Seasonal variation in the economic strategy of typical ferns in mixed broadleaved Korean pine forest

We measured the whole-plant traits (12 traits from leaves and roots) of three common fern species in the mixed broadleaved Korean pine forest, Dryopteris crassirhizoma, Athyrium brevifrons, and Matteuccia struthiopteris, during spring, summer, and autumn, and analyzed the variations of traits and economic strategies across different seasons. The results showed that interspecific differences were the primary factor influencing the variation in the whole plant traits of ferns, with an explanation rate of 37.2%. For leaf traits (including specific leaf area, leaf dry mass content, net photosynthetic rate, instantaneous water use efficiency, leaf nitrogen content, and leaf phosphorus content), seasonal variation contributed 42.7% of the total variation, while interspecific variation contributed 30.9%, and individual difference contributed 21.4%. For root traits (including root diameter, specific root length, root dry matter content, root tissue density, root nitrogen content, and root phosphorus content), individual variation accounted for 47.8% of the variance, interspecific variation contributed 43.5%, and seasonal variation accounted for only 5.3%. D. crassirhizoma exhibited a more conservative resource-use strategy compared to the other two fern species, while M. struthiopteris displayed a more acquisitive strategy. Leaf, root, and whole-plant traits of all the three species conformed to the one-dimensional economic spectrum, except for specific root length, which was independent of the root economic spectrum. From spring to autumn, the whole plant of fern shifted from an acquisitive strategy to a conservative strategy.