scholarly journals Symbiosis revisited: phosphorus and acid buffering stimulate N<sub>2</sub> fixation but not <i>Sphagnum</i> growth

2016 ◽  
Author(s):  
Eva van den Elzen ◽  
Martine A. R. Kox ◽  
Sarah F. Harpenslager ◽  
Geert Hensgens ◽  
Christian Fritz ◽  
...  
Keyword(s):  
Nitrogen Fixation ◽  
Negative Impact ◽  
Plant Performance ◽  
Phosphorus Addition ◽  
Dissolved Nitrogen ◽  
Field Situation ◽  
Deposition Area ◽  
Acid Buffering ◽  
Limiting Nutrient ◽  
Sphagnum Palustre

Abstract. In pristine Sphagnum dominated peatlands, (di)nitrogen (N2) fixing (diazotrophic) microbial communities associated with Sphagnum mosses contribute substantially to the total nitrogen input, increasing carbon sequestration. The rates of symbiotic nitrogen fixation reported for Sphagnum peatlands, are, however, highly variable and experimental work on regulating factors that can mechanistically explain this variation is largely lacking. For two common fen species (Sphagnum palustre and S. squarrosum) from a high nitrogen deposition area (25 kg N ha−1 y−1), we found that diazotrophic activity (as measured by 15–15N2 labeling) was still present. This was surprising, given that nitrogen fixation is a costly process. We tested the effects of phosphorus availability and buffering capacity by bicarbonate rich water, mimicking a field situation in fens with stronger groundwater or surface water influence, as potential regulators of nitrogen fixation rates and Sphagnum performance. We expected that the addition of phosphorus, being a limiting nutrient, would stimulate both diazotrophic activity and Sphagnum growth. We indeed found that nitrogen fixation rates were doubled. Plant performance, in contrast, did not increase. Raised bicarbonate levels also enhanced nitrogen fixation, but had a strong negative impact on Sphagnum performance. These results explain the higher nitrogen fixation rates reported for minerotrophic and more nutrient-rich peatlands. The contrasting effects of phosphorus and bicarbonate on Sphagnum spp and their diazotrophic communities reveal strong differences in optimal niche for both partners with respect to conditions and resources. This suggests a trade-off for the symbiosis of nitrogen fixing microorganisms with their Sphagnum hosts, in which a sheltered environment apparently outweighs the less favorable environmental conditions. We conclude that microbial activity is still nitrogen limited under eutrophic conditions because dissolved nitrogen is being monopolized by Sphagnum. Moreover, the fact that diazotrophic activity can significantly be upregulated by increased phosphorus addition and acid buffering, while Sphagnum spp do not benefit, reveals remarkable differences in optimal conditions for both symbiotic partners and questions the concept of a direct mutualism.

scholarly journals Symbiosis revisited: phosphorus and acid buffering stimulate N<sub>2</sub> fixation but not <i>Sphagnum</i> growth

2017 ◽  
Vol 14 (5) ◽  
pp. 1111-1122 ◽  
Author(s):  
Eva van den Elzen ◽  
Martine A. R. Kox ◽  
Sarah F. Harpenslager ◽  
Geert Hensgens ◽  
Christian Fritz ◽  
...  
Keyword(s):  
Nitrogen Fixation ◽  
Nitrogen Deposition ◽  
Negative Impact ◽  
Nitrogen Loading ◽  
Plant Performance ◽  
High Nitrogen ◽  
Phosphorus Addition ◽  
Field Situation ◽  
Acid Buffering ◽  
Limiting Nutrient

Abstract. In pristine Sphagnum-dominated peatlands, (di)nitrogen (N2) fixing (diazotrophic) microbial communities associated with Sphagnum mosses contribute substantially to the total nitrogen input, increasing carbon sequestration. The rates of symbiotic nitrogen fixation reported for Sphagnum peatlands, are, however, highly variable, and experimental work on regulating factors that can mechanistically explain this variation is largely lacking. For two common fen species (Sphagnum palustre and S. squarrosum) from a high nitrogen deposition area (25 kg N ha−1 yr−1), we found that diazotrophic activity (as measured by 15 − 15N2 labeling) was still present at a rate of 40 nmol N gDW−1 h−1. This was surprising, given that nitrogen fixation is a costly process. We tested the effects of phosphorus availability and buffering capacity by bicarbonate-rich water, mimicking a field situation in fens with stronger groundwater or surface water influence, as potential regulators of nitrogen fixation rates and Sphagnum performance. We expected that the addition of phosphorus, being a limiting nutrient, would stimulate both diazotrophic activity and Sphagnum growth. We indeed found that nitrogen fixation rates were doubled. Plant performance, in contrast, did not increase. Raised bicarbonate levels also enhanced nitrogen fixation, but had a strong negative impact on Sphagnum performance. These results explain the higher nitrogen fixation rates reported for minerotrophic and more nutrient-rich peatlands. In addition, nitrogen fixation was found to strongly depend on light, with rates 10 times higher in light conditions suggesting high reliance on phototrophic organisms for carbon. The contrasting effects of phosphorus and bicarbonate on Sphagnum spp. and their diazotrophic communities reveal strong differences in the optimal niche for both partners with respect to conditions and resources. This suggests a trade-off for the symbiosis of nitrogen fixing microorganisms with their Sphagnum hosts, in which a sheltered environment apparently outweighs the less favorable environmental conditions. We conclude that microbial activity is still nitrogen limited under eutrophic conditions because dissolved nitrogen is being monopolized by Sphagnum. Moreover, the fact that diazotrophic activity can significantly be upregulated by increased phosphorus addition and acid buffering, while Sphagnum spp. do not benefit, reveals remarkable differences in optimal conditions for both symbiotic partners and calls into question the regulation of nitrogen fixation by Sphagnum under these eutrophic conditions. The high nitrogen fixation rates result in high additional nitrogen loading of 6 kg ha−1 yr−1 on top of the high nitrogen deposition in these ecosystems.

scholarly journals Active layer slope disturbances affect seasonality and composition of dissolved nitrogen export from High Arctic headwater catchments

2017 ◽  
Vol 3 (2) ◽  
pp. 429-450 ◽  
Author(s):  
Melissa J. Lafrenière ◽  
Nicole L. Louiseize ◽  
Scott F. Lamoureux
Keyword(s):  
Active Layer ◽  
High Arctic ◽  
Rainfall Runoff ◽  
Headwater Catchments ◽  
Dissolved Nitrogen ◽  
Total Dissolved Nitrogen ◽  
Nitrate Export ◽  
Limiting Nutrient ◽  
Seasonal Discharge ◽  
The Impact

This study investigates the impacts of active layer detachments (ALDs) on nitrogen in seasonal runoff from High Arctic hillslope catchments. We examined dissolved nitrogen in runoff from an undisturbed catchment (Goose (GS)) and one that was disturbed (Ptarmigan (PT)) by ALDs, prior to disturbance (2007) and 5 years after disturbance (2012). The seasonal dynamics of nitrogen species concentrations and fluxes were similar in both catchments in 2007, but the mean seasonal nitrate concentration and mass flux from the disturbed catchment were on the order of 30 times higher relative to the undisturbed catchment in 2012. Stormflow yielded 45% and 60% of the 2012 total dissolved nitrogen flux in GS and PT, respectively, although rainfall runoff provided less than 25% of seasonal discharge. Results support that through the combined effects of increased disturbance and rainfall, climate change stands to significantly enhance the export of nitrate from High Arctic watersheds. This study highlights that the increase in the delivery of nitrate from disturbance is especially pronounced late in the season when downstream productivity and the biological demand for this often limiting nutrient are high. Our results also demonstrate that the impact of ALDs on nitrate export can persist more than 5 years following disturbance.

scholarly journals Effect of UV Radiation and Salt Stress on the Accumulation of Economically Relevant Secondary Metabolites in Bell Pepper Plants

Agronomy ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 142 ◽  
Author(s):  
Jan Ellenberger ◽  
Nils Siefen ◽  
Priska Krefting ◽  
Jan-Bernd Schulze Lutum ◽  
Daniel Pfarr ◽  
...  
Keyword(s):  
Salt Stress ◽  
Secondary Metabolites ◽  
Negative Impact ◽  
Stress Conditions ◽  
Bell Pepper ◽  
Plant Performance ◽  
Production Cycle ◽  
Stress Effects ◽  
Leaf Level ◽  
Uv Stress

The green biomass of horticultural plants contains valuable secondary metabolites (SM), which can potentially be extracted and sold. When exposed to stress, plants accumulate higher amounts of these SMs, making the extraction and commercialization even more attractive. We evaluated the potential for accumulating the flavones cynaroside and graveobioside A in leaves of two bell pepper cultivars (Mavras and Stayer) when exposed to salt stress (100 mM NaCl), UVA/B excitation (UVA 4–5 W/m2; UVB 10–14 W/m2 for 3 h per day), or a combination of both stressors. Plant age during the trials was 32–48 days. HPLC analyses proved the enhanced accumulation of both metabolites under stress conditions. Cynaroside accumulation is effectively triggered by high-UV stress, whereas graveobioside A contents increase under salt stress. Highest contents of secondary metabolites were observed in plants exposed to combined stress. Effects of stress on overall plant performance differed significantly between treatments, with least negative impact on above ground biomass found for high-UV stressed plants. The usage of two non-destructive instruments (Dualex and Multiplex) allowed us to gain insights into the ontogenetical effects at the leaf level and temporal development of SM contents. Indices provided by those devices correlate fairly with amounts detected via HPLC (Cynaroside: r2 = 0.46–0.66; Graveobioside A: r2 = 0.51–0.71). The concentrations of both metabolites tend to decrease at leaf level during the ontogenetical development even under stress conditions. High-UV stress should be considered as a tool for enriching plant leaves with valuable SM. Effects on the performance of plants throughout a complete production cycle should be evaluated in future trials. All data is available online.

scholarly journals What prevents nitrogen depletion in the oxygen minimum zone of the eastern tropical South Pacific?

2015 ◽  
Vol 12 (4) ◽  
pp. 1113-1130 ◽  
Author(s):  
B. Su ◽  
M. Pahlow ◽  
H. Wagner ◽  
A. Oschlies
Keyword(s):  
Nitrogen Fixation ◽  
Ocean Circulation ◽  
Deep Ocean ◽  
South Pacific ◽  
Open Ocean ◽  
Nitrogen Depletion ◽  
Biogeochemical Models ◽  
Model Domain ◽  
Limiting Nutrient ◽  
Oxygen Minimum

Abstract. Local coupling between nitrogen fixation and denitrification in current biogeochemical models could result in runaway feedback in open-ocean oxygen minimum zones (OMZs), eventually stripping OMZ waters of all fixed nitrogen. This feedback does not seem to operate at full strength in the ocean, as nitrate does not generally become depleted in open-ocean OMZs. To explore in detail the possible mechanisms that prevent nitrogen depletion in the OMZ of the eastern tropical South Pacific (ETSP), we develop a box model with fully prognostic cycles of carbon, nutrients and oxygen in the upwelling region and its adjacent open ocean. Ocean circulation is calibrated with Δ14C data of the ETSP. The sensitivity of the simulated nitrogen cycle to nutrient and oxygen exchange and ventilation from outside the model domain and to remineralization scales inside an OMZ is analysed. For the entire range of model configurations explored, we find that the fixed-N inventory can be stabilized at non-zero levels in the ETSP OMZ only if the remineralization rate via denitrification is slower than that via aerobic respiration. In our optimum model configuration, lateral oxygen supply into the model domain is required at rates sufficient to oxidize at least about one fifth of the export production in the model domain to prevent anoxia in the deep ocean. Under these conditions, our model is in line with the view of phosphate as the ultimate limiting nutrient for phytoplankton, and implies that for the current notion of nitrogen fixation being favoured in N-deficit waters, the water column of the ETSP could even be a small net source of nitrate.

scholarly journals Source Locality Effects on Restoration Potential in Sphagnum palustre L. from 3 Ohio Sites

2018 ◽  
Vol 118 (2) ◽  
pp. 34
Author(s):  
Tony Miller ◽  
Randall J. Mitchell
Keyword(s):  
Local Adaptation ◽  
Water Source ◽  
Length Change ◽  
Plant Performance ◽  
Peat Moss ◽  
Moss Species ◽  
Source Effects ◽  
Study Team ◽  
Full Factorial ◽  
Sphagnum Palustre

Understanding whether propagules from different donor sources differ in their performance at a site may be important for restoration of many habitats. This study aimed at evaluating source effects in Sphagnum palustre L, a peatland moss species, for potential use in a restoration setting. Tamarack Bog, a remnant peatland in Bath Township, Ohio, is being restored. One goal is to increase Sphagnum coverage. This study focused on the dominant species of peat moss at the bog, S. palustre. To test for source effects, S. palustre and water samples were collected from 3 different locations (Mentor Marsh, Tamarack Bog, and Singer Lake) and used in 2 experiments. Plant performance was assessed by measuring growth in length and increase in mass. In the first experiment, a full factorial test was conducted: moss sampled from each location was grown directly in water collected from each location. In the second experiment—also a full factorial test—moss sampled from each location was separately grown on a uniform, commercially harvested, peat substrate and supplied with water collected from each location. In the design of both experiments, local adaptation would be indicated by better performance (both experiments measured length change and mass change, plus capitulum counts in the second experiment) for plants grown in their home water source than for plants grown in water from other sites. Ultimately, the study team did not observe evidence for local adaptation in these experiments. However, there were strong plant source effects in both experiments and some indication of differences in response to the water from different sources. Interpreting these results from a restoration standpoint, using donor plants from several source sites may improve the success of restoration.

scholarly journals Maize Silage Digestate Application Affecting Germination and Early Growth of Maize Modulated by Soil Type

Agronomy ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 473 ◽  
Author(s):  
Ana A. Robles-Aguilar ◽  
Vicky M. Temperton ◽  
Nicolai D. Jablonowski
Keyword(s):  
Negative Impact ◽  
Biogas Production ◽  
Inorganic Nitrogen ◽  
Germination Rate ◽  
Water Repellency ◽  
Low Fertility ◽  
Plant Performance ◽  
Nutrient Cycle ◽  
Npk Fertilizer ◽  
Fertilization Effects

During biogas production anaerobic digestion of plant material produces a nutrient-rich residue called digestate. The application of the nutrients present in the digestate should improve soil fertility, particularly in nutrient poor soils, and thus crop yield, promoting the closure of the nutrient cycle. This study evaluated the effect of digestate application on the germination and early stages of plant development since these are the first steps to be considered when studying the benefits on plant growth in low fertility substrates. A greenhouse experiment was conducted to evaluate the effects of three substrates of different texture and fertility (field loam, field sand, sand), as well as type and amount of fertilizer (pure maize digestate vs. inorganic nitrogen/phosphorus/potassium (NPK) fertilizer) on both germination and early plant performance of maize (Zea mays L. subsp. mays). While digestate and NPK fertilizer applications had no significant effect on germination in the two field soils, digestate applications significantly decreased the germination rate in sand (36–82% reduction) due to an increase of surface water repellency. In contrast, for aboveground biomass yield, the most positive fertilization effects of digestate application were found on sand (up to 3.5 times the biomass of the unamended control) followed by field sand (1.5 times), compared to no effect for field loam. Our findings suggest that digestate application have positive fertilization effects in low-fertility substrates, similar to NPK, even though digestate application may have a negative impact on the permeability in sandy substrates that could interfere with germination.

scholarly journals Effect of UV Radiation and Salt Stress on the Accumulation of Economically Relevant Secondary Metabolites in Bell Pepper Plants

2019 ◽  
Author(s):  
Jan Ellenberger ◽  
Nils Siefen ◽  
Priska Krefting ◽  
Jan-Bernd Schulze Lutum ◽  
Daniel Pfarr ◽  
...  
Keyword(s):  
Salt Stress ◽  
Secondary Metabolites ◽  
Plant Biomass ◽  
Negative Impact ◽  
Stress Conditions ◽  
Bell Pepper ◽  
Plant Performance ◽  
Promising Tool ◽  
Leaf Level ◽  
Uv Stress

The green biomass of horticultural plants contains valuable secondary metabolites (SM) which can potentially be extracted and sold. When exposed to stress, plants accumulate higher amounts of these SMs, making the extraction and commercialization even more attractive. We evaluated the potential for accumulating of the flavones cynaroside and graveobioside A in leaves of two bell pepper cultivars (Mavras and Stayer) when exposed to salt stress (100 mM NaCl), UVA/B excitation (UVA 4-5 W/m²; UVB 10-14 W/m² for 3 hours per day) or a combination of both stressors. HPLC analyses proved the enhanced accumulation of both metabolites under stress conditions. Cynaroside accumulation is effectively triggered by high-UV stress, whereas graveobioside A contents increase under salt stress. Highest contents were observed in plants exposed to combined stress. Effects of stress on overall plant performance differed significantly between treatments, with least negative impact on aboveground biomass found for high-UV stressed plants. The usage of two non-destructive instruments (Dualex and Multiplex) allowed us to gain insights in ontogenetical effects at the leaf level and temporal development of SM contents over time. Indices provided by those devices correlate fairly with amounts detected via HPLC (Cynaroside: R2 = 0.46 – 0.66; Graveobioside A: R2 = 0.51 – 0.71). The concentrations of both metabolites tend to decrease at leaf level during the ontogenetical development even under stress conditions. High-UV stress is a promising tool for enriching plant leaves with valuable SM without major effects on plant biomass. All data is available online [1].

scholarly journals Barley shoot biomass responds strongly to N:P stoichiometry and intraspecific competition, whereas roots only alter their foraging

2020 ◽  
Author(s):  
Amit Kumar ◽  
Richard van Duijnen ◽  
Benjamin M. Delory ◽  
Rüdiger Reichel ◽  
Nicolas Brüggemann ◽  
...  
Keyword(s):  
Root System ◽  
Plant Competition ◽  
Specific Root Length ◽  
Plant Performance ◽  
Shoot Biomass ◽  
Plant Responses ◽  
P Availability ◽  
N:P Stoichiometry ◽  
Limiting Nutrient ◽  
Plant Plant

AbstractBackground and AimsPlants respond to various environmental stimuli, and root systems are highly responsive to the availability and distribution of nutrients in the soil. Root system responses to the limitation of either nitrogen (N) or phosphorus (P) are well documented, but how the early root system responds to (co-) limitation of one (N or P) or both (N and P) in a stoichiometric framework is not well known despite its relevance in agriculture. In addition, how plant-plant competition (here intra-specific) alters plant responses to N:P stoichiometry is understudied. Therefore, we aimed to investigate the effects of N:P stoichiometry and competition on root system responses and overall plant performance.MethodsPlants (Hordeum vulgare L.) were grown in rhizoboxes for 24 days in the presence or absence of competition (three vs. one plant per rhizobox), and fertilized with different combinations of N:P (low N+low P, low N+high P, high N+low P, and high N+high P).Key ResultsShoot biomass was highest when both N and P were provided in high amounts. In competition, shoot biomass decreased on average by 22%. Interestingly, N:P stoichiometry and competition had no clear effect on root biomass. However, we found distinct root responses in relation to biomass allocation across depths. Specific root length depended on the identity of limiting nutrient (N or P) and presence/absence of competition. Plants rooted deeper when N was the most limiting compared to shallower rooting when P was the most limiting nutrient.ConclusionsOverall, our study sheds light on the early plant responses to plant-plant competition and stoichiometric availability of two macronutrients most limiting plant performance. With low N and P availability during early growth, higher investments in root system development can significantly trade off with aboveground productivity, and strong intra-specific competition can further strengthen such effects.

scholarly journals Nitrogen fluxes in Western streams

2017 ◽  
Vol 40 ◽  
pp. 61-68
Author(s):  
Hilary L. Madinger ◽  
Robert O. Hall Jr.
Keyword(s):  
Nitrogen Fixation ◽  
Primary Production ◽  
Aquatic Ecosystems ◽  
Additional Data ◽  
Gross Primary Production ◽  
Dissolved Gas ◽  
Dissolved Nitrogen ◽  
Relationship Types ◽  
Stream Nitrate ◽  
The Relationship

Nitrogen pollution to streams is altering the nitrogen cycling in unknown ways, causing challenges for predicting nitrogen fixation fluxes within aquatic ecosystems. Increasing nitrate pollution decreases the amount of nitrogen fixation occurring in streams. However, the relationship between stream nitrate concentration and the rate of nitrogen fixation is unknown. We predict that lower nitrate streams will have the highest rates of nitrogen fixation. Additionally, there will be much more energy produced in streams with nitrogen fixation compared to the amount required to fix the nitrogen. We estimated whole-stream gross primary production and nitrogen fixation fluxes using the diel change in dissolved nitrogen and oxygen gases compared to the expected dissolved gas saturation. Our whole-stream method is preferable to chamber estimates to understand the relationship between energy requirements for nitrogen fixation and gross primary production, but additional data is needed to distinguish between relationship types and make our measurements generalizable.   Featured photo by Intermountain Forest Service, USDA Region 4 Photography on Flickr. https://flic.kr/p/jbTRUj

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