| Cunninghamia lanceolata is one of the most important species of fast-growing timber in the south of China,facing the problem of land degradation and productivity unsustainable.Understory vegetation and litter are important components of forest ecosystem.Understory is traditionally considered to compete nutrients and water with the trees,and it was always removed,however,its specific functional ecological is still unclear.Litter decomposition is the key source of soil nutrients,how litter accumulation affect soil ecological process is the research hotspot.In this study,four treatments with four replicates were carried out under the conditions of understory vegetation removal(UR),litter addition(LA),litter addition and understory vegetation removal(LUR)and control(CK).Soil nutrients,litter decomposition,soil respiration and nitrogen mineralization were measured to detect how understory removal and litter addition affect soil key ecological process.The main results are as follows:(1)Understory removal(UR)significantly decreased soil: total nitrogen(P=0.021),total phosphorus(P=0.009)and available carbon content(P=0.013);UR decreased soil fungi PLFAs(P=0.02).Litter addition(LA)increased soil organic carbon(P=0.003),inorganic nitrogen content(P<0.001)and soil pH(P=0.007);LA significantly increased fungi PLFAs(P=0.007)and the ratio of fungi / bacteria(P<0.001).The interactive effect of understory removal and litter addition significantly increased soil bacteria PLFAs(P=0.035),total microbial biomass(P=0.04)and soil organic carbon content(P=0.013).(2)Both UR and LA significantly inhibited litter decomposition rate,and the inhibition of UR was stronger than that of LA.In the process of litter decomposition,the concentration of phosphorus was always enrich,and the residual amount of phosphorus was higher than that of the initial value at the decomposition days of 480.The concentration of nitrogen shows a mode of alternate fluctuation of release enrichment.The residual nitrogen was about 83% related to the initial content under UR treatment leaf litter at the days of 480.in the processes of twigs litter decomposition,the residual nitrogen content was higher than the initial value under UR and LA treatments.The carbon content in residual leaf litter was between 26.16%-31.04%,and in residual amount of twig was between 40.31%-49.75%.(3)UR significantly increased soil respiration rate,soil respiration and heterotrophic respiration increased by 33.13% and 14.91%,respectively.LA significantly reduced the total respiration rate by 17.95%.The proportion of root respiration to total respiration was UR(41.85%),CK(32.32%),LA(16.6%)and LUR(14.92%).(4)UR did not significantly affect nitrogen mineralization rate.LA significantly increased ammonification rate and nitrogen mineralization.The interactive effect of UR and LA significantly increased soil nitrogen mineralization.In general,UR decreased soil nutrients content,fungi PLFAs,then inhibited litter decomposition and nutrient return rate,we recomment that in Cunninghamia lanceolata plantation,understory plants should not be removed.Litter addition suppressed litter decomposition and soil respiration rate,we assume that under the condition of global change increased litter biomass,more carbon would be sequested in forest ecosystems. |
