| As the material basis for human survival and sustainable development,the forest resources services to human society are embodied in the ecosystem multifunction(EMF).And the plantations have expanded rapidly worldwide to meet the growing demand for ecosystem services and avoid excessive deforestation of natural forests.However,the loss of ecosystem multifunctional caused by continuous planting of pure plantations is causing widespread concern in the international community.In recent years,although the advantages of multispecies plantations over single-species plantations have been widely recognized,but little research has been done on ecosystem multifunctionality with the coniferous and broad-leaved tree mixing impact,especially unclear on the mechanism driving these advantages.Moreover,we can't fully elaborate the law and mechanism of the tree species mixing impact on ecosystem multifunction,because most of the current studies are focus on the comparative study of single stand,single or simple functions.In this study,34-years-old plantations of pure Castanopsis hystrix(PCH),pure Pinus massoniana(PPM),and 34-years-old plantations of mixed C.hystrix and P.massoniana(MIX)in the Chinese Academy of Forestry were selected as the research objects.And the effects of mixed coniferous and broad-leaved tree species on ecosystem multifunction were studied by field investigation,systematic sampling,biochemical analysis and comprehensive comparison.At the same time,variance analysis was used to test the difference of ecosystems multifunction between pure plantations and plantations.In addition,regression analysis,redundancy analysis and path analysis were used to reveal the regulatory pathways and mechanisms of above-and under-ground biodiversity on ecosystem multifunctionality.The main results are as follows:(1)The ecosystem multifunction of 34-year-old mixed plantations with C.hystrix and P.massoniana was better than that of 34-year-old pure P.massoniana and 34-year-old pure C.hystrix plantations,because of the ecosystem multifunction index in MIX(2.96)was significantly higher than that in PCH(-0.90)and in PPM(-1.77).(2)The ecosystem multifunctional index increased with the increase of functional richness and evenness on underground microbial community,and there was a significant linear positive correlation between the multifunctional index and diversity.However,different with that between ecosystem multifunction and aboveground plant species diversity,the multifunction of ecosystem increases with the increase of plant richness and Shannon-Wiener index,then decreases with the increase of plant richness and Shannon-Wiener index.Our results suggested that there is a significant trinomial correlation between ecosystem multifunction and aboveground plant diversity.(3)Great influences on the ecosystem multifunction were found by the mixture of C.hystrix and P.massoniana.Tree species mixing can directly or indirectly affect ecosystem multifunction by affecting underground functional diversity and soil Gram-positive bacteria.Tree species mixing can also affect aboveground plant diversity by affecting soil pH,and then directly or through affecting soil Gram-positive bacteria affect ecosystem multifunction.In addition,the difference of LAI among different stands has a negative effect on the ecosystem multifunction,it affects the multi-function of ecosystem by affecting the diversity of underground functions,and also affects the soil Gram-positive bacteria by affecting the diversity of aboveground plants,thus affecting the multi-function of ecosystem.(4)Significant high plant biomass,litter production and qualities were found in 34-yearold plantations of mixed C.hystrix and P.massoniana than in 34-year-old pure P.massoniana and 34-year-old pure C.hystrix plantations.These changes significantly enhanced soil microbial biomass and carbon source metabolism of soil microorganisms in mixed plantations,thus significantly improving the ecosystems multifunction.(5)The same number of species was found in 34-years-old plantations of pure P.massoniana,and 34-years-old plantations of mixed C.hystrix and P.massoniana,which was significantly higher than that in 34-years-old plantations of pure C.hystrix.What worth pointing out is that the original pure P.massoniana plantation has gradually evolved into semi-natural mixed coniferous-broad-leaved plantation after 34 years of stand growth and succession,it dominated by P.massoniana(important value 111.85)and C.hystrix(important value 93.26).On the contrary,the original mixed plantations of C.hystrix and P.massoniana gradually transformed into the mixed coniferous-broad-leaved plantation with C.hystrix dominant(the important value was 182.12)(the P.massoniana important value decreased to 42.85).At the same time,we also found that C.hystrix were dominant in the shrub layers of the three stands,while P.massoniana hardly regenerated naturally under the three stands.Therefore,our results predict that the original pure P.massoniana plantations will further evolve into mixed coniferous-broad-leaved plantations with C.hystrix and P.massoniana if there is no artificial interference or control.And the original mixed plantations of C.hystrix and P.massoniana may evolve into a community dominated by C.hystrix,because P.massoniana will gradually withdraw from the community.(6)The long-term(34a)mixing of C.hystrix and P.massoniana has significant net biodiversity effect,which complementary effect is dominant.And the improvement of single functional index and ecosystem multifunction index in mixed plantations are closely related to the complementary effect. |
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