title: Suppression of nighttime sap flux with lower stem photosynthesis in Eucalyptus trees.
abstract: It is widely accepted that substantial nighttime sap flux (J s,n) or transpiration (E) occurs in most plants, but the physiological implications are poorly known. It has been hypothesized that J s,n or E serves to enhance nitrogen uptake or deliver oxygen; however, no clear evidence is currently available. In this study, sap flux (J s) in Eucalyptus grandis × urophylla with apparent stem photosynthesis was measured, including control trees which were covered by aluminum foil (approximately 1/3 of tree height) to block stem photosynthesis. We hypothesized that the nighttime water flux would be suppressed in trees with lower stem photosynthesis. The results showed that the green tissue degraded after 3 months, demonstrating a decrease in stem photosynthesis. The daytime J s decreased by 21.47%, while J s,n decreased by 12.03% in covered trees as compared to that of control, and the difference was statistically significant (P < 0.01). The linear quantile regression model showed that J s,n decreased for a given daytime transpiration water loss, indicating that J s,n was suppressed by lower stem photosynthesis in covered trees. Predawn (ψ pd) of covered trees was marginally higher than that of control while lower at predawn stomatal conductance (g s), indicating a suppressed water flux in covered trees. There was no difference in leaf carbon content and δ(13)C between the two groups, while leaf nitrogen content and δ(15)N were significantly higher in covered trees than that of the control (P < 0.05), indicating that J s,n was not used for nitrogen uptake. These results suggest that J s,n may act as an oxygen pathway since green tissue has a higher respiration or oxygen demand than non-green tissue. Thus, this study demonstrated the physiological implications of J s,n and the possible benefits of nighttime water use or E by the tree.
authors: Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, People's Republic of China.
authors: Jianguo
authors: J
authors: Gao
authors: Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, People's Republic of China.
authors: Juan
authors: J
authors: Zhou
authors: Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, People's Republic of China.
authors: Zhenwei
authors: Z
authors: Sun
authors: Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, People's Republic of China.
authors: Junfeng
authors: J
authors: Niu
authors: Guangxi Institute of Botany, Chinese Academy of Sciences, Guilin, 541006, People's Republic of China.
authors: Cuiming
authors: C
authors: Zhou
authors: Guangxi Institute of Botany, Chinese Academy of Sciences, Guilin, 541006, People's Republic of China.
authors: Daxing
authors: D
authors: Gu
authors: Guangxi Institute of Botany, Chinese Academy of Sciences, Guilin, 541006, People's Republic of China.
authors: Yuqing
authors: Y
authors: Huang
authors: Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, People's Republic of China. zhaoping@scib.ac.cn.
authors: Ping
authors: P
authors: Zhao
mesh_terms: D002244:Carbon / Q000378:metabolism; D005052:Eucalyptus / Q000033:anatomy & histology / Q000502:physiology*; D006813:Humidity; D009584:Nitrogen / Q000378:metabolism; D010507:Periodicity; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000502:physiology; D018547:Plant Stems / Q000033:anatomy & histology / Q000502:physiology*; D018526:Plant Transpiration; D013696:Temperature; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water; D002244:Carbon; D009584:Nitrogen
keywords: Eucalyptus grandis × urophylla; Nighttime sap flux; Nitrogen uptake; Quantile regression; Stem photosynthesis