Nitrate uptake and carbon exudation – do plant roots stimulate or inhibit denitrification?

Abstract Background and aims Plant growth affects soil moisture, mineral N and organic C availability in soil, all of which influence denitrification. With increasing plant growth, root exudation may stimulate denitrification, while N uptake restricts nitrate availability. Methods We conducted a double labeling pot experiment with either maize (Zea mays L.) or cup plant (Silphium perfoliatum L.) of the same age but differing in size of their shoot and root systems. The 15N gas flux method was applied to directly quantify N2O and N2 fluxes in situ. To link denitrification with available C in the rhizosphere, 13CO2 pulse labeling was used to trace C translocation from shoots to roots and its release by roots into the soil. Results Plant water and N uptake were the main factors controlling daily N2O + N2 fluxes, cumulative N emissions, and N2O production pathways. Accordingly, pool-derived N2O + N2 emissions were 30–40 times higher in the treatment with highest soil NO3− content and highest soil moisture. CO2 efflux from soil was positively correlated with root dry matter, but we could not detect any relationship between root-derived C and N2O + N2 emissions. Conclusions Root-derived C may stimulate denitrification under small plants, while N and water uptake become the controlling factors with increasing plant and root growth.

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NO3- uptake and C exudation – do plant roots stimulate or inhibit denitrification?

10.5194/egusphere-egu2020-19445 ◽

2020 ◽

Author(s):

Pauline Sophie Rummel ◽

Reinhard Well ◽

Birgit Pfeiffer ◽

Klaus Dittert ◽

Sebastian Floßmann ◽

...

Keyword(s):

Soil Moisture ◽

N Uptake ◽

Root Exudation ◽

Soil Surface ◽

N Fertilization ◽

Plant N Uptake ◽

Mineral N ◽

Double Labeling ◽

Total N ◽

Organic C

Growing plants affect soil moisture, mineral N and organic C (Corg) availability in soil and may thus play an important role in regulating denitrification. The availability of the main substrates for denitrification (Corg and NO3-) is controlled by root activity and higher denitrification activity in rhizosphere soils has been reported. We hypothesized that (I) plant N uptake governs NO3- availability for denitrification leading to increased N2O and N2 emissions, when plant N uptake is low due to smaller root system or root senescence. (II) Denitrification is stimulated by higher Corg availability from root exudation or decaying roots increasing total gaseous N emissions while decreasing their N2O/(N2O+N2) ratios.We tested these assumptions in a double labeling pot experiment with maize (Zea mays L.) grown under three N fertilization levels S / M / L (no / moderate / high N fertilization) and with cup plant (Silphium perfoliatum L., moderate N fertilization). After 6 weeks, all plants were labeled with 0.1 g N kg-1 (Ca(15NO3)2, 60 at%), and the 15N tracer method was applied to estimate plant N uptake, N2O and N2 emissions. To link denitrification with available C in the rhizosphere, 13CO2 pulse labeling (5 g Na213CO3, 99 at%) was used to trace C translocation from shoots to roots and its release by roots into the soil. CO2 evolving from soil was trapped in NaOH for &#948;13C analyses, and gas samples were taken for analysis of N2O and N2 from the headspace above the soil surface every 12 h.Although pots were irrigated, changing soil moisture through differences in plant water uptake was the main factor controlling daily N2O+N2 fluxes, cumulative N emissions, and N2O production pathways. In addition, total N2O+N2 emissions were negatively correlated with plant N uptake and positively with soil N concentrations. Recently assimilated C released by roots (13C) was positively correlated with root dry matter, but we could not detect any relationship with cumulative N emissions. We anticipate that higher Corg availability in pots with large root systems did not lead to higher denitrification rates as NO3- was limited due to plant uptake. In conclusion, plant growth controlled water and NO3- uptake and, subsequently, formation of anaerobic hotspots for denitrification.

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Frequency Versus Quantity: Phenotypic Response of Two Wheat Varieties to Water and Nitrogen Variability

Journal of soil science and plant nutrition ◽

10.1007/s42729-021-00467-3 ◽

2021 ◽

Author(s):

Olivia H. Cousins ◽

Trevor P. Garnett ◽

Amanda Rasmussen ◽

Sacha J. Mooney ◽

Ronald J. Smernik ◽

...

Keyword(s):

Soil Moisture ◽

Plant Growth ◽

Carbon Allocation ◽

N Uptake ◽

N Availability ◽

Soil N ◽

High Moisture ◽

Mineral N ◽

Wheat Varieties ◽

The Impact

AbstractDue to climate change, water availability will become increasingly variable, affecting nitrogen (N) availability. Therefore, we hypothesised watering frequency would have a greater impact on plant growth than quantity, affecting N availability, uptake and carbon allocation. We used a gravimetric platform, which measures the unit of volume per unit of time, to control soil moisture and precisely compare the impact of quantity and frequency of water under variable N levels. Two wheat genotypes (Kukri and Gladius) were used in a factorial glasshouse pot experiment, each with three N application rates (25, 75 and 150 mg N kg−1 soil) and five soil moisture regimes (changing water frequency or quantity). Previously documented drought tolerance, but high N use efficiency, of Gladius as compared to Kukri provides for potentially different responses to N and soil moisture content. Water use, biomass and soil N were measured. Both cultivars showed potential to adapt to variable watering, producing higher specific root lengths under low N coupled with reduced water and reduced watering frequency (48 h watering intervals), or wet/dry cycling. This affected mineral N uptake, with less soil N remaining under constant watering × high moisture, or 48 h watering intervals × high moisture. Soil N availability affected carbon allocation, demonstrated by both cultivars producing longer, deeper roots under low N. Reduced watering frequency decreased biomass more than reduced quantity for both cultivars. Less frequent watering had a more negative effect on plant growth compared to decreasing the quantity of water. Water variability resulted in differences in C allocation, with changes to root thickness even when root biomass remained the same across N treatments. The preferences identified in wheat for water consistency highlights an undeveloped opportunity for identifying root and shoot traits that may improve plant adaptability to moderate to extreme resource limitation, whilst potentially encouraging less water and nitrogen use.

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Nitrate and water uptake, rather than rhizodeposition, control denitrification in the presence of growing plants

10.5194/egusphere-egu21-1223 ◽

2021 ◽

Author(s):

Pauline Sophie Rummel ◽

Reinhard Well ◽

Birgit Pfeiffer ◽

Klaus Dittert ◽

Sebastian Floßmann ◽

...

Keyword(s):

Soil Moisture ◽

Water Uptake ◽

Plant Root ◽

Oxygen Deficiency ◽

N Uptake ◽

Root Exudation ◽

Root Systems ◽

Plant N Uptake ◽

N Losses ◽

Double Labeling

The main prerequisites for denitrification are availability of nitrate (NO3-) and easily decomposable organic substances, and oxygen deficiency. Growing plants modify all these parameters and may thus play an important role in regulating denitrification. Previous studies investigating plant root effects on denitrification have found contradictive results. Both increased and decreased denitrification in the presence of plants have been reported and were associated with higher Corg or lower NO3- availability, respectively. Accordingly, it is still unclear whether growing plants stimulate denitrification through root exudation or restrict it through NO3- uptake. Furthermore, reliable measurements of N2 fluxes and N2O/(N2O+N2) ratios in the presence of plants are scarce.Therefore, we conducted a double labeling pot experiment with either maize (Zea mays L.) or cup plant (Silphium perfoliatum L.) of the same age but differing in size of their shoot and root systems. The 15N gas flux method was applied to directly quantify N2O and N2 fluxes in situ. To link denitrification with available C in the rhizosphere, 13CO2 pulse labeling was used to trace C translocation from shoots to roots and its release by roots into the soil.Plant water uptake was a main factor controlling soil moisture and, thus, daily N2O+N2 fluxes, cumulative N emissions, and N2O production pathways. However, N fluxes remained on a low level when NO3- availability was low due to rapid plant N uptake. Only when both N and water uptake were low, high NO3- availability and high soil moisture led to strongly increased denitrification-derived N losses.Total CO2 efflux was positively correlated with root dry matter, but there was no indication of any relationship between recovered 13C from root exudation and cumulative N emissions. We anticipate that higher Corg availability in pots with large root systems did not lead to higher denitrification rates, as NO3- was limiting denitrification due to plant N uptake. Overall, we conclude that root-derived C stimulates denitrification only when soil NO3- is not limited and low O2 concentrations enable denitrification. Thus, root-derived C may stimulate denitrification under small plants, while N and water uptake become the controlling factors with increasing plant and root growth.

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Manipulation of rhizosphere organisms to enhance glomalin production and C sequestration: Pitfalls and promises

Canadian Journal of Plant Science ◽

10.4141/cjps2013-146 ◽

2014 ◽

Vol 94 (6) ◽

pp. 1025-1032 ◽

Cited By ~ 11

Author(s):

F. L. Walley ◽

A. W. Gillespie ◽

Adekunbi B. Adetona ◽

J. J. Germida ◽

R. E. Farrell

Keyword(s):

Plant Growth ◽

Mycorrhizal Fungi ◽

Plant Growth Promoting Rhizobacteria ◽

C Sequestration ◽

Ionization Mass ◽

Edge Structure ◽

Organic C ◽

Soil C ◽

N Storage ◽

C And N

Walley, F. L., Gillespie, A. W., Adetona, A. B., Germida, J. J. and Farrell, R. E. 2014. Manipulation of rhizosphere organisms to enhance glomalin production and C-sequestration: Pitfalls and promises. Can. J. Plant Sci. 94: 1025–1032. Arbuscular mycorrhizal fungi (AMF) reportedly produce glomalin, a glycoprotein that has the potential to increase soil carbon (C) and nitrogen (N) storage. We hypothesized that interactions between rhizosphere microorganisms, such as plant growth-promoting rhizobacteria (PGPR), and AMF, would influence glomalin production. Our objectives were to determine the effects of AMF/PGPR interactions on plant growth and glomalin production in the rhizosphere of pea (Pisum sativum L.) with the goal of enhancing C and N storage in the rhizosphere. One component of the study focussed on the molecular characterization of glomalin and glomalin-related soil protein (GRSP) using complementary synchrotron-based N and C X-ray absorption near-edge structure (XANES) spectroscopy, pyrolysis field ionization mass spectrometry (Py-FIMS), and proteomics techniques to characterize specific organic C and N fractions associated with glomalin production. Our research ultimately led us to conclude that the proteinaceous material extracted, and characterized in the literature, as GRSP is not exclusively of AMF origin. Our research supports the established concept that GRSP is important to soil quality, and C and N storage, irrespective of origin. However, efforts to manipulate this important soil C pool will remain compromised until we more clearly elucidate the chemical nature and origin of this resource.

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Sediment community responses to marine vs. terrigenous organic matter in a submarine canyon

Biogeosciences ◽

10.5194/bg-10-67-2013 ◽

2013 ◽

Vol 10 (1) ◽

pp. 67-80 ◽

Cited By ~ 29

Author(s):

W. R. Hunter ◽

A. Jamieson ◽

V. A. I. Huvenne ◽

U. Witte

Keyword(s):

Organic Matter ◽

Feeding Activity ◽

N Uptake ◽

Bacterial Biomass ◽

Submarine Canyon ◽

Stable Isotope Labelling ◽

C And N ◽

13C Label ◽

Experimental Treatments

Abstract. The Whittard Canyon is a branching submarine canyon on the Celtic continental margin, which may act as a conduit for sediment and organic matter (OM) transport from the European continental slope to the abyssal sea floor. In situ stable-isotope labelling experiments were conducted in the eastern and western branches of the Whittard Canyon, testing short-term (3–7 days) responses of sediment communities to deposition of nitrogen-rich marine (Thalassiosira weissflogii) and nitrogen-poor terrigenous (Triticum aestivum) phytodetritus. 13C and 15N labels were traced into faunal biomass and bulk sediments, and the 13C label traced into bacterial polar lipid fatty acids (PLFAs). Isotopic labels penetrated to 5 cm sediment depth, with no differences between stations or experimental treatments (substrate or time). Macrofaunal assemblage structure differed between the eastern and western canyon branches. Following deposition of marine phytodetritus, no changes in macrofaunal feeding activity were observed between the eastern and western branches, with little change between 3 and 7 days. Macrofaunal C and N uptake was substantially lower following deposition of terrigenous phytodetritus with feeding activity governed by a strong N demand. Bacterial C uptake was greatest in the western branch of the Whittard Canyon, but feeding activity decreased between 3 and 7 days. Bacterial processing of marine and terrigenous OM were similar to the macrofauna in surficial (0–1 cm) sediments. However, in deeper sediments bacteria utilised greater proportions of terrigenous OM. Bacterial biomass decreased following phytodetritus deposition and was negatively correlated to macrofaunal feeding activity. Consequently, this study suggests that macrofaunal–bacterial interactions influence benthic C cycling in the Whittard Canyon, resulting in differential fates for marine and terrigenous OM.

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Effect of incubation time and substrate concentration on N-uptake rates by phytoplankton in the Bay of Bengal

Biogeosciences Discussions ◽

10.5194/bgd-2-1331-2005 ◽

2005 ◽

Vol 2 (5) ◽

pp. 1331-1352

Author(s):

S. Kumar ◽

R. Ramesh ◽

S. Sardesai ◽

M. S. Sheshshayee

Keyword(s):

Incubation Time ◽

Uptake Rate ◽

Nitrate Uptake ◽

N Uptake ◽

Marine Phytoplankton ◽

Total Production ◽

New Production ◽

Urea Uptake ◽

Uptake Rates

Abstract. We report here the results of three experiments, which are slight variations of the 15N method (JGOFS protocol) for determination of new production. The first two test the effect of (i) duration of incubation time and (ii) concentration of tracer added on the uptake rates of various N-species (nitrate, ammonium and urea) by marine phytoplankton; while the third compares in situ and deck incubations from dawn to dusk. Results indicate that nitrate uptake can be underestimated by experiments where incubation times shorter than 4h or when more than 10% of the ambient concentration of nitrate is added prior to incubation. The f-ratio increases from 0.28 to 0.42 when the incubation time increases from two to four hours. This may be due to the observed increase in the uptake rate of nitrate and decrease in the urea uptake rate. Unlike ammonium [y{=}2.07x{-}0.002\\, (r2=0.55)] and urea uptakes [y{=}1.88x{+}0.004 (r2=0.88)], the nitrate uptake decreases as the concentration of the substrate (x) increases, showing a negative correlation [y{=}-0.76x+0.05 (r2=0.86)], possibly due to production of glutamine, which might suppress nitrate uptake. This leads to decline in the f-ratio from 0.47 to 0.10, when concentration of tracer varies from 0.01 to 0.04μ M. The column integrated total productions are 519 mg C m-2 d-1 and 251 mg C m-2 d-1 for in situ and deck incubations, respectively. The 14C based production at the same location is ~200 mg C m-2 d-1, which is in closer agreement to the 15N based total production measured by deck incubation.

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Denitrification and denitrifying efficiencies in sediments of Port Phillip Bay: direct determinations of biogenic N2 and N-metabolite fluxes with implications for water quality

Marine and Freshwater Research ◽

10.1071/mf98054 ◽

1999 ◽

Vol 50 (6) ◽

pp. 589 ◽

Cited By ~ 26

Author(s):

David T. Heggie ◽

Graham W. Skyring ◽

Joseph Orchardo ◽

Andrew R. Longmore ◽

Geoffrey J. Nicholson ◽

...

Keyword(s):

Organic Carbon ◽

Sedimentary Facies ◽

Precision Measurements ◽

Organic C ◽

Redfield Ratio ◽

Tightly Coupled ◽

C And N ◽

Muddy Sediments ◽

Nitrate And Nitrite

High-precision measurements of N2 in benthic chamber waters indicated that denitrification occurs within the major sedimentary facies in Port Phillip Bay. The integrated fluxes of biogenic N2 , ammonia, nitrate and nitrite showed that the stoichiometric relationship between organic C and N in the muddy sediments, occupying about 70% of the seafloor, was 5.7, this being similar to the Redfield ratio of 6.6. High denitrifying efficiencies (75–85%; denitrification rates ~1.3 mmol N2 m–2 day–1) at organic carbon loadings of ~15–25 mmol m–2 day–1 indicate that most N processed through the sediments was returned to the overlying waters as biologically (generally) unavailable N2. At sites of high organic carbon loadings to the sediments (>100 mmol m–2 day–1) denitrification rates and denitrifying efficiencies were near zero and most N is returned to the Bay waters as biologically available ammonium. In chambers ‘spiked’ with 15NO3 , denitrifyers used nitrate produced in the sediments in situ, rather than the exogenous nitrate in overlying waters. The sedimentary microbial processes of ammonification, nitrification and denitrification are therefore tightly coupled.

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Seasonal trends in selected soil biochemical attributes: Effects of crop rotation in the semiarid prairie

Canadian Journal of Soil Science ◽

10.4141/s98-008 ◽

1999 ◽

Vol 79 (1) ◽

pp. 73-84 ◽

Cited By ~ 38

Author(s):

C. A. Campbell ◽

V. O. Biederbeck ◽

G. Wen ◽

R. P. Zentner ◽

J. Schoenau ◽

...

Keyword(s):

Soil Moisture ◽

Microbial Biomass ◽

Microbial Biomass Carbon ◽

Light Fraction ◽

Water Soluble ◽

Microbial Biomass C ◽

Weather Variables ◽

Total N ◽

Organic C ◽

C And N

Measurements of seasonal changes in soil biochemical attributes can provide valuable information on how crop management and weather variables influence soil quality. We sampled soil from the 0- to 7.5-cm depth of two long-term crop rotations [continuous wheat (Cont W) and both phases of fallow-wheat (F–W)] at Swift Current, Saskatchewan, from early May to mid-October, 11 times in 1995 and 9 times in 1996. The soil is a silt loam, Orthic Brown Chernozem with pH 6.0, in dilute CaCl2. We monitored changes in organic C (OC) and total N (TN), microbial biomass C (MBC), light fraction C and N (LFC and LFN), mineralizable C (Cmin) and N (Nmin), and water-soluble organic C (WSOC). All biochemical attributes, except MBC, showed higher values for Cont W than for F–W, reflecting the historically higher crop residue inputs, less frequent tillage, and drier conditions of Cont W. Based on the seasonal mean values for 1996, we concluded that, after 29 yr, F–W has degraded soil organic C and total N by about 15% compared to Cont W. In the same period it has degraded the labile attributes, except MBC, much more. For example, WSOC is degraded by 22%, Cmin and Nmin by 45% and LFC and LFN by 60–75%. Organic C and TN were constant during the season because one year's C and N inputs are small compared to the total soil C or N. All the labile attributes varied markedly throughout the seasons. We explained most of the seasonal variability in soil biochemical attributes in terms of C and N inputs from crop residues and rhizodeposition, and the influences of soil moisture, precipitation and temperature. Using multiple regression, we related the biochemical attributes to soil moisture and the weather variables, accounting for 20% of the variability in MBC, 27% of that of Nmin, 29% for LFC, 52% for Cmin, and 66% for WSOC. In all cases the biochemical attributes were negatively related to precipitation, soil moisture, temperature and their interactions. We interpreted this to mean that conditions favouring decomposition of organic matter in situ result in decreases in these attributes when they are measured subsequently under laboratory conditions. We concluded that when assessing changes in OC or TN over years, measurements can be made at any time during a year. However, if assessing changes in the labile soil attributes, several measurements should be made during a season or, measurements be made near the same time each year. Key words: Microbial biomass, carbon, nitrogen, mineralization, water-soluble-C, light fraction, weather variables

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Interactions between reserve mobilization and regulation of nitrate uptake during regrowth of Lolium perenne L.: putative roles of amino acids and carbohydrates

Botany ◽

10.1139/b08-066 ◽

2008 ◽

Vol 86 (10) ◽

pp. 1101-1110 ◽

Cited By ~ 11

Author(s):

S. Louahlia ◽

P. Laine ◽

J. H. MacDuff ◽

A. Ourry ◽

M. Humphreys ◽

...

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Lolium Perenne ◽

Nitrate Uptake ◽

N Uptake ◽

Water Soluble ◽

Mineral N ◽

Physiological Basis ◽

Lolium Perenne L ◽

Amino Acid Concentrations

In most forage grass and legume species the recovery of leaf growth following severe defoliation depends on mobilization of carbon and nitrogen reserves from the remaining tissues. Unusually, Lolium perenne L. is able to compensate for low levels of available N storage compounds by rapid up-regulation of mineral N uptake. To investigate the physiological basis of this behaviour, perennial ryegrass plants were exposed to a 10 d period of optimal mineral N (high-N plants) or zero N (low-N plants) supply before defoliation. N deprivation decreased total N and amino acid concentrations in roots, and increased root water soluble carbohydrate concentrations. Compared with high-N plants (control), fructans and fructose concentrations in roots of low-N plants were 74% and 49% higher, respectively. Low-N plants had higher rates of nitrate uptake following defoliation, and lower amino acid concentrations in the roots (mainly as asparagine and glutamine); a causal role was suggested by the inhibition of nitrate uptake by external root supply of amino acids to low-N plants or by a stimulation of N uptake of high-N plants by sucrose supply to the roots. The results suggest that down-regulation of nitrate uptake following defoliation of plants with high levels of N reserves, may be effected through an increased cycling of amino acids within the plant and by a shortage of carbohydrates. Results are discussed in relation to the proteolytic activities and mobilization of C and N reserves to leaf meristem.

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First in situ estimations of small phytoplankton carbon and nitrogen uptake rates in the Kara, Laptev, and East Siberian seas

Biogeosciences ◽

10.5194/bg-15-5503-2018 ◽

2018 ◽

Vol 15 (18) ◽

pp. 5503-5517 ◽

Cited By ~ 6

Author(s):

P. Sadanandan Bhavya ◽

Jang Han Lee ◽

Ho Won Lee ◽

Jae Joong Kang ◽

Jae Hyung Lee ◽

...

Keyword(s):

Sea Ice ◽

Nitrogen Uptake ◽

Isotope Labeling ◽

N Uptake ◽

The Arctic ◽

Carbon And Nitrogen ◽

Uptake Rates ◽

Small Phytoplankton ◽

C And N

Abstract. Carbon and nitrogen uptake rates by small phytoplankton (0.7–5 µm) in the Kara, Laptev, and East Siberian seas in the Arctic Ocean were quantified using in situ isotope labeling experiments; this research, which was novel and part of the NABOS (Nansen and Amundsen Basins Observational System) program, took place from 21 August to 22 September 2013. The depth-integrated carbon (C), nitrate (NO3-), and ammonium (NH4+) uptake rates by small phytoplankton ranged from 0.54 to 15.96 mg C m−2 h−1, 0.05 to 1.02 mg C m−2 h−1, and 0.11 to 3.73 mg N m−2 h−1, respectively. The contributions of small phytoplankton towards the total C, NO3-, and NH4+ varied from 25 % to 89 %, 31 % to 89 %, and 28 % to 91 %, respectively. The turnover times for NO3- and NH4+ by small phytoplankton found in the present study indicate the longer residence times (years) of the nutrients in the deeper waters, particularly for NO3-. Additionally, the relatively higher C and N uptake rates by small phytoplankton obtained in the present study from locations with less sea ice concentration indicate the possibility that small phytoplankton thrive under the retreat of sea ice as a result of warming conditions. The high contributions of small phytoplankton to the total C and N uptake rates suggest the capability of small autotrophs to withstand the adverse hydrographic conditions introduced by climate change.

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