| In order to clarify the influence of different tree species composition on soil carbon storage and stability,3 forest type,Populus euramericana forest,P.euramericana and Ligustrum lucidum mixed forest,as well as P.euramericana and Photinia serrulata mixed forest with the same age under the same site conditions in Zhoutie Town,Yixing City,Jiangsu Province,were selected as the research objects.The content of soil active carbon fractions and soil carbon storage in different seasons and different soil layers(0?20cm,20?40cm and 40?60cm)were measured.Combined with soil enzyme activity,physical and chemical properties and other indicators,the influencing factors of soil active carbon fractions and carbon storage were analyzed.It is expected to provide a scientific basis for the improvement of carbon storage and carbon stability of the forest ecosystem and the sustainable management of poplar plantations.The main findings are as follows:(1)The content of dissolved organic carbon in the soil under the composition of 3 tree species was between 30.21?124.70mg·kg-1,expressed as P.euramericana and L.lucidum mixed forest>P.euramericana fores t>P.euramericana and P.serrulata mixed forest,the seasonal change was spring>summer>autumn>winter;readily oxidized organic carbon content between2.09?7.51g·kg-1,the performance was P.euramericana and P.serrulata mixed forest>P.euramericana fores t>P.euramericana and L.lucidum mixed forest,and the seasonal changes were spring>autumn>summer>winter;the microbial biomass carbon content was between435.24?999.49mg·kg-1,which was P.euramericana and P.serrulata mixed forest>P.euramericana and L.lucidum mixed forest>P.euramericana forest,the seasonal change was autumn>summer>spring>winter.The content of the 3 carbon fractions all showed a downward trend with the increase of soil layer,showing surface aggregation.Compared with P.euramericana forest,the two mixed forests significantly reduced the dissolved organic carbon content in the 0?20cm soil layer in summer,significantly reduced readily oxidizable organic carbon in the 20?40cm soil layer in spring,the 0?20cm soil layer in autumn,and the 40?60cm soil layer in winter.The content significantly increased the dissolved organic carbon and microbial biomass carbon in the 3 soil layers in summer,and the microbial biomass carbon in autumn.Compared with P.euramericana and L.lucidum mixed forest,P.euramericana and P.serrulata mixed forest significantly reduces the dissolved organic carbon content of the 3 soil layers in spring,autumn and winter,significantly increases the oxidizable organic carbon content in the 0?20cm soil layer in summer and winter,and significantly increases the 3 soil layers in spring,summer and winter,microbial biomass carbon content in winter(P<0.05).Under the composition of 3 tree species,the proportion of dissolved organic carbon to organic carbon was between 0.40?1.94%,expressed as P.euramericana and L.lucidum mixed forest>P.euramericana forest>P.euramericana and P.serrulata mixed forest,seasonal changes are expressed as high in summer and low in winter,and the proportion of readily oxidizable organic carbon and microbial biomass carbon were between 19.31?87.87%and4.62?10.52%,the expression was P.euramericana forest>P.euramericana and L.lucidum mixed forest>P.euramericana and P.serrulata mixed forest.Compared with P.euramericana forest,the two mixed forests significantly reduced the proportion of readily oxidizable organic carbon and microbial biomass carbon in the 3 soil layers in spring,autumn and winter.Compared with P.euramericana and L.lucidum mixed forest,P.euramericana and P.serrulata mixed forest significantly reduces 3 soil layers,the proportion of dissolved organic carbon,readily oxidizable organic carbon and microbial biomass carbon in the four seasons.(2)The soil carbon storage under the 3 tree species composition was between 106.81 and416.76 t·hm-2,which was represented by P.euramericana and P.serrulata mixed forest>P.euramericana and L.lucidum mixed forest>P.euramericana forest.P.euramericana forest seasonal changes of soil carbon storage were winter>spring>autumn>summer,P.euramericana and L.lucidum mixed forest autumn>spring>winter>summer,P.euramericana and P.serrulata mixed forest appears as spring>autumn>summer>winter.Compared with P.euramericana forest,P.euramericana and L.lucidum mixed forest significantly increased the soil storage in 3 soil layers in spring and winter,as well as soil storage in autumn by 20?40cm soil layer;P.euramericana and P.serrulata mixed forest significantly increased the soil carbon storage of 3 soil layers in four seasons(P<0.0.5).(3)Under the composition of 3 tree species,soil total nitrogen,total phosphorus,carbon-nitrogen ratio,microbial biomass nitrogen,nitrate nitrogen,pH and water content were respectively betweem 0.30?2.03g·kg-1,207.27?412.75mg·kg-1,between 7.74?12.67,3.95?12.06mg·kg-1,5.20?10.23mg·kg-1,5.30?6.93 and 19.05?26.03%;soil invertase,urease and dehydrogenase activities were betweem 2.26?6.97 mg·g-1·24h-1,2.44?10.27mg·g-1·24h-1and40.78?168.50 mg·g-1·24h-1,litter carbon content was between 382.69?468.65g·kg-1.Compared with P.euramericana forest,P.euramericana and L.lucidum mixed forest total nitrogen,microbial biomass nitrogen,water content,invertase,urease,dehydrogenase activity and litter carbon content increased by 1.94%,11.24%,11.18%,1.36%,3.00%,22.73%,50.36%and 2.92%,total phosphorus,carbon-nitrogen ratio,nitrate nitrogen,pH decreased by 3.67%,12.01%,11.87%and 4.03%;P.euramericana and P.serrulata mixed forest Total nitrogen,microbial biomass nitrogen,invertase activity litter carbon content increased by 72.61%,24.03%,7.80%and 5.37%,total phosphorus,carbon-nitrogen ratio,nitrate nitrogen,pH,water content,urease and dehydrogenase decreased by 3.40%,17.68%,24.34%,21.19%,11.09%,0.27%,18.71%and 7.97%.The analysis results show that the content of soil dissolved organic carbon was extremely significantly positively correlated with dehydrogenase activity,nitrate nitrogen content,and soil moisture content.The oxidizable organic carbon of soil was extremely significantly negatively correlated with urease activity and pH,and was correlated with invertase activity significantly positive correlation.Soil microbial biomass carbon has a very positive and significant positive correlation with soil total nitrogen,total phosphorus and microbial biomass nitrogen,and a very significant negative correlation with soil carbon to nitrogen ratio.Litter layer carbon content,soil total nitrogen,total phosphorus,and invertase activity are the main factors for changes in soil carbon storage.In summary,due to the influence of enzyme activity,pH,litter carbon content and other factors,compared with P.euramericana forest,P.euramericana and L.lucidum mixed forest as well as P.euramericana and P.serrulata mixed forest increases the soil carbon storage,reduces the proportion of soil active carbon,and improves the stability of the soil organic carbon pool. |
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