Loss of plant biodiversity eliminates stimulatory effect of elevated CO2 on earthworm activity in grasslands

Earthworms are among the world’s most important ecosystem engineers because of their effects on soil fertility and plant productivity. Their dependence on plants for carbon, however, means that any changes in plant community structure or function caused by rising atmospheric CO₂ or loss of plant species diversity could affect earthworm activity, which may feed back on plant communities. Production of surface casts measured during three consecutive years in field experimental plots (n = 24, 1.2 m²) planted with local calcareous grassland species that varied in plant species richness (diversity levels: high, 31 species; medium, 12; low, 5) and were exposed to ambient (356 μl CO₂ l^?1) or elevated (600 μl CO₂ l^?1) CO₂ was only consistently stimulated in high diversity plots exposed to elevated CO₂ (+120 %, 31 spp: 603 ± 52 under ambient CO₂ vs. 1,325 ± 204 g cast dwt. m^?2 year^?1 under elevated CO₂ in 1996; +77 %, 940 ± 44 vs. 1,663 ± 204 g cast dwt. m^?2 year^?1 in 1998). Reductions in plant diversity had little effect on cast production in ecosystems maintained at ambient CO₂, but the stimulatory effect of elevated CO₂ on cast production disappeared when plant species diversity was decreased to 12 and 5 species. High diversity plots were also the only communities that included plant species that an earlier field study showed to be among the most responsive to elevated CO₂ and to be most preferred by earthworms to deposit casts near. Further, the +87 % CO₂-induced increase in cast production measured over the 3 years corresponded to a parallel increase in cumulative total nitrogen of 5.7 g N m^?2 and would help explain the large stimulation of aboveground plant biomass production observed in high-diversity communities under elevated CO₂. The results of this study demonstrate how the loss of plant species from communities can alter responses of major soil heterotrophs and consequently ecosystem biogeochemistry.     

Seasonal Activity and Foraging Preferences of the Leaf-Cutting Ant Atta sexdens piriventris (Santschi) (Hymenoptera: Formicidae)

Leaf-cutting ants are known for their habit of foraging. These habits can be influenced by several factors, including variations in topography, soil, and climate among others. The objective of this research was to study the seasonal activity and foraging preferences of the leaf-cutting ant Atta sexdens piriventris (Santschi). The study was carried out from January to October of 2007 in grasslands of the state of Santa Catarina, Brazil. Nests of A. sexdens piriventris were randomly selected and the forager’s activities were recorded. Damaged plant species, soil fertility, and climatic conditions were recorded. The maximum foraging activity in the summer was recorded during periods of darkness or low light (between 7 p.m. and 5 a.m.). In autumn and spring, foraging was the highest in the morning, but during winter time the foraging activity was high in the afternoon. Fourteen plant species were frequently visited during our study with the lowest foraging activity being recorded at very low (1 to 4°C) or very high temperatures (above 26°C). The number of exploited plant species was higher in winter (13) than in summer (9). Baccharis trimera (Asteraceae) (43%) and Paspalum spp. (Poaceae) (33%) were the most exploited plants among the identified species.     

Catalase Activity of Nodules in the Ureide- and Amide-transporting Legume Plants

The relations of catalase activity to the efficiency of symbiotic dinitrogen fixation and leghemoglobin (Lb) content were investigated in roots and nodules of several legume plant species together with the catalase distribution between the inner bacteroidal and the outer cortical nodule tissues. The catalase activity in the nodules exceeded that of the roots of the amide- and ureide-synthesizing plant species by one and two orders of magnitude. During the growth period, catalase activity and Lb content changed in parallel and reached their highest levels early in the stage of flowering or fruit formation, depending on plant species. In the case of effective symbiosis, catalase activity in the nodules was 2.5–5 times higher than in the case of ineffective symbiosis. Catalase activity in the bacteroidal zone of the nodules was several times higher than that of the cortical tissue, and two nodule tissues differed in catalase activity more notably in the plant species exporting ureides. The authors suggest that high catalase activity in the nodules, especially in their bacteroidal zone, is essential for the efficient functioning of the symbiotic system of dinitrogen fixation in both ureide- and amide-transporting plants.     

Marine-derived Penicillium in Korea: diversity,enzyme activity,and antifungal properties

The diversity of marine-derived Penicillium from Korea was investigated using morphological and multigene phylogenetic approaches, analyzing sequences of the internal transcribed spacer region, β-tubulin gene, and RNA polymerase subunit II gene. In addition, the biological activity of all isolated strains was evaluated. We tested for the extracellular enzyme activity of alginase, endoglucanase, and β-glucosidase, and antifungal activity against two plant pathogens (Colletotrichum acutatum and Fusarium oxysporum). A total of 184 strains of 36 Penicillium species were isolated, with 27 species being identified. The most common species were Penicillium polonicum (19.6 %), P. rubens (11.4 %), P. chrysogenum (11.4 %), and P. crustosum (10.9 %). The diversity of Penicillium strains isolated from soil (foreshore soil and sand) and marine macroorganisms was higher than the diversity of strains isolated from seawater. While many of the isolated strains showed alginase and β-glucosidase activity, no endoglucanase activity was found. More than half the strains (50.5 %) showed antifungal activity against at least one of the plant pathogens tested. Compared with other strains in this study, P. citrinum (strain SFC20140101-M662) showed high antifungal activity against both plant pathogens. The results reported here expand our knowledge of marine-derived Penicillium diversity. The relatively high proportion of strains that showed antifungal and enzyme activity demonstrates that marine-derived Penicillium have great potential to be used in the production of natural bioactive products for pharmaceutical and/or industrial use.     

Improvement on the thermal stability and activity of plant cytosolic ascorbate peroxidase 1 by tailing hyper-acidic fusion partners

Cytosolic ascorbate peroxidase 1 (APX1) plays a crucial role in regulating the level of plant cellular reactive oxygen species and its thermolability is proposed to cause plant heat-susceptibility. Herein, several hyper-acidic fusion partners, such as the C-terminal peptide tails, were evaluated for their effects on the thermal stability and activity of APX1 from Jatropha curcas and Arabidopsis. The hyper-acidic fusion partners efficiently improved the thermostability and prevented thermal inactivation of APX1 in both plant species with an elevated heat tolerance of at least 2 °C. These hyper-acidified thermostable APX1 fusion variants are of considerable biotechnological potential and can provide a new route to enhance the heat tolerance of plant species especially of inherent thermo-sensitivity.     

香蕉植株内生细菌群落多态性研究

采用平板法对香蕉(Musa nana)植株的内生细菌进行分离纯化,并采用细菌脂肪酸法进行鉴定。结果表明,从香蕉的健康植株和感病植株中共分离得到内生细菌21属24种。从健株分离得到9种内生细菌,其中根、茎和叶分别分离到6种、2种和8种内生细菌。从病株分离得到15属17种内生细菌,其中根、茎和叶分别分离到3种、11种和6种。香蕉健株根部的内生细菌含量最高,达5.195×106cfu g-1,下部叶片内生细菌的含量最低,仅为30 cfu g-1;香蕉病株茎部内生细菌的数量显著高于其他部位,达1.05×107cfu g-1。这说明香蕉在不同生长状态下,其内生细菌的种类和数量存在多样性。     

Effects of incubation temperature and oxygen tension on nitrogenase activity of legume root nodules

Summary Acetylene reduction and H₂ evolution by legume root nodules from several plant species depended on incubation temperature; some nodules were active from 2 to 40°C. Acetylene reduction rates differed between plant species, with maximum activity at temperatures between 20 and 30°C forVicia faba, V. sativa, Trifolium pratense, T. subterraneum, Medicago truncatula and soybean, at 35°C forM. sativa and at 40°C for cowpea. OnlyM. sativa and cowpea reduced substantial amounts at 37.5°C. Temperatures from 2 to 10°C only slightly lessened activity ofT. subterraneum andV. sativa nodules. Nitrogenase functioned at temperatures which prevent establishment of other aspects of the symbiosis. The rate of acetylene reduction was constant for several hours at temperatures below 15°C, and activity continued for several days at 2°C for some species, but declined with time at warmer temperatures. Some nitrogenase was denatured at warmer temperatures, but the O₂ tension in the assay vial also affected activity. In closed assay vessels nodule respiration decreased the pO₂ and reduced nitrogenase activity. Activity was restored by adding O₂ or regassing assay vials with air or Ar/O₂. When the pO₂ was maintained, acetylene reduction and H₂ evolution by detached soybean nodules continued unchanged for 6 h.     

Insecticidal effect of plant extracts on two termite species

The insecticidal contact activity of two desert plant extracts, Withania somnifera and Solanum incanum (Tubiflora: Solanaceae) was tested against the workers of the two species, Amitermes messinae and Microtermes najdensis (Isoptera: Termitidae). The insects were exposed to the plant extracts on Petri dishes (10 cm diameter) for 30 min. Mortality was calculated after 24 h. Crude extract of S. incanum leaves was more toxic to the two species of termites than W. somnifera.     

Priming fingerprint induced by Bacillus amyloliquefaciens QV15, a common pattern in Arabidopsis thaliana and in field-grown blackberry

The aim of this study is focused on determining the Bacillus amyloliquefaciens QV15 priming fingerprint in two different plant species, Arabidopsis and blackberry as a crop of agronomic interest, associated with protection upon pathogen challenge. To achieve this goal, Arabidopsis thaliana plants were challenged with Pseudomonas syringae DC3000 under controlled conditions, and field-grown blackberries were challenged by a powdery Mildew outbreak, finding plant protection in plants treated with QV15, in both conditions. Changes in ROS scavenging enzymes’ activity, defense-related enzymes’ activity and gene expression were evaluated in both plant species, before and after pathogen challenge, revealing the ability of this strain to prime both. As a result of this analysis, the priming fingerprint induced by QV15 was defined by a decrease in ROS scavenging enzymes’ activity in pre- and post-challenged plants, an increase in glucanase and chitinase activity after pathogen challenge, significantly increasing the expression of PR1, indicating a salicylic acid (SA)-mediated pathway activation. These results suggest an excellent potential of B. amyloliquefaciens QV15 to protect different plant species against different pathogens in field conditions.     

Antiviral activity of Bignoniaceae species occurring in the State of Minas Gerais (Brazil): part 1

Aims: To evaluate the antiviral activity of Bignoniaceae species occurring in the state of Minas Gerais, Brazil. Methods and Results: Ethanol extracts of different anatomical parts of bignoniaceous plant species have been evaluated in vitro against human herpesvirus type 1 (HSV‐1), vaccinia virus (VACV) and murine encephalomyocarditis virus (EMCV) by the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay. A total of 34 extracts from 18 plant species selected according to ethnopharmacological and taxonomic criteria were screened. Fifteen of the 34 extracts (44·1%) have disclosed antiviral activity against one or more of the viruses assayed with EC₅₀ values in the range of 23·2 ± 2·5–422·7 ± 10·9 μg ml^?1. Conclusions: Twelve of the 34 extracts (35·3%) might be considered promising sources of antiviral natural products, as they have shown EC₅₀ ≤ 100 μg ml^?1. The present screening discloses the high potential of the Bignoniaceae family as source of antiviral agents. Significance and Impact of the Study: Active extracts were identified and deserve bioguided studies for the isolation of antiviral compounds and studies on mechanism of action.     

Leaf temperatures mediate alpine plant communities’ response to a simulated extended summer

We use a quantitative model of photosynthesis to explore leaf‐level limitations to plant growth in an alpine tundra ecosystem that is expected to have longer, warmer, and drier growing seasons. The model is parameterized with abiotic and leaf trait data that is characteristic of two dominant plant communities in the alpine tundra and specifically at the Niwot Ridge Long Term Ecological Research Site: the dry and wet meadows. Model results produce realistic estimates of photosynthesis, nitrogen‐use efficiency, water‐use efficiency, and other gas exchange processes in the alpine tundra. Model simulations suggest that dry and wet meadow plant species do not significantly respond to changes in the volumetric soil moisture content but are sensitive to variation in foliar nitrogen content. In addition, model simulations indicate that dry and wet meadow species have different maximum rates of assimilation (normalized for leaf nitrogen content) because of differences in leaf temperature. These differences arise from the interaction of plant height and the abiotic environment characteristic of each plant community. The leaf temperature of dry meadow species is higher than wet meadow species and close to the optimal temperature for photosynthesis under current conditions. As a result, 2°C higher air temperatures in the future will likely lead to declines in dry meadow species’ carbon assimilation. On the other hand, a longer and warmer growing season could increase nitrogen availability and assimilation rates in both plant communities. Nonetheless, a temperature increase of 4°C may lower rates of assimilation in both dry and wet meadow plant communities because of higher, and suboptimal, leaf temperatures.     

Occurrence of Glycoside Hydrolases in Plant Pathogenic and Related Bacteria

One hundred and twenty-eight isolates representing 37 species and six genera of plant pathogenic and related bacteria were tested for the presence of /3–galactosidase, glucosidase. β-glucosidase and β-xylosidase; using nitrophenyl glycopyranosides as substrates. Agrobacterium tumefaciens, Corynebacterium flaccumfaciens, C. michiganense. Flavobacterium pectinovorum and Pseudomonas maltophilia showed activity on all of the four substrates. Xanthomonas albilineans and three nomenspecies of the X. campestris group had little or no o-glucosidase activity but all other tests with Xanthomonas spp . were positive. None of the fluorescen; pseudomonads examined possessed β-galactosidase but P. stizolobii, P. andropogonis and P. rubrisubalbicans , among the non-fluorescent pseudomonads showed activity.     

Geothermal bryophyte habitats in the South Sandwich Islands,maritime Antarctic

Question: How does geothermal activity influence terrestrial plant colonization, species composition and community development in the Antarctic? Location: South Sandwich Islands, maritime Antarctic. Methods: Bryophytes were documented during a biological survey of the archipelago in January and February 1997. Particular attention was given to sites under current or recent influence of geothermal activity. Temperature profiles obtained across defined areas of activity on several islands were linked with the presence of specific bryophytes. Results: Greatest bryophyte richness was associated with geothermally influenced ground. Of 35 moss and nine liverwort species recorded, only four mosses were never associated with heated ground, while eight of the liverworts and 50% of the mosses were found only on actively or recently heated ground. Some species occur in unheated sites elsewhere in the maritime Antarctic, but were absent from such habitats on the South Sandwich Islands. Several species occurred in distinct zones around fumaroles. Maximum temperatures recorded within the upper 0.5 cm of the vegetation surface were 40 ‐ 47 °C, with only Campylopus introflexus tolerating such temperatures. Maximum temperatures 2.5 or 5 cm below the vegetation surface of this moss reached 75 °C. Other bryophytes regularly present in zoned vegetation included the mosses Dicranella hookeri, Sanionia georgico‐uncinata, Pohlia nutans and Notoligotrichum trichodon, and the liverworts Cryptochila grandiflora and Marchantia berteroana. Surface temperatures of 25 ‐ 35 °C and subsurface temperatures of 50 ‐ 60 °C were recorded in these species. Conclusions: These exceptional plant communities illustrate the transport of viable propagules into the Antarctic. Individually ephemeral in nature, the longer term existence of geothermal habitats on islands along the Scotia Arc may have provided refugia during periods of glacial expansion, facilitating subsequent recolonization of Antarctic terrestrial habitats.     

Screening of plant cell culture collection for efficient host species for Agrobacterium-mediated transient expression

Agrobacterium-mediated transient expression is an approach for short-time expression of heterologous genes in plant systems. During the last decade transient expression was regarded as a potent protocol for high scale production of foreign proteins in plants including pharmaceutically valuable proteins. In vitro grown plant cell cultures represent a suitable system for accumulation of heterologous proteins under controlled conditions. Since host characteristics may strongly influence transient expression efficiency, we performed screening of undifferentiated cell cultures for transient expression ability using GUS as a reporter. Analysis of 248 plant species belonging to 49 families from the National Germplasm Bank of the World Flora of the Institute of Cell Biology and Genetic Engineering (Kyiv, Ukraine) allowed for selection of about 50 plant species exhibiting detectable β-glucuronidase activity.     

Plant endogenous β-glucuronidase activity: how to avoid interference with the use of theE. coli β-glucuronidase as a reporter gene in transgenic plants

We have detected a plant β-glucuronidase activity, present in several tissues and organs of plant species belonging to different families. The fluorimetric β-glucuronidase assay was used to partially characterize this activity in post-ribosomal supernatants of tobacco leaves. The tobacco activity is very stable at low temperatures, but quickly inactivated above 45°C. It is relatively resistant to proteases and insensitive to-SH group reagents and to ionic conditions. It does not require, nor is it inhibited by, divalent cations. Although these properties are shared by theEscherichia coli β-glucuronidase, the two activities can be distinguished by: (i) their different sensitivity to the specific inhibitor saccharic acid-1,4-lactone; (ii) their different thermal stability (iii) their different pH optima (5.0 for the plant activity and close to neutral for the bacterial enzyme). Therefore, under appropriate experimental conditions, it should be possible to assay theE. coli β-glucuronidase in transgenic plants without interference from the endogenous plant activity.     

Plant species richness, elevated CO2, and atmospheric nitrogen deposition alter soil microbial community composition and function

We determined soil microbial community composition and function in a field experiment in which plant communities of increasing species richness were exposed to factorial elevated CO₂ and nitrogen (N) deposition treatments. Because elevated CO₂ and N deposition increased plant productivity to a greater extent in more diverse plant assemblages, it is plausible that heterotrophic microbial communities would experience greater substrate availability, potentially increasing microbial activity, and accelerating soil carbon (C) and N cycling. We, therefore, hypothesized that the response of microbial communities to elevated CO₂ and N deposition is contingent on the species richness of plant communities. Microbial community composition was determined by phospholipid fatty acid analysis, and function was measured using the activity of key extracellular enzymes involved in litter decomposition. Higher plant species richness, as a main effect, fostered greater microbial biomass, cellulolytic and chitinolytic capacity, as well as the abundance of saprophytic and arbuscular mycorrhizal (AM) fungi. Moreover, the effect of plant species richness on microbial communities was significantly modified by elevated CO₂ and N deposition. For instance, microbial biomass and fungal abundance increased with greater species richness, but only under combinations of elevated CO₂ and ambient N, or ambient CO₂ and N deposition. Cellobiohydrolase activity increased with higher plant species richness, and this trend was amplified by elevated CO₂. In most cases, the effect of plant species richness remained significant even after accounting for the influence of plant biomass. Taken together, our results demonstrate that plant species richness can directly regulate microbial activity and community composition, and that plant species richness is a significant determinant of microbial response to elevated CO₂ and N deposition. The strong positive effect of plant species richness on cellulolytic capacity and microbial biomass indicate that the rates of soil C cycling may decline with decreasing plant species richness.     

Yearlong association of insect pollinator,Pseudapis oxybeloides with flowering plants: Planted forest vs. agricultural landscape

The yearlong association of a native bee, Pseudapis oxybeloides (Halictidae: Hymenoptera) was studied with 72 plant species in a sub-tropical planted forest and some adjacent agricultural landscapes at Multan, Pakistan. The study resulted in 66 interactions of P. oxybeloides with only 24 plant species in 15 families while other 48 plant species were not visited by this bee. The maximum abundance of P. oxybeloides (7–9 individuals) was recorded on Achyranthes aspera and Launaea procumbens followed by Ageratum conyzoides, Trianthema portulacastrum and Cleome viscosa (5–6 individuals). Majority (19) of plant species were visited by only 1–4 individuals. The bee activity was started in the month of March which attained its peak in May followed by a gradual decline until September. No bees were observed during the months of January and February. There was a significant positive relationship between bee abundance and number of flowering plant species. Bee abundance had a strong positive relationship with temperature while it had a strong negative relationship with relative humidity (%). Floral abundance increased with the number of flowering plant species while it was not influenced by floral span of plant species. Besides giving the floral host plants of P. oxybeloides, the current study also gives a better understanding of its seasonality along with its relationships with different biotic and abiotic factors under local conditions. These findings can help in maintaining and managing P. oxybeloides population particularly and other native bees in general at local scale.     

Host plant use by the Heath fritillary butterfly, Melitaea athalia: plant habitat, species and chemistry

We present a study of habitat use, oviposition plant choice, and food plant suitability for the checkerspot butterfly Melitaea athalia Rottemburg (Lepidoptera: Nymphalidae) in Åland, Finland. We found that in Åland, unlike in the mainland of Finland and many parts of its range, M. athalia flies mainly in open meadows. When offered an array of plants in a large (32 × 26 m) field cage, they predominately oviposited upon Veronica chamaedrys L., V. spicata L. and Plantago lanceolata L. (Plantaginaceae), which grow in open meadows. The relative abundance of the butterfly in Åland, and its habitat and host plant use there, may reflect local adaptation to land use practices and geology that maintain clusters of small open meadows with little successional change. At the scale of a plant patch, preferred species were used as frequently in mixed species patches as in mono-specific patches, and more oviposition occurred in open than in grassy patches. All of the host plants used by M. athalia are defended by iridoid glycosides (IGs). However, oviposition choice among species and among individual plants within species was largely independent of IG concentration. This contrast with the more discerning congener, M. cinxia, supports the idea that host discrimination decreases with increasing host range. Finally, although the adult butterflies chose specific plant species for oviposition, as larvae they performed well on twelve out of thirteen species of plants, including both known hosts and related novel plants that occur in Åland, indicating a much wider range of larval food plant species than adult oviposition species.     

Effects of moderate high-temperature stress on photosynthesis in three saplings of the constructive tree species of subtropical forest

During the exposition to moderate high-temperature stress, photosynthetic rates and fluorescence of chlorophyll a were measured with a photosynthetic measurement system (Li-Cor 6400) and leaf chamber fluorometer (Li-Cor6400 LCF), respectively, in leaves of saplings, sun-adapted species (Schima superba), shade-adapted species (Cryptocarya concinna), and in mesophytic plant (Castanopsis hystrix) (42°C). The results showed that moderate high-temperature stress led to a decrease in F_v/F_>m, namely the primary photochemical quantum efficiency, indicating that moderate high-temperature stress causes a partial inhibition of PSII. It also showed that such an effect was more severe in the shade-adapted plant C. concinna than in the sun-adapted species S. superba. However, except for the sun-grown leaves of C. concinna, the moderate high-temperature stress increased the photosynthetic rate of leaves at high light intensity. Simultaneously, less photoinhibition was found to occur under high-light intensity, suggesting that the capacity of resistant-photoinhibition was stimulated by moderate high-temperature stress. The quantum yield of PSII (?_PSII) decreased in the sun-grown leaves of S. superba and C. hystrix but did not show any significant change in leaves of the shade plant C. concinna and shade-grown leaves of sun plant S. superba or the mesophytic plant C. hystrix because they already had a very low ?_PSII under this condition. Moderate high-temperature stress led to a decrease in ?_PSII/?_CO2 ratios, an estimate of the quantum requirement for CO2 assimilation, in the sun plant S. superba and the mesophytic plant C. hystrix because they were associated with the dissipation of a lower fraction of excitation energy. However, no significant changes were found in shade plant C. concinna and in shade-grown leaves of the other examined plants. The effect of moderate high-temperature (42°C) on photosynthesis depends on species and leaf type (sun and shade leaves) in the saplings of subtropical broad-leaved trees.     

Functional identity versus species richness: herbivory resistance in plant communities

The resistance of a plant community against herbivore attack may depend on plant species richness, with monocultures often much more severely affected than mixtures of plant species. Here, we used a plant–herbivore system to study the effects of selective herbivory on consumption resistance and recovery after herbivory in 81 experimental grassland plots. Communities were established from seed in 2002 and contained 1, 2, 4, 8, 16 or 60 plant species of 1, 2, 3 or 4 functional groups. In 2004, pairs of enclosure cages (1 m tall, 0.5 m diameter) were set up on all 81 plots. One randomly selected cage of each pair was stocked with 10 male and 10 female nymphs of the meadow grasshopper, Chorthippus parallelus. The grasshoppers fed for 2 months, and the vegetation was monitored over 1 year. Consumption resistance and recovery of vegetation were calculated as proportional changes in vegetation biomass. Overall, grasshopper herbivory averaged 6.8%. Herbivory resistance and recovery were influenced by plant functional group identity, but independent of plant species richness and number of functional groups. However, herbivory induced shifts in vegetation composition that depended on plant species richness. Grasshopper herbivory led to increases in herb cover at the expense of grasses. Herb cover increased more strongly in species-rich mixtures. We conclude that selective herbivory changes the functional composition of plant communities and that compositional changes due to selective herbivory depend on plant species richness.