The Effects Of Carbon Stocks And Soil Carbon Cycle In Ginkgo Agroforestry Systems

There is a widespread interest in increasing carbon sequestrations by forest andagricultural production operations. Agroforestry systems are very important to carbonsequestrations and cycle. We compared the impacts of four Ginkgo agroforestry systems and areference system (a conventional agrosystem with a sequential rotation of wheat and peanuts;WP), on a variety of total carbon stocks, soil carbon cycle systems, and some factors of cycleprocesses, then analyzed the factors of soil cycle processes and carbon stocks by path analysis.The objectives of this study were to investigate the processes of carbon cycle, and evaluate thepotential carbon sequestration of Ginkgo agroforestry systems. The four agroforestry systemswere: Gingko, wheat and peanut (GWP); Gingko, rapeseed and peanut (GRP); Gingko andmulberry (GM); and Ginkgo fallow system (GNT). The results showed that:1The different Ginkgo agroforestry systems and ages significantly affected Ginkgo andcrops biomass and carbon stocks. The biomass carbon stocks in agroforestry systems weresignificantly higher than WP systems, and increased with the system age. In2012, there was nosignificantly different biomass carbon stock among Ginkgo agroforestry systems, and they stillhigher than agriculture systems.2Significant soil carbon stocks and litter carbon stocks were found in different Ginkgoagroforestry systems, and they were both significantly higher in agroforestry systems than WPsystems. GM systems had significantly higher soil carbon stocks than other Ginkgoagroforestry systems. In soil0-20cm layer, soil carbon stocks in Ginkgo agroforestry systemsincreased with the system age, while the trends of litter carbon stocks were different inagroforestry systems. After5years, the litter carbon stocks in GNT systems were significantlyhigher than other systems.3The total carbon stocks in Ginkgo agroforestry systems increased with the system age.Significantly higher total carbon stocks were found in agroforestry systems than WP systems.The proportion of soil carbon stocks was highest in all systems. From the path analysis, the soilcarbon stock is the key factor of total carbon stock.4Different litter types and compositions significantly affected the litter decomposition rate.The litter residual rates in different agroforestry systems were changed with the system age, butthey all significant lower than WP systems. Significantly higher litter carbon releases werefound in agroforestry systems than WP systems. The trends of litter carbon releases weredifferent in different systems, while they increased with system age in GM and GNT systems.In2012, GNT systems had significantly higher litter carbon releases than other systems.5The different agroforestry systems significantly affected soil total respiration, microbialrespiration, and roots respiration, and these indexes were significantly higher in agroforesteysystems than in WP system during the year of2008-2012. Soil total respiration and microbial respiration increased with system age in Ginkgo agroforestry systems. However, the trends ofroots respiration were different among different Ginkgo agroforestry systems. After5years, theGNT system had the highest soil total respiration, microbial respiration, and roots respiration.6A lot of soil carbon was sequestrated in Ginkgo agroforestry systems every year. The soilcarbon sequestration and carbon retention of agroforestry systems also grew with growth ofGinkgo. However, in the early years of fallow, a lot of soil carbon was lost in Ginkgoagroforestry systems. GM systems had the best soil carbon retention, and these systems alsoincreased carbon stocks.7Within5year, the trends of soil organic carbon and fractions were different amongdifferent systems. They were decreased in early years, and then increased. Except readyoxidized carbon fractions, soil organic carbon and other carbon fractions were increased withsystem age. After18agroforestry system, except soil inorganic carbon and heavy fractionsorganic carbon, other organic carbon and fractions were significantly higher in Ginkgoagroforestry systems than in WP systems.8The enzyme activity of cellulose and lignin, and xylanase activity were significantlyhigher in Ginkgo agroforestry systems than in WP systems. Within5years, endo-1,4-β-D-glucanase, laccase, and xylanase activity in GWP, GRP and GM systems were increasedwith systems age, while exo-1,4-β-D-glucanase, lignin peroxidase, Manganese peroxidase,laccase and xylanase activity in GNT systems were also increased with systems age. However,the endo-1,4-β-D-glucanase and β-D-glucosidase activity were decreased in early years, andthen increased.9Significant higher soil microbial biomass carbon, soil basal respiration, and totalmineralized carbon were found in Ginkgo agroforestry systems than WP systems, and theysignificantly increased with the system age in GWP and GRP systems. Besides, In GNTsystems, they decreased at early years, and then increased. After5years, GNT had thesignificantly higher soil microbial biomass carbon and soil basal respiration than other systems.The WP systems had significantly higher metabolic quotient than other systems, but themicrobial quotient was lacked regularity.In summy, Ginkgo agroforestry systems increased biomass carbon stocks, litter carbonstocks, and soil carbon stocks, and it also increased litter compositions and microbialrespiration, soil organic carbon fractions, enzyme activity, and soil biological activity. InGinkgo agroforestry systems, the light fraction organic carbon, lignin peroxidase activity, andsoil microbial biomass carbon are the the key factor of litter carbon releases; the dissolvedorganic carbon, laccase activity, and soil microbial biomass carbon are the key factor of soilmicrobial respiration; the ready oxidized carbon, xylanase activity, and total mineralized carbonare the key factor of soil carbon retention.