Nitrogen fertilisation influences low CO2 effects on plant performance

Low atmospheric CO2 conditions prevailed for most of the recent evolutionary history of plants. Such concentrations reduce plant growth compared with modern levels, but low-CO2 effects on plant performance may also be affected by nitrogen availability, since low leaf nitrogen decreases photosynthesis, and CO2 concentrations influence nitrogen assimilation. To investigate the influence of N availability on plant performance at low CO2, we grew Elymus canadensis at ambient (~400 μmol mol–1) and subambient (~180 μmol mol–1) CO2 levels, under four N-treatments: nitrate only; ammonium only; a full and a half mix of nitrate and ammonium. Growth at low CO2 decreased biomass in the full and nitrate treatments, but not in ammonium and half plants. Low CO2 effects on photosynthetic and maximum electron transport rates were influenced by fertilisation, with photosynthesis being most strongly impacted by low CO2 in full plants. Low CO2 reduced stomatal index in half plants, suggesting that the use of this indicator in paleo-inferences can be influenced by N availability. Under low CO2 concentrations, nitrate plants discriminated more against 15N whereas half plants discriminated less against 15N compared with the full treatment, suggesting that N availability should be considered when using N isotopes as paleo-indicators.

Are the Great Plains wildrye (Elymus canadensis) and the Siberian wildrye (Elymus sibiricus) conspecific? A study based on the nuclear 5S rDNA sequences

Elymus canadensis L. and Elymus sibiricus L. are difficult to separate by morphology. The latter is found mainly in Asia and extends into northern North America; the former is confined to North America. We obtained the DNA sequences of 135 5S rDNA units collected from 19 localities throughout their respective ranges. The results of statistical parsimony, analysis of molecular variance, and sequence polymorphism analyses show that the two taxa are not conspecific.

Characterisation of fungal endophytes present in Elymus canadensis (Canada wildrye)

Elymus canadensis (Canada wildrye - CWR) is a native perennial cool season bunch grass tolerant to a range of soils, winter hardy and able to grow across the United Sates and as far North as Southern Alaska. Canada wildrye is often used for prairie restoration, conservation and erosion stabilisation. Young CWR plant tissue is palatable and nutritious to grazing animals. CWR has been reported to harbour a sexual endophytic fungus, Epichloë elymi, but some accessions have been identified that have not produced stroma. We isolated and characterised the epichloë endophytes from three endophyte-infected CWR accessions collected from Mexico and Texas. We established that the endophytes present in these CWR accessions are of hybrid origin, with E. elymi and E. amarillans ancestral genomes, and are therefore considered to be asexual isolates. The endophytes were examined for their alkaloid potential, particularly the detrimental ergot alkaloids, with inconclusive results. Keywords: Elymus canadensis, Canada wildrye, hybrid, Epichloë elymi, Epichloë amarillans

Molecular marker analysis of hypoploid regenerants from cultures of barley × Canada wild rye

Canada wild rye (CWR, Elymus canadensis L., 2n = 4x = 28) is a potential source of genes for disease resistance and environmental tolerance in barley (Hordeum vulgare L., 2n = 2x = 14). Tissue cultures were initiated from immature inflorescences of CWR × 'Betzes' barley hybrids to promote CWR introgression into barley through possible tissue culture induced chromosome breakage and exchange. Among the plants regenerated, some were missing one (2n = 20) or part of one (2n = 20 + telo) chromosome. The objective of this study was to identify the missing chromosome or chromosome arm in these regenerants through the analysis of molecular (RFLP) markers that previously had been mapped in barley. Forty-six hypoploid regenerants that traced to 30 separate explants obtained from 10 interspecific hybrid plants were evaluated. DNA was digested with the restriction enzyme HindIII, Southern blotted, and probed with 39 genomic and cDNA barley clones that identified sequences polymorphic between barley and CWR. Eight of these probes identified band loss patterns that separated the regenerants into two groups. One group, all with barley cytoplasm, were missing a CWR chromosome homoeologous to barley chromosome 3; a second group, all with CWR cytoplasm, were missing a CWR chromosome homoelogous to barley chromosome 7. These results indicated that chromosome elimination in culture was not random. The two cytoplasm groups were further differentiated by probes that identified band shifts. These band shifts were caused by differences in DNA methylation. Key words : Hordeum vulgare, aneuploidy, Elymus canadensis, tissue culture.

Effects of mycorrhizae, phosphorus availability, and plant density on yield relationships among competing tallgrass prairie grasses

A replacement series experiment was used to investigate the effects of mycorrhizae, phosphorus availability, and plant density on competitive relationships between three tallgrass prairie species of varying mycorrhizal dependencies. Under mycorrhizal conditions, the obligately mycorrhizal dependent warm-season grass Andropogon gerardii (big bluestem) was a better competitor in mixture with the nonmycorrhiza-dependent cool-season grass Koeleria pyramidata (Junegrass). In the absence of mycorrhizae, however, competitive effects of big bluestem were greatly reduced and Junegrass experienced competitive release. Relative yield totals increased when mycorrhizae were suppressed, suggesting greater intensity of interspecific competition in the presence of mycorrhizae. Thus, the competitive dominance of big bluestem in tallgrass prairie is strongly related to its mycorrhizal status. Elymus canadensis (Canada wild rye) outcompeted big bluestem both with and without mycorrhizae. Relative yield totals of this species mixture were also lower under mycorrhizal conditions, indicating that mycorrhizae increase the intensity of interspecific competition between them. Relative yields of wild rye competing with big bluestem increased in the absence of mycorrhizae, suggesting that it also experiences competitive release when big blue-stem are not mycorrhizal. The outcomes of competition were generally similar among the three total plant density treatments and between P-fertilized and nonfertilized treatments. However, interactions between mycorrhizal effects and plant density confirm that outcomes of interspecific competitive interactions may be density dependent in some cases. Key words: arbuscular mycorrhizae, de Wit replacement series, Andropogon gerardii, Elymus canadensis, Koeleria pyramidata.

Hybridization and tissue culture of Hordeum vulgare × Elymus canadensis

Canada wild rye (CWR, Elymus canadensis L.) is winter hardy, drought tolerant, and resistant to barley yellow dwarf virus. Crosses between CWR and barley (Hordeum vulgare L.) produce sterile F1 hybrids. The objectives of this study were to compare callus and regeneration response with different media, to assess the effectiveness of in vitro colchicine treatment, and to determine whether chromosome changes occurred in regenerated plants. 'Betzes' barley was crossed with CWR and hybrid plants were recovered using embryo rescue. Immature inflorescences of the hybrids were placed on Gamborg's B5 medium supplemented with two levels of sucrose and two levels of 2,4-dichlorophenoxyacetic acid (2,4-D) to initiate callus growth. Media were solidified with either agar or gellum gum. Beginning at 8 weeks, a portion of the calli was placed on medium containing 20 mg/L colchicine for 10 days to double the chromosome number. Callus initiation was significantly greater with media containing gellum gum than with agar and with 5 mg/L 2,4-D than with 20 mg/L 2,4-D. Plantlet regeneration response to media paralleled the callus response. Chromosome counts of 1864 regenerants showed that 12% had chromosome numbers other than the expected 2n = 21. Chromosome numbers in regenerants ranged from 7 to 44. There was no benefit to using colchicine in the media. Evidence of chromosome recombination was observed. A backcrossing program to barley was initiated using all regenerants, while concentrating on plants with 2n = 42, which had some restored female fertility.Key words: somaclonal variation, intergeneric hybridization, Canada wild rye.