Analysis of the Variation Characteristics of Fine Root Morphological Traits in Cunninghamia lanceolata Plantation Forests at Different Forest Ages

In order to explore the variation characteristics of foraging ability of Cunninghamia lanceolata fine roots with forest age and soil depth, the variation characteristics of morphological traits (including specific root length, specific surface area, tissue density and average root diameter) of Cunninghamia lanceolata fine roots in 60 cm soil layer of 7, 10, 23, 29 and 42-year-old Cunninghamia lanceolata plantation forest in Baisha State-owned Forest Farm of Longyan City in Fujian Province were studied. The results showed that: (1) For the total fine root morphological traits in the 0~60 cm soil layer, the specific root length and specific surface area were the largest at 7 years old and the lowest at 29 years old. The tissue density was the smallest at 7 years old and the largest at 29 years old. There was no significant difference in the average diameter of roots among forest ages. (2) The specific root length and specific surface area of fine roots of Cunninghamia lanceolata were similar with the changes of forest ages in each soil layer, which were both the highest at 7 or 10 years old and the lowest at 29 years old. (3) For the average values of fine root morphological traits in the same soil layer for different stand ages, the specific root length and specific surface area of Cunninghamia lanceolata fine roots both showed a trend of decreasing first and then increasing with the increase of soil depth. Moreover, it could be found that this change trend was particularly obvious at 7 years old when distinguishing different forest ages. (4) The morphological traits of 7-year-old Cunninghamia lanceolata fine roots were significantly different among different soil layers, and the plastic changes were more active. However, there was no significant difference in the morphological traits of fine roots at 29 and 42 years old among different soil layers, and the plastic change was relatively weak. Therefore, in the late stage of stand development, the decrease of self-foraging ability of Cunninghamia lanceolata fine roots and the decrease of plasticity of the morphological traits among various soil layers may lead to the decrease of resource acquisition potential of Cunninghamia lanceolata fine roots in the late stage of stand development, which may be one factor leading to the decline of aboveground net primary productivity of Cunninghamia lanceolata in the later stage of stand development. This provided scientific basis for revealing the mechanism of productivity change of Cunninghamia lanceolata plantation forests and the rational management of Cunninghamia lanceolata plantation forests.