Effects Of Understory On Soil Microbial Properties In Poplar Plantations

Poplar plantation has great demands for nutrients during its growth.Therefore,ensuring nutrient cycling and nutrient supply is important for maintaining the productivity.Previous studies have shown that tree species mixing can,to a certain extent,improve the nutrient supply of forest site by changing the quality and quantity of litter,thus affecting the community structure and functional characteristics of soil microorganisms in forest site,as well as the decomposition process of litter and the transformation of soil nutrients.However,the selection and management of tree species in mixed forests are very complex,and the benefit of mixed forests could only be achieved after a long time scale.Understory vegetation is the important component of pure plantations.It was previously thought that the understory will compete nutrients/water with poplar under the traditional forest management,so it was often controlled or removed from the plantations to avoid competition.However,with the in-depth study on the function of understory recently,some researches proved positive effect of understory on maintening site productivity,what is similar to the functions of tree species mixing to a certain extent.Compared with mixed plantations,understory in the pure plantations usually has much higher diversity.However,it is still not clear whether higher diversity of understory corresponds to better ecological function,and whether it has better effect on site productivity.This paper takes the pure poplar forest with of hybrid 'Nanlin 3804' as the research object,sets sample plots in the forest,adjusts the species and diversity of understory by means of artificial control,and explores the effects of the presence,species and diversity of understory on soil microbial community structure,diversity and function;at the same time,studies the litter and poplar of different types and diversity of understory combined with indoor cultivation methods.Changes of soil microbial community structure and metabolic function during mixed decomposition of deciduous trees were studied,and their roles in soil nutrient transformation and cycling were discussed.The results showed that the existence of understory,the types of understory and the diversity of understory had regular effects on soil nutrient characteristics,enzyme activity characteristics and microbial community function characteristics at different growth stages of poplar.There were significant differences among the treatments in 0-5 cm soil layer.1)Compared with the treatment of clearing understory,the existence of diversified natural understory had no significant effect on the total carbon and total nitrogen of poplar soils at the peak of leaf development(June),rapid growth(August)and defoliation(November).However,the contents of inorganic nitrogen and available phosphorus in 0-5 cm soil layer decreased significantly,while the contents of soil microbial biomass carbon,nitrogen,arylamidase activity and soil microbial metabolic capacity to carbon sources increased significantly.Soil microbial biomass nitrogen was 2.58,1.36 and 1.78 times as much as that of vegetation removal in three periods.2)Compared with the single understory treatment(barnyard grass),the diversity of natural understory treatment also increased significantly in soil microbial biomass carbon,microbial biomass nitrogen content,arylamidase activity and carbon source metabolic capacity in 0-5cm soli layer,among which the arylamidase activity was 1.10 and 1.18 times of that of single understory treatment,respectively.3)Compared with the two single understory vegetation treatments,the total soil,microbial biomass and carbon utilization capacity of poplar were different in different growth stages.Among them,in 0-5cm soil layer of poplar rapidgrowth periodr,the total nitrogen content and inorganic nitrogen content of sesbania-planted forest soil were 3.92% and 42.18% higher than that of barnyard grass,respectively,and the arylamidase activity of soil was 1.14 times higher than that of barnyard grass soil.In addition,in terms of soil microbial bacteria and fungi species and diversity,natural understory can significantly increase the species and diversity of soil bacteria and fungi,but the diversity of understory has not significantly improved soil microbial diversity,and the change of understory types has no significant impact on soil microbial community structure.The results of indoor litter mixed decomposition also showed that although there were differences in different periods,the existence of various natural litters could significantly increase soil available nutrients,soil decomposition enzyme activity,microbial biomass and carbon metabolism,and the species,diversity and evenness of soil bacteria and fungi were improved.The results of mixed decomposition of litter species of different understory showed that alfalfa,as a nitrogen-fixing plant,could promote soil nutrients,soil microbial biomass,enzyme activity,carbon metabolism and soil bacterial fungi species in the process of litter decomposition.Thus,understory vegetation can promote soil nutrients,soil microbial community structure,enzyme activity,metabolic function,etc.The higher the diversity,the better the effect,and the addition of nitrogen-fixing plants also has a significant role in promoting.