Table II.

Summary of average steady-state gas exchange parameters, leaf, stem (including sheath), root, and whole-plant N, leaf mass per area, PNUE, NUE, and some growth parameters of NAD-ME and NADP-ME C4 grasses from three independent experiments (experiments 1–3; Table I)

Maximal phosphoenolpyruvate carboxylase (Vp max) and Rubisco (Vc max) activities were estimated from A/Ci curves (experiment 2) using the C4 photosynthesis model of von Caemmerer (2000). Within the same experiment, values followed by the same letter are not significantly different (P > 0.05). −, Not determined. HN, High N soil supply; LN, low N soil supply.

Experiment 1Experiment 2Experiment 3
ParameterHNHNHNLN
NAD-MENADP-MENAD-MENADP-MENAD-MENADP-MENAD-MENADP-ME
A (μmol m−2 s−1)30aa33aa39ab40ab35b35b25a24a
g (mol m−2 s−1)0.25aa0.28aa0.26ab0.28ab0.22b0.23b0.16a0.16a
Ci/Ca0.37aa0.38aa0.31ab0.33ab0.26a0.26a0.29a0.33b
Vp max (μmol m−2 s−1)81a82a
Vc max (μmol m−2 s−1)47a46a
Vp max/Vc max1.72a1.78a
Leaf N (mmol m−2)119b70a115b88a108d81c47b37a
Leaf N (mg g−1)39b32a34b31a41c37b18a18a
Stem N (mg g−1)21b19a
Root N (mg g−1)16a19b
Plant N (mg g−1)24a23a
Leaf mass per area (g m−2)44ba31aa42b37a36c31b35c28a
A/N (μmol CO2 [mol N]−1 s−1)313a525b351a478b299a388b445c611d
NUE (g dry mass [g leaf N]−1)67a111b95a116b65a88b191c218d
Tiller no. (plant−1)10b16c4a5a
Plant dry mass (g plant−1)9.2aa14.6ba9.9ab10.7ab4.4b4.5b1.5a1.3a
Leaf mass fraction (% plant dry mass)39ba33aa35bb31ab41d35c32b28a
Stem mass fraction (% plant dry mass)50aa50aa47ab54bb35c44d26a28a
Root mass fraction (% plant dry mass)11aa17ba18bb15ab24b21a42c44c
  • a Data taken from Ghannoum et al. (2001).

  • b Data taken from Ghannoum et al. (2002).