Microbiotic crusts are biological soil crusts composed of lichens, cyanobacteria, algae, mosses, and fungi. The biodiversity of these crusts is poorly understood; several cosmopolitan species dominate in most areas, but many species are confined to one or a few sites. Nitrogen fixation by organisms within the crust can be the dominant source of nitrogen input into many ecosystems, although rates of nitrogen input are limited by water availability, temperature, and nitrogen loss from the crust. Photosynthetic rates of the microbiotic crust can be 50% of those observed for higher plants, but the contribution of crusts to carbon cycling is not known. The microbiotic crust binds soil particles together, and this significantly increases soil surface stability and resistance to erosion. Greenhouse studies have found that crusts can enhance seed germination, seedling survivorship, and plant nutrient status, but further experiments are needed under field conditions. Crusts are extremely susceptible to surface dis...

Microbiotic Crusts and Ecosystem Processes

Algae occur in nearly all terrestrial environments on earth and are invariably encountered both on and beneath soil surfaces. The algal flora of the soil includes members of the Cyanochloronta, Chlorophycophyta, Euglenophycophyta, Chrysophycophyta, and Rhodophycophyta. Thirty-eight genera of prokaryotic and 147 genera of eukaryotic algae include terrestrial species, the majority of which are edaphic. Whereas systematic nomenclature of blue-green algae adheres to traditional classification based upon morphological features, proper taxonomic treatment of eukaryotic soil algae is predicated on standard methods of culture and interpretation of physiological attributes, plant mass characteristics, and morphological properties of axenic clones. While knowledge of the physiological ecology of soil algae is primarily based on laboratory evidence, it is well established that solar radiation, water, and temperature are the most important abiotic factors governing their distribution, metabolism, and life history strategies. Biotic interactions are often as important, whereas ionic factors (including pH), oxidation-reduction potential, and soil texture are less important, if only because their influences are less well understood. Algae play an important role in primary and secondary plant community succession by acting as an integral part of the colonial synusium. The principal functional attributes of algal communities in soil include primary production, dinitrogen fixation, and stabilization of aggregates. Although as many as 108 algae per gram have been documented, soils commonly support between 103 and 104 per gram. As an avenue for the incorporation of carbon and nitrogen and for minimizing erosion through stabilization of aggregates, algae are valuable in agriculture. Although manipulation of edaphic algal populations in temperate countries is of novel occurence, their successful use in India as a means for reclaiming saline soils and as a source of fertilizer nitrogen is well documented. Soil algae are affected by synthetic pesticides and pollutants. In general, most herbicides, fungicides, and soil fumigants are detrimental to soil algae while most insecticides are not. Algae have been utilized as biological assay organisms for anticipating crop response to both fertilizers and pesticides because of their biochemical similarity to higher plants and their quick generation time. As future research with soil algae leads to a greater awareness of their importance in soil, it might be anticipated that manipulation of populations in agricultural systems of temperate regions will become more widespread with consideration of the potential benefits of soil algae made by scientists in other disciplines.

The systematics and ecology of soil algae

Publisher Summary The role of microscopically small organisms in numerous soil processes, particularly those affecting plant productivity, is well recognized. Less well known is the quantity of recently gathered information concerning microorganisms as the components of major plant communities and the extent to which they participate in the total energy flow therein. Although the soil microflora is the single most important group in the annual turnover of energy trapped by photosynthesis, no broad general review of the microflora of grassland has heretofore been compiled. There is a rich microflora associated with the surfaces of living plants that is either nonpathogenic or at most functioning at an extremely marginal level of pathogenicity. This microflora feeds primarily on exudates and sloughed cellular material. It commonly is divided into two categories: (a) the aboveground, shoot-associated microflora, or broadly referred as the “phyllosphere” and (b) the belowground, root-associated microflora, broadly referred as the “rhizophere.” This chapter examines the microflora of grassland litter, the microflora of grassland soils, biomass and bioactivity measurements, the humic component of grassland soil, and nitrogen transformations in grassland soils.

The microflora of grassland.

Introduction ................................................................................................................................................................. 92 Role of Soil Algae ................................................................................................................................................ 94Colonization ................................................................................................................................................ 94 P lan t Succession .................................................................................................................................... 95 Contribution to Tota l Nitrogen ............................................................................................. 96 Conditions Gove rn ing Growth and Distr ibut ion of Soil Algae ........................... 101 Substrate ......................................................................................................................................................... 102 Soil pH ............................................................................................................................................................ 103 W a t e r Requirement ........................................................................................................................... 105 Depth in Soil ............................................................................................................................................. 107 Floristic Pa t te rns of Soil Algae ............................................................................................................ 108 Cul ture of Soil Algae .......................................................................................................................................... 113 Summary ........................................................................................................................................................................... 116 Li terature Cited ..................................................................................................................................................... 120

Algae in relation to soil fertility

Soil surface growths dominated by cyanobacteria and the lichen Collema in southeastern Utah are shown to be associated with greater tissue content of several bio‐essential elements in two co‐occurring seed plants (Festuca octoflora, Poaceae, and Mentzelia multiflora, Loasaceae). The elements N, P, K, Ca, Mg, and Fe were present in significantly greater concentrations in Festuca growing on soils heavily encrusted with cyanobacteria and cyanolichens than in plants on the same soil where foot traffic had destroyed the cryptobiotic crusts. With Mentzelia, N, Mg, and Fe were present in significantly greater concentrations in plants from sites with encrusted soil surfaces than on blow‐sand sites. The cryptobiota appeared to compete vigorously with Mentzelia for available P: Mentzelia plants from crusted sites contained significantly smaller concentrations of P than plants grown on soils where wind action precluded development of surface crusts. These cryptobiotic crusts fix considerable amounts of N, which appa...

Influence of cryptobiotic soil crusts on elemental content of tissue of two desert seed plants

The algae are important constituents of the living, changing complex that we call the soil. Soil contains not only minute mineral fragments but also water, gases, dead plant materials, insect larvae, nematodes, protozoa, bacteria, fungi and algae. This is an intricate association and the algae have a part in it. They add organilc matter to the soil, influence chemical changes therein, are known to fix nitrogen and are a food source for small animal life in the soil. Several workers throughout the world have listed the various algaethey have found in the soil (Bristol-Roach, 1927; Fritsch, 1922; Fritsch and Salisbury, 1915; Russell, 1923) and a few have studied the activities of these micro-organisms (Bristol, 1920; Petersen, 1935; Skinner, 1932). Most of these studies were made in Europe. In this country as early as 1912, W. W. Robbins examined 22 soils and found 12 species of algae living in them. Later, G. T. Moore and associates (1919; 1926) listed 31 species of algae found existing in soils at the Missouri Botanical Gardens, some of them rather deep below the surface. In 1925, Bonar and Goldsmith made a study of desert soils in the Southwest and found that such soils contained a total of 14 genera of algae; no specific list was published. Lowe and Moyse (1934) listed 27 species of algae from soils of Manitoba, Canada. The limited information on soil algae in this country suggests a need for further inventory, especially in the intermountain West. It is the purpose of the following paper to list such algae as have been found in Colorado soils, with brief mention of the conditions of their habitat.

L. W. Durrell

Papers

Algae in Colorado Soils