复层异龄林林下植物多样性与土壤性质对杉木保留密度的响应
Response of plant diversity and soil properties to Cunninghamia lanceolata retention density in the understorey of a compound heterogeneous forest
[目的]杉木(Cunninghamia lanceolata)是我国南方最重要的速生用材树种之一。本文通过研究杉木不同保留密度对杉阔复层异龄林林下植物多样性、土壤理化性质和酶活性的影响，为杉木人工林地力维持和可持续经营提供理论依据。[方法]以湖南省永州市金洞管理区金洞林场杉阔复层异龄林为研究对象，设置3种杉木保留密度(525 株/hm2、675 株/hm2、975 株/hm2)，通过林下植被调查与多样性分析(草本、木本植物的科、属、种组成、Simpson多样性指数、Shannon-Wiener多样性指数和Pielo u 均匀度指数和群落相似度指数)、土壤理化性质(容重、含水率、总孔隙度、全碳、全氮、全磷、全钾、全钙、全镁)和酶活性(酸性磷酸酶、蔗糖酶、脲酶、过氧化氢酶)测定，分析林下植物多样性、土壤理化性质和酶活性对杉木保留密度的响应机制。[结果](1)草本植物多样性指数随杉木保留密度的增加而增加，而木本多样性指数的变化规律与之相反。D525 密度的林分中草本植物前三优势物种重要值之和最高，达到 38.81%，D975 密度的林分中木本植物前三优势物种重要值之和最高，达到 77.39%。(2)土壤容重、含水率、总孔隙度在3种杉木保留密度的林分中无显著性差异(P>0.05)，但随着杉木保留密度的降低，土壤的容重、含水率、总孔隙度都小范围增加，土壤全碳、全氮、全磷、全钾、全钙、全镁含量均随杉木保留密度的增加呈先增后减趋势，并在D675密度林分中含量达到最大，且与其它两个密度差异显著(P<0.05)，杉木保留密度的降低有助于土壤养分积累。(3)土壤酸性磷酸酶、蔗糖酶、脲酶、过氧化氢酶活性在 3 种杉木不同保留密度的林分中大都随着保留密度的增大呈先增后减的趋势，且均在D675 密度林分中达到最大，与其它两个密度有显著差异(P<0.05)。(4)从相关性分析来看，草本植物与木本植物多样性指标大都呈负相关关系，且木本植物较草本植物来说与土壤理化性质、土壤酶活性相关性更高，土壤理化性质大都与土壤酶活性呈正相关关系;D975、D675密度林分中草本植物与密度的关系表现为正相关，且D975 密度林分表达更为强烈，说明高保留密度更利于草本植物生长，D525、D675 密度林分中木本植物与密度的关系表现为正相关，说明木本植物在低杉木保留密度下有更好的生长环境;D975、D525密度林分中土壤理化性质、酶活性与密度的关系绝大都表现为负相关，而 D675 密度林分中土壤理化性质、酶活性与密度的关系都表现为正相关，说明过高或过低的杉木保留密度对土壤理化性质改善、酶活性提高都有负面影响。[结论]本研究中，杉木保留密度为 675 株/hm2 是杉阔复层异龄林经营的最适密度。林下植被的演替存在着密度效应，密度过高或过低易使林分出现生态位垄断的现象。保留密度的降低有助于改善土壤通气透水状况，促进土壤养分积累，提高酶活性，从而促进养分转化，提高林地土壤肥力，促进杉木人工林退化生态系统的恢复与重建。
[Objective]Cunninghamia lanceolata is one of the most important fast-growing timber species in southern China.This paper investigates the effects of different retention densities of cedar on understorey plant diversity,soil physicochemical properties and enzyme activities,and provides a theoretical basis for the maintenance of woodland fertility and sustainable management of cedar plantation forests.[Method]Three types of retention densities(525 plants/hm2,675 plants/hm2,975 plants/hm2)were set up in the fir-coppice multi-storey xeric forest of the Jindong Forest Farm of the Jindong Management Area in Yongzhou City,Hunan Province.Understory vegetation surveys and diversity analyses(family,genus,and species composition of herbaceous and woody plants,Simpson's diversity index,Shannon-Wiener's diversity index,and Pielou's evenness index and community similarity index),soil physicochemical properties(bulk density,water content,total porosity,total carbon,total nitrogen,total phosphorus,total potassium,total calcium,and total magnesium),and enzyme activities(acidic phosphatase,sucrase,urease,catalase)were measured to analyse the response mechanism of understorey plant diversity,soil physicochemical properties and enzyme activities to cedar retention density.[Result](1)Herbaceous diversity index increased with the increase of cedar retention density,while the change pattern of woody diversity index was opposite.the sum of the importance values of the top three dominant species of herbaceous plants was the highest in the stand with D525 density,reaching 38.81%,and the sum of the importance values of the top three dominant species of woody plants was the highest in the stand with D975 density,reaching 77.39%.(2)Soil bulk weight,water content and total porosity did not differ significantly among the three cedar retention densities(P>0.05),but with the decrease of cedar retention density,soil bulk weight,water content and total porosity increased slightly,and the contents of soil total carbon,total nitrogen,total phosphorus,total potassium,total calcium and total magnesium showed a tendency of increasing and then decreasing with the increase of cedar retention density and reached the maximum in the stand with the density of D675 and differed significantly from the other two densities(P<0.05),which helped the accumulation of soil nutrients.The content reached the maximum in the D675 density stand,and the difference with the other two densities was significant(P<0.05),and the reduction of the cedar retention density contributed to the accumulation of soil nutrients.(3)Soil acid phosphatase,sucrase,urease,and catalase activities mostly showed an increasing and then decreasing trend with increasing retention density in the stands of the three fir species at different retention densities,and all of them reached the maximum activity in the D675 density stand,which was significantly different from the other two densities(P<0.05).(4)From the correlation analysis,most of the diversity indicators of herbaceous plants and woody plants were negatively correlated,and the correlation between woody plants and soil physicochemical properties and soil enzyme activities was higher than that of herbaceous plants,and most of the soil physicochemical properties were positively correlated with soil enzyme activities.The relationship between herbaceous plants and density in D975 and D675 density stands showed a positive correlation,and the D975 density stands showed a stronger expression,indicating that high retention density is more favourable to the growth of herbaceous plants,and the relationship between woody plants and density in D525 and D675 density stands showed a positive correlation,indicating that woody plants have a better growing environment in low cedar retention density;the relationship between the physical and chemical properties of the soil and enzyme activity and density in D975 and D525 density stands mostly showed a negative correlation,whereas soil In D975 and D525 density stands,the relationships between soil physical and chemical properties,enzyme activity and density were all positively correlated,indicating that too high or too low cedar retention density had a negative effect on the improvement of soil physical and chemical properties and enzyme activity.[Conclusion]In conclusion,the cedar retention density of 675 plants/hm2 is the optimal density for the management of cedar and broadleaf old-growth forest.There is a density effect in the succession of understorey vegetation,and too high or too low density will easily make the forest stand monopolise the ecological niche.Reduced retention density can help to improve soil aeration and water permeability,promote soil nutrient accumulation,and increase enzyme activity,thus promoting nutrient transformation,improving forest soil fertility,and facilitating the recovery and reconstruction of degraded ecosystems in cedar plantation forests.
张心艺;李铁华;
中南林业科技大学林学院 湖南 长沙 410004##中亚热带林学国家长期科研基地 湖南 长沙 410004;中南林业科技大学林学院 湖南 长沙 410004##中亚热带林学国家长期科研基地 湖南 长沙 410004;
Cunninghamia lanceolata density understorey vegetation soil physicochemical properties soil enzyme activity
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