Photosynthetic Capacity and Effect of Drought on Leaf Gas Exchange in Two Rubber (Hevea brasiliensis) Clones

Abstract

Photosynthetic capacity, water-use efficiency and nitrogen-use efficiency were compared between two different rubber clones, PB 260 and PB 217. Plants were grown in 50 dm³ pots in a greenhouse at Clermont-Ferrand, France under controlled condition. Net CO₂ assimilation rate at 1800 ppm CO₂ (A₁₈₀₀) and at 360 ppm CO₂ (A₃₆₀), maximum carboxylation rate (V_cmax), electron transport capacity (J_max) and nitrogen-use efficiency (A₁₈₀₀/Na, A₃₆₀/Na, V_cmax/Na and J_max/Na) of clone PB 260 were significantly higher than those of clone PB 217. However, the dark respiration rate (R_d), the ratio of lightsaturated rate of electron transport and maximum rate of carboxylation (J_max/V_cmax), leaf mass per area (M_a), leaf nitrogen content (N_m), leaf nitrogen per area (Na), water use efficiency (WUE), SPAD value (SPAD) and chlorophyll fluorescence ratio (F_v/F_m) were non- significantly different between these clones. Effects of drought on leaf gas exchange rates was also studied. Net CO₂ assimilation rate (A), stomatal conductance (g_s) and transpiration rate (E) showed a declining curve as a function of increased water stress. WUE was high under severe stress, due to a more rapid decrease of E than A. At 14 days after stress, gs and E decreased by 80-85%, while A decreased by 60-70%. Drought also reduced leaf water potential, which was possitively related to stomatal conductance. These results confirmed the potential genotypic variability of some photosynthetic traits under non-water-limited condition and stomatal behavior related with hydraulic properties during water stress in rubber trees.