title: Wood anatomical correlates with theoretical conductivity and wood density across China: evolutionary evidence of the functional differentiation of axial and radial parenchyma.
abstract: OBJECTIVE
  In recent years considerable effort has focused on linking wood anatomy and key ecological traits. Studies analysing large databases have described how these ecological traits vary as a function of wood anatomical traits related to conduction and support, but have not considered how these functions interact with cells involved in storage of water and carbohydrates (i.e. parenchyma cells).
  
  
  METHODS
  We analyzed, in a phylogenetic context, the functional relationship between cell types performing each of the three xylem functions (conduction, support and storage) and wood density and theoretical conductivity using a sample of approx. 800 tree species from China.
  
  
  RESULTS
  Axial parenchyma and rays had distinct evolutionary correlation patterns. An evolutionary link was found between high conduction capacity and larger amounts of axial parenchyma that is probably related to water storage capacity and embolism repair, while larger amounts of ray tissue have evolved with increased mechanical support and reduced hydraulic capacity. In a phylogenetic principal component analysis this association of axial parenchyma with increased conduction capacity and rays with wood density represented orthogonal axes of variation. In multivariate space, however, the proportion of rays might be positively associated with conductance and negatively with wood density, indicating flexibility in these axes in species with wide rays.
  
  
  CONCLUSIONS
  The findings suggest that parenchyma types may differ in function. The functional axes represented by different cell types were conserved across lineages, suggesting a significant role in the ecological strategies of the angiosperms.
authors.affiliation: Key Laboratory for Silviculture and Conservation of Ministry of Education, Beijing Forestry University, Beijing, 100083, China. zhjmbjfu@gmail.com
authors.forename: Jingming
authors.initials: J
authors.lastname: Zheng
authors.forename: Hugo I
authors.initials: HI
authors.lastname: Martínez-Cabrera
mesh_terms: D005075:Biological Evolution; D002454:Cell Differentiation; D002681:China; D019684:Magnoliopsida / Q000033:anatomy & histology* / Q000502:physiology; D058503:Mesophyll Cells / Q000502:physiology*; D010802:Phylogeny; D018515:Plant Leaves / Q000033:anatomy & histology / Q000502:physiology; D014867:Water / Q000502:physiology; D014934:Wood / Q000033:anatomy & histology* / Q000502:physiology; D052584:Xylem / Q000033:anatomy & histology / Q000502:physiology
chemical_list: D014867:Water
keywords: Ecological strategies; evolutionary conservatism; hydraulic conductivity; parenchyma; water storage; wood anatomy; wood density
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