Carbon isotope discrimination during branch photosynthesis of F agus sylvatica : a B ayesian modelling approach

• Published in: Plant, cell and environment cell and environment, 2014-07, Vol.37 (7), p.1516-1535
• Main Authors: GENTSCH, LYDIA, HAMMERLE, ALBIN, STURM, PATRICK, OGÉE, JÉRÔME, WINGATE, LISA, SIEGWOLF, ROLF, PLÜSS, PETER, BAUR, THOMAS, BUCHMANN, NINA, KNOHL, ALEXANDER
• Format: Article
• Language: English
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/pce.12262

Field measurements of photosynthetic carbon isotope discrimination ( 13 Δ) of F agus sylvatica , conducted with branch bags and laser spectrometry, revealed a high variability of 13 Δ, both on diurnal and day‐to‐day timescales. We tested the prediction capability of three versions of a commonly used model for 13 Δ [called here comprehensive ( 13 Δ comp ), simplified ( 13 Δ simple ) and revised ( 13 Δ revised ) versions]. A B ayesian approach was used to calibrate major model parameters. Constrained estimates were found for the fractionation during CO 2 fixation in 13 Δ comp , but not in 13 Δ simple , and partially for the mesophyll conductance for CO 2 ( g i ). No constrained estimates were found for fractionations during mitochondrial and photorespiration, and for a diurnally variable apparent fractionation between current assimilates and mitochondrial respiration, specific to 13 Δ revised . A quantification of parameter estimation uncertainties and interdependencies further helped explore model structure and behaviour. We found that 13 Δ comp usually outperformed 13 Δ simple because of the explicit consideration of g i and the photorespiratory fractionation in 13 Δ comp that enabled a better description of the large observed diurnal variation (≈9‰) of 13 Δ. Flux‐weighted daily means of 13 Δ were also better predicted with 13 Δ comp than with 13 Δ simple . Molecular interaction between NRT2.1 transcript levels and the ethylene signaling pathway under nitrate deficiency is still elusive. Here, we report a low nitrate (LN) treatment‐induced rapid burst of ethylene production and regulated expression of ethylene signaling components CTR1 , EIN3 and EIL1 in wild‐type Arabidopsis thaliana (Col‐0) seedlings, and enhanced ethylene response reporter EBS:GUS activity in both Col‐0 and the ethylene mutants ein3‐1eil1‐1 and ctr1‐1 . Comparison of ethylene production and EBS:GUS activity between nrt1.1 , nrt2.1 mutants and Col‐0 indicated that this up‐regulation of NRT2.1 expression caused a positive effect on ethylene biosynthesis/signaling under LN treatment, and ethylene down‐regulated NRT2.1 expression and reduced the high‐affinity nitrate uptake. Together, these findings uncover a negative feedback loop between NRT2.1 expression and ethylene biosynthesis/signaling under nitrate deficiency, which may contribute to finely tuning of plant nitrate acquisition during exploring dynamic soil conditions. Commentary: Advances in measurements and models of photosynthetic