Effects Of Precipitation Exclusion And Nitrogen Deposition On Arbuscular Mycorrhizal Fungi And Fine Root In Cunninghamia Lanceolata Plantation

Mycorrhizal fungi and fine roots are two important ways for plants to obtain soil moisture and nutrients.The interaction process of plant roots-soil-microbes and their ecological feedback effects are becoming increasingly important.Chinese fir plantations play an important role in China's forestry production,forest carbon sink and mitigation of global climate change.At present,there is no consensus on how to affect arbuscular mycorrhizal fungi(AMF)and fine roots in subtropical Chinese fir plantations and the relationship between them under the conditions of precipitation exclusion and nitrogen deposition.Therefore,this study selected Chinese fir plantation as the research object,and set up four treatments: control(CT),nitrogen deposition(N),precipitation exclusion(PE),precipitation exclusion and nitrogen deposition interactions(PEN),to study the effects of precipitation exclusion and nitrogen deposition and its interaction on AMF and fine roots morphological structure in Chinese fir plantations.We also discussed the main factors that caused the differences in climate change,in order to reveal the adaptation mechanism and survival strategies of Chinese fir plantations to climate change.The results show that:1.Precipitation exclusion treatment and precipitation exclusion-nitrogen deposition interaction significantly reduced the infection rate of AMF in summer(P<0.05);Precipitation exclusion treatment significantly increased summer mycelium density by 33.1%(P<0.05);Precipitation exclusion,nitrogen deposition and their interaction all significantly increased the spore density(P<0.05);Precipitation exclusion treatment significantly reduced the content of easy-to-extract glomalin by23.1% in winter(P<0.05).Compared with soil microbial community structure,soil physical and chemical properties had a greater influence on AMF,and TN,TP and AP were the main factors affecting AMF.2.Nitrogen deposition treatment significantly increased the second-order root growth by 52.3%(P<0.05),precipitation exclusion and nitrogen deposition interaction significantly reduced primary root growth by 49.2%(P<0.05).Precipitation exclusion and nitrogen deposition had no significant effects on fine root diameter,specific root length and tissue density;Nitrogen deposition significantly reduced the specific surface area of primary and secondary roots in winter(P<0.05).Redundancy analysis showed that water content was the most important explanatory variable for the change of fine roots morphological structure index,with an explanation degree of 24.3%.3.Among the indicators of AMF,the infection rate had the least correlation with the morphological structure of fine roots,while the spore density and easy-to-extract glomalin had a greater correlation with fine roots.Under the treatment of nitrogen deposition,the spore density and hypha density of AMF had greater plasticity,and significantly reduced the specific surface area and root biomass of fine roots.Therefore,under the treatment of N deposition,plants mainly relied on AMF to absorb soil nutrients.Under the treatment of precipitation exclusion,the specific root length and easy-to-extract glomalin showed negative moderate plasticity to precipitation exclusion in winter,and the specific root length,spore density and hypha density showed positive moderate plasticity to precipitation exclusion in summer.The results indicated that on the one hand,plants expand the absorption area and accessibility by increasing the mycelium density,on the other hand enhance the absorption of water,improve the spatial expansion ability of fine roots.Under the treatment of precipitation exclusion and nitrogen deposition interaction,the effect of precipitation exclusion in winter was not significant.The specific root length and specific surface of the fine roots showed negative moderate plasticity to the interaction of precipitation exclusion and nitrogen deposition interaction.The nutrients and water absorbed by the roots could meet the requirements of plant growth and reduced the dependence on AMF.Precipitation exclusion significantly reduced the soil moisture content in summer.The ratio of fine root length,AMF spore density,infection rate and easy-to-extract glomalin exhibited moderate plasticity to the interaction of Precipitation exclusion and nitrogen deposition.Plants were more dependent on more on the construction of low-cost hyphae to increase the absorption area and absorption space of host plants.