Soil organic nitrogen: an overlooked but potentially significant contribution to crop nutrition.

BACKGROUND: For more than a century, crop N nutrition research has primarily focused on inorganic N (IN) dynamics, building the traditional model that agricultural plants predominantly take up N in the form of NO3 - and NH4 +. However, results reported in the ecological and agricultural literature suggest that the traditional model of plant N nutrition is oversimplified. SCOPE: We examine the role of organic N (ON) in plant N nutrition, first by reviewing the historical discoveries by ecologists of plant ON uptake, then by discussing the advancements of key analytical techniques that have furthered the cause (stable isotope and microdialysis techniques). The current state of knowledge on soil ON dynamics is analyzed concurrently with recent developments that show ON uptake and assimilation by agricultural plant species. Lastly, we consider the relationship between ON uptake and nitrogen use efficiency (NUE) in an agricultural context. CONCLUSIONS: We propose several mechanisms by which ON uptake and assimilation may increase crop NUE, such as by reducing N assimilation costs, promoting root biomass growth, shaping N cycling microbial communities, recapturing exuded N compounds, and aligning the root uptake capacity to the soil N supply in highly fertilized systems. These hypothetical mechanisms should direct future research on the topic. Although the quantitative role remains unknown, ON compounds should be considered as significant contributors to plant N nutrition.

Nitrogen Use Efficiency Definitions of Today and Tomorrow.

Crop production has a large impact on the nitrogen (N) cycle, with consequences to climate, environment, and public health. Designing better N management will require indicators that accurately reflect the complexities of N cycling and provide biological meaning. Nitrogen use efficiency (NUE) is an established metric used to benchmark N management. There are numerous approaches to calculate NUE, but it is difficult to find an authoritative resource that collates the various NUE indices and systematically identifies their assets and shortcomings. Furthermore, there is reason to question the usefulness of many traditional NUE formulations, and to consider factors to improve the conceptualization of NUE for future use. As a resource for agricultural researchers and students, here we present a comprehensive list of NUE indices and discuss their functions, strengths, and limitations. We also suggest several factors-which are currently ignored in traditional NUE indices-that will improve the conceptualization of NUE, such as: accounting for a wider range of soil N forms, considering how plants mediate their response to the soil N status, including the below-ground/root N pools, capturing the synchrony between available N and plant N demand, blending agronomic performance with ecosystem functioning, and affirming the biological meaning of NUE.

Cadmium and copper induced changes in growth, oxidative metabolism and terpenoids of Tanacetum parthenium.

Morphological and biochemical responses of feverfew plants exposed to low (5 µM) and high (35 and 70 µM) levels of Cd or Cu were investigated. Increasing metal supply notably reduced the plant biomass. Elevated Cd and Cu levels also resulted in an increase in the leaf proline content. Besides, decrease in ascorbic acid (AsA) and glutathione (GSH) contents was similar in the leaves of Cd- and Cu-treated plants, indicating altered biosynthesis of AsA and GSH under metal excess. High metal doses stimulated increase in antioxidative enzyme activities that could be related to elevated hydrogen peroxide (H2O2) content and subsequent lipid peroxidation. Cd was typically more accumulated in shoots and roots than Cu, leading to higher translocation factor at high Cd doses. In terms of essential oil content, it seems that Cd had an inhibitory effect during the experiment, whereas Cu was found to stimulate it only at 5 µM. Furthermore, high Cd supply enhanced the relative proportion of monoterpene hydrocarbons, while Cu increased the proportion of sesquiterpenes, especially at 5 µM. This result provides the first evidence of the response of feverfew plants to Cd or Cu by associating stress-related responses with changes in terpenoids.

Magnesium and manganese affect photosynthesis, essential oil composition and phenolic compounds of Tanacetum parthenium.

The accumulation of plant defense metabolites is closely associated with the concentration of nutrient elements, yet data related to the interactive effects of two nutrients on the deployment of phenolics and terpenoids are scare. In the present study, the interaction between magnesium (Mg) and manganese (Mn) on nutrient uptake, photosynthesis, oxidative status and the accumulation of phenolics and terpenoids in the leaves of feverfew plants grown at different concentrations of Mg and Mn was investigated. Nutrient uptake and photosynthesis were associated with the amount of applied Mg but could be modified by the concentration of Mn. Phenolic biosynthetic enzymes and individual phenolics were not only induced by Mg, but their levels were also dependent on the Mn supply. Additionally, the proportion of monoterpenes was enhanced by a deficiency of Mg rather than an excess of Mn. Deprivation of Mg also decreased the proportion of sesquiterpenes in the essential oil. Therefore, it appears that a high Mg and a low Mn supply lead to a marked shift from monoterpene to sesquiterpene production. Phenolic compounds also differentially accumulated under varying Mg and Mn concentrations. These results suggest a profound effect of the combined supply of Mg and Mn on the biosynthesis of terpenes and phenolics.

Magnesium and manganese interactively modulate parthenolide accumulation and the antioxidant defense system in the leaves of Tanacetum parthenium.

A balanced nutrient supply is a critical factor affecting accumulation of terpenoids in plants, yet data related to the interactive effects of two essential nutrients for the biosynthesis of sesquiterpenes are scarce. Here, the interactional effects between magnesium (Mg) and manganese (Mn) on plant growth, oxidative status, parthenolide accumulation and expression of key genes involved in parthenolide biosynthesis including 1-deoxy-d-xylulose-5-phosphate reductoisomerase (DXR), hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate reductase (HDR), 3-hydroxy-3-methylglutarylcoenzyme A reductase (HMGR), germacrene A synthase (GAS), germacrene A oxidase (GAO), costunolide synthase (COS) and parthenolide synthase (PTS) in the leaves of feverfew plants grown at different Mn and Mn levels were assessed. Plant growth and leaf pigment concentrations were associated with the amount of applied Mg but could be modified by the Mn level. Deprivation and the addition of both Mg and Mn induce oxidative stress. Mg supply also alleviated the adverse effects of Mn excess on plant growth and oxidative status. In addition, parthenolide biosynthesis decreased under deprivation of Mg or Mn, but the addition of Mn up to 50µM under 2mM Mg supply considerably increased its accumulation. The parthenolide accumulation trend might reflect the up-regulation of terpenoid-related genes and enzyme activities as well as the oxidative status of feverfew leaves. Our data suggest a profound effect of the combined supply of Mg and Mn on parthenolide biosynthesis through the activation of terpene synthases, which concomitantly modulate by oxidative status.

Exogenously applied calcium alleviates cadmium toxicity in Matricaria chamomilla L. plants.

Cadmium (Cd) toxicity in plants leads to serious disturbances of physiological processes, such as inhibition of chlorophyll synthesis, oxidative injury to the plant cells and water and nutrient uptake. Response of Matricaria chamomilla L. to calcium chloride (CaCl(2)) enrichment in growth medium for reducing Cd toxicity were studied in this study. Hydroponically cultured seedlings were treated with 0, 0.1, 1, and 5 mM CaCl(2), under 0, 120, and 180 µM CdCl(2) conditions, respectively. The study included measurements pertaining to physiological attributes such as growth parameters, Cd concentration and translocation, oxidative stress, and accumulation of phenolics. Addition of CaCl(2) to growth media decreased the Cd concentration, activity of antioxidant enzymes, and reactive oxygen species accumulation in the plants treated with different CdCl(2), but increased the growth parameters. Malondialdehyde and total phenolics in shoots and roots were not much affected when plants were treated only with different CaCl(2) levels, but it showed a rapid increase when the plants were exposed to 120 and 180 CdCl(2) levels. CaCl(2) amendment also ameliorated the CdCl(2)-induced stress by reducing oxidative injury. The beneficial effects of CaCl(2) in ameliorating CdCl(2) toxicity can be attributed to the Ca-induced reduction of Cd concentration, by reducing the cell-surface negativity and competing for Cd(2+) ion influx, activity enhancement of antioxidant enzymes, and biomass accumulation.