Understory fine roots are more ephemeral than those of trees in subtropical Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) stands

Abstract

We tested the life span of fine roots of Chinese fir trees and understory plants in two stands in subtropical China. Fine roots from understory plants were much more ephemeral than those from trees. The life span of fine roots of understory plants and Chinese fir was shorter in the younger than in the older stand, although most of the factors affecting fine-root life spans were similar between trees and understory plants. Understory fine root can contribute significantly to total fine root biomass and belowground carbon. The contribution of understory vegetation to belowground carbon and nutrient cycling is often neglected in forest stands. Potential differences in fine-root life span between understory and trees remain poorly known. This study aimed to document fine-root life spans in trees and understory plants in two Chinese fir plantations with different ages. We measured fine-root (≤2 mm in diameter) life span for trees and understory vegetation in 16- and 88-year-old Chinese fir plantations in southern China during 4 years with minirhizotron. Factors controlling fine-root life spans were identified with Cox proportional hazards regression. Fine roots were more ephemeral in understory plants than in trees in the two plantations. Fine-root life spans for both trees and understory plants were longer in the older than in the younger plantation. Root diameter at appearance, rooting depth, and season of emergence had a significant effect on fine-root life span. These results highlight the importance of taking into account understory fine-root life span estimates when assessing the dynamics of fine-root recycling in Chinese fir forests.