Simulation of Aerenchyma Function in Phosphorus Deficient Maize and Bean.

Root cortical aerenchyma (RCA), i.e. air spaces in the cortex of the root due to programmed cell death, is not only formed in response to hypoxia, but also in response to deficiencies of several nutrients, including phosphorus. To study the function of RCA in phosphorus deficient plants, we developed SimRoot into a whole plant simulation model with special focus on root architecture, root anatomy and the carbon economy of roots. In the model, nutritional status of the plant affects sink-source relationships. For example, phosphorus deficiency reduces the potential leaf area expansion rate, which is a measure for sink strength of the shoot. Carbon availability determines root growth. We tested the hypothesis that RCA permits greater soil exploration by reducing the maintenance cost of root tissue and by permitting phosphorus recycling to maintain root growth in phosphorus deficient bean and maize plants. For plants with RCA, the model predicts up to 47% increase in plant biomass after 40 days of growth in low P soils. Both extra carbon, from reduced maintenance respiration, and additional phosphorus contribute to this increase. The relative importance of these two functions depends on the phosphorus availability in the soil and time. Our results support the hypothesis that RCA is an adaptive trait for soil resource acquisition.