Effects of elevated CO2 and nitrogen on wood structure related to water transport in seedlings of two deciduous broad-leaved tree species

Abstract

Wood structure might be altered through the physiological responses to atmospheric carbon dioxide concentration ([CO2]) and nitrogen (N) deposition. We investigated growth, water relations and wood structure of 1-year-old seedlings of two deciduous broad-leaved tree species, Quercus mongolica (oak, a ring-porous species) and Alnus hirsuta (alder, a diffuse-porous species and N2–fixer), grown under a factorial combination of two levels of [CO2] (36 and 72 Pa) and nitrogen supply (N; low and high) for 141 days in phytotron chambers. In oak, there was no significant effect of [CO2] on wood structure, although elevated [CO2] tended to decrease stomatal conductance (g s) and increased water use efficiency regardless of the N treatment. However, high N supply increased root biomass and induced wider earlywood and larger vessels in the secondary xylem in stems, leading to increased hydraulic conductance. In alder, there was significant interactive effect of [CO2] and N on vessel density, and high N supply increased the mean vessel area. Our results suggest that wood structures related to water transport were not markedly altered, although elevated [CO2] induced changes in physiological parameters such as g s and biomass allocation, and that N fertilization had more pronounced effects on non-N2-fixing oak than on N2-fixing alder.