Distinguishing Abiotic from Biotic Stressors in Perennial Grain Crops: Nutrient Deficiency Symptoms in Silphium integrifolium and Thinopyrum intermedium

Perennial grains have been proposed as a soil-healthy alternative to annual grains. Intermediate wheatgrass (Thinopyrum intermedium), whose seed is currently sold under the trade name Kernza®, and silflower (Silphium integrifolium), which is in the early stages of domestication at The Land Institute in Central Kansas, lack characterization for their deficiency symptoms. This has complicated attempts to assess the causes of visible stress on plants in the field and the greenhouse. By growing Th. intermedium and S. integrifolium in a set of hydroponic solutions, each containing all but one selected nutrient—including nitrogen, phosphorous, potassium, calcium, magnesium, sulfur, iron, boron, zinc, copper, molybdenum, and manganese—we were able to assess the effects of twelve different nutrient deficiencies across the two species. Visible symptoms were described and documented via photographs. The effects of the deficiencies on height, leaf biomass, root biomass, gas exchange and photosynthesis (silflower), and resin production (silflower) were measured. Calcium, nitrogen, and potassium were found to alter growth responses in intermediate wheatgrass; in silflower, growth, resin production, and photosynthetic traits were affected by many nutrient deficient treatments. Our results suggest that further work addressing how symptoms might look at the time of flowering, seed production, and in the field at different concentrations of key nutrients would help ongoing plant-breeding efforts.