Nature-based soil amendments improve water retention but differentially modulate plant drought responses

determinant of plant water availability. However, whether improvements in substrate water retention induced by nature-based amendments translate into enhanced plant hydraulic performance remains unclear. Here, we tested whether amendments derived from Aloe vera (Av) and the brown macroalga Saccharina latissima (Sl) modify substrate water retention and plant water relations in Capsicum annuum. Methods Substrate water retention curves, gas exchange, leaf traits and hydraulic vulnerability were assessed under well-watered and drought conditions. Results Both amendments increased substrate water retention leading to approximately 60% higher gravimetric plant-available water content compared with control. Despite similar effects on water retention properties, plant responses differed markedly between treatments. Av-treated plants developed structurally lighter leaves with lower leaf mass per area, higher saturated water content and increased cell wall stiffness and showed more negative leaf water potential thresholds for to dehydration-induced hydraulic dysfunction. These coordinated trait adjustments were associated with delayed turgor loss during drought and faster post-drought recovery. In contrast, Sltreated plants displayed intermediate physiological responses despite comparable improvements in substrate water retention. Conclusion Increased substrate water availability alone did not translate into plant performance differences. Instead, plant responses depended on how substrate water retention properties were integrated through plant hydraulics, highlighting the importance of substrate-plant hydraulic coordination in mediating drought responses to organic amendments