Temperature effects on photosynthesis, growth respiration, and maintenance respiration of marigold

Marigolds (Tagetes patula) were grown from seed to flowering at either 20 or 30 degreesC, and the CO2 exchange rate of the plants was measured throughout the 60-day growing period. Plants grew faster at 30 than at 20 degreesC, because of higher whole-plant photosynthesis (P-net) from 5 to 40 days after seeding. The maintenance respiration coefficient (r(m)) was lower at 20 than at 30 degreesC (Q(10) = 1.3), while the growth respiration coefficient was not affected by temperature (0.51 g(.)g(-1)). The ratio of maintenance respiration to total respiration increased throughout plant development and reached 43 and 55% at 20 and 30 degreesC, respectively. Carbon use efficiency (CUE) of the plants increased during germination, and then decreased throughout the remainder of the growing period. This decrease in CUE was the result of a decrease in relative growth rate (RGR). Plants grown at 20 degreesC had a higher CUE than those at 30 degreesC from 40 to 51 days after seeding, which was the result of a lower RGR and higher r(m) at 30 degreesC. Although plants grown at 20 degreesC had equal or higher CUE, a lower r(m), and less dark respiration (R-dark), their growth was less than that of plants at 30 degreesC, suggesting that whole-plant P-net is a more important determinant of growth than CUE, r(m), or R-dark.