Abstract: The spatial patterns and spatial association of plant populations are the results of coordinated adaptation of plants to environment. The spatial distribution and spatial association of Myricaria bracteata and Tamarix ramosissima were studied by using the methods of community survey and point pattern analysis. Four types of soil texture plots were chosen, including gravelly soil (Ⅰ), half naked gravel soil (Ⅱ), coarse sand (Ⅲ), and silty sand (Ⅳ) in the floodplain wetland of middle reaches of the Heihe River. The results showed that, with the size fraction of soil changing from coarse to fine, the M. bracteata plant height decreased firstly and then increased, twig number, branch density and the proportion of small bunch declined, while the T. ramosissima plant height and twig number increased, branch density and the proportion of small bunch increased firstly and then decreased. At the plots Ⅰ, Ⅱ and Ⅲ, the M. bracteata population showed a clumped distribution on different scales, which shifted from a larger scale to a smaller scale, while it showed a random distribution on all scales at the plot Ⅳ. At the plots Ⅰ, Ⅱ and Ⅲ, the T. ramosissima population showed a clumped distribution but with an opposite variation trend, while it showed a random distribution on all scales at the plot Ⅳ. At the plots Ⅰ and Ⅲ, the spatial association between M. bracteata and T. ramosissima showed a negative correlation or no significant correlation; at the plot Ⅱ, the spatial association transferred from significantly negative to significantly positive; at the plot Ⅳ, the spatial association shifted from significantly negative to not significantly. With the effects of environmental heterogeneity in the floodplain wetland, the plants’ asymmetric competition caused the change of dominant position of plant population and the scale transformation of spatial patterns, reflecting the strategy of plant’s adaptation to environment.

Key words: soil respiration, nitrogen fertilizer, R₁₀., Keerqin sandy land, Q₁₀