Bundle-sheath leakiness and intrinsic water use efficiency of a perennial C4 grass are increased at high vapour pressure deficit during growth.

Xiao Ying Gong,Hans Schnyder,Rudi Schäufele

doi:10.1093/jxb/erw417

Xiao Ying Gong, Hans Schnyder + Show 1 more

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https://doi.org/10.1093/jxb/erw417

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Abstract

Bundle-sheath leakiness (ϕ) is a key parameter of the CO2-concentrating mechanism of C4 photosynthesis and is related to leaf-level intrinsic water use efficiency (WUEi). This work studied short-term dynamic responses of ϕ to alterations of atmospheric CO2 concentration 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 WUEi by 14%, with similar effects at both N levels. ϕ responded dynamically to intercellular CO2 concentration (C i), increasing with C i Across treatments, ϕ was negatively correlated to the ratio of CO2 saturated 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 C3 and C4 cycles. 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 WUEi Also, the data indicate a trade-off between WUEi and energetic efficiency in C. squarrosa.

Highlights

The CO2 concentrating mechanism (CCM) is a specialized feature of C4 photosynthesis and enables the maintenance of a very high CO2 partial pressure at the site of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), effectively minimizing photorespiration (Hatch, 1987)
This work studied short-term dynamic responses of φ to alterations of atmospheric CO2 concentration 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
Φ was negatively correlated to the ratio of CO2 saturated assimilation rate to carboxylation efficiency indicating that the long-term environmental effect on φ was related to the balance between C3 and C4 cycles

Summary

Introduction

The CO2 concentrating mechanism (CCM) is a specialized feature of C4 photosynthesis and enables the maintenance of a very high CO2 partial pressure at the site of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), effectively minimizing photorespiration (Hatch, 1987). In C4 photosynthesis, CO2 is first fixed by phosphoenolpyruvate carboxylase (PEPc) in mesophyll cells to form C4 acids (the C4 cycle), which are transported into bundle-sheath cells, where the acids are decarboxylated and CO2 is fixed by Rubisco (the C3 cycle). Related to the cost of the regeneration of phosphoenolpyruvate (PEP; Hatch, 1987; Furbank et al, 1990). The ratio of this leakage rate to the C4 cycle rate is termed bundle-sheath leakiness (Farquhar, 1983), or leakiness (φ), and is a key parameter of C4 photosynthesis

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