Abstract
Fine roots are the most active and functional component of root systems and play a significant role in the acquisition of soil resources. Density is an important structural factor in forest plantations but information on changes in fine roots along a density gradient is limited. In this study, plantations of black locust (Robinia pseudoacacia L.) and Chinese pine (Pinus tabuliformis Carr.) with four density classes were analyzed for the influence of soil and leaf traits on fine root growth. Fine root biomass increased with stand density. High fine root biomass was achieved through increases in the fine root production and turnover rate in the high-density black locust plantations and through an increase in fine root production in the pine plantations. In the high-density Chinese pine stand, there was a high fine root turnover which, coupled with high fine root production, contributed to a high fine root biomass. Overall, fine root production and turnover rate were closely related to soil volumetric water content in both kinds of plantations, while fine root biomass, especially the component of necromass, was related to soil nutrient status, which refers to phosphorous content in black locust plantations and nitrogen content in Chinese pine plantations. There was a close linkage between leaf area index and fine root dynamics in the black locust plantations but not in the pine plantations.
Highlights
Materials and methodsThis study was conducted in southern Yan’an, Shaanxi Province, China. This area is characterized by a temperate semi-arid climate in the “forest to forest-steppe” ecosystem transition zone (Yamanaka et al 2014)
The results showed that fine root biomass in black locust could be explained by soil P and leaf area index, and fine root production and turnover rate was closely related to soil volumetric water and leaf area index
In the Chinese pine plantations, fine root biomass increased with stand density was achieved by increasing the fine root production
Summary
This study was conducted in southern Yan’an, Shaanxi Province, China. This area is characterized by a temperate semi-arid climate in the “forest to forest-steppe” ecosystem transition zone (Yamanaka et al 2014). Two soil samples were collected as replicates for each depth in each plot. Soil water content was measured at 20-cm intervals along the profile, and the average for each layer obtained from the replicated tubes. The average of the three measurements was taken as the plot soil water content used in the analysis. Representative trees were selected in each plot and healthy, mature leaves were collected from the upper and middle crowns. Three groups of leaf samples were collected from each plot and brought to the laboratory for nutrient content analysis. Leaf area index (LAI, m 2 m−2) was calculated from litterfall data from three litter traps (50 cm × 50 cm) in each plot.
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