| Land use change has significant effects on the soil carbon pools and the process of soil respiration. Conversion from natural forests to plantations can bring a lot of economic benefits. Consequently, the vegetation characteristics and management way has been changed, and the species composition, the characteristics of the litter, soil physical and chemical properties has also greatly changed. These changes led to a significant influence on the dynamic characteristics of soil carbon pools. Moso bamboo is one kind of very important economic forest tree species in southern China, accounting for 70% of the bamboo forest in China. It plays an important role in carbon balance in the subtropical area. To obtain more economic benefits, many managers converted natural hardwood forests into Moso bamboo plantations. The Moso bamboo plantations are usually managed by chemical fertilizer application, understory vegetation removal, and other intensive management. The land use change and these intensive management methods would significantly affect the soil carbon pools. However, up to now, the effects and associated mechanisms are still unclear. In this study, the dynamics characteristic of soil respiration components(total soil respiration, soil autotrophic and heterotrophic respirations) and environmental factors(soil temperature, soil water content, soil water-soluble organic carbon content, and soil microbial biomass carbon content in natural evergreen broad-leafed forests and Moso bamboo plantations were determined. The responses of soil respiration components and soil organic carbon pools to land use change were elucidated and the relationships between soil respiration components and environmental factors were discussed. The main results obtained from this study were as follows:(1) The soil respiration, autotrophic and heterotrophic respiration in natural hardwood forests and Moso bamboo plantations all reflects the seasonal variations characteristic. The highest rates of soil total respiration in two forests appeared in summer, the lowest in winter. The highest rates of autotrophic respiration in two forests also appeared in summer and the lowest in winter; but heterotrophic respiration maximum value in autumn, the minimum value in winter.(2) The accumulative respiration effluxes was 31.60 t CO2 hm-2 yr-1 and 37.25 t CO2 hm-2 yr-1 in the Evergreen broad-leaf forest and Moso bamboo, respectively. The soil total, autotrophic and heterotrophic respiration rates in the evergreen broad-leaf forest were 2.48, 1.57, and 0.91 μmol CO2 m-2 s-1, respectively. The soil total, autotrophic and heterotrophic respiration rates were 2.93, 1.92 and 1.01 μmol CO2 m-2 s-1 in Moso bamboo forest, respectively. Heterotrophic respiration accounted for a higher proportion in total respiration and the percentage was 63.57 and 66.07% in the evergreen broad-leafed forest and Moso bamboo, respectively. Likewise, autotrophic respiration accounted for 36.43% and 33.93%. After the transformation from evergreen broad-leaf forest into Moso bamboo forest, soil respiration components significantly increased. Soil total, autotrophic and heterotrophic respiration rate increased by 17.87, 22.51 and 9.78%, respectively.(3) Soil water-soluble organic carbon(WSOC) and microbial biomass carbon(MBC) also reflect significant seasonal variations. The lowest soil respiration rate of the evergreen broad-leaf forest and Moso bamboo appeared in February, the highest rates in June. In the evergreen broad-leaf forest, the higher of MBC concentration appeared in summer-autumn, lower in winter. In the Moso bamboo forest, soil microbial biomass carbon(MBC) is higher in October-December, but lower in July-August with highest of soil temperature, the lowest appeared in February. The conversion of evergreen broad-leafed forest into the Moso bamboo forest, the average value of WSOC concentration was increased by 10.26%, while the MBC concentration was decreased by 6.23%.(4) Our analysis revealed significant correlation(P < 0.01) between soil respiration components in the two forests and the soil temperature at the 5 cm soil depth. The Q10 value of total respiration, autotrophic respiration and heterotrophic respiration in evergreen broad-leafed forest were 1.80, 1.92, and 1.70, respectively. In the Moso bamboo forest, the soil Q10 value of total respiration, autotrophic respiration and heterotrophic respiration were 1.95, 2.05, and 2.34, respectively. In the context of temperature rises, heterotrophic respiration may be most sensitive to rising temperature in Moso bamboo forest. But autotrophic respiration may be most sentitive to rising temperature in evergreen broad-leafed forest.(5) In the evergreen broad-leafed forest, both soil respiration and heterotrophic respiration were correlated to soil WSOC concentration(P < 0.01), and in the Moso bamboo forest, both soil respiration and heterotrophic respiration were correlated to soil WSOC concentration(P < 0.05). There was no correlation between autotrophic respiration and soil WSOC concentration regardless of the forest type. In addition, in both evergreen broad-leafed forest and Moso bamboo forest, there were no significant relationships between soil respiration components and soil moisture content and MBC concentration. |
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