The effect of humidity on photosynthesis and water relations of white spruce seedlings during the early establishment phase

Abstract

Newly transplanted, 3-year-old bare-root white spruce (Piceaglauca (Moench) Voss) seedlings were grown in three levels of absolute humidity difference (AHD), under water-stressed and well-watered conditions in growth chambers. Stomatal conductance to CO2 as well as net assimilation were more than twice as high in the low AHD treatment (6.8 μg H2O•cm−3) as in the high AHD treatment (21.0 μg H2O•cm−3). Transpiration rates were uniform among humidity treatments, but in the low AHD treatment water use efficiency was more than double that of the high AHD treatment. Water use efficiency was greatest in the low AHD conditions, in the water-stressed seedlings, and during the time immediately after planting. There were no differences in the number of new roots produced among humidity treatments, despite the different levels of photosynthesis. In the stress treatment, bud flush of seedlings in the high AHD treatment occurred 3 days later than in the low AHD treatment. A field study on the effects of varying aspen (Populustremuloides Michx.) canopies on humidity levels showed that AHD under partial and full canopies was lower than that of the clearcut. Results suggest that silvicultural treatments that promote higher humidity levels on planting sites should improve white spruce seedling photosynthesis immediately after planting.

Using nature’s template to best advantage in the Canadian boreal forest

“…The major fi ndings of the study to date are: 1) there is no difference in survival of planted spruce in clearcuts versus 40-70 year old aspen stands; 2) 40-70 year old aspen stands provide a less extreme environment for seedling establishment than clearcuts; 3) spruce perform better in the clearcuts after establishment; and 4) spruce growth under the aspen is adequate to meet current legislated performance standards. The fi ndings of this study, plus others by Lieffers et al (1996) and Man and Lieffers (1997), indicate that underplanting aspen stands with white spruce represents a feasible alternate silvicultural system for establishing mixed stands. The results may also be applicable to management of birch spruce stands in Fenno Scandinavia where the productivity and economics of two-storied spruce and birch stands has been demonstrated to be profi table (Valkonen and Valsta 2001).…”

“…are common throughout the boreal forest. One of the more common pathways for the natural establishment of these mixed stands is for spruce to recruit gradually into the stands after an initial regeneration delay of approximately 20 years, when the deciduous stands are very dense (DeLong 1991, Lieffers et al 1996. I will describe a study which Tanner et al (1996) and DeLong (2000).…”

Effects of shelterwood and site preparation on microclimate and establishment of white spruce seedlings in a boreal mixedwood forest

“…1. Seasonal soil temperatures (mean kSE) at 0.10 m (n = 30 for canopy density and 40 for site preparation) and 0.30 m (n=18 for canopy density and 24 for site preparation) depths in relation to canopy (CT-control, HD-high residual density of shelterwood, LD-low residual density of shelterwood, and CC-clearcut) and site preparation (CN-control, MX-mixing, and BL-blading) Time ( Marsden et al 1996). Decreased light transmission and ods in spring and fall.…”

“…Suggested causes for the poor initial establishment of white spruce include excess or deficient soil moisture, excess solar radiation and daytime temperature, summer frosts, low soil temperature, and nutrient deficiency (Mullin 1963, Burdett et al 1984. Some studies suggest that water stress resulting from low soil moisture and temperature and a high vapour pressure deficit (VPD) is the primary causal factor (Grossnickle 1988, Marsden et al 1996 limiting the ability of newly planted seedlings to absorb water from soil (Burdett 1990).…”

Are mixtures of aspen and white spruce more productive than single species stands?

“…Aspen shelter trees reduce frost frequency and severity and increase relative humidity (Man and Lieffers 1998). Relative humidity increases from 30 to 80% resulted in a doubling in mid-day photosynthetic rates of white spruce (Marsden et al 1996). In central Alberta, planted white spruce seedlings under an aspen canopy maintain healthy growth while similar seedlings in open conditions show reduced shoot growth and needle discoloration, especially in spring and fall when night frosts are frequent (Man and Lieffers 1997a).…”