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- Title
Height-related decreases in mesophyll conductance, leaf photosynthesis and compensating adjustments associated with leaf nitrogen concentrations in Pinus densiflora.
- Authors
Han, Qingmin
- Abstract
Hydraulic limitations associated with increasing tree height result in reduced foliar stomatal conductance (gs) and light-saturated photosynthesis (Amax). However, it is unclear whether the decline in Amax is attributable to height-related modifications in foliar nitrogen concentration (N), to mesophyll conductance (gm) or to biochemical capacity for photosynthesis (maximum rate of carboxylation, Vcmax). Simultaneous measurements of gas exchange and chlorophyll fluorescence were made to determine gm and Vcmax in four height classes of Pinus densiflora Sieb. & Zucc. trees. As the average height of growing trees increased from 3.1 to 13.7 m, gm decreased from 0.250 to 0.107 mol m−2 s−1, and the CO2 concentration from the intercellular space (Ci) to the site of carboxylation (Cc) decreased by an average of 74 µmol mol−1. Furthermore, Vcmax estimated from Cc increased from 68.4 to 112.0 µmol m−2 s−1 with the increase in height, but did not change when it was calculated based on Ci. In contrast, Amax decreased from 14.17 to 10.73 µmol m−2 s−1. Leaf dry mass per unit area (LMA) increased significantly with tree height as well as N on both a dry mass and an area basis. All of these parameters were significantly correlated with tree height. In addition, gm was closely correlated with LMA and gs, indicating that increased diffusive resistance for CO2 may be the inevitable consequence of morphological adaptation. Foliar N per unit area was positively correlated with Vcmax based on Cc but negatively with Amax, suggesting that enhancement of photosynthetic capacity is achieved by allocating more N to foliage in order to minimize the declines in Amax. Increases in the N cost associated with carbon gain because of the limited water available to taller trees lead to a trade-off between water use efficiency and photosynthetic nitrogen use efficiency. In conclusion, the height-related decrease in photosynthetic performance appears to result mainly from diffusive resistances rather than biochemical limitations.
- Subjects
JAPANESE red pine; WATER efficiency; LEAVES; PHOTOSYNTHESIS; GAS exchange in plants; NITROGEN in the body; CHLOROPHYLL; PLANT size
- Publication
Tree Physiology, 2011, Vol 31, Issue 9, p976
- ISSN
0829-318X
- Publication type
Article
- DOI
10.1093/treephys/tpr016