Ecophysiology of dominant plant species during old-field succession in a high tropical Andean ecosystem

We compared ecophysiological characteristics of plant species that dominate during different stages of succession in fallow fields of a traditional agroecosystem in the Venezuelan High Andes. For each species we determined during the dry and wet seasons the photosynthetic light response and photosynthesis rate at tight saturation (A(max)), specific leaf area (SLA), stomatal conductance at light saturation (g(max)), midday water potential (psi), and intrinsic water use efficiency (WUEi, photosynthesis rate per unit of stomatal conductance). The species studied were the forbs Rumex acetosella (early succession dominant) and Lupinus meridanus (intermediate stages), the shrubs Acaena elongata and Baccharis prunifolia (late succession), the giant rosette Espeletia schultzii, and the shrub Hypericum laricifolium (mature ecosystem dominant). Clear ecophysiological trends were identified: early and intermediate successional species had higher A(max), g(max), and SLA but lower WUEi. E. schultzii maintained a high water potential during the dry season and, together with B. prunifolia, was the only species with no significant differences in A(max) between seasons. The results indicate that traits generally linked to fast growth (high A(max) and SLA) are associated with dominance during early succession, while traits linked with drought resistance (e.g., high WUEi and thick xeromorphic leaves) are associated with dominance during late succession in this tropical mountain environment.