Environmental regulation of xylem sap flow and total conductance of Larix gmelinii trees in eastern Siberia

• Published in: Tree Physiology
• Main Authors: Arneth, A., Kelliher, F. M., Bauer, G., Hollinger, D. Y., Byers, J. N., Hunt, J. E., McSeveny, T. M., Ziegler, W., Vygodskaya, N. N., Milukova, I., Sogachov, A., Varlagin, A., Schulze, E.-D.
• Format: Text
• Language: English
• Published: Oxford University Press 1996
• Subjects: Original Articles; Yakutsk; Siberia
• Online Access: http://treephys.oxfordjournals.org/cgi/content/short/16/1-2/247; https://doi.org/10.1093/treephys/16.1-2.247

Xylem sap flow and environmental variables were measured on seven consecutive midsummer days in a 130-year-old Larix gmelinii (Rupr.) Rupr. forest located 160 km south of Yakutsk in eastern Siberia, Russia (61° N, 128° E, 300 m asl). The site received 20 mm of rainfall during the 4 days before measurements, and soil samples indicated that the trees were well watered. The tree canopy was sparse with a one-sided leaf area index of 1.5 and a tree density of 1760 ha−1. On a clear day when air temperature ranged from 9 to 29 °C, and maximum air saturation deficit was 3.4 kPa, daily xylem sap flux ( F ) among 13 trees varied by an order of magnitude from 7 l day−1 for subcanopy trees (representing 55% of trees in the forest) to 67 l day−1 for emergent trees (representing 18% of trees in the forest). However, when based on xylem sap flux density ( F ′), calculated by dividing F by projected tree crown area (a surrogate for the occupied ground area), there was only a fourfold range in variability among the 13 trees, from 1.0 to 4.4 mm day−1. The calculation of F ′ also eliminated systematic and large differences in F among emergent, canopy and subcanopy trees. Stand-level F ′, estimated by combining half-hourly linear relationships between F and stem cross-sectional area with tree size distribution data, ranged between 1.8 ± 0.4 (standard deviation) and 2.3 ± 0.6 mm day−1. These stand-level F ′ values are about 0.6–0.7 mm day−1 (30%) larger than daily tree canopy transpiration rates calculated from forest energy balance and understory evaporation measurements. Maximum total tree conductance for water vapor transfer ( G tmax , including canopy and aerodynamic conductances), calculated from the ratio of F ′ and the above-canopy air saturation deficit ( D ) for the eight trees with continuous data sets, was 9.9 ± 2.8 mm s−1. This is equivalent to a leaf-scale maximum stomatal conductance ( g smax ) of 6.1 mm s−1, when expressed on a one-sided leaf area basis, which is comparable to the published porometer data for Larix . ...