Symbiotic Nitrogen Fixation in Regenerating Black Locust (Robinia pseudoacacia L.) Stands

Author： Boring Lindsay R. Swank Wayne T.

Publisher： Society of American Foresters

ISSN： 0015-749X

Source： Forest Science, Vol.30, Iss.2, 1984-06, pp. : 528-537

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Abstract

Black locust (Robinia pseudoacacia L.) is a dominant early successional tree in the southern Appalachians that symbiotically fixes N, grows rapidly, and has a relatively short life span. Objectives of this research were to study seasonal patterns of nodule biomass and N-fixation activity in 4-year-old black locust stands over the span of one year, and to determine the importance of symbiotic N fixation as an input to a regenerating forest at the Coweeta Hydrologic Laboratory. Acetylene (C₂H₂) reduction activity for nodules >3 mm in length was highest during midday assays in June and September, attaining maximum values of 1.00 μl c₂H₄ mg dw hr^-1 and 0.94 μl c₂H₄ mg dw hr^-1, respectively. No activity was detected in November and March. Live nodule biomass was mostly (67 percent) concentrated in the upper 15 cm of soil. Nodule biomass decreased from 3.59 g m^-2 in May to 0.83 g m^-2 in November potentially because of a summer drought during the study year. The 4-year-old stands were estimated to have fixed 30 kg N ha^-1 yr^-1 during the study period. Nitrogen input to the early successional forest from symbiotic fixation is large in comparison to atmospheric inputs of N and free-living N fixation reported by other investigators. Forest Sci. 30:528-537.