Production And Morphological Characteristics Of Fine Roots In Three Chinese Fir (Cunninghamia Lanceolata) Plantations At Different Stand Ages

Fine roots are the primary organ to uptake water and essential nutrients from soil to support tree growth. The growth and turnover of fine root play an important role in the ecological process underground, including energy flow and nutrient cycling in forest ecosystems. Fine roots have been studied mostly based on the arbitrary size classes, such as the defined diameter less than 2 mm. This approach has provided an effective way for estimating biomass and production underground. However, it ignored the relationships between the morphology of the branching root system and its function. In this study, standing fine root mass, vertical distributions and production were investigated in Chinese fir (Cunninghamia Lanceolata) plantations at different stand ages (7 yr,17 yr and 25 yr) by using the sequential soil core method in Huitong National Forest Ecosystem Research Station, Hunan Province, China. To study the heterogeneity of morphology of different roots orders, fine root samples were collected from Chinese fir plantations of different stand ages and were grouped into different orders. The biomass, average diameter, specific root length, specific surface area and tissue density of different root orders were measured. The main results are shown as follows:(1) The total fine root biomass of Chinese fir plantations decreased with the stand age increasing, the values were 636.50 g·m-2、555.64 g·m-2 and 434.32 g·m-2 at 7 yr, 17 yr and 25 yr stand, respectively. The average live fine root biomass of Chinese fir trees were 231.65 g·m-2,257.39 g·m-2,207.01 g·m-2 at 7 yr,17 yr and 25 yr stand, respectively, which accounted for 53.45%,52.32% and 54.77% of the total fine root biomass of fir trees, fine root biomass increased with stand age at the beginning and then decreased over time after the plantations reached the mature stage.(2) Biomass of fine roots in different aged Chinese fir plantations were mainly distributed at top soil depth.83.87% tree fine roots biomass was distributed at soil depth of 0-45cm and 81.19% shrub and herbs fine root biomass was distributed at soil depth of 0-30cm. Using asymptotic model (y= 1-βd) to fit fine root biomass at different soil depth, the result showed that fine root biomass in 7-yr Chinese fir stand was distributed at surface soil depth, while fine root biomass in 25-yr Chinese fir stand shifted to the deep soil.(3) Biomass of live fine root in Chinese fir plantations had high values in January and October, and decreased in April and July. Biomass of dead fine root in the three-aged plantations reached the maximum values in October and showed an increase tendency from January to October. The tissue density of fine roots decreased from January to October.(4) Fine root productivity in Chinese fir plantations estimated by maximum-minimum method were 80.36 g·m-2 for the 7-yr stand,79.62 g·m-2 for the 17-yr stand, and 98.51 g·m-2 for the 25-yr stand. Estimations by the decision matrix method, fine root productivity in Chinese fir plantation were 173.47 g·m-2 for the 7-yr stand,191.94 g·m-2 for the 17-yr stand, and 139.49 g·m-2 for the 25-yr stand, which were 2.16 times,2.41 times and 1.42 times than that of the maximum-minimum method. The annual turnover in Chinese fir plantation estimated by the decision matrix method were 0.749 times a-1 for the 7-yr stand,0.746 times a-1 for the 17-yr stand, and 0.674 times a-1 for the 25-yr stand.(5) As the stand age increased, specific fine root length (SRL) and specific fine root surface area (SRA) of Chinese fir decreased at first and then increased, the average diameter decreased and the tissue density increased. The tissue density decreased with soil depth.(6) With increase in root orders, the average diameter and tissue density of fine roots increased, but SRL and SRA decreased. According to the length and surface area parameter,45.9% and 44.2% of the fine roots was belong to the diameter class between 0.500.75mm, which is also the maximum value of the 7 diameter classes divided from 0mm to 1.75mm.