Trait Plasticity, Resource Redirection and Strong Recovery Capacity Enhance Volkameria inermis Tolerance and Adaptation to Long-Term Foliar Salt Stress

Salt tolerance is a key factor limiting coastal vegetation restoration. In backshore areas, foliage is frequently exposed to salt mist and wave splash, which severely constrains plant survival and restoration outcomes. While root salt tolerance under short-term stress has been widely studied, foliar salt tolerance remains poorly understood. Here, using a self-developed experimental apparatus, we investigated the salt tolerance mechanisms of the coastal shrub Volkameria inermis through a long-term (159-day) foliar salt stress experiment (0–3.0% NaCl), followed by a 64-day recovery period. Field suitability was also evaluated at different coastal locations in Quanzhou Bay, Fujian Province. The results show that: (1) trait plasticity (e.g., leaf thickening), resource redirection (e.g., reduced growth rate, and new bud emergence in unstressed parts), and strong recovery capacity together enhance V. inermis adaptation to long-term foliar salt stress; (2) V. inermis exhibits adaptability to salinity ≤2.0% and survival under 3.0% despite severe injury; (3) besides osmotic adjustment, proline accumulation helps alleviate oxidative damage; and (4) field data demonstrated that leaf thickness and leaf water content were significantly associated with distance from the sea and elevation, thereby validating the salt-adaptation strategies observed under controlled conditions. This study provides a novel methodological framework and practical insights for selecting salt-tolerant species in coastal restoration.