Rapid growth in clonal Juglans nigra L. is most closely associated with early foliation, robust branch architecture, and protandry

Abstract

The advantages of clonal forestry have been well described, but little progress has been made in the identification of phenotypes best suited to this method in high-value hardwood species. The genetic variation within, clonal repeatability (broad-sense heritability) of, and Pearson's correlations among phenological, morphological, physiological, and growth traits (N = 22) of black walnut (Juglans nigra L.) were investigated using 25 grafted clonal genotypes. The trees were grown at wide spacing (4.6 m × 6.1 m) in an intensively managed plantation in north-central Indiana, USA. Clonal effect was significant (p < 0.05) for most traits except gas exchange variables. Many phenological traits showed high clonal repeatability (R_c² > 0.70), including foliation dates, first female bloom, first pollen shed, and crown retention rate (autumnal defoliation). Some traits showed moderate repeatability (0.35 < R_c² < 0.7), such as branch angle, branch frequency, tree diameter, height, anthracnose severity, and foliar carbon and nitrogen concentration. Net CO₂ assimilation rate and stomatal conductance had low repeatability (R_c² < 0.35). We observed a previously unreported association between sexual morph and tree stem growth, i.e., protandrous trees generally grew faster than protogynous trees. This association between sexual morph and stem growth may be an evolutionary consequence of differences in reproductive costs in protandrous versus protogynous trees, and needs to be tested in other monoecious woody species. Overall, our analyses indicated that the following traits are associated with rapid stem growth: 1) early foliation; 2) early male flowering or late female flowering, i.e., more likely a protandrous variety; 3) large average branch diameter; 4) high branch frequency; 5) small (more vertical) average branch angle; 6) early leaf fall; 7) low laterseason foliar carbon concentration; and 8) large number of small fruits and seeds. These traits may be used, with further testing, to define a biomass ideotype for J. nigra.

Keywords

Ideotypes, Crown architecture, Broad-sense heritability, Dichogamy, Hardwood species, Clonal forestry

Citation

Pang, Kejia; Woeste, Keith E.; Saunders, Michael R.; McKenna, James R.; Mickelbart, Michael V.; Jacobs, Douglass F.; Michler, Charles H. 2021. Rapid growth in clonal Juglans nigra L. is most closely associated with early foliation, robust branch architecture, and protandry. Forest Ecology and Management. 499(3): 119590. 18 p. https://doi.org/10.1016/j.foreco.2021.119590.