Abstract
An experiment was conducted with the aim to analyze the effects of soil flooding and leaf position on net primary productivity and whole plant carbon balance of Annona glabra L. (Annonaceae) seedlings, a highly flood-tolerant tree, native to the tropical Americas. All seedlings survived a period of 56 days of flooding without symptoms of stress. Flooding induced significant increments in root, stem and whole-plant biomass (P <0.01), and in the root:shoot mass ratio (P <0.05). Measurements of leaf gas exchange were conducted at days four, 11, 18 and 56 after flooding, on the first (L1), fourth (L4) and seventh (L7) fully expanded leaves from the apex of each seedling. The mean values of stomatal conductance to water vapour (g s) and net photosynthetic rate (A) in the control seedlings were around 0.26 mol m-2s-1 and 8.8 µmol m-2s-1, respectively. Significant reductions (P <0.05) in A were observed from L1 to L7 in controls at all four days of measurements. Reductions in A with increasing leaf age also ocurred for flooded plants, but only at days four and 18. Flooding induced significant changes in gs (P <0.05), reaching 65% of controls at day four but 152% of controls at day 56. Based on the results we conclude that the high survival and growth rates of A. glabra seedlings are directly related to the capacity to mantain a high stomatal conductance and net photosynthetic rate under soil flooding.
Highlights
Soil flooding is a common environmental stress in gallery forests, wetlands and some regions with high rainfall and poor soil drainage (Pezeshki 1994; Kozlowski 1997)
The seedlings grew in polyethylene bags containing 2.5 kg of soil under partially shaded environment until September 2002, when they were transferred to the shade house at the campus of the Universidade Estadual de Santa Cruz (UESC), Ilhéus, Bahia, Brazil
Decreases in stomatal conductance under flooded conditions are attributed to a decrease in root hydraulic conductivity (Davies & Flore, 1986; Pezeshki, 2001) or to the production of abscisic acid in the roots or leaves (Zhang & Zhang, 1994)
Summary
Soil flooding is a common environmental stress in gallery forests, wetlands and some regions with high rainfall and poor soil drainage (Pezeshki 1994; Kozlowski 1997). Seedlings of some flood-tolerant trees have the potential to keep the stomata open during waterlogging (Sena Gomes & Kozlowski 1980; Pezeshki et al 1996; Gravatt & Kirby 1998). The re-opening of stomata in flood-tolerant trees was generally related to anatomical and morphological adaptations, such as the appearance of hypertrophic lenticels or adventitious roots. Metabolic inhibition of photosynthesis under soil flooding conditions, on the other hand, can be related to decreases in the activity of Ribulose 1,5 bisphosphate carboxilase/oxigenase (Rubisco), alterations in the sink-source relationships and decreases in nutrient absorption and leaf chlorophyll content (Kozlowski 1997; Pezeshki 2001)
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