| Fine root,as the main source of nutrient pools of forest soils,is the main component of underground ecological system.Fine root decomposition is an important way of soil nutrient returning to plantation,so further study of the decomposition of fine root is helpful to understand the forest ecosystem energy flow and material cycle.We study the 5-year-old Toona sinensis plantation under forest gaps with low-efficiency cypress forest in central Sichuan hilly region..On the one hand,we used Fitter's river drainage branch method and divided fine root into 1-5 root order,used clod method to research the root distribution rule of fine root biomass and morphology of Toona sinensis plantation.On the other hand,we divided fine root into 1-3,4,and 5 root order by refer-ence to the functional modules of fine root,used litter bags and minirhizotron technique to research the dynamic of fine root decomposition for a year under 50m(L1)?100m(L2)and 150m2(L3)forest gap.And we also used litter bags technique to research the nutrient releasing with different fine root of Toona sinensis.In this paper,the study gives reference to the mode of forest gap with low-efficiency cypress forest,and provides technical sup-port to promotion the ecosystem services of Toona sinensis plantation and maintain soil fertility.The main results were found as follow:(1)The average of total fine root biomass of Toona sinensis was 1725.95kg/hm·.The living root biomass and necromass were 1564.93kg/hm2 and 161.02 kg/hm2 respectively,accounting for 90.7%and 9.3%of the total fine root biomass.Total fine root biomass of Toona sinen.sis decreased with increase soil depth.The fine root biomass and morphology of different root orders of Toona sinensi.s plantation had obvious change rule.The specific root length(SRL)of the first order root were the largest,but the average diameter?>biomass and root length of the first order root were the smallest.Fine root biomass?average diame-ter and root length of Toona sinensis increased with increase in order,while SRL decreased.The biomass,SRL and root length of the fine root of Toona sinensis decreased with incre-ase soil depth,while the average diameter increased.Fine root biomass and morphology were closely related with soil resource availability.(2)The decomposition with litter bags method of fine root of Toona sinensis was the fastest in the top 90 days and the residue rate of L1?L2 and L3 were 82.96%?80.36%and 76.91%respectively.With the passage of time,the decomposition rate has slowed down.One year later,residue rate was 75.44%?73.92%and 72.07%respectively.The fine root decomposition rate of L3 was greater than L2.The fine root decomposition rate of L2 was greater than L1.So 150m2 forest gaps was advantageous to the fine root decomposition.One year later,the decomposition rate of the 1-3,4 and 5 order fine root were 29.62%?24.80%and 19.26%respectively.The decomposition rate of the fine root in L3 were significantly higher than the L1(P<0.05).But there were no significant difference between L1 and L2(P>0.05).We using nonlinear equation of Olsen(Xt/Xo=e-kt)to simulate the L1?L2 and L3 of fine root decomposition,the results showed that:the correlation of all index model were above 0.72,the decomposition coefficient of every year was 0.1359?0.2446,The time of half-decomposition of fine root was 851?1737d.While the method of minirhi-zotron using Kaplan-Meier to simulate the L1?L2 and L3 of fine root decomposition,The time of half-decomposition of fine root was 215?370d,3?4 times that of litter bags method.(3)The decomposition rate of fine root of Toona sinensis decreased with increase root order and diameter.Fine root decomposition rate were negatively correlated with fine root initial C,C/N and C/P signally,it was positively correlated with fine root initial P and N significantly(P<0.05).Fine root decomposition rate of Toona sinensis under three kinds of forest gaps was positively correlated with total nitrogen,hydrolysis nitrogen,available phosphorus,available potassium,total potassium,temperature and water content of soil.(4)During the decomposition of fine root,the dynamic of nutrient concentrations of fine root was changed.The C,P and K concentration of the fine root showed a declined trend in forest gaps,the N,Ca and Mg concentration of the fine root showed a increase trend in total.The release of fine root decomposition were the essential source of soil nutrient.The different residual nutrients of fine root have different change rule.In the study period,the C,P and K residual nutrients of fine root showed a release trend in all modes always,they released quickly in the early stage of the decomposition,but them released slowly in the late decomposition.The N residual nutrients of all 1-3 order root and 5 order root in L1 showed the rule of release-enrichment-release.The N residual nutrients of 4 order root in L1 and 4 to 5 order root in L2 and L3 showed the rule of enrichment-release.The Mg residual nutrients of all fine root showed the rule of release-enrichment.The Ca residual nutrients of the L2 and L3 showed the rule of enrichment-release,while the 1-3 order root in L1 showed the rule of enrichment-release-enrichment-release.In conclusion,the three kinds of forest gaps improved the environment and soil ferti-lity of forest significantly,promoted the fine root decomposition and nutrient release.It is advantageous to maintain soil fertility and promotion the forest ecosystem services.The 150m2 forest gap has a better effect in the early. |
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