|Sponsor:||Alberta-Pacific Forest Industries Inc.|
Object & Deliverables
The primary purpose of this project was to specifically address how shade and soil moisture impacts spruce photosynthetic performance and growth in the first two years after planting. The project objectives included documenting the seasonality and degree of photoinhibition in newly planted white spruce seedlings, assessing the impact of photoinhibition on spruce growth, and assessing the interaction of soil moisture and photoinhibitory light on white spruce photosynthesis and growth.
Maintenance of photosynthetic systems by protecting seedlings from photoinhibition and photooxidation may increase survival and growth of planted seedlings. Photoinhibition is a short-term disruption of photosynthesis that occurs when light-harvesting pigments collect more solar energy than the photosynthetic system can productively utilize. This disruption is common under natural conditions especially for shade-tolerant plants that have relatively low light-saturated photosynthetic capacities. The study was designed to assess how moderation of the light environment through artificial shade would affect planted white spruce survival and early growth in harvested cutblocks.
This study area was located approximately 100 km northwest of Lac La Biche and occurred during the summer field seasons of 1999 and 2000. The trial was established in two adjacent cutblocks that had 120 year old aspen in the overstory prior to harvest in early 1998. The sites were straight-bladed in the spring following harvest and operationally planted with white spruce seedlings in 1998. The trial was made up of 60 experimental plots per cutblock with five seedlings per plot. The trial tested three levels of shading: no-shade control, all-season shade, and summer only shade. Light transmission through the shade frames was between 50-60% under either sunny or cloudy conditions which was high enough to saturate the photosynthetic systems of white spruce.
The treatment effect of shading on soil temperature and soil moisture was not significant. Shading decreased daylight air temperatures and relative humidity and increased nighttime temperatures. Shading treatments had minimal impact on seedling quality as measured by chlorosis, terminal damage and mortality. Seedlings of different shading treatments did not show significant difference in height increment however, no-shade seedlings had slightly more diameter growth than shaded seedlings. Though shading did not significantly change measured root response variables, it did significantly increase fluorescence yield and chlorophyll content to indicate reduced photoinhibition and photooxidation in white spruce seedlings.
The results are contained in a May 2001 twenty-six page report entitled, “Role of Photoinhibition of Photosynthesis and Soil Water in the Initial Establishment of Clearcut-Planted White Spruce Seedlings” authored by Ken Greenway and Rongzhou Man.