Efficiency of three halophyte species in removing nutrients from saline water: a pilot study

Saline wetlands may be well suited for purifying contaminated water from saline agriculture and aquaculture or from freshwater-based agriculture in areas subject to increased salinity. However, case studies on the nutrient removal efficiency of halophyte species are scarce, especially for temperate regions. Here we tested the nutrient removal efficiency and ability to store nutrients in aboveground and belowground biomass of three halophyte species, Aster tripolium, Bolboschoenus maritimus subsp. compactus, and Spartina anglica, in a greenhouse microcosm experiment at two salinity levels. Nutrient removal from water differed among the species: Spartina had the highest nitrogen removal, Bolboschoenus and Spartina had the highest phosphorus removal. The species also differed in the allocation of the nutrient uptake. Bolboschoenus had the highest absolute uptake of nitrogen and phosphorus in shoots, whereas Spartina had the highest uptake of nitrogen and phosphorus in roots. The applicability of these three species in constructed saline wetlands depends on the local salinity and water regime.     

Kin recognition in plants with distinct lifestyles: implications of biomass and nutrient niches

Kin recognition has been demonstrated by plant biomass allocation and morphology traits as well as by nitrogen (N) uptake, but has not been examined from a nutrient-niche view yet. In this study, four species with distinct lifestyles, including Glycine max (L.) Merr. (herbaceous legume), Belamcanda chinensis (L.) DC. (herbaceous non-legume), Caesalpinia pulcherrima (L.) Sw. (woody legume), and Populus tomentosa (L.) Carr. (woody non-legume) were used to demonstrate kin recognition by estimating their biomass and allocation, as well as nutrient niches based on their uptake efficiency for N, phosphorus (P), sulfur (S), potassium (K), calcium (Ca), magnesium (Mg), and iron (Fe). For G. max, kin recognition was achieved by increased biomass, and by reduced nutrient-uptake efficiency of N, P, S, K, Ca, Mg, and Fe (decreased nutrient niches) to decrease nutrient competition among kin plants compared to the strangers. Although B. chinensis and C. pulcherrima had no biomass response, kin plants of B. chinensis increased, whereas C. pulcherrima decreased their S-uptake efficiency compare to strangers. Therefore, kin competition occurred in B. chinensis through increased nutrient niche whereas kin recognition occurred in C. pulcherrima through decreased nutrient niche. By comparison, P. tomentosa showed the co-occurrence of kin recognition and competition by increased root allocation and decreased P-uptake efficiency. These findings suggest that the biomass allocation and plant nutrient niches based on their nutrient-uptake efficiency can be used as potential parameters to identify kin recognition.     

Resource pulses of dead periodical cicadas increase the growth of American bellflower rosettes under competitive and non-competitive conditions

This experiment investigates how pulsed nutrient resources interact with intraspecific competition to influence biomass production and nutrient use efficiency in the American bellflower (Campanulastrum americanum). The competitive environment of these plants was manipulated by growing plants alone or with neighboring conspecifics, and the occurrence of pulsed nutrient resources was manipulated through the addition of 17-year periodical cicada (Magicicada septendecim) carcasses in order to simulate naturally occurring pulsed resources in this system. The addition of cicada carcasses increased mean plant biomass by 61 % compared to non-supplemented plants, while competition decreased mean plant biomass by 44 % compared to plants grown without competition; these effects were additive. In comparison, nutrient use efficiency decreased in fertilized plants (cicada-supplemented plants showed 20 % greater foliage nitrogen concentrations compared to non-supplemented plants), but was not significantly affected by the plant’s competitive environment. In addition, cicada supplementation did not significantly increase the biomass asymmetry in competing pairs of plants. These results suggest that these plants increased their total nutrient uptake at a timescale commensurate with the pulsed increase in nutrient availability due to cicada carcass decomposition.     

Effects of competition on induction of crassulacean acid metabolism in a facultative CAM plant

Abiotic drivers of environmental stress have been found to induce CAM expression (nocturnal carboxylation) in facultative CAM species such as Mesembryanthemum crystallinum. The role played by biotic factors such as competition with non-CAM species in affecting CAM expression, however, remains largely understudied. This research investigated the effects of salt and water conditions on the competition between M. crystallinum and the C₃ grass Bromus mollis with which it is found to coexist in California’s coastal grasslands. We also investigated the extent to which CAM expression in M. crystallinum was affected by the intensity of the competition with B. mollis. We found that M. crystallinum had a competitive advantage over B. mollis in drought and saline conditions, while B. mollis exerted strong competitive effects on M. crystallinum in access to light and soil nutrients in high water conditions. This strong competitive effect even outweighed the favorable effects of salt or water additions in increasing the biomass and productivity of M. crystallinum in mixture. Regardless of salt conditions, M. crystallinum did not switch to CAM photosynthesis in response to this strong competitive effect from B. mollis. Disturbance (i.e., grass cutting) reduced the competitive pressure by B. mollis and allowed for CAM expression in M. crystallinum when it was grown mixed with B. mollis. We suggest that moderate competition with other functional groups can enhance CAM expression in M. crystallinum, thereby affecting its plasticity and ability to cope with biological stress.     

Salinity tolerance of four freshwater microalgal species and the effects of salinity and nutrient limitation on biochemical profiles

Microalgae are ideal candidates for bioremediation and biotechnological applications. However, salinity and nutrient resource availability vary seasonally and between cultivation sites, potentially impacting on biomass productivity. The aim of this study was to screen pollutant-tolerant freshwater microalgae (Desmodesmus armatus, Mesotaenium sp., Scenedesmus quadricauda and Tetraedron sp.), isolated from Tarong power station ash-dam water, for their tolerance to cultivation at a range of salinities. To determine if biochemical composition could be manipulated, the effects of 4-day nutrient limitation were also determined. Microalgae were cultured at 2, 8, 11 and 18 ppt salinity, and nutrient uptake was monitored daily. Growth, total lipid, fatty acid (FA), and amino acid contents were quantified in biomass harvested while nutrient-replete and, after 4 days, nutrient-deplete. D. armatus showed the highest salinity tolerance actively growing in up to 18 ppt while Mesotaenium sp. was the least halotolerant with decreasing growth rates from 11 ppt. However, Mesotaenium sp. at 2 and 8 ppt had the highest biomass productivity and nutrient requirements of the four species, making it ideal for nutrient remediation of eutrophic freshwater effluents. Salinity and nutrient status had minimal influence on total lipid and FA contents in D. armatus and Mesotaenium sp., while nutrient depletion induced an increase of total lipid and FAs in S. quadricauda and Tetraedron sp., which was further increased with increasing salinity. As none of the growth conditions affected amino acid profiles of the species, these findings provide a basis for species selection based on site-specific salinity conditions and nutrient resource availability.     

Fast seedling root growth leads to competitive superiority of invasive plants

The competitive superiority of invasive plants plays a key role in the process of plant invasions, enabling invasive plants to overcome the resistance of local plant communities. Fast aboveground growth and high densities lead to the competitive superiority of invasive species in the competition for light. However, little is understood of the role belowground root competition may play in invasion. We conducted an experiment to test the effect of root growth on the performance of an invasive shrub Cassia alata, a naturalized, non-invasive shrub Corchorus capsularis, and a native shrub Desmodium reticulatum. We compared seedling growth of the three species and their competitive ability in situ. The roots of the C. alata seedlings grew much faster than those of C. capsularis and D. reticulatum during the entire growth period although C. alata had shorter shoots than D. reticulatum. Furthermore, C. alata showed an apparent competition advantage compared to the other two species as evidenced by less biomass reduction in intraspecific competition and higher competitive effects in interspecific competition. Our study reveals that fast seedling root growth may be important in explaining the competitive advantages of invasive plants. Future studies should pay more attention to the belowground traits of invasive plants, the trade-off between shoot and root growth, and the role of root competition in affecting the population dynamics of invasive plants and the structures of invaded communities.     

The optimum Se application time for reducing Cd uptake by rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) and its mechanism

Background and aims

Intraspecific aggregation of plant individuals can promote species coexistence by delaying competitive exclusions. However, such impacts may differ among species with contrasting spatial architecture and rely on the spatial distribution of resources.

Methods

We grew a phalanx clonal plant Carex neurocarpa (with aggregated ramets) and a guerilla one Bolboschoenus planiculmis (with diffused ramets) in monocultures or in 1:1 mixtures with an even or a clustered distribution pattern of the two species in homogeneous or heterogeneous soils.

Results

After 16 months, shoot biomass and ramet number were greater in mixtures than in monocultures in C. neurocarpa, but smaller in B. planiculmis. However, the growth of neither C. neurocarpa nor B. planiculmis differed between even and clustered mixtures. Soil nutrient heterogeneity did not significantly affect the growth of either species, but increased relative yield of B. planiculmis and decreased that of C. neurocarpa.

Conclusions

The relative importance of intra- vs. interspecific competition depends on the spatial architecture of plants, and soil nutrient heterogeneity slows down competitive exclusion by decreasing differences in competitive ability between plants. However, our results do not support the idea that intraspecific aggregation of individuals alters competitive interactions between species.

     

Competition between native Antarctic vascular plants and invasive <Emphasis Type="Italic">Poa annua</Emphasis> changes with temperature and soil nitrogen availability

Over the last decades human have introduced non-native organisms to Antarctica, including the grass species Poa annua. This non-native grass under constant growth temperatures has been shown negatively affect the growth of the only two native Antarctic vascular plants, Deschampsia antarctica and Colobanthus quitensis, under constant growth temperatures. However, whether there are changes in the interaction between these species under warmer conditions is an important question. In cold ecosystems, soil nutrient status directly affects plant responses to increases in temperature and Antarctic soils are highly variable in nutrient supply. Thus, in this study we experimentally assessed the interaction between the non-native Poa with the two native Antarctic vascular plant species at two different temperatures and levels of nutrient availability. Individual mats of the study species were collected in King George Island, and then transported to Concepcion where we conducted competition experiments. In the first experiment we used soil similar to that of Antarctica and plants in competition were grown at two temperatures: 5°/2° and 11°/5 °C (day/night temperature). In a second experiment plants were grown in these two temperature regimes, but we varied nitrogen (N) availability by irrigating plants with Hoagland solutions that contained 8000 or 300 µM of N. Overall, Poa exerted a competitive effect on Deschampsia but only at the higher temperature and higher N availability. At 5°/11 °C the competitive response of Deschampsia to Poa was of similar magnitude to the competitive effect of P. Deschampsia, and the competitive effect was greater with at low N. The competitive effect of Poa was similar to the competitive response of Colobanthus to Poa at both temperatures and N levels. Thus, at low temperatures and N soil content the native Antarctic species might withstand Poa invasion, but this might change with climate warming.     

The role of flood regime on invasive success of exotic species growing in riparian environments

To elucidate the conditions under which exotic species become invasive, we compared the performance of Veronica anagallis-aquatica (exotic) and V. undulata (native) in Kansai, southern-central Japan, where the former species is highly invasive, with performance in a region where this species is less invasive (Kanto, eastern Japan). We compared the micro-environments, including scale and frequency of flooding, of these species in both Kansai and Kanto. We also conducted growth experiments on seedlings from both regions to compare their responses to varying water conditions. Four treatments were conducted: a dry treatment where neither roots nor shoots were flooded; a flooded treatment where both roots and shoots were flooded; a moist treatment where only roots were flooded; and a variable treatment where the water level was shifted between that in the flooded and dry treatments. We found that the flooding frequency was higher in Kansai than in Kanto, whereas the flow peaks were almost four times higher in Kanto than in Kansai. The mean stem internode length was longer in the variable treatments than in the other treatments in the V. anagallis-aquatica seedlings derived from Kansai, but did not differ among treatments in both V. anagallis-aquatica and V. undulata seedlings derived from Kanto. V. anagallis-aquatica in Kansai evolved a strategy to evade flooding by stem elongation. However, that species did not show elongation traits in Kanto, possibly because it could not respond to large-scale flooding. V. anagallis-aquatica may show adaptive evolution in specific habitats where it can respond adaptively.     

Contribution of different arbuscular mycorrhizal fungal inoculum to <Emphasis Type="Italic">Elymus nutans</Emphasis> under nitrogen addition

Arbuscular mycorrhizal (AM) fungi are known to promote plant growth and nutrient uptake, but their role in nitrogen (N) uptake still remains unclear. Therefore, a pot experiment was set up to evaluate the impacts of N addition and AM inoculation (Diversispora eburnea, Claroideoglomus etunicatum, Paraglomus occultum, and their mixture) on AM root colonization, plant biomass, N and P nutrition in Elymus nutans. Our results showed that AM root colonization was unaffected by N addition but was significantly affected by different AM fungal species. D. eburnea and C. etunicatum showed significant higher root colonization than P. occultum. The E. nutans exhibited the highest biomass when inoculated with D. eburnea and significantly higher than non-mycorrhizal (the control) regardless of N addition. Under N addition treatment, D. eburnea significantly enhanced P content of roots, N content of shoots and roots, while AM mixture significantly enhanced shoot P content compared with non-mycorrhizal. However, N and P content in shoots and roots did not significantly vary among treatments when no N was added. In addition, inoculation with C. etunicatum and P. occultum showed no significant effect on plant biomass, N and P content regardless of N addition. In conclusion, this study revealed that the plant response to N addition depends on AM fungal species and also confirmed that significant functional diversity exists among AM fungal species.     

Characterization of the lipopolysaccharide of <Emphasis Type="Italic">Escherichia coli</Emphasis> 126

The lipopolysaccharide (LPS) of Escherichia coli 126 was isolated and studied. The lipid A fatty acid composition of the investigated LPS was similar to that of other members of the family Enterobacteriaceae. The E. coli 126 LPS was more toxic than the LPSs of previously studied E. coli strains and of other members of the Enterobacteriaceae (Budvicia aquatica and Pragia fontium), and was less pyrogenic than pyrogenal. SDS-PAG electrophoresis showed a bimodal distribution typical of S-form LPSs. The LPS of E. coli 126 decreased the adhesive index indicating a possible competition between LPS molecules of E. coli 126 and adhesins of E. coli F-50 on rabbit erythrocytes. The LPS of E. coli 126 in a homologous system showed antigenic activity in the reactions of double immunodiffusion in agar by Ouchterlony. No serological cross-reaction of the LPS of other E. coli strains, as well as of that of the B. aquatica type strain, with the antiserum to E. coli 126 was observed. The structural components of the lipopolysaccharide obtained by mild acid hydrolysis were lipid A, the core oligosaccharide, and the O-specific polysaccharide. Based on the data of monosaccharide analysis and ¹H and ¹³C NMR spectroscopy it was found that the O-specific polysaccharide had the structure characteristic of the representatives of E. coli serogroup O15.     

Sediments influence accumulation of two macroalgal species through novel but differing interactions with nutrients and herbivory

Despite increasing concern that sediment loads from disturbed watersheds facilitate algal dominance on tropical reefs, little is known of how sediments interact with two primary drivers of algal communities, nutrients and herbivory. We examined the effects of sediment loads on the thalli of two increasingly abundant genera of macroalgae, Galaxaura and Padina, in a bay subject to terrestrial sediment influx in Mo’orea, French Polynesia. Field experiments examining (1) overall effects of ambient sediments and (2) interacting effects of sediments (ambient/removal) and herbivores (caged/uncaged) demonstrated that sediments had strong but opposite effects on both species’ biomass accumulation. Sediment removal increased accumulation of Padina boryana Thivy 50% in the initial field experiment but had no effect in the second; rather, in a novel interaction, herbivores overcompensated for increases in tissue nutrient stores that occurred with sediments loads, likely by preferential consumption of nutrient-rich meristematic tissues. Despite negative effects of sediments on biomass, Padina maintained rapid growth across treatments in both experiments. In contrast, positive growth in Galaxaura divaricata Kjellman only occurred with ambient sediment loads. In mesocosm experiments testing interactions of added nutrients and sediments on growth, Galaxaura grew at equivalent rates with sediments (collected from thalli on the reef) as with additions of nitrate and phosphate, suggesting sediments provide a nutrient subsidy. For Padina, however, the only effect was a 50% reduction in growth with sediment. Overall, retention of thallus sediments creates a positive feedback that Galaxaura appears to require to sustain net growth, while Padina merely tolerates sediments. These results indicate that sediments can modify nutrient and herbivore control of algae in ways that differ among species, with the potential for strong and unexpected effects on the abundance and composition of tropical reef macroalgae.     

Light energy partitioning,photosynthetic efficiency and biomass allocation in invasive <Emphasis Type="Italic">Prunus serotina</Emphasis> and native <Emphasis Type="Italic">Quercus petraea</Emphasis> in relation to light environment,competition and allelopathy

This study addressed whether competition under different light environments was reflected by changes in leaf absorbed light energy partitioning, photosynthetic efficiency, relative growth rate and biomass allocation in invasive and native competitors. Additionally, a potential allelopathic effect of mulching with invasive Prunus serotina leaves on native Quercus petraea growth and photosynthesis was tested. The effect of light environment on leaf absorbed light energy partitioning and photosynthetic characteristics was more pronounced than the effects of interspecific competition and allelopathy. The quantum yield of PSII of invasive P. serotina increased in the presence of a competitor, indicating a higher plasticity in energy partitioning for the invasive over the native Q. petraea, giving it a competitive advantage. The most striking difference between the two study species was the higher crown-level net CO₂ assimilation rates (A_crown) of P. serotina compared with Q. petraea. At the juvenile life stage, higher relative growth rate and higher biomass allocation to foliage allowed P. serotina to absorb and use light energy for photosynthesis more efficiently than Q. petraea. Species-specific strategies of growth, biomass allocation, light energy partitioning and photosynthetic efficiency varied with the light environment and gave an advantage to the invader over its native competitor in competition for light. However, higher biomass allocation to roots in Q. petraea allows for greater belowground competition for water and nutrients as compared to P. serotina. This niche differentiation may compensate for the lower aboveground competitiveness of the native species and explain its ability to co-occur with the invasive competitor in natural forest settings.     

Strong increase of durum wheat iron and zinc content by field-inoculation with arbuscular mycorrhizal fungi at different soil nitrogen availabilities

Background and aims

The changes in the characteristics of Panicum virgatum, an exotic invasive species, after invading various plant communities on the Loess Plateau in China and the main soil nutrient factors in these communities closely associated with invasion remain unclear.

Methods

A pot culture experiment was carried out to simulate the changes in photosynthesis, biomass, and biomass allocation in P. virgatum and to identify the main soil nutrient factors in various soils collected from local plant communities. P. virgatum was grown in soils collected from communities of P. virgatum (PS treatment), Setaria viridis (SS treatment), Bothriochloa ischaemum (BS treatment), and Artemisia sacrorum (AS treatment) and in a mixed soil from the communities of S. viridis, B. ischaemum, and A. sacrorum (MS treatment).

Results

Photosynthesis in P. virgatum differed significantly among the soil treatments. Net photosynthetic rate, stomatal conductance, and photochemical efficiency (Fv/Fm) were highest in PS, whereas single-photon avalanche diode values were highest in PS and SS. The variation of biomass differed significantly in different tissues of P. virgatum in the treatments. Leaf and stem biomasses were highest in PS and SS, and root biomass was highest in PS and MS. Total biomass differed significantly among the treatments, except between BS and MS. Both the leaf to total and stem to total biomass ratios were highest in AS and SS, but the root to total biomass ratio was lowest in these two treatments. A constrained redundancy analysis and a path analysis suggested that the water-soluble nitrate-nitrogen (W-NN) concentration of the soil could significantly affect photosynthesis, biomass, and biomass allocation in P. virgatum.

Conclusions

Photosynthesis, biomass, and biomass allocation in P. virgatum differed significantly when grown in soils from different local plant communities on the Loess Plateau. The soil W-NN concentration in these local plant communities likely has a large impact on the invasive success of P. virgatum.

     

Effects of leaf litter on inter-specific competitive ability of the invasive plant <Emphasis Type="Italic">Wedelia trilobata</Emphasis>

Allelochemicals released by invasive plants contribute to the successful invasion of new habitats. However, the relationship between allelopathic effects and competitive ability of invasive plants has not been characterized. We quantified the neighbor effects of Wedelia trilobata (family: Asteraceae) and the allelopathic effects of its leaf litter on two Asteraceae competitor species (invasive Eupatorium catarium and non-invasive Lactuca sativa) and on its own ramet growth. The seed germination rate and seedling biomass of the two competitor species decreased following treatment with W. trilobata leaf extracts. When co-cultured with W. trilobata, the total biomass of the two competitor species significantly decreased regardless of whether leaf extracts were present. Under low plant density co-culture conditions, W. trilobata leaf extracts enhanced the inhibitory effects on E. catarium. In contrast, W. trilobata leaf extracts promoted the growth of W. trilobata adventitious roots, resulting in increased competitive ability. Therefore, W. trilobata growth was promoted by its own allelochemicals in leaf extracts, whereas the growth of the invasive and non-invasive competitors was inhibited by the same chemicals. These responses facilitated the invasion by W. trilobata. Our study demonstrates that leaf litter of invasive plants may inhibit the growth of neighboring species to enhance the competitive ability of the invasive plants during the early stages of invasion.     

<Emphasis Type="Italic">Parthenium hysterophorus</Emphasis> L. (Asteraceae) invasion had limited impact on major soil nutrients and enzyme activity: Is the null effect real or reflects data insensitivity?

Background and aims

Competition from the annual grass Bromus tectorum threatens aridland perennial bunchgrass communities. Unlike annuals, perennials must allocate part of their first year nitrogen (N) budget to storage rather than growth, potentially placing them at a competitive disadvantage.

Methods

We evaluated N acquisition and conservation for two perennial bunchgrasses, Agropyron desertorum and Pseudoroegneria spicata, at the seedling stage to investigate potential trade-offs between storage and growth when grown with and without B. tectorum under two levels of soil N.

Results

Agropyron desertorum had higher growth rates, N uptake, and N productivity than P. spicata when grown without B. tectorum, but trait values were similarly low for both species under competition. Without competition, N resorption was poor under high soil N, but it was equally proficient among species under competition.

Conclusions

A. desertorum had higher growth rates and N productivity than P. spicata without competition, suggesting these traits may in part promote its greater success in restoration programs. However, B. tectorum neighbors reduced its trait advantage. As plant traits become more integral to restoration ecology, understanding how N capture and conservation traits vary across candidate species and under competition may improve our ability to select species with the highest likelihood of establishing in arid, nutrient-limited systems.

     

Effects of intrapopulation phenotypic traits of invasive crayfish on leaf litter processing

Environmental gradients and competition influence aquatic macrophyte distribution in estuaries. The competition-to-stress hypothesis states that some species are excluded from lower estuaries (high salinity) due to abiotic stress and others from upper estuaries (low salinity) by competition. The growth of Crinum americanum L. and Spartina alterniflora Loisel. in monoculture (10:0/0:10) and mixed culture (5:5) under different salinity levels (4/12/26) was analysed by a laboratory experiment (3 cultures × 3 sediment types × 3 replicate) to understand the role of competition and salinity on the distribution of these species in a tropical estuary as well as to verify whether the competition-to-stress hypothesis explains their zonation. We tested the hypothesis that S. alterniflora is not established in the upper estuary due to the effect of competition with C. americanum, whereas the latter presents restrictions to high salinity and has greater competitive ability in the upper estuary. Our data confirm the competition-to-stress hypothesis but not as proposed originally. We conclude that abiotic stress (low nutrient availability) is responsible for the absence of S. alterniflora in the upper estuary and that the competition between the two species is responsible for the absence of C. americanum in the lower estuary.     

No fitness cost of glyphosate resistance endowed by massive <Emphasis Type="Italic">EPSPS</Emphasis> gene amplification in <Emphasis Type="Italic">Amaranthus palmeri</Emphasis>

Amplification of the EPSPS gene has been previously identified as the glyphosate resistance mechanism in many populations of Amaranthus palmeri, a major weed pest in US agriculture. Here, we evaluate the effects of EPSPS gene amplification on both the level of glyphosate resistance and fitness cost of resistance. A. palmeri individuals resistant to glyphosate by expressing a wide range of EPSPS gene copy numbers were evaluated under competitive conditions in the presence or absence of glyphosate. Survival rates to glyphosate and fitness traits of plants under intra-specific competition were assessed. Plants with higher amplification of the EPSPS gene (53-fold) showed high levels of glyphosate resistance, whereas less amplification of the EPSPS gene (21-fold) endowed a lower level of glyphosate resistance. Without glyphosate but under competitive conditions, plants exhibiting up to 76-fold EPSPS gene amplification exhibited similar height, and biomass allocation to vegetative and reproductive organs, compared to glyphosate susceptible A. palmeri plants with no amplification of the EPSPS gene. Both the additive effects of EPSPS gene amplification on the level of glyphosate resistance and the lack of associated fitness costs are key factors contributing to EPSPS gene amplification as a widespread and important glyphosate resistance mechanism likely to become much more evident in weed plant species.     

Opposite effects of litter and hemiparasites on a dominant grass under different water regimes and competition levels

Direct and indirect biotic interactions may affect plant growth and development, but the magnitude of these effects may vary depending on environmental conditions. In grassland ecosystems, competition is a strong structuring force. Nonetheless, if hemiparasitic plant species are introduced the competition intensity caused by the dominant species may be affected. However, the outcome of these interactions may change between wet or dry periods. In order to study this, we performed a pot experiment with different densities of the dominant species Schedonorus arundinaceus (1, 2 or 4 individuals) under constantly moist or intermittently dry conditions. The different Schenodorus densities were crossed with presence or absence of hemiparasites (either Rhinanthus minor or R. alectorolophus). Additionally, pots remained with bare ground or received a grass litter layer (400 g m^?2). We expected that indirect litter effects on vegetation (here Schedonorus or Rhinanthus) vary depending on soil moisture. We measured Schedonorus and Rhinanthus aboveground biomass and C stable isotope signature (δ¹³C) as response variables. Overall, Schedonorus attained similar biomass under moist conditions with Rhinanthus as in pots under dry conditions without Rhinanthus. Presence of Rhinanthus also increased δ¹³C in moist pots, indicating hemiparasite-induced water stress. Litter presence increased Schedonorus biomass and reduced δ¹³C, indicating improved water availability. Plants under dry conditions with litter showed similar biomass as under wet conditions without litter. Hemiparasites and litter had opposite effects: hemiparasites reduced Schedonorus biomass while litter presence facilitated grass growth. Contrary to our expectations, litter did not compensate Schedonorus biomass when Rhinanthus was present.     

Host plants influence female oviposition and larval performance in West Indian sweet potato weevils <Emphasis Type="Italic">Euscepes postfasciatus</Emphasis> (Coleoptera: Curculionidae)

Euscepes postfasciatus (Fairmaire) is an invasive pest of the sweet potato (Ipomoea batatas) and is also parasitic to other wild host plants of the Ipomoea genus. The population density of E. postfasciatus is sometimes greater in Ipomoea pes-caprae L. than in Ipomoea indica (Burm. f.). We investigated the desirability of I. pes-caprae as a host plant for E. postfasciatus in terms of reproductive and developmental potential. Females laid fewer eggs on I. pes-caprae, and the eclosion of their larvae was delayed compared with on I. indica. Furthermore, the larval growth rate was slower on I. pes-caprae than on I. indica. These results suggest that I. pes-caprae is not always the preferred host for egg laying and growth rate in the early developmental stages. However, the larval survival rate after the initial period of development was markedly better on I. pes-caprae than on I. indica. The present simulation study demonstrated that the population density of E. postfasciatus on I. pes-caprae overwhelmed that on I. indica over generations. Comparing the two wild host plant species, I. pes-caprae outweighs I. indica with respect to total population growth, but reproduction on I. indica may be advantageous for the colonization of the new habitat.