Seven-year changes in growth and crown shape of Thujopsis dolabrata var. hondai saplings after release from suppression

We investigated changes in sapling growth and morphology of Thujopsis dolabrata var. hondai (hiba) for 7 years after release from suppressed lighting by selection cutting. We examined changes in aboveground biomass, elongation of stems and lateral branches, and annual diameter increment at the stem base. Vertical distributions of leaves per branch and per individual were also measured for morphological analysis. Under the suppressed condition before cutting, the crown consisted of orthotropic lateral branches, elongating up to the top of the stem or farther, and no branch was aborted. This crown type with large crown depth and concavity of the upper part had a bowl-like appearance. After the selection cutting, relative light intensity on the saplings increased from 4% to 26%. The increment enhanced aboveground biomass and stem elongation 7 years after the cutting. Diameter growth at the stem base was particularly accelerated 2 years after the cutting. While crown shape transformation of the saplings was not conspicuous at 7 years after the cutting, some released saplings showed a superior stem elongation ratio to that of the lateral branches. Thus, the upper part of the crown of these saplings changed from a bowl-like shape to a convex shape like that of a dome. Our study suggested that suppressed hiba saplings with the unique bowl-shaped crown enhanced their growth rates rapidly in response to improved light conditions, but required much more than 7 years for the full process of crown transformation for us to identify future trees in this stand. An erratum to this article is available at.     

Photosynthesis and growth of Thujopsis dolabrata var. hondai seedlings in the understory of trees with various phenologies

We have studied the photosynthetic production and growth of Thujopsis dolabrata var. hondai (hiba) seedlings under typical light conditions found in mixed forests, including constant shade, phenological gaps under broad-leaved trees with different lengths of foliation period, and in an open plot. Leaves sampled from the open plot had significantly higher rates of light-saturated gross photosynthesis and dark respiration, and a significantly lower specific leaf area than leaves from the other plots. The relative growth rate of whole plant biomass was significantly higher in plots that received larger amounts of light. The variations in these properties under the various light conditions are considered to reflect the ability of hiba seedlings to adapt to available light. In the late autumn, leaves sampled from the open and from the gap under deciduous trees indicated photoinhibition. However, the estimated value of monthly net photosynthesis of hiba seedlings was greater in these plots, indicating that the benefit of a greater light intensity for photosynthesis seems to be larger than the detriment of photoinhibition. The seasonal pattern of photosynthesis by understory hiba seedlings was affected by the phenology of canopy trees. Light availability under the canopy of deciduous trees associated with phenological gaps helped hiba seedlings to tolerate the relatively dark conditions during the subsequent foliation period. These results for reaction to the light regime and for the phenology of hiba seedlings are practicable for hiba forest management.     

ATP-driven exchange of histone H2AZ variant catalyzed by SWR1 chromatin remodeling complex

The conserved histone variant H2AZ has an important role in the regulation of gene expression and the establishment of a buffer to the spread of silent heterochromatin. How histone variants such as H2AZ are incorporated into nucleosomes has been obscure. We have found that Swr1, a Swi2/Snf2-related adenosine triphosphatase, is the catalytic core of a multisubunit, histone-variant exchanger that efficiently replaces conventional histone H2A with histone H2AZ in nucleosome arrays. Swr1 is required for the deposition of histone H2AZ at specific chromosome locations in vivo, and Swr1 and H2AZ commonly regulate a subset of yeast genes. These findings define a previously unknown role for the adenosine triphosphate-dependent chromatin remodeling machinery.