Contrasting Waterlogging Response Strategies of Two Alpine Wetland Plants from Different Hydrological Niches: Insights from Root Traits, Rhizosphere Processes, and Transcriptomic Responses

Alpine wetland ecosystems on the Qinghai–Tibet Plateau are highly vulnerable to hydrological alterations, yet whether alpine wetland plants occupying different hydrological niches exhibit distinct adaptive strategies under waterlogging remains poorly understood. Here, two dominant alpine wetland species, Kobresia tibetica and Blysmus sinocompressus, were exposed to four waterlogging treatments: control (CK), slight waterlogging (SW), moderate waterlogging (MSW), and severe waterlogging (SSW). Root functional traits, rhizosphere soil enzyme activities, physiological responses, and root transcriptomic profiles were analyzed to elucidate species-specific responses to waterlogging stress. Slight waterlogging promoted root growth, whereas moderate and severe waterlogging inhibited root development and impaired physiological functions in both species. Root transcriptomic analysis under moderate waterlogging identified 123 and 2806 differentially expressed genes in K. tibetica and B. sinocompressus, respectively. These genes were mainly associated with redox regulation and stress responses in K. tibetica, whereas carbon metabolism, energy metabolism, and stress-related pathways were enriched in B. sinocompressus. Overall, the two alpine wetland species exhibited contrasting species-specific waterlogging response strategies, with B. sinocompressus showing greater capacity to maintain belowground functional stability under moderate and severe waterlogging. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) validation further confirmed that waterlogging-responsive genes involved in anaerobic metabolism and antioxidant regulation showed species-specific expression patterns under severe waterlogging conditions.