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The Effects of Elevated CO2 and Drought on Floral Traits and Pollinator Visitation Rates of Four Forbs

Paper Reviewed
Glenny, W.R., Runyon, J.B. and Burkle, L.A. 2018. Drought and increased CO2 alter floral visual and olfactory traits with context-dependent effects on pollinator visitation. New Phytologist 220: 785-798.

Introducing their work, Glenny et al. (2018) write that "examining how floral traits, pollinator visitation rates and pollinator community composition are affected by climate factors is key to understanding and predicting how global change will impact pollination services." And, therefore, it became their objective to investigate the impact of both drought and elevated atmospheric CO2 concentrations on floral visual traits (i.e., plant size, mean petal area and floral display), floral olfactory traits (i.e., total volatile organic compound (VOC) emissions, VOC composition and VOC dispersion) and pollinator visitation rate (per plant and per flower) in single-species and multi-species forb assemblages.

To accomplish their design, the three ecologists from Montana State University, Bozeman, MT, USA, grew samples of four forb species (Campanula rotundifolia, Heterotheca villosa, Phacelia hastate and Potentilla recta) from seeds collected from a nearby mountain meadow site (Mt. Ellis). The seeds were sown in a glasshouse for 5-6 weeks and then transplanted into climate-controlled chambers for 100-130 days. Thereafter, they were transported back again to the glasshouse for an additional 4-6 weeks before flowering. Upon the first signs of flowering, the plants were transferred back into growth chambers representing one of four treatment conditions: (1) well-watered and ambient CO2, (2) drought and ambient CO2, (3) well-watered and elevated CO2 and (4) drought and elevated CO2. The ambient CO2 concentration was 400 ppm and the elevated CO2 concentration was maintained at 800 ppm. Drought was simulated by withholding water from the plants until the first sign of wilting was observed. Thereafter, plants were re-watered to capacity and monitored again without the addition of water until wilting again appeared. Plants remained in these well-watered and simulated drought conditions and ambient and elevated CO2 treatments for a period of 25 days. At the end of this period, Glenny et al. measured important floral visual, olfactory and pollinator visitation traits.

In general, the results indicated that drought had a negative impact on floral visual traits and pollinator visitation rates, but increased VOC emissions. Elevated CO2, on the other hand, and as noted by the authors, "positively affected floral visual traits, VOC emissions and pollinator visitation rates." In combination, elevated CO2 and drought had little interactive influence on the parameters measured.

In light of the above, it may be concluded that elevated CO2 will enhance plant-pollinator interactions given the positive impacts of higher CO2 levels on floral visual, olfactory and pollinator visitation rates. However, much remains to be learned in this regard and additional studies will help further our knowledge on this topic. But for now, the future appears bright.

Posted 21 January 2019