Estimation of carboxylation efficiency from net CO2 assimilation rate as a function of chloroplastic CO2 concentration in strawberry (Fragaria x ananassa cv. Maehyang) leaves

Carboxylation efficiency in fully expanded leaves of strawberry (Fragaria x ananassa cv. Maehyang) was estimated based on net CO2 assimilation rate (A (n)) as a function of chloroplastic CO2 concentration (C (c)). To estimate the mesophyll conductance (g (m)) and then construct A (n)-C (c) curves, A (n) and electron transport rate as a function of intercellular CO2 concentration (C (i)) were simultaneously determined at a range of 50 to 2,200 mu mol CO2/mol air at a saturating photosynthetic photon flux (PPF), 1,200 mu mol center dot m(-2)center dot s(-1). Mitochondrial respiration rate (R (d)) and CO2 compensation point in the absence of R (d) required for calculating g (m) were found to be 0.15 mu mol center dot m(-2)center dot s(-1) and 44.1 mu mol CO2/mol air, respectively, as determined from A (n)-C (i) curves below 200 mu mol CO2/mol air at three different PPFs. Both stomatal conductance (g (s)) and g (m) decreased with increasing C (i). However, the g (m) responded more sensitively to various C (i) than the g (s). The g (m) was significantly lower than the g (s) at C (i) beyond 600 mu mol center dot mol(-1) air examined. Maximum carboxylation efficiency (alpha (cmax)) derived from A (n)-C (c) curves was 0.28 mu mol center dot m(-2)center dot s(-1) and 2.2 times higher than that from A (n)-C (i) curve. Since the A (n)-C (i) curve was based on infinite g (m), the alpha (cmax) derived from the A (n)-C (i) curve might be underestimated. Actually, g (m) was rather dynamic with changing C (i) and thus a crucial component of the diffusional limitation of A (n). For estimating photosynthetic characteristics in strawberry leaves more accurately, A (n)-C (c) curve should be constructed in consideration of g (m), especially for closed plant production systems.