Responses of edaphic factors and microbial community to terrestrial succession and experimental warming in coastal salt marshes

To date, how the combined effects of terrestrial succession and climate warming will affect the edaphic factors and microbial community of coastal salt marshes remains unclear. To address this question, we compared the growth traits (i.e., morphology and biomass), edaphic properties, microbial community and function of Phragmites australis and Imperata cylindrica communities under natural vegetation succession (i.e., shift from P. australis to I. cylindrica) with or without warming treatment of I. cylindrica over two growing seasons (2019–2020). The results showed that after terrestrial succession, soil water content (SWC), electrical conductivity, clay content, total organic carbon and total nitrogen decreased significantly, while soil pH and contents of nitrate (NO₃^--N) and ammonium (NH₄⁺-N) increased. The microbial community structure was greatly altered by terrestrial succession. The combination of terrestrial succession and experimental warming reinforced the change trends of SWC and pH but caused NO₃^--N and NH₄⁺-N to decline to levels as low as those before succession. Although little response in microbial community structure was detected, the relative abundances of some dominant microorganisms and functional groups involved in C and N cycling were altered under the combination treatment. These variations in dominant microorganisms and predicted functional groups were related to changes in SWC, pH and particle size fractions and further influenced soil aeration and C/N availability. We concluded that in coastal salt marshes, experimental warming could further alter soil edaphic factors after terrestrial succession with little effect on microbial community structure. The changes in microbial community composition and function had a close correlation with edaphic factors. Our results suggested that adaptive soil management practices (i.e., inoculation of important microorganisms) should be considered to mitigate the soil degradation of coastal salt marshes with terrestrial succession under predicted climate warming.