Growth and nutrition of small Betula pendula plants at different relative addition rates of manganese.

In a series of experiments, growth of small birch plants (Betula pendula Roth) was controlled by the relative addition rate of manganese, R(Mn) (day(-1)). The R(Mn) treatments were 0.05, 0.10, 0.15 and 0.20 day(-1) with free access to all other nutrients. In an additional treatment, FA, there was free access to all nutrients including Mn. The pH of the nutrient solution ranged between 3.9 and 4.1, and the conductivity was between 100 and 200 micro S cm(-1). After an adjustment phase to steady-state growth, there was a one-to-one relationship between the relative growth rate, R(G) (day(-1)), and the supply of manganese, R(Mn) (day(-1)). The Mn concentration of the plants ranged from 6 to 13 micro g g(DW) (-1) in all treatments with limiting R(Mn) and was approximately 200 micro g g(DW) (-1) in the FA treatment. At steady-state growth, the plants showed specific Mn deficiency symptoms, including leaf mortality, that were more pronounced at severe Mn limitation. Total nonstructural carbohydrate concentrations were low, less than 7.5% of dry weight at Mn limitation, and the fraction of plant dry matter partitioned to roots was much less at Mn limitation than has previously been reported for equivalent rates of N or P supply. Manganese uptake rate per unit root growth rate, dMn/dW(r) ( micro mol g(DW) (-1)) was unaffected by the supply of Mn. At Mn limitation, low rates of plant growth were associated with high values of specific leaf area (37 versus 36 m(2) kg(DW) (-1)), and lower values of leaf weight ratio (40 versus 61%) and net assimilation rate (3 versus 10 kg(DW) (-1) m(-2) day(-1)) than were found at higher R(Mn).