Tissue Nitrogen Content Research Articles

Cover crop systems impact on biomass production, carbon-to-nitrogen ratio, forage quality, and soil health in a semi-arid environment

Cover cropping is a soil restorative strategy that can save degraded soils and offer additional benefits relative to the traditional fallow-based practice in semi-arid cropping systems. This study aimed to (i) quantify the above (shoot)- and belowground (root) biomass production, nutritive value, and tissue carbon and nitrogen concentrations from different annual cool-season cover crop systems, and (ii) determine their effects on soil organic carbon, total nitrogen, soil respiration, and soil microbial population biomass in a semi-arid environment. Treatments used were monocultures of annual ryegrass (Lolium multiflorum Lam.), oat (Avena sativa L.), faba bean (Vicia faba L.), yellow sweetclover [Melilotus officinalis (L.) Lam], winter pea (Pisum sativum L.), two three-species mixtures (Mix 1: annual ryegrass + faba bean + yellow sweetclover and Mix 2: Oat + faba bean + winter pea), and a fallow laid out in a randomized complete block design with three replications. Averaged across years, Mix 2 produced greater shoot biomass (9714 kg DM ha−1; SE = 699) than all other cover crop systems except, the monoculture of oat (7970 kg DM ha−1; SE = 699). The plant tissue C/N ratio of the mixtures and monoculture legumes was mostly similar (range = 19.4–29.1). Overall, legumes produced superior relative feed value (RFV; 112–161) compared to grass monocultures and mixtures (RFV; 80–95). Soil gram-negative bacteria biomass was greatest under the yellow sweetclover monoculture. Based on the results of this study, the mixed cover crop systems (Mix 1 and Mix 2) offered a better chance of fulfilling the dual role of soil health improvement and feed quality for livestock in this semi-arid environment.

Validation of In-House Imaging System via Code Verification on Petunia Images Collected at Increasing Fertilizer Rates and pHs.

In a production environment, delayed stress recognition can impact yield. Imaging can rapidly and effectively quantify stress symptoms using indexes such as normalized difference vegetation index (NDVI). Commercial systems are effective but cannot be easily customized for specific applications, particularly post-processing. We developed a low-cost customizable imaging system and validated the code to analyze images. Our objective was to verify the image analysis code and custom system could successfully quantify the changes in plant canopy reflectance. 'Supercascade Red', 'Wave© Purple', and 'Carpet Blue' Petunias (Petunia × hybridia) were transplanted individually and subjected to increasing fertilizer treatments and increasing substrate pH in a greenhouse. Treatments for the first trial were the addition of a controlled release fertilizer at six different rates (0, 0.5, 1, 2, 4, and 8 g/pot), and for the second trial, fertilizer solution with four pHs (4, 5.5, 7, and 8.5), with eight replications with one plant each. Plants were imaged twice a week using a commercial imaging system for fertilizer and thrice a week with the custom system for pH. The collected images were analyzed using an in-house program that calculated the indices for each pixel of the plant area. All cultivars showed a significant effect of fertilizer on the projected canopy size and dry weight of the above-substrate biomass and the fertilizer rate treatments (p < 0.01). Plant tissue nitrogen concentration as a function of the applied fertilizer rate showed a significant positive response for all three cultivars (p < 0.001). We verified that the image analysis code successfully quantified the changes in plant canopy reflectance as induced by increasing fertilizer application rate. There was no relationship between the pH and NDVI values for the cultivars tested (p > 0.05). Manganese and phosphorus had no significance with chlorophyll fluorescence for 'Carpet Blue' and 'Wave© Purple' (p > 0.05), though 'Supercascade Red' was found to have significance (p < 0.01). pH did not affect plant canopy size. Chlorophyll fluorescence pixel intensity against the projected canopy size had no significance except in 'Wave© Purple' (p = 0.005). NDVI as a function of the projected canopy size had no statistical significance. We verified the ability of the imaging system with integrated analysis to quantify nutrient deficiency-induced variability in plant canopies by increasing pH levels.

Microbial inoculants as a means of improving soil and crop yields

The article presented the results of studies of the influence of microbial inoculants Rhizobium japonicum and Azospirillum brasilense on the growth and development of soybean (Glycine max) at the initial stages of its development. The study was conducted on three experimental plots: a control plot without treatment, a plot with Rhizobium japonicum inoculum and a plot with Azospirillum brasilense inoculum. The main indicators were evaluated: plant height, number of leaves, root system development and total biomass at different stages of plant growth, as well as laboratory analysis of nitrogen content in plant tissues. The results of the study showed that the inoculants had a significant impact on all measured parameters compared to the control plot. In particular, the plants in the plot with Rhizobium japonicum showed 50% higher growth and development of the root system, which was confirmed by the formation of root nodules responsible for nitrogen fixation. Azospirillum brasilense also improved plant growth and root system development, but its effect was less pronounced compared to Rhizobium japonicum. Nitrogen content analysis showed that plants in the Rhizobium japonicum plot had 45% higher tissue nitrogen content compared to the control plot, indicating effective nitrogen fixation. In plants treated with Azospirillum brasilense, the nitrogen content was also 25% higher, but without nodule formation, the effect was less pronounced. The aim of the study was to evaluate the effectiveness of microbial inoculants in improving plant growth and development in the early stages of vegetation, to investigate their effect on root system productivity, nitrogen uptake and total plant biomass, and to determine the optimal conditions for maximising the impact of inoculants in agricultural conditions. The results emphasised the importance of using microbial inoculants to increase soybean productivity and resistance in the early stages of its development. The application of Rhizobium japonicum provided a greater increase in biomass, root system and nitrogen assimilation, which makes this inoculant more effective than Azospirillum brasilense

Would reducing chlorophyll content result in a higher photosynthesis nitrogen use efficiency in crops?

AbstractDecreasing antenna size is considered a potential option for improving photosynthesis and increasing yield potential. Reducing chlorophyll content has been employed as a strategy to decrease antenna size. One of the commonly mentioned advantages of this approach is its ability to enhance crop nitrogen use efficiency (NUE); however, there is limited field evidence supporting this claim. In this study, we utilized a rice mutant called p35s‐Ami‐YGL1, which exhibits lower chlorophyll content and smaller antenna size, to investigate the effects of modifying leaf chlorophyll content on tissue nitrogen content and NUE. Our results demonstrate that the nitrogen contents in various tissues, including seed tissue, increased on a weight basis in p35s‐Ami‐YGL1 mutants while exhibiting a decrease in C:N ratio. Simultaneously, we observed a reduction in tissue carbon content along with an increase in the levels of chlorophyll precursors such as Proto IX. Specifically, we observed an upregulation in the expression of genes associated with photosynthetic light reactions and chlorophyll metabolism, while there was no increase in the expression of genes involved in the CBB cycle and nitrogen metabolism. In addition, p35s‐Ami‐YGL1 experienced increased photodamage. These findings suggest that the alterations in the C:N ratio and nitrogen content in plants may be attributed to Proto IX‐mediated photodamage and chloroplast reverse transduction signaling. Besides, these results suggest that the observed increase in tissue nitrogen content in p35s‐Ami‐YGL1 does not reflect an increase in plant nitrogen absorption or use efficiency, rather it is a result of stunted carbon fixation capacity.

Assessment of nitrate reductase activity and nitrogen content in foliar tissues of wheat variety PBW-343 under oil refinery effluent irrigation ​

Assessment of nitrate reductase activity and nitrogen content in foliar tissues of wheat variety PBW-343 under oil refinery effluent irrigation ​

Morpho-physiological traits and tissue burdens of Ecklonia radiata linked to environmental variation in an urban estuary

Organisms respond to their environment in various ways, including moving, adapting, acclimatising or a combination of responses. Within estuarine habitats, organisms are exposed to naturally variable environmental conditions. In urbanised estuaries, these natural variations can interact with human stressors such as habitat modification and pollution. Here, we investigated trait variation in the golden kelp Ecklonia radiata across an urban estuary - Sydney Harbour, Australia. We found that kelp morphology differed significantly between the more human-modified inner and the less modified outer harbour. Kelp individuals were smaller, had fewer laminae, and lacked spines in the inner harbour where it was warmer, more contaminated and less light was available. Inner harbour populations were characterised by lower tissue nitrogen and higher lead concentrations. These findings provide insights into how environmental variation could affect kelp morphology and physiology, and the high trait variation suggests adaptive capacity in E. radiata.

Using hyperspectral signatures for predicting foliar nitrogen and calcium content of tissue cultured little-leaf mockorange (Philadelphus microphyllus A. Gray) shoots

Determining foliar mineral status of tissue cultured shoots can be costly and time consuming, yet hyperspectral signatures might be useful for determining mineral contents of these shoots. In this study, hyperspectral signatures were acquired from tissue cultured little-leaf mockorange (Philadelphus microphillus) shoots to determine the feasibility of using this technology to predict foliar nitrogen and calcium contents. After using a spectroradiometer to take hyperspectral images for determining foliar N and Ca contents, the correlation between the hyperspectral bands, vegetation indices, and hyperspectral features were calculated from the spectra. Features with high correlations were selected to develop the models via different regression methods including linear, random forest (RF), and support vector machines. The results showed that non-linear regression models developed through machine learning techniques, including RF methods and support vector machines provided satisfactory prediction models with high R2 values (%N by RF with R2 = 0.72, and %Ca by RF with R2 = 0.99), that can estimate nitrogen and calcium content of little-leaf mockorange shoots grown in vitro. Overall, the RF regression method provided the most accurate and satisfactory models for both foliar N and Ca estimation of little-leaf mockorange shoots grown in tissue culture.

Microarthropods improve oat nutritional quality and mediate fertilizer effects on soil biological activity

AbstractSoil biological processes are important drivers of crop productivity in agroecosystems. Soil microarthropods play key roles in nutrient cycling and plant nutrient acquisition, though little is known about how these effects manifest in crop production under different organic fertilizer amendments. We explored the interactive effects of microarthropods and fertilizers on crop productivity in two greenhouse experiments: experiment one involved a single Collembola species, and experiment two involved diverse microarthropod communities. Oats were grown as a model crop in both experiments under one of three initial fauna abundance levels (none, low, and high). In both experiments, four organic fertilization treatments were compared: alfalfa green manure, Kreher's Poultry Litter Compost, Chilean nitrate, and a nonamended control. Oat growth and development were evaluated weekly. During each experiment, 48 pots were selected randomly for destructive harvest at two separate times to mimic forage and grain harvest stages. At each harvest, multiple soil metrics (microarthropods, microbial biomass, microbial enzymes, and soil carbon and nitrogen) and plant metrics (biomass, reproduction, and tissue carbon and nitrogen content) were evaluated. Our findings indicated that microarthropods, both single species and diverse communities, stimulated nitrogen cycling and enhanced crop nutrient status. As microarthropod abundance and diversity increased, microarthropods exerted more effects on soil microbial activity. The effects of the microarthropods enhance the breakdown of fertilizers, ultimately making fertilizer choice less important for soil processes and plant nutrient availability. Our findings suggest that microarthropods drove oat production yields primarily through their effects on soil biological processes.

Does spatial variation in insect herbivory match variations in plant quality? A meta-analysis.

Variation in herbivore pressure has often been predicted from patterns in plant traits considered as antiherbivore defences. Here, we tested whether spatial variation in field insect herbivory is associated with the variation in plant quality by conducting a meta-analysis of 223 correlation coefficients between herbivory levels and the expression of selected plant traits. We found no overall correlation between herbivory and either concentrations of plant secondary metabolites or values of physical leaf traits. This result was due to both the large number of low correlations and the opposing directions of high correlations in individual studies. Field herbivory demonstrated a significant association only with nitrogen: herbivore pressure increased with an increase in nitrogen concentration in plant tissues. Thus, our meta-analysis does not support either theoretical prediction, i.e., that plants possess high antiherbivore defences in localities with high herbivore pressure or that herbivory is low in localities where plant defences are high. We conclude that information about putative plant defences is insufficient to predict plant losses to insects in field conditions and that the only bottom-up factor shaping spatial variation in insect herbivory is plant nutritive value. Our findings stress the need to improve a theory linking plant putative defences and herbivory.

Joint Impacts of Meloidogyne incognita and Soil Nutrition on Solanum lycopersicum var. cerasiforme.

Strategies for plant nutrient resource allocation under Meloidogyne spp. infection and different soil nutrient conditions are not well established. In response, the objectives of this research are to determine if increased vegetative growth of Solanum lycopersicon var. cerasiforme (cherry tomato) under high nutrition enhances resistance to M. incognita and whether adaptive strategies for growth, reproduction, and nutrient uptake by cherry tomato infected with M. incognita alter nutrient availability. The study was conducted under greenhouse conditions using high, medium, and low soil nutrient regimes. The research results indicate that the total biomass of cherry tomato was less in the presence of M. incognita infection under all three nutrient conditions, compared with plants grown in the absence of this nematode. However, the increase in the root/shoot ratio indicates that cherry tomato allocated more resources to belowground organs. Under the combined impacts of M. incognita infection and low or medium soil nutrition, the nitrogen content in root system tissues and the phosphorus content in shoot system tissues were increased to meet the nutrient requirements of galled root tissue and plant fruit production. It is suggested that plants increase the allocation of reproductive resources to fruits by improving phosphorus transportation to the aboveground reproductive tissues under low and medium nutrient conditions. Overall, the study highlights a significant impact of soil nutrient levels on the growth and resource allocation associated with M. incognita-infected cherry tomato. In response, soil nutrient management is another practice for reducing the impacts of plant-parasitic nematodes on crop production.

Temporal and spatial drivers of the structure of macroinvertebrate assemblages associated with Laminaria hyperborea detritus in the northeast Atlantic

Kelp forests occur on more than a quarter of the world's coastlines, serving as foundation species supporting high levels of biodiversity. They are also a major source of organic matter in coastal ecosystems, with the majority of primary production released and exported as detritus. Kelp detritus also provides food and shelter for macroinvertebrates, which comprise important components of inshore food-webs. Hitherto, research on kelp detritus-associated macroinvertebrate assemblages remains relatively limited. We quantified spatiotemporal variability in the structure of detritus-associated macroinvertebrate assemblages within Laminaria hyperborea forests and evaluated the influence of putative drivers of the observed variability in assemblages across eight study sites within four regions of the United Kingdom in May and September 2015. We documented 5167 individuals from 106 taxa with Malacostraca, Gastropoda, Isopoda and Bivalvia the most abundant groups sampled. Assemblage structure varied across months, sites, and regions, with highest richness in September compared to May. Many taxa were unique to individual regions, with few documented in all regions. Finally, key drivers of assemblage structure included detritus tissue nitrogen content, depth, sea surface temperature, light intensity, as well as L. hyperborea canopy density and canopy biomass. Despite their dynamic composition and transient existence, accumulations of L. hyperborea detritus represent valuable repositories of biodiversity and represent an additional kelp forest component which influences secondary productivity, and potentially kelp forest food-web dynamics.

Changes in Carbon, Nitrogen, and Oxygen Stable Isotope Ratios and Mercury Concentrations in Killer Whales (Orcinus orca) during and after Lactation

The changes in the stable isotope ratios of carbon (δ13C), nitrogen (δ15N), oxygen (δ18O), and mercury (Hg) concentrations in muscle and liver tissues during and after lactation were studied in killer whales stranded along the coast of Hokkaido, in the northern area of Japan (n = 16). Calf muscles displayed δ13C- and δ15N-enriched peaks and a δ18O-depleted peak during lactation. The δ13C- and δ15N-enriched peaks appear to reflect the extensive nursing of 13C- and 15N-enriched milk and the onset of weaning, whereas the δ18O-depleted peak may be attributable to the extensive nursing of 18O-depleted milk and the onset of weaning. The δ13C and δ15N values tended to gradually increase after the weaning, whereas the δ18O values tended to decrease. The δ13C and δ15N levels in calves were similar between liver and muscle samples, whereas those in mature animals were higher in liver than in muscle samples. The isotopic turnover rates of C and N may be similar between the liver and muscle tissues in calves, which are rapidly growing animals. The Hg concentrations in muscle tissues were slightly higher in small calves than in large calves, probably due to the Hg transfer across placenta. The Hg concentrations in liver and muscle samples increased with increasing body length, and those in two liver samples from mature animals exceeded the high-risk threshold for marine mammal health effects (82 μg/wet g).

Soil microenvironmental variation drives below‐ground trait variation and interacts with macroclimate to structure above‐ground trait variation of arctic shrubs

Abstract Intraspecific trait variation can influence plant performance in different environments and may thereby determine the ability of individual plants to respond to climate change. However, our understanding of its patterns and environmental drivers across different spatial scales is incomplete, especially in understudied regions like the Arctic. To fill this knowledge gap, we examined above‐ground and below‐ground traits from three shrub taxa expanding across the tundra biome and evaluated their relationships with multiple microenvironmental and macroclimatic factors. The traits reflected plant size and structure (plant height, leaf area and root to shoot ratio), leaf economics (specific leaf area, nitrogen content), and root economics and collaboration with mycorrhizal fungi (specific root length, root tissue density, nitrogen content, and ectomycorrhizal colonisation intensity). We also measured leaf and root δ15N and leaf δ13C to characterise nitrogen source and acquisition pathways and plant water stress. Traits were measured in replicated plots (N = 135) varying in soil microclimate, thaw depth and organic layer thickness established across five sites spanning a macroclimate gradient in northern Alaska. This hierarchical design allowed us to disentangle the independent and combined effects of fine‐scale and broad‐scale factors on intraspecific trait variation. We found substantial intraspecific variation at fine spatial scales for most traits and less variation along the macroclimate gradient and between shrub taxa. Consistent with these patterns, microenvironmental factors, mainly soil moisture and thaw depth, interacted with macroclimate, mainly climatic water deficit, to structure size‐structural and leaf trait variation. In contrast, most root traits responded additively to thaw depth and macroclimate. Synthesis. Our results demonstrate that above‐ground and below‐ground tundra shrub traits respond differently to microenvironmental and macroclimatic variation. These differing responses contribute to substantial trait variation at fine spatial scales and may decouple above‐ground and below‐ground trait responses to climate change.

Growth and photosynthetic physiology of holopelagic Sargassum (Phaeophyceae) under laboratory conditions

SummarySpecies of holopelagic Sargassum are responsible for Caribbean golden tides, commonly known as ‘Sargassum events’. These events mainly comprise Sargassum fluitans and Sargassum natans I, which are exposed to high levels of irradiance, but also self‐shading within their floating masses. In this study, we grew S. fluitans and S. natans I and acclimated them to low‐light conditions at 23°C in the laboratory to explore their responses to increasing light intensities. Photosynthesis, respiration, growth, and pigment content were evaluated over 3 weeks. S. fluitans and S. natans I photoacclimate to higher irradiances by decreasing their chlorophyll a and c contents. An increase in maximum photosynthesis and respiration rates was observed under high light, although differences occurred in the saturation irradiance and the initial slope of the photosynthesis versus irradiance curve. These adjustments were reflected in S. fluitans daily growth (from 2% to 7% d−1 at low to high light, respectively) and tissue nitrogen content (1.6–2.7%) but were absent in S. natans I (~1% d−1). The photosynthetic physiology of S. fluitans under these conditions suggests lower light requirements without compromising growth; however, under high light a higher photosynthetic performance was observed. Combining physiological and growth studies in holopelagic Sargassum species will serve as a baseline to understand and explain the success and overgrowth of these species along the Caribbean coast.

Responses of Soil Fungi to Long‐Term Nitrogen‐Water Interactions Depend on Fungal Guilds in a Mixed Pinus koraiensis Forest

AbstractDifferent fungal guilds within the soil fungal community regulate forest ecosystem processes. Soil fungi are dictated by edaphic factors such as soil water and nutrient availabilities. However, how the total number of fungi and the composition of different fungal guilds in the soil vary under covarying pattern of nitrogen deposition and precipitation regime in temperate forests has not been well documented. In this study, we explored the effects of long‐term nitrogen‐water interactions on the diversity and composition of soil overall fungi and different fungal guilds, and their relationships with fine‐root and soil fungal mycelial traits in a temperate forest. The diversity of the totality of soil fungi or any fungal guilds did not change, but the community composition of saprotrophic and symbiotrophic fungi was significantly changed by nitrogen addition (N), showing increased abundance of soil symbiotrophic fungi but decreased abundance of soil saprotrophic fungi. Precipitation reduction (W) significantly altered soil overall and pathotrophic fungal community. Precipitation reduction combined with nitrogen addition (WN) significantly changed soil overall, pathotrophic and symbiotrophic fungal community composition. Soil pathotrophic, saprotrophic and symbiotrophic fungal community composition was variously related to fine‐root diameter, root tissue density, nitrogen and/or phosphorus concentration. Long‐term nitrogen‐water interactions decreased the complexity of soil fungal networks, reflected by the lower edges and average degree, but the higher average path distance and modularity. These findings of soil fungal guild‐specific responses to nitrogen‐water interactions will deepen our understanding of soil carbon sequestration potential and nutrient cycling in temperate forest ecosystems under future climate changes.

Potential of a novel endophytic diazotrophic Serratia sp. Wed4 for pyrene biodegradation

Endophytic diazotrophic Serratia sp. Wed4 with high nitrogenase activity (1260.9 ± 8.3 nmol C2H4 mL−1h−1) was isolated from Glycine max Linn growing in PAH contaminated soil for improving PAH removal and crop growth. Strain Wed4 biodegraded 37.0% of pyrene within 14 d via phthalate pathway in vitro and could biodegraded other PAHs with 2–5 rings effectively. Its capabilities on promoting crop growth included indole acetic acid (IAA) production (30.8 ± 3.3 μg mL−1), iron carrier production (A/Ar = 0.841 ± 0.002), inorganic phosphate dissolution (D/d = 1.184 ± 0.032) and organic phosphate dissolution (D/d = 1.154 ± 0.025). Strain Wed4 successfully colonized in barley tissues (>104 CFU g−1 FW), significantly promoted barley growth and nitrogen nutrition, reduced pyrene residues especially in shoots. Under sufficient nitrogen condition, strain Wed4 significantly promoted the dry weight of barley by 18.9%–33.9%, and decreased the pyrene residues by 46.4% in shoots and by 32.1% in roots. Meanwhile, under the deficient nitrogen condition, strain Wed4 significantly promoted the dry weight of barley by 40.1%–63.3% and decreased the pyrene residues by 39.0% in shoots and by 28.0% in roots. The pyrene contents were significantly negatively correlated with the total nitrogen contents in barley tissues, suggesting that nitrogen fixation of strain Wed4 also stimulated the pyrene removal. Based on its performance, Serratia sp. Wed4 provided a great potential to increasing crop yield and reducing PAH pollution in nitrogen deficient soils.

Towards a mechanistic understanding of animal-ecosystem interactions.

Research Highlight: Ferraro, K. M., Welker, L., Ward, E. B., Schmitz, O. J., & Bradford, M. A. (2023). Plant mycorrhizal associations mediate the zoogeochemical effects of calving subsidies by a forest ungulate. Journal of Animal Ecology, https://doi.org/10.1111/1365-2656.14002. Animals play large roles in ecosystem elemental cycling but predicting effects in diverse contexts remains a substantial challenge. Fundamental to progress is (1) identifying mechanisms by which animals impact nutrient distribution and cycling, and (2) disentangling how environmental context mediates the operation of alternative mechanisms. In an elegant field experiment, Ferraro etal. (2023) provide the first detailed exploration of the impact of nutrient inputs from mammalian parturition on soil functioning and the stoichiometry of plant tissues. The authors find that nitrogen from experimental additions of ungulate parturition material (natal fluids) is rapidly incorporated into microsite soil organic pools and plant tissues. They also find that soil processes (soil microbial biomass, rates of carbon mineralization, nitrogen mineralization and nitrification) and the nitrogen content of plant tissues above- and belowground are increased by addition of parturition material. Notably, the authors identify that increases in some soil processes and plant tissue nitrogen are weaker in microsites dominated by ericoid mycorrhizal plants than those dominated by ectomycorrhizal plants. These findings demonstrate that parturition depositions, a ubiquitous but overlooked mechanism of mammalian impacts on ecosystems, impact ecosystem processes and plant tissue stoichiometry. Furthermore, plant-fungal associations are a predictive axis of context dependency mediating zoogeochemical effects at fine scales. Ferraro etal.'s (2023) novel approach simultaneously advances mechanistic understanding of animal-ecosystem interactions at fine scales and facilitates prediction of ungulate effects on nutrient availability at landscape extents.

Using post‐season tissue nitrogen concentrations to predict adequacy of in‐season nitrogen management

AbstractHigh‐yielding mechanized rice production requires large amounts of nitrogen (N) fertilizer, which can be particularly costly to producers when applied in excess. The development of a tissue test to detect overapplication of N to rice is needed. Nitrogen response trials arranged in a randomized complete block design were established to identify a critical concentration threshold for a tissue test to detect excess N availability. Rice stalk samples were collected from 0 to 20 cm above the soil within 5 days of harvest and analyzed for NO3−‐N concentration. Two models were fit to the data to represent rice grain yield as a function of N concentration: the linear plateau model and the quadratic plateau model. The data were well represented by both models; however, the linear plateau model more accurately described the data with a normalized root mean square error of 0.128 for linear plateau and 0.131 for quadratic plateau and a significant F‐test (p &lt; 0.0001). The join point of the linear response region and the plateau region of the model serves as a critical value that separates the responsive (N deficient) and non‐responsive (N optimum or excessive) regions. The 95% confidence interval of the join point (2.1 mg NO3−‐N kg−1) was selected as a practical, agronomic critical concentration threshold to reduce false positive errors. The data presented here further supports the use of a post‐season tissue test in rice to detect overfertilization and establish a critical concentration threshold for this tissue test.

Tissue nutrient contents of the red alga Ellisolandia elongata as a tool to assess the ecological status in NW Mediterranean coastal waters

Eutrophication is a major threat to aquatic ecosystems because excessive nutrient enrichment may result in biodiversity loss, profound functional changes and reduction of ecosystem services. Unless several water quality indexes have been developed following the implementation of the EU Water Framework Directive (WFD), there is still room for improvement. In particular, the stress-tolerant articulated red coralline alga Ellisolandia elongata (=Corallina elongata) is dominant in a wide range of environmental conditions, hampering a proper evaluation of the water quality of some of these places. Here we have checked whether E. elongata can be used as a eutrophication bioindicator by measuring the tissue phosphorus and nitrogen contents. Our results detect an increase in tissue nutrient contents in E. elongata along a gradient of nutrient enrichment and, thus, it can be used as bioindicator of water quality status. Their measurement will allow a more accurate water quality assessment in places dominated by E. elongata where WFD compliant indexes based whether on species/assemblages presence and/or abundance do not provide enough resolution.

Leaf yield and mineral content of mizuna in response to cut-and-come-again harvest, substrate particle size, and fertilizer formulation in a simulated spaceflight environment

The Veggie plant-growth unit deployed onboard the International Space Station (ISS) grows leafy vegetables to supplement crew diets. “Cut-and-come-again” harvests are tested to maximize vegetative yield while minimizing crew time. Water, oxygen, and fertilizer delivery to roots of leafy greens growing in microgravity have become the center of attention for Veggie. Current Veggie technology wicks water into particulate root substrates incorporating controlled-release fertilizer (CRF). Mizuna mustard (Brassica rapa) was grown under ISS-like environments in ground-based Veggie-analogue units comparing crop response to combinations of two different substrate particle sizes, two different fertilizer formulations, and three leaf-harvest times from each plant. Fine-particle porous ceramic substrate (Profile©) was compared with a 40:60 mix of fine-particle porous ceramic Profile© + coarse porous ceramic Turface© substrate. Identical 18-6-8 (NPK) CRF formulations consisting of [50% fast-release (T70) + 50% intermediate-release (T100) prills] vs. [50% fast-release (T70) + 50% slow-release (T180) prills] were incorporated into each substrate, and leaf tissues were harvested from each treatment combination at 28, 48, and 56 days after sowing. The combination of T100 CRF in 100% Profile© substrate gave the highest fresh mass (FM) and leaf area (LA) across harvests, whereas T180 CRF in 40% Profile© gave the lowest. Dry-mass (DM) yields varied with effects on leaf area. Tissue nitrogen (N) and potassium (K) specific contents declined across harvests for all treatment combinations but tended to be highest for T100 CRF/100% Profile©, and lowest for T180 CRF/40% Profile©. These major macronutrients were taken up faster by roots growing in small particle-size substrate incorporating intermediate-rate CRF, but also were depleted faster from the same treatment combination, suggesting it may not continue to be the best combination for additional harvests. Micronutrients did not decline in tissue specific content across treatment combinations, but manganese (Mn) accumulated in leaf tissue across treatments and apparently comes mainly from the ceramic substrate, regardless of particle size. Substrate leachate analysis following final harvest indicated that pH remained in the range for nominal availability of mineral nutrients for root uptake, but electro-conductivity measurements suggested depletion of fertilizer salts from root zones, especially from the treatment combination supporting the highest yields and major macronutrient contents. Although 100% Profile© was the better growth substrate for mizuna in combination with intermediate-rate CRF and three cut-and-come-again harvests in ground-based studies, mixed-particle-size substrates may be a better choice for plant growth under microgravity conditions, where capillary forces predominant and tend to cause saturation of a fine medium with water. Since there were no statistically significant interactions between substrate and fertilizer in this study, our ground-based findings for CRF choice should translate to the best substrate choice for microgravity, but if NASA wants to consider additional cut-and-come-again harvests from the same mizuna plants, more complex CRF formulations likely will have to be investigated.