Response Of Biomass Partitioning And The Phenotypic Plasticity Of Leaf Traits Of Five Common Annual Herb Plants To The Urban Habitat Heterogeneity In Shanghai

As one of the three components of urban vegetation, weed communities are essential to the maintenance and conservation of urban biodiversity. Weeds distributed in urban area widely without human intervention, and they had high sensitivity, strong plasticity and diversified adaptation strategies to the heterogeneity of habitats. Due to these factors, weeds can quickly respond to the formation of high degree variation of habitat attributes in urbanization. Therefore, study on the distribution pattern of the biomass partitioning of the community will help to reveal the influence of urbanization on urban vegetation and the respondence of urban vegetation to urbanization.Plant species have evolved specialized strategies to regulate their resource and hypotheses regarding different "strategies" of biomass are among the most important theories in plant ecology and evolution. Study of resource allocation and their determinants provides insight into a better understanding of plants’ adaptation to environment, and helps to understand how the plants respond to the urban habitat heterogeneity. Phenotypic plasticity is to point to the same genotype for different environmental responses and producing the phenotype of different characteristics. It is the organ in a complex environment caused a series of different relatively suitable for the potential of the phenotype, involving the morphological and anatomical, physiological, biochemical and life history and other aspects. In the process of evolution and the interactions of environment, plants have gradually formed many internal physiological and external of adapting strategies. With the maximum degree to reduce environmental adverse effect, plant traits are the direct reflect of the adaptive strategies of plants, plant traits can reflect the objective external environment and these traits belong to the phenotypic plasticity. The plasticity of the leaf traits is the study hotspot in recent years. On the population level research plant biomass patitioning and the phenotypic plasticity of leaf traits can reveal its growth strategy and the response to the urban habitat heterogeneity.This study take the5widespread annual herb as objects, through the research on the community level for the above-below ground biomass distribution pattern, the biomass partitioning and leaf traits to reveal the characteristics of five annual plant growth strategy and the phenotypic plasticity of functional traits. The main results as followings:1. The below-ground and above-ground community biomass distribution patternIn the autumn of2012(September-November) plant growth season (namely the flowers and fruits) surveyed and collected120communities, according to the field investigation data and clustering analysis showed that there were five community types, which were Eclipta prostrate community, Solanum nigrum community, Acalypha australis community, Echinochloa crusgalli community and Eclipta prostrate community. These5kinds of community types in the urban and rural gradient all have distribution. CCA analysis showed that the effect of community species composition of the five main habitat factors are soil moisture content, soil total nitrogen, total phosphorus, soil C:N, soil compactibility. Through the correlation analysis found that influence of the habitat factors which effect the species composition of community didn’t have significant influence on the biomass partitioning, the biomass of community in urban are larger than suburbs and rural, presumably, the main factors of influence community biomass may be light condition combing with the result of SMA analysis. The relationship of below-ground and above-ground biomass growth is accorded with constant growth hypothesis. Moreover, in the urban and rural gradient the ratio of below-ground and above-ground community biomass has no significant variance. This may be due to the selected community are annual which have the same life strategies.2. The plant biomass partitioning and the phenotypic plasticity of leaf traits in population levelThe five dominant species of the community are taken as the research object and making the comparison of biomass partitioning and leaf traits of these species. The biomass of population, leaf traits and habitat factors have the notable correlation through the Pearson correlation analysis. Although there were differences between these five species in biomass partitioning and phenotypic plasticity of leaf traits, which showed a certain consistency:Nitrogen content of leaves and soil total nitrogen have a significant negative correlation; Population biomass and leaf nitrogen content have a significant positive correlation; Population biomass and soil total nitrogen have the significant negative correlation. Which means that in the place of high soil nitrogen content, the plant leaves take the strategy of reducing the absorption of nitrogen to reduce this environmental stress, its external performance is plant individual short. At the same time in the urban and rural gradient, population biomass, leaf nitrogen content and soil nitrogen content showed opposite tendency. The soil in nitrogen is the main effect on the plant population biomass and phenotypic plasticity of leaf traits. While on the population level, the biomass of root and shoot didn’t show significant difference in the gradient of urban and rural gradient, this could also due to the selected species which have the similar growth strategy.