Crop photosynthesis, respiration and dry matter production of maize.

Abstract

Above-ground net photosynthesis and respiration of a maize crop (Zea mays L.) was deter­ mined in the field during the growing season (mid June-end of October) at regular intervals (1 à 2 weeks) at two temperatures (12.5 and 22.5 °C) by measuring the C02 uptake or release in mobile crop enclosures. The actual growth rate of the crop was determined from fortnightly harvests. Temperature dependence of photosynthesis was highest in the early (till mid July) and very late (begin October) stages of crop growth, showing a reduction of about 50 % at the higher irradiances (> 400 W m~2). In the period of major dry matter produc­ tion (mid July-September) the reduction was only 12-15 %. Assuming maintenance respira­ tion to become constant for cobs and grain exceeding a yield of 1000 kg ha 1 and for stems exceeding 2500 kg ha1, the measured and calculated dark respiration at 22.5 °C matched fairly well. At 12.5 °C the calculation, using the same assumtions, overestimated significantly dark respiration during the first part of the growing period. The carbon balance sheet showed t h a t f r o m t h e t o t a l a m o u n t o f C 0 2 a b s o r b e d b y t h e c r o p ( e q u i v a l e n t t o 3 0 . 7 t D M h a 1 ) , 30 <% was lost by above-ground respiration and 50 % was invested in above-ground harvestable material. The remaining 20 % is assumed to be transported to plant parts under the ground. Substantial losses of dry matter at the end of the growing season did not occur.