Contribution and consequences of xylem-transported CO 2 assimilation for C 3 plants

• Published in: The New phytologist Vol. 223; no. 3; pp. 1230 - 1240
• Main Authors: Stutz, Samantha S, Hanson, David T
• Format: Journal Article
• Language: English
• Published: England 01-08-2019
• Subjects: Biological Transport - radiation effects; Carbon - metabolism; Carbon Dioxide - metabolism; Light; Photosynthesis - radiation effects; Plant Leaves - metabolism; Plant Leaves - radiation effects; Xylem - metabolism; Xylem - radiation effects; stem [CO2]; Populus deltoides; internally transported CO2; leaf photosynthesis models; tunable diode laser absorption spectroscopy; Brassica napus; CO2 efflux; xylem-transported CO2
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.15907

Traditionally, leaves were thought to be supplied with CO
for photosynthesis by the atmosphere and respiration. Recent studies, however, have shown that the xylem also transports a significant amount of inorganic carbon into leaves through the bulk flow of water. However, little is known about the dynamics and proportion of xylem-transported CO
that is assimilated, vs simply lost to transpiration. Cut leaves of Populus deltoides and Brassica napus were placed in either KCl or one of three [NaH
CO
] solutions dissolved in water to simultaneously measure the assimilation and the efflux of xylem-transported CO
exiting the leaf across light and CO
response curves in real-time using a tunable diode laser absorption spectroscope. The rates of assimilation and efflux of xylem-transported CO
increased with increasing xylem [
CO
*] and transpiration. Under saturating irradiance, rates of assimilation using xylem-transported CO
accounted for c. 2.5% of the total assimilation in both species in the highest [
CO
*]. The majority of xylem-transported CO
is assimilated, and efflux is small compared to respiration. Assimilation of xylem-transported CO
comprises a small portion of total photosynthesis, but may be more important when CO
is limiting.