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Effects Of Earthworm On Soil Microbial Growth Activity In Tropical Forests In Xishuangbanna, Yunnan, SW China

Posted on:2008-11-03Degree:MasterType:Thesis
Country:ChinaCandidate:G B YuFull Text:PDF
GTID:2120360215464074Subject:Ecology
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Earthworms play important roles in regulating soil processes through stimulating the activity of soil microbe. We initiated this study to examine the influence of tropical earthworms on the soil microbial growth activity in a tropical seasonal rainforest, rubber plantation and limestone rainforest of Xishuangbanna, SW China. We employed two treatments: control with natural earthworm population, and earthworm reduction using an electroshocking technique. We compared soil inorganic nitrogen, soil nitrogen mineralization rate, soil respiration rate, soil microbial biomass carbon and soil microbial biomass nitrogen between the controls and earthworm-reduced plots from February in 2005 to February in 2006, using close-top tube incubation method, infra-red gas analyzer (Licor-820), chloroform fumigation-incubation technique and Kjeldahl assimilation method, respectively. The results showed:(1) There were much different in earthworm species and population in the three forests. Pheretima was the only native earthworm species in seasonal rainforest and limestone rainforests. A mass of exotic earthworm Pontoscolex corethrurus had invaded when converting original forest to artifical rubber plantation and it had been the dominant species which account for 97.6% of quantity and 92.5% of biomass. The date of earthworm population showed that there was highest quantity of earthworm in rubber plantation (182.22 ind. m-2) while seasonal rainforest (88.89 ind. m-2) was closed to limestone rainforest (92.33 ind. m-2). There was highest biomass of earthworm in limestone rainforest (0.36 g ind.-1) while rubber plantation was lowest (0.19 g ind.-1). The character of vertical distribution was that the individuals of earthworm at the surface floor (0 ~ 10 cm, including floor litter) was more than others. Earthworm was limited by soil water and temperature so they varied with seasonal changes.(2) Electroshocking was an effective nondestructive technique for reducing earthworm populations under field conditions. Earthworm population had significantly reduced by 85% in seasonal rainforest and limestone rainforest, while 54.93% in rubber plantation.(3) Earthworms had different effects on the soil N mineralization in the three forests. They had increased the nitrate rate and net N mineralization rate in dry and wet season in the three forests. Earthworm had marked effect on ammonification rate in wet season in seasonal rainforest, in dry season in limestone rainforest and no effect in rubber plantation. NH4+ was decreased in earthworm-reduced plot in the three forests, NO3- and total inorganic nitrogen also decreased in seasonal rainforest and limestone rainforest.(4) Earthworm had much different effect on soil respiration in the three tropical forests. Soil respiration in control plot was significant higher than that in earthworm-reduced plot in seasonal rainforest, lower in rubber plantation and no change in limestone rainforest. The inoculated experiment indicated that earthworm affected on soil respiration through their species but not their quantity.(5) Earthworm had no effect on soil microbial biomass carbon and nitrogen in the three tropical forests.In sum, our experiment suggests that earthworms may change the flux rate of soil microbial biomass carbon and nitrogen, rather than by improving soil physical/chemical condition or altering the size of microbial biomass.
Keywords/Search Tags:Tropical forest, Earthworm, Soil microbe, Soil nitrogen mineralization, Soil respiration
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