PHOTOSYNTHETIC POTENTIAL OF THYMUS-VULGARIS SELECTIONS UNDER 2 LIGHT REGIMES AND 3 SOIL-WATER LEVELS

A greenhouse experiment was conducted to measure the effects of two li ght regimes (LR) (supplemental, SL of 200 mumol m-2 s-1 and natural, N L) and three different soil water levels (SWL) (50, 70 and 90% field c apacity) on biomass production, relative growth rate (RGR), net CO2 as similation (Pn), stomatal (g(s)) and mesophyll (g(m)) conductance, chl orophyll a and b (chl a and chl b) content and leaf water potential (L WP) on two Thymus vulgaris L. clonal selections. There was a significa nt increase in total dry matter (DM) production and RGR due to SL and increased SWL. The highest Pn, 24.6 mumol CO2 m-2 s-1, was obtained fr om Selection 1, grown under SL at 70% SWL. The lowest Pn, 6.3 mumol CO 2 m-2 s-1, was obtained from Selection 2, grown under NL at 50% SWL. S election 1 had higher Pn, g(s) and g(m) than Selection 2 under all gro wing conditions. Thymus vulgaris leaves developed under SL were more q uantum-use efficient than those grown under NL. Total leaf chlorophyll concentration per leaf area basis was significantly (P lesser-than-or -equal-to 0.01) higher in plants grown under SL than NL. The lowest LW P was recorded for Selection 2 grown under SL at 50% SWL.