CO2 transfer conductance, leaf structure and carbon isotope composition of Polygonum cuspidatum leaves from low and high altitudes

ABSTRACT Anatomy and some physiological characteristics of the leaves in Polygonum cuspidatum Sieb. et Zucc., a dioecious clonal herb, were compared between two populations, one from a lowland in Shizuoka City (10 m above sea level), and another from a highland on Mt. Fuji (2500 m above sea level). Leaf mass per area (LMA) of the highland plants was about twice that of the lowland plants. The greater leaf thickness, thicker mesophyll cell walls and higher mesophyll cell density in the highland leaves contributed to the larger LMA. Although mesophyll area exposed to intercellular airspaces was greater in the highland leaves than in the lowland leaves by 30%, the surface area of chloroplasts facing intercellular airspaces was similar between these leaves. CO2 transfer conductance inside the leaf (gi) of the highland leaves (0·75 μmol m−2 s−1 Pa−1) is the lowest recorded for herbaceous plants and was only 40% of that in the lowland leaves. On the other hand, the difference in stomatal conductance was small. δ13C values in the leaf dry matter were greater in the highland leaves by 4‰. These data and the estimation of CO2 partial pressures in the intercellular air spaces and in the chloroplast suggested that the greater dry matter δ13C in the highland leaves, indicative of lower long‐term ratio of the chloroplast stroma to the ambient CO2 partial pressures, would be mainly attributed to their lower gi.