Study Of The Stoichiometric Characteristics And Turnover Of Fine Root Of Pinus Massoniana In Three Gorges Reservior Area

Fine roots(‘ 2mm in diameter),which are the importang organs of plant nutrient and water absorption,and have the characteristics of no xylem,small diameter,short live-span and fast cycle life,are the most important component contributing to belowground carbon pool and the most active component in the forest ecosystems.Fine root turnover,which refers to the process of continuing growth,aging,death and decomposition,and inner nutrient concentration are key to calculate the contribution of fine root to material cycle in underground ecosystem.Pinus massoniana is the main component of vegetation and plays an important role in forest resources and ecological services in the Three Gorges Reservior Area.So,understanding and quantifying the turnoverand intrinsic nutrient pattern of fine root of Pinus massoniana,which great for accuratlly predicting the contribution of Pinus massoniana to below ground carbon storage and nutrient cycling in the Three Gorges Reservior Area.From May 2014 to December 2015,by the method of complete clod,samples recycling was sampled from 0-30 cm soil layer every other mother,to study the fine root stoichiometry characteristics of Pinus massoniana in the Three Gorges Reservoir Area.Meanwhile,sequential soil cores and buried bags were used to measure the production and turnover of fine root of Pinus massoniana.The soil cores were separated into 3 sections,0-10,10-20,20-30 cm,and the fine root biomass was investigated in the fixed points.Both the biomass samples and buried bags recycling were carried out also every other month.The paper was to explore the distribution patterns of fine root nutrient with different diameters and the correlationships of fine root dynamics and inner or outer factors.The results showed that:1.Fine root C content of Pinus massoniana in the Three Gorges Reservior Area increased with the increase of diameter,and the temporal dynamics change was to increase and then to decrease;Fine root N,P,K,Ca,Mg content decreased with the increase of diameter,and the dynamics trends were to increase first,then to increase,and to then increase again,but N,P,and Ca content of 1.5-2mm fine root were to increased gradually;The values of C:N,C:P and N:P increasedwith the increase of diameter,and the temporal dynamics changes were to decrease first,then toincrease,and then to decrease again,but C:N and C:P of 1.5-2mm fine root were decreased gradually.2.The annual changes of fine root elements of Pinus massoniana were different with each diameter.Fine root C was releasing;Fine root N,K,Mg were enriching;Fine root Ca was different in each diameter fine root,‘ 1.5mm fine root were releasing,1.5-2mm fine root was enriching;Fine root P was different with other elements and was almost no changes.3.During the fine root decomposition of Pinus massoniana in the Three Gorges Reservior Area,C content decreased with time increasing,N,P and Ca content increased with time increasing,K and Mg content decreased first,then increased,and then decreased again;The transfer models of all elements were different,C,K,Mg were releasing,Ca was enriching,N and P of ‘ 0.5mm fine root were releasing,but 0.5-2mm showed rich stage during the decomposition process.4.The root decomposition characteristics of Pinus massoniana showed a bi-phase pattern,being decomposed faster in prophase and slower in anaphase.Through the non-liner exponential model,the fine root decomposition coefficients of ‘ 0.5mm,0.5-1mm,1-2mm were 0.5180,0.3058,0.3058,respectively.Person correlation analysis indicated that: the decomposition rate of fine root(‘ 2mm)was significantly positive correlation with the initial N,P,K,Ca,Mg content,and significantly negative correlation with the C/N,C/P;Redundancy correlation analysis indicated that: During the decomposition of fine root,Ca content of fine root and soil temperature were the dominant factors for fine root decomposition.what’s more,the influence of fine root Ca content to fine root decomposition was to decrease with the diameter increasing,but soil temperature was to increase.5.The seasonal changes of live or dead fine root biomass in the stand level of Pinus massoniana in the Three Gorges Reservior Area were obvious.For live fine root,the dynamic trends of each diameter class were consistent,and there were two peaks,in March and September respectively.For dead fine root,the changes of each diameter class were also same,the maximum value appeared in December and the minimum values appeared in September.Principal component analysis indicated that: fine root biomass(‘ 0.5mm)and fine root chemical elements or soil Ca content were highly correlated with each other as also fine root biomass(0.5-2mm)and external factors(soil temperature,soil moisture,soil nitrate and soil ammonium nitrogen).6.According to compartmental-flow method,the annual production of ‘ 0.5mm,0.5-1mm,1-2mm fine root were 0.13t/(hm~2·a),0.49t/(hm~2·a),0.37t/(hm~2·a),respectively,and the annual turnover rate were 1.49/a,1.01/a,0.40/a,respectively.The correlation and regression analysis indicated that the correlations between factors(fine root biomass,fine root chemical elements,soil temperature,soil moisture,soil nitrate,soil ammonium nitrogen)and fine root production or turnover of each diameter class were different.Soil temperature and soil Ca content had significant effects on production and turnover of ‘ 0.5mm fine root,which were able explain32.80% and 25.00% of the variation by soil temperature respectively,65.60% and 73.10% by soil Ca content respectively.There was a close positive relationship between fine root biomass and fine root production,and biomass of ‘ 0.5mm,0.5-1mm and 1-2mm fine root were able to explain 41.00%,41.10% and 54.50% of the v-ariation in production,respectively.There was also a close negative relationship between ‘ 0.5mm fine root production and N,P content of‘ 0.5mm fine root,which were able explain 32.80% and 25.00% of the variation in ‘ 0.5mm fine root production,respectively.