A review of performance optimization of constructed wetland based on rhizosphere microenvironment regulation

Constructed wetlands (CW) represent a highly promising wastewater treatment technology that provides an environmentally sustainable alternative to conventional treatment processes. However, despite their widespread implementation and technological advancements, CW still encounter challenges in achieving optimal pollutant removal efficiencies. The rhizosphere microenvironment constitutes the most dynamic and complex region within CW, which serves as the primary site for complex interactions among plants, microorganisms, substrates, and pollutants. Targeted manipulation of the rhizosphere microenvironment can optimize root system architecture and functionality, stimulate plant growth, enhance root exudation activity, and consequently attract diverse functional microbial communities. This cascade of effects ultimately improves pollutant degradation efficiency while enhancing ecosystem stability and system resilience. This study systematically reviews primary approaches for regulating the rhizosphere of CW plants through three distinct perspectives: physical, chemical, and biological. Physical regulation encompasses spatial constraints within the root zone, aeration control, and hydraulic condition modulation, which collectively affect root morphology, oxygen loss from roots, and pollutant retention capacity. Chemical regulation emphasizes nutrient management strategies, salinity stress mitigation, and acid-base balance adjustment to influence plant growth dynamics, root development patterns, and root exudate composition. Biological regulation involves optimization of plant configurations, rhizosphere microbial community engineering, and plant hormone regulation to enhance overall ecological functions in CW. The impacts of various rhizosphere regulation methods on wetland plant growth, microbial community composition, pollutant removal efficiency, and ecosystem stability are analyzed comprehensively. Mechanisms of action, applicable conditions, and associated challenges across different methods are summarized to establish theoretical references for future integration of multiple regulatory approaches under the concept of "multi-method synergistic regulation" aimed at enhancing comprehensive CW performance. Particular emphasis is placed on feasibility assessments of rhizosphere regulation methods and potential post-regulation environmental impacts, including non-target effects on organisms and long-term ecosystem health. Consequently, developing robust monitoring and modeling tools becomes imperative for evaluating regulatory strategy effectiveness and predicting their long-term consequences on CW performance. Future research should prioritize the integration of advanced monitoring and predictive modeling techniques to elucidate complex rhizosphere interactions and forecast the outcomes of diverse root modulation strategies. Comprehensive assessment of environmental impacts associated with root regulation, coupled with systematic exploration of sustainable modulation approaches, remains crucial for developing effective management strategies amidst growing environmental complexity. Strategic harnessing of rhizosphere regulatory potential offers promising pathways to transcend current performance limitations in CW while unlocking their full capacity for wastewater treatment and ecosystem restoration. Sustained innovation in this domain constitutes an essential component for addressing emerging environmental challenges through resource-efficient and ecologically sound management paradigms.