Suppression of Salvinia molesta Mitchell in Texas and Louisiana by Cyrtobagous salviniae Calder and Sands

Release and evaluation studies of the Brazil population of Cyrtobagous salviniae on Salvinia molesta were conducted originally at 18 sites in Texas and Louisiana from 1999 through 2005. However, overall project results could only be continually evaluated at two release and two control sites because the remainder were eventually destroyed or corrupted by floods, droughts, or herbicides. Mean fresh weight biomass of S. molesta ranged from 15.5 kg FW m⁻² during the summer to as low as 2.1 kg FW m⁻² during the winter prior to the release of C. salviniae. Insect populations established within a year of release and initially spread slowly. Damage to S. molesta increased with increasing C. salviniae detections while S. molesta biomass and surface coverage declined at both release sites by more than 99% while remaining unchanged at the control sites. Water in release sites registered higher levels of dissolved oxygen, higher temperatures, and higher pH than water in control sites. This study provides another example of the effectiveness of C. salviniae against S. molesta even in more temperate climates.     

Competition between Lemna minuta and Lemna minor at different nutrient concentrations

We investigated the differential responses of invasive alien Lemna minuta and native Lemna minor to nutrient loading as well as the mechanism of competition between the species. The role of nutrients, species identity, species influence in determining the outcome of competition between the species was estimated using the Relative Growth Rate Difference (RGRD) model. The two species differed in their response to nutrient loading. The native L. minor responded indifferently to nutrient loading. The species Relative Growth Rate (RGR) was 0.10 d⁻¹, 0.11 d⁻¹ and 0.09 d⁻¹ in high, medium and low nutrients, respectively. On the other hand, the invasive L. minuta responded opportunistically to high nutrient availability and had an RGR of 0.13 d⁻¹, 0.10 d⁻¹ and 0.08 d⁻¹ in high, medium and low nutrients, respectively. As a result, the invasive species was dominant in high nutrient availability but lost to the native species at low nutrient availability. The invader formed approximately 60% and less than 50% of the stand final total dry biomass in high and low nutrient availability, respectively. Species RGR were reduced by both intra- and interspecific competition but intraspecific effects were stronger than interspecific effects. On the overall, the species significantly differed in their constant RGR. These differences in RGR between the species (species identity) and the differential response to nutrient loading were the main determinant of change in final biomass composition of these species in mixture. Species influence (competition) only had a small influence on the outcome of competition between the species. The observed species response to nutrient loading could be targeted in management of the invasive species. Lowering nutrients can be proposed to reduce the impact of the invasive L. minuta.     

Nutritional value and intake of aquatic ferns (Azolla filiculoides Lam. and Salvinia molesta Mitchell.) in sows

Aquatic ferns (AFs) such as Azolla filiculoides and Salvinia molesta are grown on swine lagoons in the tropics and used in diets for pigs. The present work is aimed at evaluating their potential as feed ingredients for sows. When presented with ad libitum AFs, gilts weighing 110 ± 14 kg (mean ± SD), were able to ingest 9.1–9.7 kg fresh AF per day (from 597 to 630 g dry matter (DM) per day) and from 1240 to 1428 g DM per day when presented in a dry, ground form. A digestibility study was conducted, using sows weighing 213 ± 9 kg (mean ± SD), which were fed diets containing maize, soybean meal and 0, 150 or 300 g AF kg⁻¹ diet. The presence of AFs had a negative impact on the faecal digestibility of the crude protein, NDF and energy content of the whole diet (P<0.001) and on the ileal protein digestibility, especially with 300 g AFs kg⁻¹ diet. The level of AFs in the diet had no effect on stomach weight (P>0.05) but increased the weight of the rest of the gastrointestinal tract (P<0.001). The rate of AF fibre fermentation in the pig large intestine was measured using an in vitro gas test. The rates were much lower than tropical tree foliage, which can also be used in pig diets in the tropics. This could partly explain the low apparent digestibility of AFs in pigs. In conclusion, the inclusion level of AFs in rations for sows should be limited to 150 g AFs kg⁻¹ diet due to the low digestibility and energy density, as well as the negative impact on the digestibility of the whole diet.     

Seasonal growth dynamics of Laurencia papillosa and Gracilaria coronopifolia from a highly eutrophic reef in southern Taiwan: temperature limitation and nutrient availability

Both field and laboratory studies were used to investigate the effects of temperature limitation and nutrient availability on seasonal growth dynamics of Laurencia papillosa and Gracilaria coronopifolia from a nearshore coral reef in the southern tip of Taiwan during 1999-2000. L. papillosa was a summer blooming alga abundant in August-November and G. coronopifolia was abundant year round except April-May. L. papillosa blooms in the summer were attributed to its preference for high temperatures and highly sensitivity to low temperatures. A wider temperature range and a significant stimulation of growth by high N inputs can explain the appearance of G. coronopifolia year round and also its maximum growth in November-March. Levels of dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) in water column were extremely high, but the growth of these two rhodophytes still suffered nutrient limitation that the type and severity of nutrient limitation were variable over time and also between two species. The growth of L. papillosa was limited by P in the early growth stage (August-September) as indicated by decreased tissue P contents, increased C/P and N/P molar ratios and increased alkaline phosphatase activity (APA) and in the later growth stage, it was subjected to N-limitation, evidenced by decreased tissue N contents and C/P and N/P molar ratios and increased tissue P contents. The growth of G. coronopifolia was also P-limited as indicated by increased tissue N contents and concomitantly decreased tissue P contents, while marked drops in tissue P contents below the subsistence level in mid September and December 1999 reveal severe P limitation, which was supported by increased alkaline phosphatase activity. Higher critical nutrient contents and nutrient thresholds for maximum growth of G. coronopifolia suggest that G. coronopifolia faced more frequent nutrient limitation compared to L. papillosa. In conclusion, the results from these laboratory and field studies provide evidence that the seasonal abundance of L. papillosa and G. coronopifolia from southern Taiwan was determined by seasonal variations in seawater temperatures and nutrient concentrations as well as different physiological growth strategies. Seawater temperature and nutrient availability were important determinants of seasonal abundance of L. papillosa while the seasonal abundance of G. coronopifolia was influenced by nutrient availability.     

Competition and facilitation between the alien mussel Mytilus galloprovincialis and indigenous species: Moderation by wave action

As the alien species that most dominates space along the South African coast, the Mediterranean mussel Mytilus galloprovincialis has radically altered community composition on invaded shores. We experimentally assessed interspecific interactions between this invasive species and dominant indigenous species in conjunction with considering how wave action moderates such interactions. The density of both M. galloprovincialis and the limpet Scutellastra granularis increased with wave action. Conversely, the tube-building polycheate Gunnarea capensis was negatively affected by wave exposure, being most abundant on sheltered shores. The influence of wave action on the indigenous mussel Aulacomya ater, however, remains unclear. M. galloprovincialis outcompeted both G. capensis and A. ater at moderate to high exposure levels, whereas it had both positive and negative effects on S. granularis. It outcompeted adult limpets on primary rock space on semi-exposed and exposed shores, reducing densities of this portion of the population. However, recruitment of S. granularis was facilitated by M. galloprovincialis, as greater numbers recruited to the secondary substratum offered by mussel shells. Again this interaction intensified with wave action. Due to the extremely high density of recruits on secondary space, the net effect of M. galloprovincialis on S. granularis was positive. Thus, wave action not only influences the abundance of individual species, but also mediates both positive and negative interspecific interactions in rocky shore communities, including the impact of alien species such as M. galloprovincialis.     

Trophic interactions between two introduced suspension-feeders, Crepidula fornicata and Crassostrea gigas, are influenced by seasonal effects and qualitative selection capacity

The effects of season and qualitative selection capacity on trophic relationships between two sympatric invasive suspension-feeders, Crepidula fornicata and Crassostrea gigas, were investigated in Bourgneuf Bay (France) from January 2003 to June 2004. Carbon and nitrogen stable isotopic deviations, δ¹³C and δ¹⁵N, of common Atlantic slippersnails and Pacific oysters were analysed relative to isotopic composition and availability of end-members.Slippersnail deviations were less variable over the sampling period compared with those of oysters. Significant differences between δ¹³C and δ¹⁵N of C. fornicata and C. gigas were found from winter to early summer, and linked to major isotopic changes in oysters. We identified three distinct seasonal periods: January to March when oysters were ¹⁵N-enriched compared to slippersnails and to themselves at other times of the year, April to June-July when oysters showed a ¹⁵N-depletion and a more marked ¹³C-depletion compared to slippersnails and to themselves at other times of the year, and July-August to December when both species presented similar carbon and nitrogen deviations. Species-specific differences in qualitative selection capability may explain these seasonal differences in isotopic deviations. Whereas the isotopic composition of the indiscriminate suspension-feeding slippersnails reflects the composition of the seston throughout the year, the oyster is capable of qualitative selection. The oyster isotopic compositions are consistent with a facultative activation of selection mechanisms under conditions of qualitative and quantitative food limitation, notably the preferential ingestion and assimilation of the dominant organic source in the suspended pool.We conclude that C. fornicata and C. gigas are trophic competitors only in winter and spring at this site, where detrital end-members are major POM components. These results underscore (1) the importance of long-term (annual) studies in the evaluation of potential trophic competition, and (2) the necessity to include the qualitative selection capacities of suspension-feeders in future interpretations of trophic relationships in marine coastal ecosystems.     

Growing duckweed in swine wastewater for nutrient recovery and biomass production

Spirodela oligorrhiza, a promising duckweed identified in previous studies, was examined under different cropping conditions for nutrient recovery from swine wastewater and biomass production. To prevent algae bloom during the start-up of a duckweed system, inoculating 60% of the water surface with duckweed fronds was required. In the growing season, the duckweed system was capable of removing 83.7% and 89.4% of total nitrogen (TN) and total phosphorus (TP) respectively from 6% swine lagoon water in eight weeks at a harvest frequency of twice a week. The total biomass harvested was 5.30 times that of the starting amount. In winter, nutrients could still be substantially removed in spite of the limited duckweed growth, which was probably attributed to the improved protein accumulation of duckweed plants and the nutrient uptake by the attached biofilm (algae and bacteria) on duckweed and walls of the system.     

Influence of salinity and high temperature on turion formation in the duckweed Spirodela polyrhiza

The influence of NaCl (salinity; 0-5 ‰) and higher temperature (heat stress; 32 °C) on yield of turion formation has been tested in the duckweed Spirodela polyrhiza for the first time. Turion formation was more sensitive to both stressors than the growth of the vegetative fronds: (1) the concentration of NaCl which produces half-maximal inhibition was lower for turion formation than for growth by the factor of five. (2) At 32 °C turion formation was completely blocked whereas growth rates decreased by only 20% as compared with 28 °C.     

Heavy metal removal from a multi-metal solution and wastewater by Salvinia natans

Salvinia showed capacity to accumulate and hence remove more than one heavy metal from multi-metal solutions, though efficiency for heavy metal uptake varied for each metal present in different combinations. The pattern of heavy metal accumulation was confirmed by energy-dispersive X-ray fluorescence (EDXRF) analysis. There was a gradual decrease in heavy metal content in the wastewater samples when fresh biomass was replenished at definite time intervals of treatment. Zn, Cu, Ni and Cr removal to the extent of 84.8%, 73.8%, 56.8%, and 41.4%, respectively, was noted after four samplings of fresh biomass replenishment. Salvinia therefore can be recommended as a species for cleaning water contaminated with heavy metals.     

芦苇、香蒲和藨草3种挺水植物的养分吸收动力学

采用常规耗竭法研究了浅水富营养化湖泊———乌梁素海湖滨植被带3种挺水植物芦苇、香蒲和藨草对H2PO-4、NH+4、NO-3的吸收动力学特征及差异。结果表明:3种挺水植物吸收H2PO-4时,藨草的吸收速率显著大于芦苇和香蒲,但三者对低浓度H2PO-4的适应能力均无显著差异;藨草对NH+4和NO-3的吸收速率均显著大于芦苇和香蒲,且在低浓度NO-3环境下仍能吸收该离子,但对低浓度NH+4环境的适应能力较差;与藨草相比,香蒲对NH+4的亲和力最强,吸收低浓度NH+4的效果最好。3种植物对NH+4的吸收能力均大于NO-3。挺水植物的养分吸收特征具有物种特异性并受根系结构的影响。利用植物的养分吸收特征,在富营养化湖泊生态修复中适宜用藨草治理含高浓度H2PO-4,NH+4和NO-3的水体,修复到一定程度后再种植香蒲来维持水质。     

Successful Agrobacterium mediated transformation of Thielaviopsis basicola by optimizing multiple conditions

Thielaviopsis basicola is a hemibiotrophic root pathogen causing black root rot in a wide range of economically important crops. Our initial attempts to transform T. basicola using standard Agrobacterium tumefaciens–mediated transformation (ATMT) protocols were unsuccessful. Successful transformation required the addition of V8 juice (to induce germination of T. basicola chlamydospores) and higher concentrations of acetosyringone in the co-cultivation medium, and of chlamydospores/endoconidia, A. tumefaciens cells during co-cultivation. With these modifications, two T. basicola strains were successfully transformed with the green (egfp) or red (AsRed) fluorescent protein genes. Chlamydospores/endoconidia transformed with the egfp gene exhibited strong green fluorescence, but their fluorescence became weaker as the germ tubes emerged. Transformants harbouring the AsRed gene displayed strong red fluorescence in both chlamydospores/endoconidia and germ tubes. Fluorescent microscopic observations of an AsRed-labelled strain colonizing roots of transgenic Nicotiana benthamiana plants, which express the actin filaments labelled with EGFP, at 24 hours post inoculation showed varying levels of fungal germination and penetration. At this stage, the infection appeared to be biotrophic with the EGFP-labelled host actin filaments not being visibly degraded, even in host root cells in close contact with the hyphae. This is the first report of ATMT of T. basicola, and the use of an AsRed-labelled strain to directly observe the root infection process.     

RPB2 sequences reveal a close phylogenetic relationship between tetraploid Hordelymus and diploid Hordeum species in Triticeae (Poaceae)

The origin of Hordelymus genome has been debated for years, and no consensus conclusion was reached. In this study, we sequenced and analyzed the RPB2 (RNA polymerase subunit II) gene from Hordelymus europaeus (L.) Harz, and its potential diploid ancestor species those were suggested in previous studies. The focus of this study was to examine the phylogenetic relationship of Hordelymus genomes with its potential donor Hordeum, Psathyrostachys, and Taeniatherum species. Two distinguishable copies of sequences were obtained from H. europaeus. The obvious difference between the two copies of sequences is a 24 bp indel (insertion/deletion). Phylogenetic analysis showed a strong affinity between Hordeum genome and Hordelymus with 85% bootstrap support. These results suggested that one genome in tetraploid H. europaeus closely related to the genome in Hordeum species. Another genome in H. europaeus is sister to the genomes in Triticeae species examined here, which corresponds well with the recently published EF-G data. No obvious relationship was found between Hordelymus and either Ta genome donor, Taeniatherum caput-medusae or Ns genome donor, Psathyrostachys juncea. Our data does not support the presence of Ta and Ns genome in H. europaeus, and further confirms that H. europaeus is allopolyploid.     

Competition for phosphorus between two dinoflagellates: A toxic Alexandrium minutum and a non-toxic Heterocapsa triquetra

The understanding of the dominance of one species with respect to others is a pertinent challenge in HAB growth dynamics studies and the nutrient supply mode is one of the factors potentially involved. The competition for phosphorus (P) between a toxic species, Alexandrium minutum, and a non-toxic species, Heterocapsa triquetra, was studied (1) along a gradient of P depletion, (2) testing different P depletion degrees before a single PO₄ supply and (3) experimenting different PO₄ supply frequencies. In conditions of PO₄ depletion, H. triquetra stopped growing after two days both in monospecific and mixed batch cultures whereas A. minutum grew progressively from day 2 until the end of the experiment. This time-lag growth of A. minutum is associated to its ability to store P intracellularly and then mobilize it for cell division when P depletion becomes severe. Heterocapsa triquetra outcompeted A. minutum when it was submitted to less than three days of P depletion before the pulse. In contrast, A. minutum outcompeted H. triquetra after more than three days of depletion. This transition was related to the capacity for A. minutum to increase its cell PO₄ uptake rate in a higher proportion to face potential PO₄ supply. As a result of this physiological acclimatation to P starvation, A. minutum consumed the whole PO₄ pulse supplied after 3 to 10 days of P depletion. This resulted in a reduction of H. triquetra growth. These two acclimatations were confirmed in a P limited semi-continuous culture experiment testing several PO₄ supply frequencies (1, 2, 4, 6 day intervals). These experiments revealed that A. minutum is a “storage specialist” species for P, which uptakes PO₄ pulses for luxury consumption, survives depletion periods and, then, utilizes P for cell growth. In contrast, H. triquetra is more a “velocity adapted” species, which utilizes PO₄ just after supply to increase their cell division rate.     

Grazing of the invasive alga Codium fragile ssp. tomentosoides by the common periwinkle Littorina littorea: Effects of thallus size, age and condition

We examined the potential of herbivory by the common periwinkle Littorina littorea to limit recruitment and vegetative re-growth of the invasive green alga Codium fragile ssp. tomentosoides in a series of manipulative field experiments in tidepools on a wave-exposed rocky shore in Nova Scotia, Canada. Snails were excluded or included from circular plots (14 to 20 cm diameter) with cages to compare growth and survival of C. fragile against procedural (partial cages) or natural (uncaged) control plots. Our results show that L. littorea may restrict growth and survival of C. fragile by grazing new recruits (< 2 cm thallus length), fronds of adult thalli that are bleached and necrotic, and residual holdfasts (< 2 mm thickness) of detached thalli (artificially severed to mimic wave dislodgement). Once recruits grow beyond a critical size (~ 3 cm), or damaged tissues or holdfasts regenerate, grazing of C. fragile by L. littorea appears to be limited and ineffectual. Our experimental results corroborate correlative evidence from previous studies that herbivory by L. littorea limits the abundance of C. fragile in tidepools on the Atlantic coast of Nova Scotia, particularly pools in the high intertidal zone where these snails are abundant. Lower on the shore, littorinid grazing and physical stressors that render algae more vulnerable to grazers (e.g. UV radiation and freezing) are less intensive, and probably have less of a regulatory effect on populations of C. fragile.