Microenvironment in the canopy rivals the host tree water status in controlling sap flow of a mistletoe species.
Mistletoes absorb water from the vascular system of their hosts and thus the water use of mistletoes can be influenced by the water status of their hosts besides abiotic environmental conditions; however, there is a lack of studies on the dynamics of mistletoe water utilization in relation to both types of controlling factors. By building a canopy platform at 20 m above the ground, we monitored the dynamic changes of sap flow of Viscum coloratum (Kom.) Nakai (Loranthaceae) in combination with continuous measurements of microclimatic variables and volumetric water content (VWC) of its host tree branch xylem. We found that the host tree VWC exhibited substantial fluctuations during sunny days but lower VWC of the host did not negatively affect the sap flow of V. coloratum. Hourly and daily mean transpiration rates (Esap) of V. coloratum calculated from sap flow measurements showed strong positive correlations with photosynthetic photon flux density (PPFD) and vapor pressure deficit (VPD) measured in close vicinity to the point of mistletoe attachment. The mean Esap of V. coloratum was substantially higher than that of their host during clear days (4.55 ± 0.54 vs 2.01 ± 0.15 kg m-2 day-1). Moreover, the mistletoe-to-host transpiration ratio was not constant but became increasingly larger with the increase of PPFD or VPD on both hourly and daily bases, suggesting a weaker control of water loss in the mistletoe in comparison to its host species. The strong dependence of mistletoe Esap on micrometeorological variables and its decoupling from the host tree xylem water status suggests that the development of dense tree canopy functions as a potential mechanism for the host trees in reducing the competitive water use of mistletoes. These findings have important implications for the interactions between mistletoe species and their host trees in temperate forests.
Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110010, China.|College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
Da
D
Yang
Department of Biology, University of Miami, PO Box 249118, Coral Gables, FL 33124, USA.|Departamento de Ecología, Genética y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Nuñez, Buenos Aires C1428EGA, Argentina.
Guillermo
G
Goldstein
Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110010, China.
Miao
M
Wang
Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110010, China.
Wei-Wei
WW
Zhang
Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110010, China.|College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
Ai-Ying
AY
Wang
Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110010, China.|College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
Yan-Yan
YY
Liu
Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110010, China.
Guang-You
GY
Hao
D008834:Microclimate; D010788:Photosynthesis; D018526:Plant Transpiration; D014197:Trees / Q000469:parasitology*; D028181:Viscum / Q000502:physiology*; D014867:Water / Q000502:physiology*; D052584:Xylem / Q000502:physiology*
D014867:Water
hemi-parasitic plant; plant water relations; transpiration; vascular parasitic plant; water use