3.4 | Intrinsic water use efficiency
(WUEi)
WUEi is a key variable in the GPPiso/SFestimation procedure (Figure 4).For all three gmassumptions, WUEi showed a significant seasonal pattern
(‘date’ effect, p-value < 0.0001, df = 1, F = 29), decreasing
sharply as the thermal growing season began and increasing as it ended
(Figure 4). It also decreased gradually over the summer. In 2012, the
mean values on the fertilised plot were 6% higher for
gm∞, 7% higher for
gm/\(g_{C\hat{\alpha}}\) = 2.67, and 9% higher for,
gm = 0.31 mol CO2 m-2s-1 respectively. In 2013, the relative increase in
WUEi on the F plot was similar: 6%, 7% and 8%
respectively. For both years, there was a significant ‘plot’ effect
(p-value < 0.0001, df = 1,) and a significant effect of the
gm assumptions (p-value < 0.0001, df = 2)
(Figure 4).