Nitrogen, Volume 4, Issue 2 (June 2023) – 6 articles

Although NH₄⁺ fertilization is known to acidify rhizosphere and enhance nutrient uptake, the effects on a nutrient-sufficient acidic soil amended with lime are not demonstrated. Thus, the influence of NH₄⁺ fertilization of an unlimed and limed (3 g calcium carbonate per kg soil) acidic soil on the nutrient uptake and growth of maize was studied in comparison to NH₄NO₃ fertilization. The pH of limed rhizosphere soil was about two units higher than that of the unlimed soil. The maize plants were grown in pots under greenhouse conditions for about two months. The results showed that the pH of the NH₄⁺-fertilized unlimed and limed soil was 0.54 and 0.15 units lower than the NH₄NO₃-fertilized soil. Liming negatively affected shoot and root dry matter production, whereas the NH₄⁺-fertilized plants produced higher dry matter than the NH₄NO₃-fertilized plants, with significant difference of 28% in the limed soil only. Liming decreased Fe concentration in rhizosphere soil from 99 to 69 mg kg⁻¹ and decreased plant-available Mn the most (71%), whereas the NH₄⁺-fertilized unlimed and limed soil had 48% and 21% higher Mn concentration than the respective NH₄NO₃-fertilized soils. Similarly limed rhizosphere soil had 50% lower plant-available Zn concentration than the unlimed soil, and the NH₄⁺-fertilized soil had an 8% higher Zn concentration than the NH₄NO₃-fertilized unlimed soil. The liming negatively affected P, K, Mn, and Zn concentrations and contents in maize shoot to a lower degree in the NH₄⁺-fertilized soil, whereas the positive effect of NH₄⁺ on the nutrient concentration and contents was vigorous in the unlimed soil than the limed soil. It is concluded that NH₄⁺ fertilization could be beneficial in enhancing nutrient uptake and growth of maize in both acidic and alkaline soils, despite the higher inherent plant-available concentrations of the nutrient in soil. Full article

In higher plants, hydrogen sulfide (H₂S) is a recognized signaling molecule that performs multiple regulatory functions. The enzyme L-cysteine desulfhydrase (LCD) catalyzes the conversion of L-cysteine (L-Cys) to pyruvate and ammonium with the concomitant generation of H₂S, and it is considered one of the main sources of H₂S in plants. Using non-denaturing polyacrylamide gel electrophoresis (PAGE) in combination with a specific assay for LCD activity, this study aims to identify the potential LCD isozymes in wild-type Arabidopsis thaliana seedlings of 16 days old grown under in vitro conditions, and to evaluate the potential impact of nitric oxide (NO) and H₂S on these LCD isozymes. For this purpose, an Atnoa1 mutant characterized to have a low endogenous NO content as well as the exogenous application of H₂S were used. Five LCD isozymes were detected, with LCD IV being the isozyme that has the highest activity. However, the LCD V activity was the only one that was positively modulated in the Atnoa1 mutants and by exogenous H₂S. To our knowledge, this is the first report showing the different LCD isozymes present in Arabidopsis seedlings and how their activity is affected by NO and H₂S content. Full article

The utilization of compost to enhance plant productivity and symbiotic nitrogen fixation (SNF) has been recognized as an effective alternative to synthetic nitrogen fertilizers. This environmentally sustainable method is readily accessible to farmers. This study investigated the effect of olive pomace (“alperujo”, AL) compost on the nodulation and SNF of soybeans (Glycine max L.) and their natural symbiont (Bradyrhizobium diazoefficiens). For that, soybean plants were subjected to several doses of AL compost under controlled greenhouse conditions. At the end of the experiment, the dry weight of plant biomass (aerial part and roots), the number and fresh weight of nodules, and nitrogen and leghaemoglobin contents were analyzed. The application of AL compost significantly improved soybean growth, as demonstrated by an increase in both plant biomass and height. Furthermore, nodular leghaemoglobin content and nitrogen content were found to be enhanced by the addition of AL compost (7 and 40%, respectively), indicating an increase in nodule effectiveness and symbiotic efficiency. Our results provide clear evidence of the synergetic effect of AL compost on the soybean-B. diazoefficiens association, probably due to AL-compost improved soybean roots development, and rhizospheric organic matter and nutrients assimilation by rhizobia. Full article

Soybean plants can fix atmospheric N₂ in the root nodule, a symbiotic organ with rhizobia. The primary forms of N transported from N₂ fixation are ureides, allantoate, and allantoin, supplemented with asparagine. The nitrate absorbed in the roots is transported to the shoots in the forms of NO₃⁻ and asparagine with a little portion of ureides. The concentrations of N-metabolites were analyzed by capillary electrophoresis after supplying various concentrations of urea, precursors of ureides, and allopurinol, an inhibitor of xanthine dehydrogenase, to investigate the ureide synthesis pathway in the roots. When the non-nodulated soybean plants were treated with 0–5 mM of urea, the concentrations of asparagine and glutamine in the xylem sap and the roots increased remarkably. In addition, allantoate concentration increased with the urea concentrations becoming higher. Allopurinol inhibited the accumulation of allantoate but did not affect the asparagine and glutamine accumulation in roots, stems, leaves, and xylem sap, supporting that allantoate is synthesized by purine degradation in roots the same as in the nodules. When ureide precursors were supplied to the nodulated soybean plants, the concentrations of asparagine and glutamine in the xylem sap and roots increased, suggesting that the ureide precursors were absorbed and assimilated to amides in the roots. Full article

Mixed-species grassland containing legumes were suggested to increase yield compared to monocultures. Furthermore, some legumes were suggested to be able to sustain growth, even under drought conditions. The first aim of the current study was to measure if multispecies grassland with legumes is also more productive when their N input due to symbiotic N₂ fixation is taken into account. Our second aim was to determine the benefit of grass–legume mixtures in terms of dry matter production under naturally occurring drought conditions. Mixed-species grasslands, consisting of monocultures and variable mixtures of (a) Trifolium pratense, (b) Trifolium. repens, (c) Lolium perenne, and (d) a mixture of drought-tolerant grasses (GSWT based), were assessed for their dry matter production over two years with contrasting weather patterns. The legume–grass seeding mixtures received either a fixed (180 kg N ha⁻¹) or adapted N-fertilizer application (0–180 kg N ha⁻¹), with the latter taking the assumed symbiotic N₂ fixation by legumes into account. Mixed-species grassland showed improved yield compared to monocultures both in comparably humid and drought-affected years. The benefits of multispecies grass–legume mixtures were considerably more obvious under a fixed but still measurable under an adapted N-fertilizer regime. The species diversity effect appears to be significantly dependent on the additional N supply enabled by legumes’ symbiotic N₂-fixation. Legumes and drought-tolerant grasses yielded equally well under drought conditions, although legumes showed major advantages during moderate drought and humid conditions. White and red clover, although both legumes, differed significantly in their persistence under elevated-N and their dry matter production under low-N fertilizer application, but were equal in their tolerance towards drought. Full article

Anthropogenic nitrogen (N) emissions can have considerable effects on terrestrial ecosystems, with chronic N deposition leading to changes in plant species composition. The Athabasca Oil Sands Region (AOSR) represents a large point source of N emissions, which has prompted concern for surrounding habitats. The objective of this study was to determine the relative importance of N deposition as a driver of plant species community composition against bioclimatic and soil chemical variables. Further, we sought to identify community thresholds in plant species composition across a N deposition gradient. This assessment was performed for 46 Jack pine (Pinus banksiana Lamb.)-dominant forest sites surrounding the AOSR spanning Alberta and Saskatchewan. In total, 35 environmental variables were evaluated using redundancy analysis (RDA), followed by gradient forest analysis applied to plant species abundance data. Soil chemical variables accounted for just over 26% of the total explainable variation in the dataset, followed by bioclimatic variables (19%) and deposition variables (5%), but joint effects between variables also explained a significant portion of the total variation (p < 0.001). Total deposited nitrogen (TDN), and sulphur (TDS) along with bioclimatic and soil chemical variables, were identified as important variables in gradient forest analysis. A single, definitive threshold across TDN was identified at approximately 5.6 kg N ha⁻¹ yr⁻¹ (while a TDS threshold was found at 14.4 kg S ha⁻¹ yr⁻¹). The TDN threshold range was associated primarily with changepoints for several vascular species (Pyrola asarifolia, Pyrola chlorantha, Cornus canadensis, and Arctostaphylos uva-ursi) and bryophyte and lichen species (Pleurozium schreberi, Vulpicida pinastri, and Dicranum polysetum). These results suggest that across Jack pine-dominant forests surrounding the AOSR, the biodiversity-based empirical critical load of nutrient N is 5.6 kg N ha⁻¹ yr⁻¹. Full article