Author(s)

Qing-Lai Dang^1*, Junlin Li¹, Rongzhou Man²

¹Faculty of Natural Resources Management, Lakehead University, Thunder Bay, Canada.
²Ontario Ministry of Natural Resources, Ontario Forest Research Institute, Sault Ste. Marie, Ontario, Canada.

The relationship between photosynthesis and leaf nitrogen concentration is often used to model forest carbon fixation and ratios of different nutrient elements can modify this relationship. However, the effects of nutrient ratios on this important relationship are generally not well understood. To investigate whether N/P/K ratios and CO₂ concentration ([CO₂]) influence relationships between photosynthesis and nitrogen, we exposed one-year-old black spruce seedlings to two [CO₂] (370 and 720 μmol·mol^-1), two N/P/K ratio regimes (constant (CNR) and variable (VNR) nutrient ratio) at 6 N supply levels (10 to 360 μmol·mol^-1). It was found that photosynthesis (P_n) was more sensitive to nitrogen supply and N/P/K ratios under the elevated [CO₂] than under ambient [CO₂]; under the elevated [CO₂], P_n declined with increases in N supplies above 150 μmol·mol^-1 in the CNR treatment but was relatively insensitive to N supplies of the same range in the VNR treatment. Further, our data suggest that the nutrient ratio and the CO₂ elevation effects on photosynthesis were via their effects on the maximum rate of carboxylation (V_cmax) but not electron transport (J_max) or triose phosphate utilization (TPU). The results suggest that the CO₂ elevation increased the demand for all three nutrient elements but the increase was greater for N than for P and K. The CO₂ elevation resulted in greater photosynthetic use efficiencies of N, P and K, but the increases varied with the nutrient ratio treatments. The results suggest that under elevated [CO₂], higher net photosynthetic rates demand different optimal N-P-K ratios than under the current [CO₂].

Maximum Rate of Carboxylation, Photosynthetic Electron Transport, Triose Phosphate Utilization, Nutrient Use Efficiency

Dang, Q. , Li, J. and Man, R. (2021) N/P/K Ratios and CO₂ Concentration Change Nitrogen-Photosynthesis Relationships in Black Spruce. American Journal of Plant Sciences, 12, 1090-1105. doi: 10.4236/ajps.2021.127076.