Danthonia Spicata Research Articles

Weed Survey of Nova Scotia Lowbush Blueberry (Vaccinium Angustifolium Ait.) Fields

ABSTRACT Weed surveys provide the basis for weed management research in lowbush blueberry, but have not been conducted in Nova Scotia since 2001. Documented declines in herbicide efficacy, loss and/or acquisition of herbicide active ingredients, confirmation of herbicide-resistant weed biotypes, and documented vectoring of weed seeds by machinery necessitate a new weed survey. A total of 165 bearing year lowbush blueberry fields were surveyed from 2017 to 2019, within which approximately 211 weed species were identified. Most weed species were herbaceous perennial forbs (89 species) and woody perennials (50 species), followed by annual broadleaf (24 species) and perennial grass weeds (20 species). The remaining flora consisted of a range of ferns, biennials, sedges and rushes, and orchids. The most common weed species were red sorrel (Rumex acetosella L.), poverty oatgrass (Danthonia spicata L. Beauv.), haircap moss (Polytrichum commune Hedw.), hair fescue (Festuca filiformis Pourr.), narrow-leaved goldenrod (Euthamia graminifolia (L) Nutt.), tickle grass (Agrostis hyemalis (Walter) BSP.), woolly panicum (Panicum lanugosum Ell.), cow wheat (Melampyrum lineare Desr.), bunchberry (Cornus canadensis L.), and yellow hawkweed (Hieracium caespitosum Dumort). Increased occurrence of these weed species is likely the result of documented or observed reductions in hexazinone and terbacil efficacy, confirmation of triazine-resistant biotypes, and common occurrence of seeds of these weed species on machinery. Low crop prices have also caused reduced pronamide use, contributing to increased occurrence of hair fescue. Results are guiding future research priorities for weed management in lowbush blueberry.

Genetic variation of the fungus Atkinsonella hypoxylon infecting poverty oat grass

AbstractPoverty oat grass [Danthonia spicata (L.) P. Beauv. ex Roem. & Schult.] is a perennial bunch‐type grass native to North America. Poverty oat grass is often present in managed turfgrass areas of the United States where cool‐season grasses are adapted and has potential for development as a seeded low‐input turfgrass option. Naturally occurring poverty oat grass plants occasionally exhibit choke on the flowering stems because of a proliferation of fungal hyphae by the ascomycete Atkinsonella hypoxylon (Peck) Diehl. (family Clavicipitaceae). Twenty‐five A. hypoxylon isolates were cultured from choke‐exhibiting poverty oat grass plants collected from five different populations. DNA variation was evaluated at the 5.8S ribosomal ribonucleic acid (rRNA) internal transcribed spacer (ITS) first (ITS‐1) and second (ITS‐2) regions and 10 simple sequence repeat (SSR) loci. Five single nucleotide polymorphisms (SNPs) in the ITS‐1 region and an addition–deletion in the ITS‐2 region identified two isolate groups present in four of the five populations. The 10 SSR loci exhibited 28 scorable alleles and support the two groupings with variation appearing as random mutations and high linkage disequilibrium providing no evidence for sexual recombination within or between the two identified groups.

PCR‐based detection of the epibiotic fungus Atkinsonella hypoxylon associated with its host grass Danthonia spicata

AbstractDanthonia spicata (L.) Beauv., commonly known as poverty oatgrass, is a perennial bunch‐type grass native to North America. Danthonia spicata is often managed as a turfgrass in areas of the United States where cool‐season grasses are adapted, and it has potential for development as a low‐input turfgrass option. Naturally occurring D. spicata plants occasionally exhibit “choke” of the flowering stems due to a proliferation of fungal hyphae by the ascomycete Atkinsonella hypoxylon (Peck) Diehl. (family Clavicipitaceae). Polymerase chain reaction (PCR) primers were designed to amplify a 116‐bp A. hypoxylon‐specific fragment within the 5.8S ribosomal RNA Internal Transcribed Spacer 1 (ITS 1) region. The primer set was then used to amplify the fragment from 24 A. hypoxylon isolates and 24 D. spicata terminal seed head DNA extractions collected from a greenhouse‐maintained population that has never exhibited choke. The A. hypoxylon ITS 1 fragment was amplified from all fungal samples and all terminal seed head samples tested. The plant and fungal amplified fragments produced the same melt peak in high‐resolution melt analysis, and sequence analysis of all terminal seed head samples showed highly significant blast hits with the ITS 1 sequence of A. hypoxylon GenBank Accession U57405.1 and the 24 A. hypoxylon isolates. These results provide evidence that all sampled D. spicata plants are associated with the fungus A. hypoxylon and provide a useful tool for the study A. hypoxylon and its association with D. spicata.

Lowbush blueberry fruit yield and growth response to inorganic and organic N-fertilization when competing with two common weed species.

Inorganic N fertilizers are commonly used in commercial blueberry fields; however, this form of N can favor increased weed species’ growth, which can ultimately reduce the benefits of fertilization. We hypothesized that chipped ramial wood (CRW) compost is an effective alternative organic fertilizer for blueberry plants when weeds are present, as ericaceous shrub species are generally more efficient in utilizing organic N than herbaceous weed species. In this study, we measured the growth, fruit yield, and foliar N response of lowbush blueberry (Vaccinium angustifolium Aiton) to an application of 45 kg N ha-1 in the form of organic (CRW) or inorganic N (ammonium sulfate) in two areas of a commercial field colonized by either poverty oat grass (Danthonia spicata (L.) Beauv.) or sweet fern (Comptonia peregrina (L.) Coult.). We also assessed the impact of the fertilization treatments on litter decomposition rates. Contrary to our hypothesis, we found no significant increase in blueberry fruit yield or growth using CRW. By contrast, inorganic N-fertilization increased fruit yield by 70%. The effect was higher in the area colonized by D. spicata (+83%) than by C. peregrina (+45%). Blueberry fruit yield was on average twice higher in the area of the field having D. spicata than C. peregrina, suggesting a stronger competition with the latter. However, the increase in D. spicata density from 0–1 to >25 plants m-2 reduced fruit production by three-fold and strongly impacted vegetative growth in both fertilized and unfertilized plots. The impact of increased C. peregrina density was comparatively much lower, especially on vegetative growth, which was much higher in the area having C. peregrina. These patterns are likely due to a lower competition for N uptake with C. peregrina as this species can derive N from the atmosphere. Interestingly, the higher fruit yield in the area colonized by D. spicata occurred even in plots where the weeds were nearly absent (density of 0–1 plant m-2), revealing the influence of unidentified variables on blueberry fruit yield. We hypothesized that this difference resulted from over-optimal foliar N concentrations in the area colonized by C. peregrina as suggested by the significantly higher foliar N concentrations and by the negative correlation between foliar N concentrations and fruit yields in this area. The possibility of an influence of C. peregrina on flowering and pollination success, as well as of unidentified local site conditions is discussed. The tested N-fertilization treatments did not affect foliar N concentrations or litter decomposition rates. Overall, our results show that ammonium sulfate is very effective at increasing fruit yields but that both fruit yields and the efficiency of the N-fertilization treatment are decreased by increased D. spicata density, especially above 25 plants m-2. Although CRW did not significantly enhance fruit yields in the short term, this fertilizer may have a long-term beneficial effect.

Evaluation of foramsulfuron for poverty oat grass [Danthonia spicata (L.) P. Beauv. ex Roem. & Schult.] and rough bentgrass (Agrostis scabra Willd.) management in lowbush blueberry (Vaccinium angustifolium Ait.)

The susceptibility of poverty oat grass and rough bentgrass to foramsulfuron was assessed in greenhouse and field experiments. A dose response study was conducted in a greenhouse with treatments consisting of 0, 4.4, 8.8, 17.5, 35, 70, 140, and 280 g foramsulfuron ha−1. Field experiments were conducted using a similar dose response and also included industry standard fluazifop-P-butyl and sethoxydim applications. Foramsulfuron application rates of 4.04 ± 0.73 and 6.6 ± 1.3 g a.i. ha−1 reduced poverty oat grass biomass by 50% in the greenhouse. In contrast, 4.4 g a.i. ha−1 foramsulfuron caused >70% reduction in rough bentgrass biomass in the greenhouse. In the field, 280 g a.i. ha−1 of foramsulfuron was required to reduce poverty oat grass total and flowering tuft density and >35 g a.i. ha−1 (registered foramsulfuron rate) was required to reduce flowering tuft inflorescence number by 50%. In contrast, rough bentgrass was injured by 4.4 and 8.8 g a.i. ha−1 of foramsulfuron and total and flowering tuft density and flowering tuft inflorescence number were reduced by all other foramsulfuron rates evaluated. Foramsulfuron application rates of 13.1 ± 2.4, 10.3 ± 1.2, and 5.4 ± 0.9 g a.i. ha−1 reduced rough bentgrass total tuft density, flowering tuft density, and tuft inflorescence number, respectively, by 50%. Lowbush blueberry growers can consider foramsulfuron for postemergence management of rough bentgrass, but additional research is required to identify new herbicides for postemergence poverty oat grass management.

Contrasting impacts of two weed species on lowbush blueberry fertilizer nitrogen uptake in a commercial field.

Numerous studies have speculated that lowbush blueberry (Vaccinium angustifolium) is less efficient than weed species at taking up inorganic nitrogen (N) derived from fertilizers, thus raising questions as to the effectiveness of N fertilization in commercial fields. However, competition for acquiring N as well as specific interactions between blueberry and companion weeds characterized by contrasted functional traits remain poorly documented. Here, we assessed fertilizer-derived N acquisition efficiency and biomass production in lowbush blueberry and two common weed species that have different functional traits—sweet fern (Comptonia peregrina), a N2-fixing shrub, and poverty oat grass (Danthonia spicata), a perennial grass—in a commercial blueberry field in Québec, Canada. In 2015, 15N-labelled ammonium sulfate was applied at a rate of 45 kg ha-1 to 1 m2 field plots containing lowbush blueberry and one of the two weeds present at several different density levels (0 to 25 plants m-2). In 2016, each plot was harvested to determine vegetative biomass and the percentage of fertilizer-derived N recovered (PFNR) in each species. The PFNR was higher in blueberry (24.4 ± 9.3%) than in sweet fern (13.4 ± 2.6%) and poverty oat grass (3.3 ± 2.9%). However, lowbush blueberry required about four times more root biomass than sweet fern and poverty oat grass to uptake an equivalent amount of N from ammonium sulfate. The PFNR in poverty oat grass increased with plant density (from 0.8% to 6.4% at 2–3 and >6 plants m-2, respectively), which resulted in a decrease in blueberry’s PFNR (from 26.0 ± 1.4% to 8.6 ± 1.8%) and aboveground vegetative biomass production (from 152 ± 58 to 80 ± 28 g m-2). The increase in biomass production and N content in sweet fern with increasing plant density was not accompanied by an increase in PFNR (29.7 ± 8.4%), suggesting an increasing contribution of atmospherically-derived N. This mechanism (i.e., N sparing) likely explained blueberry’s higher biomass production and N concentration in association with sweet fern than with poverty oat grass. Overall, our study confirms lowbush blueberry low efficiency (on a mass basis) at taking up N derived from the fertilizer as compared to weeds and reveals contrasted and complex interactions between blueberry and both weed species. Our results also suggest that the use of herbicides may not be necessary when poverty oat grass is present at a low density (<15 plants of poverty oat grass m-2) and that adding inorganic N fertilizer is counterproductive when this species is present at a high density as it takes up as much fertilizer as lowbush blueberry.

Poecilus lucublandus (Coleoptera: Carabidae) and Pterostichus mutus Do Not Feed on Hair Fescue, Red Sorrel, and Poverty Oatgrass Seeds.

Poecilus lucublandus (Say), Pterostichus mutus (Say), and Harpalus rufipes (De Geer) are abundant Carabidae in lowbush blueberry fields and may contribute to weed seed predation. We used laboratory no-choice test experiments to determine if these beetles feed on seeds of hair fescue (Festuca filiformis Pourr., Poales: Poaceae), poverty oatgrass (Danthonia spicata L.), and red sorrel (Rumex acetosella L., Caryophyllales: Polygonaceae), which are common weeds in lowbush blueberry (Vaccinium angustifolium Ait., Ericales: Ericaceae) fields. Poecilus lucublandus and P. mutus did not feed on seeds of the test weed species, but H. rufipes consumed on average over 30 seeds of each species. There are other weed seeds in blueberry fields that could be palatable to P. lucublandus and P. mutus, which warrants further research on the granivory potential of these important carabid species.

Genetic diversity of Danthonia spicata (L.) Beauv. based on genomic simple sequence repeat markers

Danthonia spicata (L.) Beauv., commonly known as poverty oatgrass, is a perennial bunch-type grass native to North America. D. spicata is often found in low input turfgrass areas on the East Coast of the United States and has potential for development as a new native low input turfgrass species. Roche 454 sequenced randomly sheared genomic DNA reads of D. spicata were mined for SSR markers using the MIcroSAtellite identification tool. A total of 66,553 singlet sequences (approximately 37.5 Mbp) were examined, and 3454 SSR markers were identified. Trinucleotide motifs with greater than six repeats and possessing unique PCR priming sites within the genome, as determined by Primer-BLAST, were evaluated visually for heterozygosity and mutation consistent with stepwise evolution using CLC Genomics software. Sixty-three candidate markers were selected for testing from the trinucleotide SSR marker sites meeting these in silico criteria. Ten primer pairs that amplified polymorphic loci in preliminary experiments were used to screen 91 individual plants composed of at least 3–5 plants from each of 23 different locations. The primer pairs amplified 54 alleles ranging in size from 71 to 246 bp. Minimum and maximum numbers of alleles per locus were two and 12, respectively, with an average of 5.4. A dendrogram generated by unweighted pair group method with arithmetic mean cluster analysis using the Jaccard’s similarity coefficient was in agreement with the grouping obtained by Structure v2.3. The analyses were dominated by clonal groupings and lack evidence for gene flow with some alleles present in a single plant from a single location. Fourteen multilocus genotype groups were observed providing strong evidence for asexual reproduction in the studied D. spicata populations.

Species interactions in green roof vegetation suggest complementary planting mixtures

Facilitation between species could be used to increase the number of plant species that can survive on an extensive green roof. Green roofs are associated with high substrate temperatures and water loss which can lead to plant death. Therefore, species that are known to cool substrate temperatures and reduce water loss may be able to act as facilitators. Three drought tolerant, mat-forming species native to Nova Scotia were tested. Species included Cladonia spp. (lichen), Polytrichum commune (acrocarpous moss), and Danthonia spicata (bunchgrass). The target species was the forb Solidago bicolor. Additional neighbour treatments included an artificial plant, conspecific neighbours (S. bicolor surrounded by 8 S. bicolor), and a no-neighbour control. This study was conducted over a two year period in green roof modules. Overall, none of the neighbour treatments appeared to facilitate the growth of S. bicolor species. However, the S. bicolor in both the moss and lichen treatments had similar growth measurements to the control, likely due to a mulching effect, an indication that these species can successfully co-exist. Additionally, the substrate temperature in the lichen and moss treatments was significantly cooler than the control. The bunchgrass treatment had a net competitive interaction with S. bicolor. However since no S. bicolor died in this treatment the smaller stature of the S. bicolor in these treatments may improve drought tolerance. Overall, the incorporation of functional diversity, especially varied growth forms, increases the diversity of green roofs potentially improving the resilience and performance of green roof systems over the long term.

Effects of Soil Disturbance on Success of a Rare Savanna Forb, Liatris scariosa var. nieuwlandii in Habitats Dominated by Early and Late Successional Grasses

Abstract In tallgrass prairie restoration, dominance by competitive late succession prairie grasses may cause loss of species that are poor competitors. In a field experiment we tested whether disturbance could reverse this process for Liatris scariosa var. nieuwlandii, a threatened savanna species thought to be a poor competitor. At our study site, this species appears to be stable in vegetation dominated by Danthonia spicata, an early successional grass, but declining in the presence of Andropogon gerardii, a dominant prairie grass restored to the study area. We used correlation analysis to test whether cover of grasses affected L. s. nieuwlandii abundance and experimental disturbance to test whether competition could be reduced. We disturbed soil at small (<100 cm2) and large (2.25 m2) scales within vegetation dominated by D. spicata or A. gerardii. We measured the response of L. s. nieuwlandii to disturbance by planting seeds within undisturbed and disturbed patches. In undisturbed patches, cover of D...

Impact of Wild Blueberry Harvesters on Weed Seed Dispersal within and between Fields

Agricultural equipment can disperse weed seeds over large distances. Efforts to minimize or prevent equipment-mediated dispersal should be a key component in any integrated weed management plan. Several experiments were initiated in commercial wild blueberry fields to examine the potential impact of harvesting equipment on weed seed dispersal within and between blueberry fields. Seed loads were examined on harvesting equipment between fields and results suggest that harvesting equipment is a major vector of seed dispersal. Seed loads were 397,000 in 2006 and 194,000 in 2007. Of all seeds located on the harvester, 66 to 79% were located on the belts or affiliated components. In 2006, a second experiment was established to examine within-field seed dispersal. A sampling grid was established over multiple distinct poverty oatgrass patches with seed heads at 44% of all sampling points. Following harvest, seeds were located at 67% of all sampling points. In 2006 and 2007, short-distance secondary dispersal of poverty oatgrass by harvesting equipment was measured. The relationship between distance from patch perimeter and seeds per unit area on the side approached by harvesting equipment and the far side of the patch was adequately modeled with an exponential decay model. Secondary dispersal within blueberry fields by harvesting equipment is inevitable. Dispersal may be reduced by avoiding dense weed patches, or altering harvest timing. Periodic cleaning of harvesting equipment between fields will help prevent the spread of weed seed.

Effect of long-term burn-pruning on the flora in a lowbush blueberry (Vaccinium angustifolium Ait.) stand

The effect of burn-pruning on the flora in a natural stand of lowbush b lueberry was studied over a 24-yr period in Newfoundland and Labrador, Canada. Treatments were: not burned and burn-pruned every 2nd, 3rd, or 4th year. A vegetative survey was conducted before burning and periodically in succeeding years. Following statistical analyses, species were grouped according to their response to burning, as follows: those not significantly affected; those eliminated or whose frequency of occurrence was reduced; and those whose occurrence was increased. Initially, burning virtually eliminated Juniperus communis var. depressa, Empetrum nigrum, Cladina rangiferina, Lycopodium clavatum and Pleurozium schreberi, reduced the frequency of occurrence of nine species by 6 to 69%, and increased 13 others by 1 to 2050%. With burning, Polytrichum commune and Fragaria virginiana ssp. glauca, in particular, increased very early in the study to become two of the most prevalent species. Also, except for some initial effects of burning, the lowbush blueberry and some initially prevalent species (Festuca filiformis, Maianthemum canadense, Danthonia spicata, Cornus canadensis and Luzula multiflora var. acadiensis) remained among the most dominant species. Of the species studied, only seven each of those increased or decreased by burning were affected by the burn-pruning cycle. In both groups, the greatest increases or decreases in the frequency of occurrence were obtained with the 2-yr burn-pruning cycle. Key words: Lowbush blueberry, Vaccinium angustifolium, burning, pruning, plant succession, weeds, fire, flora

Plasticity of Chasmogamous and Cleistogamous Reproductive Allocation in Grasses

Cleistogamy is more common in grasses than in any other angiosperm family. Both self-fertilized cleistogamous (CL) spikelets and open-pollinated chasmogamous (CH) spikelets are typically produced. Relative allocation to CL and CH varies among species and populations, and is influenced by ontogeny and environment. The balance between reproductive modes can be expressed as a CH/CL ratio. This ratio is very plastic, and stressful conditions can result in values Amphicarpum purshii, an annual with subterranean CL spikelets, CH/CL declined as density increased because CH decreased more than CL as size was reduced by intraspecific competition. In the shade-tolerant annual Microstegium vimineum, CH/CL was lowest in large greenhouse-grown plants in an unlimited, sunny environment, but was highest in small plants from a shady forest interior; tiller vegetative mass often showed a negative allometric relation to CH and CL allocation. In the perennial Dichanthelium clandestinum, CH and CL allocation varied among populations, but there was no consistent effect of light on CH/CL. The phenology of reproduction strongly affects CH/CL. In Danthonia spicata, CH/CL was high early in the season as CH flowering commenced, but dropped quickly as axillary CL spikelets matured; A. purshii showed the opposite pattern because CL reproduction occurred first. The assumption that cleistogamy simply provides reproductive assurance should be reevaluated in light of new information on phenology and allometry. Changes in the balance between CH and CL caused by environmental factors may be indirect effects of size. Evolutionary models that do not explore the plasticity and allometry of CH and CL reproduction may not be useful in predicting the myriad patterns in nature.

Vascular Flora of Beadles Barrens Nature Preserve, Edwards County, Illinois

Abstract The floristic composition of Beadles Barrens Nature Preserve, located in west-central Edwards County, Illinois was studied during the growing seasons of 1999–2002. The vascular flora of this 4.0 ha preserve consisted of 306 species in 75 families, including 65 species not previously reported from Edwards County. The herbaceous layer was dominated by prairie grasses with Schizachyrium scoparium (Michx.) Nash (IV = 61.5 of 100) being the most abundant. Many other prairie species were common with Soliadgo nemoralis Ait., Pycnanthemum tenuifolium Schrad. and Carex spp. having the highest importance values. Trees were sparse with most occurring in a small (0.125 ha) grove located in the northwest corner of the barrens. Tree density in the grove was 432 trees/ha with Diospyros virginiana L. (IV = 54.6) and Quercus stellata Wangh. (IV = 53.9) being co-dominants. Herbaceous species were also sparse in the grove, consisting of Danthonia spicata (L.) Roem. & Schultes, Antennaria spp., and Lechea tenuifolia...

Vascular Flora of Gray's Post Oak Woodland, Saline County, Illinois

Abstract Gray's Post Oak Woodland is an open wooded community located on the western edge of the Wabash Border Natural Division about 9 km southeast of Harrisburg, Saline County, IL. Associated with a clayey soil missing most of the surface layer, the trees were stunted and gnarled. Quercus stellata dominated the canopy, accounting for nearly all of the importance value. Although six other tree species were present, few individuads exceeded 15 cm dbh. The open understory contained few saplings, averaged 1520 stems/ha, with young post oaks common. The herbaceous layer was sparse with a bare ground and litter cover of 48.90%. Danthonia spicata dominated, along with various moss and lichen species, some tree seedlings, and Carex spp.

The influence of soil moisture on losses of buried seeds to fungi

Although soil fungi are likely to be a major cause of mortality for buried seeds, few ecological studies have examined the role these pathogens play in natural systems. In particular, few studies have investigated whether losses of seeds to soil fungi are habitat-dependent. We used fungicide treatments to investigate whether losses of buried seeds of four grasses (Bromus inermis, Danthonia spicata, Glyceria striata, and Poa pratensis) to soil fungi differed among meadows differing in soil moisture. We also applied water to some treatments, to determine whether this increased losses of seeds to fungi. For all four grasses, fungicide additions improved one or more measures of seed viability, though this effect was small. For Danthonia and Glyceria, fungicide was less likely to improve viability in dry meadows than in wet and/or mesic meadows. Adding water reduced some measures of viability of seeds of Danthonia and Poa in dry meadows, but fungicide partly counteracted these negative effects, suggesting that adding water reduced performance by increasing fungal attack. These results indicate that fungi represent a hazard for buried seeds of these species, particularly in wetter soils, and potentially may contribute to the reduction of populations of vulnerable species in wetter sites.

Additions and Range Extensions to the Vascular Plant Flora of the Continental Northwest Territories and Nunavut, Canada, II

Based on field reconnaissance since the publication of Flora of the Continental Northwest Territories in 1980, particularly in the District of Keewatin and northeastern District of Mackenzie (Nunavut) and Nahanni National Park, information is provided on geographically significant plant occurrences. One new taxon, Polemonium boreale forma albiflorum, is described, fourteen native taxa are reported as new to the region: Carex hoodii, C. microptera, C. petasata, Corispermum hookeri, C. ochotense, Danthonia spicata, Draba stenoloba, Erysisnum coarctatum, Halenia deflexa, Polygonum fowleri, P. ramosissimum, Salix rotundifolia ssp. rotundifolia, Silene uralensis ssp. ogilviensis, and Vaccinium ovalifolium. Five introduced taxa, Crepis tectorum, Corispermum villosum, Deschampsia elongata, D. incisa var. incisa, and Medicago sativa ssp. falcata are new to the flora of the region. Two native taxa, Danthonia intermedia and Potentilla porsildiorum are deleted from the flora and Ranunculus aquatilis var hispidulus is placed in synonymy. Significant range extensions for 125 native and one introduced taxon are included.

VEGETATION COMPOSITION AND STRUCTURE OF EVERSGERD POST OAK FLATWOODS, CLINTON COUNTY, ILLINOIS

Abstract Eversgerd Post Oak Flatwoods is a 16 ha woodlot that is part of an extensive band of timber associated with the broad Kaskaskia River valley in the Southern Till Plain Natural Division of Illinois. This flatwoods was studied to determine its woody composition and structure, and the effects of fire suppression on canopy closure and plant succession. Tree density within the site averaged 266 trees/ha with a basal area of 24.8 m2/ha. Quercus stellata Wang. (post oak) dominated the overstory and woody understory with an importance value of 171 (200 possible). Quercus bicolor Willd. (swamp white oak) and Q. palustris Muenchh. (pin oak) were common species in a shallow depression, accounting for their second and third in importance value ranking. The forest has an open, park-like appearance. Small woody saplings averaged 820 stems/ha and large saplings averaged 221 stems/ha. Grasses and sedges dominated the herbaceous layer; Danthonia spicata (L.) Roem. & Schultes and Carex cephalophora Willd. were the...

Maintenance of Diversity within Plant Communities: Soil Pathogens as Agents of Negative Feedback

The effect of soil pathogens on plant communities was investigated using four old-field perennial plant species and five isolates of a pathogenic oomycete in the genus Pythium. These Pythium strains were isolated from the roots of two of the plant species, Danthonia spicata and Panicum sphaerocarpon, used in a previous experiment on the consequences of changes in the soil community on plant growth. In this previous experiment, Danthonia and Panicum changed the soil community in a manner that reduced their growth relative to that of a third plant species, Anthoxanthum odoratum. In the current experiments, we found that inoculation with Pythium reduced overall plant mass and root:shoot ratios, but Danthonia and Panicum were more susceptible to the presence of Pythium than the other two plant species, Anthoxanthum and Plantago lanceolata. In addition, Pythium accumulates at different rates on different plant species, with a greater than tenfold higher population observed in association with Panicum compared to Anthoxanthum. The results of these experiments suggest that the accumulation of species-specific soil pathogens could account for the previous observation of negative feedback on plant growth through changes in the soil community. As negative feedback may act to maintain plant species diversity within a community, these results suggest that soil pathogens may themselves contribute to the maintenance of plant species diversity.

MAINTENANCE OF DIVERSITY WITHIN PLANT COMMUNITIES: SOIL PATHOGENS AS AGENTS OF NEGATIVE FEEDBACK

The effect of soil pathogens on plant communities was investigated using four old-field perennial plant species and five isolates of a pathogenic oomycete in the genus Pythium. These Pythium strains were isolated from the roots of two of the plant species, Danthonia spicata and Panicum sphaerocarpon, used in a previous experiment on the consequences of changes in the soil community on plant growth. In this previous experiment, Danthonia and Panicum changed the soil community in a manner that reduced their growth relative to that of a third plant species, Anthoxanthum odoratum. In the current experiments, we found that inoculation with Pythium reduced overall plant mass and root:shoot ratios, but Danthonia and Panicum were more susceptible to the presence of Pythium than the other two plant species, Anthoxanthum and Plantago lanceolata. In addition, Pythium accumulates at different rates on different plant species, with a greater than tenfold higher population observed in association with Panicum compared to Anthoxanthum. The results of these experiments suggest that the accumulation of species-specific soil pathogens could account for the previous observation of negative feedback on plant growth through changes in the soil community. As negative feedback may act to maintain plant species diversity within a community, these results suggest that soil pathogens may themselves contribute to the maintenance of plant species diversity.