Effects of hydrological regimes on competitive interactions of Schoenoplectus fluviatilis and two co-occurring wetland plants

We investigated the effects of different hydrological regimes (wet [flooded at a constant water depth for duration of the study], cycle [reflooded at eight weeks following natural drying], and wet–dry [initially flooded and allowed to naturally dry for duration of the study]) on the competitive ability of Schoenoplectus fluviatilis (Torr.) M. T. Strong with an annual, native wetland plant (Polygonum pensylvanicum L.) and a perennial, wetland plant (Schoenoplectus tabernaemontani [C. C. Gmel.] Palla). To assess competitive response of the plants, we used a greenhouse target-neighbor study with neighbor plants planted at varying densities (0 [control], 1, 10, and 15 plants pot⁻¹). Our results suggest that S. fluviatilis is competitively superior to S. tabernaemontani and P. pensylvanicum. S. tabernaemontani and P. pensylvanicum biomass declined by 90% and 75% in presence of S. fluviatilis, respectively. However, the competitive ability of S. fluviatilis was generally not enhanced by flooding regime. The competitive coefficients of S. fluviatilis were similar among the three hydrological regimes under intraspecific competition and interspecific competition with S. tabernaemontani, but for interspecific competition with P. pensylvanicum, the competitive coefficient for S. fluviatilis was higher for the cycle treatment compared to the wet–dry and dry treatments. Interestingly, S. tabernaemontani was a strong competitor against S. fluviatilis in the wet and cycle treatments, indicating that maintaining longer hydroperiods could be used as a management tool to encourage growth of S. tabernaemontani and reduce encroachment of S. fluviatilis.     

Comparison of salinity tolerance of three Atriplex spp. in well-watered and drying soils

Members of the Chenopodiaceae are well adapted to both salt and drought stress and can serve as model species to understand the mechanisms of tolerance in plants. We grew Atriplex hortensis (ATHO), A. canescens (ATCA), and A. lentiformis (ATLE) along a NaCL salinity gradient under non-water-limited conditions and in drying soils in greenhouse experiments. The species differed in photosynthetic carbon fixation pathway, capacity for sodium uptake, and habitat preferences. Under non-water-limited conditions, ATLE (C4) maintained high growth rates up to 30 g L⁻¹ NaCl. ATHO (C3) had lower growth than ATLE at high salinities, while ATCA (C4) grew more slowly than either ATLE or ATHO and showed no net growth above 20 g L⁻¹ NaCl. ATHO and ATLE accumulated twice as much sodium in their shoots as ATCA, but all three species had increasing sodium levels at higher salinities. Potassium, magnesium and calcium levels were relatively constant over the salinity gradient. All three species showed marked accumulation of chloride across the salinity gradient, whereas nitrate, phosphorous and sulfate decreased with salinity. The effect of drought was simulated by growing plants in sealed pots with an initial charge of water plus NaCl, and allowing them to grow to the end point at which they no longer were able to extract water from the soil solution. Drought and salinity were not additive stress factors for Atriplex spp. in this experiment. NaCl increased their ability to extract water from the soil solution compared to fresh water controls. ATLE showed increased shoot dry matter production and increased water use efficiency (WUE) as initial salinity levels increased from 0 to 30 g L⁻¹ NaCl, whereas dry matter production and WUE peaked at 5 g L⁻¹ for ATHO and ATCA. Final soil moisture salinities tolerated by species were 85 g L⁻¹, 55 g L⁻¹ and 160 g L⁻¹ NaCl for ATHO, ATCA and ATLE, respectively. C4 photosynthesis and sodium accumulation in shoots were associated with high drought and salt tolerance.     

Potential human health risk assessment of cylindrospermopsin accumulation and depuration in lettuce and arugula

The cyanobacterial toxin cylindrospermopsin (CYN) has become a globally important secondary metabolite due to the negative effect it has on human and animal health. As a means of evaluating the risk of human exposure to CYN, the bioaccumulation and depuration of the toxin in lettuce (Lactuca sativa L.) and arugula (Eruca sativa Mill.) were investigated, after irrigation with contaminated water. The vegetables were irrigated for 7 days with CYN (3, 5 and 10 μg/L) contaminated water (bioaccumulation phase), and subsequently, irrigated for 7 days with uncontaminated distilled water (depuration phase). In general, the bioaccumulation of CYN in both vegetables decreased with increasing exposure concentration. Bioconcentration factor (BCF) of CYN increased with the progression of the experiment at 3.0 μg/L CYN, while the reverse occurred at 5 and 10 μg/L CYN. In arugula, BCF increased at all CYN exposure concentrations throughout the study. The depuration of CYN decreased with increasing exposure concentration but was highest in the plants of both species with the highest bioaccumulation of CYN. Specifically, in plants previously irrigated with water contaminated with 3, 5 and 10 μg/L CYN, the depuration of the toxin was 60.68, 27.67 and 18.52% for lettuce, and 47, 46.21 and 27.67% for arugula, respectively. Human health risks assessment revealed that the consumption of approximately 10 to 40 g of vegetables per meal will expose children and adults to 1.00-6.00 ng CYN/kg body mass for lettuce and 2.22-7.70 ng CYN/kg body mass for arugula. The irrigation of lettuce and arugula with contaminated water containing low CYN concentrations constitutes a potential human exposure route.     

Selenium accumulation in the floral tissues of two Brassicaceae species and its impact on floral traits and plant performance

Selenium (Se) is a metalloid that can occur naturally in soils from the Cretaceous shale deposits of a prehistoric inland sea in the western United States. Agricultural irrigation and runoff solubilizes Se from these shales, causing buildups of toxic levels of selenate (SeO₄²⁻) in water and soil. Our main objective was to investigate the accumulation of Se in two Brassicaceae species chosen for their potential as phytoremediators of Se contaminated soils. We tested the hypothesis that Se will accumulate in the pollen and nectar of two plant species and negatively affect floral traits and plant reproduction. Certain species of Brassicaceae can accumulate high concentrations of Se in their leaf tissues. In this study Se accumulation in plant tissues was investigated under greenhouse conditions. Se accumulator (Brassica juncea) and Se hyperaccumulator (Stanleya pinnata) plants were irrigated in sand culture with 0 μM selenate (control), 8 μM selenate, and 13 μM selenate.Nectar and pollen in S. pinnata contained up to 150 μg Se mL⁻¹ wet weight and 12900 μg Se g⁻¹ dry weight when irrigated with 8 μM selenate. Se levels in nectar (110 μg Se mL⁻¹ wet weight) and pollen (1700 μg Se g⁻¹ dry weight) were not as high in B. juncea. Floral display width, petal area and seed pod length were significantly reduced in the 13 μM selenate Se treatment in B. juncea. S. pinnata floral traits and seeds were unaffected by the Se treatments.This study provides crucial information about where some of the highest concentrations of Se are found in two phytoremediators, and may shed light on the potential risks pollinators may face when foraging upon these accumulating plants. In the field, duration of the plant's exposure, Se soil and water concentrations as well as other environmental factors may also play important roles in determining how much Se is accumulated into the leaf and floral tissues. Our greenhouse study shed light on two species’ ability to accumulate Se, as well as determined the specific plant tissues where Se concentrations are highest.     

Effects of salinity and inundation regime on growth and distribution of Schoenoplectus triqueter

In Ireland, Schoenoplectus triqueter is confined to areas in the upper part of the Shannon estuary where average summer soil pore water salinity levels do not exceed 7.0 ppt. Soil-based and nutrient solution-based experiments showed that growth and reproduction of S. triqueter was significantly reduced at salinity of 10 ppt and significantly enhanced at 2.0 ppt compared to a freshwater control. Young plants were less tolerant of salinity than older plants. A transplantation trial showed that S. triqueter could grow at higher salinities in the field but that growth and reproduction were significantly inhibited at higher field salinities. The effect of simulated diurnal tidal inundation on the growth and reproduction of S. triqueter was examined by growing plants in a tank with fluctuating water levels. S. triqueter was able to grow and produce seed when inundated for up to 12 h per 24-h period, indicating a considerable capacity to withstand periodic inundation. Growth responses to simulated tidal inundation were also examined in Bolboschoenus maritimus. Long periods of daily inundation reduced growth of B. maritimus proportionately more than that of S. triqueter. It is concluded that S. triqueter occupies a narrow ecological niche in the Shannon Estuary that is circumscribed by competition from more robust emergent species but is facilitated by the ability of S. triqueter to tolerate lengthy periods of inundation by the tides.     

Experiment of emergent macrophytes growing in contaminated sludge: Implication for sediment purification and lake restoration

Three emergent macrophytes (Zizania latifolia (Turcz) Hand.-Mazz., Phragmites australis (Cav.) Trin. ex Steud. and Typha angustifolia Linn.) and three different sediments from Lake Dianchi of Yunnan province, China, were studied through orthogonal pot-planting experiment in order to compare the ability of the three emergent macrophytes in dealing with the contaminated sludge and to evaluate the possibility of purifying the sediment through aquatic plant rehabilitation. The results show that the number of sprouts and biomass of all the species growing in the sediment of site 3 were higher than those growing in the sediment of sites 1 and 2; the plants growing in the sediment of site 3 also exhibited the highest root activities; in each sediment, the sequence of root activity of the species was: Z. latifolia > P. australi > T. angustifolia; TP content in the sediments grown with different plants reduced significantly than those of control. These results indicated that these emergent plants were able to grow well in the contaminated sediment though it is black with a strong odor. Z. latifolia shows the highest root activity in the sediment of site 3, from which we can deduce that this plant should be the preferred pioneer species for purifying the sediment. According to their biomass and TN content and TP content, Z. latifolia, P. australi and T. angustifolia retained TN 16.6, 29.8, 12.8, and TP 2.2, 3.6, 3.9 g m^?2, respectively. Based on the climate of Dianchi valley, these plants can be harvested twice in a year. Thus, the amount of nutrient can be removed almost doubly. Therefore, the sludge can be purified through macrophytes restoration and not through sediment dredging, which was proved to be expensive and invalid in the large shallow lakes.     

Stress responses and specific metal exclusion on mine soils based on germination and growth studies by Australian golden wattle

We reported the Australian golden wattle as a copper stabilizer in abandoned copper mine soils earlier. Here we investigate to confirm this plant’s suitability to grow on metal contaminated mine soils based on stress indication. The seeds of Acacia pycnantha collected from mining area were germinated after heat and no heat treatment on two types of irrigation. The daily irrigated and heat treated seeds gave up to 85% germination on sandy soil. The A. pycnantha was grown under greenhouse condition in six different soils collected from abandoned copper mine at Kapunda in South Australia. Among the six soil samples, soil-1 with the highest copper concentration produced 2.05 mmol g⁻¹ tissue of proline. Proline expression was prominent in more saline soils (1, 5 and 6) having electrical conductivity (EC) 1184, 1364 and 1256 μS, respectively. Chlorophyll a, b and carotenoid levels in plants showed a gradually decreasing trend in all the soils as experiment progressed. The plants grown on soil sample-1, containing 4083 ± 103 mg kg⁻¹ of copper resulted in 18 ± 2 mg kg⁻¹ accumulation in its leaf. The calcium accumulation was significant up to 11648 ± 1209 mg kg⁻¹ in leaf. Although pore water samples showed higher Cu concentration in soils, an increased mobility of arsenic and lead was observed in all the soil samples. Our experiment points out the need for proper monitoring of revegetation processes to avoid revegetation and reclamation failure.     

The drag and reconfiguration experienced by five macrophytes from a lowland river

Drag and flexibility of five macrophytes (fresh mass 3 g) collected from the same river were measured at velocities from 0 to 0.5 m s⁻¹ in a flume. Drag increased with increasing velocity for all five species examined. Sparganium emersum Rehmann, which has simple strap-like leaves experienced significantly less drag than the other, bushier species whilst there was no significant difference between the drag on Callitriche stagnalis Scop., Ranunculus penicillatus pseudofluitans (Syme) S.D. Webster, and Myriophyllum spicatum L. above 0.4 m s⁻¹. Potamogeton x zizii W.D.J. Koch ex Roth, which has large flat leaves, experienced significantly higher drag than all the other species. All the plants were very flexible but flexibility (as angle of bend) did not explain the drag experienced by the plants, e.g. S. emersum was the least flexible. The plants also changed shape and compressed (reconfigured) under increasing water velocity which reduced the rate at which drag increased. Reconfiguration capacity was assessed as E-values. There were no significant differences in E-values between species indicating that all the samples examined had a similar capacity to reconfigure. It is concluded that measurement of the drag experienced by plants is useful and may prove helpful in explaining the distribution of macrophytes in rivers.     

Changes in root system structure,leaf water potential and gas exchange of maize and triticale seedlings affected by soil compaction

The physiological reasons associated with differential sensitivity of C₃ and C₄ plant species to soil compaction stress are not well explained and understood. The responses of growth characteristics, changes in leaf water potential and gas exchange in maize and triticale to a different soil compaction were investigated. In the present study seedlings of triticale and maize, representative of C₃ and C₄ plants were subjected to low (L – 1.10 g cm⁻³), moderate (M – 1.34 g cm⁻³) and severe (S – 1.58 g cm⁻³) soil compaction level. Distinct differences in distribution of roots in the soil profile were observed. Plants of treatments M or S in comparison to treatment L, showed a decrease in leaf number, dry mass of stem, leaves and roots, and an increase in the shoot to root ratio. A drastic decrease in root biomass in M and S treatments in the soil profile on depth from 15 to 40 cm was observed. Any level of soil compaction did not influence the number of seminal and seminal-adventitious roots but decreased their length. The number and total length of nodal roots decreased with compaction. Changes of growth traits in M and S treatments in comparison to the L were greater for maize than for triticale and were accompanied by daily changes in water potential (ψ) and gas exchange parameters (P_N, E, g_s). Differences between M and S treatments in daily changes in ψ for maize were in most cases statistically insignificant, whereas for triticale, they were statistically significant. Differences in the responses of maize and triticale to soil compaction were found in P_N, E and g_s in particular for the measurements taken at 12:00 and 16:00. The highest correlation coefficients were obtained for the relationship between leaf water potential and stomatal conductance, both for maize and triticale, which indicates the close association between stomata behavior and changes in leaf water status.     

Influence of rhizospheric microbial inoculation and tolerant plant species on the rhizoremediation of lindane

Application of rhizospheric microbes to enhance the phytoremediation of organic pollutants has gained considerable attention recently due to their beneficial effects on the survival and growth of plants in contaminated soil sites. The present study was demonstrated to test the combined rhizoremediation potential of Staphylococcus cohnii subspecies urealyticus in the presence of tolerant plant Withania somnifera grown in lindane spiked soil. Withania was grown in garden soil spiked with 20 mg kg⁻¹ of lindane and inoculated with 100 ml of microbial culture (8.1 × 10⁶ CFU). Effect of microbial inoculation on plant growth, lindane uptake, microbial biomass carbon, dehydrogenase activity, residual lindane concentration and lindane dissipation percentage were analyzed. The microbial inoculation significantly enhances the growth and lindane uptake potential of test plant (p < 0.05). Furthermore, there was an enhanced dissipation of lindane observed in microbial inoculated soil than the dissipation rate in non-inoculated soil (p < 0.01) and the dissipation rate was positively correlated with the soil dehydrogenase activity and microbial biomass carbon (p < 0.05). The study concludes that the integrated use of tolerant plant species and rhizospheric microbial inoculation can enhance the dissipation of lindane, and have practical application for the in situ remediation of contaminated soils.     

Influence of inoculation with plant growth promoting rhizobacteria (PGPR) on tomato plant growth and nematode reproduction under greenhouse conditions

Numerous species of soil bacteria which flourish in the rhizosphere of plants or around plant tissues stimulate plant growth and reduce nematode population by antagonistic behavior. These bacteria are collectively known as PGPR (plant growth promoting rhizobacteria). The effects of six isolates of PGPR Pseudomonas putida, Pseudomonas fluorescens, Serratia marcescens, Bacillus amyloliquefaciens, Bacillus subtilis and Bacillus cereus, were studied on tomato plant growth and root knot nematode reproduction after 45 days from nematode infection. The highest number of shoot dry weight/g (43.00 g) was detected in the plant treated with S. marcescens; then P. putida (34.33 g), B. amyloliquefaciens (31.66 g), P. fluorescens (30.0 g), B. subtilis (29.0 g), B. cereus (27.0 g) and nematode alone (untreated) 20 g/plant. While the highest number of plant height was observed when plant was treated with S. marcescens, P. fluorescens, P. putida, B. amyloliquefaciens and P. putida 52.66, 50.66, 48 and 48 cm respectively. No significant differences were seen between previous treatments but only had significant differences compared with untreated plant. The highest number of fruit/plant was observed when plants were treated with S. marcescens (10.66), then B. amyloliquefaciens (8.66), P. putida (8), P. fluorescens (8) and B. cereus (7.66). No significant differences between the last 4 treatments, but all had significant differences compared with untreated plants. The highest weight of plant yield (g) was observed with S. marcescens (319.6 g/plant) and the lowest weight of plant yield was observed in plants treated with nematode alone (untreated). On the other hand, the lowest numbers of J₂/10 g of soil (78), galls/root, (24.33) galls/root, egg masses/root (12.66) and egg/egg masses were observed in the plants treated with S. marcescens.     

Management of Frankliniella occidentalis (Thysanoptera: Thripidae) with granular formulations of entomopathogenic fungi

Western flower thrips (WFT), Franklinella occidentalis, is a major pest of ornamentals. Mycotized millet grains with entomopathogenic fungi applied to soil of potted marigold plants were tested to target the soil-dwelling stages of thrips. Two experimental fungal isolates, (Beauveria bassiana [ARS7060] and Metarhizium anisopliae [ERL1171]), were compared with the registered B. bassiana strain GHA [commercialized as BotaniGard®] and untreated controls in greenhouse caged trials. Mycotized millet grains were mixed into the upper surface of the potting soil in pots of flowering ‘Hero Yellow’ marigolds (4 g/pot). One week after application five mated WFT females were released onto each plant (four plants per cage). At 8 weeks post-infestation, the mean total number of thrips per plant was 81% and 90% less in the ERL1171 and ARS 7060 treatments, respectively, than in the control. The mean numbers of thrips per plant for the control and GHA treatments were not significantly different. Plant damage was 60% less on plants treated with the experimental fungi than the control and GHA treatments. At 10 weeks post-application, 75–90% of WFT collected from the treatments of the experimental fungi were infected with the fungal species applied. These results demonstrate that soil applications of entomopathogenic fungi can reduce WFT populations significantly and prevent major damage.     

Local variation in conspecific plant density influences plant–soil feedback in a natural grassland

Several studies have argued that under field conditions plant–soil feedback may be related to the local density of a plant species, but plant–soil feedback is often studied by comparing conspecific and heterospecific soils or by using mixed soil samples collected from different locations and plant densities. We examined whether the growth of the early successional species Jacobaea vulgaris in soil collected from the field is related to the local variation in plant density of this species. In a grassland restoration site, we selected eight 8 m × 8 m plots, four with high and four with low densities of J. vulgaris plants. In 16 subplots in each plot we recorded the density and size of J. vulgaris, and characteristics of the vegetation and the soil chemistry. Soil collected from each subplot was used in a greenhouse pot-experiment to study the growth of J. vulgaris, both in pure field soil and in sterile soil inoculated with a small part of field soil.In the field, flowering J. vulgaris plants were taller, the percentage of rosette plants was higher and seed density was larger in High- than in Low-density plots. In the pot experiment, J. vulgaris had a negative plant–soil feedback, but biomass was also lower in soil collected from High- than from Low-density plots, although only when growing in inoculated soil. Regression analyses showed that J. vulgaris biomass of plants growing in pure soil was related to soil nutrients, but also to J. vulgaris density in the field.We conclude that in the field there is local variation in the negative plant–soil feedback of J. vulgaris and that this variation can be explained by the local density of J. vulgaris, but also by other factors such as nutrient availability.     

Biomonitoring of mercury pollution: A case study from the Dniester River

Biomonitoring of mercury pollution of Dubasari reservoir of the Dniester River has been carried out using macrophytes, epiphytosuspensions and lichens. Macrophytes uptake mercury from water column and bottom sediments in the succession Potamogeton pectinatus L. > Myriophyllum verticillatum L. > Potamogeton perfoliatus L. > Butomus umbellatus L. These species possess the properties of bio-indicators. The mercury content in their biomass is in good positive correlation (r = 0.908–0.990) with the mercury content both in water and bottom sediments. It has been shown that the maximum mercury content in these bio-indicators is found in the area of the Rezina–Rybnitsa industrial complex that consists of two cement plants and a metallurgical one. The use of lichens as bio-indicators for the ecological state of the air in the vicinity of the investigated aquatic ecosystem and of the epiphytosuspensions precipitated on submerged macrophytes, denote the active state of the source for mercury pollution of the Dubasari reservoir.     

Apocynum venetum: A newly found lithium accumulator

Apocynum venetum has antidepressant and anxiolytic effects according to the traditional Chinese medicine. Lithium (Li) is a proven mood stabilizer. According to the similar drug efficacy, we hypothesized that A. venetum may contain high levels of Li. Here, we investigated Li tolerance and accumulation potential of A. venetum in the field and in greenhouse cultivation. Li concentration in leaves of A. venetum was substantially higher than that of its main accompanying plants. Under a soil Li supply of 50 mg kg⁻¹ the plant did not show obvious symptom of phytotoxicity. Rather, A. venetum could accumulate >1800 mg kg⁻¹ Li in leaf tissues, and survived still under 400 mg kg⁻¹ Li supply. The bioconcentration factor (except control) and translocation factor values were greater than 1.0. Thus, A. venetum has the characteristics of, at least, a Li-accumulator, if not a Li-hyperaccumulator. A. venetum may serve as an interesting model species to study the influence of Li on plants.     

Does soil nutrient availability influence night-time water flux of aspen saplings?

Previous investigations have been demonstrated that night-time water flux may increase or remain unchanged at low mineral nutrient availability. At the same time, it is a well-known fact that night-time water flux is relatively high in fast-growing species, which typically grow in fertile soil. To test the impact of soil nutrient deficiency on night-time water flux and fine-root acclimation in saplings of hybrid aspen (Populus tremula L. × Populus tremuloides Michx.), a growth chamber experiment was carried out. We set up a hypothesis that night-time sap flux density (F) and night-time water use percentage from daytime water use (NWU) are more intense in fertile conditions, in order to enhance or sustain the high intrinsic growth potential of hybrid aspen. The main limiting element in the low nutrient availability treatment (low-n) was nitrogen. The nitrogen concentrations of leaves and fine-roots exhibited the strongest (R² = 0.95; P < 0.001) positive relationship with NWU and foliar biomass. Both the night-time F and NWU were several times higher in the case of fertilized soil (high-n treatment) compared to low-n treatment (P < 0.01). The differences in nocturnal (and in diurnal) F disappeared at the end of the period of sap flow measurements, when the foliage area of trees was almost full-grown. Endogenous increase in water flux during predawn hours was observable only in the high-n treatment. Significantly greater NWU (P < 0.01) and specific fine-root length (P < 0.05), but smaller fine-root biomass (P < 0.05) in saplings of the high-n treatment potentially allow plants to use mass flow in soil more efficiently for transportation nutrients towards roots and to decrease construction costs for fine-root biomass production. Our results suggest that decreased night-time water flux as a result of strong nutrient (especially nitrogen) deficit could be characteristic to fast-growing tree species, which are adapted to grow in fertile soil.     

Environmental driving factors affecting plant biomass in natural grassland in the Loess Plateau,China

Plant biomass is a key parameter for estimating terrestrial ecosystem carbon (C) stocks, which varies greatly as a result of specific environmental conditions. Here, we tested environmental driving factors affecting plant biomass in natural grassland in the Loess Plateau, China. We found that above-ground biomass (AGB) and below-ground biomass (BGB) had a similar change trend in the order of Stipa bungeana > Leymus secalinus > Artemisia sacrorum > Artemisia scoparia, whereas shoot ratio (R/S) displayed an opposite change trend. There was a significantly positive linear relationship between the AGB and BGB, regardless of plant species (p < 0.05). Furthermore, more than 50% of the AGB were found in 20–50 cm of plant height in Compositae plants (A. sacrorum, A. scoparia), whereas over 60% of the AGB were found in 20–80 cm of plant height in Gramineae plants (S. bungeana, L. secalinus). For each plant species, more than 75% of the BGB was distributed in 0–10 cm soil depth, and 20% was distributed in 10–20 cm soil depth, while less than 5% was distributed in 20–40 cm soil depth. Further, AGB and BGB were highly affected by environmental driving factors (soil properties, plant traits, topographic properties), which were identified by the structural equation model (SEM) and the generalized additive models (GAMs). In addition, AGB was directly affected by plant traits, and BGB was directly affected by soil properties, and soil properties associated with plant traits that affected AGB and BGB through interactive effects were 9.12% and 3.59%, respectively. However, topographic properties had a weak influence on ABG and BGB (as revealed by the lowest total pathway effect). Besides, soil organic carbon (SOC), soil microbial biomass carbon (MBC), and plant height had a higher relative contribution to AGB and BGB. Our results indicate that environmental driving factors affect plant biomass in natural grassland in the Loess Plateau.     

What role do plant–soil interactions play in the habitat suitability and potential range expansion of the alpine dwarf shrub Salix herbacea?

Mountain plants may respond to warming climates by migrating along altitudinal gradients or, because climatic conditions on mountain slopes can be locally very heterogeneous, by migrating to different microhabitats at the same altitude. However, in new environments, plants may also encounter novel soil microbial communities, which might affect their establishment success. Thus, biotic interactions could be a key factor in plant responses to climate change. Here, we investigated the role of plant–soil feedback for the establishment success of the alpine dwarf shrub Salix herbacea L. across altitudes and late- and early snowmelt microhabitats. We collected S. herbacea seeds and soil from nine plots on three mountain-slope transects near Davos, Switzerland, and we transplanted seeds and seedlings to substrate inoculated with soil from the same plot or with soils from different microhabitats, altitudes and mountains under greenhouse conditions. We found that, on average, seeds from higher altitudes (2400–2700 m) and late-exposed snowbeds germinated better than seeds from lower altitudes (2200–2300 m) and early-exposed ridges. However, despite these differences in germination, growth was generally higher for plants from low altitudes, and there were no indications for a an home-soil advantage within the current range of S. herbacea. Interestingly, seedlings growing on soil from above the current altitudinal distribution of S. herbacea grew on average less well than on their own soil. Thus, although the lack of a home-soil advantage in the current habitat might be beneficial for S. herbacea in a changing environment, migration to habitats beyond the current altitudinal range might be limited, probably due to missing positive soil-feedback.     

Formulation of a soil biofungicide for control of damping-off of Chinese cabbage (Brassica chinensis) caused by Rhizoctonia solani

A granulate biofungicide named PBGG was developed by combining Pseudomonas boreopolis with Brassica seed pomace, glycerin and sodium alginate. Application of 1.0% (w/w) of PBGG to the soil infested with Rhizoctonia solani AG-4 significantly reduced the percentage of colonization of cabbage seeds by the pathogen and stimulated proliferations of actinomycetes. Among Streptomyces populations, Streptomyces padanus (strain SS-07) and Streptomyces xantholiticus (strain SS-09) were the two most effective strains with strong antagonistic effects to R. solani. Application of 1% (w/w) PBGG in soil significantly increased population densities of S. padanus and S. xantholiticus. Treating soil with S. padanus (strain SS-07) or S. xantholiticus (strain SS-09) alone or in combination with 1% (w/w) PBGG significantly reduced the percentage of colonization of cabbage seeds by R. solani, compared to untreated controls. S. padanus was the most effective agent in reducing the percentage of seed colonization by the pathogen. Results of greenhouse tests showed that the most effective treatment was the amendment of pathogen-infested soil by S. padanus + 1% (w/w) PBGG which resulted in a disease incidence of 6.5–8.6%, compared to 27.8–31.7% for the treatment of S. xantholiticus + 1% (w/w) PBGG, 36.9–38.6% for the treatment of 1% (w/w) PBGG alone, and 61.8–64.8% for the treatment of control (unamended soil). Results of greenhouse and field tests also showed that soil amendment of 1% (w/w) PBGG alone or 1% (w/w) PBGG mixed with S. padanus (strain SS-07) or S. xantholiticus (strain SS-09) was not harmful to seed germination of Chinese cabbage. The study suggests that amendment of R. solani infested soil with S. padanus + 1% (w/w) PBGG prior to sowing is an effective method for control of damping-off of Chinese cabbage.     

Potential of restoration and phytoremediation with Juncus roemerianus for diesel-contaminated coastal wetlands

Oil spills may considerably damage sensitive coastal wetlands. In this study, the tolerance limits of a dominant coastal salt marsh plant, Juncus roemerianus, to diesel oil and its phytoremediation effectiveness in wetland environments were investigated in the greenhouse. J. roemerianus was transplanted into salt marsh sediment contaminated with diesel fuel at concentrations of 0, 20, 40, 80, 160, 320, and 640 mg diesel g^?1 dry sediment. Plant stem density, shoot height, aboveground biomass and belowground biomass were detrimentally impacted at high oil dosages even 1 year after transplantation. Tolerance limits were estimated between 160 and 320 mg g^?1 based on various plant variables. Importantly, J. roemerianus enhanced oil degradation; at the 40 mg/g diesel dosage, concentrations of residual total petroleum hydrocarbons (TPH) in the sediment planted with J. roemerianus were significantly lower than those of unplanted sediments 1 year after treatment initiation. Furthermore, concentrations of total targeted polycyclic aromatic hydrocarbons (PAHs) and n-alkanes in the J. roemerianus planted treatment were, respectively, about 3% and 15% of the unplanted treatment. Concentration reduction in all categories of hydrocarbons suggested that J. roemerianus effectively phytoremediated the diesel-contaminated wetlands.