| Popis: |
Despite significant research efforts, the question of whether rising atmospheric CO2 concentrations (Ca) affect leaf respiration remains unanswered. Here, I reanalyse published hydrogen isotope abundances in starch glucose of sunflower leaves. I report that, as Ca increases from 450 to 1500 ppm, respiration by the oxidative pentose phosphate pathway in chloroplasts increases from 0 to ≈ 5% relative to net carbon assimilation. This is consistent with known regulatory properties of the pathway. Summarising recent reports of metabolic fluxes in plant leaves, a picture emerges in which mitochondrial processes are distinctly less important for overall respiration than the oxidative pentose phosphate pathways in chloroplasts and the cytosol. Regulatory properties of these pathways are consistent with observations of lower-than-expected stimulations of photosynthesis by increasing Ca. Reported advances in understanding leaf respiratory mechanisms may enable modelling and prediction of respiration effects (inter alia) on biosphere-atmosphere CO2 exchange and plant performance under climate change. |
