刺槐油松混交比对土壤质量的影响

Effect of different mixed proportion on soil quantity in mixed Robinia pseudoacacia and Pinus tabulaeformis plantations

为探讨合理的刺槐混交比例,使其既发挥培肥地力作用,又不致过度排挤与之混交的树种,以泰山景区10刺槐、7刺槐3油松、4刺槐6油松、10油松4种林分类型为研究对象,分析土壤微生物数量、酶活性及土壤养分含量,并应用综合指数法(MDS-PCA)对土壤质量进行评估。结果表明:1)土壤养分含量、微生物数量与酶活性随刺槐比例增加而增加。当刺槐混交比例超过40%时,土壤4种微生物数量、硝态氮、有效氮、速效磷含量及过氧化氢酶活性显著高于油松纯林,而土壤酸性磷酸酶与脲酶活性在刺槐比例达到70%时,显著高于油松纯林。2)筛选出土壤p H、硝态氮、酸性磷酸酶、真菌作为最小数据集(MDS),土壤质量指数(SQI)表现为:刺槐纯林(0. 99)> 7刺槐3油松(0. 78)> 4刺槐6油松(0. 67)>油松纯林(0. 10)。综合分析表明,增加刺槐混交比例能显著改善林地的土壤质量,考虑刺槐的入侵性和泰山景区风景林经营,应调控刺槐的比例介于40%～70%之间,既能保持土壤肥力,又能维持生物多样性。

[Background]Robinia pseudoacacia is nitrogen-fixing pioneer tree,which has been extensively naturalized in the temperate regions of North America,Europe,and Asia and can improve soil quality and alter soil microbial community.Due to its root-sucker reproduction,R.pseudoacacia formed specific plant communities,whose herb layer is markedly different from that in forest dominated by native trees,resulting in the ecological risk.It causes both plant richness loss and shifts in species composition.In order to lift the reasonable utilization of R.pseudoacacia and let it play a greater role,the appropriate proportion of R.pseudoacacia was explored in Mount Tai.[Methods]The main soil types are crude brown soil and common brown soil.The elevation range of the sample in this study are 580-700 m and the slope are southeast.The sampling sites were determined based on the mixed proportion of R.pseudoacacia and Pinus tabulaeformis.Four types and three repeats for each type were set:typeⅠ:pure R.pseudoacia(100%);typeⅡ(70%R.pseudoacia+30%P.tabulaeformis);typeⅢ(40%R.pseudoacia+60%P.tabulaeformis);typeⅣ:pure P.tabulaeformis(100%).The four types presented continuous patch distribution in this scenic spot,and the habitat characteristics were relatively consistent.Soil microorganisms,soil enzyme activities and soil nutrients for four types were analyzed.Soil quality of these forest stands was further assessed with principal component analysis(MDS-PCA).[Results]1)Soil microorganisms,soil enzyme activities and soil nutrients increased with the increasing of proportion of R.pseudoacia.The soil microorganisms,NO3-N,available N,available P and catalase were significantly higher than typeⅣwhen the proportion of R.pseudoacia reached 40%.Acid phosphatase and urease were significantly higher than typeⅣwhen the proportion of R.pseudoacia reached 70%.2)The pH,NO3-N,acid phosphatase and fungi were selected as the minimum data set(MDS).The soil quality index(SQI)of typeⅠ,typeⅡ,typeⅢ,typeⅣwas 0.99,0.78,0.67 and0.01,respectively.In general,all three types of plantations improved soil quality compared to typeⅣ.With the increasing of the proportion of R.pseudoacacia,the soil quality was significantly better than that of pure P.tabulaeformis forest.When the proportion of R.pseudoacia reached 40%,the soil quality was improved significantly.But the soil quality was not improved significantly when the proportion of R.pseudoacacia continued to increase.[Conclusions]Comprehensive analysis shows that increasing the proportion of R.pseudoacacia can significantly improve the soil quality.Therefore,adjusting the proportion of R.pseudoacacia and maintaining the proportion at 40%-70%are suggested to improve the general fertility quality of forest stands.