The Carbon Economy of Developing Leaves of White Clover (Trifolium repens L.)

The assimilation, respiration, import and export of carbon by developing leaves of white clover (Trifolium repens L.) plants were measured in two controlled environment experiments. Leaves were classified into nine stages of development (0·1–0·9) using the scale of Carlson (1966, Crop Science6, 293–4). Net photosynthetic capacity in the light was negative for leaves at stage 0·4 (10% unfolded), but was positive at stage 0·5 and continued to increase as leaves unfolded. Positive carbon balance (i.e. net photosynthesis > dark respiration) over 24 h (12 h photoperiod) occurred soon after stage 0·6 when leaves had expanded about 35% of their maximum surface area and reached about 50% of their maximum weight. Simultaneously, leaves switched from being sinks for carbon at stage 0·6 and younger to being sources of C for the rest of the plant at stage 0·7 and older. The results indicate that, in addition to leaves on the main stolon, other sources contribute C to the growth of young leaves and, probably, to other meristems associated with the main stolon apex; branches and reserve carbohydrate pools are the most likely sources.