Photosynthetic Response of Carrots to Varying Irradiances

Abstract

Response to irradiance of leaf net photosynthetic rates (P N ) of four carrot cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) were examined in a controlled environment. Gas exchange measurements were conducted at photosynthetic active radiation (PAR) from 100 to 1 000 µmol m -2 s -1 at 20 o C and 350 µmol(CO 2 ) mol -1 (air). The values of P N were fitted to a rectangular hyperbolic nonlinear regression model. P N for all cultivars increased similarly with increasing PAR but Cascade and Oranza generally had higher P N than CC. None of the cultivars reached saturation at 1 000 µmol m -2 s -1 . The predicted P N at saturation (P Nmax ) for Cascade, CC, Oranza, and RCC were 19. 78, 16.40, 19.79, and 18.11 µmol(CO 2 ) m -2 s -1 , respectively. The compensation irradiance (I c ) occurred at 54 µmol m -2 s -1 for Cascade, 36 µmol m -2 s -1 for CC, 45 µmol m -2 s -1 for Oranza, and 25 µmol m -2 s -1 for RCC. The quantum yield among the cultivars ranged between 0.057-0.033 mol(CO 2 ) mol -1 (PAR) and did not differ. Dark respiration varied from 2.66 µmol m -2 s -1 for Cascade to 0.85 µmol m -2 s -1 for RCC. As P N increased with PAR, intercellular CO 2 decreased in a non-linear manner. Increasing PAR increased stomatal conductance and transpiration rate to a peak between 600 and 800 µmol m -2 s -1 followed by a steep decline resulting in sharp increases in water use efficiency.

Compensatory effects of elevated CO₂ concentration on the inhibitory effects of high temperature and irradiance on photosynthetic gas exchange in carrots

“…At 1 200 μmol m -2 s -1 these mechanisms may begin to break down as observed in the reduced enhancement of P N and beyond this level a further reduction may be expected. The positive influence of doubling C a on P N is in accordance with findings of Kyei-Boahen et al (2003b). However, with PAR only a hyperbolic response is widely reported (Kyei-Boahen et al 2003a).…”

“…The individual and/or interactive effects of some of these parameters on photosynthesis have been investigated in many crops. Generally, net photosynthetic rate (P N ) increases with irradiance in cucumber, tomato, pepper, and carrots (Warren Wilson et al 1992, Nederhoff and Vegter 1994, Kyei-Boahen et al 2003b. Also, an increase in PAR results in increases in stomatal conductance (g s ) and transpiration rate (E) to certain extent.…”

Stomatal development and associated photosynthetic performance of capsicum in response to differential light availabilities

“…In addition, the light-saturation point also increases with increasing irradiance during growth (Boardman 1977, Evans and Poorter 2001, Kyei-Boahen et al 2003. Some observations reported that plants grown under low irradiance affected the height of the plant by increasing ---the length of the stem, and making the leaves wider and thinner (Stitt andSchulze 1994, Liu andWang 2006).…”

A coupled model of stomatal conductance and photosynthesis for winter wheat

“…Rectangular and non-rectangular hyperbolae (Thornley 1976) have been used widely to describe the irradiance-response curves of P N (e.g. Thornley 1976, Evans et al 1993Kyei-Boahen et al 2003, Yu et al 2004, Messinger et al 2006. However, the maximum net photosynthetic rate (P max ) calculated by these hyperbolas is much higher than the measured data (e.g.…”

“…However, the maximum net photosynthetic rate (P max ) calculated by these hyperbolas is much higher than the measured data (e.g. Kyei-Boahen et al 2003, Yu et al 2004, Messinger et al 2006. Ye (2007) proposed a new photosynthesis model which can accurately describe the irradiance-response curve of photosynthesis, including irradiance below compensation (I c ) and above I max (Ye 2007).…”