A model analysis of the photosynthetic response of <i>Vitis vinifera</i> L. cvs Riesling and Chasselas leaves in the field: I. Interaction of age, light and temperature

Abstract

The photosynthetic activity (A) of leaves of different ages on primary and secondary shoots of Riesling and Chasselas vines was measured under  field  conditions  in relation to photon flux density  (PFD) at various leaf temperatures. The data sets from 4 years and two locations (Geisenheim, Germany; Changins, Switzerland) were  analysed  using  non-linear  regression models  to determine possible  genetic  and/or  climate-induced differences  in  the  light  and  temperature  response between different  leaf ages. A non-rectangular hyperbola with  physiologically meaningful  parameters was  found  to  adequately describe  the  response to photon  flux density. For both  varieties, maximum photosynthetic  rates were  observed  on  leaves  of primary  shoots,  opposite  to  the  clusters,  at  a  leaf  temperature  of  27-32  °C  and  at  light  saturation. Young leaves  showed  a  less  pronounced  temperature  optimum. The  light  response  curves  of photosynthesis  of the  two  cultivars were  similar  over  a  temperature range  of  20-30  °C. Below  this  temperature, Riesling showed higher values of A than Chasselas in most cases, whereas  it was  the reverse when leaf  temperature exceeded 30 °C. This was particularly evident for leaves on secondary shoots and was related to differences  in the photorespiration rate. Mature Riesling  leaves had higher  apparent quantum  yields  (a)  and  lower  light saturation  indices (Is) than Chasselas at  leaf temperatures below  30-35 °C. Dark  respiration  (RD)  and  the light  compensation  point  (Ic)  responded  strongly  to temperature with differences between leaf ages but no consistent difference between varieties. Leaves on secondary shoots of both cultivars had the highest photo-synthetic  activity  during  the  ripening  period  of  the fruit.