| 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. |
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