【作者】 李茜；

【导师】 刘增文；

【作者基本信息】 西北农林科技大学 ， 生态学， 2013， 博士

【摘要】 黄土高原地区人工纯林由于物种组成单一，层次结构简单加之复杂的自然条件原因而出现了林木老化、更新困难、土壤衰退等现象，严重影响着当地林地的稳定性和林业的可持续经营。通过研究不同树种的种间关系来营造科学合理的混交林是解决人工纯林问题的有效途径。不同树种枯落叶混合分解对土壤性质的影响及相互作用的探讨是种间关系研究的重要内容之一。土壤是森林生态系统中林木赖以生存的物质基础，而枯落叶作为养分的基本载体，是连接林木与土壤的中间体，在维持土壤肥力、促进森林生态系统正常物质循环和养分平衡方面起着重要的作用。枯落叶的分解影响着林地土壤的生物学和化学性质，进而影响着林木的种间协调性和森林的可持续性。因此，研究不同树种枯落叶混合分解对土壤性质的影响以及在对土壤性质的影响中是否存在相互作用，可以为林木种间关系的探索和科学营造混交林提供依据。该研究通过对黄土高原常见的13个树种枯落叶进行单独和混合分解试验，探讨了不同树种枯落叶混合分解对土壤微生物、酶活性和化学性质的影响及在对土壤性质影响中是否存在相互促进或抑制作用，同时用主成分分析法综合判断了枯落叶混合分解对土壤性质影响的综合效应。结果表明:（1）13个树种枯落叶单独混土分解不同程度提高了土壤脲酶（油松54%～柠条110%）、脱氢酶（樟子松85%～紫穗槐288%）和磷酸酶（白桦81%～柠条301%）活性，增加了有机质（沙棘29%～白桦55%）和碱解N（樟子松11%～柠条49%）含量。同时，这13种枯落叶单独分解后土壤蔗糖酶、蛋白酶活性和速效K含量也有一定程度的提高。不同树种枯落叶单独分解对土壤速效P和CEC的影响差异较大，油松、刺槐、白桦、辽东栎、白榆、旱柳、柠条和紫穗槐枯落叶单独分解后土壤速效P含量均有显著增加，而落叶松、侧柏、小叶杨和沙棘均显著减少。除小叶杨和辽东栎外，各个树种枯落叶单独分解均使土壤CEC显著降低。柠条和紫穗槐枯落叶进行单独分解对土壤性质的改善作用最明显。（2）针叶树种与其他树种枯落叶混合分解的研究表明：油松分别与沙棘、刺槐、小叶杨和紫穗槐枯落叶成对混合分解对土壤性质的影响综合表现为相互促进，而与柠条、落叶松、白桦、辽东栎和侧柏枯落叶成对混合分解对土壤性质综合表现为相互抑制，与白榆枯落叶作用不明显；樟子松分别与白桦、刺槐、白榆和柠条枯落叶混合分解对土壤性质的影响存在相互促进作用，而与小叶杨、沙棘、紫穗槐、侧柏和辽东栎枯落叶混合分解对土壤性质的影响存在相互抑制作用，与落叶松枯落叶无明显作用；落叶松分别与刺槐、紫穗槐和白桦枯落叶混合分解对土壤性质的影响存在相互促进作用，而分别与柠条、侧柏、白榆、辽东栎、小叶杨枯落叶存在相互抑制作用，与沙棘枯落叶无明显作用；侧柏分别与紫穗槐、白桦、柠条和沙棘枯落叶混合分解对土壤存在相互促进作用，而与小叶杨、白榆、刺槐和辽东栎枯落叶则相反。（3）阔叶树种枯落叶混合分解的研究表明：小叶杨与白榆枯落叶混合分解对土壤性质的影响存在相互促进作用，而与柠条、紫穗槐、沙棘和辽东栎枯落叶则存在相互抑制作用，分别与刺槐、白桦枯落叶混合分解对土壤影响的作用不明显；刺槐分别与白桦和沙棘枯落叶分解对土壤的影响存在相互促进作用，而与辽东栎和柠条枯落叶则存在相互抑制作用，刺槐与白榆枯落叶分解相互作用不明显；白桦分别与沙棘、紫穗槐和柠条3种灌木树种枯落叶分解对土壤性质的影响存在相互促进作用，而分别与辽东栎和白榆相反；辽东栎分别与柠条和沙棘枯落叶分解对土壤性质的影响存在相互促进作用，而分别与紫穗槐和白榆相反；白榆分别与沙棘和旱柳枯落叶分解对土壤性质的影响存在相互促进作用，而分别与紫穗槐和柠条相反；旱柳分别与沙棘和紫穗槐枯落叶混合分解对土壤性质的影响存在相互促进作用，而与柠条枯落叶分解则相反。（4）灌木树种沙棘、柠条和紫穗槐枯落叶两两混合分解后，沙棘与紫穗槐枯落叶、柠条与紫穗槐枯落叶两种组合对土壤性质的影响综合表现为相互促进作用，而沙棘与柠条枯落叶对土壤性质的影响综合表现为相互抑制。沙棘、柠条和紫穗槐这3种固氮树种枯落叶混合分解并不总是对土壤氮素和其他养分的影响产生促进作用，可能与分解过程中产生的化合物有关。（5）不同类型枯落叶混合分解后存在两大情况，一种是对土壤性质作用的叠加效应，也称加性效应（additive effects），本文中表现为不同枯落叶混合分解后土壤性质实测值与预测值无明显差异，即对土壤性质无明显相互作用，占全部作用结果的少数部分；另一种是非加性效应（nonadditive effects），表现为不同枯落叶分解对土壤性质的影响存在相互促进或抑制作用，占全部结果的大多数。产生促进作用的原因是枯落物混合为分解者提供更为有利的微环境，使得微生物数量、活性和群落结构更加完善，同时，高质量的枯落叶通过分解者将有效养分通过被动扩散和菌丝桥转移给了质量较低的枯落叶，从而加快了混合枯落叶的分解速度和土壤养分的提高。而抑制作用是因为不同枯落叶在混合分解过程中释放了一些次级化合物，如单宁酸、多酚类，它们能抑制枯落物的分解，影响养分的输入。更多还原

【Abstract】 On the Loess Plateau, recent observations have found a decline in the plantationproductivity and the presence of soil degradation on planted monoculture stands of differenttree species because of single species composition and hierarchical structure, and toughnatural conditions. This phenomena have serious affected the local forest ecosystem stabilityand sustainable development. To study the interspecific relationship of the different treespecies and plant scientific mixed forest is the effective way of solving the problems ofplanted monoculture stands.Soil is an important component of forest ecosystems, and it is the material foundation ofthe survival of trees. As the basic carrier of nutrients, litterfall become intermediates betweenforest and soil. Litterfall controls nutrient cycling and primary productivity and contributes tothe maintenance of soil fertility. Litter decomposition affects the physicochemical propertiesand biological activities of forest soil, and then affects coordination between the species andthe sustainability of the forest. Therefore, knowledge about the decomposition of mixed litterand its effect on soil properties is important for evaluating interspecific relationships andcompatibility in mixed forests.In this study, leaf litter mixtures consisting of13trees species were ground and mixedwith soil to analyze the effects of their decomposition on the quantity of soil microbes, theactivities of soil enzymes and the soil chemical properties and to determine the interactionsbetween the different types of litter within a mixture during decomposition. Meanwhile, thesynthetical effects of different decomposed litter mixtures on soil properties were judgedusing principal component analysis. The results showed that:(1) The decomposition of single-species leaf litter increased urease activity by54～110%, dehydrogenase activity by85～288%, phosphatase activity by81～301%, soil organicmatter by29～55%, and available N by11～49%. Meanwhile, the saccharase activity,protease activity and available K content have been increased to some extent. Single-speciesleaf litter had mixed effects on available P and cation exchange capacity (CEC). Decomposedsingle litter from Pinus tabulaeformis, Robinia pseudoacacia, Betula platyphylla, Quercusliaotungensis, Ulmus pumila, Salix matsudana, Caragana microphylla and Amorpha fruticosa increased available P content, but single litter form Larix principis-rupprechtii, Platycladusorientalis, Populus simonii, Hippophae rhamnoides decreased the available P. Except for P.simonii and Q. liaotungensis, decomposed single litter from other species decreased the CEC.The leaf litters from C. microphylla and A. fruticosa showed the best in improving soil.(2) The result of the decomposition from coniferous species litter with other speciesshowed that: in terms of soil properties as a whole, the decomposed litter mixtures made fromP. tabulaeformis combined separately with H. rhamnoides, R. pseudoacacia, P. simonii or A.fruticosa showed synergistic interactive effects on soil, but litter mixtures from P.tabulaeformis combined separately with C. microphylla, L. principis-rupprechtii, B.platyphylla, Q. liaotungensis, or P. orientalis showed antagonistic interaction effects, and thelitter mixtures from P. tabulaeformis combined with U. pumila had no obvious interactiveeffects on soil; The decomposed litter mixtures made from Pinus sylvestris var. mongolicacombined separately with B. platyphylla, R. pseudoacacia, U. pumila, or C. microphyllashowed synergistic interactive effects on soil, but litter mixtures form Pinus sylvestris var.mongolica combined separately with P. simonii, H. rhamnoides, A. fruticosa, P. orientalis, orQ. liaotungensis showed antagonistic interaction effects, and the litter mixtures form P.tabulaeformis with U. pumila had no obvious interactive effects; The litter of L.principis-rupprechtii was mixed with that of R. pseudoacacia, A. fruticosa, or B. platyphylla,separately showed synergistic interaction effects on soil, whereas L. principis-rupprechtiilitter was mixed with that of C. microphylla, P. orientalis, U. pumila, Q. liaotungensis, or P.simonii, separately showed antagonistic interaction effects, L. principis-rupprechtii litter wasmixed with that of H. rhamnoides had no obvious interactive effects; The litter of P.orientalis was mixed with that of A. fruticosa, B. platyphylla, C. microphylla, or H.rhamnoides, separately showed synergistic interaction effects on soil, but P. orientalis litterwas mixed with P. simonii, U. pumila, R. pseudoacacia, or Q. liaotungensis did reversely.(3) The result of the decomposition between broadleaf tree species litter showed that:When P. simonii litter was mixed with litter from U. pumila, the resulting litter mixturesshowed synergistic interaction effects on soil. But when P. simonii litter was mixed separatelywith litter from C. microphylla, A. fruticosa, H. rhamnoides, or Q. liaotungensis, the resultinglitter mixtures showed antagonistic interaction effects. When P. simonii litter was mixedseparately with litter from R. pseudoacacia or B. platyphylla, the resulting litter mixtures hadno obvious interactive effects; When R. pseudoacacia litter was mixed separately with litterfrom B. platyphylla or H. rhamnoides, the resulting litter mixtures showed synergisticinteraction effects on soil. But when R. pseudoacacia litter was mixed separately with litterfrom Q. liaotungensis or C. microphylla, the resulting litter mixtures showed antagonistic interaction effects. R. pseudoacacia litter was mixed with that from U. pumila had no obviousinteractive effects; The litter of B. platyphylla was mixed separately with that of H.rhamnoides, A. fruticosa, or C. microphylla showed synergistic interaction effects on soil, butmixed with Q. liaotungensis or U. pumila did reversely; The litter of Q. liaotungensis wasmixed separately with that of C. microphylla or H. rhamnoides showed synergistic interactioneffects on soil, but mixed with A. fruticosa or U. pumila did reversely; Q. liaotungensis litterwas mixed separately with that of H. rhamnoides or S. matsudana showed synergisticinteraction effects on soil, but mixed with A. fruticosa or C. microphylla did reversely; S.matsudana litter was mixed separately with that of H. rhamnoides or A. fruticosa showedsynergistic interaction effects, whereas mixed with C. microphylla showed antagonisticinteraction effects on soil.(4) When shrub species (H. rhamnoides, C. microphylla and A. fruticosa) litter wasmixed with pair-wise decomposition, the resulting litter mixtures made from H. rhamnoidescombined with A. fruticosa, and litter mixtures made from C. microphylla combined with A.fruticosa showed synergistic interaction effects on soil, but the resulting litter mixtures madefrom H. rhamnoides combined with C. microphylla showed antagonistic interaction effects.Litter mixtures form tree species of fixing nitrogen did not always increase the soil available,may because of the release of antimicrobial compounds during decomposition.(5) There are two cases after the decomposition of different litter mixtures, one is thesuperposition effect of litter mixtures on soil properties, also called additive effects, our resultshowed that there was no obvious difference between measured and predicted value of soilproperties. That is, different litter had no obvious interaction on soil properties. The additiveeffects were a few part of all action results; Another is nonadditive effect, characterized thatthe decomposed litter mixture showed synergistic or antagonistic interactive effects on soilproperties, which is the majority of all of result. As for synergistic interactions, it has beenreconsider that litter mixtures create diverse microhabitats and niches supporting a diverseand abundant decomposer community. And the preferential exploitation of high-quality litterby decomposers leads to a high nutrient availability and allows nutrient transfer, by passivediffusion and/or through fungal hyphae, to the low-quality litter that will undergo a morerapid decomposition in the mixture. As for antagonistic interactions, it has been found that therelease of antimicrobial compounds, such as tannins and polyphenols, from a litter componentwithin a mixture, may slow down litter decay thus generating antagonistic interactions.更多还原