title: Bundle-sheath leakiness and intrinsic water use efficiency of a perennial C4 grass are increased at high vapour pressure deficit during growth.
abstract: Bundle-sheath leakiness (ϕ) is a key parameter of the CO2-concentrating mechanism of C4photosynthesis and is related to leaf-level intrinsic water use efficiency (WUEi). This work studied short-term dynamic responses of ϕ to alterations of atmospheric CO2concentration in Cleistogenes squarrosa, a perennial grass, grown at high (1.6 kPa) or low (0.6 kPa) vapour pressure deficit (VPD) combined with high or low N supply in controlled environment experiments. ϕ was determined by concurrent measurements of photosynthetic gas exchange and on-line carbon isotope discrimination, using a new protocol. Growth at high VPD led to an increase of ϕ by 0.13 and a concurrent increase of WUEiby 14%, with similar effects at both N levels. ϕ responded dynamically to intercellular CO2concentration (Ci), increasing with CiAcross treatments, ϕ was negatively correlated to the ratio of CO2saturated assimilation rate to carboxylation efficiency (a proxy of the relative activities of Rubisco and phosphoenolpyruvate carboxylase) indicating that the long-term environmental effect on ϕ was related to the balance between C3and C4cycles. Our study revealed considerable dynamic and long-term variation in ϕ of C. squarrosa, suggesting that ϕ should be determined when carbon isotope discrimination is used to assess WUEiAlso, the data indicate a trade-off between WUEiand energetic efficiency in C. squarrosa.
authors.affiliation: Lehrstuhl für Grünlandlehre, Technische Universität München, Alte Akademie 12, 85354 Freising, Germany xgong@wzw.tum.de schnyder@wzw.tum.de.
authors.forename: Xiao Ying
authors.initials: XY
authors.lastname: Gong
authors.affiliation: Lehrstuhl für Grünlandlehre, Technische Universität München, Alte Akademie 12, 85354 Freising, Germany.
authors.forename: Rudi
authors.initials: R
authors.lastname: Schäufele
authors.affiliation: Lehrstuhl für Grünlandlehre, Technische Universität München, Alte Akademie 12, 85354 Freising, Germany xgong@wzw.tum.de schnyder@wzw.tum.de.
authors.forename: Hans
authors.initials: H
authors.lastname: Schnyder
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D002247:Carbon Isotopes / Q000378:metabolism; D009584:Nitrogen / Q000502:physiology*; D010788:Photosynthesis; D018515:Plant Leaves / Q000502:physiology*; D006109:Poaceae / Q000502:physiology*; D014867:Water / Q000502:physiology*
chemical_list: D002247:Carbon Isotopes; D014867:Water; D002245:Carbon Dioxide; D009584:Nitrogen
keywords: C4 photosynthesis; CO2-concentrating mechanism; carbon isotope discrimination; gas exchange; nitrogen nutrition; vapour pressure deficit.