Nutrients exported from upland stream water enlarge perennial biomass crops.

Rawanbuki, a variety of Japanese butterbur (Petasites japonicus subsp. giganteus), grow naturally along the Rawan River, Hokkaido, northern Japan. Most plants reach 2-3 m in height and 10 cm in diameter in 2 months and are much larger than those grown along other rivers. We examined the hypothesis that nutrients exported from upland streams enhance the growth of the Rawanbuki. Nutrient concentrations, including nitrogen, phosphorus, and base cations, in the Rawan River were much higher than those in rivers of adjacent watersheds. High nutrient concentrations and moisture contents were found in soil along the Rawan River and a significant relationship was found between physicochemical soil conditions and aboveground biomass of butterburs. This indicates that extremely large Rawanbuki plants could be caused by these high nutrient concentrations and moisture contents in the soils. A manipulation experiment showed that fertilization simulated the growth environment along the Rawan River and enhanced the stem height and stem diameter of butterburs. This study concluded that the extremely large butterburs are caused by a large amount of nutrients exported from upland areas. These results are the first demonstration of the role of stream water nutrients in enlarging agricultural crops.

Suppression of growth and death of meristematic tissues in Abies sachalinensis under strong shading: comparisons between the terminal bud, the terminally lateral bud and the stem cambium.

The suppression of apical growth and radial trunk growth in trees under shade is a key factor in the competition mechanism among individuals in natural and artificial forests. However, the timing of apical and radial growth suppression after shading and the physiological processes involved have not been evaluated precisely. Twenty-one Abies sachalinensis seedlings of 5-years-old were shaded artificially under a relative light intensity of 5% for 70 days from August 1, and the histological changes of the terminal bud and terminally lateral bud of terminal leader and the cambial zone of the trunk base were analyzed periodically. In shade-grown trees, cell death of the leaf primordia in a terminal bud of terminal leader was observed in one of the three samples after 56 and 70 days of shading, whereas the leaf primordia in a terminal bud of terminal leader in all open-grown trees survived until the end of the experiment. In addition, the leaf primordia of the terminally lateral buds of terminal leader retained their cell nuclei until the end of the experiment. No histological changes were observed in the cambial cells after shading, but the shade-grown trees had less cambial activity than the open-grown trees through the experiment. Strong shading appeared to inhibit the formation and survival of cells in the terminal bud of terminal leader rather than the terminally lateral buds of terminal leader and the cambium. The suppression of the terminal bud growth and elongation of the surviving lateral buds would result in an umbrella-shaped crown under shade.

Cessation of annual apical growth and partial death of cambium in stem of Abies sachalinensis under intensive shading.

This study evaluated variation in the height at which absent rings and internodes were detected along stem of Abies sachalinensis trees grown under shade for 39 years. Eight sample trees planted in 1974 under a secondary forest in Japan were felled in 2013 and analyzed. A. sachalinensis is a monopodial species in which it is possible to measure annual apical growth using the distinct internodes. We applied microscopic analysis on 154 stem disks from the stem base to the top to evaluate the cessation of apical and radial growth caused by intensive shading. Cessation of apical stem growth for one or more years was found in 6 out of 8 sample trees. We termed this phenomenon as "absent internode". In addition, the absent growth rings were detected more frequently in the lower part of sample stems, and the number of absent rings at the stem base did not correspond with the number of absent internodes in the six trees. From cellular level observation, the five suppressed trees had no living cambial cells at the stem base but had living cells at the stem top. The cessation of the apical and radial growth did not occur synchronously but did occur independently under a shade environment in A. sachalinensis.