Nodulation of legumes, nitrogenase activity of roots and occurrence of nitrogen-fixing Azospirillum ssp. in representative soils of central Amazonia

Sylvester-Bradley, Rosemary; Oliveira, Luiz Antonio de; PodestáFilho, J.A. De; John, T. V. St.

doi:10.1016/0304-3746(80)90025-6

Cited by 58 publications

(32 citation statements)

References 10 publications

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“…1). Such high estimates of symbiotic BNF are consistent with the large number of leguminous trees in tropical forest (18)(19)(20). However, many legume species do not form N-fixing nodules (21), and of those species that do, nodulation in individuals varies with soil nutrient status, N demand, and tree age (22).…”

Section: Significancementioning

confidence: 50%

Spatially robust estimates of biological nitrogen (N) fixation imply substantial human alteration of the tropical N cycle

Sullivan

Smith

Townsend

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

149

185

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Significance Biological nitrogen fixation (BNF) is the largest natural source of new nitrogen (N) to terrestrial ecosystems. Tropical forest ecosystems are a putative global hotspot of BNF, but direct, spatially explicit measurements in the biome are virtually nonexistent. Nonetheless, robust estimates of tropical forest BNF are critical for understanding how these important ecosystems may respond to global change and assessing human perturbations to the N cycle. Here, we introduce a spatial sampling method to assess BNF and present evidence that tropical forest BNF is much lower than previously assumed. Our results imply that humans have roughly doubled N inputs to the tropical forest biome relative to N inputs through BNF.

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Section: Significancementioning

confidence: 50%

Spatially robust estimates of biological nitrogen (N) fixation imply substantial human alteration of the tropical N cycle

Sullivan

Smith

Townsend

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

149

185

View full text Add to dashboard Cite

show abstract

“…When interpreted retrospectively, previous field studies appear to support our finding of facultative N 2 fixation. Mature forests are often characterized by low rates of nodulation (Sylvester-Bradley et al 1980;Walter and Bien 1989;Moriera and Franco 1994;Pearson and Vitousek 2001). In addition, secondary and flooded forests often report elevated nodulation (Sylvester-Bradley et al 1980;Moriera and Franco 1994;Saur et al 1998;Koponen et al 2003).…”

Section: Ecosystem Nutrient Feedbacksmentioning

confidence: 97%

Facultative nitrogen fixation by canopy legumes in a lowland tropical forest

2010

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Symbiotic dinitrogen (N(2)) fixation is often invoked to explain the N richness of tropical forests as ostensibly N(2)-fixing trees can be a major component of the community. Such arguments assume N(2) fixers are fixing N when present. However, in laboratory experiments, legumes consistently reduce N(2) fixation in response to increased soil N availability. These contrasting views of N(2) fixation as either obligate or facultative have drastically different implications for the N cycle of tropical forests. We tested these models by directly measuring N(2)-fixing root nodules and nitrogenase activity of individual canopy-dominant legume trees (Inga sp.) across several lowland forest types. Fixation was substantial in disturbed forests and some gaps but near zero in the high N soils of mature forest. Our findings suggest that canopy legumes closely regulate N(2) fixation, leading to large variations in N inputs across the landscape, and low symbiotic fixation in mature forests despite abundant legumes.

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“…The general consensus from these studies is that the presence of fixers points to N fixation input capacity, though nodulation is a species-dependent property that varies across ecosystem conditions (Sylvester-Bradley et al, 1980;Sprent and Raven, 1985). Free-living rates of fixation in rocks and soil are lower than symbiotic ones, but the widespread distribution of cryptograms, and the capacity of such organisms to respond rapidly to change, means that this functional group is globally important, perhaps accounting for up to 50 % of terrestrial N fixation (Elbert et al, 2012).…”

Section: Organismsmentioning

confidence: 99%

A new synthesis for terrestrial nitrogen inputs

Houlton

Morford

2015

SOIL

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Abstract. Nitrogen (N) inputs sustain many different aspects of local soil processes, their services, and their interactions with the broader Earth system. We present a new synthesis for terrestrial N inputs that explicitly considers both rock and atmospheric sources of N. We review evidence for state-factor regulation over biological fixation, deposition, and rock-weathering inputs from local to global scales and in transient vs. steady-state landscapes. Our investigation highlights strong organism and topographic (relief) controls over all three N input pathways, with the anthropogenic factor clearly important in rising N deposition rates. In addition, the climate, parent material, and time factors are shown to influence patterns of fixation and rock-weathering inputs of N in diverse soil systems. Data reanalysis suggests that weathering of N-rich parent material could resolve several known cases of "missing N inputs" in ecosystems, and demonstrates how the inclusion of rock N sources into modern concepts can lead to a richer understanding of spatial and temporal patterns of ecosystem N availability. For example, explicit consideration of rock N inputs into classic pedogenic models (e.g., the Walker and Syers model) yields a fundamentally different expectation from the standard case: weathering of N-rich parent material could enhance N availability and facilitate terrestrial succession in developmentally young sites even in the absence of N-fixing organisms. We conclude that a state-factor framework for N complements our growing understanding multiple-source controls on phosphorus and cation availability in Earth's soil, but with significant exceptions given the lack of an N fixation analogue in all other biogeochemical cycles. Rather, non-symmetrical feedbacks among input pathways in which high N inputs via deposition or rock-weathering sources have the potential to reduce biological fixation rates mark N as fundamentally different from other nutrients. The new synthesis for terrestrial N inputs provides a novel set of research issues and opportunities in the multidisciplinary Earth system sciences, with implications for patterns of N limitation, tectonic controls over biogeochemical cycling, and carbon-nutrient-climate interactions.

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Nodulation of legumes, nitrogenase activity of roots and occurrence of nitrogen-fixing Azospirillum ssp. in representative soils of central Amazonia

Cited by 58 publications

References 10 publications

Spatially robust estimates of biological nitrogen (N) fixation imply substantial human alteration of the tropical N cycle

Spatially robust estimates of biological nitrogen (N) fixation imply substantial human alteration of the tropical N cycle

Facultative nitrogen fixation by canopy legumes in a lowland tropical forest

A new synthesis for terrestrial nitrogen inputs

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