Gas exchange in litchi under controlled and field conditions

Gas exchange of 3-year-old potted '73-S-20' litchi (Litchi chinensis Sonn.) plants were measured under controlled conditions. At 28.8 +/- 0.3 degrees C, dark respiration (R-d) was estimated at 0.6 CO2 mu mol m(-2) s(-1), quantum yield (Phi) was 0.024 mol CO2, mol(-1) and light compensation point (PPFDcomp) was 24 mu mol m(-2) s(-1) photosynthetic photo flux density (PPFD). Maximum net CO2 assimilation (A(CO2)) (6.5-8 mu mol m(-2) s(-1)), stomatal conductance (g(s)) (0.07-0.09 mol m(-2) s(-1)) and transpiration (E) (0.7 mmol m(-2) s(-1)) were recorded at PPFD > 800 mu mol m(-2) s(-1), leaf temperature (T-L) between 27 and 32 degrees C, and vapor pressure deficit (VPD) < 0.7 kPa. When VPD and T-L simultaneously increased maximum A(CO2) was obtained between 25 and 28 degrees C. CO2 compensation point (C-comp) was recorded between 90 and 100 ppm. A(CO2) saturated at external CO2 concentration > 800 ppm. A(CO2) responses to light, and VPD were mainly regulated by stomata. On the other hand, A(CO2) response to internal CO2 was mainly through leaf photochemistry. At T-L < 28 degrees C leaf photochemistry dominated A(CO2), responses, while at T-L > 28 degrees C stomatal regulated A(CO2), responses. Effects of leaf age and location as well as cropping on gas exchange were also studied on 9-year-old in the field trees. Leaf A(CO2), g(s) and E on the well-exposed, younger flushes and adjacent to fruit were greater than those on shaded older flushes and woods or those on de-fruiting shoots. Our findings indicated that potential depression of leaf photosynthetic efficiency in litchi might occur due to low temperature in bloom season and early fruit set, as well as due to hot and dry mid-day in early summer. (C) 2007 Elsevier B.V. All rights reserved.