Rapidly developing droughts, including flash droughts, have occurred frequently in recent years, causing significant damage to agroforestry ecosystems, and they are expected to increase in the future due to global warming. The artificial forest area in China is the largest in the world, and its carbon budget is crucial to the global carbon sink. As the most prominent plantation plant in the tropics, the rubber (Hevea brasiliensis (Willd. ex A. Juss.) Muell. Arg.) ecosystem not only has important economic significance, but also has the potential to be a major natural carbon sink in hot areas. Frequent drought events have a significant impact on rubber ecosystem productivity, yet there have been few reports on the vulnerability of rubber productivity to drought. The objective of this study is to evaluate the vulnerability of rubber ecosystem gross primary production (GPP) to short-term flash drought (STFD) in Hainan Island, utilizing the localized EC-LUE model (eddy covariance–light use efficiency) validated by flux tower observations as the research tool to conduct the scenario simulations which defined by standard relative humidity index (SRHI), in a total of 96 scenarios (timing × intensity). The results show that, in terms of time, the rubber ecosystem in Hainan Island has the highest vulnerability to STFD during the early rainy season and the lowest at the end of the rainy season. From the dry season to the rainy season, the impact of STFD gradually extends to the northeast. Spatially, the vulnerability of the northern island is higher than that of the southern island and that of the western part is higher than that of eastern Hainan Island. With the increase in STFD intensity, the spatial distribution center of the vulnerability of rubber ecosystem GPP in Hainan Island gradually moves southward. The spatiotemporal pattern of the vulnerability of the rubber ecosystem GPP to STFD over Hainan Island plotted by this study is expected to provide decision makers with more accurate information on the prevention and control of drought disaster risk in rubber ecosystems.

Background: Although numerous studies have been carried out in recent decades, soil respiration remains one of the less understood elements in global carbon budget research. Tropical forests store a considerable amount of carbon, and a well-established knowledge of the patterns, components, and controls of soil respiration in these forests will be crucial in global change research. Methods: Soil respiration was separated into two components using the trenching method. Each component was measured at multiple temporal scales and in different microhabitats. A commercial soil efflux system (Li8100/8150) was used to accomplish soil respiration monitoring. Four commonly used models were compared that described the temperature dependence of soil heterotrophic respiration using nonlinear statistics. Results and Conclusions: Trenching has a limited effect on soil temperature but considerably affects soil water content due to the exclusion of water loss via tree transpiration. Soil respiration decreased gradually from 8 to 4 μmol·m⁻²·s⁻¹ 6 days after trenching. Soil autotrophic (R_a) and heterotrophic respiration (R_h) have contrasting diel patterns and different responses to temperature. R_h was negatively correlated with temperature but positively correlated with relative humidity. Both R_a and R_h varied dramatically among microhabitats. The Q₁₀ value of R_h derived using the Q₁₀ model was 2.54. The Kirschbaum–O’Connell model, which implied a strong decrease of Q₁₀ with temperature, worked best in describing temperature dependence of R_h. Heterotrophic respiration accounted for nearly half of the total soil efflux. We found an unexpected diurnal pattern in soil heterotrophic respiration which might be related to diurnal moisture dynamics. Temperature, but not soil moisture, was the major controller of seasonal variation of soil respiration in both autotrophic and heterotrophic components. From a statistical perspective, the best model to describe the temperature sensitivity of soil respiration was the Kirschbaum–O’Connell model. Soil respiration varied strongly among the microhabitats and played a crucial role in stand-level ecosystem carbon balance assessment.

As a unique type of ecosystem, tropical coastal sandy vegetation lies in the transition zone extending from coastal beaches to further inland and provides important ecosystem services such as windproofing, tourism, and agriculture. However, the energy and matter fluxes of these tropical coastal ecosystems have been rarely studied. We reported one-year eddy flux observations in a tropical sandy coastal ecosystem and specifically focused on the carbon and water exchanges between the atmosphere and the ecosystem. The studied ecosystem was a carbon sink (approximately –560 gC m⁻² yr⁻¹) and approximately 1000 mm of water evaporated from the ecosystem into the atmosphere during the study year. The highest levels of vegetation photosynthesis occurred in April, shortly before the wet season. This can be attributed to an endogenous self-adjustment of the ecosystem to improve the water- and carbon-use efficiency during the wet season. This study is expected to not only fill the data gap with respect to the gas exchange between tropical sandy coastal plains and the atmosphere but also provide knowledge about the function and ecological service of these specific ecosystems.