Interactive Effects of CO2 and O2 in Soil on Root and Top Growth of Barley and Peas

Barley and pea plants were grown under several regimens of different compositions of soil atmosphere, the O(2) concentration varying from 0 to 21% and the CO(2) concentration from 0 to 8%. In absence of CO(2), the effect of O(2) on root length in barley was characterized by equal root lengths within the range of 21 to 7% O(2) and a steep decline between 7 and 0%. In peas, while showing the same general response, the decline occurred between 14 and 7% O(2). Root numbers of the seminal roots of barley decreased already with reduction in O(2) concentration from 21 to 14%. Dry matter production was affected somewhat differently by O(2) and CO(2) concentration. Dry matter production in barley was reduced at 14% O(2) while root length decreased between 7 and 0%. In peas, dry matter production was favored by low CO(2) concentrations except where there was no oxygen. At 21% O(2), increasing CO(2) concentrations did not seem to affect root length up to concentrations of 2% CO(2). At 8% CO(2), root length was decreased. The inter-active effects of CO(2) and O(2) are characterized by a reduced susceptibility to CO(2) at O(2) values below 7%, and a very deleterious effect of 8% CO(2) at 7% O(2).