期刊
TREE PHYSIOLOGY
卷 31, 期 9, 页码 985-996出版社
OXFORD UNIV PRESS
DOI: 10.1093/treephys/tpr021
关键词
carbon isotope discrimination; carboxylation; mesophyll conductance; mesophyll limitation; stomatal conductance
类别
资金
- Foundation for Research, Science and Technology, New Zealand
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 CO2 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 CO2 partial pressure at the chloroplasts, C-c, compared with V-cmax on the basis of intercellular CO2 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.
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