Topic
Nitrogen fixation
About: Nitrogen fixation is a research topic. Over the lifetime, 7940 publications have been published within this topic receiving 232921 citations. The topic is also known as: GO:0009399.
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78 citations
TL;DR: Snowbrush did not add to the soil any significant amount of nitrogen by nitrogen fixation, but the species contributes to the formation of a new organic layer, however, through large amounts of nitrogen—rich litter.
Abstract: Twelve stands of snowbrush were selected for a biomass study to estimate nitrogen fixation under field conditions west of the summit of the Oregon Cascades Total nitrogen in the upper 2 ft of soil was higher under snowbrush than in the open, but the difference may have been caused by loss of nitrogen from open areas rather than by nitrogen fixation Total nitrogen in the upper 15 cm of soil under snowbrush did not differ from that found under nonfixing shrub species Various shrub species may increase the total soil nitrogen under their canopies, however, if only by accumulation from sites that lack vegetation More nitrogen may be tied up in the biomass of mature snowbrush stands than in stands of other shrubs The difference could be explained by nitrogen fixation, which may range from zero to about 20 kg/ha per year under conditions of this study Nodulated snowbrush seedlings produced 25 times the dry weight that non—nodulated seedlings produced in a nitrogen deficient soil Sixty—one per cent of the nitrogen in nodulated greenhouse seedlings was fixed Such fixation rates may be reached on infertile soils in the field, but they seem unlikely on soils of medium or better fertility This point seems to be substantiated by delay in nodulation of snowbrush in soils with increased levels of organic matter Bioassay tests using Douglas fir seeds and hemlock seedlings showed that snowbrush did not add to the soil any significant amount of nitrogen by nitrogen fixation The species contributes to the formation of a new organic layer, however, through large amounts of nitrogen—rich litter
78 citations
TL;DR: Seasonal variation in the ARA of excised plant roots from field cores appears to be related to the annual cycle of net photosynthesis in S. alterniflora.
Abstract: The coupling of root-associated nitrogen fixation and plant photosynthesis was examined in the salt marsh grass Spartina alterniflora. In both field experiments and hydroponic assay chambers, nitrogen fixation associated with the roots was rapidly enhanced by stimulating plant photosynthesis. A kinetic analysis of acetylene reduction activity (ARA) showed that a five-to-sixfold stimulation occurred within 10 to 60 min after the plant leaves were exposed to light or increase CO/sub 2/ concentrations (with the light held constant). In field experiments, CO/sub 2/ enrichment increased plant-associated ARA by 27%. Further evidence of the dependence of ARA on plant photosynthate was obtained when activity in excised roots was shown to decrease after young greenhouse plants were placed in the dark. Seasonal variation in the ARA of excised plant roots from field cores appears to be related to the annual cycle of net photosynthesis in S. alterniflora.
78 citations