Interaction of the Onset of Spring and Elevated Atmospheric C[O.Sub.2] on Ragweed (Ambrosia Artemisiifolia L.) Pollen Production
Rogers, Christine A., Wayne, Peter M., Macklin, Eric A., Muilenberg, Michael L., Wagner, Christopher J., Epstein, Paul R., Bazzaz, Fakhri A., Environmental Health Perspectives
Increasing atmospheric carbon dioxide is responsible for climate changes that are having widespread effects on biological systems. One of the clearest changes is earlier onset of spring and lengthening of the growing season. We designed the present study to examine the interactive effects of timing of dormancy release of seeds with low and high atmospheric C[O.sub.2] on biomass, reproduction, and phenology in ragweed plants (Ambrosia artemisiifolia L.), which produce highly allergenic pollen. We released ragweed seeds from dormancy at three 15-day intervals and grew plants in climate-controlled glasshouses at either ambient or 700-ppm C[O.sub.2] concentrations, placing open-top bags over inflorescences to capture pollen. Measurements of plant height and weight; inflorescence number, weight, and length; and days to anthesis and anthesis date were made on each plant, and whole-plant pollen productivity was estimated from an allometric-based model. Timing and C[O.sub.2] interacted to influence pollen production. At ambient C[O.sub.2] levels, the earlier cohort acquired a greater biomass, a higher average weight per inflorescence, and a larger number of inflorescences; flowered earlier; and had 54.8% greater pollen production than did the latest cohort. At high C[O.sub.2] levels, plants showed greater biomass and reproductive effort compared with those in ambient C[O.sub.2] but only for later cohorts. In the early cohort, pollen production was similar under ambient and high C[O.sub.2], but in the middle and late cohorts, high C[O.sub.2] increased pollen production by 32% and 55%, respectively, compared with ambient C[O.sub.2] levels. Overall, ragweed pollen production can be expected to increase significantly under predicted future climate conditions. Key words: allergenic pollen, Ambrosia artemisiifolia, climate change, climate variability, elevated C[O.sub.2], global warming, ragweed, springtime warming. Environ Health Perspect 114:865-869 (2006). doi:10.1289/ehp.8549 available via http://dx.doi.org/ [Online 9 February 2006]
Global climate changes, driven by increased concentrations of greenhouse gases such as carbon dioxide, are having widespread impacts on biotic systems, including both direct and indirect effects on human health (Epstein 1999; Patz et al. 2005). One of the most dramatic effects of climate change seen thus far is on the timing of reproductive processes in plants (Fitter and Fitter 2002), including wind-pollinated types, many of which have highly allergenic pollen (Clot 2003; van Vliet et al. 2002). Hence, predicted increases in C[O.sub.2], coupled with further changes in climate, could have important implications for individuals with allergies and asthma.
Many regions are currently experiencing warming effects associated with global climate change, including longer growing seasons and earlier arrival of spring (Intergovernmental Panel on Climate Change 2001; Karl and Trenberth 2003; Menzel 2000). These changes have already greatly affected plant and animal populations by significantly influencing interannual population dynamics and phenology (Loeuille and Ghil 2004; Root et al. 2003). Analysis of temporal events since the 1950s, across a wide array of plant and animal species, indicates that spring phenology in northern temperate zones is advancing about 5 days each decade (Root et al. 2003). The trend toward earlier spring onset is particularly evident in early spring flowering of wind-pollinated tree species, for which reproductive development and bud burst in spring are highly temperature sensitive (Clot 2003; van Vliet et al. 2002). However, early spring onset may also affect temperature-dependent processes occurring over the entire growing season, not just those in early spring. For example, an early spring could also influence developmental and reproductive processes in later flowering plants.
Although atmospheric C[O.sub.2] has no apparent direct effect on human health, it does have well-known direct effects on plants. …