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Rates of stomatal opening in conifer seedlings in relation to air temperature and daily carbon gain

Summary

Published in Plant, Cell and Environment 20: 1462-1472

Experiments were conducted on well watered 1-year-old Douglas fir [Pseudotsuga menziesii (Mirb.) Franco], western hemlock [Tsuga heterophylla (Raf.) Sarg.] and western redcedar (Thuja plicata Donn) seedlings to determine the effects of temperature on whole-plant photosynthetic and stomatal responses to short-term fluctuations in irradiance (Q). Following a step change in Q, time constants (t, the period over which 63% of the total change occurs) for stomatal conductance (gs) and assimilation rate (A) decreased linearly with increasing air temperature (Tair). For example, in western redcedar tA  decreased from 30 ± 4 min at 5 °C to 10 ± 1 min at 25 °C. In all cases, tA was within 10-15% of tgs. There was considerable variation in t among individuals within a given species. Differences between species became more pronounced with decreasing temperature. Multiplicative models that included functions for t accounted for 99% of the diurnal variability in A and gs for seedlings exposed to varying air temperature, irradiance and vapour pressure deficit. Estimates of daily A were within 2% of those measured.  Intermittent cloud cover and understory shading were approximated by exposing seedlings to 3—4 episodes (³ 1 h) of shade (200 or 500 mmol m-2 s-1 or complete darkness during the day. In such cases, daily A was overestimated by up to 4 and 21%, respectively, if a function for t was excluded from the models. Our results suggest that there is scope for selecting seedling stock for increased carbon assimilation on the basis of reduced time constants. For example, in western redcedar, a 40% reduction in t could lead to increases in daily carbon gains of almost 5%  depending on the frequency and degree of shading. If these daily gains were translated into increased dry matter production and compounded, seasonal gains would be even larger.

Sector(s): 

Forests

Categorie(s): 

Scientific Article

Theme(s): 

Forestry Research, Forests, Silviculture

Author(s)

PEPIN, Steeve et Nigel J. LIVINGSTON

Year of publication :

1997

Format :

Paper

Keywords :

assimilation rate, carbon gain, conductance, Pseudotsuga menziesii, stomatal conductance, douglas fir, temperature, time constant, werstern hemlock, Tsuga heterophylla, Thuja plicata, western redcedar, sylviculture des forêts naturelles résineuses, silviculture and yield of natural forests - softwood stands, sylviculture et rendement des forêts naturelles - peuplements résineux

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