Comparison of canopy transpiration between Pinus sylvestris var. mongolica and Pinus tabuliformis plantations in a semiarid sandy region of Northeast China

Abstract

Mongolian pine (Pinus sylvestris var. mongolica) has been introduced to vast areas of semiarid sandy region of northern China to create plantations, and it plays an important role in improving environmental conditions. These trees often show obvious dieback after age of 35–40 during extreme drought years, while native Chinese pine (Pinus tabuliformis) plantations grow healthily. Water is the most important resource for tree growth and survival in these regions; however, the transpiration dynamics of introduced Mongolian pine, unlike those of native Chinese pine, are still unknown, limiting proper management of plantations. Here, canopy transpiration and canopy conductance of Mongolian pine and Chinese pine plantations that were both 18 years old were quantified using sap flow method, and environmental variables were monitored concurrently. Results showed that canopy transpiration per unit leaf area (EL) averaged 1.1 and 0.7 mm d − 1 for Mongolian pine and Chinese pine, respectively, indicating that in comparison to native pine species, introduced pine species had a higher transpiration rate due to higher canopy conductance. Sensitivity of EL response to meteorological variables decreased with increasing soil moisture stress for both pine species, but the larger decrease for Mongolian pine indicated a higher sensitivity to drought. Additionally, canopy conductance per unit leaf area for Mongolian pine was 70% higher than that for Chinese pine, and reference canopy conductance decreased with increasing soil moisture stress for both pine species, indicating there are soil water limitations on canopy conductance. However, a higher decrease in stomatal sensitivity to vapor pressure deficit with increasing soil moisture stress in Mongolian pine than in Chinese pine indicates a greater decrease in hydraulic conductance. These findings indicated that in comparison to Chinese pine, Mongolian pine consumes more water but is less able to control transpiration under drought conditions, showing vulnerability to dieback in extreme drought years.