When comparing nutrient foraging among plants species, root precision -- proliferation in a nutrient patch relative to background soil -- is a common response variable. Sectoriality -- the restriction of transport of resources along vascular pathways -- is expected to constrain this capacity to proliferate. Alternatively, sectoriality might enhance precision if increased nutrient supply to shoots directly connected to roots in a patch results in increased photosynthesis and thus higher carbon supply to those roots. Surprisingly, the relationship between sectoriality and precision has not been critically evaluated. To address this relationship we extended existing plant growth models to include sectoriality, modeled as the resistance to transport between two sectors.
We simulated plants with the roots of one sector in a nitrogen patch three times the background concentration. We evaluated root precision and biomass accumulation in three aboveground scenarios: 1) saturating light to both sectors (="uniform light"), 2) saturating light on the leaves of the high N sector and low (30% saturating) light on the opposite sector (="same sector light"), and 3) low light to the high nitrogen sector and high light to the other (="opposite sector light").
Results/Conclusions
Under "uniform light", root precision was not strongly affected by sectoriality, but total biomass accumulation correlated positively with sectoriality. In the same sector light treatment, more sectored plants consistently showed the highest precision and biomass accumulation. In the opposite sector light treatment, integrated plants showed the highest precision and biomass accumulation. Our results indicate that the influence of sectoriality on plant performance in patchy soil depends on aboveground conditions. We argue that attention to these factors would greatly increase the power of root foraging studies. The role of sectoriality should especially be considered in split-root experiments, where nutrient patch treatments are sometimes applied to one or two lateral roots, possibly from a single vascular sector.