Concentrations Of Secondary Compounds Research Articles

Sustainable intensification of livestock systems using forage legumes in the Anthropocene

AbstractSustainable intensification of livestock systems implies greater efficiency in resource utilization resulting in greater output of products and other ecosystem services per unit of resource input. Integrating forage legumes into livestock systems is a viable way to reduce the input of industrial N fertilizer, reducing the use of fossil fuels and helping to mitigate global warming, a major problem during the Anthropocene. Some forage legumes have greater concentrations of secondary compounds, such as condensed tannins, that might reduce the emission of greenhouse gases (GHG) from ruminant eructation and excreta. Furthermore, forage legumes might enhance cattle performance because of greater nutritive value, resulting in greater production per unit of GHG released. Shortening the production cycle and improving cattle reproductive efficiency could have a major impact on reducing the overall carbon footprint of the system. Grazing systems with more diversified plant species are typically more resistant and resilient, adapting to current climate changes during the Anthropocene. Novel technologies might accelerate the development of future grazing systems using forage legumes as a key component. Breeding efforts for the next‐generation legumes must focus on adaptation and potential use for mitigation of negative environmental impacts. There are examples of successful integration of forage legumes into livestock systems in different regions of the world, with a major reduction in off‐farm inputs and maintaining the system productive. These successful examples could be used to increase adoption and improve the efficiency of current livestock systems.

The functional role of ericoid mycorrhizal plants and fungi on carbon and nitrogen dynamics in forests.

Ericoid mycorrhizal (ErM) shrubs commonly occur in forest understories and could therefore alter arbuscular (AM) and/or ectomycorrhizal (EcM) tree effects on soil carbon and nitrogen dynamics. Specifically, ErM fungi have extensive organic matter decay capabilities, and ErM plant and fungal tissues have high concentrations of secondary compounds that can form persistent complexes in the soil. Together, these traits could contribute to organic matter accumulation and inorganic nutrient limitation. These effects could also differ in AM- vs EcM-dominated stands at multiple scales within and among forest biomes by, for instance, altering fungal guild interactions. Most work on ErM effects in forests has been conducted in boreal forests dominated by EcM trees. However, ErM plants occur in c. 96, 69 and 29% of boreal, temperate and tropical forests, respectively. Within tropical montane forests, the effects of ErM plants could be particularly pronounced because their traits are more distinct from AM than EcM trees. Because ErM fungi can function as free-living saprotrophs, they could also be more resilient to forest disturbances than obligate symbionts. Further consideration of ErM effects within and among forest biomes could improve our understanding of how cooccurring mycorrhizal types interact to collectively affect soil carbon and nitrogen dynamics under changing conditions.

Using biological invasions to improve plant defense theory

AbstractTheory to explain how plants defend themselves against herbivorous insects is rich, but can be difficult to test. Biological invasions provide unique opportunities to test and improve upon plant defense theory, as plants experience predictable shifts in insect herbivory after introduction to a new range. Here, we use an invasion to evaluate the power of three cornerstone hypotheses to predict the evolution of defense against herbivorous insects. These three hypotheses represent increasing refinements of classic plant‐insect theory regarding optimal defense, and each rests on the same three assumptions: that introduced plant populations escape natural enemies, that insect herbivory reduces plant fitness, and that putative defenses decrease herbivory. These assumptions remain untested in most invasions, which likely contributes to conflicting support for many plant defense hypotheses. We provide evidence that these assumptions are met in common mullein, Verbascum thapsus L. (Scrophulariaceae), which we propose can thus be used as a model system to test plant defense theory. We find that the hypothesis that integrates predictions of within‐plant optimal defense theory and the evolutionary dilemma model (i.e., the ‘shifting defense allocation’ hypothesis) provides strong insights into both invasion and evolution of plant defense. Specifically, we show that introduced populations that escape important specialist herbivores increase the concentration of secondary compounds in high‐quality tissue in particular, in this case protecting valuable young leaves from generalist herbivores that dominate in the introduced range. We would not have detected this shift without exploring within‐plant defense allocation across native and introduced populations, a task rarely undertaken when assessing evolutionary change in plant defenses. This finding provides broad insight into how native and introduced plant populations alike may respond to shifts in herbivore pressure. We close by highlighting future directions of inquiry using introduced plant populations to develop and test plant defense theory more generally.

Increasing plant performance, fruit production and nutritional value of tomato through foliar applied rutin

Rutin is a widely distributed natural flavonoid in higher plants and is considered a signal molecule responsible for inducing defense responses against biotic and abiotic stresses. This study evaluated the effect of foliar spray of rutin (0, 0.5, 1.0, 1.5, and 2.0 mmol L−1) 20 days after transplanting the seedlings to the pots, in three consecutive applications. The effect of rutin on the metabolism of tomato plants was evaluated through on photosynthetic performance, crop development and yield, fruit bioactive compounds, and antioxidant activity in tomato variety ‘IPA 6’. Beneficial effects of rutin in tomato are associated with increased photosynthetic performance and higher concentration of leaf primary metabolites, such as chlorophyll, carbohydrates, and protein; which provides evidence for improved plant growth parameters and fruit production. At the same time, rutin pulverization also resulted in a higher concentration of secondary compounds in tomato fruits such as polyphenol, flavonoid, lycopene, β-carotene, and lutein, providing them a greater antioxidant capacity. Cross-talks among plant physiological responses, fruit production and fruit quality as a result of rutin application implicates the benefits of using this elicitor for sustainable commercial cultivation of Solanum lycopersicum.

Exogenous salicylic acid and ferulic acid improve growth, phenolic and carotenoid content in tomato

Salicylic acid (SA) and ferulic acid (FA) are considered phenolic compounds that act as elicitors due to their regulatory functions on plant growth, development, metabolic and physiological responses in plants. The aim of this research was to evaluate the effect of SA and FA on growth, fruit quality and synthesis of secondary metabolites in tomato (Solanum lycopersicum cultivar Santa Clara). The experiment was conducted in pots in a greenhouse. The application of SA and FA was performed at concentration of 1.0 mmol L-1 alone and in combination, with water treated plants as control. Exogenous application of SA and FA either alone or in combination (SA + FA) resulted in increases in biomass accumulation and chlorophyll contents in tomato plant; and soluble sugar, total polyphenol, flavonoids, lycopene and β-carotene contents in fruits. It was concluded that application of SA and FA resulted in higher production and concentration of secondary compounds in tomato.

Diversity of bioactive secondary metabolites produced by medicinal plants of Physalis angulata L. (Ciplukan)

Plants are a main source of various types of secondary compounds. Plant secondary compounds play a greater role in interacting with the environment than contributing to the growth and development. Therefore, different environmental conditions besides influencing growth can also affect the profile and concentration of secondary compounds. Ciplukan (Physalis angulata L.) has been known as medicinal plants. The medicinal properties are derived from bioactive secondary compounds especially withanolide and physalin. This study aims to identify the diversity of secondary metabolites found in in vitro callus and plants tissue of ciplukan. Withanolide and physalin profiles of callus tissues, cotyledonary shoot-derived plantlet and germinated seeds-derived plant, were evaluated by LC-MS analysis. The LC-MS analysis of methanol extract showed the diversity in the amount and type of withanolide and physalins. This study confirmed that in undifferentiated callus cultures and in vitro induced plantlet of P. angulata the biosynthesis activity was not altered and the accumulation sites of withanolides were not missing. However in vitro regenerated plant produced withanolides and physalins in higher number. Therefore, modification of plant cell culture system to improve withanolide including physalin production of P. angulata is a good future prospect.

Use of arbuscular mycorrhizal fungi and phosphorus for increase in the concentration of compounds with antioxidant activity in Libidibia ferrea

The increase of the concentration of secondary compounds in medicinal plants can be influenced by the association with arbuscular mycorrhizal fungi (AMF). Pharmacological studies have shown that secondary compounds, found ing Libidibia ferrea (Mart. ex Tul.) L. P. Queiroz, confer phytotherapeutic potential to the species due to antidiabetic, antibiotic and anticancer activity. Therefore, the aim of this work was to verify if the presence of AMF associated or not with phosphate fertilization has an effect on the concentration of foliar phenolic compounds with antioxidant activity in L. ferrea seedlings. The seedlings were transferred to pots with 1.2 kg of soil with phosphate fertilization (P2O5) or not. In the roots was deposited soil-inoculum, containing 300 spores {100 spores of each AMF species: Claroideoglomus etunicatum, Gigaspora albida and Acaulospora longula Acaulospora longula. The plants were maintained in greenhouse for seven months. AMF favored an increase in shoot dry matter production, accumulation of flavonoids and greater total antioxidant activity, dispensing fertilization of the soil. The mycorrhizal inoculation associated with phosphate fertilization maximized the biosynthesis of total chlorophyll and soluble carbohydrates. AMF inoculation presents as a possible biotechnological alternative to increase antioxidant activity and foliar flavonoid production in L. ferrea seedlings, avoiding expenses with agricultural inputs, such as phosphate fertilization, making phytomass more attractive for the production of phytotherapics.

Effect of light stress on Crotalaria spectabilis (Fabaceae) and on its herbivore insect, the moth Utetheisa ornatrix (Erebidae: Arctiinae)

ABSTRACT The Plant Stress Hypothesis predicts that stressed plants are more attacked by herbivorous insects. In this work, we investigated the influence of light stress on Crotalaria spectabilis Roth (Fabaceae) and on its main herbivore, the moth Utetheisa ornatrix (L., 1758) (Erebidae: Arctiinae). Specifically, we verified whether plants stressed by shading differ from non-stressed plants in terms of productivity, morphological characteristics and water percentage. We also evaluated the performance of moths in stressed and non-stressed plants. Seeds were sown in pots. When the plants reached 50 cm in height, they were randomly divided into two groups: stressed plants (treatment group) and non-stressed plants (control group). The stressed plants were covered by a black mesh, providing 50% of shading. Eight characteristics of stressed and non-stressed C. spectabilis plants were evaluated: height, fresh and dry aerial biomass, number of pods and seeds, leaf hardness, number of trichomes, leaf area, specific leaf mass and percentage of leaf water. Moths were raised individually on leaves of stressed and non-stressed plants and we obtained the larval survival, larval development time, pupal weight and female fecundity. The non-stressed plants had significantly higher percentage of water in the leaves, greater fresh aerial biomass and a higher number of trichomes than the stressed plants. The survival rate was 98% for larvae raised on leaves from stressed plants and 92% on leaves from non-stressed plants. The larval developmental time was significantly shorter and the weight of female pupae significantly higher in non-stressed plants than in stressed plants. Thus, the Plant Stress Hypothesis was only corroborated by two tested variables: number of trichomes (lower in stressed plants) and larval survival (higher in stressed plants). Trichomes are among the main types of plant defenses against herbivory and reducing their number on leaves would make stressed plants more susceptible to attack by moth larvae, a fact corroborated by a greater larval survival. One of the possible explanations for the lack of corroboration of the Plant Stress Hypothesis for most of the variables tested is that other characteristics can be changed under stress conditions, such as the concentration of secondary compounds.

Changes in light spectra modify secondary compound concentrations and BVOC emissions of Norway spruce seedlings

Our objective was to study how changes in the light spectra affect growth; the concentration of carbohydrate, chlorophyll, carotenoid, terpene, alkaloid, and phenolic compounds; and the emissions of BVOC (biogenic volatile organic compound) of Norway spruce (Picea abies (L.) Karst.) seedlings. This study was conducted during the growth of the third needle generation in plant growth chambers. The plants were exposed to two light spectra with equal photon flux densities but different proportions of blue light (400–500 nm) produced by LED (light-emitting diode) lamps: (i) control (white light + 12% blue light) and (ii) increased blue light (+B) (white light + 45% blue light). The +B treatment increased the concentrations of total flavonoids and acetophenones in needles. The major changes in the phenolic profile were an accumulation of astragalin derivatives and the aglycone of picein. The +B treatment also decreased concentrations of the main alkaloid compound, epidihydropinidine, and its precursor, 2-methyl-6-propyl-1,6-piperideine; the emission rates of limonene, myrcene, and total monoterpenes; and the concentrations of a few terpenoid compounds, mainly in stems. Growth as well as the carbohydrates and pigments present in the needles were not affected. The results suggest that supplemental blue light shifts carbon allocation between secondary metabolism routes — from alkaloid and terpenoid synthesis to flavonoid and acetophenone synthesis. The changes may affect herbivory and abiotic stress tolerance of Norway spruce.

Contribution of macroinvertebrate shredders and aquatic hyphomycetes to litter decomposition in remote insular streams

Shredders play a crucial role in litter decomposition in streams. However, in oceanic islands, many streams have low shredder density and richness, and microbes seem to be the main litter decomposers. Here, we evaluate the effects of shredders and aquatic hyphomycetes on litter decomposition in insular streams. Three leaf species differing in physical and chemical characteristics, Alnus glutinosa, Clethra arborea, and Cryptomeria japonica, were enclosed in bags of coarse and fine mesh to allow and avoid macroinvertebrate access to the litter, respectively, and incubated in six streams along a gradient of Limnephilus atlanticus (Trichoptera) density in Sao Miguel Island. In streams with higher L. atlanticus density, leaf mass loss was higher in coarse than fine mesh bags. However, no difference in litter mass loss was found between bag types in streams with no L. atlanticus, despite the presence of other shredder taxa. These results suggest that when L. atlanticus are present at relatively high densities, they significantly contribute to litter decomposition, while litter decomposition is mainly driven by microbes when L. atlanticus density is low, or they are absent. Moreover, litter decomposition depends on litter quality, with leaves with high nutrient concentration and low concentration of secondary compounds being preferred by shredders.

Geographical and seasonal variation in water hemlock (Cicuta maculata) toxins

Water hemlock (Cicuta spp.) plants are typically found in wet areas and are toxic to all species of livestock. The toxic components in water hemlock are C17 polyacetylenes, with cicutoxin being the most studied. The objective of this study was to evaluate the variation in cicutoxin and total C17 polyacetylene compounds in water hemlock populations across western North America. Cicutoxin and total C17 polyacetylene concentrations varied among the six collection locations and among plant parts. Tubers contained the highest cicutoxin and total C17 polyacetylene concentrations of all plant parts. Green seeds contained the second most abundant total C17 polyacetylene concentrations. Total C17 polyacetylene and cicutoxin concentrations were also compared in different plant parts at several different phenological stages over the growing season. Cicutoxin and total C17 polyacetylene concentrations in the tubers increased until the green seed stage whereupon the concentrations decreased as the seeds matured and the plant began to senesce. Concentrations of secondary compounds in the stems were consistent with the optimal defense theory in which secondary compounds were higher in stems in earlier development stages compared to later stages and concentrations in seeds were higher than other above ground parts. The toxic compounds are found in all plant parts, with tubers posing the most significant risk of livestock poisoning. Results presented in this study suggest that the toxic risk to livestock likely does not differ between water hemlock (Cicuta maculata) populations across western North America under similar circumstances of ingestion.

Phenological changes in the nutritive value of honey mesquite leaves, pods, and flowers in the Chihuahuan Desert

AbstractHoney mesquite [Prosopis glandulosa (Torr.) glandulosa] is a potential foraging resource in southwestern United States rangelands and in other semi‐arid rangelands. Yet, intake by ruminants is limited. We conducted an in vitro digestion experiment to assess phenological changes in nutrient value and relative digestibility of honey mesquite leaves, pods, and flowers throughout the 2012 growing season. Crude protein (CP) content of leaves decreased (P < .001) during the year, while acid detergent fiber (ADF) and neutral detergent fiber (NDF) increased (P < .05). Crude protein content of pods decreased (P = .009) over time, but we did not detect (P > .10) any phenological changes in ADF or NDF levels during the study. A cubic response was observed with in vitro gas production and Julian date for both leaves and pods (P ≤ .01). Gas production from leaves collected in spring and early summer were lower than during late summer and early fall. Gas production and nutrient content values suggest that concentration of secondary compounds of mesquite leaves may decrease in late summer. Gas production values of mesquite leaves were lowest in early and mid‐summer when CP levels were high and fiber levels were low. Mesquite flowers and pods can be valuable forage resources for cattle. Although mesquite leaves contain nutrients, secondary compounds likely limit intake, especially in late spring and early summer when the CP in mesquite leaves would be most beneficial because quality of herbaceous forages in southwestern United States rangelands at that time is usually low.

How do herbivorous insects respond to drought stress in trees?

Increased frequency and severity of drought, as a result of climate change, is expected to drive critical changes in plant-insect interactions that may elevate rates of tree mortality. The mechanisms that link water stress in plants to insect performance are not well understood. Here, we build on previous reviews and develop a framework that incorporates the severity and longevity of drought and captures the plant physiological adjustments that follow moderate and severe drought. Using this framework, we investigate in greater depth how insect performance responds to increasing drought severity for: (i) different feeding guilds; (ii) flush feeders and senescence feeders; (iii) specialist and generalist insect herbivores; and (iv) temperate versus tropical forest communities. We outline how intermittent and moderate drought can result in increases of carbon-based and nitrogen-based chemical defences, whereas long and severe drought events can result in decreases in plant secondary defence compounds. We predict that different herbivore feeding guilds will show different but predictable responses to drought events, with most feeding guilds being negatively affected by water stress, with the exception of wood borers and bark beetles during severe drought and sap-sucking insects and leaf miners during moderate and intermittent drought. Time of feeding and host specificity are important considerations. Some insects, regardless of feeding guild, prefer to feed on younger tissues from leaf flush, whereas others are adapted to feed on senescing tissues of severely stressed trees. We argue that moderate water stress could benefit specialist insect herbivores, while generalists might prefer severe drought conditions. Current evidence suggests that insect outbreaks are shorter and more spatially restricted in tropical than in temperate forests. We suggest that future research on the impact of drought on insect communities should include (i) assessing how drought-induced changes in various plant traits, such as secondary compound concentrations and leaf water potential, affect herbivores; (ii) food web implications for other insects and those that feed on them; and (iii) interactions between the effects on insects of increasing drought and other forms of environmental change including rising temperatures and CO2 levels. There is a need for larger, temperate and tropical forest-scale drought experiments to look at herbivorous insect responses and their role in tree death.

Secondary compounds of Pinus massoniana alter decomposers' effects on Quercus variabilis litter decomposition.

A major gap to understand the effects of plant secondary compounds on litter decomposition in the brown food web is lack of information about how these secondary compounds modify the activities of soil decomposers. To address this question, we conducted an experiment where aqueous extracts and tannins prepared from Pinus massoniana needles were added to soils collected either from P. massoniana (pine soil) or Quercus variabilis (oak soil). Our objective was to investigate the cascading effects of the two compounds on isopod (Armadillidium vulgare) activity and subsequent change in Q. variabilis litter decomposition. We found that in pine soil, both aqueous extracts and tannins (especially at high concentrations) had positive effects on litter decomposition rates when isopods were present. While without isopods, litter decomposition was enhanced only by high concentrations of aqueous extracts, and tannins had no significant effect on decomposition. In oak soil, high concentrations of aqueous extracts and tannins inhibited litter decomposition and soil microbial biomass, regardless of whether isopods were present or not. Low concentrations of aqueous extracts increased litter decomposition rates and soil microbial biomass in oak soil in the absence of isopods. Based on our results, we suggest that the high concentration of secondary compounds in P. massoniana is a key factor influencing the effects of decomposers on litter decomposition rates, and tannins form a major part of secondary compounds. These funding particularly provide insight into form‐ and concentration‐oriented effects of secondary compounds and promote our understanding of litter decomposition and soil nutrient cycling in forest ecosystem.

Seasonal and diurnal changes in aucubin, catalpol and acteoside concentration of plantain herbage grown at high and low N fertiliser inputs

ABSTRACTThis experiment aimed to characterise the concentration of secondary compounds aucubin, catalpol and acteoside in plantain (Plantago lanceolata) herbage and determine if harvesting at different times or nitrogen (N) fertiliser inputs alter concentrations. Herbage of plantain was harvested each season over two years from plots fertilised at 180 or 450 kg N/ha/yr. At each harvest date, samples were taken in at 0700 h and 1600 h. The concentration of secondary compounds in plantain herbage was greatest for acteoside (range 1.77-36.0 mg/g DM), intermediate for aucubin (range 0.566–5.85 mg/g DM) and lowest for catalpol (<0.390 mg/g DM). Compound concentrations were unaffected by N fertiliser and showed limited diurnal fluctuation. There was a strong seasonal effect on all secondary compounds with peaks in concentration occurring in spring for aucubin and acteoside. This experiment suggests environmental factors other than soil N fertility and diurnal patterns influence the concentration of secondary compounds in plantain.Abbreviations: DR: digestibility-reducing; DM: dry matter; HPLC: High performance liquid chromatography; N: nitrogen; NH3: ammonia

Effect of some chemical and physical elicitors on some secondary compound induction of Ricinus communis through callus induction

The results of the present study showed that AgNo3 and ABA has a negative effect on fresh and dry weight, where both of weight significantly decreased when treated with ABA and AgNo3 compare to control treatment, except callus treated with AgNo3 at 4mg/l, the rate of fresh and dry weight significantly increased reached to 434,77mg respectively compared to control. Physical treatment also had a significant effect on fresh and dry weight for callus, the highest fresh and dry weight significantly reached to 491,93 mg respectively when callus exposure for 10 minutes to UV ray. The exposure to light for different period had negative effect on the rates of fresh and dry weight, as the control superior significantly for all lighting treatment.The concentration of all the secondary compounds extracted from callus increased significantly compared to their concentration in the seed extract. The addition of chemical treatments to callus lead to the difference in the concentration of secondary compounds. The quercetin compound reached its highest and significantly to 95.17μg/ml at the concentration of 4mg/l of AgNo3. while kaempferol suffer significantly decrease at all concentration of AgNo3, and reached to highest value significantly at control 114.76μg/ml, added concentration at 6 mg/l of AgNo3 had a positive effect in increasing the concentration of Ricinin significantly to 119.90μg/ml. Show the results of Callus treatment with ABA, different in the concentration of secondary compounds compared with control, where control treatment significantly increase kaempferol and qurecetin compound, were reaching to71.41,114.76μg/ml respectively. While the concentration of ricinin significantly increased to 194.34μg/ml at 2mg/l ABA concentration compared to control. The physical treatment had a significant effect on the concentration of secondary compounds, the concentration of all compounds was highest significantly when callus exposure for 24 hour to light compared to control. There was no significant effect on the concentration of secondary compounds at callus exposure to UV for tow period of exposure

Initial evaluation of willow (Salix acmophylla) irrigated with treated wastewater as a fodder crop for dairy goats

This research aimed at providing a first evaluation of willow tree (Salix acmophylla) irrigated by secondarily-treated wastewater as a fodder for goats. The nutrient and mineral contents in stems and leaves of two willow types (termed “red” and “white” for their bark color) and the concentration of secondary compounds were established. The adaptation of naïve goats to willow forage and its effect on the milk composition of late lactating goats were also studied. Willow fodder was composed of 45% leaves and 55% stems, on a DM basis; the weighted content of CP, ME, NDF, Ca, and P were (on a DM basis): 13.6%, 1.8 Mcal, 44.9%, 1.1%, and 0.2%, respectively. Lead, nickel and cadmium were found below the detection threshold in willow fodder and the concentrations of metals did not exceed the recommended ranges in feed. Intake was higher for red than for white willow fodder. The adaptation rate to white willow was low (27g/d) but steady and intake was similar to that of clover hay after one week. White willow contained 1.2-fold more salicin (P<0.05), 1.5-fold more gallic acid (P<0.01) and 1.8-fold more kaempferol than red willow. The two types of willow did not differ in their concentrations of salicylic acid, hyperin, salidroside and helicon. No evidence was found that willow at the amounts consumed in this study – up to 500g/d during the adaptation period and ca. 600g/d in late lactation – could be harmful to goats, as neither of the liver enzymes increased in blood, following exposure to willow. When Baladi (Mamber) goats at their third lactation at 240days post-partum were provided with willow after grazing hours for a period of 10days, milk yield was not affected. Somatic cell counts soared from 1.3*106 to up to 2.9*106 in the control group, but did not change in the group that was fed willow. These initial results imply that willow that is irrigated with treated wastewater can serve as medium-quality forage for dairy goats. Specific compounds contained in willow fodder may be of significant value in maintaining and improving the health and welfare of dairy goats.

Size-resolved aerosol composition at an urban and a rural site in the Po Valley in summertime: implications for secondary aerosol formation

Abstract. The aerosol size-segregated chemical composition was analyzed at an urban (Bologna) and a rural (San Pietro Capofiume) site in the Po Valley, Italy, during June and July 2012, by ion-chromatography (major water-soluble ions and organic acids) and evolved gas analysis (total and water-soluble carbon), to investigate sources and mechanisms of secondary aerosol formation during the summer. A significant enhancement of secondary organic and inorganic aerosol mass was observed under anticyclonic conditions with recirculation of planetary boundary layer air but with substantial differences between the urban and the rural site. The data analysis, including a principal component analysis (PCA) on the size-resolved dataset of chemical concentrations, indicated that the photochemical oxidation of inorganic and organic gaseous precursors was an important mechanism of secondary aerosol formation at both sites. In addition, at the rural site a second formation process, explaining the largest fraction (22 %) of the total variance, was active at nighttime, especially under stagnant conditions. Nocturnal chemistry in the rural Po Valley was associated with the formation of ammonium nitrate in large accumulation-mode (0.42–1.2 µm) aerosols favored by local thermodynamic conditions (higher relative humidity and lower temperature compared to the urban site). Nocturnal concentrations of fine nitrate were, in fact, on average 5 times higher at the rural site than in Bologna. The water uptake by this highly hygroscopic compound under high RH conditions provided the medium for increased nocturnal aerosol uptake of water-soluble organic gases and possibly also for aqueous chemistry, as revealed by the shifting of peak concentrations of secondary compounds (water-soluble organic carbon (WSOC) and sulfate) toward the large accumulation mode (0.42–1.2 µm). Contrarily, the diurnal production of WSOC (proxy for secondary organic aerosol) by photochemistry was similar at the two sites but mostly affected the small accumulation mode of particles (0.14–0.42 µm) in Bologna, while a shift to larger accumulation mode was observed at the rural site. A significant increment in carbonaceous aerosol concentration (for both WSOC and water-insoluble carbon) at the urban site was recorded mainly in the quasi-ultrafine fraction (size range 0.05–0.14 µm), indicating a direct influence of traffic emissions on the mass concentrations of this range of particles.

Nectar microbes can reduce secondary metabolites in nectar and alter effects on nectar consumption by pollinators

Secondary metabolites that are present in floral nectar have been hypothesized to enhance specificity in plant-pollinator mutualism by reducing larceny by non-pollinators, including microorganisms that colonize nectar. However, few studies have tested this hypothesis. Using synthetic nectar, we conducted laboratory and field experiments to examine the effects of five chemical compounds found in nectar on the growth and metabolism of nectar-colonizing yeasts and bacteria, and the interactive effects of these compounds and nectar microbes on the consumption of nectar by pollinators. In most cases, focal compounds inhibited microbial growth, but the extent of these effects depended on compound identity, concentration, and microbial species. Moreover, most compounds did not substantially decrease sugar metabolism by microbes, and microbes reduced the concentration of some compounds in nectar. Using artificial flowers in the field, we also found that the common nectar yeast Metschnikowia reukaufii altered nectar consumption by small floral visitors, but only in nectar containing catalpol. This effect was likely mediated by a mechanism independent of catalpol metabolism. Despite strong compound-specific effects on microbial growth, our results suggest that the secondary metabolites tested here are unlikely to be an effective general defense mechanism for preserving nectar sugars for pollinators. Instead, our results indicate that microbial colonization of nectar could reduce the concentration of secondary compounds in nectar and, in some cases, reduce deterrence to pollinators.

Effect of light intensity and wavelength on concentration of plant secondary metabolites in the leaves of Flourensia cernua

Flourensia cernua (tarbush) is a shrub that has encroached into grasslands in many areas of the northern Chihuahuan Desert and contains high levels of carbon-based secondary compounds. Concentrations of secondary compounds are affected by numerous biotic and abiotic influences, including amount and wavelength of solar radiation. However, responses to shade and ultraviolet light restriction are inconsistent among plant species and compound class. We conducted a three-year study to evaluate the effect of shade and UV light restriction on total phenolic and terpene concentrations in tarbush. Sixty plants were randomly assigned to one of three treatments (control, UV light restriction, or 50% incident light restriction). Mean concentrations of total phenolics and total volatiles in tarbush were 82.4 and 12.5 mg/g DM, respectively. Total phenolics did not differ between UV-restricted and control plants, but were lower in shaded plants than the other treatments (P < 0.05). Total volatiles tended to be greater for the UV-restricted treatment than control plants (P = 0.056), with shaded plants not different from either treatment. Treatment effects were detected for 18 individual compounds (P < 0.05). Our results partially support the hypothesis that UV restriction and shading alter carbon-based secondary chemical concentrations.