Leaf silicon content in banana (Musa spp.) reveals the weathering stage of volcanic ash soils in Guadeloupe

Several plant species accumulate silicon, which is taken up by roots in soil solution. The Si concentration in soil solution can be governed by silicate dissolution and formation, and thus soil constitution. Here, we study the Si leaf content of mature banana plants (Musa acuminata cv Grande Naine) cropped on soils derived from andesitic ash in Guadeloupe through standard foliar analysis. The soils strongly differ in weathering stage and total Si content. The most desilicated soils (Andosol–Nitisol–Ferralsol) occur in the wettest areas, on the Eastern slopes (Es) of the volcano exposed to rain bearing winds. Least weathered soils (Andosol–Cambisol) occur on Western slopes (Ws). The average leaf Si concentration ranges from 2.7 to 3.9 g kg^?1 for bananas cropped in Es soils, and from 7.7 to 9.6 g kg^?1 in Ws soils. The leaf Si concentrations are lowest for the Es gibbsite-rich Andosols and Ferralsols. The leaf Si concentration is positively correlated with soil CaCl₂-extractable Si content, soil Si content and total reserve in weatherable minerals. The silicon content of banana leaves thus reveals the weathering stage of volcanic ash soils in Guadeloupe.     

Caloric content of plant species and its role in a Leymus chinensis steppe community of Inner Mongolia, China

The caloric contents of 42 species and their composition in a Leymus chinensis steppe community of Inner Mongolia, China were determined and analyzed based on the field experiment for 11 years. The caloric content (x ± SD) of aboveground parts of plant species varied from (13156 ± 1141) J·g^?1 (ash contained) to (18141 ± 527) J·g^?1. The average caloric content of all species was (16899 ± 840) J·g^?1 and the inter-specific CV (coefficient of variation) was 4.9%. Of all the species, Caragana microphylla had the highest caloric content (18142 J·g^?1). Grasses had a higher average caloric content ((17425 ± 291) J·g^?1) than forbs ((16734 ± 844)J·g^?1). When the herbaceous species were classified into subgroups according to life-form and growth-form, the order of average caloric contents, from high to low, was: tall grasses ((17717 ± 92) J·g^?1) > legume ((17228 ± 433) J·g^?1) > short grasses ((17250 ± 218) J·g^?1) > remaining forbs ((16784 ± 529) J·g^?1) > subshrubs ((16719 ± 69) J·g^?1) > annuals and biennials ((15911 ± 1759) J·g^?1). There was a positive correlation (P < 0.05) between the caloric contents of 42 species and their relative biomass in the community. When all species were classified into 3 groups according to their composition in the community, the average caloric contents, weighed by the species relative biomass, followed the order: dominant (17740 J·g^?1) > companion (17244 J·g^?1) > incidental (16653 J·g^?1). The plants with high caloric contents were more competitive, which allowed them to gain a dominant status, whereas the competitive abilities of plants with low caloric contents were generally weak. The latter made up the companion or incidental species in a steppe community.     

Caloric content of plant species and its role in a Leymus chinensis steppe community of Inner Mongolia, China

The caloric contents of 42 species and their composition in a Leymus chinensis steppe community of Inner Mongolia, China were determined and analyzed based on the field experiment for 11 years. The caloric content (x ± SD) of aboveground parts of plant species varied from (13156 ± 1141) J·g^?1 (ash contained) to (18141 ± 527) J·g^?1. The average caloric content of all species was (16899 ± 840) J·g^?1 and the inter-specific CV (coefficient of variation) was 4.9%. Of all the species, Caragana microphylla had the highest caloric content (18142 J·g^?1). Grasses had a higher average caloric content ((17425 ± 291) J·g^?1) than forbs ((16734 ± 844)J·g^?1). When the herbaceous species were classified into subgroups according to life-form and growth-form, the order of average caloric contents, from high to low, was: tall grasses ((17717 ± 92) J·g^?1) > legume ((17228 ± 433) J·g^?1) > short grasses ((17250 ± 218) J·g^?1) > remaining forbs ((16784 ± 529) J·g^?1) > subshrubs ((16719 ± 69) J·g^?1) > annuals and biennials ((15911 ± 1759) J·g^?1). There was a positive correlation (P < 0.05) between the caloric contents of 42 species and their relative biomass in the community. When all species were classified into 3 groups according to their composition in the community, the average caloric contents, weighed by the species relative biomass, followed the order: dominant (17740 J·g^?1) > companion (17244 J·g^?1) > incidental (16653 J·g^?1). The plants with high caloric contents were more competitive, which allowed them to gain a dominant status, whereas the competitive abilities of plants with low caloric contents were generally weak. The latter made up the companion or incidental species in a steppe community.     

Biogeographic Patterns of Structural Traits and C:N:P Stoichiometry of Tree Twigs in China’s Forests

There have been a number of studies on biogeographic patterns of plant leaf functional traits; however, the variations in traits of other plant organs such as twigs are rarely investigated. In this study, we sampled current-year twigs of 335 tree species from 12 forest sites across a latitudinal span of 32 degrees in China, and measured twig specific density (TSD), twig dry matter content (TDMC), and carbon (C), nitrogen (N) and phosphorous (P) contents, to explore the latitudinal and environmental patterns of these twig traits. The overall mean of TSD and TDMC was 0.37 g cm⁻³ and 41%, respectively; mean twig C, N and P was 472 mg g⁻¹, 9.8 mg g⁻¹ and 1.15 mg g⁻¹, respectively, and mean N:P mass ratio was 10.6. TSD was positively correlated with TDMC which was positively associated with twig C but negatively with twig N and P. There were no significant differences in TSD between conifer, deciduous-broadleaf and evergreen-broadleaf plants, but evergreen-broadleaf plants had the lowest and conifers the highest TDMC. Conifer twigs were lowest in C, N, P and N:P, whereas deciduous-plant twigs were highest in N and P and evergreen-plant twigs were highest in C and N:P. As latitude increased or temperature/precipitation dropped, TDMC and P increased, but N:P ratio decreased. Our results also showed that the patterns of twig P and N:P stoichiometry were consistent with those reported for leaves, but no significant trends in twig N were observed along the gradient of latitude, climate and soils. This study provides the first large-scale patterns of the twig traits and will improve our understanding of the biogeochemistry of carbon and other key nutrients in forest ecosystems.     

Important foliar traits depend on species-grouping: analysis of a remnant temperate forest at the Keerqin Sandy Lands, China

Foliar traits are often interpreted to reflect strategies for coping with water and nutrient supply limitations. In this study, we measured several important leaf traits for 147 species sampled from a remnant, temperate deciduous broad-leaved forest in Keerqin Sandy Lands, Northeast China to test whether these traits are ‘invariant’ or dependent on water supply limitations. Our data show that average specific leaf area (SLA), nitrogen (N) and phosphorus (P) concentrations, leaf C/N, C/P and N/P were 273 cm²?g^?1, 18.1 mg?g^?1, 1.60 mg?g^?1, 28.2, 343 and 12.4, respectively. However, most of these traits were significantly different (P?<?0.05) for different species groupings based on growth forms, phylogenetic history, photosynthetic pathways, or habitats. SLA was positively correlated with leaf P concentration across the broad spectrum of 118 species and most species functional groupings. However, SLA was not correlated with N concentration across all species or within each species functional group. SLA and N and P concentrations in dry habitats were lower than those in wet habitats, whereas leaf C/N, C/P, and N/P had the opposite trend both across all species and within major species functional groupings (herb, monocots and C3 species). Our data indicate that SLA vs. leaf N and SLA vs. P relationships may be regulated differentially for different species functional groupings and that water limitation may have a greater influence than nutrient limitation for plant growth.     

Chemical composition and construction cost for roots of Mediterranean trees, shrub species and grassland communities

The construction cost of fine roots was studied in 23 woody species and two grassland communities, growing under natural conditions in southern Spain. Calculation of the energy (glucose) required for their synthesis was based on the quantification of chemical components present in tissues. Despite considerable differences in the chemical composition of the three life forms studied (trees, shrubs and herbaceous), detected differences in construction cost were non‐significant (mean value: 1·64 ± 0·13 g glucose g^?1). However, shrubs and herbaceous plants growing in more fertile habitats expended significantly less energy on root synthesis (1·58 ± 0·06 and 1·41 ± 0·05 g glucose g^?1, respectively) than those growing in less fertile areas (1·80 ± 0·06 and 1·57 ± 0·1 g glucose g^?1, respectively), because they contained smaller amounts of either waxes (shrubs) or lignins (herbaceous), both expensive to synthesize, and, proportionately, more cellulose; which is inexpensive to synthesize. Deciduous and evergreen tree species also differed mainly with regard to wax and cellulose contents, giving rise to a significantly higher construction cost in evergreens (1·57 ± 0·07 g glucose g^?1 versus 1·78 ± 0·02 g glucose g^?1). The differences observed in construction cost appeared to be due more to habitat‐induced differences in chemical composition than to any intrinsic difference between the species studied.     

A frozen feast: thawing permafrost increases plant‐available nitrogen in subarctic peatlands

Many of the world's northern peatlands are underlain by rapidly thawing permafrost. Because plant production in these peatlands is often nitrogen (N)‐limited, a release of N stored in permafrost may stimulate net primary production or change species composition if it is plant‐available. In this study, we aimed to quantify plant‐available N in thawing permafrost soils of subarctic peatlands. We compared plant‐available N‐pools and ‐fluxes in near‐surface permafrost (0–10 cm below the thawfront) to those taken from a current rooting zone layer (5–15 cm depth) across five representative peatlands in subarctic Sweden. A range of complementary methods was used: extractions of inorganic and organic N, inorganic and organic N‐release measurements at 0.5 and 11 °C (over 120 days, relevant to different thaw‐development scenarios) and a bioassay with Poa alpina test plants. All extraction methods, across all peatlands, consistently showed up to seven times more plant‐available N in near‐surface permafrost soil compared to the current rooting zone layer. These results were supported by the bioassay experiment, with an eightfold larger plant N‐uptake from permafrost soil than from other N‐sources such as current rooting zone soil or fresh litter substrates. Moreover, net mineralization rates were much higher in permafrost soils compared to soils from the current rooting zone layer (273 mg N m^?2 and 1348 mg N m^?2 per growing season for near‐surface permafrost at 0.5 °C and 11 °C respectively, compared to ?30 mg N m^?2 for current rooting zone soil at 11 °C). Hence, our results demonstrate that near‐surface permafrost soil of subarctic peatlands can release a biologically relevant amount of plant available nitrogen, both directly upon thawing as well as over the course of a growing season through continued microbial mineralization of organically bound N. Given the nitrogen‐limited nature of northern peatlands, this release may have impacts on both plant productivity and species composition.     

Non‐symbiotic nitrogen fixation during leaf litter decomposition in an old‐growth temperate rain forest of Chiloé Island,southern Chile: Effects of single versus mixed species litter

Heterotrophic nitrogen fixation is a key ecosystem process in unpolluted, temperate old‐growth forests of southern South America as a source of new nitrogen to ecosystems. Decomposing leaf litter is an energy‐rich substrate that favours the occurrence of this energy demanding process. Following the niche ‘complementarity hypothesis’, we expected that decomposing leaf litter of a single tree species would support lower rates of non‐symbiotic N fixation than mixed species litter taken from the forest floor. To test this hypothesis we measured acetylene reduction activity in the decomposing monospecific litter of three evergreen tree species (litter C/N ratios, 50–79) in an old‐growth rain forest of Chiloé Island, southern Chile. Results showed a significant effect of species and month (anova , Tukey's test, P < 0.05) on decomposition and acetylene reduction rates (ARR), and a species effect on C/N ratios and initial % N of decomposing leaf litter. The lowest litter quality was that of Nothofagus nitida (C/N ratio = 78.7, lignin % = 59.27 ± 4.09), which resulted in higher rates of acetylene reduction activity (mean = 34.09 ± SE = 10.34 nmol h^?1 g^?1) and a higher decomposition rate (k = 0.47) than Podocarpus nubigena (C/N = 54.4, lignin % = 40.31 ± 6.86, Mean ARR = 4.11 ± 0.71 nmol h^?1 g^?1, k = 0.29), and Drimys winteri (C/N = 50.6, lignin % = 45.49 ± 6.28, ARR = 10.2 ± 4.01 nmol h^?1 g^?1, k = 0.29), and mixed species litter (C/N = 60.7, ARR = 8.89 ± 2.13 nmol h^?1g^?1). We interpret these results as follows: in N‐poor litter and high lignin content of leaves (e.g. N. nitida) free‐living N fixers would be at competitive advantage over non‐fixers, thereby becoming more active. Lower ARR in mixed litter can be a consequence of a lower litter C/N ratio compared with single species litter. We also found a strong coupling between in situ acetylene reduction and net N mineralization in surface soils, suggesting that as soon N is fixed by diazotroph bacteria it may be immediately incorporated into mineral soil by N mineralizers, thus reducing N immobilization.     

Variability of stomatal conductance, leaf anatomy, and seasonal leaf wettability of young and adult European beech leaves along a vertical canopy gradient

This study assessed the variation of leaf anatomy, chlorophyll content index (CCI), maximal stomatal conductance (g _s ^max ) and leaf wettability within the canopy of an adult European beech tree (Fagus sylvatica L.) and for beech saplings placed along the vertical gradient in the canopy. At the top canopy level (CL_28m) of the adult beech, CCI and leaf anatomy reflected higher light stress, while g _s ^max increased with height, reflecting the importance of gas exchange in the upper canopy layer. Leaf wettability, measured as drop contact angle, decreased from 85.5°?±?1.6° (summer) to 57.5°?±?2.8° (autumn) at CL_28m of the adult tree. At CL_22m, adult beech leaves seemed to be better optimized for photosynthesis than the CL_28m leaves because of a large leaf thickness with less protective and impregnated substances, and a higher CCI. The beech saplings, in contrast, did not adapt their stomatal characteristics and leaf anatomy according to the same strategy as the adult beech leaves. Consequently, care is needed when scaling up experimental results from seedlings to adult trees.     

Non-invasive measurements of leaf epidermal transmittance of UV radiation using chlorophyll fluorescence: field and laboratory studies

Ratios of chlorophyll fluorescence induced by ultraviolet (UV) and bluegreen (BG) radiation [F(UV)/F(BG)] were determined with a Xe‐PAM fluorometer to test the utility of this technique as a means of non‐intrusively assessing changes in the pigmentation and optical properties of leaves exposed to varying UV exposures under laboratory and field conditions. For plants of Vicia faba and Brassica campestris, grown under controlled‐environmental conditions, F(UV‐B)/F(BG) was negatively correlated with whole‐leaf UV‐B‐absorbing pigment concentrations. Fluorescence ratios of V. faba were similar to, and positively correlated with (r²=0.77 [UV‐B]; 0.85 [UV‐A]), direct measurements of epidermal transmittance made with an integrating sphere. Leaves of 2 of 4 cultivars of field‐grown Glycine max exposed to near‐ambient solar UV‐B at a mid‐latitude site (Buenos Aires, Argentina, 34° S) showed significantly lower abaxial F(UV‐B)/F(BG) values (i.e., lower UV‐B epidermal transmittance) than those exposed to attenuated UV‐B, but solar UV‐B reduction had a minimal effect on F(UV‐B)/F(BG) in plants growing at a high‐latitude site (Tierra del Fuego, Argentina, 55° S). Similarly, the exotic Taraxacum officinale did not show significant changes in F(UV‐B)/F(BG) when exposed to very high supplemental UV‐B (biologically effective UV‐B=14–15 kJ m^?2 day^?1) in the field in Tierra del Fuego, whereas a native species, Gunnera magellanica, showed significant increases in F(UV‐B)/F(BG) relative to those receiving ambient UV‐B. These anomalous fluorescence changes were associated with increases in BG‐absorbing pigments (anthocyanins), but not UV‐B‐absorbing pigments. These results indicate that non‐invasive estimates of epidermal transmittance of UV radiation using chlorophyll fluorescence can detect changes in pigmentation and leaf optical properties induced by UV‐B radiation under both field and laboratory conditions. However, this technique may be of limited utility in cold environments where UV and low temperatures can stimulate the production of BG‐absorbing pigments that interfere with these indirect measurements of UV‐transmittance.     

Irrigation of Three Wetland Species and a Hyperaccumlating Fern with Arsenic-Laden Solutions: Observations of Growth,Arsenic Uptake,Nutrient Status,and Chlorophyll Content

Engineered wetlands can be an integral part of a treatment strategy for remediating arsenic-contaminated wastewater, wherein, As is removed by adsorption to soil particles, chemical transformation, precipitation, or accumulation by plants. The remediation process could be optimized by choosing plant species that take up As throughout the seasonal growing period. This report details experiments that utilize wetland plant species native to Ohio (Carex stricta, Pycnanthemum virginianum, and Spartina pectinata) that exhibit seasonally related maximal growth rates, plus one hyperaccumulating fern (Pteris vittata) that was used to compare arsenic tolerance. All plants were irrigated with control or As-laden nutrient solutions (either 0, 1.5, or 25 mg As L^?1) for 52 d. Biomass, nutrient content, and chlorophyll content were compared between plants treated and control plants (n = 5). At the higher concentration of arsenic (25 mg L^?1), plant biomass, leaf area, and total chlorophyll were all lower than values in control plants. A tolerance index, based on total plant biomass at the end of the experiment, indicated C. stricta (0.99) and S. pectinata (0.84) were more tolerant than the other plant species when irrigated with 1.5 mg As L^?1. These plant species can be considered as candidates for engineered wetlands.     

Leaf-root-soil N:P stoichiometry of ephemeral plants in a temperate desert in Central Asia

Ephemeral plants are a crucial vegetation component in temperate deserts of Central Asia, and play an important role in biogeochemical cycle and biodiversity maintenance in desert ecosystems. However, the nitrogen (N) and phosphorus (P) status and interrelations of leaf-root-soil of ephemeral plants remain unclear. A total of 194 leaf-root-soil samples of eight ephemeral species at 37 sites in the Gurbantunggut Desert, China were collected, and then the corresponding N and P concentrations, and the N:P ratio were measured. Results showed that soil parameters presented no significant difference among the eight species. The total soil N:P was only 0.116 (geomean), indicating limited soil N, while the available soil N:P (4.896, geomean) was significantly larger than the total N:P. The leaf N (averagely 30.995 mg g^?1) and P (averagely 1.523 mg g^?1) concentrations were 2.64–8.46 and 0.93–3.99 times higher than the root N (averagely 8.014 mg g^?1) and P (averagely 0.802 mg g^?1) concentrations, respectively. Thus, leaf N:P (averagely 21.499) was 1.410–2.957 times higher than root N:P (averagely 11.803). Meanwhile, significant interspecific differences existed in plant stoichiometric traits. At the across-species level, N content scaled as the 3/4-power of P content in both leaves and roots. Leaf and root N:P ratios were mainly influenced by P; however, the leaf-to-root N or P ratio was dominated by roots. Leaf and root N, P contents and N:P were generally unrelated to soil nutrients, and the former presented lower variation than the latter, indicating a strong stoichiometric homeostasis for ephemerals. These results demonstrate that regardless of soil nutrient supply capacity in this region, the fast-growing ephemeral plants have formed a specific leaf-root-soil stoichiometric relation and nutrient use strategy adapting to the extreme desert environment.

     

Effect of water content and temperature on seed longevity of seven Brassicaceae species after 5 years of storage

Maximising seed longevity is crucial for genetic resource preservation and longevity of orthodox seeds is determined by environmental conditions (water content and temperature). The effect of water content (down to 0.01 g·H₂O·g^?1) on seed viability was studied at different temperatures for a 5‐year storage period in taxonomically related species. Seeds of seven Brassicaceae species (Brassica repanda, Eruca vesicaria, Malcolmia littorea, Moricandia arvensis, Rorippa nasturtium‐aquaticum, Sinapis alba, Sisymbrium runcinatum) were stored at 48 environments comprising a combination of eight water contents, from 0.21 to 0.01 g·H₂O·g^?1 DW and six temperatures (45, 35, 20, 5, ?25, ?170 °C). Survival curves were modelled and P50 calculated for those conditions where germination was reduced over the 5‐year assay period. Critical water content for storage of seeds of six species at 45 °C ranged from 0.02 to 0.03 g·H₂O·g^?1. The effect of extreme desiccation at 45 °C showed variability among species: three species showed damaging effects of drying below the critical water content, while for three species it was neither detrimental nor beneficial to seed longevity. Lipid content could be related to longevity, depending on the storage conditions. A variable seed longevity response to water content among taxonomically related species was found. The relative position of some of the species as long‐ or short‐lived at 45 °C varied depending on the humidity at which storage behaviour was evaluated. Therefore, predictions of survival under desiccated conditions based on results obtained at high humidity might be problematic for some species.     

Leaf life span as a simple predictor of evergreen forest zonation in China

Aim Our aim was to investigate how the average life span of canopy leaves might be used to predict the geographical distribution of natural forests at large geographical scales, and to explore the link between leaf characteristics and ecosystem functioning. We examine whether there is a general relationship between canopy mean leaf life span and climate (i.e. temperature and precipitation) that can be used to predict evergreen forest zonation in China. Location Forest areas in China. Methods During July and August of 2002–2004, we conducted a latitudinal forest transect spanning about 30° of latitude in eastern China. The canopy mean leaf life span was calculated to include all tree species (groups) in each forest plot through weighted averages scaled up from branch‐level measurements. Data from our previous work conducted in the Tibetan Alpine Vegetation Transects (TAVT) and from other investigators were compiled to supplement our results. Based on regression equations developed on the pooled data, and using gridded temperature and precipitation datasets, we simulated the distribution of canopy mean leaf life span for forests in China. The predicted leaf life span zonation was compared with a map of Chinese forest vegetation divisions published in 1980. Results Canopy mean leaf life span across 10 evergreen forest plots in eastern China showed a decreasing trend as mean annual temperature increased, following a common logistic pattern consistent with the data from the TAVT and other investigators. In pooled data for 40 evergreen forest plots across tropical and boreal regions, canopy mean leaf life span generally showed a negative relationship with mean annual temperature (r² = 0.72, P < 0.001), and a positive correlation with mean annual precipitation where mean annual temperature was > 8°C (r² = 0.45, P < 0.01). The climate‐based simulations of leaf life span zonation compared well with the previously published boundaries of forest vegetation divisions in eastern China. Main conclusions Our results reveal that mean leaf life span in evergreen forests follows a common logistic pattern associated with mean annual temperature and precipitation, which can in turn be used to predict evergreen forest zonation in eastern China.     

Phenotypic plasticity and biogeographic variation in physiology of habitat‐forming seaweed: response to temperature and nitrate

Southeastern Australian waters are warming at nearly four times the global average rate (~0.7°C · century^?1) driven by strengthening incursions of the warm oligotrophic East Australian Current. The growth rate hypothesis (GRH) predicts that nutrient depletion will impact more severely on seaweeds at high latitudes with compressed growth seasons. This study investigates the effects of temperature and nutrients on the ecophysiology of the habitat‐forming seaweed Phyllospora comosa in a laboratory experiment using temperature (12°C, 17°C, 22°C) and nutrient (0.5, 1.0, 3.0 μM NO₃^?) scenarios representative of observed variation among geographic regions. Changes in growth, photosynthetic characteristics (via chlorophyll fluorescence), pigment content, tissue chemistry (δ¹³C, % C, % N, C:N) and nucleic acid characteristics (absolute RNA and DNA, RNA:DNA ratios) were determined in seaweeds derived from cool, high‐latitude and warm, low‐latitude portions of the species’ range. Performance of P. comosa was unaffected by nitrate availability but was strongly temperature‐dependent, with photosynthetic efficiency, growth, and survival significantly impaired at 22°C. While some physiological processes (photosynthesis, nucleic acid, and accessory pigment synthesis) responded rapidly to temperature, others (C/N dynamics, carbon concentrating processes) were largely invariant and biogeographic variation in these characteristics may only occur through genetic adaptation. No link was detected between nutrient availability, RNA synthesis and growth, and the GRH was not supported in this species. While P. comosa at high latitudes may be less susceptible to oligotrophy than predicted by the GRH, warming water temperatures will have deleterious effects on this species across its range unless rapid adaptation is possible.     

Bioremediation potential of Chondrus crispus (Basin Head) and Palmaria palmata: effect of temperature and high nitrate on nutrient removal

To evaluate the nutrient removal capabilities of two red macroalgae, apical blades were cultured in the lab for 4?weeks at either 6, 10, or 17°C and nitrate at either 30 or 300?μM, typical of the seasonal range of conditions at a land-based Atlantic halibut farm. Stocking density was 2.0?g?L^?1, irradiance 125?μmol?photons?m^?2?s^?1, photoperiod 16:8 (L:D), and nitrogen to phosphorus ratio 10:1. For both species, the highest growth rate was at 300?μM NO ₃ ^? with Palmaria palmata growing fastest at 6°C, 5.8%?day^?1, and Chondrus crispus growing best at 17°C, 5.5%?day^?1. Nitrogen and carbon removal by P. palmata was inversely related to temperature, the highest rate at 6°C and 300?μM NO ₃ ^? of 0.47?mg N and 6.3?mg C per gram dry weight per day. In contrast, C. crispus removal of N was independent of temperature, with mean removal of 0.49?mgN?gDW^?1?day^?1 at 300?μM NO ₃ ^? . The highest carbon removal by C. crispus was 4.4?mgC?gDW^?1?day^?1 at 10°C and 300?μM nitrate, though not significantly different from either 6 or 17°C and 300?μM nitrate. Tissue carbon:nitrogen ratios were >20 in both species at 30?μM nitrate, and all temperatures indicating nitrogen limitation in these treatments. Phycoerythrin content of P. palmata was independent of temperature, with means of 23.6?mg?gFW^?1 at 300?μM nitrate. In C. crispus, phycoerythrin was different only between 6°C and 17°C at 300?μM nitrate, with the highest phycoerythrin content of 12.6?mg?gFW^?1 at 17°C. Morphological changes were observed in P. palmata at high NO ₃ ^? concentration as curling of the fronds, whilst C. crispus exhibited the formation of bladelets as an effect of high temperature.     

The influence of temperature and nitrogen source on growth and nitrogen uptake of two polar-desert species,Saxifraga caespitosa and Cerastium alpinum

Polar-desert plants experience low average air temperatures during their short growing season (4–8 °C mean July temperature). In addition, low availability of inorganic nitrogen in the soil may also limit plant growth. Our goals were to elucidate which N sources can be acquired by polar-desert plants, and how growth and N-uptake are affected by low growth temperatures. We compared rates of N-uptake and increases in mass and leaf area of two polar-desert species (Cerastium alpinum L. and Saxifraga caespitosa L.) over a period of 3 weeks when grown at two temperatures (6 °C vs. 15 °C) and supplied with either glycine, NH₄ ⁺ or NO₃ ⁻. At 15 °C, plants at least doubled their leaf area, whereas there was no change in leaf area at 6 °C. Measured mean N-uptake rates varied between 0.5 nmol g⁻¹ root DM s⁻¹ on glycine at 15 °C and 7.5 nmol g⁻¹ root DM s⁻¹ on NH₄ ⁺ at 15 °C. Uptake rates based upon increases in mass and tissue N concentrations showed that plants had a lower N-uptake rate at 6 °C, regardless of N source or species. We conclude that these polar-desert plants can use all three N sources to increase their leaf area and support flowering when grown at 15 °C. Based upon short-term (8 h) uptake experiments, we also conclude that the short-term capacity to take up inorganic or organic N is not reduced by low temperature (6 °C). However, net N-uptake integrated over a three-week period is severely reduced at 6 °C. This revised version was published online in June 2006 with corrections to the Cover Date.     

Manganese application alleviates the water deficit-induced decline of N2 fixation

Water deficit is a very serious constraint on N₂ fixation rates and grain yield of soybean (Glycine max Merr.). Ureides are transported from the nodules and they accumulate in the leaves during soil drying. This accumulation appears responsible for a feedback mechanism on nitrogen fixation, and it is hypothesized to result from a decreased ureide degradation in the leaf. One enzyme involved in the ureide degradation, allantoate amidohydrolase, is manganese (Mn) dependent. As Mn deficiency can occur in soils where soybean is grown, this deficiency may aggravate soybean sensitivity to water deficit. In situ ureide breakdown was measured by incubating soybean leaves in a 5 mol m ^{? 3} allantoic acid solution for 9 h before sampling leaf discs in which remnant ureide was measured over time. In situ ureide breakdown was dramatically decreased in leaves from plants grown without Mn. At the plant level, allantoic acid application in the nutrient solution of hydroponically grown soybean resulted in a higher accumulation of ureide in leaves and lower acetylene reduction activity (ARA) by plants grown with 0 mol m ^{? 3} Mn than those grown with 6·6 mol m ^{? 3} Mn. Those plants grown with 6·6 mol m ^{? 3} Mn in comparison with those grown with 52·8 mol m ^{? 3} Mn had, in turn, higher accumulated ureide and lower ARA. To determine if Mn level also influenced N₂ fixation sensitivity to water deficit, a dry‐down experiment was carried out by slowly dehydrating plants that were grown in soil under four different Mn nutritions. Plants receiving no Mn had the lowest leaf Mn concentration, 11·9 mg kg ^{? 1}, and had N₂ fixation more sensitive to water deficit than plants treated with Mn in which leaf Mn concentration was in the range of 21–33 mg kg ^{? 1}. The highest Mn treatments increased leaf Mn concentration to 37·5 mg kg ^{? 1} and above but did not delay the decline of ARA with soil drying, although these plants showed a significant increase in ARA under well‐watered conditions.     

Bioethanol production from the hydrolysate of Palmaria palmata using sulfuric acid and fermentation with brewer’s yeast

Seaweeds, particularly species of red macroalgae, are promising resources for bioethanol production because of their exceptionally high carbohydrate content. Of 20 seaweeds evaluated, Palmaria palmata (Rhodymenia palmata) contained the highest carbohydrate content (469.8 mg g^?1 seaweed) with a carrageenan content of 354 mg g^?1 seaweed. Such a high carrageenan content makes the high-volume production of bioethanol feasible. Acid hydrolysis of P. palmata in 0.4 M H₂SO₄ at 125 °C for 25 min released 27 mg of glucose, 218.4 mg of reducing sugars, and 127.6 mg of galactose per gram of seaweed. Ethanol fermentation of these hydrolysis products using an inoculum concentration of 1.5 mg mL^?1 at 30 °C and 72 h in a shaking incubator at 130 rpm yielded 17.3 mg of ethanol per gram of seaweed.     

The occurrence and accumulation of <Emphasis Type="SmallCaps">d</Emphasis>-pinitol in fenugreek (<Emphasis Type="Italic">Trigonella foenum graecum</Emphasis> L.)

This article presents changes in concentrations of d-pinitol (and other cyclitols as well as low molecular weight carbohydrates) in vegetative and reproductive organs of fenugreek (Trigonella foenumgraecum L.) during an entire plant growing period. d-Pinitol was the major cyclitol in all tested organs, representing 43–94% of total cyclitols and 2–77% of total soluble carbohydrates. The highest concentration of d-pinitol was found in pods (14–23 mg g^?1 of dry weight, DW), lower in leaves and stems (5–20 and 9–10 mg g^?1 DW, respectively), and the lowest in maturing seeds (2–5 mg g^?1 DW). Although maturing seeds accumulate α-d-galactosides of d-pinitol (galactosyl pinitols, up to 6.6 mg g^?1 DW), the major storage sugars were raffinose family oligosaccharides (RFOs, 65.37 mg g^?1 DW). Both RFOs and galactosyl pinitols are hydrolyzed during seed germination, releasing sucrose and d-pinitol, respectively. Accumulation of free galactose was not detected. Owing to the high concentration of d-pinitol (up to 23.70 mg g^?1 DW) and low concentration of soluble sugars, developing pods seem to be the best source of d-pinitol.