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.