Impact of litter quality and soil nutrient availability on leaf decomposition rate in a semi-arid grassland of Northeast China

It was hypothesized that litter with higher N concentration would decompose faster than that with lower N concentration and that increased soil nutrient availability would stimulate litter decomposition. To examine the interspecific differences in decomposition rate of leaf litter in relation with differences in litter chemistry and soil nutrient availability, senescent leaves of four species Pennisetum flaccidum, Artemisia scoparia, Chenopodium acuminatum and Cannabis sativa, and soil samples with different fertilization treatments (no fertilization, N, P, and N + P fertilizations, respectively) were collected from a sandy grassland in Northeast China and incubated under laboratory conditions. The decomposition rate of leaf litter was determined by measuring the CO₂ emission during decomposition of litter. We found remarkable interspecific differences in leaf decomposition rates. Moreover, rates of litter decomposition at different incubation stages were correlated with different litter quality indices. The rate of litter decomposition was positively correlated with initial litter N concentration in the initial stage of the incubation, whereas it was negatively correlated with litter N and P concentrations in the late stage. Responses of litter decomposition to soil nutrient availability differed among species. Our results suggest that both indirect changes in litter quality through shifts of species composition/dominance and direct changes in soil nutrient availability under nutrient addition conditions could affect litter decomposition and consequently C and nutrient cycling of grassland ecosystems.     

制度能力在水污染治理中的作用——珠江广州段与泰晤士河伦敦段的治理比较分析

在对珠江广州段与东江、西江、北江的部分地段及广州市水务局、猎德污水处理厂、猎德村居民和英国泰晤士河等实地调查、资料分析的基础上,对珠江广州段近年污水治理与泰晤士河伦敦段两次成功治理进行比较、综合分析,提出制度能力对中国水污染治理的作用与意义.制度能力是针对解决某一具体事物而综合相关各个层面因素形成的能力.文中从规划、科研、体制、公众参与、立法五个方面总结了伦敦的经验,以期为广州治水提供借鉴.分析了广州治水过程中的制约因素,包括地方政府权力过大,以GDP为政绩的最主要考核指标,体制上有缺陷(多头管水,各主管