Xylem trait studies have enhanced our understanding of how plants strategically adapt their morphological and anatomical features to diverse climates. Despite the importance of the phloem in plant functioning, similar studies of phloem traits are lacking. To tackle this knowledge gap, we analyzed phloem anatomical traits of woody angiosperm species in relation to climate and the distance of samples to the stem tip. We collected main stem or branch cross-sections of 188 angiosperm woody species, which represent a wide range of climates and diverse families. Measurements of xylem vessel and phloem sieve element diameter, density, and lumen fraction were used in phylogenetic structural equation models to disentangle internal and climatic constraints on their morphological and anatomical features. Our results showed that distance-to-tip mainly affects sieve element and vessel diameter and density, while climate more strongly influenced conduit lumen fraction. Vessel size was positively correlated with temperature after correcting for the distance-to-tip, while sieve element diameter was correlated with water availability. Our results highlight the need to account for distance-to-tip when accessing anatomical variations linked to the environment, and show that sieve element traits respond to other climatic drivers than vessel traits rather than simply mirroring them.

Ailaoshan Station of Subtropical Forest Ecosystem Studies Xishuangbanna Tropical Botanical Garden Chinese Academy of Sciences Jingdong Yunnan 676209 China

AMAP University of Montpellier CIRAD CNRS INRAE IRD Montpellier 34398 France

CAS Key Laboratory of Tropical Forest Ecology Xishuangbanna Tropical Botanical Garden Chinese Academy of Sciences Mengla Yunnan 666303 China

Department of Agricultural Forest and Food Sciences University of Torino Largo Paolo Braccini 2 Grugliasco 10095 Italy

Department of Botany Faculty of Science University of South Bohemia Branišovská 1760 České Budějovice 837005 Czech Republic

Department of Forest Physiology and Genetics Slovenian Forestry Institute Ljubljana 1000 Slovenia

Faculty of Forestry and Wood Sciences Czech University of Life Sciences Prague Kamýcká 129 Prague 16521 Czech Republic

Fédération Wallonie Bruxelles Service Général de l'Enseignement supérieur et de la Recherche scientifique Bruxelles 1080 Belgium

Forest Biometrics Laboratory Faculty of Forestry 'Stefan cel Mare' University of Suceava Str Universitatii 13 Suceava 720229 Romania

Hans Em Faculty of Forest Sciences Landscape Architecture and Environmental Engineering Ss Cyril and Methodius University in Skopje Skopje 1000 North Macedonia

Institute for Atmospheric and Earth System Research Forest Sciences Faculty of Agriculture and Forestry University of Helsinki P O Box 27 Latokartanonkaari 7 Helsinki 00014 Finland

Institute for Atmospheric and Earth System Research Physics Faculty of Science University of Helsinki P O box 68 Gustaf Hällströmin katu 2b Helsinki 00014 Finland

Institute of Biology University of Graz Graz 8010 Austria

Institute of Botany Czech Academy of Sciences Dukelská 135 Třeboň 37901 Czech Republic

Laboratory of Environmental and Applied Botany Department of Biotechnology and Life Science University of Insubria Via Dunant 3 Varese 21100 Italy

Laboratory of Forest Genetics and Ecophysiology School of Engineering and Applied Sciences National University of Mongolia Ulaanbaatar 14201 Mongolia

Meise Botanic Garden Meise 1860 Belgium

Royal Botanic Gardens Kew TW9 3AE UK

Université de Lorraine AgroParisTech INRAE SILVA Nancy F 54000 France

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