Physiological parameters
Total biomass, leaf photosynthesis (under standard conditions) and
respiration were also measured to appreciate the general impact of
nutrient conditions on carbon assimilation (Fig. 2). After 3 weeks under
high Ca, shoot and root biomass was significantly affected by K
conditions. Conversely, the effect of Ca and putrescine was modest under
high K. After 4 weeks, the effect of K conditions was very clear, with
no effect at all of Ca and putrescine in shoots. In roots, low Ca and
putrescine increased biomass very slightly (Fig. 2a). Net
CO2 assimilation was significantly lower at low K under
high Ca, and this effect disappeared at low Ca in young leaves (Fig.
2b). Putrescine was also beneficial to photosynthesis and suppressed the
effect of low K conditions in young leaves. In old leaves, K
availability always had an effect on photosynthesis, and putrescine
increased photosynthesis only slightly under low K. In old leaves,
changes in photosynthesis were mostly caused by the effect of nutrient
conditions on conductance, the variations of which paralleled that of
photosynthesis (Fig. 2c). In young leaves, the effect of nutrient
conditions (K in particular) on conductance was not mirrored by
photosynthesis showing that photosynthetic capacity was also affected.
As expected, low K was associated with higher respiration rates (Fig.
2d). Surprisingly, low Ca conditions further increased respiration rates
in all leaves.