soil. These results suggest that biocrusts may influence crop N availability and soil health during growth periods of plant nutrient demand.

Technical Abstract: Biological soil crusts (biocrusts) recently discovered in agroecosystems have the potential to enrich soil moisture and nitrogen (N) concentrations and structure the subsurface microbiome. In citrus agroecosystems, year-round N availability is vital for production, with vegetative flushes in the spring and fall and fruit development in the fall and winter. Due to the N demand and natural formation of biocrusts in citrus orchards, we investigated the influence of biocrusts on soil moisture content, N cycling, and microbiome composition in the upper root zone of a sandy soil citrus orchard (Florida, USA). Soils sampled from below biocrusts (1–5 cm) were collected at eight sampling dates over a one-year period in the orchard from biocrust-covered and proximate bare areas. Samples were analyzed for moisture content, soluble and microbial N pools, and potential ammonia oxidation. Bacterial and fungal communities were characterized using the 16S rRNA gene and ITS region sequences, respectively, at five sampling dates from September 2019 through March 2020. Biocrust presence and sampling date signifi-cantly impacted soil moisture and soluble and microbial N pools (p < 0.05). Soil moisture and inorganic N were enriched below biocrusts compared to below bare soil controls during the dry season from fruit set through harvest. Microbial biomass N and potential ammonia oxidation activity were also higher in September and November during fruit set. During fruit set and maturation, there was a corresponding greater abundance of copiotrophic bacteria and fungi capable of heterotrophic nitrification in soil below biocrusts. Overall, these results indicate soil under biocrusts had increased moisture, N concentrations, and relative abundances of microbiota with functional potential for cycling N. These results support a potential role for biocrust influence on crop N availability and soil health during periods of plant nutrient demand.