Publication Date:
2011-11-24
Description:
Mesophyll conductance, g m , was estimated from measurements of stomatal conductance to carbon dioxide transfer, g s , photosynthesis, A , and chlorophyll fluorescence for Year 0 (current-year) and Year 1 (1-year-old) fully sunlit leaves from short (2 m tall, 10-year-old) and tall (15 m tall, 120-year-old) Nothofagus solandrii var. cliffortiodes trees growing in adjacent stands. Rates of photosynthesis at saturating irradiance and ambient CO 2 partial pressure, A satQ , were 25% lower and maximum rates of carboxylation, V cmax , were 44% lower in Year 1 leaves compared with Year 0 leaves across both tree sizes. Although g s and g m were not significantly different between Year 0 and Year 1 leaves and g s was not significantly different between tree heights, g m was significantly (19%) lower for leaves on tall trees compared with leaves on short trees. Overall, V cmax was 60% higher when expressed on the basis of CO 2 partial pressure at the chloroplasts, C c , compared with V cmax on the basis of intercellular CO 2 partial pressure, C i , but this varied with leaf age and tree size. To interpret the relative stomatal and mesophyll limitations to photosynthesis, we used a model of carbon isotopic composition for whole leaves incorporating g m effects to generate a surface of ‘operating values’ of A over the growing season for all leaf classes. Our analysis showed that A was slightly higher for leaves on short compared with tall trees, but lower g m apparently reduced actual A substantially compared with A satQ . Our findings showed that lower rates of photosynthesis in Year 1 leaves compared with Year 0 leaves were attributable more to increased biochemical limitation to photosynthesis in Year 1 leaves than differences in g m . However, lower A in leaves on tall trees compared with those on short trees could be attributed in part to lower g m and higher stomatal, L s , and mesophyll, L m , limitations to photosynthesis, consistent with steeper hydraulic gradients in tall trees.
Print ISSN:
0829-318X
Electronic ISSN:
1758-4469
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Permalink
