Root system architecture: The invisible trait in container longleaf pine seedlings

Longleaf pine (Pinus palustris Mill.) seedlings cultured in four cavity volumes (60 to 336 ml [3.7 to 20.5 cubic inches]), two root pruning treatments (with or without copper coating), and 3 nitrogen levels (low to high) were grown for 29 weeks before they were outplanted into an open area in central Louisiana. Twenty-two months after outplanting, 3 seedlings were excavated from each of the 24 treatment combinations to evaluate effects of nursery cultural treatments on seedling growth and root system architecture. This paper reports some preliminary observations from that sample. Seedlings cultured in copper coated cavities had more lateral roots egressing into the top 10 cm (3.9 in) of soil whereas those cultured without copper root pruning had most of their lateral roots egressing into deeper (> 10cm [> 3.9 in]) soil layers. Regardless of nursery treatments, adventitious roots that originated near the air-pruned taproot end in some seedlings grew horizontally instead of vertically downward as in most container seedlings. Relationships between root system architecture and long - leaf growth and mechanical stability are discussed.