Influence of light and nitrogen on the phlorotannin content of the brown seaweeds Ascophyllum nodosum and Fucus vesiculosus

Phlorotannins, C-based defence compounds in brown seaweeds, show a high degree of spatial and temporal variation within seaweed species. One important model explaining this variation is the Carbon Nutrient Balance Model (CNBM), which states that the relative supply of carbon and limiting nutrients will determine the level of defence compounds in plants. Nitrogen is often considered to be the limiting nutrient for marine macroalgal growth and the CNBM thus predicts that when the carbon:nitrogen ratio is high, photosynthetically fixed carbon will be allocated to production of phlorotannins. In the present study, we evaluated the effects of light (i.e. carbon) and nitrogen on the phlorotannin content of two intertidal brown seaweeds, Ascophyllum nodosum and Fucus vesiculosus. This was done in an observational field study, as well as in a manipulative experiment where plants from habitats with different light regimes were subjected to different nitrogen and light treatments, and their phlorotannin content was measured after 14 days. The results showed that there was a negative relationship between tissue nitrogen and phlorotannin content in natural populations of F. vesiculosus, but not in A. nodosum. In the short term, the phlorotannin content in both algal species was not affected by changes in nitrogen availability. Exposure to sunlight had a positive effect on the phlorotannin content in natural populations of both algal species but, in the manipulative experiment, only F. vesiculosus showed a rapid response to changes in light intensities. Plants subjected to sunlight contained higher phlorotannin content than shaded plants. In conclusion, the results imply that nitrogen availability explains some of the natural variation in the phlorotannin content of F. vesiculosus, but the light environment has greater importance than nitrogen availability in predicting the phlorotannin content of each species.     

Acoustic observations of zooplankton in lakes using a Doppler current profiler

1. In this paper we test the usefulness of acoustic backscatter measurements from a 614 kHz Acoustic Doppler Current Profiler (ADCP) for the qualitative and quantitative characterisation of zooplankton distributions in lakes. ADCP‐based backscatter estimates were compared with frequent net hauls obtained during a calibration experiment in which the acoustic backscatter was strongly dominated by vertical migrating Chaoborus flavicans larvae. 2. The correlation between backscatter estimates and the C. flavicans concentration was very good. Vertical swimming speed of larvae, measured directly by the ADCP, was up to a maximum of 5 mm s^?1 and agreed very well with the observed vertical movement of the backscatter contour lines. Although the strong backscatter from C. flavicans overwhelmed the signal from the remaining zooplankton, a good correlation between backscatter strength and the total remaining zooplankton concentration, dominated by Cyclops spp., was found for the depth and time intervals where no C. flavicans were present. 3. In addition to the calibration experiment, longer‐term ADCP measurements from different lakes revealed a strong temporal correlation between the onset of the up‐ and downward migration of zooplankton and the local sunset and sunrise. 4. We conclude that ADCPs can be used to monitor plankton distributions both temporally and spatially. It also seems possible to estimate plankton densities after appropriate calibration.     

Interactive effects of elevated summer temperature,nutrient availability,and irradiance on growth and chemical compositions of juvenile kelp,Eisenia bicyclis

Previous experiments with a factorial design have revealed the effects of several environmental factors on species performance and their interactions, which indicate synergistic or antagonistic effects. Temperature, nutrient availability, and irradiance are well‐known environmental factors that affect the growth and chemical composition of brown algae. However, relatively few studies have tested their combined effect on brown algal growth and chemical composition using a three‐way factorial design. We conducted a culture experiment to test the combined effects of elevated summer temperatures (23 and 26°C), irradiance (180 and 30 μmol photon m^?2 s^?1), and nutrient availability (enriched and non‐enriched seawater) on four relative growth rates (RGRs; based on wet weight, blade width, length, and area) and three chemical compositions (including carbon, nitrogen, and phlorotannin content) in juvenile sporophytes of the kelp Eisenia bicyclis. RGR based on blade width was the most sensitive to abiotic factors among all RGRs. A significant interaction between temperature and nutrient availability on this RGR suggested that the negative effect of elevated temperature was antagonized by a reduction in nutrient availability. Similarly, the positive effect of elevated irradiance on carbon content was synergized by reduced nutrient availability. Moreover, the negative effect of increased irradiance on nitrogen content was antagonized by elevated temperature in nutrient‐enriched treatments, but not in non‐enriched treatments. The content of carbon‐based phlorotannins increased with reduced nutrient availability but not with elevated irradiance. These results suggest that these abiotic factors have complex interactions on the growth and chemical composition of this species.     

Effects of light and nutrient availability on the growth,allocation, carbon/nitrogen balance,phenolic chemistry,and resistance to herbivory of two freshwater macrophytes

Phenotypic responses of Potamogeton amplifolius and Nuphar advena to different light (7% and 35% of surface irradiance) and nutrient environments were assessed with field manipulation experiments. Higher light and nutrient availability enhanced the growth of P. amplifolius by 154% and 255%, respectively. Additionally, biomass was allocated differently depending on the resource: high light availability resulted in a higher root/shoot ratio, whereas high nutrient availability resulted in a lower root/shoot ratio. Low light availability and high nutrient availability increased the nitrogen content of leaf tissue by 53% and 40% respectively, resulting in a 37% and 31% decrease in the C/N ratio. Root nitrogen content was also increased by low light and high nutrient availability, by 50% (P=0.0807) and 77% respectively, resulting in a 20% and 40% decrease in root C/N ratio. Leaf phenolics were significantly increased 72% by high light and 31% by high nutrient availability, but root phenolic concentrations were not altered significantly. None of these changes in tissue constituents resulted in altered palatability to crayfish. N. advena was killed by the same high nutrient treatment that stimulated growth in P. amplifolius, preventing assessment of phenotypic responses to nutrient availability. However, high light availability increased overall growth by 24%, but this was mainly due to increased growth of the rhizome (increased 100%), resulting in a higher root/shoot ratio. High light tended to increase the production of floating leaves (P=0.09) and significantly decreased the production of submersed leaves. High light availability decreased the nitrogen content by 15% and 25% and increased the phenolic concentration by 88% and 255% in floating and submersed leaves, respectively. These differences in leaf traits did not result in detectable differences in damage by herbivores.     

Productivity, carbon isotope discrimination and leaf traits of trees of Eucalyptus globulus Labill. in relation to water availability

The stand basal area, carbon isotope discrimination (Δ) in tree rings and leaves, leaf area index and leaf traits of trees were measured in 6‐ to 8‐year‐old stands of Eucalyptus globulus Labill. across a gradient of rainfall of 600–1400 mm year^?1 in south‐western Australia to better understand the importance of leaf traits and gas‐exchange as determinants of stand productivity. Δ ranged from 17‰ to 21‰. Δ and basal area were highly, positively correlated with each other and the ratio of mean annual rainfall to potential evaporation (P/PE). Leaf area index, soil water holding capacity and leaf nitrogen content were only weakly correlated with basal area. Δ and P/PE were negatively correlated with leaf nitrogen content. Δ was negatively correlated with leaf density but positively correlated with specific leaf area. This is consistent with the theory that larger leaf nitrogen content and smaller specific leaf area are associated with increased photosynthetic capacity and increased leaf‐scale water‐use‐efficiency, and that Δ is influenced by mesophyll conductance. It is concluded that canopy conductance is a more important determinant of growth in water‐limited conditions than either leaf area index or leaf traits in fertilized stands of E. globulus. Water availability was dictated more by rainfall than soil type.     

Effects of nutrient enrichment and herbivory on morphology,reproduction and chemical content of Turbinaria conoides (Phaeophyceae)

The effects of nutrient enrichment and herbivory on resource allocation patterns among morphology, reproduction, and chemical content of the brown alga, Turbinaria conoides (J. Agardh) Kützing were tested in the shallow subtidal zone of the Gulf of Thailand. The field experimental design comprised 36 plots (50 × 50 cm²) with and without herbivores, and two nutrient levels. Cages (uncaged and fully caged plots) were used to exclude herbivorous fishes and two nutrients levels were achieved by experimental enrichment above ambient nutrient concentrations. For morphology of Turbinaria, the maximum length (holdfast to frond apex), the width of the base of the stipe, number of blades, holdfast and stipe diameter were measured. Biomass, reproductive output, and tissue nutrient (carbon: nitrogen: phosphorus) content of T. conoides were examined. Phlorotannin concentrations were examined using a modified Folin‐Ciocalteu method. The results showed that herbivory had no effect on morphology, reproduction, or phlorotannin concentrations. This could be due to the structural and morphological deterrents of alga, which might minimize grazing effects from herbivorous fishes. Nutrient enrichment had no effect on morphology and reproduction of T. conoides, possibly due to low nutrient demand in Turbinaria. However, nutrient enrichment did affect phlorotannin concentrations, as phlorotannins in the enriched plots were lower than the ambient plots. These results support, in part, the carbon–nutrient balance hypothesis that states algae will allocate fewer resources to production of anti‐herbivore chemical compounds when enriched with potential growth‐limiting nutrients.     

LACK OF DEFENSE OR PHLOROTANNIN INDUCTION BY UV RADIATION OR MESOGRAZERS IN DESMARESTIA ANCEPS AND D. MENZIESII (PHAEOPHYCEAE)1

Phlorotannins are polyphenoloic metabolites occurring only in the Phaeophyceae that have numerous putative primary roles (e.g. cell‐wall construction and storage) as well as secondary metabolic roles, which include herbivore feeding deterrence and protection from UV radiation. The proposed role of phlorotannins in the defense against UV radiation is of particular importance in the Antarctic due to depletion of the stratospheric ozone layer in that area. Several studies of brown algae have found evidence of an induction response (the production of defensive metabolites, including phlorotannins) after grazing by various mesograzers, after simulated grazing/wounding, and after exposure to increases in UV radiation. This study aimed to determine if phlorotannin production or other defenses in two dominant, endemic Antarctic species (Desmarestia menziesii Montagne and Desmarestia anceps J. Agardh) could be induced by an increase in exposure to UV radiation or by natural and artificial grazing. An in situ experiment failed to detect any effect of UV radiation on phlorotannin concentrations in either species or on subsequent palatability in feeding bioassays. A laboratory‐based experiment did not detect any effect of mesoherbivore grazing or simulated grazing (wounding) on palatability or the concentration of phlorotannins in D. menziesii. Instead, phlorotannin concentrations increased in all treatments in both experiments, consistent with an increase in overall resource availability due to an increase in available PAR compared with the in situ irradiance at the algal collection sites.     

Feeding efficiency of planktivores under disturbance,the effect of water colour,predation threat and shoal composition

The consumption of phantom midge Chaoborus flavicans larvae by Perca fluviatilis showed clear response to water colour, predation threat and shoal composition with the most significant negative effect for water colour. In the case of Rutilus rutilus, no similar combined response was observed and the total prey consumption was significantly negatively affected by predation threat of Esox lucius. The results suggest that differences in life‐history traits may result in disparity in species‐specific responses to disturbance.     

Diversity of phlorotannin profiles among sargassasacean species affecting variation and abundance of epiphytes

In general, epiphytes have detrimental effects on the growth of their basiphytes due to competition for light and nutrients. Therefore, basiphyte species must expend energy suppressing epiphytes. Some studies suggest that phlorotannins, i.e. brown algal polyphenols, prevent colonization by epiphytes, whereas others question their allelopathic function because there is not necessarily a negative correlation between epiphyte abundance and the phlorotannin content of the basiphyte algae. Various phlorotannin components are found in brown algal species, thus we hypothesized that the antifouling activities of polyphenolic compounds may differ and that the analysis of phlorotannin profiles could be useful for estimating their ecological functions. We surveyed the epiphyte richness in the apical portions of 373 thalli from 15 sargassacean species, demonstrating that the variation and abundance of epiphyte species differed remarkably among the basiphyte species. However, there was a weak negative correlation between the density and total phlorotannin content of the basiphyte algae in only one of the 18 epiphyte species. The interspecific differences in the phlorotannin profile were characterized by quantitative ¹H nuclear magnetic resonance spectroscopy (qNMR), and four major groups were categorized based on cluster and principal component analyses of polyphenolic signals in the qNMR spectra. The epiphyte Neosiphonia harveyi was more abundant on Sargassum hemiphyllum, S. patens and S. piluliferum than on other basiphyte species, and these three species were similar according to the cluster analysis. These results suggest that some phlorotannin components may be more effective for antifouling; thus interspecific differences in the phlorotannin profile could affect the variation and abundance of epiphytes.     

The invasive alien plant species Solidago gigantea alters ecosystem properties across habitats with differing fertility

Question: Invasive alien plants can affect biomass production and rates of biogeochemical cycling. Do the direction and intensity of such effects depend upon the functional traits of native and alien species and upon the properties of the invaded habitat, with the same alien species having differing impacts in different habitats? Location: Lowlands of Switzerland. Methods: Fourteen grassland and wetland sites invaded by Solidago gigantea and widely differing in biomass production and soil P availability were surveyed. To determine whether the impact of the species was related to site fertility, we compared the invaded and native vegetation in terms of biomass, species composition, plant traits and soil properties. Results: S. gigantea generally increased the above‐ground biomass production of the vegetation and soil C content, while reducing nutrient concentrations in biomass and N availability in the soil. However, it had no significant effect on plant species richness, soil respiration, soil pH and P availability. Leaves of S. gigantea had a greater C content than those of native species; other leaf traits and root phosphatase activity did not differ significantly. Conclusions: Our results suggest that a conservative nutrient‐use strategy allows S. gigantea to invade a broad range of habitats. The observed effects of invasion did not vary according to biomass production of the invaded sites, but some effects did depend on soil P availability, being more pronounced at more P‐rich sites. Thus, the full range of invaded habitats should be considered in studying the potential impact of plant invasions on ecosystem processes.     

In‐situ monitoring of Saccharomyces cerevisiae ITV01 bioethanol process using near‐infrared spectroscopy NIRS and chemometrics

The application feasibility of in‐situ or in‐line monitoring of S. cerevisiae ITV01 alcoholic fermentation process, employing Near‐Infrared Spectroscopy (NIRS) and Chemometrics, was investigated. During the process in a bioreactor, in the complex analytical matrix, biomass, glucose, ethanol and glycerol determinations were performed by a transflection fiber optic probe immersed in the culture broth and connected to a Near‐Infrared (NIR) process analyzer. The NIR spectra recorded between 800 and 2,200 nm were pretreated using Savitzky‐Golay smoothing and second derivative in order to perform a partial least squares regression (PLSR) and generate the calibration models. These calibration models were tested by external validation and then used to predict concentrations in batch alcoholic fermentations. The standard errors of calibration (SEC) for biomass, ethanol, glucose and glycerol were 0.212, 0.287, 0.532, and 0.296 g/L and standard errors of prediction (SEP) were 0.323, 0.369, 0.794, and 0.507 g/L, respectively. Calibration and validation criteria were defined and evaluated in order to generate robust and reliable models for an alcoholic fermentation process matrix. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:510–517, 2016     

How are nitrogen availability,fine‐root mass,and nitrogen uptake related empirically? Implications for models and theory

Understanding the effects of global change in terrestrial communities requires an understanding of how limiting resources interact with plant traits to affect productivity. Here, we focus on nitrogen and ask whether plant community nitrogen uptake rate is determined (a) by nitrogen availability alone or (b) by the product of nitrogen availability and fine‐root mass. Surprisingly, this is not empirically resolved. We performed controlled microcosm experiments and reanalyzed published pot experiments and field data to determine the relationship between community‐level nitrogen uptake rate, nitrogen availability, and fine‐root mass for 46 unique combinations of species, nitrogen levels, and growing conditions. We found that plant community nitrogen uptake rate was unaffected by fine‐root mass in 63% of cases and saturated with fine‐root mass in 29% of cases (92% in total). In contrast, plant community nitrogen uptake rate was clearly affected by nitrogen availability. The results support the idea that although plants may over‐proliferate fine roots for individual‐level competition, it comes without an increase in community‐level nitrogen uptake. The results have implications for the mechanisms included in coupled carbon‐nitrogen terrestrial biosphere models (CN‐TBMs) and are consistent with CN‐TBMs that operate above the individual scale and omit fine‐root mass in equations of nitrogen uptake rate but inconsistent with the majority of CN‐TBMs, which operate above the individual scale and include fine‐root mass in equations of nitrogen uptake rate. For the much smaller number of CN‐TBMs that explicitly model individual‐based belowground competition for nitrogen, the results suggest that the relative (not absolute) fine‐root mass of competing individuals should be included in the equations that determine individual‐level nitrogen uptake rates. By providing empirical data to support the assumptions used in CN‐TBMs, we put their global climate change predictions on firmer ground.     

Drought stress provokes the down‐regulation of methionine and ethylene biosynthesis pathways in Medicago truncatula roots and nodules

Symbiotic nitrogen fixation is one of the first physiological processes inhibited in legume plants under water‐deficit conditions. Despite the progress made in the last decades, the molecular mechanisms behind this regulation are not fully understood yet. Recent proteomic work carried out in the model legume Medicago truncatula provided the first indications of a possible involvement of nodule methionine (Met) biosynthesis and related pathways in response to water‐deficit conditions. To better understand this involvement, the drought‐induced changes in expression and content of enzymes involved in the biosynthesis of Met, S‐adenosyl‐L‐methionine (SAM) and ethylene in M. truncatula root and nodules were analyzed using targeted approaches. Nitrogen‐fixing plants were subjected to a progressive water deficit and a subsequent recovery period. Besides the physiological characterization of the plants, the content of total sulphur, sulphate and main S‐containing metabolites was measured. Results presented here show that S availability is not a limiting factor in the drought‐induced decline of nitrogen fixation rates in M. truncatula plants and provide evidences for a down‐regulation of the Met and ethylene biosynthesis pathways in roots and nodules in response to water‐deficit conditions.     

Variation in P-content in aquatic plant tissues offers an efficient tool for determining plant growth strategies along a resource gradient

1. The application of functional ecology models to aquatic plants often relies on morphological and life‐history traits which may reflect, in part, the phenotypic plasticity displayed by aquatic plants. The present study was designed to evaluate the use of physiological traits, such as nutrition patterns, to describe aquatic plant strategies along a gradient of increasing resource availablity. 2. Taking phosphorus (P) as an example, nutrition‐use efficiencies were evaluated in five species, through the P‐content in plant tissues, the variations in P‐content according to nutrient availability and the perenniality of P‐storage. Plasticity in P‐storage was also investigated in Ranunculus peltatus, a morphologically highly plastic species. 3. In 2001, P‐content was analysed in Callitriche hamulata, C. obtusangula, C. platycarpa, Elodea nuttallii and R. peltatus tissue samples. These five species were sampled at nine different sites in streams along an increasing resource gradient in the Northern Vosges Biosphere Reserve (NE France). Variations of P‐content in the roots, stems and dissected and floating leaves of R. peltatus were also studied. 4. Only C. platycarpa and R. peltatus were found to occur in low nutrient availability conditions. Callitriche hamulata, C. obtusangula and E. nuttallii were restricted to mesotrophic and eutrophic sites. The highest nutrient‐use efficiency was found for E. nuttallii which was able to adapt its P‐storage to varying resource availabilities. Ranunculus peltatus was able to store high concentrations of P, but its P‐integration within the vegetative structure was less efficient under eutrophic conditions. Callitriche spp. appeared to have relatively low nutrient‐use efficiencies, although C. obtusangula displayed a high P‐content. While P was stored preferentially in roots in R. peltatus populations occurring in nutrient‐rich sites, there was no particular P‐storage organ for populations from nutrient‐poor sites. 5. On the basis of P‐usage, R. peltatus and E. nuttallii presented competitor traits, C. hamulata and C. platycarpa displayed stress‐tolerant nutrient signatures and for C. obtusangula, ruderal or competitor characteristics dominated. The use of physiological traits, such as nutrition patterns, may provide valuable, complementary information about aquatic plant strategies, independent from the influence of morphological trait plasticity often displayed by these plants.     

Carbon and nitrogen dynamics across a natural precipitation gradient in Patagonia,Argentina

Abstract. Both ecosystem carbon gain and nutrient availability are largely constrained by the magnitude and seasonality of precipitation in arid and semi‐arid ecosystems. We investigated the role of precipitation on ecosystem processes along an International Geosphere Biosphere Programme (IGBP) transect in temperate South America. The transect consists of a contiguous precipitation gradient in the southern region of Argentinean Patagonia (44–45° S), from 100 mm to 800 mm mean annual precipitation (MAP) and vegetation ranging from desert scrub to closed canopy forest. Gravimetric soil water content tracked changes in seasonal and annual precipitation, with a linear increase in soil water content with increasing MAP. Above‐ground net primary production (ANPP) increased linearly along the gradient of precipitation (ANPP =– 31.2 + 0.52 MAP, r²= 0.84, p= 0.028), supporting the relationship that carbon assimilation is largely controlled by available water in these sites, and was in general agreement with regional models of ANPP and rainfall. However, inorganic soil nitrogen was also highly linearly correlated with both MAP ([N] = 0.19 MAP – 32, r²= 0.96, p= 0.003) and ANPP (ANPP = 2.6 [N_inorganic]+59.4, r²= 0.79, p= 0.042), suggesting a direct control of precipitation on nitrogen turnover and an interaction with nitrogen availability in controlling carbon gain. The asynchrony of precipitation and changes in dominant vegetation may play important roles in determining the carbon‐nitrogen interactions along this rainfall gradient.     

Predicting seasonal and spatial variations in diet quality of Pyrenean chamois (Rupicapra pyrenaica pyrenaica) using near infrared reflectance spectroscopy

Monitoring nutritional status of wildlife is key to understanding the population response to changes in food availability. Several direct and indirect methods have been proposed for such purposes, but faecal nitrogen (FN) is by far the most commonly used indirect non-invasive indicator of free-ranging ruminant diet quality. In this work, two methods were used to estimate the FN content in 291 pellet samples of Pyrenean chamois (Rupicapra pyrenaica pyrenaica) collected during a 2-year period (May 2009 to May 2011) in two chamois populations from the Catalan Pyrenees, Spain: the Dumas LECO analyzer and near-infrared reflectance spectroscopy (NIRS). In order to optimize further FN estimations we performed three different NIRS calibrations: (1) general, across year, season and populations; (2) population-specific; and (3) season-specific, i.e., different periods of vegetation growth. FN ranged from 1.66 % to 2.85 % (dry matter basis) and was higher in the main vegetation growing season than in winter. Concerning NIRS calibration, our study confirmed that FN of Pyrenean chamois can be accurately determined by NIRS, since the general calibration was accurate enough to predict FN. It is concluded that NIRS represents a non-destructive, emission-free and low-cost analytical technique which may reduce the use of conventional laborious methods for estimating FN in long-term wildlife monitoring.     

Near‐infrared spectroscopy for metabolite quantification and species identification

Near‐infrared (NIR) spectroscopy is a high‐throughput method to analyze the near‐infrared region of the electromagnetic spectrum. It detects the absorption of light by molecular bonds and can be used with live insects. In this study, we investigate the accuracy of NIR spectroscopy in determining triglyceride level and species of wild‐caught Drosophila. We employ the chemometric approach to produce a multivariate calibration model. The multivariate calibration model is the mathematical relationship between the changes in NIR spectra and the property of interest as determined by the reference analytical method. Once the calibration model was developed, we used an independent set to validate the accuracy of the calibration model. The optimized calibration model for triglyceride quantification yielded coefficients of determination of 0.73 for the calibration test set and 0.70 for the independent test set. Simultaneously, we used NIR spectroscopy to discriminate two species of Drosophila. Flies from independent sets were correctly classified into Drosophila melanogaster and Drosophila simulans with accuracy higher than 80%. These results suggest that NIRS has the potential to be used as a high‐throughput screening method to assess a live individual insect's triglyceride level and taxonomic status.     

Rapid Biomass Quality Determination of Corn Stover Using Near-Infrared Reflectance Spectroscopy

Near-infrared reflectance spectroscopy (NIRS) has been used extensively in the forage industry for rapid measurement of forage constituents and could be useful for determining quality of biomass feedstocks at the point of delivery. In previous work, we developed an assay that partitions feedstock carbohydrates based on their availability to be converted to fermentable sugars, including non-structural carbohydrates (C _N), biochemically available carbohydrates (C _B) with an associated first-order availability rate constant (k _B), and unavailable carbohydrates (C _U ). Additional quality parameters measured included neutral detergent lignin (NDL), total available carbohydrates (C _A), and total carbohydrates (C _T). We evaluated the variability of biomass quality parameters in a set of corn stover samples and developed calibration equations for determining parameter values using NIRS. Fifty-two corn stover samples harvested in Iowa and Wisconsin in 2005 and 2006 were analyzed using a high-throughput assay for determining feedstock quality for biochemical conversion. Non-structural carbohydrates ranged from 84 to 155?g?kg^?1 dry matter (DM); C _B ranged from 354 to 557?g?kg^?1 DM; k _B ranged from 0.199 to 0.330?h^?1; C _A ranged from 463 to 699?g?kg^?1 DM, and NDL ranged from 32 to 74?g?kg^?1 DM. Significant differences (P?<?0.0001) among samples were observed for all parameters, except k _B. Near-infrared reflectance spectroscopy calibration equations were developed for C _N, C _B, C _A, C _U , C _T, and NDL. It was not possible to generate a meaningful calibration equation for k _B. There is significant variability within the corn stover population for several key quality-related carbohydrate and lignin constituents which can be predicted reliably using NIRS.     

EFFECTS OF UV RADIATION ON GROWTH AND PHLOROTANNINS IN FUCUS GARDNERI (PHAEOPHYCEAE) JUVENILES AND EMBRYOS1

Diminishing levels of atmospheric ozone are increasing UV stress on intertidal algae. Early developmental stages tend to be more susceptible to environmental stresses; however, little research has examined how these stages are protected from UV radiation (UVR). Many brown algae contain high levels of phlorotannins, which are thought to function in screening UVR. In this study, we tested the effects of ambient levels of UV‐B and UV‐A on growth and phlorotannin production in 1‐ to 2‐cm juvenile and microscopic postsettlement embryos of the intertidal alga Fucus gardneri Silva. Algae were grown in four light treatments: 1) ambient light; 2) under cellulose acetate, which lowered light quantity but did not affect light quality; 3) under Mylar^TM, which filtered UV‐B; and 4) under Plexiglas^TM, which blocked UV‐A and UV‐B. Over a 3‐week period, UV‐B inhibited and UV‐A enhanced the growth of F. gardneri embryos, whereas the growth of juveniles was not affected. Phlorotannin concentrations of both embryos and juveniles did not differ in any of the light treatments. Our results suggest that embryos of F. gardneri are susceptible to UV light but develop a tolerance to it as they mature. This tolerance may result from increases in phlorotannin concentrations that occur during maturation; however, phlorotannin production in embryonic or juvenile stages is either not induced by UV light or takes more than 3 weeks to occur.     

Leaf traits of two Mediterranean perennial tussock grass species in relation to soil nitrogen and phosphorus availability

Studying relationships of plant traits to ecosystem properties is an emerging approach aiming to understand plant's potential effect on ecosystem functioning. In the current study, we explored links between morphological and nutritional leaf traits of two Mediterranean perennial grass species Stipa tenacissima and Lygeum spartum, widely used to prevent desertification process by stabilizing sand dunes. We evaluated also relationships in terms of nitrogen (N) and phosphorus (P) availability between leaves of the investigated species and the corresponding soil. Our results showed that leaf P was very low in comparison with leaf N for the two investigated species. In fact, chlorophyll content, photosynthesis capacity and water conservation during photosynthesis are mainly linked to leaf nitrogen content. Our findings support previous studies showing that at the species levels, morphological and nutritional leaf traits were not related. On the other hand, significant relationships were obtained between soil N and leaf N for S. tenacissima (P = 0.011) and L. spartum (P = 0.033). However, leaf P was not significantly related to soil P availability for both species. We suggest that any decrease in soil N with the predicted increasing aridity may result in reduction in leaf N and thus in worst dysfunction of some biological processes levels.