Forest Canopy Gap On Picea Asperata Fine Root Decomposition And Nutrient Release

China is the world’s largest plantation area country, soil degradation in plantation reduced forest productivity, not only has infected forestry production, but also infected the develop of forestry ecological benefits and has been a serious problem of forestry sustainable development. Fine root is the subject of underground litter, its death and decomposition are the main source of soil nutrient. Fine root decomposition is the key link of fine root turnover and nutrient returns, it’s also the important self-nutrient supply mechanism in forest ecosystem, so study the fine root decomposition has in favour of understand the material cycle and energy flow in forest ecosystem. In this paper, we study the50a Picea asperata in subalpine area of western Sichuan, used litter bag technique to research the decomposition dynamic and nutrient releasing rule in each root order of fine root of Picea asperata under understory (CK) and forest gap (50m2(L50)and150m2(L150)).The main results were found as follows:(1) In the early90d of decomposition of Picea asperata, fine root had the biggest mass loss and fastest decomposition, L150, L50and CK loss26.61%,23.14%and20.47%respectively. After90d decomposition, the rate had slow down obvious, then, after la, residue rate is61.87%.65.74%and71.62%respectively. Fine root decomposition has been connected with the natural environment, as the fine root decomposition, what’s in gap(L50, L150) are significantly higher than that in understory, gap of150m2had higher rate than gap of50m2(p<0.05).(2) Fine root decomposition of1-5levels fine root shows that, level3fine root decomposition fastest, then followed levels4-5, the slowest are the levels1-2.According to variance analysis, except levels4-5fine root, other levels root fine all showed a significant difference(p<0.05).What’s more, decomposition between gap and understory also had a difference, that’s shows that in understory is the slowest, take the second place is that in gap of50m2, but in gap of150m2, it’s the fastest. Each fine order decomposition rate in CK were30.70%,32.16%,41.20%,37.45%and33.12%, in the area of L150, the rate were33.20%,38.04%,42.59%,39.82%and40.12%.(3) By Olsen’s nonlinear equation:Xt/X0=e-kt, to simulation different treatment methods of fine root decomposition, the results showed that:by used negative exponential function, it had high simulation fitting degree of fine root decomposition, the correlation coefficient was above0.71, the decomposition coefficient was0.00055-0.00139d-1, rate of understory were significantly different with that of gap(p<0.05).The half-decomposition time were507-1147d,95%decomposition(we usually use decomposition of95%as completely decomposition) were2101-5328d, using simulation equation we got that theoretical value of dry weight loss were approach with actual value in one years decomposition, standard deviation were1.79%-4.45%. (4) Study the inner factor of fine root decomposition showed that, root order (diameter) had essential effects on the root decomposition, Picea asperata fine root of levels1-3decomposition rate were higher with the root diameter bigger, but levels3-5root showed the opposite rule. By used linear regression fitting method, it showed that only12.39%years decomposition rate changes can be explained by diameter. Fine root decomposition rate were significantly positively correlated with fine root initial C, C/N and C/P, it were negatively correlated with initial P content, and negatively correlated with cellulose/C, lignin/C, also positively correlated with initial cellulose, lignin, cellulose/N, lignin/N and lignin/P contents.(5) Fine root decomposition were influenced not only by matrix mass, but also eternal environmental condition. In1a decomposition period, soil microbial community changed variously, decomposition rate were significantly positively correlated with bacteria and cellulose community numerical(p<0.05), were highly significantly positively correlated with fungus and actinomycetes community numerical(p<0.01).The process of fine root decomposition is a enzymatic hydrolysis process, enzyme activities influenced rate of root decomposition significantly. Study showed that decomposition were significantly positively correlated with urease, sucrase, peroxidase and cellulolytic enzyme (p<0.05), and there were no correlation with acid phosphatase and polyphenol oxidase. Decomposition were correlated with soil temperature and humidity, in this paper, We realized that fine root decomposition were significantly positively with fine temperature while negatively with soil water content.(6) In the study period, each chemical component concentration in fine roots were dynamic changed with its decomposition. C concentration of levels1-5fine root were declined in3plots, in early90d the phenomenon were obvious, but with the time went on, the rate slowed down. While cellulose in each root order were increased before decomposition in3plots, to May,2011, it showed the decline trend, after July,2011, the concentration were less than initial ones. The change trend of lignin were different with cellulose, in the days before decomposition270d, it were fluctuated with a little range until1a then showed the decline trend. In each root order of every plot, N, Mg component showed a increase trend while P, K component declined, Ca component showed a little fluctuated as the time goes on before decomposition in270d, composition la showed net release, with the component declined.(7) Fine root decomposition release were the essential source of soil nutrient, the whole N mass relic of Picea asperata fine root each level root order showed the rule of enrichment-release-enrichment, average rate of N enrichment in3plots were27.06%,20.70%and16.72%respectively. P mass relic in3plot showed consistent rule, that’s means they all release in same speed with the average rate were56.51%,55.99%and63.69%.Compared to other nutrients, K release were the fastest in each processing, and its absolute content showed a sudden drop. With the time went on, K mass relic showed the rule of enrichment-release with a little wave range in3plots of each root order, after1a decomposition, K average release rate were71.09%,75.55%and76.87%in plot CK, L50and L150.In conclusion, a appropriate forest gap thinning(50m2、150m2) has in favour of fine root decomposition and nutrient release, also timely added the site consuming of volume of forest tree growth. It can make a contribution to not only maintaining and improving land capability, but also enhancing the soil fertility.