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DINITROGEN FIXATION BY CYANOBACTERIA AND ASSOCIATIVE RHIZOSPHERE BACTERIA IN THE ARAPAHO PRAIRIE IN THE SAND HILLS OF NEBRASKA
Author(s) -
Kapustka Lawrence A.,
DuBois John D.
Publication year - 1987
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1987.tb08584.x
Subject(s) - diazotroph , biology , rhizosphere , cyanobacteria , grassland , heterotroph , botany , ecology , nitrogen fixation , zoology , agronomy , bacteria , genetics
Free‐living and lichenized cyanobacterial (cyanolichen) colonies occupy 12–29% of the surface area in the Sand Hills grasslands on the Arapaho Prairie in southwestern Nebraska. During brief periods of favorable conditions (i.e., moderate temperature and high moisture), these diazotrophs are capable of high rates of dinitrogen fixation. Maximum rates of acetylene reduction measured during 1981 and 1982 were 2,237 μg N m ‐2 hr ‐l . The duration of dinitrogen fixation activity is dependent upon moisture conditions; rates of acetylene reduction were shown to decline 90% in as little as three hr. Desiccated colonies resumed acetylene reduction activity within one hr and achieved equilibrium rates within four hr following rehydration. Associative, heterotrophic diazotrophs were isolated from the rhizospheres of several grass species. These bacteria exhibited a range of culturing characteristics which may reflect differing plant‐bacterial interaction potentials important to the establishment and maintenance of the plant species. None of the field assays for heterotrophic dinitrogen fixation performed over the two‐yr period indicated a capacity of this group to provide ecologically significant levels of N in this grassland. Our gross estimate of the annual contribution was 3.5 kg N ha ‐1 from cyanolichens and 0.8 kg N ha ‐1 from associative heterotrophs.