Decades of ecological restoration on the Loess Plateau has achieved significant on-site benefits to reduce soil erosion and improve soil quality, with remarkable off-site effects of reducing sediment delivery to Yellow River. However, regional forest community succession is still far from being adequately developed. The Ziwuling forest region and its highly developed forest community, as an advanced eco-zone, can lend practical experience to other regions on the Loess Plateau and help to identify the most suitable tree species for a better regional restoration in the future. With the aim to systematically understand the potential effects of typical local tree species to soil properties, three typical and well-established artificial forests in the Ziwuling region, Robinia pseudoacacia, Pinus tabuliformis and Platycladus orientalis were investigated in this study, with the climax community Quercus wutaishanica as a reference. All the four forest type had comparable stand age (25 years). Soil samples from 0-20 cm layers were collected from those four plantations. The soil microbial biomass (carbon and nitrogen), soil enzyme (invertase, urease and alkaline phosphatase) activities and their correlations were measured and analyzed. The results showed that: 1) soil invertase activity ranged from 16.94 to 64.49 mg·g-1·24 h-1, the soil urease activity from 0.15 to 0.26 mg·g-1·24 h-1, and the alkaline phosphatase activity from 0.65 to 1.23 mg·g-1·24 h-1. The activities of those three enzymes were significantly higher in the P. orientalis soil that in the R. pseudoacacia and P. tabuliformis soils. The geometric average values in the P. orientalis soil were even greater than that in the Q. wutaishanica soil. 2) The soil microbial biomass carbon and nitrogen varied from 247.37 to 529.84 mg·kg-1 and 41.48 to 77.91 mg·kg-1, respectively. Both of them were significantly greater in the P. orientalis soil than that in the R. pseudoacacia and P. tabu-liformis soils. Even though the soil microbial biomass carbon in the P. orientalis soil remained lower than that in the Q. wutaishanica soil, its soil microbial biomass nitrogen was greater than in the Q. wutaishanica soil. 3) The dissolved organic carbon and nitrogen in the P. tabuliformis soil were much greater than that in other species, even greater than their own soil microbial biomass carbon and nitrogen. Such a result indicated that dissolved organic matter might play a more important role in providing plant available nutrients than microbial biomass in the P. tabuliformis soil. 4) The microbial biomass carbon and nitrogen were significantly positively correlated with the total organic carbon and the total nitrogen, particularly for the R. pseudoacacia and P. tabuliformis soils. There were significantly positive relationships between the soil invertase activity, urease activity and alkaline phosphatase activity, and their soil organic carbon, total nitrogen and total phosphorus contents. 5) Based on the results of principal component analysis, we concluded that the artificial forests types had obvious effects on soil microbial carbon and nitrogen, soil organic carbon, total nitrogen, the ratio of carbon to phosphorus, the ratio of nitrogen to phosphorus and urease activity. Overall, our findings suggested that P. orientalis is better than R. pseudoacacia and P. tabuliformis in term of improving soil properties in the south forest zone on the Chinese Loess Plateau.
数十年来,黄土高原的生态恢复取得了显著的效益,不仅遏制了当地的土壤流失,改善了土壤质量,同时也减少了向黄河的输沙量.但是,区域森林物种和群落演替还远未得到充分发展.子午岭林区及其高度发达的森林群落,作为先进的生态区,可以将实践经验和知识借鉴到中国黄土高原的其他地区,有助于确定最有效的人工林树种,以便今后更好地进行生态恢复.为了系统地了解典型的当地树种对土壤性质的潜在影响,本研究以黄土高原子午岭天然次生林区生长状况较好的人工林(刺槐、油松和侧柏)为研究对象,并以子午岭林区顶极群落辽东栎天然林为对照,这4种林型具有较一致的树龄(25年)、立地条件等.采用传统方法测定4种乔木林0～20 cm土壤理化性质、土壤酶活性(蔗糖酶、脲酶和碱性磷酸酶)和土壤微生物生物量碳、氮.结果表明: 1)土壤蔗糖酶活性为16.94～64.49 mg·g-1·24 h-1,脲酶活性为0.15～0.26 mg·g-1·24 h-1,碱性磷酸酶为0.65～1.23 mg·g-1·24 h-1,且侧柏土壤的3种酶活性均显著高于刺槐和油松土壤.从3种酶活性几何平均值来看,侧柏土壤酶活性甚至高于辽东栎;2)土壤微生物生物量碳、氮变化范围分别为247.37～529.84 mg·kg-1、41.48～77.91 mg·kg-1,均为侧柏>油松>刺槐,且侧柏显著高于油松和刺槐.辽东栎土壤微生物生物量碳高于侧柏,而微生物生物量氮低于侧柏,但差异均不显著;3)油松土壤溶解性碳、氮含量较高,甚至高于土壤微生物生物量碳、氮,说明油松土壤中溶解性有机物是较微生物生物量更主要的活性养分;4)土壤微生物生物量碳、氮与土壤有机碳和全氮含量呈显著正相关性,刺槐和油松土壤蔗糖酶、脲酶和碱性磷酸酶活性分别与土壤有机碳、全氮和全磷含量呈显著正相关;5)主成分分析结果表明,植被类型对土壤微生物生物量碳和氮、有机碳、全氮、碳磷比、氮磷比、脲酶影响较大,土壤微生物生物量碳、氮、碳磷比、氮磷比和氮与磷呈负相关,土壤溶解性碳、氮与碳氮比呈负相关.表明侧柏是较油松和刺槐更适用于南部森林带的造林树种.
Keywords: Loess Plateau; alkaline phosphatase activity; invertase activity; microbial biomass carbon and nitrogen; soil; urease activity.