Elevated CO2 Increases Root Mass and Leaf Nitrogen Resorption in Red Maple (Acer rubrum L.)

Abstract

To understand whether the process of seasonal nitrogen resorption and biomass allocation are different in CO2-enriched plants, seedlings of red maple (Acer rubrum L.) were exposed to three CO2 concentrations (800 µL L−1 CO2 treatments—A800, 600 µL L−1 CO2 treatments—A600, and 400 µL L−1 CO2 treatments—A400) in nine continuous stirred tank reactor (CSTR) chambers. Leaf mass per area, leaf area, chlorophyll index, carbon (C), nitrogen (N) contents, nitrogen resorption efficiency (NRE), and biomass allocation response were investigated. The results indicated that: (1) Significant leaf N decline was found in senescent leaves of two CO2 treatments, which led to an increase of 43.4% and 39.7% of the C/N ratio in A800 and A600, respectively. (2) Elevated CO2 induced higher NRE, with A800 and A600 showing significant increments of 50.3% and 46.2%, respectively. (3) Root biomass increased 33.1% in A800 and thus the ratio of root to shoot ratio was increased by 25.8%. In conclusion, these results showed that to support greater nutrient and water uptake and the continued response of biomass under elevated CO2, Acer rubrum partitioned more biomass to root and increased leaf N resorption efficiency.