Bio-energy retains its mitigation potential under elevated CO2

Background If biofuels are to be a viable substitute for fossil fuels, it is essential that they retain their potential to mitigate climate change under future atmospheric conditions. Elevated atmospheric CO2 concentration [CO2] stimulates plant biomass production; however, the beneficial effects of increased production may be offset by higher energy costs in crop management. Methodology/Main findings We maintained full size poplar short rotation coppice (SRC) systems under both current ambient and future elevated [CO2] (550 ppm) and estimated their net energy and greenhouse gas balance. We show that a poplar SRC system is energy efficient and produces more energy than required for coppice management. Even more, elevated [CO2] will increase the net energy production and greenhouse gas balance of a SRC system with 18%. Managing the trees in shorter rotation cycles (i.e. 2 year cycles instead of 3 year cycles) will further enhance the benefits from elevated [CO2] on both the net energy and greenhouse gas balance. Conclusions/significance Adapting coppice management to the future atmospheric [CO2] is necessary to fully benefit from the climate mitigation potential of bio-energy systems. Further, a future increase in potential biomass production due to elevated [CO2] outweighs the increased production costs resulting in a northward extension of the area where SRC is greenhouse gas neutral. Currently, the main part of the European terrestrial carbon sink is found in forest biomass and attributed to harvesting less than the annual growth in wood. Because SRC is intensively managed, with a higher turnover in wood production than conventional forest, northward expansion of SRC is likely to erode the European terrestrial carbon sink

Konvensyen Myprospec tumpu revolusi industri 4.0

Rising atmospheric concentrations of CO 2 (C a) can reduce stomatal conductance and transpiration rate in trees, but the magnitude of this effect varies considerably among experiments. The theory of optimal stomatal behaviour predicts that the ratio of photosynthesis to transpiration (instantaneous transpiration efficiency, ITE) should increase in proportion to C a. We hypothesized that plants regulate stomatal conductance optimally in response to rising C a. We tested this hypothesis with data from young Eucalyptus saligna Sm. trees grown in 12 climate-controlled whole-tree chambers for 2 years at ambient and elevated C a. Elevated C a was ambient + 240 ppm, 60% higher than ambient C a. Leaf-scale gas exchange was measured throughout the second year of the study and leaf-scale ITE increased by 60% under elevated C a, as predicted. Values of leaf-scale ITE depended strongly on vapour pressure deficit (D) in both CO 2 treatments. Whole-canopy CO 2 and H 2O fluxes were also monitored continuously for each chamber throughout the second year. There were small differences in D between C a treatments, which had important effects on values of canopy-scale ITE. However, when C a treatments were compared at the same D, canopy-scale ITE was consistently increased by 60%, again as predicted. Importantly, leaf and canopy-scale ITE were not significantly different, indicating that ITE was not scale-dependent. Observed changes in transpiration rate could be explained on the basis that ITE increased in proportion to C a. The effect of elevated C a on photosynthesis increased with rising D. At high D, C a had a large effect on photosynthesis and a small effect on transpiration rate. At low D, in contrast, there was a small effect of C a on photosynthesis, but a much larger effect on transpiration rate. If shown to be a general response, the proportionality of ITE with C a will allow us to predict the effects of C a on transpiration rate

Growth of a poplar short rotation coppice under elevated atmospheric CO2 concentrations (EUROFACE) depends on fertilization and species

Growth and woody biomass production of three Populus species (P. nigra L. clone Jean Pourtet, P. alba L. clone 2AS-11 and P. × euramericana clone I-214), were followed during the first growing season after coppice of a short rotation coppice culture exposed to elevated atmospheric CO2 concentrations by means of Free-Air Carbon dioxide Enrichment (FACE), and to a nitrogen (N) fertilization treatment. FACE significantly increased the number of shoots per stool, but did not significantly increase height nor total basal area per stool. In September, FACE significantly increased the Leaf Area Index (LAI) with 5.5 to 16.4%, depending on species. FACE significantly stimulated the woody biomass production by up to 25%, but the stimulation of P. alba and P. × euramericana was restricted to the fertilized treatment. Significant differences between species were observed. We concluded that coppice diminished the FACE effect, that the positive FACE effect was restricted under lower soil fertility, and that species differed in their response to FACE.La croissance de taillis de peuplier à courte rotation dans une atmosphère à concentration en CO2 élevée dépend de la fertilisation et de l’espèce. La croissance et la production ligneuse de biomasse de trois espèces de peuplier (Pinus nigra L. clone J. Pourtet, P. alba L. clone 2AS-11 et P. × euramericana clone I-214) ont été suivies pendant la première saison de croissance après la coupe du taillis à courte rotation exposé à une concentration élevée en CO2, au moyen d’un système FACE et à une fertilisation azotée. Le FACE accroît significativement le nombre de pousses par pied. En septembre, le FACE a augmenté l’indice foliaire (LAI) de 5,5 à 16,4 % selon les espèces. FACE stimule significativement la production de biomasse ligneuse (25 %) mais pour P. alba et P. × euramericana cette stimulation ne concerne que le traitement fertilisé. Des différences significatives ont été observées entre les espèces. Nous concluons que le taillis amoindrit l’effet du FACE, que l’effet positif du FACE était limité pour un sol peu fertile et que les espèces diffèrent dans leur réponse au FACE