Effects of low temperature on rhizosphere phosphate-mineralizing microbial populations in constructed wetlands

In constructed wetlands (CWs), the rhizosphere acts as a critical zone for phosphorus (P) mineralization and the sustenance of microbial activity. However, low temperatures can significantly inhibit microbial processes and enzyme activities, particularly phosphatase activities that are crucial for P mineralization. Despite this, the impact of low temperatures on phosphorus-related phosphatase activities and the composition and function of microbial communities during the winter is not fully comprehended. This study investigates the response of phosphatase activity and P-mineralizing microbial communities to decreased winter temperatures in two contrasting CWs. The research was conducted at two CWs, designated as LCW and HCW, to assess the effects of winter temperatures on phosphatase activity and P-mineralizing microbial communities, with a focus on the suppressive effects of low temperatures. The study suggests that while the acid phosphatase (ACP) in HCW remains stable, the LCW shows a significant decrease. Correspondingly, the phoC community in HCW shows minimal variation, whereas community in LCW exhibits significant variation. Alkaline phosphatase (ALP) exhibits greater tolerance to low temperatures compared to ACP. The random forest analysis reveals that Pseudomonas is the primary contributor to ALP secretion, whereas Stenotrophomonas, possessing the phoC gene, is identified as the key contributor to ACP secretion during the winter season. ALP activity was significantly affected by soil temperature and soluble sugar, whereas ACP activity was strongly negatively associated with pH, organic acid and total organic carbon (TOC). Additionally, low temperatures caused phoC-harboring bacteria to cluster more closely, which may help maintain their functional potential in P mineralization. These findings highlight the significance of regulating ice thickness in CWs to optimize P availability, especially during the colder seasons, by revealing the microbial community's adaptive mechanisms to environmental stress. This research elucidates the complex relationship between winter temperature gradients and phosphorus mineralization processes. The findings are particularly relevant for optimizing nutrient management in wetland ecosystems under temperature fluctuations and contribute significantly to the discourse on sustainable management and the maintenance of microbial mineralization processes in the context of climate change.