Physiological Responses of Four Eucalyptus camaldulensis Clones to Waterlogging in a Hydroponic System

Abstract

Waterlogging has a detrimental effect on environmental stress in Eucalyptus camaldulensis (Dehn.), as does calcareous soil, while together they act synergistically to induce stress in the plants. In the western region of Thailand, both conditions are deleterious to the eucalypt plantation industry. These stresses can reduce the biomass and yield of eucalypts at all stages of growth. To assist the eucalypt breeding program, powerful tools to screen a population are needed. Leaf gas exchange parameters can be used to study the photosynthetic capacity of plants during flooding, except in some flood-tolerant plants that have developed adaptive mechanisms to better maintain photosynthetic capacity. In this study, a physiological method was developed and applied to four Eucalyptus camaldulensis (Dehn.) clones to screen for the effects of waterlogging on net photosynthesis, maximum quantum yield, chlorophyll content and biomass. Four two-month-old eucalypt clones (C1 and C2 were calcicole clones and C3 and C4 were calcifuge clones) were grown in half-strength Hoagland’s solution and subjected to waterlogging conditions for 16 days. Physiological parameters were monitored at days 0, 8 and 16 under a plant growth incubator. The net photosynthetic rate (A_max), stomatal conductance (g_s) and transpiration rate (E) rapidly reduced in C2 and C4 after 16 days of waterlogging. The maximum quantum yield (F_v/F_m), chlorophyll content and biomass of the four clones decreased in all cultivars under waterlogging at day 16. From measured physiological parameters, C2 and C4 suffered more severe stress under waterlogging than C1 and C3. Overall, a difference between the control and treated plants could be observed at 16 days after treatment. The physiological parameters of gas exchange and the F_v/F_m ratio were proven to be suitable indicators of waterlogging-tolerant traits.