Abstract:

Objectve: The dominant species including Populus deltoides, Liquidambar styraciflua, Quercus phellos, Betula nigra, and Taxodium ascendens in the three freshwater wetland plantations(broad-leaved plantation, coniferous and broad-leaved mixed plantation, coniferous plantation) in the Tangpu Reservoir area of Shaoxing City, Zhejiang Province were used to study the composition of δD of plant stem water within nine days after three different magnitudes of rainfall, and the contribution rate of different magnitudes of rainfall to plant stem water of every arbor species and use strategy of plant species was quantitatively clarified, providing scientific theoretical basis for quantitative research of water cycle process, rational utilization and management of water resources in the reservoir area. Method: Hydrogen and oxygen stable isotopes technique were used to study the dynamic change of water δD of dominant plants during the sampling time (within 9 days after each rainfall) and its comparison with δD values of precipitation, soil water before rainfall, and shallow underground water, etc., to determine the water source of the species. On this basis, Bayesian isotope mixing model MixSIAR (version 3.1.7) was used to calculate the contribution rate of three magnitudes of rainfall to plant stem water of dominant arbor species. Result: For the dominant plant water was mainly obtained from atmospheric precipitation, soil water before rainfall and shallow underground water in freshwater wetland plantation in the Tangpu Reservoir area, rainfall event was the main factor affecting the water δD and the water contribution rate of the plant. Within 9 days after rainfall, the sequence of contribution rate of light rain (7.5 mm) to plant stem water of dominant plants in broad-leaved plantation was L. styraciflua (45.2%-1.5%) > P. deltoides (38.0%-0.6%) > Q. phellos (31.2%-0.8%), the sequence of contribution rate of light rain to plant stem water of dominant plants in the coniferous and broad-leaved mixed plantation was B. nigra (39.0%-0.6%) >T. ascendens (32.4%-0.8%) > Q. phellos (25.5%-0.6%). The order of contribution rate of moderate rain (14.5 mm) and heavy rain (35.0 mm) to plant stem water of tree species in the broad-leaved plantation was P. deltoides > Q. phellos > L. styraciflua, and contribution rate of moderate rain and heavy rain to plant stem water of B. nigra was the highest in the coniferous and broad-leaved mixed plantation. The contribution rate of light rain, moderate rain and heavy rain to plant stem water to T. ascendens in the coniferous plantation were 40.2%-2.6%, 58.2%-2.7%, and 67.4%-20.9%, respectively. Conclusion: The dominant tree species can quickly absorb the precipitation in the freshwater wetland plantation in the Tangpu Reservoir area. The contribution rate of light rain to plant stem water of trees with abundant roots at surface layer (0-20 cm) is higher, while the contribution rate of moderate rain and heavy rain to plant stem water of trees with deeper root distribution is higher. Trees with deep root and shallow root in the coniferous and broad-leaved mixed plantation and in the broad-leaved plantation of Tangpu Reservoir area have different water use strategies, which is conducive to the stability of the wetland plantation community and the coexistence of various tree species in the wetland plantation. It was suggested that tree species with different root distribution should be selected to achieve the rational use of water resources, and maintain the stability of wetland plantation ecosystems in the process of vegetation restoration in freshwater wetlands in the Yangtze River Delta region of China.

Key words: plant water use, stable isotope, freshwater wetland plantation, root distribution, Tangpu Reservoir