We compared flavonoids in green, mature, and senescing flag leaves of wheat grown under ambient (AC - 370 μmol mol-1) and elevated (EC - 550 μmol mol-1) concentrations of CO2 in a FACE (Free Air CO2 Enrichment) system. The concentrations of flag leaf flavonoids (e.g., isoorientin and tricin) decreased to one third in mature leaves, and the majoritary isoorientin almost disappeared in senescing leaves. Flavonoid concentrations increased in green well-developed flag leaves under EC (46 % isoorientin and 55 % tricin), whereas the differences disappeared in mature and senescing flag leaves. Predictions of changes in litter phenolic concentrations and their effects on decomposition rates under EC based on changes in green leaves need to be revised. and J. Peñuelas, M. Estiarte, B. A. Kimball.
In the internal French Alps, subalpine grasslands become dominated by the tussock grass, Festuca paniculata, when mowing ceases. Does litter or living plants affect seedling recruitment in these subalpine communities, and does this vary between mown and unmown grasslands? Can the vegetation patterns observed in the field be related to the effects of F. paniculata? These hypotheses were tested using both a field and pot experiment. Seedlings of Bromus erectus, a subordinate species in these grasslands, were used as phytometers in both experiments. At both mown and unmown subalpine grassland sites in the French Alps, a removal experiment was established. This field experiment included removal of litter and living vegetation in order to differentiate their respective effect on seedling establishment. Vegetation and litter had contrasting effects. Vegetation affected the recruitment success of B. erectus by limiting seedling growth at the mown site and survival at the unmown site. Litter modified recruitment only at the unmown site, where it increased survival but limited growth. Survival and growth of seedlings responded to different environmental factors. Survival was determinedmore by soilmoisture, while growth probably dependedmore on light availability.Where there is a thick litter layer, as is the case in unmown subalpine grasslands, the competitive effect of vegetation can be counterbalanced by an increase in soil moisture due to the litter reducing rate of evaporation of water. The effect on seedlings of the presence of Festuca paniculata, the dominant species at these sites, was also quantified using a pot experiment, including a cutting treatment. This experiment showed that the competitive effect of the vegetation could be largely explained by the inhibitory effect on growth of the dominant species, F. paniculata. This study provides a better understanding of the processes that result in conservative plants, such as F. paniculata, becoming dominant in these subalpine environments upon cessation of traditional management practices.