Photosynthesis–nitrogen relationships: interpretation of different patterns between Pseudotsuga menziesii and Populus × euroamericana in a mini-stand experiment

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Tree Physiology, 23:137–144

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Photosynthesis–nitrogen relationships: interpretation of different patterns between Pseudotsuga menziesii and Populus × euroamericana in a mini-stand experiment

Francesco Ripullone (1, 2), Giacomo Grassi (3), Marco Lauteri (4) and Marco Borghetti (1)

1. Dipartimento di Produzione Vegetale, Università della Basilicata, Italy / 2. Author to whom correspondence should be addressed (rf464agr@unibas.it) / 3. Dipartimento di Colture Arboree, Università di Bologna, Italy / 4. Istituto di Biologia Agro-ambientale e Forestale, CNR, Porano, Italy / Received May 29, 2002; accepted August 9, 2002; published online January 2, 2003

Summary

We compared photosynthesis–nitrogen relationships of one broad-leaved (poplar; Populus × euroamericana (Dole) Guinier) and one conifer (Douglas-fir; Pseudotsuga menziesii (Mirb.) Franco) species. Plants were grown in large pots to allow free root development and were kept well watered. We determined effects of low, intermediate and high nitrogen supply rates on area-based leaf nitrogen (N_a) and chlorophyll concentrations, leaf mass per area (LMA), light-saturated photosynthesis (A_max), maximum carboxylation (V_cmax) and electron transport rate (J_max), photosynthetic nitrogen-use efficiency (PNUE), and proportions of leaf N in active Rubisco (P_R), bioenergetic pools (P_B) and the light-harvesting complex (P_LH). Nitrogen supply significantly affected leaf N_a. Leaf mass per area did not differ between species and was unaffected by the N treatments. In both species, there was a positive correlation between leaf N_a and chlorophyll concentration, and between leaf N_a and the photosynthetic parameters A_max, J_max and V_cmax. At comparable leaf N_a, however, poplar showed twofold higher PNUE and a threefold steeper slope of the A_max– nitrogen relationship than Douglas-fir. Leaf N_a was negatively correlated with PNUE in Douglas-fir but not in poplar. Leaf N_a was also negatively correlated with P_R, P_B and P_LH in Douglas-fir, whereas in poplar, a negative correlation was found only for P_LH. Parameter P_R was significantly higher in poplar than in Douglas-fir. The ratio of CO₂ concentration in the intercellular space to that in ambient air was higher in poplar than in Douglas-fir. Overall, our data suggest that differences in the photosynthesis–nitrogen relationship and PNUE between Douglas-fir and poplar primarily reflect a different investment of N to active Rubisco, and possibly a different constraint to CO₂ diffusion.

Keywords: conifer, hardwoods, leaf mass per area, light-saturated photosynthesis, nitrogen partitioning, photosynthetic nitrogen-use efficiency.