Photoinhibition and pigment composition in relation to needle reddening in sun-exposed Cryptomeria japonica at different altitudes in winter

Some gymnosperms, such as Cryptomeria japonica, exhibit needle reddening due to rhodoxanthin synthesis in winter. It is assumed that the rhodoxanthin-induced change in needle coloration occurs earlier at higher altitude in C. japonica, reflecting altitudinal temperature differences. To elucidate the cold acclimation processes and photoinhibition of the photosynthetic apparatus in needles experiencing different temperatures according to altitudes, we monitored seasonal changes in pigment composition and chlorophyll fluorescence in sun-exposed C. japonica needles on a south facing slope at four different altitudes (150, 630, 900 and 1,120 m). Rhodoxanthin started to accumulate in early December at all altitudes. At the highest altitude, rhodoxanthin increased more rapidly than at the other altitudes in late December. However, the maximum rhodoxanthin content did not differ significantly among altitudes, because the variation in rhodoxanthin content at altitude of 1,120 m was large. Therefore, temperature did not directly affect the accumulation of rhodoxanthin. By contrast, the maximum PSII efficiency (F-v/F-m) correlated with rhodoxanthin content at all altitudes, indicating that rhodoxanthin accumulation partly reflects the degree of photoinhibition. In experiments examining recovery from photoinhibition, F-v/F-m at the highest altitude did not fully recover even after the conversion of antheraxanthin (A) and zeaxanthin (Z) to violaxanthin, and the disappearance of rhodoxanthin during recovery treatments. These results indicated that the lower F-v/F-m at altitude of 900 and 1,120 m may have been caused not only by the nocturnal retention of A + Z, but also by a decrease in PSII reaction centres.

Automated summary

The accumulation of rhodoxanthin in Cryptomeria japonica is not directly affected by altitude, but is related to the degree of photoinhibition of the photosynthetic apparatus. The slower recovery of PSII efficiency at higher altitudes may be due to a decrease in PSII reaction centers, rather than solely the retention of A + Z.