| Phragmites communis and Phalaris arundinacea are both rhizomatous grasses which have highly similar biological characteristics.The two species not only have high biological yield, but also have strong reproductive and competitive abilities.Therefore, if the two species live together in the same region, a series of the interspecific competition,especially about nutrient utilization is bound to be fierce.So if there is no compromise strategy of nutrient competition and colonization about between the two species, it is extremely difficult to achieve stable coexistence in the community.The study area is located in Zhenjiang waterfront wetland in the lower reaches of the Yangtze River. P. communis and P. arundinacea are the two dominant plants in this wetland.In this study,the amount of litterfall, release dynamic of C?N?P,nutrient loss dynamics of litter per unit area about P. communis and P. arundinacea and the dynamics of soil nutrient increment and microbial biomass during the litter decomposition of the two species were measured by field decomposition bag method and simulated decomposition method.Based on the perspective of decomposition of litter, the theoretical maximum of nutrient complementary utilization and the actual growth of soil nutrient were measured in this paper by calculating the nutrient loss and nutrient transfer of litter decomposition of P. communis and P. arundinacea. Then, combined with the growth process of the two species, the study explored P. communis and P. arundinacea realized the community pattern of competitive coexistence through adopting the ecological strategies of nutrient complementary utilization..The main findings are as follows:(1)The litter decomposition dynamics is a integrated result which is effected by environmental factors, such as temperature, hydrology and microbiological activities.etc. and internal factors, such as litter composition and litter quality,etc. At day 621, the litter of P. communis and P. arundinacea had been decomposed completely, and C, N and P were basically released. In the decomposition, the C content in litter was decreased continuously, but the N and P were enriched at localized time.(2)At the end of decomposition, the surface soil nutrients of all treatments increased. Organic carbon, total nitrogen, total phosphorus and available phosphorus concentration all continued to increase with the decomposition of litter, and nutrients were transferred to soil and accumulated. With the increase of soil depth, soil nutrient growth rate became smaller.(3) The number of bacteria, fungi and actinomycetes and microbial biomass carbon in soil increased gradually in the early peried, but decreased in the later period due to the decrease of temperature in winter during litter annual decomposition process.The three kinds of microbes and microbial biomass carbon decreased with soil depth increasing. Both microorganism quantity and microbial biomass carbon in soil during the progress of P. arundinacea litter decomposition were higher than the soil during the progress of P. communis litter decomposition.Soil surface covered litter can increase soil microbial activity and microbes play a stimulative role in litter decomposition.(4)According to the litter nutrient loss, 39.37%, 41.27% and 13.72% of organic carbon, total nitrogen and total phosphorus released from litter decomposition of P. communis will be utilized by P. arundinacea, while 60.63%, 58.73% and 86.28% will be utilized by itself. 65.99%, 27.60% and 68.03% of organic carbon, total nitrogen and total phosphorus released from litter decomposition of P. arundinacea will be utilized by P. communis, while 34.01%, 72.40% and 31.97% will be utilized by itself.According to the soil nutrient increment, 46.54%?55.54%?77.59% and 72.32% of organic carbon, total nitrogen, total phosphorus and available phosphorus increased in soil under P. communis will be utilized by itself,while 53.46%?46.73%?37.68% and 12.52%l will be utilized by P. arundinacea. 64.72%?41.33%?74.40%and 71.75% of organic carbon, total nitrogen, total phosphorus and available phosphorus increased in soil under P. arundinacea will be utilized by P. communis, while 50.72%?44.46%?22.41% and 27.68% will be utilized by itself.Therefore,this study not only revealed that there was obvious complementarity of nutrient utilization between P.australis and P.communis,but also further revealed this kind complementarity had non-reciprocity with complementary capabilities and the inter-annual feature of compensation time. |
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