Individual and combined effects of waterlogging and alkalinity on yield of wheat (Triticum aestivum L.) imposed at three critical stages

Effects of different drainage conditions on nitrogen losses of an agricultural sandy loam soil

Prolonged waterlogging in agricultural fields has severe consequences for the crop development and growth, and could potentially lead to higher N losses. In this study, a 3.93 ha agricultural field in Denmark was separated into two parts of well-drained (WD) and poorly-drained (PD) based on the installation depth of the tile drains. The field was continuously monitored for drainage, soil water dynamics, nitrogen leaching through the drains, and grain dry matter and nitrogen yields in a 4-year period (2017-2020). Furthermore, denitrification potential of the top 1 m of the soil at both parts of the field was measured through the denitrifying enzyme activity assay, and a 1D Daisy model was utilized to capture the differences between water and nitrogen balances at WD and PD. Results indicated that on average over the 4 years, annual harvested nitrogen in the crops at PD was 14% lower compared to WD, with a significant reduction of 33% in 2017-2018, that coincided with the longest period of waterlogging at PD. Moreover, greater losses of nitrogen through leaching from drainage and other pathways were measured at the PD (109 kg N ha^-1 ya^-1) compared to the WD (95 kg N ha^-1 ya^-1). Based on the simulations, losses through preferential flow pathways to the drains dominated at PD and most of the denitrification is expected to occur within the topsoil. Future studies could significantly benefit from monitoring the redox dynamics in the top 30 cm of the PD soils, and increasing the depth of tiles drains by redrainage could reduce the N losses of poorly drained agricultural soils.

The efficiency of arbuscular mycorrhiza in increasing tolerance of Triticum aestivum L. to alkaline stress

BACKGROUND

Evaluation of native soil microbes is a realistic way to develop bio-agents for ecological restoration. Soil alkalinity, which has a high pH, is one of the most common concerns in dry and semi-arid climates. Alkaline soils face problems due to poor physical properties, which affect plant growth and crop production. A pot experiment was carried out to investigate the impact of native mycorrhizal fungi (AMF) on the wheat plant (Triticum aestivum L.) under two levels of alkalinity stress -T1 (37 mM NaHCO₃), T2 (74 mM NaHCO₃) - at two developmental stages (the vegetative and productive stages).

RESULTS

Alkalinity stress significantly inhibited the germination percentage, plant biomass, photosynthetic pigments, and some nutrients (K, N, and P). Mycorrhizal inoculation improved growth parameters and productivity of wheat-stressed plants. However, lipid peroxidation was significantly lowered in mycorrhizal-inoculated plants compared to non-inoculated plants. Catalase and peroxidase were inhibited in wheat leaves and roots by alkalinity, while mycorrhiza promoted the activity of these enzymes.

CONCLUSION

The results of this study demonstrated that alkalinity stress had highly negative effects on some growth parameters of the wheat plant, while AMF inoculation attenuated these detrimental effects of alkalinity stress at two stages by reducing the pH and Na concentration and increasing the availability of P and the productivity of wheat in particular crop yield parameters.

Ribosome profiling reveals the effects of nitrogen application translational regulation of yield recovery after abrupt drought-flood alternation in rice

Abrupt drought-flood alternation is a frequent meteorological disaster during the summer in Southern China. The study of physiological and translation mechanisms of rice yield recovery after abrupt drought-flood alternation has great potential benefits in field production. Our results showed that yield recovery upon nitrogen (N) application after abrupt drought-flood alternation was due to the increase in effective panicle numbers per plant. The N application resulted in the regulation of physiological and biochemical as well as growth development processes, which led to a rapid growth recovery effect after abrupt drought-flood alternation stress in rice. Using ribosome profiling combined with RNA sequencing (RNA-seq) technology, the interactions between transcription and translation for N application after abrupt drought-flood alternation were analyzed. It was found that a small proportion of response genes were shared at the transcriptional and translational levels, that is, 14% of the expressed genes were upregulated and 6.6% downregulated. Further analysis revealed that the translation efficiency (TE) of the genes was influenced by their sequence characteristics, including their GC content, coding sequence length and normalized minimal free energy. Compared with the number of untranslated upstream open reading frames (uORFs), the increased number of translated uORFs promoted the improvement of TE. The TE of the uORFs for N application was lower than the control without N application after abrupt drought-flood alternation. This study characterizes the translational regulatory pattern in response to N application after abrupt drought-flood alternation stress.

δ15 N values in plants are determined by both nitrate assimilation and circulation

Nitrogen (N) assimilation is associated with ¹⁴ N/¹⁵ N fractionation such that plant tissues are generally ¹⁵ N-depleted compared to source nitrate. In addition to nitrate concentration, the δ¹⁵ N value in plants is also influenced by isotopic heterogeneity amongst organs and metabolites. However, our current understanding of δ¹⁵ N values in nitrate is limited by the relatively small number of compound-specific data. We extensively measured δ¹⁵ N in nitrate at different time points, in sunflower and oil palm grown at fixed nitrate concentration, with nitrate circulation being varied using potassium (K) conditions and waterlogging. There were strong interorgan δ¹⁵ N differences for contrasting situations between the two species, and a high ¹⁵ N-enrichment in root nitrate. Modelling shows that this ¹⁵ N-enrichment can be explained by nitrate circulation and compartmentalisation whereby despite a numerically small flux value, the backflow of nitrate to roots via the phloem can lead to a c. 30‰ difference between leaves and roots. Accordingly, waterlogging and low K conditions, which down-regulate sap circulation, cause a decrease in the leaf-to-root isotopic difference. Our study thus suggests that plant δ¹⁵ N can be used as a natural tracer of N fluxes between organs and highlights the potential importance of δ¹⁵ N of circulating phloem nitrate.

Soil Enzyme Activity in Soils Subjected to Flooding and the Effect on Nitrogen and Phosphorus Uptake by Oilseed Rape

Waterlogging presents one of the greatest constraints for agricultural crops. In order to elucidate the influences of waterlogging stress on the growth of oilseed rape, a pot experiment was performed investigating the impact of waterlogging on nitrogen (N) and phosphorus (P) accumulation in oilseed rape, and mineral N and available P profiles and enzyme activities of soils. The experiment included waterlogging treatments lasting 3 (I), 6 (II), and 9 (III) days, and a control treatment without waterlogging (CK). Results showed that waterlogging lasting 3 or more days significantly depressed the growth of oilseed rape, and prolonged the recovery time of plant growth with the period of flooding. Waterlogging notably influenced the N and P concentrations in plant tissues, and also affected mineral N, available P profiles, and activities of enzymes (including urease, phosphatase, invertase, and catalase) in the soils. With the exception of catalase, flooding suppressed the activity of urease, phosphatase, and invertase to varying degrees, and the longer the flooding time, the greater the suppression. The effect of waterlogging on mineral N and P profiles resulted from the altered proportions of NH₄ ⁺-N and NO₃ ^--N, and the decreased available P concentrations in these soils, respectively. The effect on P was more significant than on N in both soil nutrient profile and plant utilization.

Responses to K deficiency and waterlogging interact via respiratory and nitrogen metabolism

K deficiency and waterlogging are common stresses that can occur simultaneously and impact on crop development and yield. They are both known to affect catabolism, with rather opposite effects: inhibition of glycolysis and higher glycolytic fermentative flux, respectively. But surprisingly, the effect of their combination on plant metabolism has never been examined precisely. Here, we applied a combined treatment (K availability and waterlogging) to sunflower (Helianthus annuus L.) plants under controlled greenhouse conditions and performed elemental quantitation, metabolomics, and isotope analyses at different sampling times. Whereas separate K deficiency and waterlogging caused well-known effects such as polyamines production and sugar accumulation, respectively, waterlogging altered K-induced respiration enhancement (via the C₅ -branched acid pathway) and polyamine production, and K deficiency tended to suppress waterlogging-induced accumulation of Krebs cycle intermediates in leaves. Furthermore, the natural ¹⁵ N/¹⁴ N isotope composition (δ¹⁵ N) in leaf compounds shows that there was a change in nitrate circulation, with less nitrate influx to leaves under low K availablity combined with waterlogging and more isotopic dilution of lamina nitrates under high K. Our results show that K deficiency and waterlogging effects are not simply additive, reshape respiration as well as nitrogen metabolism and partitioning, and are associated with metabolomic and isotopic biomarkers of potential interest for crop monitoring.