Growth and Nitrate Uptake Properties of Higher Plants: Relations to External and Internal Nitrogen
Nitrate-N supplied by fertilization or produced via microbial activity becomes available to plants by mass flow and/or diffusion. Under well-irrigated and -fertilized conditions in the field, it does not appear that movement of solutes to the root surface limits yield, even at very high levels of productivity (Barraclough 1986). However, in a natural environment or in less intensive agricultural practice, nutrient flow to the plants may become limiting for growth. Under these conditions, the overall limitation of nutrient availability is that set by integration of nutrient flux and root growth, not by nutrient concentration (for reviews on these matters, see e.g. Nye and Tinker 1977; Ingestad 1982; Haynes 1986; Robinson 1986). Physiological effects of nutrient flux limitation has, however, only received minor attention in experimental studies on plant nutrition, where the concept of concentration control has been favoured. As alternatives to concentration control, nutrients can be supplied to the plants in a desired relation to either a previously established growth curve (programmed nutrient addition; Asher and Cowie 1970, reviewed by Asher and Edwards 1983), or the amount of nutrient already bound in biomass (the relative addition rate concept: Ingestad and Lund 1979; reviewed by Ingestad 1982; Ingestad and Lund 1986). In the sense that nutrients are added in a fixedrelation to biomass and/or nutrients bound in the culture, these concepts have principal similarities to that used for culture of microorganisms in chemostats. In the present communication growth and nitrate uptake kinetics will be described for plants maintained under flux limitation, using the relative addition rate concept and nitrate-N as the limiting nutrient.
KeywordsNitrate Uptake Plant Cell Environ Unstirred Layer Intensive Agricultural Practice Swedish Natural Science Research Council
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