, Volume 2, Issue 1, pp 29-37

Plant response to variations in nitrogen availability in a desert shrubland community

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Abstract

Spatial variations in nitrogen availability were studied in a desert community codominated byLarrea tridentata (DC.) Cov. andProsopis glandulosa Torr. Measurements of natural δ15N values in tissues suggested thatProsopis obtains approximately half of its nitrogen through direct symbiotic fixation. Soils were collected under 1)Prosopis shrubs, 2)Larrea shrubs ⩽ 2 m fromProsopis (LP), and 3)Larrea ⩽ 2 m from otherLarrea but> 5 m from the nearestProsopis (LL).Prosopis soils showed significantly higher rates of nitrogen mineralization than LL soils in both A and B horizons. Rates of mineralization in LP soils were significantly higher than rates in LL soils only in the B horizon and were not significantly different from rates inProsopis soils. Leaf nitrogen concentrations were significantly higher in LP shrubs (2.06%) than in LL shrubs (1.78%), although δ15N values did not differ between the two shrub types. Nitrogen concentrations inPerezia nana Gray, a perennial herb, were greater in plants underProsopis shrubs (2.09%) than under LP shrubs (1.93%) or LL shrubs (1.67%). Despite apparent differences in nitrogen availability, biomass ofLarrea and density ofPerezia did not differ significantly among these sites.