以油松(Pinus tabuliformis Carriere)和5种阔叶树的凋落叶为对象,使用分解袋法在室内进行为期6个月的针阔混合分解实验,研究产生的混合分解效应、针阔凋落叶对彼此分解速率的影响及其可能产生机理.结果 显示:(1)油松分别与红桦(Betula albo-sinensis Burk.)、灰楸(Catalpa fargesii Bur.)、太白杨(Populus purdomii Rehd.)凋落叶混合对分解速率均产生加性效应,但其中油松凋落叶分解受到显著促进,而阔叶凋落叶分解受到显著抑制.油松与杜仲(Eucommia ulmoides Oliver)凋落叶混合时两者分解速率均显著降低,油松与槭树(Acer tsinglingense Fang et Hsieh)凋落叶混合时两者分解速率均显著提高;(2)总体而言,在蔗糖酶、羧甲基纤维素酶和多酚氧化酶参与凋落叶分解的主要时期,红桦、灰楸、太白杨分别与油松凋落叶混合分解使土壤中这3种酶的活性较油松单独分解时显著提高,而较阔叶凋落叶单独分解时显著降低;油松与杜仲混合分解使这3种酶活性较两者单独分解时显著降低,而油松与槭树混合分解则产生相反效果.本研究结果表明,从凋落叶混合分解对物质循环影响的角度考虑,红桦、灰楸、太白杨和槭树可以用于油松纯林的混交改造,但应注意混交对阔叶树种分解的抑制;杜仲与油松凋落叶混合分解将会妨碍彼此养分循环,不宜混交改造.

Mixed-decomposition effects are commonly observed in natural and planted forests and affect nutrient cycling in a forest ecosystem. However, how one litter type affects the decomposition of another is still poorly understood. In this study, Pinus armandii litter was mixed with Betula albosinensis, Catalpa fargesii, Populus purdomii, Eucommia ulmoides, and Acer tsinglingense litter. The mixtures were placed in litterbags and buried in soil with consistent moisture for a 180-day indoor simulated decomposition experiment. The litterbags were periodically harvested during decomposition; the litter residues of different species were separated, and the biomass dynamics of each litter type were simulated. In addition, the soil sucrase, cellulase and polyphenol oxidase activities were also detected three times. The mutual effects of needle and broadleaf litter during mixed decomposition and the possible underlying mechanisms were investigated. The results indicated that (i) during the decomposition experiment, P. armandii needles significantly inhibited the decomposition of broadleaf litter in the first 3 months, while the broadleaf litter accelerated the decomposition of P. armandii needles in only approximately 40% of the cases. However, the inhibitory effects of needles on broadleaf litter decomposition subsequently exhibited significant weakening, while the accelerating effects of broadleaf litter were significantly enhanced. The effects of mixed decomposition on the activities of three enzymes can only partially explain the interactions between different litter types; (ii) the prediction by the decomposition model showed that most of the broadleaf litter types could continuously accelerate the decomposition of P. armandii needles throughout the mixed decomposition process, while the decomposition of broadleaf litter would be significantly inhibited at least in the short term. In general, four of the five broadleaf litter types (excluding E. ulmoides) could accelerate the early decomposition of P. armandii needles and consequently accelerate nutrient cycling in P. armandii pure forests. These species could be used for the transformation of pure P. armandii pure forests to mixed forests.

明确混合分解过程中凋落物的相互影响对于深入分析混合分解非加和效应的真实结果和产生机制,据此评价混合分解对生态系统物质循环的影响、指导混交造林和纯林混交改造具有重要意义.以云杉(Picea asperata)及拟与其混交的红桦(Betula albo-sinensis)、灰楸(Catalpa fargesii)、太白杨(Populus purdomii)、杜仲(Eucommia ulmoides)和秦岭槭(Acer tsinglingens)等6种树种为研究对象,采集其当年凋落物,采用分解袋法在室温(20-25℃)恒湿条件下进行为期180 d的室内模拟针阔混合分解试验.测定混合分解过程中针阔凋落物分解残留量的动态变化,以及与分解密切相关的土壤蔗糖酶、羧甲基纤维素酶和多酚氧化酶的活性动态,分析凋落物在混合分解过程中彼此影响的机理,并据此选择适宜的阔叶树种对云杉纯林进行混交改造.结果表明,(1)混合分解非加性效应及凋落物间的相互影响均随分解的进行趋于明显.至分解试验结束时,杉×桦混合促进彼此分解(分解率分别提高8.67％和8.11％);杉×楸混合显著促进云杉分解(分解率提高7.83％),同时显著抑制灰楸分解(分解率降低11.50％),但整体呈加性效应;杉×杨和杉×槭混合促进太白杨和秦岭槭分解(分解率分别提高3.11％和15.89％);杉×杜混合则抑制杜仲分解(分解率降低13.33％);上述结果与Olson模型拟合计算结果有所差异.(2)混合分解对土壤蔗糖酶、羧甲基纤维素酶和多酚氧化酶的非加和性影响与其对凋落物分解的影响一致.总之,某些情况下混合分解的总体非加和效应因凋落物间相互促进或抑制而无法被检测,但鉴于不同凋落物分解特征的差异,混合后其对彼此分解的影响仍可能干扰林地物质循环.仅从引入阔叶树种后应不妨碍林地凋落物分解的角度考虑,除杜仲外,其他4种阔叶树种均适宜于云杉纯林改造.

In this study, leaf litters of Betula albo-sinensis and 5 coniferous species were used as samples. The B. albo-sinensis leaf litter was buried in soil and termly treated with the water extracts of five types of coniferous leaf litter for a 6-month simulation decomposition experiment. The dynamics of mass loss and nutrients (C, N, P, and K) content of leaf litter and the soil enzymatic activities were measured to investigate the effects of plant secondary metabolites (PSM) from coniferous leaf litters on the decomposition processes of B. albo-sinensis leaf litter. The results indicated that the extracts of Pinus tabuliformis, Platycladus orientalis, P. armandii and Larix principis-rupprechtii leaf litters significantly inhibited the whole decomposition process and overall nutrients release of B. albo-sinensis leaf litter, while the extracts of Picea asperata leaf litter exhibited no significant influence. The general suppression of PSM on the soil sucrase, carboxymethyl cellulase and β-glucosidase activities might be the main reason leading to the inhibitory effects of the extracts of P. tabuliformis, P. orientalis, P. armandii and L. principis-rupprechtii leaf litter. The species causing inhibitory effects, especially L. principis-rupprechtii, was not recommended to be planted mixed with B. albo-sinensis, or their planting density should be lower in the mixed forests.

A decomposition experiment of Populus purdomii litter, a commonly used afforestation species in the Qinling Mountains, China, was conducted. Water extracts of five conifer litters were used to treat P. purdomii litter and its soil. The P. purdomii litter was incubated at room temperature（20–25 °C） and constant soil moisture for 6 months. During the decomposition period, the dynamics of litter mass and nutrient contents were detected to investigate the impacts of plant secondary metabolites. The results indicate that litter extracts of Pinus tabuliformis,Platycladus orientalis, Pinus armandii and Larix principisrupprechtii significantly inhibited the overall nutrient release of P. purdomii litter, while the last three types of litter extracts simultaneously inhibited its decomposition.Conversely, the litter extracts of Picea asperata significantly accelerated the overall nutrient release of P. purdomii. Generally, most of the conifer species, whose litter released terpenoids, phenolics, steroids, and aliphatic acids,will inhibit the decomposition and/or nutrient release from P. purdomii litter. Their negative effects on the decomposers and soil enzymatic activities indicates that planting diversity should be lower when mixed planted with P.purdomii.

[Objective] The effects of leachates from understory medicinal plants on decomposition of Pinus tabuliformis litter and soil enzyme activities were investigated to provide scientific basis for selecting suitable understory species.[Method] In this paper,and the effects of 9 leachates (water-extraction solution) from the stems and leaves of common medicinal plants (Taraxacum mongolicum,Corydalis bunF eana,Mentha haplocalyx,Houttuynia cordata,Asarum sieboldii,Nepeta cataria,Lonicera japonica,Gynostemma pentaphyllum and Prunella vulgaris) in typical Pinus tabuliformis forest in Qinling Mountains on litter decomposition,nutrient releases (C,N,P,Cu,Zn and Mn) and soil enzyme activities were studied.[Result] The leachates from Taraxacum mongolicum,Corydalis bungeana,Mentha haplocalyx,Houttuynia cordata,Lonicera japonica and Nepeta cataria had significant inhibitory effects on litter decomposition rates and release of nutrients (except L.japonica had no significant effect of N and N.cataria had no significant effect on N and P).The leachates from T.mongolicum,C.bungeana,M.haplocalyx,H.cordata and L.japonica lowered the activity of polyphenol oxidase.The leachates from L.japonica lowered activities of carboxymethyl cellulose,and N.cataria lowered activities of carboxymethyl cellulose and beta-glucosidase.[Conclusion] A.sieboldii,G.pentaphyllum and P.vulgaris were suggested to plant under P.tabuliformis forests,where other 6 species were not suggested as understory species or their inter planting density should be diminished to avoid the inhibitory effects.

In this study, the litter of Catalpa fargesii and Eucommia ulmoides was treated with the water extracts of 5 types of coniferous litter for a 0.5-year indoor, simulated decomposition experiment, and the effects of plant secondary metabolites (PSMs) from coniferous litter on the mass loss and C, N and P release of the 2 types of litter were detected. The results indicated that the litter extracts of Platycladus orientalis, Pinus tabuliformis, Pinus armandii and Larix principis-rupprechtii significantly reduced the decomposition and overall final nutrient release rates of the litter of C. fargesii and E. ulmoides (in which only the extracts of P. orientalis litter did not affect the mass loss of E. ulmoides litter). Correspondingly, significant decreases in the activity of soil cellulase and polyphenol oxidase were observed during the entire decomposition period, especially during the middle and later decomposition stages, indicating that the PSM release from coniferous litter might inhibit the decomposition and nutrient cycling of C. fargesii and E. ulmoides litter by depressing the activity of lignocellulolytic enzymes during mixed decomposition. In conclusion, more attention should be given to the effects of leached litter PSMs on the decomposition of other types of litter during mixed afforestation or in the mixed transformation of pure forests.