TITLE:
N/P/K Ratios and CO2 Concentration Change Nitrogen-Photosynthesis Relationships in Black Spruce
AUTHORS:
Qing-Lai Dang, Junlin Li, Rongzhou Man
KEYWORDS:
Maximum Rate of Carboxylation, Photosynthetic Electron Transport, Triose Phosphate Utilization, Nutrient Use Efficiency
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.12 No.7,
July
28,
2021
ABSTRACT: 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 (Pn)
was more sensitive to nitrogen supply and N/P/K ratios under the elevated [CO2]
than under ambient [CO2]; under the elevated [CO2], Pn 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 (Vcmax) but not electron
transport (Jmax) 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].