Photosynthetic duration, carboxylation efficiency and stomatal limitation of sun and shade leaves of different ages in field-grown grapevine (<i>Vitis vinifera</i> L.)

Abstract

The relationship of photosynthesis (A) of grapevine (Vitis vinifera L.) sun and shade leaves of primary and secondary (lateral) shoots to insertion level was investigated over two seasons in the field. The leaf plastochron index (LPI) was used to denote leaf position on the shoot. Additionally, laboratory and field measurements of the response of A to CO₂ were conducted. An empirical model was developed to estimate carboxylation efficiency (CE) and stomatal limitations (1) of A. In sun leaves, the relationship of A to LPI changed little until the end of the season (October), whereas stomatal conductance (g) and the intercellular partial pressure of CO₂ (c_i) increased. Leaves acclimated to low light and leaves older than LPI 5 had 30 % lower A and were operating at a slightly higher ci as sun leaves. During September and October, lateral leaves had highest rates of CO₂ assimilation and CE. In mid-October, A and g decreased rapidly and simultaneously for all leaf types, leaf positions and both treatments (sun and shade). Photosynthesis responded similar to individual leaf age as to leaf position. A was linearly related to c_i up to non-limiting conductances for sun and shade leaves, for all ages and at all times during the season. The CE and 1 were highest at the beginning of the season and strongly dependent on leaf position. Stomatal limitation declined continuously from about 55 % at the beginning to about 23 and 18 % for sun and shade leaves, respectively, at the end of the season.