Nitrogen-fixing bacterial communities differ between perennial agroecosystem crops

Authors: SOROCHKINA, KIRA - University Of Florida; MARTENS-HABER, WILLIAM - 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: N/A
Citation: N/A

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, communities of microorganisms within the top centimeter of soil, are common in natural ecosystems. Recently, biocrusts in agroecosystems were shown to have similar rates of nitrogen (N) fixation as natural ecosystem biocrusts. However, it is unclear how agricultural management practices influence biocrust community composition and function. Therefore, this study examined the bacterial and diazotrophic composition of biocrusts adjacent to crops in a citrus orchard and a vineyard with similar climate and soil type but different management. To contrast climate and soil type, these biocrusts were also compared to those from an apple orchard. All agroecosystem biocrust diazotrophs were dominated by N-fixing cyanobacteria from the Nostocales order, similar to natural ecosystem cyanobacterial biocrusts. Unlike natural ecosystem biocrusts, these agroecosystem biocrusts were dominated by proteobacteria and had a lower abundance of other cyanobacteria. Lower irrigation and fertilizer in the vineyard compared to the citrus orchard appeared to contribute to differences of these biocrust communities, whereas soil type and climate appeared to differentiate apple orchard biocrust microbial composition from the vineyard and citrus orchard. However, season did not influence bacterial and diazotrophic community composition of any agroecosystem biocrusts, suggesting that agricultural management practices could be reducing the effects of seasonal climatic differences.