| Sichuan Province,as an important reserve province for the national reserve forest project,designated a total of 60,000 ha of national reserve forest in 2014,including 41,466ha of Pinus massoniana,Cunninghamia lanceolate,and Cupressus funebris plantations,accounting for 69.1%.However,there are phenomena such as pure forestation,intensification,and successive generations of plantation forests,and their ecological problems have become increasingly prominent.The crop-tree release is an important approach to forest management in the near nature forest.meets the objectives of human forest management.The crop-tree release accords with the goal of mankind's management of forests,it is conducive to the production of high-quality wood,and achieves good economic returns.It is also conducive to improving the structure of forest stands,taking into account the environmental requirements,and balancing various ecological functions.Soil nematodes,as typical indicator organisms in soil,can sensitively reflect the superiority of habitats.Therefore,studying the response of soil nematodes to crop-tree release is of great significance for evaluating the near-natural management effects of planted forests.In October 2015,three kinds of artificial forests(Cupressus funebris,Pinus massoniana and Cunninghamia lanceolate)were selected from the hilly areas of Sichuan Basin(Suining,Guangan and Yibin)to adopt crop trees.In other words,6 trees,9 trees or 12 trees that can be preserved for a long time,regenerated from natural species and reach the target diameter,were selected as crop trees in the sample plot of 667m~2.The disturbance trees that affect the growth of the crop trees are also felled(the remaining trees are retained).Soil nematodes were collected from three different stands in October(autumn),January(winter),April(spring)and July(summer).The soil nematodes were extracted by Baermann wet funnel method.The results of the study are as follows:(1)A total of 15,945 nematodes were isolated from soil samples from four seasons of Cypress plantation in Sui'ning City.The average density of nematodes in the litter was4253/100g,and in soil was 159/100g dry soil.A total of 59 families and 143 genera were identified.Prionchulus is a dominant genus.Its individual number accounts for 10.46%of the total.The order of different feeding types of soil nematodes was as follows:Omnivores/Predators>Bacterivores>Plant parasite>Fungivores.The nematode colonizer persister(c-p)was dominated by the c-p 4 group,accounting for 44.33%of the total.The largest number of soil nematodes genera was 12C,which were 27.9±16.6 genera.The highest density of nematode was 9C,which was 1829.3±875.2/100g dry soil.The largest density of nematode was in spring,which was 2598.6±591.3/100g dry soil.The Simpson index(?)is the highest in 9C,the Margalef's richness(D)is the highest in 9N,and the Shannon-Wiener index(H'),Trophic Diversity(TD),and Maturity index(MI)are all based on crop trees.Higher than CK;Shannon-Wiener index(H')and Maturity index(MI)were highest in autumn and lowest in winter.(2)A total of 7594 nematodes were isolated from soil samples from 4 seasons of Pinus massoniana plantation in Guang'an City.The average density of nematodes in the litter was1608/100g,and in soil was 110/100g dry soil.A total of 60 families and 146 genera were identified.Prionchulus and Mononchus are dominant genera,and their individual numbers account for 10.82%and 10.50%of the total respectively.The order of different feeding types of soil nematodes was as follows:Omnivores/Predators>Bacterivores>Plant parasite>Fungivores.The nematode colonizer persister(c-p)was dominated by the c-p 4group,accounting for 48.97%of the total.The number of nematodes was vertically distributed as follows:litter>0-10 cm>10-20 cm.The 9N nematode had the highest density of 776.8±425.9/100g dry soil.The density of soil nematode was the largest in summer which was 1071.4±334.9/100g dry soil.Trophic Diversity(TD)and Maturity index(MI)retained the highest of 9 strains;Shannon-Wiener index(H')and Pielou evenness index(J)were the highest in autumn.(3)A total of 15,924 nematodes were isolated from soil samples from four seasons of Cunninghamia lanceolata plantation in Yi'bin City.The average density of nematodes in the litter was 2659/100g,and in soil was 303/100g dry soil.A total of 56 families and 143genera were identified.Nothotylenchus and Mononchus are dominant genera.Their individual numbers account for 10.53%and 10.06%of the total respectively.The order of different feeding types of soil nematodes was as follows:Plant parasite>Omnivores/Predators>Bacterivores>Fungivores.The nematode colonizer persister(c-p)was dominated by the c-p 2 group,accounting for 48.06%of the total.The number of nematodes was vertically distributed as follows:litter>0-10cm>10-20cm.Density of nematodes in different seasons showed:autumn>spring>winter>summer.The 6C nematode had the highest density of 1661.7±343.2/100g dry soil.The density of soil nematode was the largest in autumn which was 1634.1±343.1/100g dry soil.Shannon-Wiener index(H'),Pielou evenness index(J),Trophic Diversity(TD)crop-tree release were all higher than CK,and Shannon-Wiener index(H')6C was the highest.In summary,due to the differences in tree species and environment among the three forest types,there are also differences in the characteristics of soil nematode communities.However,the crop-tree release of the three plantation made the soil nematode community structure more stable,and played an active role in the development of the soil nematode community.Among them,9 trees/667m~2 are the most favorable for the optimization of the soil nematode community and ecosystem in both Cupressus funebris and Pinus massoniana plantations.For Cunninghamia lanceolata plantation,6 trees/667m~2 were best preserved for the crop tree. |
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