Sustained growth suppression in forest-floor seedlings of Sakhalin fir associated with previous-year springtime photoinhibition after a winter cutting of canopy trees

Abstract

Springtime photoinhibition in 1-year-old shoots, exacerbated by a clear-cutting during winter, was recently found to reduce the current-year shoot growth of forest-floor seedlings of Sakhalin fir (Abies sachalinensis). In the present study, we conducted a follow-up survey in the following year in these seedlings, which were subjected to different cutting rates of canopy trees (100: clear-cutting, 66, 50, 30, and 0%: control) in the previous spring. No photoinhibition (Fv/Fm ≈ 0.8) was observed in the 1-year-old needles, developed after the cuttings in spring and summer, across the sites with different cutting rates. The ratio of current-shoot dry mass to 1-year-old needle dry mass (Shootcurrent/Needle1-year) measured in early summer, as a measure of photosynthetic carbon gain in the 1-year-old needles, showed an increasing trend with increasing growth irradiance when excluding the data of clear-cutting sites, which had a large variation. The variation in Shootcurrent/Needle1-year within the clear-cutting sites can be explained by the remaining amount of 2-year-old needles, which suggests that defoliation of 2-year-old needles damaged by photoinhibition in the previous spring may associate with a sustained suppression in the growth of current shoot even in the second year.