Impact of drought stress and fertilization on plant traits and nonstructural carbohydrates of Red-Heart Chinese fir

Understanding how drought stress and fertilization influence plant physiological responses is essential for improving forest management under climate change. Previous research has primarily focused on the effects of drought stress on resource allocation and mortality. However, the interaction effect of fertilization and drought on key plant traits and non-structural carbohydrates (NSCs) dynamics remains uncertain, particularly in Red-Heart Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.). In this study, the effects of different drought stress gradients and fertilization on aboveground plant traits (different organ biomass, water content, needle number, needle area), belowground plant traits (tap root depth and lateral root spreads), leaf water potential and NSCs were examined in a pot experiment. The trade-offs in growth between aboveground and belowground plant traits become increasingly evident with soil drought gradients. Saplings in the wettest (W_25min) and driest (W_0min) group in both fertilized and unfertilized groups show clear differentiation along the two principal component axes, which are primarily determined by variations in the number of leaves on branches and leaf predawn water potential. Drought intensity mainly influences the leaf total NSCs, and the drought duration mainly influences the branch total NSCs. Fertilization typically promotes the growth of plants, especially below ground tissues. However, fertilization during drought exacerbated mortality in our experiment, especially for the moderate drought. The work highlights that Red-heart Chinese fir traits respond to drought stress gradients and fertilization, demonstrates that fertilization in combination with drought has an antagonistic effect on the growth and survival of red-heart Chinese fir saplings.