Tracing Photosynthetic Response Curves with Internal CO₂ Measured Directly

Abstract

In this study, a system to measure leaf internal CO2 (Ci) was incorporated into an open gas exchange system (LI-COR, Lincoln, NE, USA). The Ci was directly measured with a cup attached to the abaxial surface of sunflower (Helianthus annuus L.) leaves with open stomata while normal CO2 and water vapor exchange through the same section of adaxial surface was simultaneously detected. The potential problems in the system, namely bulk air flow through the leaf, diffusion leaks, and change in the CO2 gradient inside the leaf, were examined with the aim to apply the system to measure net photosynthesis at various Ci (i.e. A Ci curves). A micro blower constantly circulated the air in a loop without pressure pulses or bulk air movement through the leaf. The measured Ci (Ci(m)) generally followed the external CO2 as much as the calculated one (Ci(c)). There was close agreement between the Ci(m) and the Ci(c) particularly at low Ci, and the diffusion leak hardly affected the relationship between the two. Despite possible alterations of leaf properties by cup attachment, the direct measurement is expected to cast a new light on leaf gas exchange.

Direct measurement of intercellular CO2 concentration in a gas-exchange system resolves overestimation using the standard method

“…were estimated as 0.21 ± 0.079 and 0.71 ± 0.13 μmol s –1 , respectively, values that were comparable to those determined for the smaller LI-6400-40 chamber ( Rodeghiero et al , 2007 ; Tominaga and Kawamitsu, 2015 a ), suggesting a similar rate of diffusion leak on a chamber basis. Accounting for the larger chamber interface (i.e.…”

“…For species having a fast assimilation rate, such as sunflower ( Helianthus annuus L.), the gradient is generally too small to affect C i(m) ( Mott and O’Leary, 1984 ; Boyer and Kawamitsu, 2011 ). The small effect observed for sunflower leaves was confirmed recently when a direct-measurement system for C i ( Boyer and Kawamitsu, 2011 ) was incorporated into a commercial open gas-exchange apparatus ( Tominaga and Kawamitsu, 2015 a ). Using a similar system, however, Tominaga and Kawamitsu (2015 b ) demonstrated that C i(c) markedly differed from C i(m) as stomata began to close after abscisic acid (ABA) was applied to this species.…”

“…The gas-exchange system has been reported in detail elsewhere ( Tominaga and Kawamitsu, 2015 a ), and we used a modified system (the design drawings are available upon request). Briefly, the small cup of the Tominaga and Kawamitsu system was replaced with the bottom half of an assimilation chamber (LI6400-40; Li-Cor, Lincoln, NE, USA) of a commercial gas-exchange system (LI-6400XT; Li-Cor).…”

“…Each leaf was illuminated with three metal-halide lamps (D-400, Toshiba) located approximately 1 m above the chamber. Fine net shades were inserted between the light source and the chamber so that the irradiance was adjusted to 300 μmol m –2 s –1 PAR, which was less than the 800 μmol m –2 s –1 PAR used in a previous study ( Tominaga and Kawamitsu, 2015 a , b ). We reduced the irradiance to control leaf temperature as the light source containing a broad thermal ray otherwise warmed the leaf.…”

Responses of leaf gas exchange rate to acute soil drying in Jatropha curcas L

“…significantly disturbed when gs was suppressed at pF 3.8 or more (Figures 3(d, h and 5j)). The fluctuation in C i was probably an error problem with the calculation formula (Tominaga & Kawamitsu, 2015a, 2015bTominaga, Shimada & Kawamitsu, 2018).…”