Morphological assessments evidence that higher number of pneumatophores improves tolerance to long-term waterlogging in oil palm (Elaeis guineensis) seedlings

Abstract

Oil palm (Elaeis guineensis Jacq.) apparently tolerates long-term waterlogging and numerous pneumatophores are evident morphological adaptation. The number of pneumatophores per plant is, however, quite variable. Thus we hypothesized that a higher number of pneumatophores may attenuate the stress effects on root system growth and induce higher tolerance to long-term waterlogging in oil palm seedlings. To test this hypothesis we compared morphological and physiological traits in well-watered (control) and waterlogged plants with 2–10, 30–40, 60–70, and 90–120 pneumatophores after ca. 77 days of waterlogging. Plant height was similar between control and waterlogged plants with 90–120 pneumatophores, but it was 21% lower in plants with 2–10 pneumatophores than in control. The stem diameter and bulb diameter and biomass were 16, 20 and 42% higher in waterlogged plants than in control, independent of number of pneumatophores. Similar number of leaves and leaflets were observed regardless of watering regime and pneumatophore number, but total leaflet area and leaflet biomass were higher in plants with 90–120 pneumatophores than in other plants. Root system biomass was remarkably decreased in waterlogged plants; however, such decreases were more expressive in plants with 2–10 pneumatophores. Leaf water potential, leaf gas exchange and chlorophyll fluorescence were unaffected by waterlogging. Thus, we conclude that waterlogging causes few changes in seedlings’ above-ground morphology but remarkably affects root system development, mainly in those plants with lower number of pneumatophores. Regardless of pneumatophores, the stressed oil palm seedlings were able to adjust their leaf water status and gas exchange to cope properly with the imposed waterlogging.