Comparison of Net Ecosystem Carbon Exchange and the Driving Factors in the Xishuangbanna Tropical Rainforest and Rubber Plantation

<p indent="0mm"> Land-use change in the tropics profoundly affects the regional carbon balance. To enhance our understanding of the carbon source/sink patterns in the northern tropical Asia, this study utilized eddy covariance methods to obtain multi-year meteorological and carbon flux data from the tropical rainforest and rubber plantation in Xishuangbanna. By integrating relevant environmental factors, we quantitatively evaluated the impacts of environmental factors on net ecosystem carbon exchange (NEE) in different tropical forests in Xishuangbanna. The results indicate that the average NEE over multiple years was <sc> –157.9 g C/(m²·a) </sc><sc>(–1.6 t C</sc>/(hm²·a)) for the tropical rainforest and <sc> –491.9 g C/(m²·a) </sc><sc>(–4.9 t C</sc>/(hm²·a)) for the rubber plantation, and both showed carbon sink effects. At the seasonal scale, the NEE characteristics of the tropical rainforest and rubber plantation were opposite, with tropical rainforest exhibiting stronger NEE during the dry season <sc> (–148.3 g C/(m² </sc>·season)) compared to the wet season <sc> (–9.6 g C/(m² </sc>·season)), while the rubber plantation showed higher NEE during the wet season <sc> (–376.9 g C/(m² </sc>·season)) than the dry season <sc> (–115.0 g C/(m² </sc>·season)). Seasonal NEE variations were both affected by phenological factors (LAI) in the dry season and by air temperature and vapor pressure deficit in the wet season. At the daily scale, both tropical rainforest and rubber plantation exhibited unimodal carbon exchange patterns, with daily average NEE of <sc> –0.4 g C/(m²·d) </sc> and <sc> –1.4 g C/(m²·d), </sc>respectively. Daily NEE variations in both forests were mainly regulated by photosynthetically active radiation (PAR), with the rubber plantation demonstrating stronger photosynthetic capacity compared to the tropical rainforest. The morning period was identified as the primary carbon uptake period for both forests, while high temperatures in the afternoon inhibited carbon absorption. These results reveal the differential impacts of similar environmental conditions on net ecosystem carbon exchange between tropical rainforest and rubber plantation, providing insights for estimating the carbon balance of tropical forest regions under future land use change.