Nitrogen assimilation
Nitrogen assimilation was examined using elemental N content analysis
and 15N-nitrate labelling to measure nitrate
absorption and distribution in shoots and roots (Fig. 3). In all
tissues, N elemental content was significantly lower at low K, showing
the general inhibition of N assimilation under low K availability (Fig.
3a). Low Ca conditions resulted in slightly lower N content in old
leaves under high K. Putrescine was beneficial to the N content in young
leaves under low K. N absorption measured via15N-labelling was much lower under low K, and this was
alleviated to some extent by putrescine. Interestingly, low Ca was
beneficial to N absorption at low K but detrimental at high K,
suggesting that the balance between cation species was essential for
nitrate absorption by root cells.