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.

The role of legumes as a component of biodiversity in a cross‐European study of grassland biomass nitrogen

Abstract: To investigate how plant diversity loss affects nitrogen accumulation in above-ground plant biomass and how consistent patterns are across sites of different climatic and soil conditions, we varied the number of plant species and functional groups (grasses, herbs and legumes) in experimental grassland communities across seven European experimental sites (Switzerland, Germany, Ireland, United Kingdom (Silwood Park), Portugal, Sweden and Greece). Nitrogen pools were significantly affected by both plant diversity and community composition. Two years after sowing, nitrogen pools in Germany and Switzerland strongly increased in the presence of legumes. Legume effects on nitrogen pools were less pronounced at the Swedish, Irish and Portuguese site. In Greece and UK there were no legume effects. Nitrogen concentration in total above-ground biomass was quite invariable at 1.66 ± 0.03% across all sites and diversity treatments. Thus, the presence of legumes had a positive effect on nitrogen pools by significantly increasing above-ground biomass, i.e. by increases in vegetation quantity rather than quality. At the German site with the strongest legume effect on nitrogen pools and biomass, nitrogen that was fixed symbiotically by legumes was transferred to the other plant functional groups (grasses and herbs) but varied depending on the particular legume species fixing N and the non-legume species taking it up. Nitrogen-fixation by legumes therefore appeared to be one of the major functional traits of species that influenced nitrogen accumulation and biomass production, although effects varied among sites and legume species. This study demonstrates that the consequences of species loss on the nitrogen budget of plant communities may be more severe if legume species are lost. However, our data indicate that legume species differ in their N 2 fixation. Therefore, loss of an efficient N 2 -fixer (Trifolium in our study) may have a greater influence on the ecosystem function than loss of a less efficient species (Lotus in our study). Furthermore, there is indication that P availability in the soil facilitates the legume effect on biomass production and biomass nitrogen accumulation.

Nitrogen Fixation and Nitrogen Isotope Abundances in Zooplankton of the Oligotrophic North Atlantic

Abstract: Deep-water nitrate is a major reservoir of oceanic combined nitrogen and has long been considered to be the major source of new nitrogen supporting primary production in the oligotrophic ocean. 15N:14N ratios in plankton provide an integrative record of the nitrogen cycle processes at work in the ocean, and near-surface organic matter in oligotrophic waters like the Sargasso Sea is characterized by an unusually low 15N content relative to average deep-water nitrate. Herein we show that the low dΔ15N of suspended particles and zooplankton from the tropical North Atlantic cannot arise through isotopic fractionation associated with nutrient uptake and food web processes but are instead consistent with a significant input of new nitrogen to the upper water column by N2 fixation. These results provide direct, integrative evidence that N2 fixation makes a major contribution to the nitrogen budget of the oligotrophic North Atlantic Ocean.

Manipulation of rhizobia microflora for improving legume productivity and soil fertility: a critical assessment

Abstract: Inputs of biologically fixed nitrogen derived from the symbiotic relationship between legumes and their root-nodule bacteria into terrestrial ecosystems amount to at least 70 million metric tons per year. It is obvious that this enormous quantity will need to be augmented as the world's population increases and as the natural resources that supply fertilizer nitrogen diminish. This objective will be achieved through the development of superior legume varieties, improvement in agronomic practice, and increased efficiency of the nitrogen fixation process itself by better management of the symbiotic relationship between plant and bacteria. This paper considers ways and means by which populations of root-nodule bacteria, established and introduced, can be manipulated ecologically, agronomically, edaphically and genetically to improve legume productivity and, as a consequence, soil fertility.

Nitrogen isotopes link mycorrhizal fungi and plants to nitrogen dynamics

Abstract: Contents Summary 367 I. Introduction 367 II. Background on isotopes 368 III. Patterns of soil δ15N 370 IV. Patterns of fungal δ15N 372 V. Biochemical basis for the influence of fungi on δ15N patterns in plant–soil systems 373 VI. Patterns of δ15N in plant and fungal culture studies 374 VII. Mycoheterotrophic and parasitic plants 375 VIII. Patterns of foliar δ15N in autotrophic plants 376 IX. Controls over plant δ15N 377 X. Conclusions and research needs 378 Acknowledgements 379 References 379 Summary In this review, we synthesize field and culture studies of the 15N/14N (expressed as δ15N) of autotrophic plants, mycoheterotrophic plants, parasitic plants, soil, and mycorrhizal fungi to assess the major controls of isotopic patterns. One major control for plants and fungi is the partitioning of nitrogen (N) into either 15N-depleted chitin, ammonia, or transfer compounds or 15N-enriched proteinaceous N. For example, parasitic plants and autotrophic hosts are similar in δ15N (with no partitioning between chitin and protein), mycoheterotrophic plants are higher in δ15N than their fungal hosts, presumably with preferential assimilation of fungal protein, and autotrophic, mycorrhizal plants are lower in 15N than their fungal symbionts, with saprotrophic fungi intermediate, because mycorrhizal fungi transfer 15N-depleted ammonia or amino acids to plants. Similarly, nodules of N2-fixing bacteria transferring ammonia are often higher in δ15N than their plant hosts. N losses via denitrification greatly influence bulk soil δ15N, whereas δ15N patterns within soil profiles are influenced both by vertical patterns of N losses and by N transfers within the soil–plant system. Climate correlates poorly with soil δ15N; climate may primarily influence δ15N patterns in soils and plants by determining the primary loss mechanisms and which types of mycorrhizal fungi and associated vegetation dominate across climatic gradients.

Gas Exchange of Legume Nodules and the Regulation of Nitrogenase Activity

Abstract: CONTENTS INTRODUCTION 483 METHODS FOR MEASURING NITROGENASE ACTIVITY IN LEGUME NODULES... 484 The Acetylene Reduction Assay (ARA) 485 Measurement of Nodule H2 Evolution . .... 487 Measured Values of Nitrogenase Activity: Past and Present 489 IN VIVO NITROGENASE ACTIVITY: POTENTIAL AND LIMITATIONS 490 H2 Inhibition of N2 Fixation 490 02 Limitation of Nitrogenase Activity 492 ENVIRONMENTAL FACTORS AFFECTING NITROGENASE ACTIVITy 498 Restriction of Phloem Sap Supply 498 Nitrate Fertilization 500 Drought Stress 502 DEVELOPMENTAL AND LONG-TERM ADAPTA nON TO RHIZOSPHERE p02 ......... 503 CONCLUDING REMARKS 504