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1. Nitrogen Accumulation and Root Distribution of Grafted Tomato Plants as Affected by Nitrogen Fertilization

   https://doi.org/10.21273/HORTSCI14066-19  

   Djidonou, Desire; Zhao, Xin; Koch, Karen E.; Zotarelli, Lincoln (November 2019, HortScience)

   Growth and yield typically increase when tomato plants are grafted to selected interspecific hybrid rootstocks from which distinctive root system morphologies are envisioned to aid nutrient uptake. We assessed these relationships using a range of exogenous nitrogen (N) supplies under field production conditions. This study analyzed the impact of N on growth, root distribution, N uptake, and N use of determinate ‘Florida 47’ tomato plants grafted onto vigorous, interspecific, hybrid tomato rootstocks ‘Multifort’ and ‘Beaufort’. Six N rates, 56, 112, 168, 224, 280, and 336 kg·ha −1 , were applied to sandy soil in Live Oak, FL, during Spring 2010 and 2011. During both years, the leaf area index, aboveground biomass, and N accumulation (leaf blade, petiole, stem, and fruit) responded quadratically to the increase in N fertilizer rates. Averaged over the two seasons, the aboveground biomass, N accumulation, N use efficiency (NUE), and N uptake efficiency (NUpE) were ≈29%, 31%, 30%, and 33% greater in grafted plants than in nongrafted controls, respectively. More prominent increases occurred in the root length density (RLD) in the uppermost 15 cm of soil; for grafted plants, RLD values in this upper 15-cm layer were significantly greater than those of nongrafted plants during both years with an average increase of 69% over the two seasons. Across all the grafted and nongrafted plants, the RLD decreased along the soil profile, with ≈60% of the total RLD concentrated in the uppermost 0 to 15 cm of the soil layer. These results demonstrated a clear association between enhanced RLD, especially in the upper 15 cm of soil, and improvements in tomato plant growth, N uptake, and N accumulation with grafting onto vigorous rootstocks. 

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2. Leaf abaxial immunity to powdery mildew in Arabidopsis is conferred by multiple defense mechanisms

   https://doi.org/10.1093/jxb/erad450  

   Wu, Ying; Sexton, W Kyle; Zhang, Qiong; Bloodgood, David; Wu, Yan; Hooks, Caroline; Coker, Frank; Vasquez, Andrea; Wei, Cheng-I; Xiao, Shunyuan (November 2023, Journal of Experimental Botany)

   Wang, Wen-Ming (Ed.)

   Abstract Powdery mildew fungi are obligate biotrophic pathogens that only invade plant epidermal cells. There are two epidermal surfaces in every plant leaf: the adaxial (upper) side and the abaxial (lower) side. While both leaf surfaces can be susceptible to adapted powdery mildew fungi in many plant species, there have been observations of leaf abaxial immunity in some plant species including Arabidopsis. The genetic basis of such leaf abaxial immunity remains unknown. In this study, we tested a series of Arabidopsis mutants defective in one or more known defense pathways with the adapted powdery mildew isolate Golovinomyces cichoracearum UCSC1. We found that leaf abaxial immunity was significantly compromised in mutants impaired for both the EDS1/PAD4- and PEN2/PEN3-dependent defenses. Consistently, expression of EDS1–yellow fluorescent protein and PEN2–green fluorescent protein fusions from their respective native promoters in the respective eds1-2 and pen2-1 mutant backgrounds was higher in the abaxial epidermal cells than in the adaxial epidermal cells. Altogether, our results indicate that leaf abaxial immunity against powdery mildew in Arabidopsis is at least partially due to enhanced EDS1/PAD4- and PEN2/PEN3-dependent defenses. Such transcriptionally pre-programmed defense mechanisms may underlie leaf abaxial immunity in other plant species such as hemp and may be exploited for engineering adaxial immunity against powdery mildew fungi in crop plants. 

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3. Nitrogen Recovery from Enhanced Efficiency Fertilizers and Urea in Intensively Managed Black Walnut (Juglans nigra) Plantations

   https://doi.org/10.3390/f12030352  

   Sloan, Joshua L.; Salifu, Francis K.; Jacobs, Douglass F. (March 2021, Forests)

   Intensively managed forest plantations often require fertilization to maintain site fertility and to improve growth and yield over successive rotations. We applied urea-based “enhanced-efficiency fertilizers” (EEF) containing 0.5 atom% 15N at a rate of 224 kg N ha−1 to soils under mid-rotation black walnut (Juglans nigra L.) plantations to track the fate of applied 15N within aboveground ecosystem components during the 12-month period after application. Treatments included Agrotain Ultra (urea coated with a urease inhibitor), Arborite EC (urea coated with water-soluble boron and phosphate), Agrium ESN (polymer-coated urea), uncoated urea, and an unfertilized control. Agrotain Ultra and Arborite EC increased N concentrations of competing vegetation within one month after fertilization, while neither Agrium ESN nor uncoated urea had any effect on competing vegetation N concentrations during the experiment. Agrotain Ultra and Arborite EC increased δ15N values in leaves of crop trees above those of controls at one and two months after fertilization, respectively. By contrast, Agrium ESN and uncoated urea had no effect on δ15N values in leaves of crop trees until three months after fertilization. Fertilizer N recovery (FNR) varied among ecosystem components, with competing vegetation acting as a sink for applied nutrients. There were no significant differences in FNR for all the urea-based EEF products compared to uncoated urea. Agrium ESN was the only EEF that exhibited controlled-release activity in this study, with other fertilizers behaving similarly to uncoated urea. 

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4. Below-ground plant traits influence tundra plant acquisition of newly thawed permafrost nitrogen

   https://doi.org/10.1111/1365-2745.13062  

   Hewitt, Rebecca E.; Taylor, D. Lee; Genet, Hélène; McGuire, A. David; Mack, Michelle C.; Mariotte, Pierre (August 2018, Journal of Ecology)

   Abstract 1. The release of permafrost‐derived nitrogen (N) has the potential to fertilize tundra vegetation, which in turn may stimulate productivity and thus offset carbon (C) losses from thawing permafrost. Below‐ground plant traits may mediate ecosystem response to permafrost thaw and associated feedbacks to the atmosphere by differentially conferring access to deep, newly thawed permafrost N. Yet, identifying roots and quantifying root N uptake from deep, cold soils in complex plant communities has proved challenging to date. 2. We investigated plant acquisition of experimentally added 15N isotope tracer applied at the permafrost boundary in graminoid‐ and shrub‐dominated tundra at Eight Mile Lake, Alaska, when the thaw front was close to its maximum depth, simulating the release of newly thawed permafrost N. We used molecular tools to verify species and estimate biomass, nitrogen, and isotope pools. 3. Root biomass depth distributions follow an asymptotic relationship with depth, typical of other ecosystems. Few species had roots occurring close to the thaw front. Rubus chamaemorus, a short‐statured non‐mycorrhizal forb, and Carex bigelowii, a sedge, consistently had the deepest roots. Twenty‐four hours after isotope addition, we observed that deep‐rooted, non‐mycorrhizal species had the highest 15N enrichment values in their fine root tissue indicating that they access deep N late in the growing season when the thaw front is deepest. Deep‐rooted plants are therefore able to immediately take up newly thawed permafrost‐derived N. During the following growing season, herbaceous, non‐mycorrhizal plants allocated tracer above‐ground before woody, mycorrhizal plants. Ectomycorrhizal deciduous and ericoid mycorrhizal evergreen shrubs, by contrast, did not have immediate access to the deep N tracer and assimilated it into new foliar tissue gradually over the following growing season. 4. Synthesis. Graminoids and forbs that have immediate access to deep N represent a modest C sink compared to C emissions from thawing permafrost. However, the effects of deep N fertilization on shrubs over longer time‐scales may stimulate productivity and account for a more considerable N and C sink, thus constraining the permafrost C‐climate feedback. 

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5. Uptake and impact of carbon dots and their copper complex on tomato health

   https://doi.org/10.1039/D5EN00576K  

   Yao, Xiaoxiao; Shen, Yu; Hu, Peiguang; Stitgen, Abigail; Kesner, Laura; Sigmon, Leslie R; Deng, Chaoyi; Jilani, Safia Z; Rosenzweig, Zeev; Fairbrother, D Howard; et al (March 2026, Environmental Science: Nano)

   Nanomaterials are being increasingly studied for their use in agriculture to promote healthy crop growth and mitigate the damaging effects of plant diseases. Copper is among the elements delivered and managed with nanoenabled-agriculture practices, but it is challenging to balance copper levels because some doses mitigate disease, but in excess, it can be harmful and interrupt photosynthetic function. Carbon dots (CDs) are an emerging, sustainable class of fluorescent nanomaterials with affinity for copper ions that possess good biocompatibility and low toxicity, making them an ideal candidate for use in crop applications. Here, a range of CDs were synthesized from citric acid and urea with varied affinity for copper ions. We investigated how chelated copper affects CD fluorescence and structure, and we propose a mechanism for the chelation of Cu2+ by CDs. Additionally, the effects of the Cu–CD complex on both healthy and disease-bearing tomato plants were evaluated. The data show that the complex had no toxic effects on the plant and can increase seedling biomass by 44–61% when applied through a vacuum seed infiltration method. The desorption of copper from the Cu–CD complex exhibited a slow-release profile, indicating that CDs could be an effective tool for mitigating excess copper in plants. 

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