We used a litterbag method to investigate litter decomposition and related soil degradative enzyme activities across four seasons in a broad-leaved forest and a coniferous forest on Zijin Mountain in sub-tropical China. Across four seasons, we quantified litter mass losses, soil pH values, and related soil degradative enzyme activities. Litter decomposition rates differed significantly by season. Litter decomposi- tion rates of broadleaf forest leaves were higher than for coniferous for- ests needles across four seasons, and maximal differences in litter de- composition rates between the two litter types were found in spring.
WANG Cong-yanLü Yan-naWANG LeiLIU Xue-yanTIAN Xingjun
Aims With the continuing increase in the impact of human activities on ecosystems,ecologists are increasingly interested in understanding the effects of high temperature on litter decomposition since litter decomposition and the accompanying release of nutrients and carbon dioxide are key processes in ecosystem nutrient cycling and carbon flux.This study was conducted to evaluate the temperature sensitivity of forest litter decomposition and soil enzymes during litter decomposition in subtropical forest in China.Methods Two dominant litter types were chosen from Zijin Mountain in China:Quercus acutissima leaves from a broadleaf forest(BF)and Pinus massoniana needles from a coniferous forest(CF).The litter samples were incubated in soil microcosms at ambient control temperature(20 C)and 10 C warmer.During a 5-month incubation,chemical composition of litter samples,litter mass losses,and related soil enzyme activities were determined.Important Findings Three main results were found:(i)high temperature accelerated decomposition rates of both litter types,and the temperature sensitivities of litter decomposition for BF leaves and that for CF needles are equivalent basically,(ii)high temperature enhanced soil enzyme activities in the two forest types,and the temperature sensitivities of polyphenol oxidase were significantly higher than those of the other soil enzymes and(iii)the temperature sensitivities of nitrate reductase were significantly higher in the CF soil than in the BF soil,while there was no significant difference in the temperature sensitivities of the other soil enzymes between BF and CF.As a long-term consequence,the high-temperature-induced acceleration of litter decomposition rates in these subtropical forests may cause carbon stored belowground to be transferred in the atmosphere,which may alter the balance between carbon uptake and release,and then alter the global carbon cycle in the coming decades.
In this work, the difference in number of dominant species in a community on global scale and successional trajectories was analyzed based on the published data. We explained the reasons of these differ-ences using a resource availability hypothesis, proposed in this work, that the distribution of available resource determined the pattern of commu-nity dominance. The results showed that on global scale the number of dominant species of community varied across latitudinal forest zone, namely from single-species dominance in boreal and temperate forest to multi-species codominance, even no dominant species in tropical forest. This was consistent with the pattern of resource distribution on global scale. Similarly, in successional trajectories, the number of dominant species gradually radiated from single-species dominance to multi-species codominance, even no dominant species in tropical forest. The changing available resources in trajectories were responsible for this difference. By contrary, a community was often dominated by single species in temperate or boreal forest. This was determined by the low available resource, especially low available water and temperature. In boreal forest, low temperature greatly reduced availability of water and nutrient, which were responsible for the single-species dominance. In addition, the conclusion that high available resources sustained low dominance of community might be deduced, based on the fact that the dominance of community declined with the increasing of species diversity. To sum up, the richer the available resources were, the lower the dominance of community was, and vice versa. The hypothesis that the resource availability controlled the dominance of community could well elucidate the difference of community dominance on global and community scale.
