It is still unknown whether the midday depression of photosynthesis under severe water stress, frequently observed in plants growing in a Mediterranean-type climate, is primarily a consequence of diffusional or nondiffusional limitations. We carried out combined measurements of gas exchanges and chlorophyll fluorescence in field-grown Arbutus unedo L. trees during late spring and mid summer, and a quantitative limitation analysis was performed to distinguish between the different limitations to photosynthesis, i.e., diffusional [D L = stomatal (S L) + mesophyll (MCL)] and non-diffusional (carboxylation capacity and electron transport, B L) limitations. Light-saturated assimilation at ambient CO2 (A max), stomatal conductance to water vapour (g sw) and maximum carboxylation rate (V cmax C i) showed a marked midday depression during both periods. The total limitations tended to increase during the day and were remarkably similar in June and July (50 and 48%, respectively); on a daily basis, D L was similar to B L (about 23%) in June; whereas, in July the former was predominant (38 and 4%, respectively). We concluded that the midday depression in photosynthesis was largely caused by diffusional limitations, with non-diffusional limitations playing a smaller role. Although stomatal closure was the main diffusional limitation, the decline in mesophyll conductance was not negligible during the hottest and driest period.

GRASSI Giacomo;  RIPULLONE Francesco;  BORGHETTI Marco;  RADDI Sabrina;  MAGNANI Federico; 

2010-02-08

SPRINGER

JRC52557

0931-1890,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC52557,   

10.1007/s00468-009-0355-7,