Growth and Physiological Response of Timothy to Elevated Carbon Dioxide and Temperature under Contrasted Nitrogen Fertilization

Abstract

ABSTRACTClimate change is expected to affect the growth and metabolism of many economically important plants including timothy (Phleum pratense L.), a major forage grass species in eastern Canada and northern Europe. Our objective was to assess the impacts of predicted increases in CO2 concentration and temperature, under contrasted N fertilization, on timothy biomass, leaf photosynthesis, and nonstructural carbohydrate concentration. Plants were grown in growth chambers under either 400 or 600 μL L−1 of CO2 and at a day/night temperature of either 22/10°C or 25/15°C, and they were fertilized with 0, 60, or 120 kg N ha−1. Two sequential harvests were taken following a 6‐wk establishment period. Elevated CO2 concentration did not affect forage biomass and increased root biomass only at first harvest, but it increased leaf photosynthesis and total soluble sugar concentration mostly when N was not limiting (120 kg N ha−1). Increased temperature reduced forage and total biomass and soluble sugar concentrations at the second harvest under 120 kg N ha−1. Combined increases of temperature and CO2 concentration (600 μL L−1 and 25/15°C) had no effect on biomass yield, but it increased leaf photosynthesis and nonstructural carbohydrates concentration compared to current conditions. Our findings show that predicted future conditions of elevated temperature and CO2 concentration will have little effect on the yield of timothy while their effect on photosynthesis and forage nonstructural concentration will depend on N availability.