Potential Nitrogen Contribution of Soil Cryptogams to Post-Disturbance Forest Ecosystems in Bandelier National Monument, NM

Loftin, Samuel; White, Carleton

The nitrogen-fixation (N2-fixation) potential and annual N contribution of soil cryptogamic crusts were estimated in three previously burned ponderosa pine (Pinus ponderosa) and one previously grazed pinyon/juniper (Pinus edulis/Juniperus monosperma) forest ecosystems in Bandelier National Monument, NM. The ponderosa pine forest sites were burned in the 1977 La Mesa Fire and burro grazing on the pinyon/juniper site ended in approximately (1983). The objective of this research was to determine whether estimated post-disturbance cryptogamic N inputs could offset N losses from the disturbance. Surface cover in each habitat was divided into litter cover, herbaceous cover, bare soil, and obvious cryptogams, in an attempt to quantify the spatial heterogeneity of soil properties. Line intercept transects were used to estimate percent surface cover of each cover type. Soil samples from each cover type were analyzed for total N, C, P, δ15N, and N2-fixation potential. At this stage in the recovery process, the potential for cryptogamic N2-fixation was determined to occur in all sampled habitats and cover types. Correlations between N2-fixation potential and other soil variables indicated that none are suitable as indirect estimators of N2-fixation potential. Estimates of ecosystem N input as a result of cryptogamic N2-fixation range from 3.6 - 27.0 kg ha-1 yr-1. Evidence from soil analyses indicated that soil loss was greatest at the pinyon/juniper site.