Atmospheric CO_2 Concentrations Within a Mixed Forest: Implications for Seedling Growth

Abstract

We studied carbon dioxide concentrations in a mixed deciduous forest in New England, USA by making continuous measurements at 0.05, 0.2, 3, and 12 m above the soil surface. The measurements began in early March and continued until the end of November 1985; therefore, they spanned the growing season and parts of the dormant seasons both before and afterwards. The data were compared with those from Mauna Loa, Hawaii, which represent global atmospheric CO 2 levels in the Northern Hemisphere. The results show strong seasonal and daily variations in CO 2 concentrations at all heights in the forest. On average, during the growing season, CO 2 levels were generally higher in the forest than in bulk air at Mauna Loa. The highest level of CO 2 was found near the forest floor and the lowest at the 12—m level. Daily levels of CO 2 were constant throughout the day in the dormant season and were the same for all heights in the forest. However, during the growing season, the CO 2 concentrations were lowest during the middle of the day, especially at the 12 m height. Thus, this study shows that the CO 2 concentrations in the forest may be quite different than those in bulk air and that seedlings, saplings, and mature trees may experience different CO 2 environments for which they may show different responses in photosynthesis, growth, and water use. Moreover, a tree may experience different CO 2 environments as it grows towards the canopy, and different modules of an individual may also be growing in different CO 2 atmospheres.