Difference of high-light stress sensitivity in the two firs, Abies mariesii and Abies veitchii, in early spring

Abies veitchii and Abies mariesii are dominant species at the tree-line in Central Japan. Recently, we observed needle death, probably due to photodamage of the photosynthetic apparatus at the tree-limit during March-April. A. veitchii survives winter without any needle death due to photodamage at the tree-line. However, there is no conspicuous damage between the two species because this phenomenon is only observed at the tree-limit. In this study, we examined the difference in winter down-regulation of PS II between A. veitchii and A. mariesii and observed the following results: In March, (1) Fv/Fm of both species was about 0.1, showing the photochemical efficiency being severely inhibited. (2) The de-epoxidation state, expressed as [(A+Z)/(V+A+Z)], was about 0.35 for both species. (3) Chlorophyll (Chl) content of A. veitchii was much less than that of A. mariesii and Pchlide was found only in A. veitchii. In April, (1) Fv/Fm increased and [(A+Z)/(V+A+Z)] decreased for both species. (2) Chl content of A. veitchii increased by four-fold while Pchlide nearly dissappeared. These results indicate the following: During cold periods, most of Chl of A. veitchii may have been converted to Pchlide which is easily re-converted to Chl in spring, an intermediate of Chl biosynthesis. Winter conversion from Chl to Pchlide in A. veitchii may provide effective protection from photodamage of the photosynthetic apparatus. Furthermore, this may explain the higher ability of A. veitchii to prevent photodamage compared to A. mariesii

WATER RELATIONS OF PINUS PUMILA IN THE SNOW MELTING SEASON AT THE ALPINE REGION OF MT. TATEYAMA (17th Symposium on Polar Biology)

During the snow melting season of 1994, some exposed needles of Pinus pumila turned yellow in the alpine zone (2450 m) on Mt. Tateyama. However, relative water content (RWC) of the needles was far over the lethal RWC. Temperatures of soil and stems below snowpack remained near 0℃ during midday on 7 May, whereas those of needles and shoots over snowpack increased to 15℃ under high solar radiation. This result shows that transpired water from needles may be sufficiently replenished with water stored in sapwood of stems in the spring. It is concluded that desiccation is an unlikely cause of needle die-back. The most likely alternative explanation appears to be freezing damage, because freezing tolerance of most plants rapidly decreases in spring when minimum air temperature is often below zero in night at high altitude