| Eucalyptus have been large-scale cultivated in the south of China. With the rapidlydevelopment of eucalyptus plantation, a great of economic benefits have been brought to thesocial, however, lots of ecological problems have been emerged because of irrationallymanagement practices. Soil respiration is the CO2efflux from the surface of soil, which playsan important role in determining whether an ecosystem is a carbon sink or source to theatmosphere. A good understanding of the dynamic changes and mechanisms underlying soilcarbon inputs or outputs will help us to better describe and estimate the global land carbonbudget. However, the effects of forest management on stocking and stability of soil carbon areuncertainty.The experimental site is located at the Experimental Center of Tropical Forestry, theChinese Academy of Forestry, Pingxiang City, Guangxi Zhuang Autonomous Region, PR.China. Based on the similar topography, soil texture, and stand management history, thefollowing four experimental stands were selected, i.e., the first pure rotation ofEucalyptusplantation(PP1), the mixed plantation of the first pure rotation of Eucalyptus andAcacia mangium(MP1), the second pure rotation of Eucalyptus plantation (PP2) and the mixedplantation of the second pure rotation of Eucalyptus and Dalbergia odorifera(MP2). Usingelemental anaysis, Li-COR infrared gas analysis, PLFA and substrate method, The fouradjacent plantations were selected to (1) examine the seasonal dynamics and the effect fators ofthe differrent rotations of pure eucalyptus plantations and the eucalyptus mixed with N-fixingspecies;(2) determine the differences and the effect factors of annually cumulative respirationcomponents between pure and mixed plantations;(3) explore the effects of N-fixing treespecies on microbial biomass C and microbial community composition and key soil biotic andabiotic properties influencing the microbial community composition;(4) understand the enzyme activity and the effect factors under different eucalyptus plantations. The main resultsare as follows:(1) Temporal variations of RSand the different components of soil respiration rate of thefour forests largely depended on soil temperature at5cm depth (T5). The maxium value ofrespiration rate appears between June and August, and the minimum value of respiration rateappears between December and January. In MP2forest, soil water content (SWC) had a weaknegative effect on the temporal variation of RS, while there is no correlation between SWC andthe other three forests.(2) Plot trenching experiments were conducted to partion soil respiration components inthe different eucalyptus plantations (PP1and MP1, PP2and MP2) in Subtropical of China.Total soil CO2efflux (RS) was partitioned into rhizospheric (RR) and heterotrophic respiration(RH)across2012. It was found that the temperal that the temporal variations of RRand RHcouldbe well explained by soil temperature at5cm depth (T5) using exponential aquation. Therewere significant differences in the RS, RRand RHduring annual gross among the fourplantations. The estimated RS, RRand RHvalues for PP1averaged1106.47g C m-2,693.13g Cm-2and413.34g C m-2respectively, and the estimated RS, RRand RHvalues for MP1averaged968.66g C m-2,403.99g C m-2and564.66g C m-2respectively. While their correspondingestimated RS, RRand RHvalues for PP2averaged1147.41g C m-2,506.72g C m-2and640.69g C m-2respectively, and the estimated RS, RRand RHvalues for MP2averaged844.08g C m-2,136.87g C m-2and707.21g C m-2. The estimated RCincreased from37.54%in the PP1to58.25%in the MP1, and increased from56.03%in the PP2to83.94%in the MP2. There wassignificant correlation between total organic carbon(TOC) of litterfall, fine root biomass(FR),C:N ratio of litterfall and RSand RR. However, there was just significant relationship betweenRHand the C:N ration of litterfall.The apparent temperature sensitivity (Q10) of RRand RHwere not different between PP1and MP1. However, the Q10of RRwas significantly higher inMP2than PP2. (3) The microbial biomass and communitycomposition were significantly differentbetween PP1and MP1. The total PLFAs in MP1, which was described as the microbialbiomass, was27.56%higher in the dry season and21.86%higher in the wet season than PP1.Thebiomass of bacterial, actinomycetes and arbuscular mycorrhizal fungi(AM) weresignificantly higer in MP1and MP2than the corresponding pure plantations PP1and PP2.However, the biomass of fungi in the mixed plantations were significantly lower than the pureplantations. The microbial biomass was significantly higer in the MP1than PP1, however therewas higher but not sinificant microbial biomass in MP2than PP2. After eight years of mixingwith N-fixing species (Acacia mangium), MP1significant increase the relative abundance ofbacteria, Gram-negative bacteria and arbuscular mycorrhizal fungi but decrease the relativeabundance of fungi. And after four years of mixing with N-fixing species (Dalbergiaodorifera), MP2significant increase the relative abundance of bacteria, but decrease therelative abundance of fungi. Redundancy analysis (RDA) indicated that the changes of themicrobial biomass and community composition were attributed to the changes of the quantityand quality of litterfall, the physical and chemical properties of soil especially for Navailabilitycaused by introduce the mixing N-fixing tree species. Mixing with N-fixing speciescould increased C accumulation and enhance the C stability though changing the microbialbiomass and community composition in the soil.(4) After eight years of mixing with N-fixing species (Acacia mangium)(MP1), there wassome influence on the enzymes activity of soil. Mixing with N-fixing (MP1) species canmarkedly increase the hydrolytic enzyme (β-glucosidase) but no difference for other threeenzyme activity at the dry season. At the wet season, hydrolytic enzyme (β-glucosidase)activity was significant increase but the oxidase enzymes (phenol oxidase and peroxidase)activity were significant decrease in MP1. After four years of mixing with N-fixing species(Dalbergia odorifera)(MP2), the trend of the effects on enzymes activity of soil was similarwith MP1. It was found that mixing with N-fixing species can markedly influence on theenzymes activity of soil. Which may because of the increase the soil carbon content and the available of nitrogen and then changing the microbial biomass and community composition inthe soil by the N-fixing species. Mixing with N-fixing species(MP1and MP2) can significantincrease the biomass and relative abundance of bacteria but markedly decrease the biomass andrelative abundance of fungi meanwhile markedly influence the related enzymes activity. It waspartly explain the enzymes activity mechanism about soil carbon accumulation and stability in. |
PDF Full Text Request