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Characteristics Of Carbon And Nitrogen In Monoculture And Mixed Young Stands Of Erythrophleum Fordii And Pinus Massoniana In Southern Subtropical China

Posted on:2015-02-25Degree:DoctorType:Dissertation
Country:ChinaCandidate:D LuoFull Text:PDF
GTID:1263330431965872Subject:Ecology
Abstract/Summary:PDF Full Text Request
Plantation is becoming a key component of the world’s forest resources and playing animportant role in the context of sustainable forest management. For a long time, however, inorder to pursuit one-side of economic efficiency, there were many problems existing inplantations at home and abroad, such as the loss of biodiversity, degradation of soil fertility,reduction of ecosystem stability. In subtropical area of China, many indigenous valuablebroadleaf tree species (include nitrogen-fixing tree species) are being developed for theconstruction of plantations in production practice so as to decrease the negative effects whichinduced by inefficient plantations, promoting the multi-purpose management and improvingthe ecological function and economic value of plantations. The research about the impact ofdifferent forest management measures on plantations were mainly concentrated in theeconomic benefit of stand productivity in this region. However, the soil microclimatecharacteristics, physical and chemical properties, as well as soil biochemical process would bedifferent result from the differences of quality and quantity of leaf litter and root, and canopystructure of different plantations. Therefore, exploring the effects of different forestmanagement mode on the characteristics of carbon and nitrogen of plantation ecosystem fromthe ecological function perspective has become extremely necessary. Additionally, Theincrease of CO2concentration and temperature, nitrogen deposition, as well as the phenologicalchange and drought stress could cause the change of forest litter input, therefore, it is soimportant to consider the influence of litter input change in the research of forest soil carbonand nitrogen dynamics.In this study, the experimental site is located at the Experimental Center of TropicalForestry, the Chinese Academy of Forestry, Pingxiang City, Guangxi Zhuang AutonomousRegion, PR. China. Based on the same stand age, similar site conditions and adjacent position,three young experimental stands (a monoculture Erythrophleum fordii, a monoculture Pinus massoniana and a mixed stand of the two species) were selected, and combined with leaf litterinput controlled experiment, by using elemental anaysis, barometric process separation (BaPS)and phospholipid fatty acid (PLFA) methods, to1) examine the carbon and nitrogen storageand spatial distribution of different tree species plantation ecosystems;2) examine the seasonalvariation of soil respiration, gross nitrification and microbial community structure in differenttree species plantations;3) explore the response of soil respiration and gross nitrification rates,as well as soil microbial community structure in different tree species plantations to litter inputchange;4) understand the relationship between environmental factors and soil respiration andgross nitrification rates. So as to provide data references and scientific basis for the tree speciesselection and rational management measures in the plantation management in southernsubtropical China. The main results are as follows:(1) There were differences in the carbon and nitrogen storage among E. fordii, P.massoniana and their mixed plantation stands. The total carbon storage of ecosystems of the E.fordii, mixed plantation stand and P. massoniana stand were134.07t hm-2,137.75t hm-2and131.10t hm-2, respectively. While the total nitrogen storage of ecosystems were10.19t hm-2,8.68t hm-2and7.01t hm-2, respectively. The spatial distribution of carbon and nitrogen poolswere identical across the three plantation stands, with the majority of carbon and nitrogenfound in the upper0-100cm of soil, occupying by an average of81.49%and96.91%of thetotal carbon and nitrogen storage, respectively, followed by above ground biomass representedby the trees, occupying by an average of17.52%and2.69%of the total carbon and nitrogenstorage, respectively, and the understory vegetation and litterfall. Average organic carbonstorage in the top0-30cm soil was52.52t hm-2(occupied47.99%of the total0-100cm),acting as the primary service to the ecosystem. While nitrogen was irregularly distributed insoil. The results showed that mixed plantation stands with a nitrogen-fixing tree speciesshowed a greater capacity for carbon storage in comparison to monoculture stands insubtropical China. The lower above-/underground ratio of carbon and nitrogen suggests thatthese three young plantation stands have a high potential for carbon and nitrogen sequestration. (2) There were significant seasonal variation in the soil respiration and gross nitrificationrates in these three plantation stands (p<0.05). From September2012to January2013(dryseason), soil respiration and gross nitrification rates decreased to the lowest (the averages were2.63mg C kg-1SDW d-1and0.34mg N kg-1SDW d-1, respectively), and then increasedcontinuously until July2013(rainy season)(the averages22.44mg C kg-1SDW d-1and1.23mg N kg-1SDW d-1, respectively). There were significant correlation between soil respirationand gross nitrification rates and soil temperature and humidity (p<0.05), which showed thatsoil temperature and humidity were the key environmental factors in affecting soil respirationand total nitrification rates. Soil total nitrogen, ammonium nitrogen and nitrate nitrogen weresignificantly correlated with soil respiration and gross nitrification rates (p<0.05), whichindicated that soil carbon and nitrogen transformation were influenced by soil microclimateconditions while synthetically affected by other soil environmental factors. In differentplantation stands, soil respiration and gross nitrification rates in the E. fordii were significantlyhigher than those in the mixed plantation and P. massoniana stand significantly (p<0.05),which were mainly attributed to the biological characteristic differences of tree species. Therewere higher quantity and quality of litter and root, and faster decomposition in the E. fordii,which resulted in soil nutrient and substrate availability higher than the other two plantationstands. Compared with other study results, we found that the soil respiration and grossnitrification rates, as well as the Q10might be varied under different forest type, site condition,stand age and climate zone.(3) The amounts of microbial total PLFAs and PLFAs of each microbial group (bacteriaPLFAs、fungal PLFAs、actinomycetes PLFAs and arbuscular mycorrhizal fungal (AMF) PLFAs)in these three plantation stand soils were significant higher by an average of170.1%、182.1%、152.1%、232.5%and185.2%in dry season than those in rainy season, respectively (p<0.05). Indry season, the amounts of microbial total PLFAs, bacterial PLFAs, fungal PLFAs, andactinomycetes PLFAs were the highest in the P. massoniana soil, then in the mixed plantationsoil, and the lowest in the E. fordii soil. But the amounts of microbial total PLFAs, bacterial PLFAs, fungal PLFAs, and AMF PLFAs in the E. fordii soil were higher than those in the P.massoniana soil significantly in rainy season (p<0.05). Principal component analysis (PCA)indicated that the variations in soil microbial community structure composition were affectedby both plantation types and seasons. Redundancy analysis (RDA) of soil microbialcommunity structure and environmental factors showed that soil temperature, soil moisture, pH,total nitrogen content, and ammonium nitrogen content had significant correlations withindividual PLFA signatures (p<0.05), which indicates that the changes of soil microbialcommunity structure were attributed to the changes of the soil microclimate conditions, thequantity and quality of litter and root, and the physical and chemical properties of soil,especially for soil nitrogen content, caused by constructing of different plantation stands. Inaddition, the ratio of fungal PLFAs to bacterial PLFAs within the whole year (dry and rainyseason) in the mixed plantation soil (0.27and0.31respectively) was significant higher thanthat in the P. massoniana (0.26and0.28respectively) soil and E. fordii soil (0.22and0.26respectively)(p<0.05), indicating that mixed plantation stands could facilitate more improvingthe stability of the soil ecosystem.(4) There were significant seasonal variation in the soil respiration and gross nitrificationrates in different leaf litter treatments in E. fordii and P. massoniana, and soil respiration in theE. fordii and P. massoniana was7.12and6.07times in the rainy season as much as those inthe dry season, respectively, while gross nitrification was3.37and3.89times in the rainyseason as much as those in the dry season, respectively. Early in the leaf litter treatments(September and November2012), the soil respiration and gross nitrification rates decreasedwith the thickening of leaf litter in these two plantation stands, which mainly attributed todifferent soil temperature. With the leaf litter treatments extended to2013, the soil respirationand gross nitrification rates increased with the thickening of leaf litter, which mainly related tosoil nutrient and substrate availability. Litter leaf removal in the E. fordii and P. massonianadecreased the soil respiration by an average of3.59%and2.68%, whereas litter leaf additionincreased it by14.08%and26.54%compared with the control, respectively. Soil gross nitrification in the E. fordii and P. massoniana were lower by an average of11.52%and17.67%in litter leaf removal, whereas it higher by9.69%and2.22%in litter leaf addition thanthat in control, respectively. Correlation analysis revealed that the soil respiration and grossnitrification rates were combinedly affected by environmental factors of soil temperature,moisture, total nitrogen, ammonium nitrogen and nitrate nitrogen. Different leaf litter inputwould affect soil microclimate characteristics and drove the variation of microbial communitystructure. The RDA showed that soil microbial community structure in E. fordii mainlyinfluenced by soil temperature and ammonium nitrogen content, while soil temperature andnitrate nitrogen content were the major environmental factors regulating soil microbialcommunity structure in P. massoniana, these suggests that there were different environmentalfactors in different plantation stands that affected the soil microbial community structure.Microorganisms as a key driver of soil nutrient cycling, its response to the change of leaf litterinput would affect the soil carbon and nitrogen transformation. Whether leaf litter was removedor added, the correlation analysis suggested that most of signature PLFAs had a significantimpact on soil carbon and nitrogen transformation.
Keywords/Search Tags:carbon and nitrogen storage, soil respiration, soil gross nitrification, microbialcommunity structure, barometric process separation (BaPS), phospholipid fatty acid (PLFA), leaf litter input, plantation, southern subtropical China
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