|Niinemets, Ü: Distribution patterns of foliar carbon and nitrogen as affected by tree dimensions and relative light conditions in the canopy of Picea abies, Trees, 11, 144-154 (1997)|
Variations in the partitioning of foliar C and N in combination with changes in needle and shoot structure were studied in trees of Picea abies along a vertical gradient of relative irradiance (RI). RI was the major determinant of needle morphology, causing all needle linear parameters - width, thickness and length - to increase. Due to the different responsiveness of needle thickness and width in respect of RI, the ratio of total to projected needle area increased with RI. Furthermore, shoot structure was also influenced by RI, and the ratio of shoot silhouette area to total needle area, which characterises the packing of needles and needle area within the shoot, was greater at lower values of irradiance. Needle dry weight(NDW) per total needle area (LWA(t)) was also increased by RI. Similarly, irrespective of the measure for surface area, needle N content per area. as the product of NDW per area and N content per NDW (N-m), scaled quasi-linearly with needle weight per area. Thus, the changes in needle and shoot morphology made it possible to invest more photosynthesising weight per unit light-intercepting surface there, where the pay-back due to elevated irradiances was the highest. However, N-m behaved in an entirely different manner, decreasing hyperbolically with LWA(t). Since non-structural (carbon in non-structural carbohydrates), and structural (total minus non-structural) needle C per NDW also increased with LWA(t) N-m was inversely correlated with both non- structural and structural carbon. Total tree height, increasing significantly LWA(t), also influenced needle structure. It appeared that total height did not affect needle thickness or width, but larger trees had greater needle density (dry weight per volume). Because needle density was positively correlated with needle C content per NDW, it was assumed that the greater values of needle C content can be attributed to increased lignification and thickening of needle cell walls.