关键词: 混交度, 青海云杉中龄林, 林分结构, 细根, 分布, 生物量, 形态特征

Abstract:

Objective: Picea crassifolia is the dominant native species in the northeast Qinghai-Tibetan Plateau, and thus is believed to be important in regulating regional soil and water conservation and carbon cycle. The objective of this research was to investigate the effects of mingling intensity on the dynamics of fine root biomass, morphological characteristics and their impact mechanism in P. crassifolia mixed natural forests. The result would provide a theoretical basis for forest rehabilitation and management in the eastern Tibetan Plateau. Method: A suite of mixed middle-aged P. crassifolia natural forests representing different mingling intensities (0, 0.2, 0.4, and 0.6) were selected in Datong, Xining, eastern Qinghai-Tibetan Plateau of China. Fine root biomass density, specific root length, specific root surface area, root surface area density, and root length density were analyzed from two soil depths (0-20 and 20-40 cm) by taking soil cores. Result: In the P. crassifolia forest of mingling intensity 0.4, the diameter class of 10-25 cm (63.72%), height classes of 24-32 cm (48.72%) and 16-20 cm (11.18%), accounted for the largest proportion of all trees, which are significantly higher than the forests with other 3 mingling intensities. Fine root biomass density was mainly distributed in 0-20 cm soil depth, accounting for 68.31%-83.49% of the total. Values of fine root biomass density in the soil depth of 0-20 cm increased with the increasing mingling intensity and peaked at the mingling intensity of 0.4 (616.26 g·m^-3) and then decreased in the mingling intensity of 0.6. Fine root biomass density in the soil depth of 20-40 cm increased with increasing mingling intensity, which peaked at the intensity of 0.6 (227.17 g·m^-3). Changes of morphological characteristics of fine root highly depended on the mingling intensity. Specifically, in the soil depth of 0-20 cm, root length density and root surface area density showed as mingling intensity of 0.4 > 0.2 > 0 > 0.6, while specific root length and specific root surface area showed as mingling intensity of 0.4 > 0.2 > 0.6 > 0. In contrast, in the soil depth of 20-40 cm, root length density, root surface area density and specific root length showed the same pattern as mingling intensity of 0.6 > 0.4 > 0.2 > 0, while specific root surface area showed as the mingling intensity of 0.6 > 0.2 > 0.4 > 0. With the increase of mingling intensity, contribution of P. crassifolia to fine root biomass density and morphology such as specific root length, specific root surface area, root surface area density, and root length density gradually reduced, whereas the contribution of Betula platyphylla to that increased in the soil depth of 0-40 cm. The effect of mingling intensity on fine root length density and root surface area density was mainly focused on the finest diameter fine roots (0-1 mm). Conclusion: In the study region of eastern Qinghai-Tibet Plateau, P. crassifolia mixed forest of mingling intensity 0.4 was characterized by proper ratio of height class and diameter class. Meanwhile, uneven-aged and multi-storied forest is benefit to reduce the competition among neighbor trees overlapping and promote the using of forest resources, and thus believed to improve the stability of the forest community in the long run. The amount of fine root biomass density, specific root length, specific root surface area, root surface area density, and root length density maximized at the mingling intensity of 0.4. The result suggested that future management of middle-aged P. crassifolia forest should appropriately control the mingling intensity of 0.4, at which growth of fine roots can be maximized and the utilization of forest resource can be promoted and thus achieving the goal of sustainable development of forest.

Key words: mingling intensity, middle-aged Picea crassifolia forest, stand structure, fine root, distribution, biomass, morphological characteristics