Light Responsibility of Juvenile Seedlings of Thujopsis dolabrata var. hondai Makino Evaluated from Chlorophyll a Fluorescence Analyses

Abstract

Seedlings of the three coniferous species including Thujopsis dolabrata var. hondai Makino were raised under weak shade in a nursery in order to examine the photochemical and nonphotochemical dissipations of excited energy at PSII. The dry matter growth 20 weeks after germination was smallest in T. dolabrata var. hondai. This was due to the low photosynthetic capacity in addition to the small leaf weight ratio of the seedlings and the large leaf specific weight. The specific ranking of rETR_max (the maximum relative electron transport rate) was different from that of NPQ_max (the maximum of non-photochemical quenching) ; T. dolabrata var. hondai was characterized by the high NPQ_max relative to the low rETR_max. A slight depression in F_v/F_m, (light stress parameter) was recognized only for Cryptomeria japonica in the cotyledon period. A large depression in F_v/F_m was observed for C. japonica and T. dolabrata var. hondai in the post-cotyledon period. These depressions in F_v/F_m seemed to be closely associated with the low levels of rETR_max but may have also been related to the effects of NPQ_max and foliage morphology and architecture. The light responsibility of T. dolabrata var. hondai seedlings differed greatly from that of Pinus densiflora Sieb. et Zucc. and differed significantly from that of C. japonica.