Sainfoin Regrowth Declines as Metabolic Rate Increases with Temperature

Abstract

Sainfoin (Onobrychis viciifolia Scop.) often exhibits poor growth following periods of high ambient temperatures. Our objective was to investigate the influence of air and soil temperature on regrowth and persistence of sainfoin. At 99 d post planting, ‘Renumex’ sainfoin grown in 5‐ by 40‐cm tubes were placed into growth chambers. Treatments were chamber air temperatures of 15, 25, or 35°C with soil temperatures of 10, 20, or 30°C. After a 21‐d adjustment period, all plants were clipped to 2 cm (Harvest 1). Plants regrew for 35 before the final harvest (Harvest 2). Measurements were number of leaves, leaf area, shoot mass, taproot mass, fine root mass, crown mass, taproot carbohydrates, tarch degrading enzyme activity, whole plant metabolism, and plant survival. Leaves per plant decreased with increasing air temperature and this caused a decrease in sainfoin leaf area per plant and shoot yield per plant. Increasing air temperature from 15 to 35°C or soil temperature from 10 to 30°C decreased crown, taproot, and fine root mass by as much as 98%. Concentration of taproot carbohydrates showed a negative correlation (P < 0.05) with increasing air temperature. Metabolic rates of leaves and roots were two and five times higher, respectively, when the air or soil temperature increased by 20°C. Increasing air temperature showed a positive correlation (P < 0.05) with the number of dead plants per treatment (R2 = 0.90). Few plants grown at 35°C survived. Severe defoliation during periods of high temperatures may cause plant death because high metabolic rates cannot be supported by existing leaf area or taproot carbohydrate