Estimating fine root production and mortality in subtropical Altingia grlilipes and Castanopsis carlesii forests

Abstract

The turnover of fine root, the most dynamic component of root system, play an important role in nutrient cycle and energy flow in forest ecosystems. Fine root production and mortality in two subtropical evergreen broadleaved forests, Altingia grlilipes forest and Castanopsis carlesii forest, in Wanmulin Natural Reserve, Jian-ou, Fujian province, were monitored for more than two consecutive years by using both minirhizotrons and the exvacation methods. The objectives of this research were to: (1) analyze the seasonal patterns of fine root production and mortality; (2) to examine the allocation of both root production and mortality among different soil depths, root diameter classes and orders. In order to extract biomass data of individual root from root image, the relationships between root biomass (M) and root diameter (D) and root length (L) were established: M = 0. 4671 D2 L for Altingia grlilipes, and M = 0. 5869 D2 L for Castanopsis carlesii, respectively. Though there were no significant differences (P>0. 05), annual fine root production and mortality in Altingia grlilipes ((230. 1.162. 8) g·m-2·a-1 and (188. 8.75. 5) g·m-2·a-1, respectively) were slightly higher than those in Castanopsis carlesii ((214. 5.185. 8) g·m-2·a-1 and (178. 8.26. 5) g·m-2·a-1, respectively). Fine root production reached a peak in the spring, and showed a normal distribution in 2009 in both two communities. There was a significant correlation between fine root production and monthly precipitation (P<0. 01, r =0. 566) in Castanopsis carlesii. Fine root mortality fluctuated seasonally in these two forests. The peak of fine root mortality occurred mainly in summer and autumn in Castanopsis carlesii and in fall in Altingia grlilipes. The fine root production of these two forest communities appeared mainly in the top soil layer (0-40 cm), accounting for 88. 6% and 95. 1% of the total production in Altingia grlilipes and Castanopsis carlesii, respectively. Fine root mortality had the same distribution pattern, and made up to 89. 7% and 99.2% of total mortality, respectively, in the 0-40 cm layer. In addition, the maximum of fine root production (Altingia grlilipes: (131. 7±91. 4) g·m-2 a-1; Castanopsis carlesii: (108. 6±100. 4) g·m-2 a-1) and mortality (Altingia grlilipes: (106. 4±69. 5) g·m-2 a-1; Castanopsis carlesii: (99. 7±2. 4) g·m-2 a-1) of these two forest communities appeared in the 2040 cm soil layer. With the root diameter increases, the number of root growth and death decreased, while fine root production and mortality had no corresponding tendency with diameter. Root production occurred mainly in 0-1mm, which accounts for 90. 4% of total production in Altingia grlilipes and 96. 1% in Castanopsis carlesii. Furthermore, fine root production in 0. 3-0. 6 mm was (100. 0±44. 0) g·m-2 a-1 in Altingia grlilipes and (94. 8±90. 4) g·m-2 a-1 in Castanopsis carlesii, which was the highest among different root diameter classes. Fine root mortality had the same trend with production, which accounted for 95. 5% and 100% of the total fine root mortality in 0-1mm in Altingia grlilipes and Castanopsis carlesii, respectively. Root production and mortality of the first root order were much higher than those of the higher order in both two forest communities.