| Fine root dynamics of loblolly pine (Pinus taeda L.) and seasonal fluctuations of nutrient concentrations in fine roots and needles as influenced by fertilization under different precipitation regimes were studied in four fertilization-responsive 15 and 16 year-old stands in East Texas from March 1996 through March 1998. Three root quantification methods were used: sequential cores, ingrowth cores, and minirhizotrons.; Fine root growth showed a strong bimodal seasonal pattern with a growth peak in both late autumn and early summer, respectively. This trend was not affected by root quantification method. Biomass of live fine roots with a diameter <1 mm was positively correlated with live root nitrogen (N), phosphorus (P), and magnesium (Mg) concentrations.; Fertilization not only significantly (P < 0.05) increased production of live and dead fine roots irrespective of fertilizer type, it also modified root morphology. Nitrogen tended to increase production of larger roots, whereas P increased both numbers of new roots and total root length. The combination of N and P produced the highest increase in fine root growth. Fertilization increased fine root growth more strongly in a high precipitation site than in a low precipitation site.; In practice, fine root biomass and root nutrient data can be integrated into wood production models for better wood production prediction. Fine root growth and root nutrient data can also be used as indicators of tree health and for nutrient diagnostic purposes. Fine root nutrient data can help forest managers to identify those growth-limiting nutrients and make fertilization plans to increase fine root and the whole tree's growth. To obtain the optimum beneficial effects of fertilizers, fertilizers should be applied under optimal soil moisture conditions. For example, in similar precipitation sites in East Texas, autumn and early spring with higher precipitation might be suitable for fertilization treatments for avoiding normal drought seasons. |
