N And P Stoichiometric Characteristics In Herbaceous Plant Leaves And Soil In Riparian Zone Under Different Land Uses

Riparian zone is an important linkage between terrestrial and fluvial ecosystems, it is at land-water interface and has a distinct edge effect, and plays a role of corridor, filter and barrier in interaction of material flow, information flow and biotic flow between land and water. As the development of agriculture and urbanlization, human activity has increasingly marked effect on riparian zone and aquatic enviroment. By a series of complicated physical, biotic and biochemical cycle processes, riparian zone carry out the interception and conversion of nitrogen and phosphorus, while the land use regime can affect the structure and function of riparian plant and soil, and be a vital fators to change the processes of interception and conversion of nitrogen and phosphorus.Nitrogen (N) and phosphorus (P) is necessary nutrient elements for the plant life, they are the most universal limited elements in most ecosystems. Nitrogen and phosphorus are independent, but also have influence with each other, they have a major function on the growth of plant, composition of community and constitute and function of ecosystem. Using the stoichiometric method, we can not only learn the relationship between environmental factors and biotic constituent elements, but also can be favor of understanding the influence of enviromental effect on the organic growth, dynamic of community and ecosystem processes. Therefore, the study of ecological stiochiometry of riparian nitrogen and phosphorus in different land uses can help us to know human impact on the nutrient elemental status and trends of riparian plant and soil, it has significance for protecting watershed ecosystem, strengthening the management of basin and planing land use rationally.The research analyzed the stoichiometric characteristic of nitrogen and phosphorus of plant leaves and soil in riparian zone under three land uses (forest, agriculture and village) in May, July and September,2011, in Yixing, Taihu Lake, and using the ecological stoichiometry and field identified fertilazation to determined and checked the limited element, meanwhile, the research studied the relationship of nitrogen and phosphorus between plant and soil, and investigated the community stability of different land uses by comparing homeostasis regulation coefficient.The results was as flowes:1The riparian soil total nitrogen (STN) content in three land uses in three periods declined first then ascended. The STN content of riparian soil in May and July had no significant differences among three land uses, while in September it was visibly lowest in village riparian zone (p<0.05). The riparian soil total phosphorus (STP) content of agriculture was significantly lowest than other two land uses in three periods (p<0.05).2Comparing the STN and STP content under different land uses, it was found that the STN and STP content of soil surface layer were the highest among three layers in all of land uses. The riparian surface soil nearby forest had the significantly higher STN content than the ones of agriculture and village (p<0.05). The agriculture had the significantly lowest STP content in three periods (p<0.05).3The total nitrogen (TN) content of riparian plant leaves was increased when the plant growing while the highest total phosphorus (TP) content appeared in July. Both of the TN and TP content of riparian leaves of agricultural land use were higher than the ones in forest and village in July (p<0.05). The riparian plant TP content of village land use in September was higer than the forest’s (p<0.05).4The results of soil and plant N:P ratio variances in different land uses showed that in September the plant TN:TP in villiages was visibly lower than the one in forest and agriculture (p<0.05), in the whole soil and all three layers in agriculture land use, STN:STP were the highest(p<0.05).5According to the results of plant TN:TP and field verified experiment, riparian plant in Taihu Lake basin was limited by N.6In forest land use, the correlation of nitrogen and phosphorus between plant and soil had no significance (p>0.05), the correlation of nitrogen in agriculture was lower than the one in villiage. The correlation of nitrogen between plant and soil was weaker than phosphorus’s, which revealed the phosphorus was more severely affected by external nutrient element in surroundings.7The riparian plant homeostasis regulation coefficent was calculated by N:P ratios of plant and soil of forest, agriculture and village land uses in July, the result showed that riparian plant community’s ability to the varition in element of surroundings and community stability in three land uses were:forest> village> agriculture.The research suggested that differentiation on some degree existed in riparian plant and soil among different land uses. Excess nitrogen and phosphorus fertilization in a long-term had caused the high absorption of plant and soil and low retention of soil in agriculture land use, the community stability declined. Riparian plant community in forest land use had a strong stabiliy, its plant and soil, especially the surface soil, had a higher retention capacity for nitrogen and phosphorus, the plant and soil had a higher phosphorus content may due to input of household sewerage and survival strategy formated by plant adapted to the environment. Meanwhile, N was identified as limited elements of riparian vegetation in our study area.