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 non-diffusional 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.

Contribution of diffusional and non-diffusional limitations to midday depression of photosynthesis in Arbutus unedo L.

RIPULLONE, Francesco
Investigation
;
BORGHETTI, Marco
Writing – Review & Editing
;
2009

Abstract

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 non-diffusional 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.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11563/873
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