Global changes alter plant growth schedule

“Under today's conditions, grasses flower early in the growing season and wildflowers flower later, but when we increased the concentration of carbon dioxide to mirror conditions 50 years from now, these two groups flowered at the same time,” said Elsa Cleland, lead author with the Jasper Ridge Global Change Experiment at Stanford University and the Carnegie Institution's Department of Global Ecology.* The results are published in the on-line early edition (September 4-8) of the Proceedings of the National Academy of Sciences.**

In recent decades, scientists have observed accelerated springtime phenology–the timing of developmental activity in many plant and animal species–and assumed it is a response to global warming. The Jasper Ridge researchers wanted to know if phenology responded similarly to other important aspects of global change, such as increasing atmospheric CO2 concentrations, altered rainfall patterns, and increased nitrogen deposition.

While the researchers found that experimental warming accelerated springtime flowering of all species, they were surprised to find differing responses to elevated CO2 and nitrogen deposition, both alone and in combination. For each of these factors, wildflowers responded by flowering earlier, while the grasses flowered later. Because grasses dominate this ecosystem, the scientists found that the overall timing of plant growth was delayed under elevated CO2.

“This research shows that global warming is just part of the picture,” said Christopher Field, director of the project. “It highlights the fact that opposing responses of different species to global changes may cause us to underestimate the degree to which natural communities are already responding to changing environmental conditions.”