Variation in carbon,nitrogen and phosphorus partitioning between above-and belowground biomass along a precipitation gradient at Tibetan Plateau

Precipitation is a potential factor that significantly affects plant nutrient pools by influencing biomass sizes and nutrient concentrations. However, few studies have explicitly dissected carbon(C), nitrogen(N) and phosphorus(P) pools between above- and belowground biomass at the community level along a precipitation gradient. We conducted a transect(approx. 1300 km long) study of Stipa purpurea community in alpine steppe on the Tibet Plateau of China to test the variation of N pool of aboveground biomass/N pool of belowground biomass(AB/BB N) and P pool of aboveground biomass/P pool of belowground biomass(AB/BB P) along a precipitation gradient. The proportion of aboveground biomass decreased significantly from mesic to drier sites. Along the belt transect, the plant N concentration was relatively stable; thus, AB/BB N increased with moisture due to the major influences by above- and belowground biomass allocation. However, P concentration of aboveground biomass decreased significantly with increasing precipitation and AB/BB P did not vary with aridity because of the offset effect of the P concentration and biomass allocation. Precipitation gradients do decouple the N and P pool of a S. purpurea community along a precipitation gradient in alpine steppe. The decreasing of N:P in aboveground biomass in drier regions may indicate much stronger N limitation in more arid area.

河南省永城市准备越冬蚊虫停落高度调查研究

目的了解河南省永城市准备越冬蚊虫种类、数量及其在居民区分布的高度梯度,为制定适宜防制措施提供科学依据。方法永城市市区近郊和市内分别选择2个小区,用目测法进行现场蚊虫数量估计,同时对其中数个单元楼道内的蚊虫用人工小时法进行蚊虫数量的校准。结果 2010年11月在永城市4个居民小区均发现有蚊虫停落栖息,捕获蚊种全部为淡色库蚊,分布在不同楼层间,1层蚊虫数量最多,在高度分布上从1层向高层呈现依次递减,6层以上数量很少;目测法与人工小时法获得类似的结论;不同小区的蚊虫密度差异与小区的外围环境以及小区的具体防蚊措施具有密切关系。结论居民区的蚊虫来源于外围环境,居民区采取适当的隔离措施对降低蚊虫密度具有良好作用;化学防蚊措施的实施应该以居民区楼层的1层为主。