The global increase in ornamental crop production has driven horticultural researchers to better understand the efficiency and sustainability of production input. Soilless substrates serve a crucial role in supporting outdoor nursery-grown plants, where container substrates must maintain sufficient moisture supply to the rootzone and continuously sustain shoot water loss. Nursery producers regularly face a changing climate, where unprecedented droughts, prolonged and increased air temperatures, and subsequent mandated water application restrictions present challenges for profitable harvests and yields. To date, there are little to no means in predicting container nursery stock performance, especially when grown in substrates with different water supply capacities (i.e., water storage and hydraulic transfer properties). Models have been used to predict plant responses to water stresses in soil systems based on dynamics of hydraulic conductance in the soil-plant-atmospheric-continuum (SPAC); though, no SPAC models have been applied to horticultural plants grown in soilless substrates. To better prepare for climate-challenges in nursery production systems, new methods of understanding substrate capabilities to withstand harsh growing conditions are needed. The study herein uses predictive tools (i.e., SPAC models) derived from measured data, namely substrate and plant hydraulic characteristics, to understand how plants respond (i.e., physiological output; water loss) when grown in harsh growing conditions (e.g., drying substrate and atmosphere). Plants were grown in four differing bark particle diameters: (1) 6.3 mm. Substrate water potential were maintained between -50 and -100 hPa to produce plants at similar water availabilities. Substrate hydraulic conductivity decreased as particle size increased, highlighting different water transfer properties across substrates at similar water availabilities. Plants produced in finer textured substrates had greater root and shoot morphological development, including greater fine root growth and aerial biomass. No differences were detected in root and shoot hydraulic conductance. The SPAC models showed that plants grown in finer textured substrates were able to maintain physiological function longer under drying substrate or atmospheric conditions, while plants grown in substrates with lower water transfer properties sharply decreased physiological output (i.e., faster stomal closure). The hydraulic models applied herein can inform growers that producing plants in finer textured substrates, or substrates that have greater hydraulic conductivity, can enable plants to maintain physiological functions even in harsh growing conditions.
