Developing estimators of ragweed pollen production from measurements of inflorescence size

Background/Question/Methods

Common ragweed (Ambrosia artemisiifolia) is a widespread North American plant that produces allergenic pollen, a concern for the 35 million Americans who get hay fever every year.  The objective of this research project was to find an efficient proxy for pollen counts so that managers or researchers conducting demographic or experimental work on ragweed can rapidly estimate pollen production. The number of pollen grains per flowering spike was counted for 62 ragweed plants using a Hemocytometer.   We also measured the length and weighed the dry biomass of each ragweed spike. We then conducted regression analyses to determine which trait would best estimate the number of pollen grains counted.  

Results/Conclusions

There was a significant relationship between inflorescence length and pollen output per inflorescence, R2 =.224 (P < .0001.) Inflorescence weight and pollen output per inflorescence weren’t correlated, R2 =.0722 (P=.0333). These results may enable maximum spike length to be used as a proxy for pollen production in future studies of ragweed.  Since ragweed has been previously shown to produce more pollen under elevated conditions of CO2 and in cities, this research contributes to our ability to better predict when and where ragweed may become more problematic under future conditions.