Effects Of Natural Secondary Forests And Cunninghamia Lanceolata Plantations Of Different Ages On Soil Nematode Communities

China has become the country with the largest area of artificial forest in the world.Soil nematodes,as one of the most abundant metazoans,are an important part of soil food web,and play an important role in promoting nutrient cycling and energy flow,and maintaining ecosystem stability.The study of the effects of intensive planting and forest ecosystem restoration on soil nematode community structure is of great significance for understanding the effects of ecosystem restoration on biodiversity and the sustainable development of forest ecosystems.In this study,secondary forests(4-5,8-12,18-22,25-30,35-40,100 years)and Cunninghamia lanceolata plantations(4-5,8-12,18-22,25-30,35-40 years)at different age stages were selected as the research objects by using the method of replacing time with space in Baisha state-owned forest farm in Shanghang County,Fujian Province.The physicochemical properties,microbial biomass,soil nematode number and community composition of secondary forests and Cunninghamia lanceolata plantations in 0-10 cm soil layer of different ages were measured to explore the dynamic response of soil nematode community structure to the change of forest type and age and the driving factors affecting nematode community.The main research conclusions of this study are as follows:(1)The total density of nematodes in secondary forests and C.lanceolata plantations was 307-654/100 g of dry soil and 464-659/100 g of dry soil,respectively.The total density of nematodes in secondary forests was significantly higher than that in C.lanceolata plantations.Moreover,the density of soil nematode in secondary forests increased with the increase of stand age.The total density of nematodes in C.lanceolata plantations increased first and then decreased.(2)The relative abundance of soil nematodes in natural secondary forests was as follows: omnivores-predators(57.66%-59.40%),plant-parasites(20.15%-36.98%),bacterivores(12.99%-18.74%)and fungivores(5.03%-11.13%).The relative abundance of soil nematode groups in C.lanceolata plantations was as follows: plant-parasites(33.22%-44.49%)> omnivores-predators(27.50%-40.33%),bacterivores(12.21%-16.82%),fungivores(5.97%-22.92%).The density of plant-parasites in secondary forests was lower than that in C.lanceolata plantations during forest restoration.With the increase of stand age,the number of omnivores-predators in secondary forests was significantly higher than that in C.lanceolata plantations.(3)Soil nematode diversity index was significantly affected by forest type.Shannon diversity index(H'),evenness index(J')and richness index(SR)of soil nematode were higher in secondary forests than in C.lanceolata plantations,but Simpson dominance index(?)was the opposite.The results showed that C.lanceolata plantations was higher than natural secondary forests.In the 8-12-to 35-40-year old stands,H' of C.lanceolata plantations showed a decreasing trend,while ? showed an increasing trend.(4)Soil nematode community structure is regulated by soil physical and chemical properties and microorganisms.Redundancy analysis(RDA)showed that p H,soil water content soil N and C were the key factors affecting the change of soil nematode community.In addition,microorganisms can promote the diversity and stability of soil nematode community structure.(5)Soil nematode channel ratio index(NCR)of secondary forests was more than0.5.The results showed that fungivores were the main decompositions of organic matter in secondary forests.NCR of C.lanceolata plantations increased with the increase of stand age.WI of secondary forests is higher than that of C.lanceolata plantations.WI of C.lanceolata plantations decreased with the increase of stand age.Secondary forests soil nematodes total maturity index(?MI)and structure index(SI)were higher than that of C.lanceolata plantations.However,the secondary forests and C.lanceolata plantations ?MI and SI did not change significantly with the increase of forest age were.The results showed that the secondary forests had higher soil nematode density and diversity than the C.lanceolata plantations.In addition,stand age increased the difference of nematode density and diversity between secondary forests and C.lanceolata plantations.The functional index analysis of nematodes showed that the soil health of secondary forest was higher and soil environment was more stable.