Evidence that synergism between potassium and nitrate enhances the alleviation of ammonium toxicity in rice seedling roots

Genome-Wide Identification and Characterization of Ammonium Transporter (AMT) Genes in Chlamydomonas reinhardtii

Ammonium transporters (AMTs) are vital plasma membrane proteins facilitating NH4+ uptake and transport, crucial for plant growth. The identification of favorable AMT genes is the main goal of improving ammonium-tolerant algas. However, there have been no reports on the systematic identification and expression analysis of Chlamydomonas reinhardtii (C. reinhardtii) AMT genes. This study comprehensively identified eight CrAMT genes, distributed across eight chromosomes, all containing more than 10 transmembrane structures. Phylogenetic analysis revealed that all CrAMTs belonged to the AMT1 subfamily. The conserved motifs and domains of CrAMTs were similar to those of the AMT1 members of OsAMTs and AtAMTs. Notably, the gene fragments of CrAMTs are longer and contain more introns compared to those of AtAMTs and OsAMTs. And the promoter regions of CrAMTs are enriched with cis-elements associated with plant hormones and light response. Under NH4+ treatment, CrAMT1;1 and CrAMT1;3 were significantly upregulated, while CrAMT1;2, CrAMT1;4, and CrAMT1;6 saw a notable decrease. CrAMT1;7 and CrAMT1;8 also experienced a decline, albeit less pronounced. Transgenic algas with overexpressed CrAMT1;7 did not show a significant difference in growth compared to CC-125, while transgenic algas with CrAMT1;7 knockdown exhibited growth inhibition. Transgenic algas with overexpressed or knocked-down CrAMT1;8 displayed reduced growth compared to CC-125, which also resulted in the suppression of other CrAMT genes. None of the transgenic algas showed better growth than CC-125 at high ammonium levels. In summary, our study has unveiled the potential role of CrAMT genes in high-ammonium environments and can serve as a foundational research platform for investigating ammonium-tolerant algal species.

Comparing combined application of biochar and nitrogen fertilizer in paddy and upland soils: Processes, enhancement strategies, and agricultural implications

Recently, biochar and N fertilizers have been used to tackle low N use efficiency (NUE) in crops across diverse environmental conditions. The coupling of biochar and N fertilizer may impact crop N utilization through different pathways in various soil types. However, there is currently a lack of comprehensive assessment of how coupling effects specifically influence N utilization in paddy and upland crops. We conducted a meta-analysis of 175 peer-reviewed studies to assess the responses of soil properties and crop traits in paddy and upland fields under coupling effects. The results indicate that NUE (+26.1 %) and N uptake (+15.0 %) in paddy fields increase more than in upland fields (+23.7 % and +8.0 %, respectively), with the coupling effect providing NH4+ predominantly for rice and NO3- for upland crops. NH4+ increases in paddy fields (+6.9 %) but decreases in upland fields (-0.7 %), while microbial biomass carbon (MBC) decreases in paddy fields (-2.9 %) and increases in upland fields (+36.0 %). These findings suggest that coupling effects supply soil inorganic nutrients in paddies and affect microbes in uplands, thereby positively affecting crop N utilization. Specifically, the greatest increase in paddy crop yield and N use efficiency occurs when the ratio of N fertilizer to biochar exceeds 1.5 %, and in uplands, it manifests when applying 10-20 t·ha-1 of biochar and <150 kg·ha-1 N fertilizer. In conclusion, this meta-analysis explores the differential effects of biochar and N fertilizer coupling in different arable land types, offering novel insights into the utilization strategies of biochar in agricultural fields.

Review: Nutrient-nutrient interactions governing underground plant adaptation strategies in a heterogeneous environment

Plant growth relies on the mineral nutrients present in the rhizosphere. The distribution of nutrients in soils varies depending on their mobility and capacity to bind with soil particles. Consequently, plants often encounter either low or high levels of nutrients in the rhizosphere. Plant roots are the essential organs that sense changes in soil mineral content, leading to the activation of signaling pathways associated with the adjustment of plant architecture and metabolic responses. During differential availability of minerals in the rhizosphere, plants trigger adaptation strategies such as cellular remobilization of minerals, secretion of organic molecules, and the attenuation or enhancement of root growth to balance nutrient uptake. The interdependency, availability, and uptake of minerals, such as phosphorus (P), iron (Fe), zinc (Zn), potassium (K), nitrogen (N) forms, nitrate (NO3-), and ammonium (NH4+), modulate the root architecture and metabolic functioning of plants. Here, we summarized the interactions of major nutrients (N, P, K, Fe, Zn) in shaping root architecture, physiological responses, genetic components involved, and address the current challenges associated with nutrient-nutrient interactions. Furthermore, we discuss the major gaps and opportunities in the field for developing plants with improved nutrient uptake and use efficiency for sustainable agriculture.

Determination of optimal NH4+/K + concentration and corresponding ratio critical for growth of tobacco seedlings in a hydroponic system

Inherently, ammonium (NH₄ ⁺) is critical for plant growth; however, its toxicity suppresses potassium (K⁺) uptake and vice-versa. Hence, attaining a nutritional balance between these two ions (NH₄ ⁺ and K⁺) becomes imperative for the growth of tobacco seedlings. Therefore, we conducted a 15-day experimental study on tobacco seedlings exposed to different concentrations (47 treatments) of NH₄ ⁺/K⁺ at different corresponding 12 ratios simultaneously in a hydroponic system. Our study aimed at establishing the optimal NH₄ ⁺-K⁺ concentration and the corresponding ratio required for optimal growth of different tobacco plant organs during the seedling stage. The controls were the baseline for comparison in this study. Plants with low or excessive NH₄ ⁺-K⁺ concentration had leaf chlorosis or dark greenish colouration, stunted whole plant part biomass, and thin roots. We found that adequate K⁺ supply is a pragmatic way to mitigate NH₄ ⁺-induced toxicity in tobacco plants. The optimal growth for tobacco leaf and root was attained at NH₄ ⁺-K⁺ concentrations 2-2 mM (ratio 1:1), whereas stem growth was optimal at NH₄ ⁺-K⁺ 1-2 mM (1:2). The study provided an insight into the right combination of NH₄ ⁺/K⁺ that could mitigate or prevent NH₄ ⁺ or K⁺ stress in the tobacco seedlings.

Multi-algorithm cooperation research of WRKY genes under nitrogen stress in Panax notoginseng

WRKY transcription factors play an important role in the immune system and the innate defense response of plants. WRKY transcription factors have great feedback on nitrogen stress. In this study, bioinformatics was used to detect the WRKYs of Panax notoginseng (PnWRKYs). The response of PnWRKYs under nitrogen stress was also well studied. PnWRKYs were distributed on 11 chromosomes. According to PnWRKY and Arabidopsis thaliana WRKY (AtWRKY) domains, these PnWRKY proteins were divided into three groups by phylogenetic analysis. MEME analysis showed that almost every member contained motif 1 and motif 2. PlantCARE online predicted the cis-acting elements of the promoter. PnWRKY gene family members obtained 22 pairs of repeat fragments by collinearity analysis. The expression levels of PnWRKYs in different parts (roots, flowers, and leafs) were analyzed by the gene expression pattern. They reflected tissue-specific expressions. The qRT-PCR experiments were used to detect 74 PnWRKYs under nitrogen stress. The results showed that the expression levels of 8 PnWRKYs were significantly induced. The PnWRKY gene family may be involved in biotic/abiotic stresses and hormone induction. This study will not only lay the foundation to explore the functions of PnWRKYs but also provide candidate genes for the future improvement of P. notoginseng.

Magnesium deficiency stress in rice can be alleviated by partial nitrate nutrition supply

The problem of nitrogen (N) excess and magnesium (Mg) deficiency in farmland is becoming more common, severe, and widespread in southern China. Magnesium is known to be an essential nutrient for higher plants; however, the physiological responses of field crops to Mg deficiency, particularly to its interaction with N forms, remain largely unknown. In this study, a hydroponic experiment was conducted using three Mg levels (0.01, 1.00, and 5.00 mM) and three nitrate/ammonium ratios (NO₃^-/NH₄⁺ of 0/100, 25/75, and 50/50) under greenhouse conditions. The results show that Mg deficiency (0.01 mM) could result in yellow leaves, dwarf plants, and fewer tillers during rice growth. Furthermore, Mg deficiency induced a major reduction in root morphology and activity, photosynthetic properties, and nutrient accumulation, while it resulted in a clear increase in malondialdehyde, superoxide dismutase, peroxidase, and catalase activities in rice. However, under Mg-deficiency stress, the supply of partial NO₃^- led to a significant drop in these antioxidant enzyme activities. Moreover, partial NO₃^- supply significantly improved the net photosynthetic rate, transpiration rate, stomatal conductance, and intercellular CO₂ concentrations under Mg-deficiency conditions. In particular, the supply of partial NO₃^- dramatically promoted the growth of the root system, boosted the occurrence of lateral roots, and enhanced root vitality under Mg-deficiency stress. Additionally, the supply of partial NO₃^- led to significant increases in dry weight and N and Mg contents under Mg deficiency. The results of this study suggest that the symptoms of Mg-deficiency stress in rice can be alleviated by partial NO₃^- supply.

The alleviation of ammonium toxicity in plants

Nitrogen (N) is an essential macronutrient for plants and profoundly affects crop yields and qualities. Ammonium (NH₄ ⁺ ) and nitrate (NO₃ ^- ) are major inorganic N forms absorbed by plants from the surrounding environments. Intriguingly, NH₄ ⁺ is usually toxic to plants when it serves as the sole or dominant N source. It is thus important for plants to coordinate the utilization of NH₄ ⁺ and the alleviation of NH₄ ⁺ toxicity. To fully decipher the molecular mechanisms underlying how plants minimize NH₄ ⁺ toxicity may broadly benefit agricultural practice. In the current minireview, we attempt to discuss recent discoveries in the strategies for mitigating NH₄ ⁺ toxicity in plants, which may provide potential solutions for improving the nitrogen use efficiency (NUE) and stress adaptions in crops.