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Abstract
Hydrogen (H2) evolution from ‘Grasslands Huia’ white clover (Trifolium repens L.) nodulated by Rhizobium trifolu TA1, was suppressed by 6% acetylene-inair during acetylene reduction (AR) assays of nitrogen (N) fixation. Field measurements showed significant H2 evolution and reduced nodule relative efficiency over summer in a laxly mown pasture, but virtually no H2 was evolved from a closely grazed pasture. Plants transferred in winter from outdoors to a controlled cabinet with good growth conditions, showed increased AR rates and a decrease in nodule relative efficiency from 1 to 0.52 in 5 weeks. Defoliation of plants in a growth cabinet greatly reduced H2 evolution, confirming that conditions of growth have large effects on H2 evolution in white clover. No diurnal patterns of H2 evolution or AR were observed in plants growing outdoors. The significance of H2 evolution to AR assays of N fixation by white clover is discussed.
