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Climate change has affected plant phenology; increasing temperatures are associated with advancing first flowering dates. The impact on flowering duration, however, has rarely been studied. In this study, we analysed first flowering dates and flowering durations from a 27 year dataset of weekly flower observations on 232 plant species from the island of Guernsey in the English Channel. The aim of this study was to explore variation in trends and relationships between first flowering dates, flowering duration and temperature. We specifically looked for evidence that traits, such as life forms and phylogenetic groups, explained variation in sensitivity of first flowering and flowering duration among species. Overall trends revealed significantly earlier flowering over time, by an average of 5.2 days decade(-1) since 1985. A highly significant shortening of flowering duration was observed by an average of 10 days decade(-1) . Correlations between first flowering, flowering duration and year varied between different species, traits and flowering periods. Significant differences among traits were observed for first flowering and to a lesser degree for flowering duration. Overall, in comparison to first flowering, more species had significant trends in flowering duration. Temperature relationships revealed large differences in strength and direction of response. 55% of the species revealed a significant negative relationship of first flowering dates and temperature. In contrast, only 19% of flowering durations had a significant negative temperature relationship. The advance in first flowering date together with a shortening of flowering duration suggests potentially serious impacts on pollinators, which might pose a major threat to biodiversity, agriculture and horticulture. Human health, in terms of pollen allergies, however, might benefit from a shortening of specific plant pollen seasons.

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Ground-level ozone (O(3)) has gained awareness as an agent of climate change. In this respect, key results are comprehended from a unique 8-year free-air O(3)-fumigation experiment, conducted on adult beech (Fagus sylvatica) at Kranzberg Forest (Germany). A novel canopy O(3) exposure methodology was employed that allowed whole-tree assessment in situ under twice-ambient O(3) levels. Elevated O(3) significantly weakened the C sink strength of the tree-soil system as evidenced by lowered photosynthesis and 44% reduction in whole-stem growth, but increased soil respiration. Associated effects in leaves and roots at the gene, cell and organ level varied from year to year, with drought being a crucial determinant of O(3) responsiveness. Regarding adult individuals of a late-successional tree species, empirical proof is provided first time in relation to recent modelling predictions that enhanced ground-level O(3) can substantially mitigate the C sequestration of forests in view of climate change.

The extraordinary drought during the summer of 2003 in Central Europe allowed to examine responses of adult beech trees (Fagus sylvatica) to co-occurring stress by soil moisture deficit and elevated O 3 levels under forest conditions in southern Germany. The study comprised tree exposure to the ambient O 3 regime at the site and to a twice-ambient O 3 regime as released into the canopy through a free-air O 3 fumigation system. Annual courses of photosynthesis (A max ), stomatal conductance (g s ), electron transport rate (ETR) and chlorophyll levels were compared between 2003 and 2004, the latter year representing the humid long-term climate at the site. ETR, A max and g s were Communicated by H. Jones lowered during 2003 by drought rather than ozone, whereas chlorophyll levels did not differ between the years. Radial stem increment was reduced in 2003 by drought but fully recovered during the subsequent, humid year. Comparison of AOT40, an O 3 exposure-based risk index of O 3 stress, and cumulative ozone uptake (COU) yielded a linear relationship throughout humid growth conditions, but a changing slope during 2003. Our findings support the hypothesis that drought protects plants from O 3 injury by stomatal closure, which restricts O 3 influx into leaves and decouples COU from high external ozone levels. High AOT40 erroneously suggested high O 3 risk under drought. Enhanced ozone levels did not aggravate drought effects in leaves and stem.

ABSTRACT:The vertical temperature structure in the area of Garmisch-Partenkirchen between the Loisach river valley and the highest mountain in Germany (Zugspitze, 2962 m a.s.l.) is analysed. Using long time series of daily mean, minimum and maximum temperatures from two meteorological stations, in the valley floor and on the mountain top, we studied seasonal variations in temperature lapse rates. By using daily data on weather types, significantly different altitudinal temperature lapse rates and daily temperature ranges for low and high pressure weather situations were found. There was no significant influence of snow cover in the valley on the lapse rate. At both stations, there has been an increase in temperature during recent decades. As there was a slight difference between these trends, the lapse rate has tended to become more negative, i.e. the difference between the mountain top and the valley has become more pronounced. In order to investigate the lapse rates in more detail, unpublished temperature data from 1989 to 1990 on slope transects near Garmisch-Partenkirchen were evaluated. Despite the fact that an exact description of the vertical structure of the atmospheric temperature is possible only from free air measurements, there are some indications that major inversions occur in the first 500 m above the valley ground, depending on season, weather situation and time of day.

Abstract. The Houston-Galveston Airshed (HGA) is one of the major metropolitan areas in the US that is classified as a nonattainment area of federal ozone standards. Formaldehyde (HCHO) is a key species in understanding ozone related air pollution; some of the highest HCHO concentrations in North America have been reported for the HGA. We report on HCHO measurements in the HGA from summer 2006. Among several sites, maximum HCHO mixing ratios were observed in the Houston Ship Channel (HSC), a region with a very high density of industrial/petrochemical operations.HCHO levels at the Moody Tower (MT) site close to downtown were dependent on the wind direction: southerly maritime winds brought in background levels (0.5-1 ppbv) while trajectories originating in the HSC resulted in high HCHO (up to 31.5 ppbv). Based on the best multiparametric linear regression model fit, the HCHO levels at the MT site can be accounted for as follows: 38.5±12.3% from primary vehicular emissions (using CO as an index of vehicular emission), 24.1±17.7% formed photochemically (using peroxyacetic nitric anhydride (PAN) as an index of photochemical activity) and 8.9±11.2% from industrial emissions (using SO 2 as an index of industrial emissions). The balance 28.5±12.7% constituted the residual which cannot be easily ascribed to the above categories and/or which is transported into the HGA. The CO related HCHO fraction is dominant during the morning rush hour (06:00-09:00 h, all times are given in CDT); on a carbon basis, HCHO emissions are up to 0.7% of the CO emissions. The SO 2 related HCHO Correspondence to: B. Rappenglück (brappenglueck@uh.edu) fraction is significant between 09:00-12:00 h. After 12:00 h HCHO is largely formed through secondary processes. The HCHO/PAN ratios are dependent on the SO 2 levels. The SO 2 related HCHO fraction at the downtown site originates in the ship channel. Aside from traffic-related primary HCHO emissions, HCHO of industrial origin serves as an appreciable source for OH in the morning.