Effects of long-term nitrogen addition and precipitation reduction on the fine root dynamics and morphology in a temperate forest.

Fine roots (< 2 mm in diameter) are the main organ for obtaining resources from the belowground part of forest and also act as a hub linking the ecological processes of plant and soil. However, in the context of global climate change, it remains unclear how fine root dynamics and morphology in temperate forests respond to increased nitrogen deposition and reduced precipitation in growing season on a year-round time scale. In this study, the minirhizotrons were used to observe the response of fine root dynamics (production, mortality, turnover and life span) and morphology (diameter, single root surface area, single root length) to long-term nitrogen addition (N, 50 kg N ha−1 yr−1), precipitation reduction (W, −200 mm yr−1) and their interactive treatments (NW) in a broad-leaved Korean pine forest in Changbai Mountains over a two-year period. The results showed that N significantly increased the average diameter of fine roots. Compared to the control treatment, all treatments significantly reduced the average monthly number and surface area of live root. However, the morphological traits of the individual root in each treatment differed between the growing and non-growing seasons. All three treatments (N, W, NW) reduced annual production of fine root over the two observation periods, while the effect on annual mortality varied between years. N, W and the interaction of NW did not significantly change the annual turnover of fine root in the first observation period but increased significantly in the second. The median life span of fine root born in both non-growing seasons was significantly lower than that of fine root born in the growing season. Our results show that changes in the growth strategy of fine root depend on the complex interrelationship between their own morphology, soil layer and seasonal climatic conditions. [ABSTRACT FROM AUTHOR]