Effects of Long-Term (17 Years) Nitrogen Input on Soil Bacterial Community in Sanjiang Plain: The Largest Marsh Wetland in China

Increased nitrogen (N) input from natural factors and human activities may negatively impact the health of marsh wetlands. However, the understanding of how exogenous N affects the ecosystem remains limited. We selected the soil bacterial community as the index of ecosystem health and performed a long-term N input experiment, including four N levels of 0, 6, 12, and 24 gN & BULL;m(-2)& BULL;a(-1) (denoted as CK, C1, C2, and C3, respectively). The results showed that a high-level N (24 gN & BULL;m(-2)& BULL;a(-1)) input could significantly reduce the Chao index and ACE index for the bacterial community and inhibit some dominant microorganisms. The RDA results indicated that TN and NH4+ were the critical factors influencing the soil microbial community under the long-term N input. Moreover, the long-term N input was found to significantly reduce the abundance of Azospirillum and Desulfovibrio, which were typical N-fixing microorganisms. Conversely, the long-term N input was found to significantly increase the abundance of Nitrosospira and Clostridium_sensu_stricto_1, which were typical nitrifying and denitrifying microorganisms. Increased soil N content has been suggested to inhibit the N fixation function of the wetland and exert a positive effect on the processes of nitrification and denitrification in the wetland ecosystem. Our research can be used to improve strategies to protect wetland health.

Automated summary

Excessive nitrogen input has negative effects on the health of marsh wetlands, particularly on the bacterial community. Through a long-term nitrogen input experiment, it was found that high-level nitrogen input significantly reduces the diversity of the bacterial community and inhibits certain dominant microorganisms. Nitrogen and ammonium were identified as critical factors affecting the soil microbial community. Furthermore, long-term nitrogen input reduces the abundance of nitrogen-fixing microorganisms and increases the abundance of nitrifying and denitrifying microorganisms, affecting the wetland ecosystem processes.