Effect Of Using Litter Of Broad-Leaved Trees To Control Soil Enzyme Polarization In Artificial Needle-Leaved Forests

The area of artificial forests was constantly expanding, and the most common planting model was continuous cultivating a single species generation after generation. Consequently, the problem of tree growth stunted, productivity reduced, soil polarization has seriously affected and restricted the sustainable development of planted forest. Our research object were typical and pure coniferous forest of three regions: semi-arid and sandy areas of northern Shaanxi (Jingbian), semi-humid loess hilly area of northern Shaanxi (Huangling) and sub-humid ruins of gully region (Chunhua) in the north of Weihe. Our method was indoor mixed culture of forest soil and leaf litter of different broad-leaf species. We applied principal component analysis to study the comprehensive improvement effect that different litter decomposition of broad-leaf species to soil enzyme activities of coniferous forest in three regions. Our research could guide the local forest management. Not only could determine rapidly the introduction of mixed tree species to plantation, but also could provide the theoretical basis to control soil degradation or polarized. The main conclusions of our research were as follows:(1)By comparison with the original forest soil, the soil enzyme activities mixed with litter of needle-leaved trees occurred negative polarization to different extent. This showed that soil enzyme polarization occurred in artificial needl-leaved forests.(2)use broad-leaf species to improve the soil enzyme activities of Jingbian forest: most of the broad-leaf species were not appropriate to be mixed planted with Pinus tabulaeformis and Pinus sylvestris. In Pinus tabulaeformis woodland, purple-leaf plum, Sea Buckthorn and willow, this three broad-leaf species had positive effect in soil enzyme activities improvement. The suitability of introduction to mixed plantation was purple-leaf plum better than Sea Buckthorn, and Sea Buckthorn better than willow. In Pinus sylvestris woodland, only Sea Buckthorn and simon poplar played positive role in improving soil enzyme activities. And the improvement result was Sea Buckthorn better than simon poplar.(3)use broad-leaf species to improve the soil enzyme activities of Huangling Larix forest: four local common broad-leaf species, like Liaodong oak, Poplar, Birch and Black Locust were not appropriate to be mixed planted with Huangling Larix. Contrary to Larix forest, the soil enzyme activities composite index of Pinus tabulaeformis forest and Platycladus orientalis forest were improved to different extent, when they were mixed cultured with the above four litter. Four local common broad-leaf species were all appropriate to be mixed planted with Pinus tabulaeformis and Platycladus orientalis. From the point of suitability of introduction to mixed plantation in improving soil enzyme activities, Poplar was the best to Pinus tabulaeformis forest, Liaodong oak was better than Birch, and Black Locust was the least. However, Liaodong oak was the best to Platycladus orientalis forest, Poplar and Birch were better than Black Locust.(4)The litter species mixed with Chunhua forest soil included pavement trees and afforestation broad-leaf tree. In the choice of broad-leaved tree species for afforestation, we advised to introduce Poplar to be mixed planted with Pinus tabulaeformis forest, and introduce weeping willow and Eucommia to be mixed planted with Platycladus orientalis forest. In this way, we can comprehensively improve the soil enzyme activities of forest. To pavement trees, when Pinus tabulaeformis soil mixed with forest,Chinese Buckeye, Koelreuteria paniculata, Paulownia and myrobalan plum, to large extent. In Platycladus orientalis forest, most broad-leaf tree species were appropriate to be mixed planted and the index of soil enzyme activities were comprehensively improved generally Among these, Magnolia, Chinese Buckeye and Phoenix tree had better effect. Therefore, if conditions allowed we could considerer to collect the litter of these pavement trees, put them in the forest and degraded in the roots of trees to improve the soil enzyme activities.