Effects Of Afforestation On Soil Organic Carbon And Nutrient Content In Different Trees Of Mid-subtropical China

In order to explore the influence of tree species on soil nutrient,we investigated Castanopsis carlesii,Michelia macclurei,Pinus massoniana and Cunninghamia lanceolata plantation in a common garden after 5 years afforestation in Geshikao Nature Reserve in Fujian Province of China.(1)Our studies showed that the afforestation had no obvious effect on soil organic carbon(SOC),total nitrogen(TN),and total phosphorus(TP)(P<0.05).The effects of tree species on soil processes need to be studied in the time scale of soil organic matter for the turnover of fine roots and litter is a long process.(2)In 5 years of afforestation,the soil available phosphorus of M.macclurel,C.carlesii,P.massoniana and C.lanceolata decreased 41.97%,63.53%,47.17%and 50.16%respectively,and the content of available phosphorus of 4 species of trees significantly decreased after afforestation(P<0.001).The content of potassium ion(K+)in the soil of M.macclurel,C.carlesii,P.massoniana and C.lanceolata decreased 10.18%,27.17%,17.76%and 30.72%,respectively(P<0.001).The content of K+ in the soil of Castanopsis carlesii decreased significantly(P<0.05),and the content of K+ in the soil of C.lanceolata was extremely significantly decreased(P<0.001).The calcium ion(Ca2+)content of M.macclurel and P.massoniana increased 24.40%and 1.32%respectively.The content of Ca2+ in the soil of C.carlesii and C.lanceolata decreased by 50.39%and 67.57%respectively.The contents of Mg2+ in M.macclurel,P.massoniana,C.carlesii and C.lanceolata decreased 33.42%,56.01%,49.61%and 80.97%,respectively.The content of magnesium ions(Mg2+)in the soil of M.macclurel and P.massoniana significantly decreased(P<0.05).The content of Mg2+ in the soil of C.carlesii and C.lanceolata extremely significant decreased(P<0.001).The results show that afforestation has a great influence on the rapid nutrient elements,and the growth of trees and leaching are the main reasons for the decrease of such nutrient elements.In addition,the content of cation exchange capacity in all four s tree species significantly decreases(P<0.05).The results indicated that nutrient elements(e.g.nitrogen,phosphorus and potassium)were easily lost in the short-term afforestation process.The content of available nitrogen,available P and available K were low,which may be the limiting factor of forest growth.In the seedling stage,the application of appropriate nitrogen fertilizer,phosphate fertilizer and potassium fertilizer would increase the content of available nitrogen,available P and available K,which may be conducive to the growth of forest trees.(3)After five years of afforestation,the dissolved organic carbon(DOC)of broadleaf trees soil was significantly higher than that of coniferous trees(P<0.01),and the dissolved organic nitrogen(DON)of the M.macclurel soil was significantly higher than other three tree species(P<0.01).Leaching of litter and soil microbial activity were the main reasons for the difference of soil.It was beneficial to the accumulation of soluble carbon and soluble nitrogen in soil in M macclurei in afforestation.(4)Soil microbial biomass carbon(MBC),microbial biomass nitrogen(MBN)and microbial biomass phosphorus(MBP)content were the highest in M.macclurel and the lowest in C.lanceolata.The size of soil microbial biomass depended greatly on soil DOC content,and there were closely related between MBC,MBN and MBP.The PLFA content of Chinese fir was lowest,because there was a small amount of nutrients released into the soil.There was no significant difference between GP:GN and F:B in the soil of different tree species,indicating that there was no significant difference in carbon structure between the 4 tree species.It proveed that the effect of different tree species on soil organic carbon in the process of afforestation was mainly reflected in quantity.On the whole,it was better for the sequestration of soil activated carbon of M.macclurei than that of Chinese fir.(5)The activity of ?G of M.macclurel,C.carlesii and C.lanceolata was significantly higher than that of P.massoniana(P<0.05).The activity of CBH of C.carlesii and M.macclurel soil was significantly higher than that of P.massoniana and C.lanceolata(P<0.05).The activity of NAG of C.carlesii was significantly higher than that of P.massoniana and C.lanceolata(P<0.05).The activity of AP of M.macclurel,P.massoniana and C.carlesii was significantly higher than that of C.lanceolata(P<0.05).DOC and microbial biomass were key factors that drive enzyme activity.The difference of enzyme activity among different tree species showed that broad-leaved trees were more beneficial to the conversion of soil carbon,nitrogen and phosphorus.