Sexual Differences In Litter Decomposition Characteristics As Well As In Nitrogen Absorption In Populus Cathayana Seedings

Carbon and nutrients from litter decomposition are input into the soil through leaching and diffusion in fungal hyphae.Then plants can directly and indirectly reuptake the nutrients after being recycled in granular and mineral adsorption and complete the whole nutrients biochemical cycle.Dioecious plants usually exhibit sex-specific differences in growth and leaf quality,however,few studies have been conducted on the sex-related differences in litter decomposition characteristics and nitrogen（N）absorption and allocation.In this thesis,the typical dioecious plant species Populus cathayana Rhed.was chosen as the research object,and the litter labeled with ¹⁵N isotope was decomposed naturally on the soil surface.I compared the differences in the litter mass loss and nutrient release between male and female P.cathayana seedlings,analyzed the nutrient variation characteristics in rhizosphere soil,and integrated microbial extracellular enzyme activities.The study is expected to elucidate the effects of litter decomposition on N absorption and allocation in P.cathayana.The main results were as follows:1.Initial litter quality characteristics（i.e.specific leaf area,leaf thickness and organic soluble component content）of P.cathayana had significant differences between the two sexes but no sex differences in the acid-soluble component and acid-insoluble component.Over the 340 d decomposition period,the decomposition rate k values of female P.cathayana was higher than that of male,and the mass residual rate of males was higher than females,the litter mass residual rate of females and males was 49.24%and56.68%respectively.These results indicated that female P.cathayana litter had a higher decomposition rate than males.Furthermore,the nutrients released from P.cathayana litter showed a net release state,and the female litter had higher C/N and lower N/P than the male.Moreover,the activities of polyphenol oxidase（PPO）,peroxidase（POD）and acid phosphatase（AP）in male litter were higher than that in female.2.Nutrients as particulate,solution and mineral adsorption were migrated to the soil during decomposition.Besides the total carbon content,contents of total nitrogen（TN）,total phosphorus and their stoichiometric ratios in rhizosphere soils showed no significant differences in gender,but the content of the soluble substance in rhizosphere soil showed significant differences between the females and males.Higher dissolved organic carbon（DOC）and ammonium nitrogen（NH₄⁺-N）contents and lower nitrate nitrogen（NO₃^--N）content in females were found than in males.PPO,POD and cellobiohydrolase activities in rhizosphere soils involved in soil nutrient mineralization were higher at the initial decomposition stage than at the other stages,and the leucine aminopeptidase,PPO and AP activities of female rhizosphere soil were higher than that of male.3.Plants absorbed soil-soluble organic matter nutrients and moderately accumulated.Over the 340 d decomposition period,litter source N absorption rate of female plant was up to 8.79%,and absorption amount was 4.67 mg.plant^-1;absorption rate of male plant was up to 15.24%,and absorption amount was 8.63 mg.plant^-1.Furthermore,the proportion of N derived from litter source absorption in male P.cathayana plant was significantly higher than in female,but no sexual difference in TN content,which indicated that male P.cathayana plant had higher N absorption efficiency.In addition,the allocation of N absorption in the root,stem,and leaf was also significantly different.With the decomposition process,both male and female leaf allocation rates gradually decreased,from 39.99%to 13.64%in females and from 66.06%to 9.21%in males.The stem allocation rate gradually increased,from 20.20%to 53.68%in females and from 16.43%to 59.99%in males.The root allocation rate was relatively stable.In addition,the root biomass,aboveground biomass and total biomass of females were significantly higher than that of males.In contrast,total phenol and condensed tannin contents in female leaves were significantly lower in male leaves over the decomposition period.This study collectively indicated that litter nutrient release showed a net release state in P.cathayana.The female litter decomposed faster than the males.Litter microbial acquirement enzyme activity in males was higher in females,but soil microbial acquisition enzyme activity in males was lower than in females.Furthermore,the litter source N absorption efficiency of male P.cathayana was higher than female and closely related to the initial litter quality and the change in rhizosphere soil nutrient content.The study investigated the differences in litter decomposition at the sex level and systematically reflected the effects of litter decomposition on nutrient absorption and allocation through linked enzyme activities and soil nutrients.The results would be helpful for understanding litter decomposition mediated the process of material circulation in the dioecious plant.