Compensatory photosynthesis as a response to partial debudding in ezo spruce, Picea jezoensis seedlings

The effects of partial debudding on photosynthesis, stomatal conductance and nitrogen contents of 1‐year‐old needles and newly grown needles were studied in Picea jezoensis (Sieb. et Zucc.). Seventy‐five percent of the buds of P. jezoensis seedlings were removed soon after bud break. Gas exchange was measured three times for 1‐year‐old needles and twice for current‐year needles. The photosynthetic rates of 1‐year‐old needles were greater in debudded seedlings than in control seedlings, and the difference increased as the growing season progressed. This greater photosynthetic rate in debudded seedlings was accompanied by greater stomatal conductance. However, neither the photosynthetic rates nor the stomatal conductance of current‐year needles differed between debudded and control seedlings after the needles had fully expanded. Debudding also had no effect on mass‐based nitrogen contents in either the 1‐year‐old or the current‐year needles. Area‐based nitrogen in the 1‐year‐old needles did not differ between debudded and control seedlings, but was greater in debudded seedlings than in control seedlings in current‐year needles. These results suggest that the enhanced photosynthetic rate is more likely a result of an increased root/leaf ratio that reduces the stomatal limitation of photosynthetic rate than a result of altered sink‐source relationships or increased leaf nitrogen content.