Bacteria of four tussock grassland soils on the old man range, Central Otago, New Zealand

Abstract

A sequence of four soils derived from schist, and ranging from 900 to 5,000 ft above sea level, has been studied bacteriologically in. association with biochemical measurements. The two soils at lower altitudes were of semi-arid to subhumid moisture regimes and weakly acid to near neutral, but the two upland soils were of the humid moisture regime and strongly acid. Of the isolates studied, 75% were Gram-negative, about one-half of them possessing carotenoid pigments. The non-pigmented Gramnegative rods included a large group of non-motile, slow-growing, psychrophilic bacteria that have not been recorded previously from these soils and have been classified as Acinetobacter. Spore-forming bacteria constituted 9%, and pleomorphic bacteria 14% of the isolates. Fungal plate counts, streptomyces, and spore-forming bacteria tended to decrease with increasing altitude, but Gram-negative bacteria became increasingly numerous. The rhizosphere of Poa colensoi appeared to have higher populations than those of Festuca novaezelandiae or Chionochloa rigida. Growth tests showed Gram-negative soil taxa to be generally more tolerant of low temperatures and acid conditions than pleomorphic, Gram-positive, or spore-forming taxa, but there was considerable variation, particularly with the Bacillus species. The variation with B. megaterillm isolates suggested that the range of temperature or pH within which population growth took place was related to the soil environment from which it was sampled.