Team ragweed

One of the many signs of Spring is the United States’ report on pollen counts across the country. These pollen counts are essential, due to the 35 million Americans who get hay fever every year from pollen. In our project, we investigated whether allergenic pollen concentrations from three ecotypes of common ragweed (Ambrosia artemisiifolia) produce more pollen in response to rising CO2 concentrations. Our objective was to test for differences in pollen production by ecotypes from these climatically distinct parts of New England. In order to predict when and where pollen allergies are most likely to increase in response to climate change, we have to determine its impact in different places.

We investigated two factors of growth and production. We analyzed the amount of pollen produced by each ecotype, and in each of the three CO2 concentrations. To do this we created a stratified random subset of approximately 90 plans out of the full experimental design. The pollen was collected and frozen from the three to five flowering spikes per plant by covering the spikes with polyethelene bags at the time of flowering until pollen was completely released and then placed in a sub-80C freezer. These plants were kept in a lab at the University of Massachusetts - Amherst (UMASS - Amherst) where we spent most of our summer. Including our mentor Kristina Stinson, the team for this project consisted of 9 people from both Harvard Forest and UMASS’ aerobiology lab.

To process the plants that were in the freezer, we extracted pollen grains from each plant with an extensive methodical procedure. For future processing, we came up with a detailed protocol to remove pollen grains from the ragweed spikes and polyethelene bag that the ragweed spike was when harvested. We constructed a solution of 12mL, comprised of distilled water and pollen from an individual ragweed spike. We used a hemocytometer to count the amount of pollen grains that were present in .5 mm3 of the solution to assess the amount of pollen produced by each ragweed plant. After harvesting the pollen, we measured the length and weighed the dry biomass of each ragweed spike. These determinants allowed us to determine the production and growth of ragweed plants in respects to CO2 and ecotype. 


We also helped with the fieldwork component of the project. Even though this portion of the project was not a part of our summer’s analysis, we helped gather field data to determine the phenology of the ragweed plants in 3 temperature gradients across Massachusetts. We went to various demography plots that were in cool, warm and hot gradients and counted the number of individual ragweed plants and identify if they are flowering and/or releasing pollen.


Predicting how increased CO2 affects ragweed growth and pollen output and achieving greater understanding of how different local ecotypes respond to such changes, will better inform decisions regarding ragweed and allergenic plant policy and management. The importance of these results will only increase over the next several decades, as climate change increases the quantity and allergenicity of pollen in certain area via rises in CO2 concentrations and temperatures.