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.

Soil development and nitrogen turnover, in montane rainforest soils on Hawaii

Abstract: Soil nutrients and nitrogen turnover were measured in two soil chronosequences on the Kilauea and Mauna Loa volcanoes, Hawai'i. Organic carbon and nitrogen accumulated rapidly in sites derived from volcanic ash and more slowly in sites derived from pahoehoe; a minimum of 22 kg N* ha-l yr-I were added to tephra sites early in soil development. Substantial nitrogen fixation by an unknown organism or organisms is probably responsible for most of the nitrogen accumulated on ash. Nitrogen turnover increased with soil age in both absolute (mg N/M2) and relative (g N/g of soil N) terms in both chronosequences. In comparison with other localities, net nitrogen mineralization potentials were extremely low in all of the sites except the two oldest ash sites. Nitrogen availability is probably not related to most of the forms of 'ohi'a dieback occurring in Hawai'i, but low nitrogen availability is observed in sites susceptible to the dryland form of dieback which occurs early in primary succession. SOIL CHRONOSEQUENCE STUDIES HAVE BEEN AN IMPORTANT MEANS FOR UNDERSTANDING THE REGULATION OF NUTRIENT accumulation and availability in natural terrestrial ecosystems. Using this approach, Dickson and Crocker (1953), Crocker and Major (1955), Olson (1958), and Van Cleve et al. (1971) demonstrated increases in soil nitrogen in chronosequences developing after mud flows, glacial recession, sand dune stabilization, and flood plain deposition respectively. Robertson and Vitousek (1981) showed that the availability of soil nitrogen (measured by net release during soil incubations) also increased with soil age on sand dunes. T. W. Walker and coworkers (summarized in Walker and Syers 1976), demonstrated progressive decreases in soil phosphorous pool sizes and availability in four separate chronosequences, with the declines reaching a "terminal steady state" of very low phosphorus availability and reduced plant productivity in some sites. Walker further suggested that symbiotic nitrogen fixers grow well on the high-phosphorus, low-nitrogen substrates early in soil development, but that the combination of increased nitrogen and decreased phosphorus later in soil development largely excludes symbiotic nitrogen fixers (Stevens and Walker 1970, Walker and Syers 1976). Low nitrogen availability should thus be more likely to limit the growth of plants unable to fix nitrogen in relatively young soils and phosphorus should be more limiting in relatively old soils. Montaine forests on the island of Hawai'i offer an excellent opportunity to examine the relationships among soil development, nutrient accumulation, and primary succession (Sherman and Ikawa 1968). Frequent eruptions have occurred from both the kilauea and Mauna Loa volcanoes, and the deposits from these eruptions can be dated by historical records since 1790 or by 14C dating of plant remains (Lockwood and Lipman 1980). Moreover, the importance of soil-forming factors other than time (climate, relief, organisms, and parent materialJenny 1941, 1980) can be minimized through the appropriate location of sample sites. The islands are in the trade winds, and climate is highly predictable from elevation and slope exposure. Both Kilauea and Mauna Loa are active shield volcanoes, so relief is gentle and relatively constant. The isolation of Hawai'i has led to a relatively impoverished flora and fauna (Mueller-Dombois 198 la). There are several woody plants in the area, but only one dominant tree species ('ohi'a Metrosideros collina ssp. polymorpha) usually forms the upper canopy. It is present at all ages and on all variations of substrate in the study area. Finally, three "parent materials" with different textures but similar chemistries are produced by these volcanoes: volcanic ash (tephra), pahoehoe (smooth ropy lava flows), and 'a'a (clinker-type lava flows). Primary plant succession in 'ahi'a forests has been described by Atkinson (1970), Eggler (1971), Smathers and Mueller-Dombois (1974), and Mueller-Dombois I Present address: Department of Biological Sciences, Stanford University, Stanford, California 94305 U.S.A. 268 BIOTROPICA 15(4): 268-274 1983 This content downloaded from 157.55.39.35 on Fri, 02 Sep 2016 05:11:21 UTC All use subject to http://about.jstor.org/terms (198 1b). There are three unusual features to the primary succession on Hawai'i. First, the sites are low in dominant tree species diversity. Second, no nitrogen fixers symbiotic with vascular plants are present in the early stages of soil development in the rain forest zone. Native nitrogen fixers (especially Acacia koa) are present at both higher and lower elevations but not within the area studied. Third, primary succession in the montane rain forest appears to proceed through a phase of biomass accumulation to a rather rapid dieback of the dominant 'ahi'a trees, followed (most often) by 'ahi'a regeneration (Mueller-Dombois et al. 1980). Several forms of dieback are recognized, including wetland, bog formation, 'ahi'a displacement, gap formation, and dryland dieback (Mueller-Dombois 1981b). The mechanisms responsible for these diebacks are not fully known, but they appear to occur naturally in primary succession rather than as an effect of an introduced pathogen (Mueller-Dombois 1981 b). This study was designed to examine the accumulation, availability, and turnover of soil nitrogen in soil chronosequences developed on tephra and pahoehoe. We tested the generalization that nitrogen availability and nitrogen turnover increase from very low levels early in primary succession and evaluated the possibility that nitrogen availability could affect the susceptibility of the 'ohi'a forest to dieback.

Effect of nitrogen and carbon supply on the development of soil organism populations and pine seedlings - microcosm experiment

Abstract: Series of pots containing Scots pine seedlings and a humus-sand mixture were watered twice weekly for 398 d with different nutrient solutions (control treatment with complete plant nutrient solution less nitrogen; glucose addition; nitrogen addition; glucose and nitrogen addition). Analyses were made of organic and nitrogen contents in the substrate, plant weights and nitrogen contents, nitrogen fixation and respiration rates, abundance, biomass and in some cases species composition of different soil organism populations. The growth rate of pine seedlings was lowest in series supplied with glucose, which is most easily explained by a deficiency of nitrogen due to microbial immobilization. The fungi and yeast were stimulated by addition of an easily available carbon source whereas the bacteria needed both nitrogen and carbon to maintain high biomass. A positive correlation between fungal feeding soil organisms and amount of fungal mycelium was found while a more complex situation prevailed with regard to bacterial numbers and bacterial feeding nematodes. The systems are evaluated in relation to the different treatments and compared with the field situation. (Less)

Expression of a Class 1 Hemoglobin Gene and Production of Nitric Oxide in Response to Symbiotic and Pathogenic Bacteria in Lotus japonicus

Abstract: Symbiotic nitrogen fixation by the collaboration between leguminous plants and rhizobia is an important system in the global nitrogen cycle, and some molecular aspects during the early stage of host-symbiont recognition have been revealed. To understand the responses of a host plant against various bacteria, we examined expression of hemoglobin (Hb) genes and production of nitric oxide (NO) in Lotus japonicus after inoculation with rhizobia or plant pathogens. When the symbiotic rhizobium Mesorhizobium loti was inoculated, expression of LjHb1 and NO production were induced transiently in the roots at 4 h after inoculation. In contrast, inoculation with the nonsymbiotic rhizobia Sinorhizobium meliloti and Bradyrhizobium japonicum induced neither expression of LjHb1 nor NO production. When L. japonicus was inoculated with plant pathogens (Ralstonia solanacearum or Pseudomonas syringae), continuous NO production was observed in roots but induction of LjHb1 did not occur. These results suggest that modulation of NO levels and expression of class 1 Hb are involved in the establishment of the symbiosis.

Molecular characterisation of the diazotrophic bacterial community in uninoculated and inoculated field-grown sugarcane (Saccharum sp.)

Abstract: To identify active diazotrophs in sugarcane, 16S rRNA and nifH transcript analyses were applied. This should help to better understand the basis of the biological nitrogen fixation (BNF) activity of a high nitrogen fixing sugarcane variety. A field experiment using the sugarcane variety RB 867515 was conducted in Seropedica, RJ, Brazil, receiving the following treatments: unfertilised and fertilised controls without inoculation, unfertilised with inoculation. The five-strain mixture developed by EMBRAPA-CNPAB was used as inoculum. Root and leaf sheath samples were harvested in the third year of cultivation to analyse the 16S rRNA and nifH transcript diversity. In addition to nifH expression from Gluconacetobacter spp. and Burkholderia spp., a wide diversity of nifH sequences from previously uncharacterised Ideonella/Herbaspirillum related phylotypes in sugarcane shoots as well as Bradyrhizobium sp. and Rhizobium sp. in roots was found. These results were confirmed using 16S cDNA analysis. From the inoculated bacteria, only nifH transcripts from G. diazotrophicus and B. tropica were detected in leaf sheaths and roots. Known as well as yet uncultivated diazotrophs were found active in sugarcane roots and stems using molecular analyses. Two strains of the inoculum mix were identified at the late summer harvest.

Plant Growth-Promoting Nitrogen-Fixing Enterobacteria Are in Association with Sugarcane Plants Growing in Guangxi, China

Abstract: Guangxi is the major sugarcane- and sugar-producing area in China and produces about 60% of China’s sugarcane and sugar. The present sugarcane mean yields are between 70 and 80 Mg ha−1. The cost of sugarcane production in Guangxi is much higher than in Brazil. One of the major factors of the high cost is high N-fertilization. Over 60% of the sugarcane fields are applied with urea at over 600 kg ha−1 yr−1 (32). In Brazil, the present sugarcane mean yields are also between 70 and 80 Mg ha−1, but N-fertilizer mean applications are between 60 and 70 kg N ha−1 yr−1 (50). 15N isotope assays have demonstrated that some Brazilian sugarcane varieties are able to obtain considerable nitrogen from biological nitrogen fixation (BNF; 25, 49, 50). A number of nitrogen-fixing bacteria have been isolated from the rhizosphere and interior of sugarcane plants, and have shown potential to fix N2 associated with sugarcane plants (5, 13, 35, 43). BNF may help farmers to maintain sugarcane yields under reduced N-fertilization and develop environmentally benign sugarcane production in Guangxi. At present, little is known about the diversity and predominant population of nitrogen-fixing bacteria associated with the sugarcane plants growing in Guangxi. Recently, some nitrogen-fixing bacteria have been isolated from sugarcane plants grown in Guangxi (26, 28, 44, 52, 53) using NFb, JNFb and LGI-P media that were respectively used to isolate Azospirillum (10), Herbaspirillum (6) and Gluconacetobacter diazotrophicus (8); however, nitrogen-fixing bacteria belonging to the genera Azospirillum, Herbaspirillum, and Gluconacetobacter, which are predominantly associated with sugarcane plants in Brazil, have not been isolated. The diversity of nitrogen-fixing bacteria associated with sugarcane plants grown with high N-fertilization in Guangxi may be different from in Brazil. The ROC22 cultivar is the main sugarcane cultivar, growing in over 60% of sugarcane-planting areas in Guangxi. It is sensitive to low nitrogen stress and requires at least 150 kg ha−1 urea fertilization at the seedling stage for tillering and elongation of the plant cane crops (23). The recommended dose of urea fertilization for plant cane crops at the seedling stage is 180 kg ha−1, 30% of urea fertilization for a season (46). Recent studies have shown that nitrogen-fixing bacterial strains isolated from other sugarcane cultivars are able to provide nitrogen to micropropagated ROC22 sugarcane seedlings via BNF and promote sugarcane growth (26, 29); however, neither indigenous nitrogen-fixing bacteria associated with ROC22 sugarcane plants nor their associative BNF under recommended N-fertilization have been investigated. Here, we attempted to isolate a large number of nitrogen-fixing bacteria associated with ROC22 sugarcane plants, investigate their diversity and predominant affiliation, and evaluate their potential for plant-growth promotion and associative BNF under the recommended N-fertilization. We initially obtained 196 fast-growing isolates from rhizosphere soil and roots of ROC22 sugarcane plants grown in 14 production areas. Nitrogen-fixing isolates were screened using the acetylene reduction assay (ARA) and PCR amplification of the nifH gene encoding the iron protein of nitrogenase (55). We found that enterobacteria were predominant among the obtained nitrogen-fixing bacteria by analyzing their 16S rRNA gene (rrs) sequences. We further screened their plant growth-promoting activities, including the production of indole acetic acids (IAA) and siderophores, phosphate solubilization and ACC (1-aminocyclopropane-1-carboxylic acid) deamination. Finally, we chose two Enterobacter spp. strains isolated from the same ROC22 plant to inoculate micropropagated ROC22 sugarcane seedlings and investigate their plant growth-promoting and associative BNF activities under the recommended N-fertilization for ROC22 crops using the 15N isotope dilution technique.