| The decomposition of leaf litter is one of the most important processes in ecosystem.This paper focused on leaf litter decomposition in Baoxing River in Southwestern Sichuan Province,China.The objective of this research was to examine how rates of leaf litter decomposition in two dominant plant species(Alnus cremastogyne and Houpoea officinalis)and their mixture(A.cremastogyne × H.officinalis)varied in different stream substrata.For the purpose,mass loss dynamics of them were investigated using coarse and fine mesh bags.The composition of substrata were gravel,sand and mud.Leaf litter bags had been deposited on the surface of substrata 30-50 cm deep under the surface of the stream water with stones for 100 days.Our results showed that after 100 days,the dry mass loss of leaf litter ranged from 34.8%?76%.The dynamics of dry mass followed the exponential decay equation.In the first 20 days,dry mass of all the leaf litter lost rapidly.This leaching period was attributed to a physical processing of soluble compound.There were notable difference of decomposition rate among A.cremastogyne,H.officinalis and their mixture on the same substrata.On the gravel and sand substrata,the decomposition rate of A.cremastogyne is higher than that of H.officinalis.(p<0.05),but no significant difference observed between both on the mud substrata.There was no significant mixing effect between the observed value and the expected value of the decomposition rate of A.cremastogyne × H.officinalis on all the three substrata.Substrata had different influences on the rates of leaf litter.Notable influence was found on A.cremastogyne and the mixture,but not on H.officinalis.It was obviously observed that the decomposition rate of three kinds of leaf litter on gravel surface was faster than that on sand or mud.The lowest rate of A.cremastogyne was on the mud with a marked difference from that on gravel,while the rate of H.officinalis did not varied significantly among the three substrata.The rate of mixture is faster on gravel,with significant difference from the other two.The N contents of A.cremastogyne and H.officinalis and their mixture released rapidly at the early stages and then got a little accumulation.The impact of substrata on the N release of A.cremastogyne was on the later period(60-100 days).The remaining percentage of N was similar on sand and mud,but higher than on gravel(p<0.05).On the contrary,the impact of substrata on H.officinalis was on the early stage(0-60 days).The release time on sand was 20 days,while extended to 60 days on gravel and mud.There was a synergistic effect on the N release of the mixture on gravel and mud,but only 20 days on sand and no mixing effects in subsequent times.The P contents in the leaf litter decreased in initial leaching period followed by a slowly increase and then decrease.The influence of substrata is different on the decomposition time among the single and mixed materials.Difference is mainly on the medium-term of A.cremastogyne and the prophase(0-60 d)of H.officinalis,while the whole decay process of the mixture.During the decomposition period,total microbial biomass of H.officinalis and A.cremastogyne x H.officinalis increased in the mud and sand substrata,while a decrease on the gravel and no difference was observed among the three substrata on A.cremastogyne.Dynamics of microbial biomass of each kind of litter was different among the three substrata,showed less relationship with decomposition rate of litter.The richness and abundance of invertebrate was higher on gravel than sand or mud,most of which were shredders.These results suggest that the initial quality characteristics of litter and the structure of invertebrate on different substrata were the determinant of decomposition of riparian plant litter. |
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