Photosynthesis and nitrogen allocation in needles in the sun and shade crowns of hybrid larch saplings: effect of nitrogen application

We studied the effects of applying 50 kg(N) ha^?1 year^?1 of nitrogen (N) on needle photosynthesis, N allocation and nutrient content in the sun- and shade crowns of the hybrid larch F₁ (Larix gmelinii var. japonica × L. kaempferi). The light-saturated net photosynthetic rate (P _Nmax) was not significantly affected by N application or crown position, although the contents of N, P, K, and chlorophyll (Chl), and the maximum rates of carboxylation and electron transport were lower in needles of the shade crown than of the sun crown. This difference was mainly due to an increase in the intercellular CO₂ concentration (C _i) in the needles of the shade crown. Analysis of N allocation in photosynthetic systems revealed that more N was allocated to functions related to electron transport and ribulose-1,5-bisphosphate (RuBP) regeneration in needles of the shade crown. N allocation in needles of the hybrid larch F₁ was regulated mainly by the light conditions, rather than by N application