Long-term carbon dioxide dynamics variability at submerged macrophyte habitat of a subtropical shallow lake

Submerged macrophytes are widespread and deemed fundamental components particularly in shallow lakes. They play a pivotal role by rendering essential ecosystem services, however, their roles in governing the carbon dioxide (CO2) budget remain controversial and unclear, likely posing a significant challenge to the comprehensive understanding of CO2 cycling within lake ecosystems. To fill the knowledge gaps, the dynamic variability of CO2 within the submerged macrophytes habitats in a shallow subtropical lake located in eastern China was comprehensively investigated based on long-term (2005–2017) field measurements span different seasons. The findings revealed that the submerged macrophytes habitats were characterized by superior water quality, manifested as low nutrient loadings, reduced algal biomass, and heightened water clarity, when juxtaposed with open water regions of the lake devoid of macrophytes. The long-term measurements demonstrated that the submerged macrophytes habit functioned as relatively low CO2 source, with an annual mean emissions flux of 13.55 ± 9.20 mmol m−2 d−1. The presence of macrophytes and good water quality (e.g. low nutrient loadings) likely contributed to low emissions within submerged macrophyte habitat via increasing CO2 fixation and reducing CO2 production, respectively. The temporal fluctuations in CO2 emissions from submerged macrophyte habitats were closely associated with water clarity, which in turn highlighted the role of water quality in determining CO2 variability within submerged macrophyte habitats. Furthermore, the long-term measurements uncovered significant inter-annual variations in the CO2 emissions, highlighting the critical importance of long-term measurements to derive unbiased estimates of the CO2 budgets within the submerged macrophyte habitats of inland lakes.