Effects of nitrogen: phosphorus supply ratios on nitrogen fixation in agricultural and pastoral ecosystems

Smith, Val H.

doi:10.1007/bf00000424

Cited by 114 publications

(80 citation statements)

References 44 publications

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“…We found that asymbiotic BNF was only detectable in intershrub soils at sites S-4 and S-44 (Figure 9a), which exhibited significantly lower N:P ratios than adjacent shrub soils (Figure 7b). These findings reinforce the theory that increases of inorganic N relative to available P inhibit nitrogenase activity, the enzyme responsible for mediating the adenosine triphosphate-reduction of N2 to ammonia in 10 BNF (Smith, 1992). However, despite intershrub soil N:P ratios remaining constant with increasing encroachment, there was an absence of asymbiotic BNF at S-56.…”

Section: Inputs Of Asymbiotically-fixed Nitrogensupporting

confidence: 79%

Soil nitrogen response to shrub encroachment in a degrading semiarid grassland

Turpin-Jelfs¹,

Michaelides²,

Anesio³

2018

Preprint

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Abstract. Transitions from grass- to shrub-dominated states in drylands by woody plant encroachment represent significant forms of land cover change with the potential to alter the spatial distribution and cycling of soil resources. Yet an understanding of how this phenomenon impacts the soil nitrogen pool, which is essential to primary production in arid and semiarid systems, is poorly resolved. In this study, we quantified how the distribution and speciation of soil nitrogen, as well as rates of free-living biological nitrogen fixation, changed along a gradient of increasing mesquite (Prosopis velutina Woot.) cover in a semiarid grassland of the Southwestern US. Our results show that site-level concentrations of total nitrogen remain unchanged with increasing shrub cover as losses from intershrub areas (sum of grass and bare-soil cover) are proportional to increases in soils under shrub canopies. However, despite the similar carbon-to-nitrogen ratio and microbial biomass of soil from intershrub and shrub areas at each site, site-level concentrations of inorganic nitrogen increase with shrub cover due to the accumulation of ammonium and nitrate in soils beneath shrub canopies. Using the acetylene reduction assay technique, we found increasing ratios of inorganic nitrogen-to-bioavailable phosphorus inhibit rates of biological nitrogen fixation by free-living soil bacteria. Consequently, we conclude that shrub encroachment has the potential to significantly alter the dynamics of soil nitrogen cycling in dryland systems.

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Section: Inputs Of Asymbiotically-fixed Nitrogensupporting

confidence: 79%

Soil nitrogen response to shrub encroachment in a degrading semiarid grassland

Turpin-Jelfs¹,

Michaelides²,

Anesio³

2018

Preprint

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“…Our model also does not consider direct biological nitrogen fixation, either by vascular plant symbioses or by heterotrophic bacteria, a potentially important ecosystem N source (28), the magnitude of which may depend on P availability (50). Incorporating biological N fixation into the model does not qualitatively change our conclusions.…”

Section: Discussionmentioning

confidence: 97%

Increased plant growth from nitrogen addition should conserve phosphorus in terrestrial ecosystems

Perring

Hedin

Levin

et al. 2008

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

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Inputs of available nitrogen (N) to ecosystems have grown over the recent past. There is limited general understanding of how increased N inputs affect the cycling and retention of other potentially limiting nutrients. Using a plant-soil nutrient model, and by explicitly coupling N and phosphorus (P) in plant biomass, we examine the impact of increasing N supply on the ecosystem cycling and retention of P, assuming that the main impact of N is to increase plant growth. We find divergent responses in the P cycle depending on the specific pathway by which nutrients are lost from the ecosystem. Retention of P is promoted if the relative propensity for loss of plant available P is greater than that for the loss of less readily available organic P. This is the first theoretical demonstration that the coupled response of ecosystem-scale nutrient cycles critically depends on the form of nutrient loss. P retention might be lessened, or reversed, depending on the kinetics and size of a buffering reactive P pool. These properties determine the reactive pool's ability to supply available P. Parameterization of the model across a range of forest ecosystems spanning various environmental and climatic conditions indicates that enhanced plant growth due to increased N should trigger increased P conservation within ecosystems while leading to more dissolved organic P loss. We discuss how the magnitude and direction of the effect of N may also depend on other processes.nitrogen cycle ͉ nitrogen inputs ͉ phosphorus cycle ͉ phosphorus retention H uman activities have caused increased nitrogen (N) inputs to ecosystems through atmospheric deposition, fertilizers, and spread of N-fixing plants (1-3). The effects of N enrichment have been considered with respect to the N cycle and in relation to carbon (C) storage (4-6), yet there is limited general understanding of how increased N inputs affect the cycling and retention of other important nutrients, such as phosphorus (P) (7). N and P are important for ecosystem functioning because both nutrients commonly limit production of plant biomass (8). The response of plant production to atmospheric deposition, climate change, and other modern human influences will therefore be mediated by changes in the availability of these elements. However, essential elements do not cycle through the ecosystem independently. Through growth and metabolism, plants couple N and P and other required elements in relatively constrained ratios (9, 10), causing nutrient cycles to be linked at the scale of entire ecosystems (11). Although recent studies have focused on the impact of increased N on ecosystem C balances (5, 6), the question of how increased N affects the internal distribution, cycling, and forms of P loss from systems remains largely unexplored, except for a few experimental studies (12, 13). Given the importance of P in regulating ecosystem processes, such as plant production or decomposition, sometimes in combination with N (8, 14, 15), and potentially governing long term ecosystem dynamics (16), ...

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“…The rate and amount of soil N-fixation activity is associated with the development of the organic C and N composition in soils, and is also known to be regulated by a feedback inhibition mechanism that is activated in the presence of higher N:P ratios or lower concentrations of P (Eisele et al 1989, Smith 1992, Israel 1993, Almeida et al 2000, Schulze 2004, Pons et al 2007, Reed et al 2007. This is consistent with the results of our work in which there were somewhat greater concentrations of total N and much lower concentrations of P in the PM-L soils, resulting in higher N:P ratios (i.e., P limited), greater soil C biomass, greater rates of both C and N biomass production, and a more fungaldominant microbial community in the PM-L soils.…”

Section: Discussionmentioning

confidence: 99%

“…Changes in N:P ratios have been associated with increases in microbial activity and biomass, N and P cycle processes, and microbial community structure (Leahy and Colwell 1990, Smith 1992, Smith et al 1998, Cleveland and Townsend 2006, Allison et al 2007, Cruz et al 2008. It has also been shown that well-established tropical forest soils tend towards more P than nitrogen limitation (Vitousek & Farrington 1997, Sollins 1998, Hedin et al 2003, resulting in higher N:P ratios, in part due to the extensive amount of nitrogen fixation that occurs (Vitousek & Howarth 1991, Cleveland et al 1999, Galloway et al 2004, and as a result of the decomposition of greater amounts of forest litter and vegetation tissues (see McGroddy et al 2004 for a review).…”

Section: Discussionmentioning

confidence: 99%