Author(s)

Koichi Takahashi^1,2*, Sohei Otsubo¹

¹Department of Biology, Faculty of Science, Shinshu University, Matsumoto, Japan.
²Institute of Mountain Science, Shinshu University, Matsumoto, Japan.

Generally, plant species with shorter leaf longevity maintain a positive carbon balance by decreasing leaf mass per area (LMA) and increasing photosynthesis. However, plants at high elevations need to increase LMA against environmental stresses. Therefore, plants need to increase both LMA and photosynthesis at high elevations. To examine how deciduous plants maintain a positive carbon balance at high elevations, photosynthesis and related leaf traits for deciduous broad-leaved tree Betula ermanii were measured at three elevations. LMA was greater at middle and high elevations than at low elevation. Leaf δ¹³C was greater at higher elevations, and positively correlated with LMA, indicating greater long-term deficiency of CO₂ in leaves at higher elevations. However, the C_i/C_a ratio at photosynthetic measurement was not low at high elevations. Nitrogen content per leaf mass and stomatal conductance were greater at higher elevations. Photosynthetic rates and photosynthetic nitrogen use efficiency (PNUE) did not differ among the three elevations. Photosynthetic rate showed a strong positive correlation with stomatal conductance on a leaf area basis (R² = 0.83, P < 0.001). Therefore, this study suggests B. ermanii compensates the deficiency of CO₂ in leaves at high elevation by increasing stomatal conductance, and maintains photosynthesis and PNUE at high elevation as much as at low elevation.

Leaf Mass per Area, Leaf Nitrogen, Photosynthesis, Stable Carbon Isotope Ratio, Stomatal Conductance

Takahashi, K. and Otsubo, S. (2017) How Betula ermanii Maintains a Positive Carbon Balance at the Individual Leaf Level at High Elevations. American Journal of Plant Sciences, 8, 482-494. doi: 10.4236/ajps.2017.83033.