[A-HW19] Hydrology & Water Environment

[AHW19-07] Fine-root water relation along an elevational change in broad-leaved and coniferous trees at alpine forests

*Taiga Masumoto¹, Yuki Hashimoto¹, Ito Takumi¹, Koichi Takahashi¹, Naoki Makita¹ (1.Shinshu University)

Keywords:Water absorption, Hydraulic conductance, Pressure-volume curve traits, Plant root , Environmental response

Water is a major limiting factor for photosynthesis in trees. Therefore, adjusting water acquisition accordingly to habitat environment is important for trees to maintain their growth. Tree fine-root (generally defined as < 2 mm in diameter) is the primary organ for water acquisition and play important role in the water cycle in terrestrial ecosystems. Although trees would change water acquisition from fine-root along an environmental change, less is known about field direct measurement. In other word, most studies have estimated fine-root water acquisition from root morphological and chemical traits indirectly. In this study, we measured directly fine-root water relation and examined that response to environmental change using elevation gradient in alpine field. Our objectives were to evaluate both water uptake from soil to roots and water holding retention, and to elucidate the elevational effects on fine-root water relation considering water uptake and retention. Since broad-leaved and coniferous trees exhibited the difference change on leaf traits along an elevational change, we also focused on inter-specific variation of elevational effects on fine-root water relation between broad-leaved and coniferous trees.
This study was conducted at 2000 m and 2500 m a.s.l. located in the east slope of Mt. Norikura (3026 m a.s.l) in central Japan. In 2500 m a.s.l., the average temperature is about 2℃ lower and the tree growing season is about one month shorter than that of 2000 m a.s.l.. We selected Betula ermanii (deciduous broad-leaved trees) and Abies mariesii (evergreen conifer) as targeting species. Fine-roots (approximately 10×10 cm in size) were collected from mature trees. The root hydraulic conductivity (m³ m ^-2 s^-1 MPa^-1) for water uptake was evaluated by applying constant pressure to a root. In addition, the turgor loss point (MPa) and capacitance (MPa^-1) through Pressure-Volume carve for water retention were measured by repeatedly measuring the water potential and relative water contents.
As a result, root hydraulic conductivity was significantly higher at 2500 m a.s.l. in Betula ermanii, but did not change significantly in Abies mariesii. Since the fine-root with high hydraulic conductivity can transport water to aboveground more efficiently, this result suggested that Betula ermanii increase fine root water uptake at high elevation. On the other hand, turgor loss point and capacitance did not change significantly in Betula ermanii, but were significantly lower at 2500 m a.s.l. in Abies mariesii. Since the fine-root with low turgor loss point and capacitance have high tolerance for water stress, this result suggest that Abies mariesii increase fine root water retention at high elevation. Our results indicated that broad-leaved and coniferous trees exhibit the difference change on fine-root water relation in response to same environmental change.