| Fine root is the main component of underground litter, it is also the main source of soil nutrient of forest land. 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 Cupressus funebris plantation in central Sichuan hilly region, used clod method to research the root distribution rule of fine root biomass and morphology of Cupressus funebris plantation, and used litter bags technique to research the dynamic of fine root decomposition and nutrient releasing with different fine root of Cupressus funebris for a year under understory of Cupressus funebris plantation (CK) and two kinds of forest gaps (LR and LZ). The main results were found as follows:(1) The Average of total fine root biomass of Cupressus funebris is 1978.44 kg/hm2. The living root biomass and necromass were 1819.67 kg/hm2 and 158.77 kg/hm2 respectively, accounting for 91.9% and 8.1% of the total fine root biomass. Total fine root biomass of Cupressus funebris decreased with increase soil depth, and 85.98% of the fine root growth is in 0～20 cm soil layer. The fine root biomass and morphology of different root orders of Cupressus funebris plantation have Obvious change rule. The specific root length(SRL) and root length density(RLD) of the first order root were the largest, but the average diameter and biomass of the first order root were the smallest. The SRL and RLD of the fifth order root were the smallest, but the average diameter and biomass of the fifth order root were thelargest. fine root biomass and average diameter of Cupressus funebris significantly increased with increase in order(P<0.05), while SRL and RLD decreased. The biomass, SRL and RLD of the first five order root of Cupressus funebris decreased with increase soil depth, while the average diameter increased. Fine root biomass and morphology were closely related with soil resource availability. (2) The decomposition of fine root of Cupressus funebris was the fastest in the top 90 days and the loss of CK, LZ and LR were 10.85%,13.49% and 15.26% respectively. With the passage of time, the decomposition rate has slowed down. One year later, residue rate was 81.04%,77.20% and 75.48% respectively. The fine root decomposition rate of LR was greater than LZ. The fine root decomposition rate of forest gaps(LZ, LR) was greater than CK. So forest gaps was advantageous to the fine root decomposition. The decomposition rate of first five fine root of Cupressus funebris is fast in the early decomposition stage but slow in the last stage and with the increase of root orders decomposition rate decreased. One year later, the decomposition rate of the first five fine root were 23.58%,21.11%, 19.48%,7.09% and 13.63% respectively compared with CK. The decomposition rate of the first five fine root in forest gaps(LZ, LR) were significantly higher than the CK (p<0.05). But there were no significant difference between LZ and LR.(3) Using nonlinear equation of Olsen(Xt/Xo=e-kt) to simulate the CK and forest gaps(LZ, LR) of fine root decomposition, the results showed that:the correlation of all index model were above 0.81, the decomposition coefficient of every year was 0.1372-0.3047, fine root decomposition rate of forest gaps was significantly different with the understory (p<0.05). The time of half-decomposition of fine root was 747-1769d, the 95% decomposition of fine root was 3505-7890d.The theoretical value of fine root decomposition rate was closed to predict value in one year of fine root decomposition.(4) The decomposition rate of fine root of Cupressus funebris decreased with increase root order and diameter. By used linear regression fitting method, it showed that 84.4% of annual decomposition rate changes can be explained by diameter,95.0% can be explained by root order. It was showed that diameter and root order have important influence on fine root decomposition.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, N and K significantly(p<0.05). Fine root decomposition rate of Cupressus funebris was signally positively correlated with hydrolysis nitrogen, available phosphorus and available potassium of soil(p<0.05). it was positively correlated with soil total N and total P, but not significant(p>0.05). Fine root decomposition rate was signally positively correlated with soil temperature. It was also positively correlated with soil water content, but no significant (p>0.05).(5) The dynamic of nutrient concentrations of fine root was changed with its decomposition in study period. The C, P and K concentration of the first five fine root showed a declined trend in forest gaps and understory. And they decompose quickly in the early stage of the decomposition, but them decompose slowly in the late decomposition. The N and Mg concentration of the first five fine root showed a increase trend. The Ca concentration of the first five fine root showed a increase trend firstly, and then it showed a declined trend. 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 release quickly in the early stage of the decomposition, but them release slow in the late decomposition. The N residual nutrients of all 1-order root and 2-order root in LR showed the rule of release-enrichment- release, while the 3-order to 5-order fine root and the 2-order fine root of the CK and LZ 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 CK and LZ showed the rule of enrichment-release, while the CK showed the rule of enrichment-release-enrichment-release.In conclusion, the two kinds of forest gaps have in favour of fine root decomposition and nutrient release in central Sichuan hilly region. The LR forest gap has a better effect in the early. |
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