Nitrogen-fixing bacterial communities differ between perennial agroecosystem crops

Authors: SOROCHKINA, KIRA - University Of Florida; MARTENS-HABBENA, W - University Of Florida; Reardon, Catherine - Kate; STRAUSS, SARAH - University Of Florida; INGLETT, PATRICK - University Of Florida

Submitted to: FEMS Microbiology Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2024
Publication Date: 4/18/2024
Citation: Sorochkina, K., Martens-Habbena, W., Reardon, C.L., Strauss, S., Inglett, P. 2024. Nitrogen-fixing bacterial communities differ between perennial agroecosystem crops. FEMS Microbiology Ecology. 100(6). Article fiae064. https://doi.org/10.1093/femsec/fiae064.
DOI: https://doi.org/10.1093/femsec/fiae064

Interpretive Summary: Biocrusts are communities of microorganisms within the top centimeter of soil that include nitrogen fixing organisms that convert (or fix) atmospheric nitrogen to ammonia in the biocrust or soil. Biocrusts form naturally and are found throughout a variety of ecosystems ranging from tundra to deserts and agricultural soils. Unlike the natural ecosystems in which biocrusts are commonly found, agricultural systems are conventionally managed with nutrients (e.g., fertilizers) and water irrigation. To better understand how agricultural management impacts the microbial composition of biocrusts in agroecosystems, this study evaluated biocrusts collected seasonally in a citrus orchard and vineyard in Florida, USA and an apple orchard in Washington, USA to contrast biocrust composition in a different climate and management system. The bacterial communities in the biocrusts were evaluated by sequencing the 16S rRNA gene (overall composition) and the nitrogenase (nifH) gene involved in nitrogen fixation. Overall, the composition of the naturally-formed biocrusts differed by crop management, soil type and climate. The agroecosystem biocrusts also contained nitrogen-fixing bacterial species common in the natural ecosystem biocrusts. More diverse bacterial nitrogen fixing communities were also shown to have greater nitrogen-fixing capacity. These results demonstrate that biocrusts in agricultural systems share similarities to those in natural ecosystems and retrain the potential to fix atmospheric nitrogen despite fertilizer inputs.

Technical Abstract: Biocrusts, common in natural ecosystems, are specific assemblages of microorganisms at or on the soil surface with associated microorganisms extending into the top centimeter of soil. Agroecosystem biocrusts have similar rates of nitrogen (N) fixation as those in natural ecosystems, but it is unclear how agricultural management influences their composition and function. This study examined the total bacterial and diazotrophic communities of biocrusts in a citrus orchard and a vineyard that shared a similar climate and soil type but differed in management. To contrast climate and soil type, these biocrusts were also compared with those from an apple orchard. Unlike natural ecosystem biocrusts, these agroecosystem biocrusts were dominated by proteobacteria and had a lower abundance of cyanobacteria. All of the examined agroecosystem biocrust diazotroph communities were dominated by N-fixing cyanobacteria from the Nostocales order, similar to natural ecosystem cyanobacterial biocrusts. Lower irrigation and fertilizer in the vineyard compared with the citrus orchard could have contributed to biocrust microbial composition, whereas soil type and climate could have differentiated the apple orchard biocrust. Season did not influence the bacterial and diazotrophic community composition of any of these agroecosystem biocrusts. Overall, agricultural management and climatic and edaphic factors potentially influenced the community composition and function of these biocrusts.