Study On Nutrient Transfer And Utilization At Different Growth Stages Of Chinese Fir Forest In Huitong, Hunan Province

In order to explore the nutrient transfer and utilization in material production at different growth stages of Chinese fir forest,based on 25 years of location continuous measurement data from National Field Observation and Research Station of Chinese Fir Ecosystem in Huitong,Hunan province,the biomass of “still living organs” at a certain growth stage was calculated by using the biomass of living tree organs at the beginning of the growth stage and organ growth cycle.The amount of nutrients reabsorbed into or transferred from the “still living organs” at a certain growth stage was estimated according to the biomass of the “still living organs” of the growth stage and the nutrient concentration difference of tree organs at the beginning and the end of the growth stage.The nutrient content transferred to living organs before the branches and leaves withered at different growth stages was estimated by using the dead amount of branches and leaves as well as the difference in nutrient concentration between living and dead branches and leaves at different growth stages.Through the above research methods,nutrient transfer before withering of branches and leaves at different growth stages of Chinese fir forests,and nutrient transfer patterns of "still living organs" at different growth stages were analyzed.The nutrient sources of stand material production at different growth stages,as well as the nutrient utilization efficiency of different organ material production and their changing patterns were explored.At the same time,the utilization efficiency of nutrient elements and its change law in organ material production were studied.The main research results are as follows:(1)At the different growth stages of the Chinese fir forest in Huitong,the amount of nutrients transferred before withering of branches and leaves were not the same.At the young forest stage,all of them were transferred before the withering of leaves.At the rapid growth stage,the tree height growth stage,the growth and accumulation stage of trunk wood and the mature stage,the proportion of nutrients were transferred before branches and leaves withering respectively accounts for 2.16% and 97.84%,14.00%and 86.00%,23.08% and 76.92%,28.68% and 71.32% of the total transferred amount.The vast majority of the nutrients transferred before the withering of branches and leaves of Chinese fir in Huitong were transferred from leaves before withering.(2)At different growth stages,the nutrient transfer rates of Chinese fir leaves before withering were 22.99%～26.06%,and the rates of branches before withering were 21.64%～22.59%,all of which increased with the increase of growth stage.The nutrient transfer rate of leaves at the same growth stage was higher than that of branches.There was no significant difference in nutrient transfer rates among branches(or leaves)at different growth stages(p>0.05),which indicated the influence of forest age on the nutrient preservation ability of the branches and leaves of Chinese fir in Huitong was not significant.Before the 17 th year of the forest stand,the order of the transfer rates of various nutrient elements before the death of the leaves was:K>P>N>Mg>Ca.After the 17 th year of the stand,the order was P>K>N>Ca>Mg.The transfer rates of various nutrient elements before branches withering at any growth stage was in the order of K>P>N>Mg>Ca.And the transfer rate of a certain element before the withering of branches and leaves was not entirely influenced by the concentration of this element in the living organs of branches and leaves.(3)From the young forest stage to the rapid growth stage,nutrients were transferred into “still living organs”.From the stage of tree height growth to its mature stage,nutrients were transferred to other parts from the “still living organs”.The nutrients content transferred into “still living organs” was in an order of leaves>branches>bark>trunk>roots while the nutrients content transferred out of the“still living organs” was ranked as trunk>branches>roots>leaves>bark.The amount of various elements transferred into “still living organs” was ordered as N>Ca>K>Mg>P,while the elements out of “surviving organs” was sorted as Ca>N>K>Mg>P.The amount of nutrients(elements)transferred into the “still living organs” were greater than that transferred out of the corresponding “still living organs”.In terms of the protection and utilization of plant nutrients and nutrient cycling function,the nutrient transfer effect of plant organs before withering was greater than that of “still living organs”.(4)The rates of nutrient transferred into the “still living organs” were leaves>branches>bark>trunk>roots while the rates of nutrient transferred out of the“still living organs” were trunk>roots>branches>leaves>bark.The “into” rates of “still living leaves,branches,and bark” were higher than that transferred out of these organs,while the nutrient transfer rates of transferred into the “still living trunk and roots”were lower than that transferred out of these organs.The transfer rates of various nutrient elements transferred into the “still living organs” were P>Mg>N>K>Ca.The transfer rates of various elements transferred out of the “still living organs” were P>Mg>Ca>K>N.As the growth stage increases,the transfer rates of N,P,Ca,and Mg from the “still living trunks and roots” first increased and then decreased,while the transfer from “still living branches,leaves,and bark” continued to decline without increasing.The transfer rates of K,transferred out of the “still living branches,trunks and roots” showed an initial increase and then a decrease as the growth stage increased,but the transfer rates from “still living leaves and bark” decreased as the growth stage increased.(5)79.35%-96.27% of the nutrients used in the material production of Huitong fir forest came from the soil which showed an “M” shape of rising,falling,rising and falling with the growth stage.There were 3.73%-17.55% nutrients,increasing with the growth stage,were transferred to the living tissue before the branches and leaves die.There were 3.10% ～ 3.39% nutrients from the migration of “still living organs”,which fluctuated with the increase of growth stage.Only after canopy closure can there be“still living organs” to transfer nutrients and reuse them for material production.The nutrient content required for stand material production showed an increasing trend from the young forest stage to the growth and accumulation stage of trunk wood,and showed a decreasing trend when entering the mature stage,it changed into a parabolic shape with the growth stages.The productivity of stand at different growth stages,the productivity of different organs,and the amount of nutrients required for the production unit output of stands at different growth stages jointly controlled the annual variation of the amount of nutrients required for stand material production.(6)At the same growth stage,the nutrient quantity used for the production and utilization of Chinese fir organs substances were leaves>branches>bark>trunk>roots.The nutrient content of each organ production and utilization showed three kinds of changes with the growth stage.The first was that the branches change in an “M” shape with the growth stage.The second was that the trunk and leaves change in a parabola with the growth stage.And the third was the N-type change of bark and roots with the growth stage increases.The growth and development characteristics of trees and the amount of production of various organs at different growth stages controlled the change law of nutrient utilization in organ production with the increase of growth stages.(7)At the same growth stage,the nutrient utilization efficiency(NUE)in the production of various organs substances was trunk>roots>bark>branches>leaves,while the nutrient element utilization efficiency was sorted as P>Mg>K>Ca>N for the organs of leaves and branches production,and as P>Mg>Ca>K>N for the organs of bark,trunk,and roots.The changes in NUE of material production in different organs during different growth stages were different.The rates of decline during the rapid growth stage were as follows: bark>branches>leaves>trunk>roots.The increasing rates of the tree height growth stage were bark>branches>roots>leaves>trunk.The rates of increase during the growth and accumulation stage of trunk wood were as follows:trunk>leaves>roots>branches>bark.The rates of increase during the mature stage were roots>trunk>branches>leaves>bark.The changes in NUE of various nutrient elements with increasing growth stages were not entirely the same.The NUE of various nutrient elements in forest stands decreased with the increase of growth stage from the young forest stage to the rapid growth stage,while the growth stage of tree height and the growth and accumulation stage of trunk wood increased with the growth stage,and at the mature stage,the utilization efficiency of N,P,and Mg were still increasing,while the utilization efficiency of Ca and K nutrients were decreasing.Therefore,the utilization efficiency of N,P,and Mg showed a “V” shape with the increase of growth stage,while the utilization efficiency of Ca and K showed an anti-“N” shape.(8)The change rate of material production and utilization efficiency of the same nutrient element in each organ varied with organs.No matter at increase or decrease rate,for the nutrient N,the trunks were less than that of other organs,while the leaves and bark were more than that of other organs.And for the nutrient P,the trunks were greater than other organs,and leaves and branches were less than other organs.And for K,leaves were more than branches and trunks.And for Ca,branches and bark were greater than leaves,roots,and trunks.And for Mg,leaves and branches were less than bark,roots and trunk.(9)Plant nutrient internal circulation can improve the NUE,but not necessarily by increasing the material yield per unit of effective nutrients,but by reusing some nutrients originally stored in the plant in the production of new substances,so as to reduce the absorption of new nutrients to improve the NUE.For the improvement of NUE,the effect of nutrient back-flow before the death of branches and leaves was much greater than that of the transferred nutrients from “still living organs”.If the nutrient migration of branches and leaves before death and the re-utilization of nutrients migrated from the “still living organs” were ignored,not only does it not correspond to the actual situation of nutrient utilization in the material production of the stand,but it may also overestimate the consumption of soil nutrients by the stand,and may underestimate the NUE of stand material production.