| Applying mesh nylon bag method, from May 2010 to November 2011, the research had been carried out in Larix prince is-rupprechtii Mayr. plantations of different age, Betula platyphylla Suk. and Populus davidiana Dode. were chosen to mixed-decompose with Larix principis-rupprechtii Mayr. leaf litter in different proportion on the base of studying the character of decomposition characteristics, nutrient element contents, nutrient release and the changing law of soil nutrients in the process of litter decomposition in xin feng Forestry Farm of weichang Manchu and Mongolian Autonomous County, Hebei province. This study aimed to understand the litter decomposition characteristics in Larix prince is-rupprechtii Mayr. plantations of different age and the inter-species relative of mixed forest cultivate Larix prince is-rupprechtii Mayr. and find one or more proper species mixed-plantation with Larix prince is-rupprechtii Mayr. which would accelerate Larix prince is-rupprechtii Mayr. litter decomposition and reduced the soil declining, and offered the reference to Larix prince is-rupprechtii Mayr. mixed forestry. The main result showed as following:1. The decomposition characteristics of Larix prince is-rupprechtii Mayr. plantations of different age had significantly differences. During 540 d decomposition process, from young stand to mature stand, the mass loss of litter ranged from 48.47% to 61.72%, and significant differences were observed in the different age groups. Decomposition rates of the leaf litters were decreased in the order of the mature forest>nearly mature forest> middle-age forest>young forest. According to the dummy variable model simulation by Olson’s exponential function, the decomposition constant were from 0.02830 to 0.03619, and the time for decomposing 50% and 95% were 1.59~2.04 years and 6.90~8.82 years, respectively. During the whole decomposition process, the dynamic changes of nutrient content in four different age groups were consistent. As decomposition time prolonging, N content in leaf litters of four different age groups showed an increasing trend, and P content appeared to decrease firstly and then increase, and K, C content and C/N ratio were weakened. The release rates and dynamic changes of nutrient elements (N, P, K and C) in leaf litters showed consistencies among four different age groups generally during decomposition process. A net release was found in the release of C and K, and it displayed a direct release mode. The nutrient N showed a decomposition pattern of eluviation- enrichment-release, while nutrient P acted as a accumulation-release mode; It meaned that the decomposition of leaf litters of mature forest and nearly mature forest are easier than that of middle-age forest and young forest, and also the nutrient elements release more easily in the former than in middle-age forest and young forest.2. The litter decomposition characteristics of different species had significant differences. During 540 d decomposition process, the loss rate of leaf litter of Larix prince is-rupprechtii Mayr., Betula platyphylla Suk. and Populus davidiana Dode. was 10.66%, 14.879% and 17.464% respeetively, and significant differences were observed in them. The average decomposition rate was 0.02944, 0.04806 and 0.05665d-1, and the time for decomposing 50% and 95% were 1.02~1.96 years and 4.41~8.48 years, respectively. During the whole decomposition process, leaf litter in three species had significant differences among leaf litters of three tree species, there was an obvious difference in each nutrient element contents. N and P content in leaf litter of three tree species appeared generally a fluctuant and slow ascending trend; K content was weakened, C/N appeared generally a fluctuant and descend trend. The release rates and dynamic changes of nutrient elements (N, P, K and C) in leaf litters exist some differences among three tree species during decomposition process. In leaf litters of three tree species, the release rate of K and C were generally in net release, and N and P in Larix prince is-rupprechtii Mayr leaf litter were in enrichment, but N and P in Betula platyphylla Suk. and N in Populus davidiana Dode. leaf litter were in enrichment in the early phase and then N in Betula platyphylla Suk. and in Populus davidiana Dode. were in a wavy net release with decomposition time prolonging. P in Populus davidiana Dode. leaf litter exhibit a monotonously net release. It meaned that the decomposition of leaf litters of broad-leaved tree species (Betula platyphylla Suk. and Populus davidiana Dode.) was easier than that of coniferous tree species (Larix prince is-rupprechtii Mayr.), and also the nutrient elements released more easily in the formers than in the latter under Larix prince is-rupprechtii Mayr. artificial forest.3. The proportion of mixture had major effect to the decomposition of leaf litter in Larix prince is-rupprechtii Mayr. in the mixed decomposition. In the course of mixed- decomposition between Larix prince is-rupprechtii Mayr. and Betula platyphylla Suk, it was no impacted by Betula platyphylla Suk in the prophase but was promoted prominently in the anaphase. In the three mixed decomposition, the more proportion of Betula platyphylla Suk., the more obvious promotion to it. While in the course of mixed- decomposition between Larix prince is-rupprechtii Mayr. and Populus davidiana Dode. with the more proportion of Betula platyphylla Suk., the weightlessness rate of Larix prince is-rupprechtii Mayr. had a descend tread, it indicated that with the more proportion of Betula platyphylla Suk. the more obvious inhibition to it.4. The proportion of mixed-decomposition between Larix prince is-rupprechtii Mayr. and broad-leaved species leaf litter had complex influences on litter decomposition rate and dynamic changes of nutrient content. The proportion of mixed-decomposition between Larix prince is-rupprechtii Mayr. and Betula platyphylla Suk. were promoted prominently to litter decomposition, but the decomposition was inhibited when the mixed- decomposition between Larix prince is-rupprechtii Mayr. and Populus davidiana Dode. During the period of mixed-decomposition between Larix prince is-rupprechtii Mayr. and Betula platyphylla Suk. leaf litter, N and P content in leaf litter of them appeared ascending trend, while C/N, K and C content were weakened, during the whole decomposition process, the releasing of N, P was inhibited except K and C when mixed-decomposed between Larix prince is-rupprechtii Mayr. and Betula platyphylla Suk. leaf litter; and releasing of N and P, especially K element was inhibited except C when mixed- decomposed withPopulus davidiana Dode. leaf litter.5. The litter decomposition had effect obviously on the soil fertility, but different nutrient had different change pattern. While hydrolyzed-N of mature forest and nearly mature forest have wave declined and then ascended during the decomposition time. With Plantation age increase, the concentration of hydrolyzed-N had also increased. As decomposition time prolonging, the concentration of available-P in four different age groups showed an increasing trend, and the available-P is in the order of the mature forest>nearly mature forest>middle-ag eforest>young forest, the concentration of available -P in four different age groups showed an increasing trend as time prolongs. During the whole decomposition, the concentration of Soil organism had presented a low-high variation pattern, and the order of it is mature forest>nearly mature forest> middle-age forest>young forest. pH in four different age groups had slightly acidic in the decomposition process.6. The proportion of mixed-decomposition between Larix prince is-rupprechtii Mayr. and broad-leaved species leaf litter had also obviously on the soil nutrients during the decomposition, hydrolyzed-N, available-P, available-K and soil organism had basically increased as Betula platyphylla Suk. leaf species proportion increased when mixed- decomposed between Larix prince is-rupprechtii Mayr. and Betula platyphylla Suk. leaf litter, and hydrolyzed-N, available-P, available-K hadbasically increased as Populus davidiana Dode leaf species proportion increased except soil organism during mixed- decomposed between Larix prince is-rupprechtii Mayr. and Populus davidiana Dode. leaf litter. |
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