34 resultados para 1361
Resumo:
To clarify the response of soil organic carbon (SOC) content to season-long grazing in the semiarid typical steppes of Inner Mongolia, we examined the aboveground biomass and SOC in both grazing (G-site) and no grazing (NG-site) sites in two typical steppes dominated by Leymus chinensis and Stipa grandis, as well as one seriously degraded L. chinensis grassland dominated by Artemisia frigida. The NG-sites had been fenced for 20 years in L. chinensis and S. grandis grasslands and for 10 years in A. frigida grassland. Above-ground biomass at G-sites was 21-35% of that at NG-sites in L. chinensis and S. grandis grasslands. The SOC, however, showed no significant difference between G-site and NG-site in both grasslands. In the NG-sites, aboveground biomass was significantly lower in A. frigida grassland than in the other two grasslands. The SOC in A. frigida grassland was about 70% of that in L. chinensis grassland. In A. frigida grassland, aboveground biomass in the G-site was 68-82% of that in the NG-site, whereas SOC was significantly lower in the G-site than in the NG-site. Grazing elevated the surface soil pH in L. chinensis and A. frigida communities. A spatial heterogeneity in SOC and pH in the topsoil was not detected the G-site within the minimal sampling distance of 10 m. The results suggested that compensatory growth may account for the relative stability of SOC in G-sites in typical steppes. The SOC was sensitive to heavy grazing and difficult to recover after a significant decline caused by overgrazing in semiarid steppes.
Resumo:
研究移动机器人在带有多移动障碍物的动态环境中的运动规划问题．基于分层最优控制理论，提出了一种新的运动规划方法来解决移动机器人的导航与避障问题．仿真实例证明了该方法的有效性。
Resumo:
通过对贵阳市红枫湖中溶解态锌、颗粒态锌及颗粒态锌中不同结合形态的研究，探讨了红枫湖生物地球化学过程中锌的主要赋存形态与季节性变化规律。结果发现，红枫湖总锌的质量浓度为0．72ug·L^-1～13．04ug·L^-1，污染较轻。红枫湖南湖总锌全年均高于北湖，主要是位于南部的羊昌河输入所致。红枫湖水体中锌的主要赋存形式是溶解态锌（占总锌的70％1；颗粒态中AEC（吸附态-可交换态-碳酸盐结合态）结合态锌是最主要的赋存形式（占颗粒态锌的72％）。溶解态锌含量夏季低而冬季高，主要是因为夏季生物吸收与吸附、以及冬季沉积物孔隙水向上覆水体的释放。颗粒物中有机结合态锌的变化主要受湖泊藻类繁殖的影响
