Adaptation of stomatal response of Camellia rusticana to a heavy snowfall environment: Winter drought and net photosynthesis

Abstract

The adaptation of Camellia rusticana, an evergreen broad-leaved shrub found in areas of heavy snowfall in Japan, to heavy snowfall environments, and the mechanisms by which it is damaged in winter above the snow, were investigated. The stomatal response and photosynthetic characteristics of C. rusticana were compared to those of Camellia japonica found in areas of light snowfall. In field conditions, the mean net photosynthesis of C. rusticana at photon flux density (PFD) over 200 μmol m⁻²s⁻¹ (Pn(_>200). was 50% larger than that of C. japonica, but in both light saturated and CO₂ saturated conditions, the O₂ evolution rate (Pc) of C. rusticana was not different from that of C. japonica. Mean leaf conductance at PFD over 200 μmol m⁻²s⁻¹ (gl(_>200)) was about 100% larger than that of C. japonica in the field. The Pn(_>200)) was 50% ratio of C. rusticana was 37% higher than that of C. japonica which suggests that C. rusticana's larger Pn(_>200) can be explained by its larger gl(_>200). When C. rusticana trees wintering underneath the snow were projected above it, the leaves of these plants showed serious drought within five days in non-freezing conditions. Their Pc and the maximum stomatal conductance decreased by half and did not recover. The leaves of C. rusticana showed larger gl(_>200) and a less sensitive stomatal response to the decrease of leaf water potential than that of C. japonica. The stomata characteristics of C. rusticana caused larger net photosynthesis than that of C. japonica during the no snow period, and caused the need for snow cover in winter as protector from winter drought.