Effects of drying-wetting cycle caused by rainfall on soil respiration: Progress and prospect

Soil respiration is an important part of the carbon cycle in terrestrial ecosystems. The changes of soil respiration caused by rainfall directly affect global carbon balance. Therefore, it is important to explore the mechanism underlying the effects of rainfall on soil respiration, which is necessary for understanding the carbon cycle and carbon budget of terrestrial ecosystems. Here, we summarized the research progress on the mechanism of drying-wetting cycle caused by rainfall on soil respiration. Soil respiration can be promoted at intermediate moisture conditions, but suppressed in both wetter and drier conditions. Dryingwetting cycles caused by rainfall affect soil respiration by changing soil moisture. On one hand, under the condition of drought, dryingwetting cycle caused by rainfall improve soil respiration rate by shortterm replacement of CO2 in soil, increases of soil microbial respiratory substrate, increases of microbial activity, and enhancement of litter decomposition. On the other hand, soils with high moisture could reach saturation more quickly or even be waterlogged after a short period of rainfall. Dryingwetting cycle caused by rainfall can significantly suppress soil respiration through restricting the entrance of O2 to the soil, forming an anaerobic environment, and inhibiting microbial and root respiration. In addition, dryingwetting cycle caused by rainfall could significantly inhibit root respiration by flooding part of the plant, reducing plant leaf area and photosynthetic products. In order to accurately estimate the interference of soil respiration on carbon budget of terrestrial ecosystems, future studies on the effects of rainfall on soil respiration should focus on three aspects: (1) microbiological response mechanisms underlying the effects of rainfall on soil respiration; (2) differentiating response mechanisms of soil autotrophic respiration and heterotrophic respiration to rainfall; and (3) modeling the effect of rainfall on soil respiration

Effects of simulated precipitation changes on plant community characteristics of wetland in the Yellow River Delta, China

Under the changing climate scenario, changes in precipitation regimes are expected to alter soil water and salinity conditions, with consequences on the characteristics of plant community in estuarine wetland. Here, we used a six-year (2015-2020) precipitation manipulation experiment to examine how plant community characteristics responded to precipitation changes in the Yellow River Delta. The results showed that soil electrical conductivity significantly decreased, while soil moisture significantly increased with increasing precipitation. Precipitation changes altered plant community composition. Increased precipitation reduced the absolute dominance of Suaeda glauca and Suaeda salsa, but increased that of Triarrhena sacchariflora and Imperata cylindrica. Shannon index and Margalef richness index of plant community significantly increased with increasing precipitation. Compared with the control, both decreased and increased precipitation decreased the plant community abundance, frequency and coverage. The treatment of 60% increased precipitation significantly decreased plant community frequency by 54.9%, while the 60% decreased precipitation, 40% decreased precipitation, 40% increased precipitation and 60% increased precipitation treatment significantly decreased plant abundance by 38.9%, 33.8%, 35.8% and 45.7%, respectively. The aboveground biomass significantly increased with increasing precipitation, but aboveground plant biomass under 60% increased precipitation treatment being lower than that reducing under 40% increased precipitation treatment, probably due to the negative effects of flooding stress. In addition, Margalef richness index had a significantly positive relationship with aboveground biomass. Aboveground biomass, Shannon diversity index, Margalef richness index, and Simpson diversity index were negatively related to soil electrical conductivity, and aboveground plant biomass was positively related to soil moisture. Our results revealed that precipitation changes regulate growth characteristics, species composition, and diversity of plant community by altering soil water and salinity conditions in a coastal wetland

Effects of changes in precipitation on soil respiration in coastal wetlands of the Yellow River Delta

Soil moisture fluctuation caused by changes in precipitation patterns associated with global change is an important driving force for the dynamic changes of soil respiration. However, it is unclear how coastal wetlands respond to changes in precipitation patterns, and thus cause changes in the ecosystem blue carbon function. To explore the response and mechanism of soil respiration and environmental and biological factors to precipitation changes, the soil carbon flux observation system was applied to monitor wetland soil respiration rates under different precipitation treatments relying on increased and decreased precipitation fields outside the control experiment platform of the Yellow River Delta coastal wetland in 2017. The results showed that: (1) with increased precipitation, the wetland soil temperature gradually decreased; simultaneously,both precipitation increase and decrease significantly increased wetland soil moisture (P &lt; 0.05); (2) changes in precipitation significantly affected vegetation species composition, aboveground and belowground biomass allocation, and root/shoot ratio (P &lt; 0.05). A 40% and 60% precipitation increase significantly increased the wetland plant species and vegetation root shoot ratio; however,it significantly reduced the aboveground biomass of wetland vegetation. In addition,a 40% increase and 60% decrease of precipitation significantly increased the aboveground biomass of wetland vegetation; (3) there was no significant effect of precipitation changes on annual soil respiration in wetlands. Nevertheless,a 60% and 40% precipitation increase both significantly increased the soil respiration rate in wetlands during the non-flooding season (P &lt; 0.05); (4) the wetland soil respiration and moisture showed a quadratic curve (P &lt; 0.05) with the correlation coefficient decreasing with precipitation increase. Furthermore, during the wetland non-flooding season, soil respiration and temperature were exponentially correlated (P &lt; 0.05) with soil temperature sensitivity (Q10) increasing with increasing precipitation. There was no significant correlation between soil respiration and temperature during flooding periods; (5) during the flooding period,the soil respiration rate was inversely correlated with the surface water level (P&lt; 0.001).</p