Effects Of Herbicides On Plant-Soil-Microorganism Of Eucalyptus Plantations

Herbicides are widely used in Eucalyptus plantations worldwide,but there is a lack of research on the effects of different concentrations and frequencies of herbicide application on biomass,carbon stocks and diversity of Eucalyptus plantations.We established different Eucalyptus plantations in 2015 with different treatments,e.g.manual tending(MT),low-dose high-frequency(LHF),medium-dose medium-frequency(MMF)and high-dose low-frequency(HLF)herbicide application.Then we investigated the community biomass,carbon stocks,plant diversity,soil microorganism and enzyme activity of these Eucalyptus plantations at 33,39 and 51 months after afforestation.The main results are as follows:(1)Herbicides have no significant effects on the biomass and carbon storage of Eucalyptus,but significantly reduced the biomass and carbon storage of understory vegetation.HLF significantly reduced the ecosystem carbon storage.(2)Herbicides have significantly affected the species and functional groups of understory with different effects at different stand age stages.At the 51 months,the dominant species of MT are Miscanthus floridulus,Blechnum orientale and Lygodium japonicum,and the dominant plant functional groups are woody plant functional group(WFG)and vine functional group(VFG),while the dominant species of herbicide treatments are Isachne globosa,Miscanthus floridulus and Blechnum orientale.Moerover,the dominant plant functional groups of LHF,MMF and HLF are different,e.g.gramineae functional group(GFG)and WFG dominated in LHF,GFG and fern functional group(FFG)dominated in MMF,WFG and VFG dominated in HLF,respectively.(3)The effects of herbicides on soil properties were different with the treatments,soil factors and stand ages.The available nutrients were greatly affected,while soil p H,soil organic matter(SOM),total nitrogen(TN),total phosphorus(TP),total potassium(TK)and soil water content(SWC)were not significantly affected.(4)Herbicides have significant effects on the structure and function of soil microbial community,which are related to the treatments and microbial groups.LHF increased the PLFAs content of bacteria and Gram-positive bacteria;MMF increased the PLFAs content of bacteria and Gram-positive bacteria while the PLFAs content of Gram-negative bacteria was inhibited;The content of PLFAs in each microbial community of HLF treatment was the same as that of MT.In the early stage of herbicide application,?-1,4-glucosidase(BG)and N-acetyl-?-glucosaminidase(NAG)were inhibited,while phenol oxidase(PHE)and acid phosphatase(ACP)were promoted.MMF significantly inhibited the activity of peroxidase(PER)and BG,while HLFsignificantly increased the activity of PHE,urease(URE)and ACP.