Selenium and sulfur influences glucosinolate metabolism in hydroponically grown rapid cycling Brassica oleracea

Glucosinolates are sulfur-containing secondary plant metabolites commonly found in plants in the family Brassicaceae. The presence of selenium in soils can result in an accumulation of selenoamino acids, an increase in the uptake of sulfur, and an inhibition in the production of glucosinolates in Brassica species. This study was undertaken to determine the extent of selenium\u27s impact on selenoamino acid accumulation, sulfur uptake, and glucosinolate production in Brassica oleracea. Rapid cycling B. oleracea plants were grown hydroponically in half strength Hoagland\u27s nutrient solution with selenium treatments delivered as sodium selenate in concentrations of 0.0, 0.5, 0.75, 1.0, and 1.5 ppm. Elevated sulfur treatments of 37 ppm sulfate and 37 ppm sulfate/ 0.75 ppm selenate were incorporated to compare with selenium treatments. Plants were harvested and freeze-dried one to two days prior to anthesis. Selenium and sulfur content of plant tissue was determined by flame atomic absorption spectrophotometry and a Leco 232 S-determinator. Glucosinolate content of leaf tissue was determined by high performance liquid chromatography (HPLC). Selenium concentration in the nutrient solution was positively correlated with selenium and sulfur uptake in the plants. The sulfur concentration of plants exposed to selenium was equal to or greater than the sulfur concentration of plants exposed to elevated sulfur in the nutrient solution. In spite of higher sulfur concentrations, there was a statistically significant decrease in production of 5 of the 7 glucosinolates analyzed in selenium enriched plants. Plants in elevated sulfur treatments had higher glucosinolate production than selenium treated plants. These results suggest that selenium either up-regulates or prevents the down-regulation of sulfur uptake in B. oleracea. In addition, selenium\u27s presence within the plant seems to have a negative impact on the production of certain glucosinolates despite adequate availability of sulfur

Mycorrhizal Stimulation of Leaf Gas Exchange in Relation to Root Colonization, Shoot Size, Leaf Phosphorus and Nitrogen: A Quantitative Analysis of the Literature Using Meta-Regression

Arbuscular mycorrhizal (AM) symbiosis often stimulates gas exchange rates of the host plant. This may relate to mycorrhizal effects on host nutrition and growth rate, or the influence may occur independently of these. Using meta-regression, we tested the strength of the relationship between AM-induced increases in gas exchange, and AM size and leaf mineral effects across the literature. With only a few exceptions, AM stimulation of carbon exchange rate (CER), stomatal conductance (gs) and transpiration rate (E) has been significantly associated with mycorrhizal stimulation of shoot dry weight, leaf phosphorus, leaf nitrogen: phosphorus ratio and percent root colonization. The sizeable mycorrhizal stimulation of CER, by 49% over all studies, has been about twice as large as the mycorrhizal stimulation of gs and E (28% and 26%, respectively). Carbon exchange rate has been over twice as sensitive as gs and four times as sensitive as E to mycorrhizal colonization rates. The AM-induced stimulation of CER increased by 19% with each AM-induced doubling of shoot size; the AM effect was about half as large for gs and E. The ratio of leaf N to leaf P has been more closely associated with mycorrhizal influence on leaf gas exchange than leaf P alone. The mycorrhizal influence on CER has declined markedly over the 35 years of published investigations

Arbuscular mycorrhizal symbiosis and osmotic adjustment in response to NaCl stress: a meta-analysis

Arbuscular mycorrhizal (AM) symbiosis can enhance plant resistance to NaCl stress in several ways. Two fundamental roles involve osmotic and ionic adjustment. By stimulating accumulation of solutes, the symbiosis can help plants sustain optimal water balance and diminish Na+ toxicity. The size of the AM effect on osmolytes has varied widely and is unpredictable. We conducted a meta-analysis to determine the size of the AM effect on 22 plant solute characteristics after exposure to NaCl and to examine how experimental conditions have influenced the AM effect. Viewed across studies, AM symbioses have had marked effects on plant K+, increasing root and shoot K+ concentrations by an average of 47% and 42%, respectively, and root and shoot K+/Na+ ratios by 47% and 58%, respectively. Among organic solutes, soluble carbohydrates have been most impacted, with AM-induced increases of 28% and 19% in shoots and roots. The symbiosis has had no consistent effect on several characteristics, including root glycine betaine concentration, root or shoot Cl- concentrations, leaf Ψπ, or shoot proline or polyamine concentrations. The AM effect has been very small for shoot Cl- concentration and root concentrations of Na+, Mg++ and proline. Interpretations about AM-conferred benefits regarding these compounds may be best gauged within the context of the individual studies. Shoot and root K+/Na+ ratios and root proline concentration showed significant between-study heterogeneity, and we examined nine moderator variables to explore what might explain the differences in mycorrhizal effects on these parameters. Moderators with significant impacts included AM taxa, host type, presence or absence of AM growth promotion, stress severity, and whether NaCl constituted part or all of the experimental saline stress treatment. Meta-regression of shoot K+/Na+ ratio showed a positive response to root colonization, and root K+/Na+ ratio a negative response to time of exposure to NaCl

Global meta-analysis reveals agro-grassland productivity varies based on species diversity over time.

Ecological research suggests increased diversity may improve ecosystem services, as well as yield stability; however, such theories are sometimes disproven by agronomic research, particularly at higher diversity levels. We conducted a meta-analysis on 2,753 studies in 48 articles published over the last 53 years to test: if biological N2 fixation (BNF) supplies adequate nitrogen (N) for plant growth relative to synthetic fertilizers; how crop physiological traits affect legume-grass symbiosis; and, how cultural practices affect BNF over a range of soils and climates overtime (in polycultures versus sole grasslands). Globally, net primary productivity (NPP; total aboveground production response of grass and legume in higher-diversity treatments) increased 44% via legume associations relative to sole grass controls (including both with and without N fertilizer). Several moderating variables affected NPP including: (i) plant photosynthetic pathway (mixtures of C3 grasses resulted in a 57% increase in NPP, whereas mixtures of C4 grasses resulted in a 31% increase; similarly cool-season legumes increased NPP 52% compared to a 27% increase for warm-season legumes relative to grasslands without diversity); (ii) legume life cycle [NPP response for perennial legume mixtures was 50% greater than sole grass controls, followed by a 28% increase for biennial, and a 0% increase for annual legumes)]; and, (iii) species richness (one leguminous species in a grassland agroecosystem resulted in 52% increase in NPP, whereas >2 legumes resulted in only 6% increases). Temporal and spatial effect sizes also influenced facilitation, considering facilitation was greatest (114% change) in Mediterranean climates followed by oceanic (84%), and tropical savanna (65%) environments; conversely, semiarid and subarctic systems had lowest Rhizobium-induced changes (5 and 0% change, respectively). Facilitation of grass production by legumes was also affected by soil texture. For example, a 122% NPP increase was observed in silt clay soils compared to 14% for silt loam soils. Niche complementarity effects were greatest prior to 1971 (61% change), compared to recent studies (2011-2016; -7% change), likely owing to reduced global sulfur deposition and increased ambient temperatures overtime. These historical trends suggest potential for legume intercrops to displace inorganic-N fertilizer and sustainably intensify global NPP. Results herein provide a framework for ecologists and agronomists to improve crop diversification systems, refine research goals, and heighten BNF capacities in agro-grasslands

Correction: Global meta-analysis reveals agro-grassland productivity varies based on species diversity over time.

[This corrects the article DOI: 10.1371/journal.pone.0200274.]

Weighted, overall summary effect sizes (response ratios) for primary productivity from legume-intercropping based on grass genera (negative values indicate inhibition from symbiosis, positive values indicate positive changes from the interaction).

<p>Change refers to raw percent affect in the effect size induced by legume-intercropping. Horizontal bars are 95% confidence intervals of the subgroup (moderator level) summary effect. <i>n</i> is number of studies contributing to the effect size. <i>P value</i> is the probability that the moderator level was statistically not different from zero.</p

Weighted, overall summary effect sizes (response ratios) for primary productivity from legume-intercropping on grass photosynthetic pathway (a), legume life cycle (b), legume seasonality (c), and number of legumes in a mix (d).

<p>Negative values indicate inhibition from symbiosis, positive values indicate positive changes from the interaction. Change refers to raw percent affect in the effect size induced by legume-intercropping. Horizontal bars are 95% confidence intervals of the subgroup (moderator level) summary effect. <i>n</i> is number of studies contributing to the effect size. <i>P value</i> is the probability that the moderator level was statistically not different from zero.</p

Moderator analysis of intercropping influence on summary effects of forage quality (acid detergent fiber, neutral detergent fiber, crude protein, and in vitro dry matter digestibility).

<p>Moderator analysis of intercropping influence on summary effects of forage quality (acid detergent fiber, neutral detergent fiber, crude protein, and in vitro dry matter digestibility).</p

Weighted, overall summary effect sizes (response ratios) for NPP from legume-intercropping relative to sole grass fertilization rate in kg N ha^-1 (a) and relative nitrogen fertilization (b).

<p>Negative values indicate inhibition from symbiosis, positive values indicate positive changes from the interaction. Change refers to raw percent affect in the effect size induced by legume-intercropping. Horizontal bars are 95% confidence intervals of the subgroup (moderator level) summary effect. <i>n</i> is number of studies contributing to the effect size. <i>P value</i> is the probability that the moderator level was statistically not different from zero.</p

Weighted, overall summary effect sizes (response ratios) for primary productivity from legume-intercropping per Koppen climate classification (a), soil texture (b), and establishment period since 1971–2016 (c) (negative values indicate yield inhibition from symbiosis, positive values indicate positive changes from the interaction).

<p>Change refers to raw percent affect in the effect size induced by legume-intercropping. Horizontal bars are 95% confidence intervals of the subgroup (moderator level) summary effect. <i>n</i> is number of studies contributing to the effect size. <i>P value</i> is the probability that the moderator level was statistically not different from zero.</p