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

Higher thermal acclimation potential of respiration but not photosynthesis in two alpine Picea taxa in contrast to two lowland congeners

The members of the genus Picea form a dominant component in many alpine and boreal forests which are the major sink for atmospheric CO2. However, little is known about the growth response and acclimation of CO2 exchange characteristics to high temperature stress in Picea taxa from different altitudes. Gas exchange parameters and growth characteristics were recorded from four year old seedlings of two alpine (Picea likiangensis vars. rubescens and linzhiensis) and two lowland (P. koraiensis and P. meyeri) taxa. Seedlings were grown at moderate (25°C/15°C) and high (35°C/25°C) day/night temperatures, for four months. The approximated biomass increment (ΔD2H) for all taxa decreased under high temperature stress, associated with decreased photosynthesis and increased respiration. However, the two alpine taxa exhibited lower photosynthetic acclimation and higher respiratory acclimation than either lowland taxon. Moreover, higher leaf dry mass per unit area (LMA) and leaf nitrogen content per unit area (Narea), and a smaller change in the nitrogen use efficiency of photosynthesis (PNUE) for lowland taxa indicated that these maintained higher homeostasis of photosynthesis than alpine taxa. The higher respiration rates produced more energy for repair and maintenance biomass, especially for higher photosynthetic activity for lowland taxa, which causes lower respiratory acclimation. Thus, the changes of ΔD2H for alpine spruces were larger than that for lowland spruces. These results indicate that long term heat stress negatively impact on the growth of Picea seedlings, and alpine taxa are more affected than low altitude ones by high temperature stress. Hence the altitude ranges of Picea taxa should be taken into account when predicting changes to carbon fluxes in warmer conditions

Application d'un modèle de pénétration de la lumière à une jeune plantation de hêtre avec abri latéral

A radiative transfer model applied to a young beech plantation. A radiative transfer model developed for row crops (Sinoquet, INRA-Clermont-Ferrand, France) was applied to a young beech row plantation, partly sheltered by a mature forest. The leaf area index of the forest was estimated by a LAI 2000 PCA (plant canopy analyser), and the leaf area uniformly distributed within the canopy. In each row, 15 beech trees were measured to establish the main dimensions of the mean tree and its crown. The rows were then modelled as a series of mean individual plants, whose leaf area was estimated from an allometric relationship with the diameter of the trees, and then uniformly distributed within the crowns. The test of the model was based on radiation measurements in the PAR waveband below and above the rows. With regard to transmitted radiation above the five rows, the outputs of the model were in close agreement with the measurements. In spite of large discrepancies in the estimation of transmitted radiation at ground level, global results suggest that the model correctly approximates light distribution inside the plantation. By testing a few simple hypotheses, it was shown that the fine structure of young beech trees (spatial variation in leaf area density, clumping) needs to be further investigated. This approach, suited to account for any canopy structure, appears to be a useful predictive tool for assessing the radiation environment within specific discontinuous canopies.Un modèle de pénétration de la lumière dans les cultures en rang, développé par Sinoquet (Inra Clermont-Ferrand), a été appliqué de manière originale à une jeune plantation de hêtres abritée latéralement par un couvert forestier adulte. L'indice de surface foliaire (LAI) de l'abri latéral a été déterminé à l'aide d'un LAI 2000 PCA (plant canopy analyser), et cette surface foliaire ensuite répartie uniformément dans le volume occupé par la forêt. Les cinq lignes de la plantation sont représentées de manière simplifiée par une succession d'individus moyens, dont les dimensions sont issues de mesures morphologiques réalisées sur 15 arbres par ligne, et dont la surface foliaire est estimée par une relation allométrique utilisant le diamètre des plants. Le test du modèle a été réalisé par la mesure du rayonnement transmis au sommet et au bas des lignes de la plantation. Il montre que le modèle rend compte de façon très satisfaisante de l'ombrage latéral dû à la forêt, alors que des écarts plus importants s'observent au sol. Le test de quelques hypothèses simples concernant la répartition et l'agencement des feuilles dans les houppiers montre que la description de la structure des jeunes hêtres demande à être approfondie. À l'issue de cette première approche, il semble que la qualité des estimations apportées par le modèle Sinoquet en fasse un outil d'un grand intérêt pour la caractérisation du microclimat lumineux de certains couverts forestiers particulièrement complexes

The effects of gap size on some microclimate variables during late summer and autumn in a temperate broadleaved deciduous forest.

The creation of gaps can strongly influence forest regeneration and habitat diversity within forest ecosystems. However, the precise characteristics of such effects depend, to a large extent, upon the way in which gaps modify microclimate and soil water content. Hence, the aim of this study was to understand the effects of gap creation and variations in gap size on forest microclimate and soil water content. The study site, in North West England, was a mixed temperate broadleaved deciduous forest dominated by mature sessile oak (Quercus petraea), beech (Fagus sylvatica) and ash (Fraxinus excelsior) with some representatives of sycamore (Acer pseudoplatanus). Solar radiation (I), air temperature (T (A)), soil temperature (T (S)), relative humidity (h), wind speed (v) and soil water content (I) were measured at four natural treefall gaps created after a severe storm in 2006 and adjacent sub-canopy sites. I, T (A), T (S), and I increased significantly with gap size; h was consistently lower in gaps than the sub-canopy but did not vary with gap size, while the variability of v could not be explained by the presence or size of gaps. There were systematic diurnal patterns in all microclimate variables in response to gaps, but no such patterns existed for I. These results further our understanding of the abiotic and consequent biotic responses to gaps in broadleaved deciduous forests created by natural treefalls, and provide a useful basis for evaluating the implications of forest management practices