Research Of Fine Root Growth Characteristics In Secondary Subtropical Evergreen Broad-leaved Forest With Different Restoration Stages

Chinese subtropical evergreen broad-leaved forests are highly productive and have an important impact on the carbon and nitrogen cycling of global terrestrial ecosystem,biodiversity conservation and ecological effects.However,some evergreen broad-leaved forests were seriously damaged due to long-term human disturbance.It is important for forest ecosystem management to explore the mechanism of restoration in damaged evergreen broad-leaved forest.Fine root(?2mm)is the main organ for trees to absorb water and nutrients,it is also important for plant growth and the processes of forest ecosystem restoration.So it is important to do the research of root characteristics,especially fine roots,and their correlation with soil nutrients.Not only can help us know the process of forest restoration and reconstruction,but also can help us know the mechanism of fine roots.In this study,a 20-year-old stand which was recovered after clear cutting and a 60-year-old stand without human disturbance were selected.Fine root samples were collected by soil drilling method.Fine root biomass and morphology in different stands,different soil layers,different tree species and different seasons were studied,and the correlation between fine root biomass,morphological characteristics and soil nutrients was analyzed.To explore fine root growth characteristics and interaction mechanism of tree species at different recovery stages.The results showed that:(1)It was significantly different of fine root growth characteristics between two stands,the biomass,root length and root tissue density of Cyclobalanopsis glauca and other woody roots in 60-year-old stand were significantly higher than that in 20-year-old stand.The specific surface area of fine roots of Lithocarpus glaber in the 60-year-old stand was significantly lower than that in the 20-year-old stand.Fine root biomass was only significantly correlated with soil organic matter in 20-year-old stand(P < 0.05).In terms of morphology,there was no significant correlation between the root tissue density and total phosphorus(P>0.05).Fine root biomass was significantly correlated with soil available nitrogen,total phosphorus and organic matter in 60-year-old stand(P<0.05).There was no significant correlation between specific surface area of fine roots and soil nutrients(P>0.05),and specific root length was only significantly correlated with soil organic matter(P<0.05).The different soil nutrient conditions between two stands led to the difference in fine root growth characteristics: Soil nutrients in 20-year-old stand limited the fine root morphology,while the biomass in 60-year-old stand was restricted by soil nutrients.(2)There was a significant vertical distribution of fine root biomass and morphology in two stands(P<0.05).With the increasing of soil depth,the biomass,root length,specific root length,root tissue density and specific surface area of fine roots decreased significantly.Fine roots are more concentrated in the soil surface.The fine root growth characteristics showed significantly seasonal dynamics,and the biomass reached its peak in autumn and its lowest in winter.There are two peaks in root length,which are spring and autumn.Root tissue density and specific surface area were single peaks,which appeared in autumn and winter respectively.(3)The biomass was significantly different with different diameter class(P < 0.05),increased with the diameter increasing.There are differences in fine root growth characteristics among main tree species.The percentage of D3 biomass of Lithocarpus glaber was the highest,and the percentage of D1 biomass of Schima superba was the highest.In 20-year-old stand,the biomass,root length and root tissue density of Lithocarpus glaber were the highest.In 60-yearold stand,the biomass and root tissue density of Cyclobalanopsis glauca were the highest,and specific root length and specific surface area were the lowest.There was no significant difference in fine root growth characteristics of Schima superba between two stands.(4)In the recovery stage of stand after clear cutting,Lithocarpus glaber can quickly occupy the dominant position in the stand,while Cyclobalanopsis glauca grows slowly,but it is more adaptable to the environment.With the development of stand,it will gradually occupy the dominant position.