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Influence of high light intensity on survival of planted Engelmann spruce
Results of three studies on photosynthesis and needle water deficits are presented. Photosynthesis was higher for Engelmann spruce seedlings grown in the shade than in the open, but it was not significantly different for lodgepole pine seedlings. Spruces reached near-maximum photosynthesis at 4,000 to 5,000 ft-c, but pines did not appear light-saturated even at 12,000 ft-c. Photosynthesis and respiration of potted spruce seedlings were highest at moisture deficits less than 10 percent; with deficits above 20 percent, photosynthesis was zero and respiration minimal. At a deficit of 58 percent seedlings died. Moisture deficits of seedlings during the summer after field planting were below 31 percent and did not differ significantly between sunrise or mid-afternoon measurements, nor between shaded or open-grown treatments. These and other results suggest that solarization occurs in unshaded spruce, has a deleterious effect on photosynthesis, and may be associated with the high mortality in plantations at elevations above 10,000 ft.
leaf water deficit
Ronco, Frank. 1970. Influence of high light intensity on survival of planted Engelmann spruce. Forest Science. 16: 331-339.