Water relations and gas exchange across developmental stages in the páramo rosette Paepalanthus alpinus Körn. (Eriocaulaceae) in the tropical high Andes

Abstract

Alpine environments impose strong and rapidly fluctuating constraints on plant function, yet ontogenetic modulation of physiological strategies in tropical alpine rosettes remains poorly understood. We examined stage-specific variations in leaf water potential and gas exchange of the acaulescent rosette Paepalanthus alpinus in a Colombian páramo (3300 m a.s.l.) across wet and dry seasons. We measured midday leaf water potential ( Ψ L ) and morning gas exchange (stomatal conductance, g s ; transpiration, E; and net CO 2 assimilation, A) and characterized local microclimate to evaluate the coupling between stomata and evaporative demand. Leaf water potential declined markedly during the dry season in both developmental stages. Juveniles generally exhibited more negative Ψ L than adults, with a significant difference observed in January, when juvenile plants reached the lowest values (approximately − 2.7 MPa vs. − 1.8 MPa in adults). Juveniles also exhibited higher g s (150–170 mmol m −2 s −1 in the wet season; < 10 mmol m −2 s −1 in the dry season) and generally higher E. Despite higher g s and E in juveniles, net CO 2 assimilation varied primarily with season rather than developmental stage, reaching maximum values during the wet season and decreasing substantially during the dry season. Stomatal conductance declined with increasing leaf-air vapor pressure deficit (VPD), indicating tight hydraulic-stomatal coupling. Together, these patterns reveal stage-specific functional strategies in which juveniles rely on a more responsive stomatal behavior, i.e., ontogenetic modulation of stomatal control, to track VPD and maintain water status under seasonal water limitations. As VPD intensifies with regional warming, stage-dependent physiological thresholds may shape recruitment and persistence of acaulescent rosettes in tropical alpine systems.