Chin J Plant Ecol ›› 2010, Vol. 34 ›› Issue (5): 535-546.DOI: 10.3773/j.issn.1005-264x.2010.05.007

• Research Articles • Previous Articles     Next Articles

Nocturnal sap flow of four urban greening tree species in Dalian, Liaoning Province, China

CHEN Li-Xin1, ZHANG Zhi-Qiang1,*(), LI Zhan-Dong1, ZHANG Wen-Juan1, ZHANG Xiao-Fang2, DONG Ke-Yu3, WANG Guo-Yu1   

  1. 1Key Laboratory of Soil and Water Conservation and Desertification Combating, Ministry of Education, Beijing Forestry University, Beijing 100083, China
    2Technical Extension Center, Dalian Bureau of Forestry, Dalian, Liaoning 116023, China
    3Landscape Architecture Bureau, Dalian Bureau of Parks and Woods, Dalian, Liaoning 116023, China
  • Received:2009-07-28 Accepted:2009-10-30 Online:2010-07-28 Published:2010-05-01
  • Contact: ZHANG Zhi-Qiang

Abstract:

Aims Nocturnal sap flow is a driving force not only for chemical transport and nutrient movement within trees, but also for water recharge caused by diurnal transpiration loss. Therefore, it is both ecologically and physiologically significant for estimating tree and stand transpiration at larger spatial and longer temporal scales. Our objective was to analyze nocturnal sap flow (18:00-5:00 next morning) and its biophysical controls in four tree species (Cedrus deodara, Zelkova schneideriana, Euonymus bungeanus and Metasequoia glyptostroboides) in Laodong Park in Dalian, China.

Methods During June 1-August 31, 2008, we measured sap flow of twelve urban trees of four species and three diameter at breast height (DBH) classes of each species continuously by thermal dissipation probes, soil moisture by ECH2O soil moisture probe and microclimate data by an automatic weather station. SPSS 13.0 was used for statistical analysis of sap flow and environmental factors.

Important findings Nocturnal sap flow was measured in all sampled trees, but varied from 0.44% to 75.96% of total daily water consumption. Nocturnal flow was larger and more active on rainy days than that on sunny ones, to the extent that it equaled or exceeded the diurnal volume. Vapor pressure deficit and wind speed were significantly correlated with nocturnal water movement (R2 > 0.6), which could provide an explanation for nocturnal transpiration. Nocturnal sap flow mainly contributed to nocturnal transpiration and water recharge. It peaked before midnight and dropped to nearly zero afterwards. Furthermore, nocturnal sap flow was remarkably correlated with diurnal sap flow (R2 = 0.356, p = 0.00) and DBH (R2Spearman > 0.80), substantiating the important role of specific structural and physiological characteristics. Nocturnal sap flow of individuals accounted for an average of < 14.4% of the total transpiration volume. Total water consumption of a forest ecosystem scaled up by daytime sap flux measurements can be underestimated without integration of nocturnal sap flux.

Key words: environmental variables, nighttime sap flow, thermal dissipation probe (TDP), urban trees