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UBC Theses and Dissertations

Ecophysiological assessment of western hemlock and western red cedar greenhouse stocktypes Major, John E.


Western hemlock (Tsuga heterophylla (Raf.) Sarg.) and western red cedar (Thuja plicata Donn) seedlings from four dormancy induction treatment(s) (DIT) (i.e. long-day dry, long-day wet, short-day dry, and short-day wet) were planted on a high available soil moisture field site in British Columbia and monitored for physiological response and morphological development over the first growing season. Stomatal conductance (gwv) and net photosynthesis (Pn) were recorded over an environmental matrix of photosynthetically active radiation (PAR) (0 - 2.2 mmol m⁻² s⁻¹ ) and vapour pressure deficit (VPD) (0 - 2.5 or 4.0 kPa) on both first year grown and fully developed second year foliage. To compare stocktypes, physiological data were collected and analyzed in the following ways: (1) replicated data at stable environmental conditions once a month, (2) physiological response to one increasing environmental variable using boundary line analysis, and (3) physiological response surface to two simultaneously changing environmental variables. For western hemlock first year needles, short-day DIT had a higher gwv response to both increasing VPD and PAR. Both short-day and moisture stressed DIT improved Pn response to PAR, and the combination had the highest response. Short-day DIT seedlings initially were smaller, shorter, had a better seedling water balance ratio and lower shoot to root ratio. Short-day second year needles showed a slightly higher gwv response to both increasing VPD and PAR as compared to long-day seedlings; however, they showed no treatment differences for Pn versus PAR. All stocktypes had similar final morphological parameter values. For western red cedar first year foliage, moisture stressed DIT seedlings had greater Pn response to increasing PAR and VPD. Also, moisture stressed seedlings gwv response to increasing VPD and PAR was higher when compared to its' non moisture stressed daylength counterpart. The long-day wet seedlings initially had a larger root and shoot system as compared to the other stocktypes. Second year foliage exhibited no treatment differences for gwv and Pn response to PAR ' and VPD. All stocktypes had similar final morphological parameter values. Attempts to test stocktypes at stable environmental conditions proved, at times, difficult. Potentially large measurement variation due to atmospheric environmental changes, and not stocktype effect, could result. Boundary line analysis, when used correctly and with sufficient data, offers a good stocktype assessment method which enables the isolation of a physiological response to one environmental variable. Three dimensional surface response technique was required to provide a clear conceptual representation of two primary environmental variables' influence on seedling physiological response.

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