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Tree Physiol. 2019 Mar 22. pii: tpz028. doi: 10.1093/treephys/tpz028. [Epub ahead of print]

Large branch and leaf hydraulic safety margins in subtropical evergreen broadleaved forest.

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State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, Guangxi University, Nanning 530004, China.
Guangxi Key Laboratory of Forest Ecology and Conservation, College of Forestry, Guangxi University, Nanning 530004, China.
Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China.
Department of Botany, Government College University, Lahore 54000, Pakistan.


As a global biodiversity hotspot, the subtropical evergreen broadleaved forest (SEBF) in southern China is strongly influenced by the humid monsoon climate, with distinct hot-wet and cool-dry season. However, hydraulic strategies of this forest are not well understood. Branch and leaf hydraulic safety margins (HSMbranch and HSMleaf, respectively), as well as seasonal changes in predawn and midday leaf water potential (Ψpd and Ψmd), stomatal conductance (Gs), leaf to sapwood area ratio (AL/AS), and turgor loss point (Ψtlp) were examined for woody species in a mature SEBF. For comparison, we compiled these traits of tropical dry forests (TDF) and Mediterranean-type woodlands (MW) from the literatures because they experience hot-dry season. We found that on average SEBF showed larger HSMbranch and HSMleaf than TDF and MW. During the dry season, TDF and MW species displayed a significant decrease in Ψpd and Ψmd. However, SEBF species showed a slight decrease in Ψpd but an increase in Ψmd. Similar to TDF and MW species, Gs was substantially lower in the dry season for SEBF species, but this might be primarily because of the low atmospheric temperature (low vapor pressure deficit). On the other hand, AL/AS and Ψtlp were not significant different between seasons for any SEBF species. Most SEBF species had leaves that were more resistant to cavitation than branches. Additionally, species with stronger leaf-to-branch vulnerability segmentation tended to have smaller HSMleaf but larger HSMbranch. Our results suggest that subtropical evergreen broadleaved forest is at low hydraulic risk under the current climate.


cavitation; hydraulic adjustment; rainfall seasonality; turgor loss point; vulnerability segmentation; water potential


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