Photosynthesis and photoinhibition in two xerophytic shrubs during drought

• DOI: 10.1007/s11099-005-7045-5
• Publication Date: 2005-04-18T11:13:38Z
• Authors: W. Tezara; O. Marín; E. Rengifo; D. Martínez; A. Herrera
• Keywords: 0106 biological sciences; 15. Life on land; 01 natural sciences; 6. Clean water

Seasonal changes in water relations, net photosynthetic rate (P(N)), and fluorescence of chlorophyll (Chl) a of two perennial C(3) deciduous shrubs, Ipomoea carnea and Jatropha gossypifolia, growing in a thorn scrub in Venezuela were studied in order to establish the possible occurrence of photoinhibition during dry season and determine whether changes in photochemical activity of photosystem 2 (PS2) may explain variations of PN in these species. Leaf water potential (psi) decreased from -0.2 to -2.1 MPa during drought in both species. The PN decreased with y in T carnea and J. gossypifolia by 64 and 74%, respectively. Carboxylation efficiency (CE) decreased by more than 50 and 70% in I. carnea and J gossypifolia, respectively. In I. carnea, relative stomatal limitation (L(s)) increased by 17% and mesophyll limitation (L(m)) by 65% during drought, while in J. gossypifolia Ls decreased by 27% and L. increased by 51%. Drought caused a reduction in quantum yield of PS2 (theta(PS2)) in both species. Drought affected the capacity of energy dissipation of leaves, judging from the changes in the photochemical (q(P)) and non-photochemical quenching (NPQ) coefficients. Photo-inhibition during drought in I. carnea and J gossypifolia was evidenced in the field by a drop in the maximum quantum yield of PS2 (F(v)/F(m)) below 0.8 and also by non-coordinated changes in phi(PS2) and quantum yield of non-photochemical excitation quenching (Y(n)). Total soluble protein content on an area basis increased with psi but the ribulose-1,5-bisphosphate carboxylase/oxygenase content remained unchanged. A reduction of total Chl content with drought was observed. Hence in the species studied photoinhibition occurred, which imposed an important limitation on carbon assimilation during drought.