Document: JAM-3-66-3

Seasonal patterns of photosynthetic response and acclimation to elevated CO₂ in strawberry.

BUNCE, J.*

USDA-ARS, Beltsville, MD 20705 USA ¹

Abstract:
Strawberry plants were grown in field plots at ambient, +300 and +600 ppm carbon dioxide concentrations. Leaf gas exchange was measured made every few weeks near midday on clear days from spring through fall under ambient conditions of air temperature, water vapor pressure, and carbon dioxide concentration. Plants grown in ambient air were also measured at the two higher concentrations, in order to determine the temperature dependence of the short-term response to elevated carbon dioxide, and also to identify seasonal patterns in the extent of photosynthetic acclimation to growth at elevated carbon dioxide. The short-term response of photosynthesis to an increase in substomatal carbon dioxide concentration from 225 to 450 ppm, was an increase in rate by a factor of 1.8 at 20 C, increasing linearly to 3.0 at 35 C. These rate increases were much larger than predicted from the kinetics of rubisco. In spring and in summer when water was non-limiting, photosynthetic down regulation was evident at elevated carbon dioxide, averaging 14% for plants grown at +300, and 23% for plants grown at +600 ppm. During dry periods in the summer, there was no evidence of acclimation, as photosynthetic rates of ambient-grown plants were more severely reduced by water stress. In the fall, with non-limiting water, there was also no evidence of acclimation. The spring-fall pattern is opposite of that expected if acclimation were caused by source-sink imbalance.

Keywords: photosynthesis, CO2, global change, acclimation

This abstract is being presented at: 10:30 AM in session:
Poster Session #18: Elevated CO₂.