Importance of First-Order Lateral Roots in the Early Development of Forest Tree Seedlings

Abstract

Abstract In spite of the importance of vesicular-arbuscular mycorrhizae (VAM) to hardwood tree growth, no consistent relationship between seedling growth in the field and initial degree of VAM feeder root colonization has been reported. Within even full-sib or half-sib progeny, where biomass differences among individual seedlings can exceed 10-fold, nopredictable difference in either tissue analysis or phosphorus metabolism have been reported for seedlings when available soil phosphorus is above a minimum value which permits comparable development of nonmycorrhizal seedlings. Field work with Liquidambar styraciflua L. shawed that percentage of seedling feeder roots of numerous half-sibseedlots with varying degrees of mycorrhizal development was unrelated to seedling size or plantation performance, while the number of permanent first-order lateral roots was strongly correlated with size and performance. From 30 to 60 percent of the progeny had inferior lateral root development, suggesting considerable genetic influence in the development of first-order lateral roots. This work with Liquidambar resulted in the following hypothesis: “Regardless of the phenotypic characteristics of a mother tree, associated progeny will exhibit a range in seedling development related to distribution of permanent, first-order lateral roots, and that seedlings with fewer lateral roots will be less competitive in a forest environment”. This work may provide a biological basis for grading seedlings. The frequency distribution hypothesis relating to lateral root morphology of seedlings has been found in Liquidambar, Juglans, Fraxinus, Quercus, Plantanus, Carya, and Pinus spp. and is currently being tested to ascertain the scope and validity of the general hypothesis.