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Abstract
Bamboos, arborescent monocotyledons without secondary growth, often show top dieback during the dry season. The potential mechanism underlying bamboo top dieback and its association with culm hydraulic architecture and positive pressure dynamics remain unclear. We investigated how the axial scaling of anatomical traits influenced physiological performances of the culm top under drought conditions, as well as how seasonal changes in positive pressure were related to top dieback and culm height. Variations in culm anatomical and physiological characteristics (hydraulic traits, leaf photosynthetic gas exchange, and water potentials) along the longitudinal axis of a bamboo (Dendrocalamus membranaceus) were investigated and seasonal changes in positive pressure were monitored to reveal potential factors associated with top dieback. The hydraulically-weighted mean vessel diameters (Dh) exhibited a widening pattern from the culm apex with a scaling exponent in the range reported for trees. However, Dh did not increase continuously and instead declined noticeably near the culm base. Theoretical hydraulic conductivity decreased to a low level near the culm top, where most of the resistance was located. The lower water potentials, maximum quantum yield of photosystem II, stomatal conductance, and photosynthetic rate indicated that culm top was subjected to severer water stress than the base part. Height supported by the maximum positive pressure declined from the wet season to the dry season, which was close to the measured culm height after top dieback. This study implies the potential impact of vessel widening pattern on water supply along the culm height, and the association of seasonal changes in positive pressure with culm height, which offers novel insights into understanding bamboo top dieback.
Published Version
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