| Globally, forest plantations have been recommended as an important measure to sequester carbon(C) from atmosphere and to mitigate future climate change. The impacts of harvest residue management in forest plantations on soil C and nitrogen(N) pools continue to receive attention, which are not only important to C balance, but also play critical roles in sustaining forest productivity. Residues from harvest of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations represented a significant proportion of site organic matter and supply. Experiments in Xiayang forest farm, Nanping City, Fujian Province, China, were established to investigate the effects of harvest residue management on soil total C and N, soil labile C and N and soil respiration (Rs). Harvest residue treatments included:(1) whole tree harvest plus forest floor removal,(2) whole tree harvest,(3) stem only harvest,(4) double residue, and (5) burning residue. The results showed that there was a trend for C and N concentrations to be higher in double residue treatment than other treatments in0—10cm layer during the first15years. However, one-way ANOVA showed that harvest residue management had no significant effects on C and N concentrations in0—10cm,10—20cm or20—40cm layers at any sampling year (P>0.05). Analysis of repeated-measures ANOVA showed that C and N concentrations for the three depth layers varied between years (P<0.01). Neither harvest residue management nor the interaction of sampling year and harvest residue management had any significant effects of on C and N concentrations in any depth of soil layers (P>0.05). Soil C stock at the0-40cm depth was88.21Mg hm"2at age15years on average. Again, one-way ANOVA showed harvest residue management had no significant effect on the soil C stocks at any soil depths (P>0.05).The effects of harvest residue management on dissolved organic C concentrations extracted by water, hot water and2M KC1were not significant in0—10cm and10—20cm soil layers in all sample years (year9,12and15,P>0.05). The soil dissolved total N concentrations extracted by water and hot water in the two soil layers were significant greater in double residue plots than in other three treatments plots that not included stem only harvest plots at year12(P<0.05). No significant impacts on soil dissolved N concentrations extracted by three methods were found at year9and year15(P>0.05). There were not significant differences in light fraction organic C concentrations between treatments plots in0—10cm soil layer in all sample years (P>0.05). While in10—20cm soil layer, light fraction organic C concentrations in double residue plots and stem only harvest plots were significant higher than whole tree harvest plots, whole tree harvest plus forest floor removal plots and burning residue treatments at year9(P<0.05), then the differences in other sample years were not significant (P>0.05). There were no significant effects of harvest residue management on mineral N concentrations in any depth of soil layers in all the three sample years (P>0.05). Analysis of repeated-measures ANOVA showed that harvest residue management treatment have significant effects on hot water extracted N concentrations in0—10cm and10—20cm soil layer, while there were no significant effects on C or N concentrations with other extracted methods.At year15, repeated measures ANOVA showed that after15years harvest residue management had little effects on Rs rate, soil temperature and soil moisture in the whole year or four different seasons. Soil respiration displayed obvious seasonal dynamics, with the maximum in June2012(3.09μmolCO·m-2·s-1, averaged from five treatments) and the minimum in February2012(0.69μmolCO·m-2·s-1). Soil temperature was found to be the most predominant factor controlling the temporal pattern of soil respiration, accounting for55.8%—72.6%seasonal variations in Rs rate. There were no significant differences in temperature sensitivity of Rs (Q10) and annual soil CO2emission among treatments, and the mean values of five treatments were2.14and701.17gC· m-2, respectively. Harvest residue treatment had no significant effects on dissolved organic carbon (DOC) concentrations (0—10cm depth) extracted by water, hot water and2M KC1. DOC concentrations extracted by water and2M KC1were correlated positively with mean annual Rs rate and the Rs rate in the given month when soil samples were collected, respectively.The results indicated that harvest residue management had no significant effects on soil C and N pools in Chinese fir plantations in subtropical China. |
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