Abstract: Aim The karst region encounters challenges such as low resistance to drought and delayed succession due to extensively exposed rocks and shallow soil layers, rendering the surface susceptible to dehydration. The study aims to investigate changes in hydraulic regulation strategies during different succession stages of species of subtropical karst forests. This exploration seeks to understand the mechanisms for adapting to drought following succession and to establish a theoretical basis for vegetation restoration and reconstruction. Methods The study centered on dominant species in forest communities across the early, middle, and late stages of succession in karst areas. Various hydraulic indicators included the vulnerability of embolism in stems and leaves (P50s and P50L), the vulnerability segmentation(P50L-s), the specific conductivity of stems and leaves (Ks and KL), the hydraulic safety margin of leaf (HSML) was assessed and calculated, and various related hydraulic indicators were measured including the density of sapwood, the huber value, and the specific leaf area (SLA). Important findings (1) No trade-off was found between hydraulic safety and efficiency between species and communities; P50s, Ks, and KL all decreased with positive succession. (2) All species exhibited positive vulnerability segmentation, ranging from 0.53 to 6.59 MPa, and vulnerability segmentation during early succession significantly exceeded that in the middle and late stages of succession. Furthermore, P50s was identified as the primary determinant of vulnerability segmentation. (3) The early stages of plant succession exhibit higher resistance to embolism, Ks, and KL, which enhance water transport and resist drought. Conversely, in the later stage, plants demonstrate a larger SLA to bolster competition for light resources. This study reveals the changing patterns of adjustment of hydraulic regulation strategies, from strategies aimed at improving hydraulic efficiency and safety to strategies aimed at increasing investment in photosynthetic carbon during the succession process of karst forest plants. This provides a theoretical basis to elucidate the mechanism of adaptation to drought of plants in the succession process of karst forest communities.

Key words: vulnerability segmentation, hydraulic traits, trade-off, community succession, karst forest