| 中文摘要 | Material cycle and energy flow is one of the important contents of ecosystem research. Litter decomposition is the important link of nutrition cyclic process, and connects the synthesis (photosynthesis) and decomposition (the decomposition of organic matter and the release of nutrient elements) of biological organism. Wetlands are the most active interfaces for energy and material movement on the earth since they are the ecotones between waters and lands. The decomposition rates of litters in wetland ecosystem, to a great extent, affect the accumulation rates of litters and the return of nitrogen (N), phosphor (P) and other elements to soil pool. This process even affects the germination, growth, species abundance and aboveground biomass of wetland plant, and further influences the construction of plant community and the competition among populations in habitat. In this paper, we aim to provide a critical review on the recent development in study of wetland litter decomposition. The study of wetland litter decomposition is constantly deepened along with the improvement of study methods. Models have been become important study means, so the researches about them are also constantly deepened. The current studies mainly focus on two aspects, that is, the change characteristics of organic matter components and element contents. Litter decomposition is mainly controlled by both biotic factors (such as the physical and chemical properties of litter and the species, abundance and activity of heterotrophic microbe and soil fauna) and abiotic factors (such as climate, soil moisture, acidity, alkalinity, salinity and wetland sediment etc). With respect to the biotic factors, the chemical properties of litter (mainly include the contents of nitrogen, phosphor, lignin and cellulose, the ratios of C/N, lignin/N and C/P) are the control factors of decomposition. Among them, the ratios of C/N and lignin/N are the best predication indexes of decomposition rates as they reflect the ratio of carbohydrate and lignin to protein in litter. However, the predication indexes of decomposition in different stages are different as the changes of litter substrate quality. The activities of microbe and soil fauna are more important to the decomposition of recalcitrant component in litter at later stage. With respect to the abiotic factors, temperature rising can increase the decomposition rates, and precipitation affects the activity of decomposer and the leaching of chemical substances in litter. Water condition affects the ventilative status of litters, and wetland nutrient status affects litter substrate quality, hence indirectly influences decomposition rates. Temperature, precipitation and other abiotic factors also indirectly influence decomposition through their effects on biotic factors. http://www.ecologica.cnUnderstanding the responses of litter decomposition to global warming, CO2 doubling, the changes of dry or wet deposition and its chemical components are of crucial importance in understanding soil organic matter formation and carbon sequestration in wetland ecosystem. In this paper, we also discussed the likely changes of wetland litter decomposition due to global change. Global warming might lead to the moving of wetland zones and the changes of the factors that control litter decomposition, thus affects the function of nutrient cycling of wetland ecosystem. The effects of global warming on wetland litter decomposition rate can be divided into direct effects and indirect ones. With respect to the direct effects, the effects of abiotic factors on litter decomposition are not consistent. On one hand, temperature rising strengthens soil N mineralization and promotes the availability of soil nutrients, which is in favor of litter decomposition. On the other hand, it causes the increase of soil evaporation and the decrease of soil humidity, which is unfavorable of litter decomposition. Temperature rising also can enhance the activities of microbes and promote decomposition rate. In addition, global warming might indirectly affect decomposition by changing wetland distributed zones, wetland community composition and structure, litter substrate quality, soil nutrient availability, and thaw depth in high latitude wetland ecosystem. The CO_2 doubling usually does not have direct effect on litter decomposition of wetland ecosystem. However, it can influence litter decomposition indirectly by changing litter substrate quality, soil moisture regimes, and the potential shift of decomposer community of wetland ecosystems. In current academia, there are two different opinions about the effects of CO_2 doubling on litter substrate quality and decomposition rate. One opinion indicated that it could decrease litter substrate quality and decomposition rate. The other one indicated that it could increase decomposition rate, but had no effect on litter substrate quality. The degree that global precipitation change will influence litter decomposition depends on the potential magnitude of this change as well as the current moisture condition. If the current moisture condition in a wetland ecosystem is optimal for litter decomposition, then the significant change in precipitation may result in a decrease in litter decomposition. However, if water is a limited factor, then the increased precipitation will enhance litter decomposition. In addition, the changes of chemical composition of dry or wet deposition (precipitation) can directly or indirectly affect decomposition mainly through influencing litter chemical composition and altering the ratios of C/N and C/P of decomposition environment. In order to obtain enough information to understand the responses of wetland litter decomposition to global change, thorough and comprehensive studies on decomposition are needed through long term ground network monitoring and observation, simulating climatic change experiments in situ, cross-site decomposition experiments, and application of reciprocal transplant technique across different climate zones, etc. |
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