The synergistic effect of soil and interspecific competition shaped foraging strategy of fine roots in Alnus cremastogyne Burkill and Cupressus funebris Endl. mixed plantations

The establishment of mixed plantations changes both soil properties and interspecific relationships, making it difficult to distinguish which of these factors dominates the variation in fine root traits. We chose pure Alnus cremastogyne Burkill plantations, pure Cupressus funebris Endl. plantations, and mixed plantations, collected absorptive roots, transport roots, soil and fine root biomass (FRB) around the selected trees, then measured soil properties (nitrogen, phosphorus, potassium, carbon, water content, and pH), fine roots traits (SRL, specific root length; SRA, specific root surface area; RD, root diameter; RTD, root tissue density; RN, root nitrogen content; RP, root phosphorus content; RK, root potassium content) and the competitive parameters (CA, competitive ability index; CR, competitive ratio; CI, hegyi competition index, represents the intensity of interspecific competition) of competing trees in the mixed plantations. The results show that A. cremastogyne and C. funebris in mixed plantations presented different foraging strategies. The growth of fine roots weakened in A. cremastogyne , and a conservative strategy was observed, which manifested as decreases in SRL, SRA, and RN of absorptive roots. In contrast, the growth of fine roots increased in C. funebris , and an acquisition strategy was followed, which resulted in increases in SRL, SRA, and RN. In transport roots, RD, RTD, and RK significantly increased in A. cremastogyne , whereas RTD and RK decreased in C. funebris . A significant common effect of soil and CI jointly affected the fine roots traits and had varying degrees of influence on fine roots with different functions. Soil factors had the highest individual effect for most absorptive root traits, while the individual effect of CI for transport root traits increases close to that of soil factor. Soil alkaline nitrogen (SAN) and CI were the most important explanatory factors. SAN was positively correlated with the acquisition strategy traits (SRL, SRA, and RN) and negatively correlated with the conservative strategy traits (RD, RTD, and RK), while CI showed the opposite correlations. This study increases the understanding of the relationships between plant fine roots and external environmental factors.