The Effects Of Levels And Orders Of Habitat Resource Gradients Based On Soil N/P Ratio On The Clonal Growth Of Zoysia Japonica

Resource and environmental heterogeneity commonly exist in the nature, which often present in the form of a patchyness or grandient. The pattern of resource and environmental heterogeneity often plays a decisive role in the formation of source-sink relationship between the ramets within a clonal plant. Through regulating the biomass allocation pattern, clonal plant achieves morphological plastic changes, effectively responding to the resource and environmental heterogeneity. We conducted a series of experiments, in which we grew typical clonal plant Zoysia japonica with various nutrient levels and orders based on different N/P ratios, so as to simulate the resource and enrionmental gradient in the natural conditions, besides, we designed the homogeneous and heterogeneous habitat patterns, and the integrated and non-integrated status between ramets, respectively, aiming to reveal the responses of Z. japonica in all these conditions, in term of clonal growth benefits. Besides, we analyzed the biomass allocation patterns and the root architecture, as well as the different responses between ramets of Z. japonica clones in the homogeneous and heterogeneous nutrient habitats. The main results were as follows:(1) The clonal growth benefits of Z. japonica. were significantly affected by the nutrient conditions in the habitats. The total biomass of Z. japonica was highest when N/P ratio was 7:1, lowest when N/P ratio was 21:1 and intermediate when N/P ratio was 14:1. When N/P ratio was same, the total biomass of Z. japonica clone changed with the gradient in the order:high nutrient level gradient> low nutrient level gradient > whole range nutrient level gradient, and in every nutrient level gradient, the total biomass of Z. japonica clone was larger in the decreasing order habitat than in the increasing order habitat, suggesting that increasing the nutrient level in habitat and matching the nutrient supply in a micro-habitat with the growth requirement of each ramet, significantly improve the clonal growth of Z. japonica.(2) The R/S ratio of Z. japonica changed with the gradient in the order:low nutrient level gradient>high nutrient level gradient, high N/P ratio>low N/P ratio and integrated condition>non-integrated condition, suggesting that the ramets of Z. japonica tended to increase its roots so that it get more soil resource and be more competitive in the habitats with unfavorable nutrient consditions.(3) The total biomass of Z. japonica was both influenced by its own characteristics and by environmental factors. The total biomass of Z. japonica basically followed the laws:branches A and root were highest, branches B was lowest, and stolons was at intermediate (the growth of ramets A was superior to ramets B), but in non-integrated status, the investment of biomass to branches B increased, and the investment of biomass to root and stolons decreased. In different treatment conditions, the distribution of biomass in every organ was different. In the heterogeneous habitats, the biomass allocation of Z. japonica to the stolon was the largest in the whole range nutrient level gradient habitat, whose total nutrient was at moderate level.(4) The total biomass of Z. japonica in the homogeneous habitats was not always higher than in that in the heterogeneous habitats. The biomass of Z. japonica changed with the gradient in the order:homogeneous habitats> heterogeneous habitats with decreaing order> heterogeneous habitats with increasing order, when N/P ratio was 7:1; heterogeneous habitats with decreasing order> homogeneous habitats> heterogeneous habitats with increasing order, when N/P ratio was 14:1; heterogeneous habitats with decreasing order> heterogeneous habitats with increasing order> homogeneous habitats, when N/P ratio was 21:1.(5) High nutrient levels in habitats increased the branchinhg intensity of Z. japonica. The position of the branches was related to the nutrient level at the micro-habitats of the ramet of Z. japonica. In the homogeneous and heterogeneous habitats, the root architecture parameters of Z. japonica changed in the wave-like form to some extent. Through the changes of the root architecture, the ability for root to acquire soil resources changed, the difference among the ramets root architecture reflected their risk spreading mechanism, reducing the adverse effect of heterogeneous habitats, and improving the fitness of the whole genet.