Patchy nitrate promotes inter-sector flow and ¹⁵N allocation in Ocimum basilicum: a model and an experiment

Root conductance increases under high nitrate conditions. This plasticity might increase water and nutrient transport between parallel xylem pathways, but restrictions to lateral flow - called sectoriality - are expected to limit this crossover. We simulated the effects of a high nitrate patch on root conductance, water uptake and inter-sector water transport, then empirically tested whether a high nitrate patch affects water uptake and nitrogen distribution (applied 15N as 14NH415NO3 to half the root system) within the crowns of split-root hydroponic basil (Ocimum basilicum L.). Simulations showed that at low sectoriality, the proportion of water taken up in a patch scales with the relative change in root resistance and that this fraction decreases with increasing tangential resistance. The effect of sectoriality decreased when a higher background root resistance was assumed. Empirically, water flow through excised basil roots was 1.4 times higher in the high nitrate than the no nitrate solution. In split-root basil, a nitrate patch resulted in a marginally significant increase in the proportion of water taken up from the patch and water uptake patterns significantly predicted the distribution of 15N. Our results suggest that root conductance can mediate nitrogen allocation between sectors, a previously unexplored benefit.