ALGA‐ AND LICHEN‐STABILIZED SURFACE CRUSTS AS SOIL NITROGEN SOURCES

Abstract

ALGAE AND LICHENS contribute significantly to soil formation in a variety of ecological habitats. Algae have been investigated from the standpoint of nitrogen nutrition in desert (Fogg, 1947) and semidesert soils (Robbins, 1912; F'letcher and Martin, 1948), as a source of oxygen (Harrison and Aiyer, 1913) and nitrogen (Watanabe et al., 1951) in rice fields, and with respect to their possible value as pioneer vegetation in volcanic deposits (Treub, 1888). Soil algae are also recognized as an important agency in stabilizing surface crust in areas denuded of macro-vegetation by drought (Piercy, 1917; Drouet, 1937) or erosion (Elwell et al., 1939; Osborn, 1950) and in improving water infiltration (Booth, 1941). The present study investigates (a) the seasonal incidence of algal species in algaand lichen-stabilized soil crusts from several semi-arid habitats and (b) the amino nitrogen and combined nitrite and nitrate of these surface strata compared to subsurface levels. Observations are based mainly on soil samples collected from the Tularosa Basin in Lincoln and Otero Counties, southcentral New Mexico, from two strikingly contrasting xeric habitats. One, the Alamogordo White Sands (fig. 1), a deposit of drifting, 97 per cent gypsum, lies in the lowest part of the basin, covering an area approximately 28 miles long and 8 to 10 miles wide to a depth of 1000 ft. (Potter, 1938). The other, a recent lava flow, the Carrizozo malpais (fig. 2), extends northward along the main axis of the basin, filling a narrow valley 1/2 to 5 miles wide and 44 miles long to a depth of around 70 ft. toward the center and 10 to 20 ft. along the margins. In addition, samples were collected from that part of the Tularosa Basin immediately surrounding the gypsum sand deposit and the lava flow. This section of the basin floor varies from semidesert, alkaline plain adjacent to the gypsum deposit to typical overgrazed range land adjoining the lava flow on either side. Average annual precipitation in the Tularosa Basin, ranging from approximately 8 in. in the White Sands to 11 in. at the northern tip of the lava flow, is correlated mainly with altitude. The depth of the water table varies from 2 to 3 ft. in the gypsum flats to well over a hundred feet in parts of the surrounding basin floor. METHOD.-Soil crust and subsurface samples were collected in the dried condition from widely separated sections of the gypsum sand, the lava flow, and the surrounding basin floor. In the field,