Effects Of Plant Carbon Inputs On Earthworm Distribution And Population Dynamics In Rubber Plantation And Secondary Forest In Xishuangbanna, SW, China

In order to understand effects of plant carbon inputs on distribution and population dynamics of earthworm in rubber plantation and secondary forest in Xishuangbanna, SW, China, we surveyed earthworm communities and set up a series of different above-ground and below-ground plant inputs treatments by removing litter, adding litter and trenching roots in these two forests from January, 2006 to April, 2007. Our results showed that:(1) Soil organic matter and total N concentration in secondary forest were significantly higher than those in rubber plantation. In constrast, soil pH showed a different pattern. We found that a higher density and biomass of P. corethururus (maximal: 200.00 ind·m-2 and 58.86 g·m-2) than native earthworm Amynthas sp. (maximal: 18.38 g·m-2 and 56.00 ind·m-2) in rubber plantation. But in secondary forest, P. corethrurus mainly occurred at its edge nearest by rubber plantation, and there were no significant difference of density and biomass between exotic earthworm (maximal: 40.00 ind·m-2 and 11.32 g·m-2) and native earthworm (maximal: 24.00 ind·m-2 and 26.77 g·m-2) in it. Density and biomass of P. corethururus in rubber plantation were significantly higher than those in secondary forest, whereas density and biomass of native earthworm Amynthas sp. in rubber plantation and secondary forest did not differ. (2) Earthworm density and biomass declined in dry season but increased in rainy season. Low soil moisture and temperature in dry season may be the ecological factor limited the increase of exotic earthworm P. corethururus. Compared to P. corethururus, native earthworm Amynthas sp. has a weaker tolerance ability of soil moisture and temperature.(3) Exotic earthworm P. corethururus reproduced all year round. An increasing population model of this earthworm was found. Density and biomass of its juveniles were significantly higher than those of the adults. Native earthworm showed a stable population. Density and biomass of its adults and juveniles did not differ.(4) Annual litter inputs in secondary forest ( about 1000 g·m-2) were about twice times than those in rubber plantation (about 580 g·m-2). Comparied with control plots, removing litter fall (reducing above-ground carbon inputs) decreased forest floor biomass significantly, whereas only a few litter-removal plots had more forest floor biomass than control plots. Fine-root biomass in root-trench (reducing blow-ground carbon inputs) plots showed a decrease pattern.(5) Effects of above-ground and below-ground plant carbon inputs on earthworm differed with different earthworm ecological types. In litter-removal (reducing above-ground carbon inputs) plots, density and biomass of epigeic native earthworm Amynthas sp. showed a decrease pattern, whereas no significant effects were found on exotic earthworm P. corethururus. And also there were no significant effects of trench roots (blower-ground carbon inputs reducing) on both two earthworms. This can be explained that our dada were based on one year's short study, thus soil carbon pool may be not significantly changed within this short study time.(6) Exotic earthworm density and biomass were positively correlated with the fine-root biomass in rubber plantation. Vegetation change and soil nutrient decrease may promote exotic earthworm reproduction when land use of secondary forest was changed to rubber plantation by human beings. Meanwhile, the ecological adaptive strategies of the exotic and native earthworms can not be ignored. Whether the development of rubber plantation will lead the spread of exotic earthworm P. corethrurus requires ecological concern. (7) Microbial biomass C showed an increasing pattern in litter-removal plots (reducing above-ground inputs) in rainy season. We guess that fewer microbes were eaten by native earthworm because density and biomass of this earthworm decreased in the same trement plots. As is mentationed above, althought no significant effects of plant carbon inputs treatments on exotic earthworm were found in our experiment, whether the increase of microbial biomass C in treatment plots contributed to the balance of exotic earthworm population should be studied further more in future.