亚热带北缘次生阔叶林土壤性状和菌根真菌多样性随坡位的变化

Effects of Slope Position on Soil properties and Mycorrhiza Fungi Diversity in Secondary Broad-leaved Forest in North Rim of Subtropical Zone

菌根真菌的侵染和共生有助于林木对土壤氮、磷等养分的吸收利用,是林木适应瘠薄土壤条件和困难立地的有效方式。以位于宁镇山脉中部空青山的次生阔叶林为对象,利用自然地形变化所产生的立地条件的差异,分别采集上、中、下坡的林木根系及土壤样品,分析菌根真菌侵染率和多样性,以及相应的土壤性状,研究亚热带北缘次生阔叶林林木根系的菌根真菌侵染情况随坡位的变化,并探讨其与土壤养分供应之间的关系。结果表明,不同坡位林地土壤的含水量、pH值、有效磷含量以及微生物生物量氮含量差异不显著,但均随坡位下降而升高。下坡和中坡的土壤有机碳含量、全氮含量、无机氮含量以及微生物生物量碳含量整体上均显著高于上坡。上、中、下坡林木菌根平均侵染率分别为92.1%、84.7%和74.6%,随着坡位的下降侵染率显著降低。不同坡位菌根真菌的Shannon-Wiener指数、Simpson指数和丰富度指数差异显著,表现为上坡>中坡>下坡,菌根真菌的均匀度指数在不同坡位间没有差异。不同坡位菌根真菌侵染率以及Shannon-Wiener指数均与土壤有机碳和硝态氮含量呈显著负相关,此外,菌根真菌Shannon-Wiener指数还与土壤pH显著负相关,与铵态氮含量显著正相关。菌根真菌的丰富度指数则与土壤含水量、有机碳含量、有效磷含量以及微生物生物量氮含量呈显著负相关。综合结果表明,亚热带北缘丘陵山区次生阔叶林菌根真菌侵染与土壤养分状态之间存在一定的权衡关系,上坡硝态氮的相对匮乏促使更多的菌根真菌侵染以及更高的菌根真菌多样性,通过林木与菌根真菌的互利共生保障林木的氮素获取和正常生长。

The infection and symbiosis of mycorrhizal fungi contributes to the absorption and utilization of soil nutrients,which is an effective way for forest trees to adapt to barren site conditions.In order to reveal the effects of slope position on soil properties and mycorrhizal fungal infection and to investigate the relationship between,this paper used the different site conditions generated by natural topographic changes to collect the tree root and soil samples for the analysis of the infection and diversity of mycorrhizal fungi as well as the corresponding soil traits from the upper,middle and lower slopes,respectively,in the secondary broad-leaved forest in Kongqingshan Mountain in the middle of Ningzhen Mountain Range.The results showed no significant differences for moisture content,pH value,available phosphorus content and microbial biomass nitrogen(MBN)content in forest soil of different slopes,but they all increased with the decline of slope position.The soil organic carbon content,total nitrogen content,inorganic nitrogen content and microbial biomass carbon(MBC)content of the middle and lower slope were significantly higher than the upper slope.The average infection ratio of mycorrhizal fungi in the upper,middle and lower slopes was 92.1%,84.7%and 74.6%,respectively,and decreased significantly with the decline of the slope position.The Shannon-Wiener index,Simpson index and Richness index of mycorrhizal fungi were significantly different in different slopes,showed also obvious downtrend from upper slope to lower slope.No differences were found for the evenness index of mycorrhizal fungi among different slopes.The mycorrhizal infection ratio and Shannon-Wiener index of different slopes were negatively correlated with soil organic carbon and NO3.-N content significantly.In addition,the Shannon-Wiener index of mycorrhizal fungi was also negatively correlated with soil pH and positively correlated with NH4+-N content significantly.On the other hand,the richness index of mycorrhizal fungi was negatively correlated with soil moisture content,organic carbon content,available phosphorus content,and MBN content significantly.The integrated results indicated a trade-off relationship between the mycorrhizal fungal infection and the soil nutrient status of the secondary broad-leaved forest in the hilly area of the north rim of subtropical area.The lack of soil nutrients supply,especially NO3.-N,of the upper slope might boost the mycorrhizal fungi infection and increase their diversity,thus ensure the N utilization and benefit tree growth through the symbiosis relation.The abundance index of the comprehensive analysis showed that there was a trade-off relationship between the mycorrhizal fungal infection and the soil nutrient status of the secondary broad-leaved forest land in the hilly area of the northern subtropical zone.The relative lack of up-state nitrate nitrogen promotes more mycorrhizal fungal infection and higher mycorrhizal fungi diversity,through the mutual benefit of forest trees and mycorrhizal fungi to ensure the nitrogen harvest and normal growth of forest trees.