Peanut ( Arachis hypogaea L.) growth and photosynthetic response to high and low temperature extremes

In some peanut (Arachis hypogaea L.) producing regions, growth and photosynthesis-limiting low and high temperature extremes are common. Heat acclimation potential of photosynthesis and respiration is a coping mechanism that is species-dependent and should be further explored for peanut. The objectives of the current study are (1) to evaluate the response of photosynthesis, its component processes, and respiration to low and high temperatures, and (2) to determine the heat acclimation potential of photosynthesis and respiration during early vegetative growth of peanut. Peanut was exposed to four different growth temperature regimes: (1) optimum temperature (30/20 degrees C day/night), (2) low temperature (20/15 degrees C), (3) moderately high temperature (35/ 25 degrees C), and (4) a high temperature extreme (40/30 degrees C). Low temperature and both high temperatures caused substantial reductions in growth and net photosynthetic rate. Mesophyll conductance and RuBP regeneration colimited net photosynthetic rate under low temperature. Rubisco carboxylation was the most negatively impacted biochemical processes by high temperatures; however, diffusional limitations were not evident under high temperature conditions. Photosynthesis did not acclimate to high temperatures, while respiration and photorespiration exhibited heat acclimation. The inability of photosynthesis to acclimate to high temperature is likely a major constraint to early season growth in peanut.