Detritus, as a major component of energy flow, contributes to the energy resource in ecosystems. The duration of stay of the leaf litter in a certain area of the stream channel determines the density and composition of the stream biocoenosis that invades the litter. Human activities accelerate degradation of ecological conditions in streams. As a result, many researches on litter breakdown in drainage areas have been conducted, which could be used for assessing for the health of streams. However, a few information on leaf litter decomposition in streams in China is available. To provide information for understanding nutrient cycling and energy flow in fluvial ecosystems, this paper focused on the leaf litter decomposition in Xiangxi River in north-west Hubei Province (China). The objective of this research was to examine how rates of leaf litter decay in three plant species (Cotinus coggygria var.pubescens, Acer oliverianum and Acer flabellatum.) varied along an elevation gradient, and mass loss dynamics of them were investigated using mesh bags. The three altitudinal plots were located in the headwater at alt.1160m、930m and 658m in Xiangxi River watershed. Leaf litter bags had been deposited in the stream water and on the riparian woodland for 90 days.
Our results showed that after 90 days, the dry mass loss of leaf litter ranged from 13% to 70%. The dynamics of dry mass loss followed the declined exponential equation. In the first 3 days, dry mass of all the leaf litter lost rapidly. Leaf litter bags in the fresh water lost 9％ to 18% of the total mass, while on the land lost 4% to 9％. This leaching period was attributed to a physical processing of soluble compound. After 30 days, rates of leaf litter decay in the rivers stabilized gradually. The dynamics of dry mass loss on the woodland showed fluctuated dynamics in 90 days. C.coggydia var.pubescens appeared medium decomposition rate（decay rates range from 0.0043 to 0.0079 d-1）, lower than A.oliverianum and A.flabellatum significantly （p<0.05）. But there was not significant difference between decay rates of A.oliverianum and A.flabellatum leaf litter. High decomposition rates had been observed in A.oliverianum and A.flabellatum litter bags in the alt.1160m and 930m streams（decay rate ranges from 0.0101 to 0.0140 d-1）, while in the alt.658m site appeared medium rates （decay rate ranges from 0.0078 to 0.0084 d-1）. However, elevation had no significant influence on the rates（p>0.05）, maybe the altitudinal differences among three streams were too small. A.flabellatum leaf litter decomposed significantly much slowly（decay rate ranges from 0.0027 to 0.0036 d-1）on the woodland than in the stream. Similar breakdown rates were found on the three woodland plots. Generally, fast breakdown rates of leaf litter in the Xiangxi River indicated that riparian leaf litter played a significant role in the nutrient cycling and benthic communities.