Soil amendment effects on the exotic annual grass Bromus tectorum L. and facilitation of its growth by the native perennial grass Hilaria jamesii (Torr.) Benth

Greenhouse experiments were undertaken to identify soil factors that curtail growth of the exotic annual grass Bromus tectorum L. (cheatgrass) without significantly inhibiting growth of native perennial grasses (here represented by Hilaria jamesii [Torr.] Benth). We grew B. tectorum and H. jamesii alone (monoculture pots) and together (combination pots) in soil treatments that manipulated levels of soil phosphorus, potassium, and sodium. Hilaria jamesii showed no decline when its aboveground biomass in any of the applied treatments was compared to the control in either the monoculture or combination pots. Monoculture pots of B. tectorum showed a decline in aboveground biomass with the addition of Na₂HPO₄ and K₂HPO_4. Interestingly, in pots where H. jamesii was present, the negative effect of these treatments was ameliorated. Whereas the presence of B. tectorum generally decreased the aboveground biomass of H. jamesii (comparing aboveground biomass in monoculture versus combination pots), the presence of H. jamesii resulted in an enhancement of B. tectorum aboveground biomass by up to 900%. We hypothesize that B. tectorum was able to obtain resources from H. jamesii, an action that benefited B. tectorum while generally harming H. jamesii. Possible ways resources may be gained by B. tectorum from native perennial grasses include (1) B. tectorum is protected from salt stress by native plants or associated soil biota; (2) when B. tectorum is grown with H. jamesii, the native soil biota is altered in a way that favors B. tectorum growth, including B. tectorum tapping into the mycorrhizal network of native plants and obtaining resources from them; (3) B. tectorum can take advantage of root exudates from native plants, including water and nutrients released by natives via hydraulic redistribution; and (4) B. tectorum is able to utilize some combination of the above mechanisms. In summary, land managers may find adding soil treatments can temporarily suppress B. tectorum and enhance the establishment of native plants. However, the extirpation of B. tectorum is unlikely, as many native grasses are likely to facilitate its growth.     

Invasion of Euryops floribundus in degraded South African communal grassland: Unpacking the invasion relationship with elevation,soil properties,the quality and quantity of the herbaceous layer

Shrub invasion is a recent occurrence in African grassland ecosystems. This study assessed the distribution of Euryops floribundus (a native shrub species) along an elevation and invasion intensity gradients, and its relationship with soil and herbaceous vegetation in a South African grassland. Shrub density increased (p < 0.05) from the uplands (2,301 plants/ha) to the bottomlands (4,888 plants/ha). Themeda triandra (a highly palatable grass) was dominant at the uplands and sloping sites, whereas Eragrostis plana and Sporobolus africanus (poorly palatable grasses) dominated the bottomlands. Upland soils had the highest organic carbon (OC), phosphorous (P), calcium and nitrogen (N) contents, but the lowest shrub density and herbaceous biomass. Canonical correspondence analysis indicated that elevation, soil OC and N contents determine important vegetation variables along the elevation gradient. In the shrub density gradient, soil P, OC and N responded positively to E. floribundus density. Grass biomass in the moderate and heavily invaded sites was high, but the abundance of palatable grasses declined, suggesting that E. floribundus invasion may be concomitant with a decrease in rangeland condition in terms of quality forage provision.     

Paclobutrazol and plant-growth promoting bacterial endophyte Pantoea sp. enhance copper tolerance of guinea grass (Panicum maximum) in hydroponic culture

As most gramineous plants, guinea grass (Panicum maximum) comprise cellulosic biomass, which may be used as a feedstock for bioenergy. In order to develop such potential energy plants on copper-polluted lands, the hydroponic experiments with Cu, Paclobutrazol (PP333, a kind of antigibberellin) and plant growth-promoting bacterial endophyte (PGPB) treatments were carried out in a greenhouse. The seedlings of two cultivars of guinea grass, GG1 (P. maximum var. Natsukomaki) and GG2 (P. maximum var. Natsukaze) in 3 weeks old were treated, respectively, with different Cu treatments [0(CK), 100, 200, 300, 400, 500 μM l⁻¹ Cu] for estimating Cu toxicity. The results showed that elevated Cu restrained plant growth and reduced biomass. According to the EC50 value [the Cu concentration when the relative gain in fresh weight ratio was 50% of control] of two tested cultivars, the concentration of Cu for further experiments was decided as 300 μM l⁻¹. Both pretreatments of PP333 (200, 400, 600 mg l⁻¹) and PGPB (Pantoea sp.) significantly alleviated the negative affect caused by stress of 300 μM l⁻¹ Cu. The pretreatment of 400 mg l⁻¹ PP333 promoted both two cultivars in biomass, compared to 300 μM l⁻¹ Cu treat. The inoculation of Pantoea sp. Jp3-3 increased shoot dry weight, compared to Cu treat. The results suggested that the main reason for both PP333 and Pantoea sp. Jp3-3 enhanced Cu tolerance in guinea grass was that their pretreatments significantly decreased Cu absorption and accumulation under excessive Cu stress. The present study has provided a new insight into the exploitation of energy plant in heavy metal polluted condition by the way of plant growth regulation for increasing heavy metal tolerance.     

Improvement of degraded physical properties of a saline-sodic soil by reclamation with kallar grass (Leptochloa fusca)

A field experiment was conducted to evaluate the effectiveness of growing salt tolerant plants to improve the physical characteristics of a saline-sodic soil. Kallar grass [Leptochloa fusca (L.) Kunth], a species tolerant to salinity, sodicity and alkalinity, was irrigated for five years with poor quality ground water (EC = 0.14 S m^–1, SAR_adj=19.3, RSC = 9.7 meq L^–1). The soil physical properties of plant available water, saturated hydraulic conductivity, structural stability, bulk density and porosity were determined at the end of each year. The growth of kallar grass for three years significantly improved the physical properties of the soil and these were maintained with further growth of grass up to five years. Kallar grass significantly increased plant available water with time (r=0.97^**). The available water was highly correlated (r=0.92^**) with increases in soil organic matter content, porosity (r=0.99^**) and other physical properties. Soil hydraulic conductivity increased substantially with time from 0.035 to 55.6 mm d^–1 in the topsoil (0–20 cm) in five years and was significantly correlated with porosity, water retention, structural stability and organic matter content of soil. The soil structural stability index improved significantly from 32 to 151 with kallar grass and showed greater increases in the surface soil than at depth. The cropping of kallar grass resulted in a linear increase of soil organic matter content (r=0.92^**) which improved porosity and other soil physical properties (r0.82^*). This study confirmed that kallar grass is effective for rehabilitation and restoration of soil fertility in saline-sodic areas on a sustainable basis.     

Influence of phosphorus nutrition on growth and metabolism of Duo grass (Duo festulolium)

Use of suitable plants that can extract and concentrate excess P from contaminated soil serves as an attractive method of phytoremediation. Plants vary in their potential to assimilate different organic and inorganic P-substrates. In this study, the response of Duo grass (Duo festulolium) to variable rates of soil-applied potassium dihydrogen phosphate (KH₂PO₄) on biomass yield and P uptake were studied. Duo grown for 5 weeks in soil with 2.5, 5 and 7.5 g KH₂PO₄ kg^?1 soil showed a significantly higher biomass and shoot P content of 8.3, 11.4 and 12.3 g P kg^?1 dry weight respectively compared to plants that received no soil added P. Also, the ability of Duo to metabolize different forms of P-substrates was determined by growing them in sterile Hoagland's agar media with different organic and inorganic P-substrates, viz. KH₂PO₄, glucose-1-phosphate (G1P), inositiol hexaphosphate (IHP), adenosine triphosphate (ATP) and adenosine monophosphate (AMP) for 2 weeks. Plants on agar media with different P-substrates also showed enhanced biomass yield and shoot P relative to no P control and the P uptake was in the order of ATP > KH₂PO₄ > G1P > IHP = AMP > no P control. The activities of both phytase (E.C.3.1.3.26) and acid phosphatases (E.C.3.1.3.2) were higher in all the P received plants than the control. Duo grass is capable of extracting P from the soil and also from the agar media and thus it can serve as possible candidate for phytoextraction of high P-soil.     

Phytoremediation potential of vetiver grass irrigated with wastewater for treatment of metal contaminated soil

A field experiment was conducted to understand the potential of vetiver grass (Vetiveria zizanioides) in heavy metal uptake from the soil and wastewater. Four main irrigation treatments including T₁ (treated industrial wastewater), T₂ (1:1 ratio of municipal:industrial wastewater), T₃ (treated municipal wastewater) and T₄ (fresh water) were applied. Moreover, the effect of arbuscular mycorrhizal fungus (AMF), Glomus mosseae, on plant growth and heavy metal concentration was evaluated. Three main criteria including bioconcentration factor (BCF), translocation factor (TF) and heavy metal uptake were applied to assess the potential of vetiver grass in accumulation and translocation of heavy metals to aerial parts. The highest concentration of heavy metals was found in plant and soil irrigated with T₁ treatment followed by T₂, T₃ and the lowest concentrations were found in T₄ treatment. Irrigation with treated municipal wastewater led to a significant increase in plant biomass and heavy metal uptake compared to other treatments. In T₁ treatment (industrial wastewater), vetiver grass caused a significant decrease in Zn, Fe, Cu, Cd and Pb concentrations in soil as compared to no-plant treatment (without planting vetiver grass). Therefore, vetiver grass, irrigated with treated industrial wastewater, is a promising method for the development of urban and industrial green space.     

The growth and nitrogen uptake of Rhodes grass grown on soils with varying histories of legume cropping

Summary Rhodes grass (Chloris gayana) was grown under glasshouse conditions on soils that had previously grown from 1 to 6 soybean (Glycine max) or Siratro (Macroptillium atropurpureum) crops. Soil mineral N contents at sowing were higher in Siratro-cropped than soybean-cropped soils and increased with cropping history.Yields of Rhodes grass at the first harvest (14 weeks) were related to soil mineral N levels at sowing by the relationship Y=138.7 (1–0.917e^–0.012x). Grass grown on all soybean soils was responsive to N at both harvests (14 and 28 weeks). Grass grown on soil that had grown three or more Siratro crops was non-responsive to N at the first harvest but responses to N were recorded on all Siratro soils at the second harvest.The amount of N removed by the grass crops was small in relation to the total amount present in the soil system. This resulted in no change in soil total N levels over the two crop periods.These results highlight the need to study N dynamics in crop systems rather than continue to measure N pool sizes when evaluating the contribution of biologically fixed N to the nutrition of subsequent non-legume crops.     

Climate change might increase the invasion potential of the alien C4 grass Setaria parviflora (Poaceae) in the Mediterranean Basin

Aim Current climate change is supposed to be beneficial to many biological invaders, especially to C4 alien plants. While several experiments have been dedicated to measuring alien plants’ response to increased atmospheric CO₂ concentration, very few studies have been undertaken to measure the response of alien plants to warming. This study was aimed to test experimentally whether the predicted climate change in the Mediterranean Basin could be beneficial to the alien C4 grass Setaria parviflora (Poir.) Kerguélen. Location Three populations of S. parviflora from Corsica, southern France, were grown in Montpellier, southern France. Methods  The C4 alien grass S. parviflora was exposed to artificial climate change conditions for 3 years in open field and in competition with the local native community. We measured the response to artificial warming of +1.5 and +3 °C and artificial drought (?30% precipitation) versus ambient conditions for phenology, biomass and fecundity of S. parviflora. We compared the response of S. parviflora individuals to the response of the local community. Results Artificial warming strongly enhanced the biomass and the fecundity of S. parviflora, while it decreased or did not affect the biomass and fecundity of the local community. The phenology (onset of growth, first spike pollinating and fruit ripeness) of S. parviflora was advanced significantly and explained the changes observed in biomass and fecundity. Main conclusions Here, we report a positive effect of climate change on the growth and fertility of S. parviflora, a C4 alien plant. Our results suggest that climate change predicted for the next decades in the Mediterranean Basin might substantially enhance the performance of S. parviflora, potentially increasing its invasion success.     

Belowground impacts of perennial grass cultivation for sustainable biofuel feedstock production in the tropics

Perennial grasses can sequester soil organic carbon (SOC) in sustainably managed biofuel systems, directly mitigating atmospheric CO₂ concentrations while simultaneously generating biomass for renewable energy. The objective of this study was to quantify SOC accumulation and identify the primary drivers of belowground C dynamics in a zero‐tillage production system of tropical perennial C4 grasses grown for biofuel feedstock in Hawaii. Specifically, the quantity, quality, and fate of soil C inputs were determined for eight grass accessions – four varieties each of napier grass and guinea grass. Carbon fluxes (soil CO₂ efflux, aboveground net primary productivity, litterfall, total belowground carbon flux, root decay constant), C pools (SOC pool and root biomass), and C quality (root chemistry, C and nitrogen concentrations, and ratios) were measured through three harvest cycles following conversion of a fallow field to cultivated perennial grasses. A wide range of SOC accumulation occurred, with both significant species and accession effects. Aboveground biomass yield was greater, and root lignin concentration was lower for napier grass than guinea grass. Structural equation modeling revealed that root lignin concentration was the most important driver of SOC pool: varieties with low root lignin concentration, which was significantly related to rapid root decomposition, accumulated the greatest amount of SOC. Roots with low lignin concentration decomposed rapidly, but the residue and associated microbial biomass/by‐products accumulated as SOC. In general, napier grass was better suited for promoting soil C sequestration in this system. Further, high‐yielding varieties with low root lignin concentration provided the greatest climate change mitigation potential in a ratoon system. Understanding the factors affecting SOC accumulation and the net greenhouse gas trade‐offs within a biofuel production system will aid in crop selection to meet multiple goals toward environmental and economic sustainability.     

Influence of ultraviolet radiation, copper, and zinc on microcystin content in Microcystis aeruginosa (Cyanobacteria)

Cyanobacterial toxin production is allied to some unknown trigger resulting in the production of toxins such as microcystin. We hypothesize that microcystins serve as metal ligands to control bioavailability and toxicity of ambient metals. Since ultraviolet radiation (UVR) promotes photo-oxidation of organic metal ligands and influences trace metal bioavailability, the present study aimed to investigate the influence of UVR, Cu, and Zn on specific growth rates, biomass, photosynthetic capacity, and microcystin content in Microcystis aeruginosa. Two toxigenic strains of Microcystis were cultivated using either Lake Erie filtered water or a chemically defined medium, with realistic concentrations of Cu and Zn combined with natural or artificial UVR exposure. Cu was more toxic than Zn on the basis of free ion concentration of trace metals in synthetic medium, although in Lake Erie water total added Zn (10 nM) or Zn plus Cu (10 nM) had a more detrimental effect on biomass and specific growth rate. Natural UVR delivered at 25% ambient levels caused no decrease on the parameters measured (chlorophyll-a, photosynthetic rate), yet artificial levels of UVR (up to 5.9 μmol UVB photons m⁻² s⁻¹) negatively affected biomass and specific growth rate. Cellular levels of microcystin (per unit chlorophyll-a) were concomitant with specific growth rather than being triggered in response either of these stressors (UVR, Zn, and Cu) alone or in combination, in agreement with a purported constitutive production of microcystins.     

Ecophysiology of the marine cyanobacterium, Lyngbya majuscula (Oscillatoriaceae) in Moreton Bay, Australia

Large blooms of the marine cyanobacterium Lyngbya majuscula in Moreton Bay, Australia (27°05′S, 153°08′E) have been re-occurring for several years. A bloom was studied in Deception Bay (Northern Moreton Bay) in detail over the period January–March 2000. In situ data loggers and field sampling characterised various environmental parameters before and during the L. majuscula bloom. Various ecophysiological experiments were conducted on L. majuscula collected in the field and transported to the laboratory, including short-term (2 h) ¹⁴C incorporation rates and long-term (7 days) pulse amplitude modulated (PAM) fluorometry assessments of photosynthetic capacity. The effects of L. majuscula on various seagrasses in the bloom region were also assessed with repeated biomass sampling. The bloom commenced in January 2000 following usual December rainfall events, water temperatures in excess of 24 °C and high light conditions. This bloom expanded rapidly from 0 to a maximum extent of 8 km² over 55 days with an average biomass of 210 g_dw⁻¹ m⁻² in late February, followed by a rapid decline in early April. Seagrass biomass, especially Syringodium isoetifolium, was found to decline in areas of dense L. majuscula accumulation. Dissolved and total nutrient concentrations did not differ significantly (P > 0.05) preceding or during the bloom. However, water samples from creeks discharging into the study region indicated elevated concentrations of total iron (2.7–80.6 μM) and dissolved organic carbon (2.5–24.7 mg L⁻¹), associated with low pH values (3.8–6.7). ¹⁴C incorporation rates by L. majuscula were significantly (P < 0.05) elevated by additions of iron (5 μM Fe), an organic chelator, ethylenediaminetetra-acetic acid (5 μM EDTA) and phosphorus (5 μM PO₄⁻³). Photosynthetic capacity measured with PAM fluorometry was also stimulated by various nutrient additions, but not significantly (P > 0.05). These results suggest that the L. majuscula bloom may have been stimulated by bioavailable iron, perhaps complexed by dissolved organic carbon. The rapid bloom expansion observed may then have been sustained by additional inputs of nutrients (N and P) and iron through sediment efflux, stimulated by redox changes due to decomposing L. majuscula mats.     

Effects of litter incorporation and nitrogen fertilization on the contents of extractable aluminium in the rhizosphere soil of tea plant (Camallia sinensis (L.) O. Kuntze)

The effects of litter incorporation and nitrogen application on the properties of rhizosphere and bulk soils of tea plants (Camellia sinensis (L.) O. Kuntze) were examined in a pot experiment. Total of 8 treatments included four levels of tea litter additions at 0, 4.9, 9.8, and 24.5 g kg^–1 in combination with two N levels (154.6 mg kg^–1 and without). After 18 months of growth the rhizosphere soil was collected by removing the soil adhering to plant roots and other soil was referred to as bulk soil. The dry matter productions of tea plants were significantly increased by N fertilization and litter incorporation. The effect of litter was time-depending and significantly decreased the content of exchangeable Al (Al_ex, by 1 mol L^–1 KCl) and Al saturation at 9 months after litter incorporation whereas soil pH was not affected, although the litter contained high Al content. After 18 months, the contents of extractable Al by dilute CaCl₂, CuCl₂ + KCl, NH₄OAC, ammonium oxalate and sodium citrate (Al_CaCl2, Al_Cu/KCl, Al_NH4OAC, Al_Oxal, and Al_Cit respectively) and Al_ex, were not affected by litter application, except that of Al_CaCl2 in the rhizosphere soil which was decreased following litter additions. Nitrogen fertilization with NH₄ ⁺ (urea and (NH₄)₂SO₄) significantly reduced soil pH, the contents of exchangeable Ca, K, Mg and base saturation while raised extractable Al levels (Al_CaCl2, Al_Cu/KCl, Al_NH4OAC, and Al_ex). In the rhizosphere soils exchangeable K accumulated in all treatments while exchangeable Ca and Mg depleted in treatments without litter application. The depletions of Ca and Mg were no longer observed following litter incorporation. This change of distribution gradients in rhizosphere was possibly due to the increase of nutrient supplies from litter decomposition and/or preferable root growth in soil microsites rich in organic matter. Lower pH and higher extractable Al (Al_CaCl2, Al_ex, and Al_NH4OAC) in the rhizosphere soils, regardless of N and litter treatments, were distinct and consistent in all treatments. Such enrichments of extractable Al in the rhizosphere soil might be of importance for tea plants capable of taking up large amounts of Al.     

Regional variation in eelgrass (Zostera marina) morphology, production and stable sulfur isotopic composition along the Baltic Sea and Skagerrak coasts

Morphology, total sulfur content and stable sulfur isotopic composition of Zostera marina were examined in the Baltic Sea–Skagerrak transition zone through surveys. The seagrass meadows were denser and less productive at the low salinities in the Baltic Sea (salinity 6–7 psu), and total sulfur accumulations in plants were lower and δ³⁴S values were higher compared to the west coast of Sweden (salinity 21–29 psu). The δ³⁴S values of the three plant compartments (leaves, rhizomes, roots) indicated lower sulfide invasion at low salinities, which was mainly due to environmental conditions (e.g. low epiphytic biomass, low sediment organic matter and low sulfate concentration) and plant characteristics (productivity, shoot morphology). Between 13% and 63% of the sulfur in the plants was derived from sediment sulfides with highest percentages in the roots (27–63%) and lower in rhizomes (13–50%) and leaves (14–51%). The high sulfide invasion on the west coast of Sweden was coincident with high sediment organic matter, probably increasing sulfide pressure on the plants, and high epiphytic biomass, probably constraining the oxygen dynamics in the plants and enhancing sulfide invasion. Regional and spatial variability in the δ³⁴S were extensive, emphasizing the need for detailed analysis of local sources when applying stable sulfur isotopes in food web analyses. The observed invasion of sulfides suggests sulfide as a contributing factor to reported declines of Z. marina in the Skagerrak region.     

Annual cycle of CO2 exchange over a reed (Phragmites australis) wetland in Northeast China

Net ecosystem exchange of CO₂ (NEE) was measured during 2005 using the eddy covariance (EC) technique over a reed (Phragmites australis (Cav.) Trin. ex Steud.) wetland in Northeast China (121°54′E, 41°08′N). Diurnal NEE patterns varied markedly among months. Outside the growing season, NEE lacked a diurnal pattern and it fluctuated above zero with an average value of 0.07 mg CO₂ m⁻² s⁻¹ resulting from soil microbial activity. During the growing season, NEE showed a distinct V-like diel course, and the mean daily NEE was −7.48 ± 2.74 g CO₂ m⁻² day⁻¹, ranging from −13.58 g CO₂ m⁻² day⁻¹ (July) to −0.10 g CO₂ m⁻² day⁻¹ (October). An annual cycle was also apparent, with CO₂ uptake increasing rapidly in May, peaking in July, and decreasing from August. Monthly cumulative NEE ranged from −115 ± 24 g C m⁻² month⁻¹ (the reed wetland was a CO₂ sink) in July to 75 ± 16 g C m⁻² month⁻¹ (CO₂ source) in November. The annual CO₂ balance suggests a net uptake of −65 ± 14 g C m⁻² year⁻¹, mainly due to the gains in June and July. Cumulative CO₂ emission during the non-growing season was 327 g C m⁻², much greater than the absolute value of the annual CO₂ balance, which proves the importance of the wintertime CO₂ efflux at the study site. The ratio of ecosystem respiration (R_eco) to gross primary productivity (GPP) for this reed ecosystem was 0.95, indicating that 95% of plant assimilation was consumed by the reed plant or supported the activities of heterotrophs in the soil. Daytime NEE values during the growing season were closely related to photosynthetically active radiation (PAR) (r² > 0.63, p < 0.01). Both maximum ecosystem photosynthesis rate (A_max) and apparent quantum yield (α) were season-dependent, and reached their peak values in July (1.28 ± 0.11 mg CO₂ m⁻² s⁻¹, 0.098 ± 0.027 μmol CO₂ μmol⁻¹ photon, respectively), corresponding to the observed maximum NEE in July. Ecosystem respiration (R_eco) relied on temperature and soil water content, and the mean value of Q₁₀ was about 2.4 with monthly variation ranging from 1.8 to 4.1 during 2005. Annual methane emission from this reed ecosystem was estimated to be about 3 g C m⁻² year⁻¹, and about 5% of the net carbon fixed by the reed wetland was released to the atmosphere as CH₄.     

Effect of the grass Leersia hexandra on the dispersal,seed germination,and establishment of Pachira aquatica seedlings

1. In wetlands, hydrochory is one of the main mechanisms of seed dispersal and there is often synchrony between propagule production and the flood season. Different sources of disturbance can prevent seed dispersal to suitable sites, and if environmental conditions are not adequate for germination and seedling establishment, recruitment will be limited, affecting succession.
2. We worked in a disturbed tropical freshwater swamp where the native grass Leersia hexandra has dominated open areas, creating a grass matrix that surrounds patches of swamp forest. Leersia grows vigorously, forming cushions of dry matter that cover the soil, forming a potential obstacle to seed dispersal. We asked whether the vegetative growth of this grass prevents the entry and dispersal of seeds of the tropical swamp tree Pachira aquatica, thwarting seed germination and seedling establishment, and arresting succession. We set up transects in the grass matrix in two zones: close to the river (R) and bordering the tree patches or fragments (F). We quantified tree seed and seedling presence, survival and growth in situ and experimentally introduced seeds and seedlings in the field and monitored seed germination and the survival and growth of their seedlings, as well as that of transplanted seedlings.
3. There was a negative relationship between the number of seeds and established seedlings, and the distance to river or fragment (r = −0.86, p < 0.001 for zone R; and r = −0.77, p < 0.001 for zone F) and with the grass cushion (r = −0.68, p = 0.005 for zone R; and r = −0.66, p = 0.007 for zone F); the grass creating a barrier to dispersal. When seeds were sown after clearing the grass cushion, germination success was high, so this stage is not limited. The transplanted seedlings had better survival and a greater final height than the seedlings of the sown seeds. Grass cover had a negative effect on both types of seedlings. Seedling survival rates were inversely related to grass cover, showing that seedlings overgrown by grass had low survival rates. Flooding is a stress factor for seedlings and produced mortality, in addition to the effects of the grass.
4. Together, the field survey and the experiment show that succession is being arrested in two ways: (1) by limiting seed dispersal because the grass cushion slows the dispersal and penetration of seeds into the vegetation; and (2) by limiting seedling establishment because the grass competes for space and light. Our results show that even where the grass is native, slower growing, seed-dependent species may struggle to compete and establish. If grass cover is increasing, these swamps are very vulnerable to a decrease in area because it is very difficult for them to regenerate naturally.

     

Assessment of Cu,Pb and Zn content in selected species of grasses and in the soil of the roadside embankment

It was assumed in the study that heavy metals occurring in soils and the air accumulate in grasses constituting the main species used in the turfing of soil in road verges and embankments along traffic routes and in other parts of urbanized areas. The aim of the present study was to assess the bioaccumulation of Cu, Pb, and Zn in three selected lawn cultivars of five grass species and in the soil of the roadside green belt in terms of soil properties and heavy metal uptake by plants in the aspect of determining their usefulness in protecting the soils from contamination caused by motor vehicle traffic. Samples of the plant material and soil were collected for chemical analysis in the autumn of 2018 (October) on the embankment along National Road No. 17 between Piaski and ?opiennik (Poland), where 15 lawn cultivars of five grass species had been sown 2 years earlier. During the study, Cu, Pb, and Zn levels were determined in the aboveground biomass of the grasses under study and in the soil beneath these grasses (the 0–20 cm layer). All the grass species under study can thus be regarded as accumulators of Cu and Zn because the levels of these elements in the aboveground biomass of the grasses were higher than in the soil beneath these grasses. The present study demonstrates that the grasses can accumulate a large amount of Cu and Zn from soils and transfer it to the aboveground biomass. Tested species of grasses are not a higher bioaccumulators for Pb. The best grass species for the sowing of roadsides embankment, with the highest BCF values for the studied metals, is Lolium perenne (Taya variety).     

Neotropical C3/C4 grass distributions – present,past and future

Changes in C₄ grass distribution and abundance are frequently observed in Quaternary, Holocene and future environmental‐change scenarios. However, the factors driving these dynamics are not fully understood, and conflicting theories have been reported. In this paper, we present a very large dataset of modern altitudinal distribution profiles of C₃ and C₄ grasses covering the entire Neotropical Andes, which was compared with actual climate data. The results of multivariate analysis demonstrate that, in the Neotropical Andes, mean annual temperature is the main factor governing the modern altitudinal distribution of C₃ and C₄ grass species. The C₃ and C₄ grass distributions were compared with simulations based on the Lund‐Potsdam‐Jena dynamic global vegetation model (LPJ‐DGVM), which allowed the present grass distribution to be estimated. Finally, the DGVM was employed to simulate past and future scenarios, using the IPCC's climate projections for 2100 and PMIP2 models for the Holocene Optimum (HO, 6000 years bp ) and the Last Glacial Maximum (LGM, 21 000 years bp ). The results were found to be significantly different from those obtained using a simple photosynthetic model. According to LPJ forced with the PMIP2 models for the LGM, during the LGM, the C₄ grasses would not have reached higher altitudes than found in the present day.     

Morphological and physiological responses of the halophyte, Odyssea paucinervis (Staph) (Poaceae), to salinity

In this study, salt tolerance was investigated in Odyssea paucinervis Staph, an ecologically important C₄ grass that is widely distributed in saline and arid areas of southern Africa. Plants were subjected to 0.2%, 10%, 20%, 40%, 60% and 80% sea water dilutions (or 0.076, 3.8, 7.6, 15.2, 22.8, and 30.4 parts per thousand) for 11 weeks. Increase in salinity from 0.2% to 20% sea water had no effect on total dry biomass accumulation, while further increase in salinity to 80% sea water significantly decreased biomass by over 50%. Morphological changes induced by salinity included reductions in the number of culms, leaves and internodes as well as decreases in internode length and leaf length:leaf width ratios. Carbon dioxide exchange, leaf conductance and transpiration decreased at salinities of 40% and higher, while quantum yield of photosystem II (PSII), electron transport rate (ETR) through PSII and intrinsic photosynthetic efficiency generally decreased at salinities of 60% and higher compared to 0.2% sea water. Concentrations of Na⁺ and Cl⁻ increased significantly with salinity increase in both roots and shoots. Na⁺/K⁺ ratios in the roots and shoots ranged from 0.66 to 3.28 and increased with increase in substrate salinity. The maximal rate of secretion at 80% sea water was 415 nmol cm⁻² d⁻¹ for Na⁺ and 763 nmol m⁻² d⁻¹ for Cl⁻ with high selectivity for these two ions. Predawn and midday ψ decreased with increase in salinity and were more negative than those of the treatment solutions. The concentration of proline increased with increase in salinity in both roots and shoots. The data clearly indicated that O. paucinervis is a highly salt-tolerant species that is morphologically and physiologically adapted to a saline environment.     

Sorption of Co, Cu, Ni and Zn from industrial effluents by the submerged aquatic macrophyte Myriophyllum spicatum L.

The submerged aquatic plant Myriophyllum spicatum L. (Eurasian water milfoil) has been suggested as an efficient plant species for the treatment of metal-contaminated industrial wastewater. The process of metal removal by plants involves a combination of rapid sorption on the surface and slow accumulation and translocation in the biomass. This study focussed on the sorption/desorption characteristics of the surface of M. spicatum for Co, Cu, Ni and Zn. Batch sorption tests with mixed metal solutions covering a range of 0, 1, 5, 10, 50 and 100 mg l⁻¹ of each metal, were performed. For Co, Ni and Zn, the sorption process was well described by the Langmuir model, whereas sorption of Cu was better described by the Freundlich model. The biomass showed the highest affinity for Cu and Zn. Langmuir sorption maxima of Co, Ni and Zn were 2.3, 3.0 and 6.8 mg g⁻¹ DM, respectively. At the highest initial concentration of 100 mg l⁻¹, a maximum of 29 mg g⁻¹ DM of Cu was sorbed onto the surface of the biomass. Desorption by 0.1 M HCl did not fully recover the metals sorbed onto the surface and there was evidence of leaching from within the biomass. Recovery of heavy metals and regeneration of the biomass by washing with 0.1 M HCl was therefore not suggested as a viable strategy.     

Survival of Rumex obtusifolius L. in an unmanaged grassland

Survival of broad-leaved dock (Rumex obtusifolius) plants exposed to grass (mainly Festuca rubra and Elymus repens) competition in unmanaged grassland in Central Europe was investigated. Individual plants (n = 244) were marked in a 35 × 28 m experimental plot divided into 20 quadrats. The mortality of the dock plants was recorded twice a year, and plant size (number of flowering stems) recorded for 8 years (2000–2007). Half of the plants died within 4 years and 4% survived to the end of the experiment. On average, winter mortality (October–April, 60%) was greater than summer mortality (May–September, 40%) but both varied between years. The plants decreased in size as they approached death. The survival of dock plants in particular quadrats was negatively correlated with the biomass of grass roots and rhizomes. Intensity of below-ground competition and possibly water deficiency contributed most to dock mortality.