Erythrina speciosa (Leguminosae-Papilionoideae) under soil water saturation: morphophysiological and growth responses

Abstract

Background and aims: Erythrina speciosa is a Neotropical tree that grows mainly in moist habitats. To characterize the physiological, morphological and growth responses to soil water saturation, young plants of E. speciosa were subjected experimentally to soil flooding.

Methods: Flooding was imposed from 2 to 4 cm above the soil surface in water-filled tanks for 60 d. Non-flooded (control) plants were well watered, but never flooded. The net CO(2) exchange (A(CO2)), stomatal conductance (g(s)) and intercellular CO(2) concentration (C(i)) were assessed for 60 d. Soluble sugar and free amino acid concentrations and the proportion of free amino acids were determined at 0, 7, 10, 21, 28 and 45 d of treatments. After 28, 45 and 60 d, dry masses of leaves, stems and roots were determined. Stem and root cross-sections were viewed using light microscopy.

Key results: The A(CO2) and g(s) were severely reduced by flooding treatment, but only for the first 10 d. The soluble sugars and free amino acids increased until the tenth day but decreased subsequently. The content of asparagine in the roots showed a drastic decrease while those of alanine and gamma-aminobutyric increased sharply throughout the first 10 d after flooding. From the 20th day on, the flooded plants reached A(CO2) and g(s) values similar to those observed for non-flooded plants. These events were coupled with the development of lenticels, adventitious roots and aerenchyma tissue of honeycomb type. Flooding reduced the growth rate and altered carbon allocation. The biomass allocated to the stem was higher and the root mass ratio was lower for flooded plants when compared with non-flooded plants.

Conclusions: Erythrina speciosa showed 100 % survival until the 60th day of flooding and was able to recover its metabolism. The recovery during soil flooding seems to be associated with morphological alterations, such as development of hypertrophic lenticels, adventitious roots and aerenchyma tissue, and with the maintenance of neutral amino acids in roots under long-term exposure to root-zone O(2) deprivation.

Fig. 1.

Photosynthetic rates (A_CO2), stomatal conductance (g_s) and water use efficiency (WUE) in Erythrina speciosa under control and flooding conditions. Data are expressed as the mean ± s.e.; n = 4 leaves per treatment, each leaf from a different individual. Different letters indicate a significant difference between means (P < 0·05 %; Tukey test).

Fig. 2.

Internal CO₂ concentration (C_i) in Erytrina speciosa under control and flooding conditions. Data are expressed as the mean ± s.e.; n = 4 leaves per treatment, each leaf from a different individual. Different letters indicate a significant difference between means (P < 0·05 %; Tukey test).

Fig. 3.

Changes in total free amino acids in root tissue of E. speciosa plants subjected to flooding of the root system. Data are the means ± s.e. of three replicates.

Fig. 4.

Changes in soluble sugars in root tissue of E. speciosa plants subjected to flooding of the root system. Data are the means ± s.e. of three replicates.

Fig. 5.

Height and stem diameter for E. speciosa under control and flooding conditions. Data are expressed as mean ± s.e.; n = 10 plants per treatment. Different letters indicate a significant difference between means (P < 0·05 %; Tukey test).

Fig. 6.

Relative growth rate of E. speciosa under control and flooding conditions. Data are expressed as the mean ± s.e.; n = 6 plants in each treatment. Different letters indicate a significant difference between means (P < 0·05 %; Tukey test).

Fig. 7.

(A) Leaf mass ratio (LMR; leaf dry mass/total dry mass); (B) stem mass ratio (SMR; stem dry mass/total dry mass); (C) root mass ratio (RMR; root dry mass/total dry mass) in E. speciosa under control and flooding conditions. Data are expressed as the mean ± s.e.; n = 6 plants in each treatment. Different letters indicate a significant difference between means (P < 0·05 %; Tukey test).

Fig. 8.

Stem transverse sections of E. speciosa under (A) control conditions and (B) after 60 d of flooded conditions. Note the lenticel hypertrophy on plants under flooded conditions. Scale bars = 100 µm.

Fig. 9.

Root transverse sections of Erythrina speciosa under (A) control conditions and (B) after 60 d of flooded conditions. Root sections were made between 2 and 3 cm from the root tip, in roots with a length of no more than 5–6 cm. Note the aerenchyma development in flooded plants. Scale bars = 100 µm.