SURVIVAL PATTERNS IN FOUR PRAIRIE GRASSES TRANSPLANTED TO CENTRAL TEXAS

Transplanted clones of four widespread prairie grasses, Andropogon scoparius, A. gerardii, Panicum virgatum, and Sorghastrum nutans, that had survived in cultivation 1958-1962 in central Texas were studied without cultivation 1963-67 to determine survival patterns. In all four species, clones from northern and eastern sites in the United States were eliminated. Survival of A. scoparius was restricted to plants originating in central and southern Texas and in northern Mexico. Surviving clones of A. gerardii, P. virgatum, and S. nutans were chiefly of Texas origin but included other clones mostly from the south central United States. Population samples of the four species from a central Texas grassland community showed greatest survival in a multi-ramet comparison of clones originating from North Dakota to Mexico City and in a multi-clone comparison from six sites in Texas and one in New Mexico. While the superior adaptation to the local habitat by the local populations might have been expected, this study documented the survival potential of organisms in the local ecosystem.     

ECOTYPIC DIFFERENTIATION WITHIN FOUR NORTH AMERICAN PRAIRIE GRASSES. II. BEHAVIORAL VARIATION WITHIN TRANSPLANTED COMMUNITY FRACTIONS

Ecotypic differentiation in transplanted clones of Andropogon scoparius Michx., A. gerardi Vitman, Panicum virgatum L. and Sorghastrum nutans (L.) Nash showed north-south correlations. In Austin, Texas, during 1959–1962, southern populations had earliest spring activity, latest flowering and latest dormancy. Northern community fractions from Massachusetts to North Dakota showed early flowering and a short span separating initial anthesis among the species-populations. Community fractions from Virginia to Nebraska had initial anthesis over a longer period than in more northern or more southern samples. Community fractions from South Carolina to eastern Texas had late flowering over a short period. Western community fractions, latitudinally and altitudinally diverse, were behaviorally uniform. The length of the growing period and its recurrent selection have sorted out ecological variants in harmony with the habitat gradients. Whether they are of the predominant physiognomic types, as in the true prairie region, or understory plants in the pine forests, the 4 grass taxa are in the climax matrix.     

Fire Season and Dominance in an Illinois Tallgrass Prairie Restoration

North American prairie remnants and restorations are normally managed with dormant‐season prescribed fires. Growing‐season fire is of interest because it suppresses dominant late‐flowering grasses and forbs, thereby making available light and other resources used by subdominant grasses and forbs that comprise most prairie diversity. Here we report a twofold increase in mean frequency and richness of subdominant species after late‐summer fire. Stimulation of subdominants was indiscriminate; richness of prairie and volunteer species increased in species that flowered in early, mid‐, or late season. Early spring fire, the management tool used on this site until this experiment, had no effect on subdominant richness or frequency. Neither burn treatment affected reproductive tillering of the tallgrasses Sorghastrum nutans or Panicum virgatum. Flowering of Andropogon gerardii increased 4‐fold after early‐spring fires and 11‐fold after late‐summer fires. These preliminary results suggest that frequency and species richness of subdominants can be improved by late growing‐season fire without compromising vigor of warm‐season tallgrasses.     

Plant demographic responses to mycorrhizal symbiosis in tallgrass prairie

The effects of mycorrhizal symbiosis on seedling emergence, flowering and densities of several grasses and forbs were assessed in native tallgrass prairie and in sown garden populations at the Konza Prairie in northeastern Kansas. Mycorrhizal activity was experimentally suppressed with the fungicide benomyl. Flowering and stem densities of the cool-season grass, Dichanthelium oligosanthes, sedges (Carex spp.), and the forb Aster ericoides were higher in non-mycorrhizal (benomyl-treated) than in mycorrhizal plots and the magnitude of these differences was significantly affected by burning. Mycorrhizae significantly enhanced flowering of the warmseason grasses Andropogon gerardii and Sorghastrum nutans in burned prairie, but not in unburned sites. These patterns suggest that mycorrhizal effects on the dynamics of cool-season graminoid and forb populations are likely to be mediated indirectly through effects of the symbiosis on the competitive dominance of their neighbors. Seedling emergence rates of the cool-season C₃ grasses Elymus canadensis and Koeleria cristata were significantly reduced in the benomyl-treated plots, whereas benomyl treatment had no significant effect on seedling emergence of the warm-season C₄ grasses A. gerardii and Panicum virgatum. The forbs showed variable responses. Seedling emergence of Liatris aspera was greater under mycorrhizal conditions, but that of Dalea purpurea was unaffected by mycorrhizal treatment. These results show that effects of mycorrhizal symbiosis on the population dynamics of co-occurring prairie plants vary significantly both among species and among different life history stages within species. The results also indicate that mycorrhizas and fire interact to influence competitive interactions and demographic patterns of tallgrass prairie plant populations.     

Prairie Revegetation of a Strip Mine in Illinois: Fifteen Years after Establishment

We examined the long-term success of prairie planting on a former strip mine in northeastern Illinois. The site was reclaimed and planted with prairie species in the 1970s. Total biomass increased over time, largely as a result of an increase in biomass of non-prairie species. Biomass of prairie species remained unchanged because of an increase in Panicum virgatum (switchgrass) offsetting decreases in Sorghastrum nutans (Indian grass). Total biomass was less than values published for other restored prairies (78 ± 4 g/m²to 298 ± 72 g/m² for our site, as opposed to 302-489 g/m² for the Trelease Prairie). Mycorrhizal inoculum potential (MIP) was variable across the site. There were also relatively few species of mycorrhizal fungi present as spores. Gigaspora sp., Scutellospora sp., Glomus sp., Glomus geosporum, and Glomus cf. fasciculatum were identified from spores. On a transect dominated by warm-season (C4) prairie grasses, MIP of rhizosphere soil collected under these species was lower than the MIP of rhizosphere soil collected under exotic cool-season (C3) grasses on a transect dominated by C3 species. On a transect with mixed warm-and cool-season vegetation, however, MIP did not differ under the two vegetation types. These results suggest that within-site patchiness rather than cover type is influencing MIP. Values of MIP were lower than those reported for native Illinois prairie.     

Photosynthetic rates and vegetative production of Sorghastrum nutans in response to competition at two strip mines and a railroad prairie

The effect of differing environmental conditions on competition for resources was investigated by a comparison of net photosynthetic rate (PN) and vegetative production of Indiangrass [Sorghastrum nutans (L.) Nash.] at two strip mine sites with differing reclamation histories, and a railroad prairie site where this species occurs naturally. The treatment for a competition experiment consisted of tying back all species of neighboring plants around a target plant, and measuring its PN and vegetative performance during the growing season. Environmental variables at each site were also measured during the growing season. Soil bulk density and pH were higher at the two mine sites than at the prairie site, and soil texture, nutrients, and water potential were different at each of the three sites. PN of target plants compared closely among the three sites, and were lowest for plants at the railroad prairie. The competition experiment indicated that lower canopy leaves were most affected by competition for photosynthetically active radiation (PAR) at all sites. Significant differences in PN of upper canopy leaves were found between treatment and control plants at one of the mine sites. This site had higher soil water potentials and higher soil levels of P and K than the other mine site or the railroad prairie. Target plants at the other mine site experienced a low competition for PAR, likely due to lower soil moisture availability and therefore lower aboveground productivity. The largest differences in PN and irradiances between upper and lower canopy leaves occurred in target plants with neighbors at the railroad prairie, likely due to inter-specific competition. Vegetative production of the target plants also reflected the environment at each site, but did not reflect PN differences between treatments. S. nutans is well adapted to the varying environment at these three sites, and aboveground competition for radiant energy was probably not as limiting for this C4 grass as belowground competition.     

Productivity and Subordinate Species Response to Dominant Grass Species and Seed Source during Restoration

Grasses can be important regulators of species diversity and ecosystem processes in prairie systems. Although C₄ grasses are usually assumed to be ecologically similar because they are in the same functional group, there may be important differences among species or between seed sources that could impact restorations. I tested whether C₄ grass species identity, seed source, or grass species richness scales to influence aboveground net primary productivity (ANPP), resistance to weed invasion, or establishment of subordinate prairie species during restoration. Plots in western Iowa, United States, were planted with equal‐sized transplants of one of five common grass species (Panicum virgatum L., Sorghastrum nutans (L.) Nash, Andropogon gerardii Vitman, Schizachyrium scoparium (Michx.) Nash, and Bouteloua curtipendula (Michx.) Torrey) either from local seed or from cultivar seed sources. These plots were compared to plots containing all five species in mixture and to nonplanted plots. Differences in ANPP were found among species but not between cultivars and noncultivars or between monocultures and mixtures. Panicum virgatum, S. nutans, and S. scoparium were more productive than A. gerardii and B. curtipendula. Weed invasion was much higher when plots were not planted with grasses. Schizachyrium scoparium allowed greater establishment of subordinant prairie species than all other focal grass species. There were two separate mechanisms by which grasses suppressed prairie species establishment either (1) by growing tall and capturing light or (2) by quickly filling in bare space by spreading horizontally through rhizome growth in short species. These results suggest that high ANPP can be found with noncultivar plantings during the first 2 years after planting and that subordinate species establishment is most likely when shorter bunchgrasses such as S. scoparium are dominant.     

Intraspecific Chromosome Number Variation and Prairie Restoration—A Case Study in Northeast Iowa,U.S.A

Genome duplication has played an important role in plant evolution. Variation in genome size within species is common, particularly in grasses, but rarely considered when planning restorations. We surveyed ploidy variation within one habitat (tall grass prairie) in one region (northeast Iowa, U.S.A.) to assess the risk of ploidy mismatch in restoration plantings. Genome sizes were estimated using flow cytometry for samples from 19 remnant prairies, 5 restoration plantings, and 2 seed sources. Intraspecific ploidy variation in remnant prairie populations was found for two species of grasses, Andropogon gerardii (big bluestem) and Panicum virgatum (switchgrass). Restoration seeds differed from remnants in ploidy for three species of grass, P. virgatum, Sorghastrum nutans (Indian grass), and Spartina pectinata (prairie cordgrass), and for one species of forb, Amorpha canescens (lead plant). In the case of S. pectinata, local ecotype seeds were found to consist of two different ploidy levels. Restorations in grasslands in the United States and elsewhere are likely to create mixed ploidy populations, probably resulting in lower reproductive success for the remnant population. Prevention of mixed ploidy populations will require the screening of restoration seed sources and regional surveys for ploidy variation.     

ECOTYPIC DIFFERENTIATION WITHIN FOUR NORTH AMERICAN PRAIRIE GRASSES. I. MORPHOLOGICAL VARIATION WITHIN TRANSPLANTED COMMUNITY FRACTIONS

Ecological variation within transplanted community fractions, containing Andropogon scoparius Michx., A. gerardi Vitman, Panicum virgatum L. and Sorghastrum nutans (L.) Nash, included broad behavioral and morphological differentiation. In Austin, Texas, during 1958–1962, southern community fractions that contained early spring activity, late flowering and late fall dormancy included taller plants than early-flowering, northern community fractions. The tallest populations in all 4 species originated in Texas. In P. virgatum, size of leaves and panicles showed north-south trends similar to culm height values. Leaf pubescence and leaf glaucousness in all 4 species showed geographic patterning that was not correlated with north-south maturity gradients. Greatest pubescence was on clones in community fractions from pine woods in the Southeast. Glaucousness was concentrated in community fractions from central Texas northward to Nebraska.     

Variation in grazing tolerance among three tallgrass prairie plant species

Three tallgrass prairie plant species, two common perennial forbs (Artemisia ludoviciana and Aster ericoides [Asteraceae]) and a dominant C(4) perennial grass (Sorghastrum nutans) were studied under field and greenhouse conditions to evaluate interspecific variation in grazing tolerance (compensatory growth capacity). Adaptation to ungulate grazing was also assessed by comparing defoliation responses of plants from populations with a 25-yr history of no grazing or moderate ungulate grazing. Under field conditions, all three species showed significant reductions in shoot relative growth rates (RGR), biomass, and reproduction with defoliation. In the two forbs, clipping resulted in negative shoot RGR and reductions in both number and length of shoot branches per ramet. Sorghastrum nutans maintained positive RGR under defoliation due to a compensatory increase in leaf production. Defoliation reduced rhizome production in A. ericoides and S. nutans, but not in A. ludoviciana. Clipping significantly reduced sexual reproductive allocation in all three species, although S. nutans showed a smaller reduction than the forbs. All three species showed similar responses to defoliation in burned and unburned sites. Under greenhouse conditions, a similar clipping regimen resulted in smaller reductions in growth and reproduction than those observed in the field. For all three species, the grazing tolerance indices calculated under natural field conditions were significantly lower than those estimated from greenhouse-grown plants, and the interspecific patterns of grazing tolerance were different. Aster ericoides exhibited the highest overall defoliation tolerance under greenhouse conditions, followed by S. nutans. Artemisia ludoviciana, the only study species that is typically not grazed by ungulates in the field, showed the lowest grazing tolerance. In the field experiment S. nutans showed the highest grazing tolerance and the two forbs had similar low tolerance indices. These patterns indicate that, despite high compensatory growth potential, limited resource availability and competition in the field significantly reduce the degree of compensation and alter interspecific differences in grazing tolerance among prairie plants. In all three species, defoliation suppressed sexual reproduction more than growth or vegetative reproduction. Significant interactions between plant responses to defoliation and site of origin (historically grazed or ungrazed sites) for some response variables (root/shoot ratios, rhizome bud initiation, and reproductive allocation) indicated some degree of population differentiation and genetic adaptation in response to a relatively short history of ungulate grazing pressure. The results of this study indicate that patterns of grazing tolerance in tallgrass prairie are both genetically based and also environmentally dependent.     

A soil heat and water transfer model to predict belowground grass rhizome bud death in a grass fire

Question: Grasses often resprout from surviving belowground buds following a fire in which aboveground matter is consumed. We used a soil heat and water transport model to present a general method for determining the potential mortality of rhizome buds due to fire for three tallgrass species (Andropogon gerardii, Sorghastrum nutans, and Panicum virgatum). Methods: Soil heating was described by physical processes that include heat conduction through the soil and heating and evaporation of soil water. We considered the following factors: soil moisture, texture, mineral thermal conductivity, maximum surface temperature, and fire residence time. Simulated soil temperature profiles were combined with measured belowground bud distributions to determine the proportion of buds expected to be heated to lethal temperatures under various conditions. Location: Wisconsin, USA. Results: Lethal temperatures for buds do not occur below ～2 cm, and at least 30% of rhizome buds remain below lethal temperatures, even under extreme conditions. Conclusions: The model explains the possible mechanisms for grass belowground rhizome bud survival in fires. Changes in fire and soil conditions do not notably impact soil temperatures and rhizome bud survival.     

The Role of Seed and Vegetative Reproduction in Plant Recruitment and Demography in Tallgrass Prairie

Recruitment, establishment and survivorship of seed- and vegetatively-derived shoots were quantified biweekly in annually burned and infrequently burned tallgrass prairie to investigate the contributions of seed and vegetative reproduction to the maintenance and dynamics of tallgrass prairie plant populations, the demography of seedlings and ramets, and the influence of fire on the demography of grasses and forbs. Clonally produced grass and forb ramets comprised >99%of all established shoots present at the end of the growing season, whereas established seedlings accounted for <1%,emphasizing the rarity of successful seedling establishment and the importance of vegetative reproduction in driving the annual regeneration and dynamics of aboveground plant populations in tallgrass prairie. Most recruitment from vegetative reproduction occurred early in the growing season and was higher in annually burned than infrequently burned sites, although low levels of new stem recruitment occurred continuously throughout the growing season. Peak recruitment on annually burned prairie coincided with peak recruitment of the dominant C₄ grasses Andropogon gerardii and Sorghastrum nutans prior to prescribed spring fire, with a second peak in recruitment occurring following fire. On infrequently burned prairie, grass and forb recruitment was highest in early April and declined steadily through May. The naturalized C₃ grass, Poa pratensis, was responsible for most of the early recruitment on unburned sites, whereas A. gerardii contributed most to recruitment later in May. Infrequently burned prairie was dominated by these two grasses and contained a larger forb component than annually burned prairie. The principal demographic effect of fire was on ramet natality rather than mortality. Fire regime, plant functional group, or timing of cohort emergence before or after fire did not affect ramet survivorship. C₄ grass shoots that emerged early and were damaged by fire showed similar survivorship patterns to tillers that emerged after fire. Differences in species composition between annually burned and infrequently burned prairie are driven by fire effects on vegetative reproduction and appear to be related principally to the effect of fire and detritus accumulation on the development of belowground vegetative meristems of C₄ grasses and their emergence dynamics.     

Soil carbon increased by twice the amount of biochar carbon applied after 6 years: Field evidence of negative priming

Applying biochar to agricultural soils has been proposed as a means of sequestering carbon (C) while simultaneously enhancing soil health and agricultural sustainability. However, our understanding of the long‐term effects of biochar and annual versus perennial cropping systems and their interactions on soil properties under field conditions is limited. We quantified changes in soil C concentration and stocks, and other soil properties 6 years after biochar applications to corn (Zea mays L.) and dedicated bioenergy crops on a Midwestern US soil. Treatments were as follows: no‐till continuous corn, Liberty switchgrass (Panicum virgatum L.), and low‐diversity prairie grasses, 45% big bluestem (Andropogon gerardii), 45% Indiangrass (Sorghastrum nutans), and 10% sideoats grama (Bouteloua curtipendula), as main plots, and wood biochar (9.3 Mg/ha with 63% total C) and no biochar applications as subplots. Biochar‐amended plots accumulated more C (14.07 Mg soil C/ha vs. 2.25 Mg soil C/ha) than non‐biochar‐amended plots in the 0–30 cm soil depth but other soil properties were not significantly affected by the biochar amendments. The total increase in C stocks in the biochar‐amended plots was nearly twice (14.07 Mg soil C/ha) the amount of C added with biochar 6 years earlier (7.25 Mg biochar C/ha), suggesting a negative priming effect of biochar on formation and/or mineralization of native soil organic C. Dedicated bioenergy crops increased soil C concentration by 79% and improved both aggregation and plant available water in the 0–5 cm soil depth. Biochar did not interact with the cropping systems. Overall, biochar has the potential to increase soil C stocks both directly and through negative priming, but, in this study, it had limited effects on other soil properties after 6 years.     

Root Dynamics of Cultivar and Non‐Cultivar Population Sources of Two Dominant Grasses during Initial Establishment of Tallgrass Prairie

Dominance of warm‐season grasses modulates tallgrass prairie ecosystem structure and function. Reintroduction of these grasses is a widespread practice to conserve soil and restore prairie ecosystems degraded from human land use changes. Seed sources for reintroduction of dominant prairie grass species include local (non‐cultivar) and selected (cultivar) populations. The primary objective of this study was to quantify whether intraspecific variation in developing root systems exists between population sources (non‐cultivar and cultivar) of two dominant grasses (Sorghastrum nutans and Schizachyrium scoparium) widely used in restoration. Non‐cultivar and cultivar grass seedlings of both species were isolated in an experimental prairie restoration at the Konza Prairie Biological Station. We measured above‐ and belowground net primary production (ANPP and BNPP, respectively), root architecture, and root tissue quality, as well as soil moisture and plant available inorganic nitrogen (N) in soil associated with each species and source at the end of the first growing season. Cultivars had greater root length, surface area, and volume than non‐cultivars. Available inorganic N and soil moisture were present in lower amounts in soil proximal to roots of cultivars than non‐cultivars. Additionally, soil NO₃–N was negatively correlated with root volume in S. nutans cultivars. While cultivars had greater BNPP than non‐cultivars, this was not reflected aboveground root structure, as ANPP was similar between cultivars and non‐cultivars. Intraspecific variation in belowground root structure and function exists between cultivar and non‐cultivar sources of the dominant prairie grasses during initial reestablishment of tallgrass prairie. Population source selection should be considered in setting restoration goals and objectives.     

ECOTYPIC DIFFERENTIATION WITHIN FOUR NORTH AMERICAN PRAIRIE GRASSES. III. CHROMATOGRAPHIC VARIATION

Four widespread grasses, Andropogon scoparius Michx., A. gerardi Vitman, Sorghastrum nutans (Nash) Hitchc. and Panicum virgatum L., have been studied behaviorally and morphologically. In the present comparison characteristic flavonoid patterns were shown whereby the four grass taxa can be separated at the generic and specific level. The greatest similarity was shown by the two Andropogon species. Panicum was most dissimilar. Although intrapopulational and interpopulational variation was demonstrated within each of the four taxa, both in transplanted material and in native plants of the original transplant site, there was no decisive correlation of biochemical variation with geographic origin, vegetative characteristics or maturity pattern. Early-flowering clones with short flowering culms and glabrous leaves, originating in northern and western areas, were essentially similar biochemically to later-flowering clones with tall flowering culms and extremely pubescent leaves, originating in southeastern areas. Blade samples collected in late fall, 1963, and in early spring, 1964, from the same transplanted clones were similar in flavonoid pattern. In P. virgatum. individual clonal patterns were characteristic of ramets grown under various day-length-thermoperiod conditions. Although biochemical markers for ecotypes would be useful êological tools, partially replacing their cultivation in transplant gardens, geographically correlated patterns were not revealed in this study. However, this study supports the present systematic position of the various morphologically and behaviorally diverse populations within the four taxa.     

Host plant species effects on arbuscular mycorrhizal fungal communities in tallgrass prairie

Symbiotic associations between plants and arbuscular mycorrhizal (AM) fungi are ubiquitous in many herbaceous plant communities and can have large effects on these communities and ecosystem processes. The extent of species-specificity between these plant and fungal symbionts in nature is poorly known, yet reciprocal effects of the composition of plant and soil microbe communities is an important assumption of recent theoretical models of plant community structure. In grassland ecosystems, host plant species may have an important role in determining development and sporulation of AM fungi and patterns of fungal species composition and diversity. In this study, the effects of five different host plant species [Poa pratensis L., Sporobolus heterolepis (A. Gray) A. Gray, Panicum virgatum L., Baptisia bracteata Muhl. ex Ell., Solidago missouriensis Nutt.] on spore communities of AM fungi in tallgrass prairie were examined. Spore abundances and species composition of fungal communities of soil samples collected from patches within tallgrass prairie were significantly influenced by the host plant species that dominated the patch. The AM fungal spore community associated with B. bracteata showed the highest species diversity and the fungi associated with Pa. virgatum showed the lowest diversity. Results from sorghum trap cultures using soil collected from under different host plant species showed differential sporulations of AM fungal species. In addition, a greenhouse study was conducted in which different host plant species were grown in similar tallgrass prairie soil. After 4 months of growth, AM fungal species composition was significantly different beneath each host species. These results strongly suggest that AM fungi show some degree of host-specificity and are not randomly distributed in tallgrass prairie. The demonstration that host plant species composition influences AM fungal species composition provides support for current feedback models predicting strong regulatory effects of soil communities on plant community structure. Differential responses of AM fungi to host plant species may also play an important role in the regulation of species composition and diversity in AM fungal communities. Received: 29 January 1999 / Accepted: 20 October 1999     

Changes in prairie vegetation under elevated carbon dioxide levels and two soil moisture regimes

Abstract. It is important to know how increasing levels of atmospheric CO₂ will affect native vegetation. The objective of this study was to determine the effect of elevated CO₂ concentrations on species composition in a tallgrass prairie kept at a high water level (730 mm of water in a 2000 mm soil profile) and a low water level (660 mm of water in 2000 mm). 16 cylindrical plastic chambers were placed on the prairie to maintain two levels of CO₂ (ambient or twice ambient) during two growing seasons in 1989 and 1990. Frequency of species was determined on 25 July 1989 and on 5 and 10 October 1990. At the beginning of the study, Poa pratensis (Kentucky bluegrass), the dominant C₃ species, had the highest frequency of 43.3%, but decreased with time. However, at the end of the experiment and under the high soil-water level, there were more P. pratensis plants in the elevated CO₂ treatment (frequency: 13.5%) than in the ambient CO₂ treatment (1.0%). Under the low soil water regime, the reverse occurred (frequencies: 3.6% and 11.0% for high and low CO₂, respectively). The frequency of major C₄ plants, Andropogon gerardii (big bluestem), A. scoparius (little bluestem) and Sorghastrum nutans (Indian grass) was not affected by CO₂. However, water did affect their frequency. Under low water, the frequency of A. gerardii decreased between 1989 and 1990. Under both soil moisture levels, the frequencies of S. nutans and A. scoparius increased. At the end of the study, Indian grass grown with high water had the highest frequency of all species on the prairie (frequency at the end of the study in October, 1990, of 44.4% and 47.4% for the high and low CO₂ levels, respectively). Unlike Indian grass, little bluestem grew better under low water conditions than under high water conditions. These results suggest that, if the climate becomes drier, A. scoparius will flourish more than S. nutans or A. gerardii, and P. pratensis may die out. Elevated CO₂ might not increase survival of C₃ plants under dry conditions, if temperatures are too high for them.     

Perennial warm‐season grasses for producing biofuel and enhancing soil properties: an alternative to corn residue removal

Removal of corn (Zea mays L.) residues at high rates for biofuel and other off‐farm uses may negatively impact soil and the environment in the long term. Biomass removal from perennial warm‐season grasses (WSGs) grown in marginally productive lands could be an alternative to corn residue removal as biofuel feedstocks while controlling water and wind erosion, sequestering carbon (C), cycling water and nutrients, and enhancing other soil ecosystem services. We compared wind and water erosion potential, soil compaction, soil hydraulic properties, soil organic C (SOC), and soil fertility between biomass removal from WSGs and corn residue removal from rainfed no‐till continuous corn on a marginally productive site on a silty clay loam in eastern Nebraska after 2 and 3 years of management. The field‐scale treatments were as follows: (i) switchgrass (Panicum virgatum L.), (ii) big bluestem (Andropogon gerardii Vitman), and (iii) low‐diversity grass mixture [big bluestem, indiangrass (Sorghastrum nutans (L.) Nash), and sideoats grama (Bouteloua curtipendula (Michx.) Torr.)], and (iv) 50% corn residue removal with three replications. Across years, corn residue removal increased wind‐erodible fraction from 41% to 86% and reduced wet aggregate stability from 1.70 to 1.15 mm compared with WSGs in the upper 7.5 cm soil depth. Corn residue removal also reduced water retention by 15% between ?33 and ?300 kPa potentials and plant‐available water by 25% in the upper 7.5 cm soil depth. However, corn residue removal did not affect final water infiltration, SOC concentration, soil fertility, and other properties. Overall, corn residue removal increases erosion potential and reduces water retention shortly after removal, suggesting that biomass removal from perennial WSGs is a desirable alternative to corn residue removal for biofuel production and maintenance of soil ecosystem services.     

Establishing Tallgrass Prairie on Grazed Permanent Pasture in the Upper Midwest

The goal of the study was to learn whether native prairie grasses and, eventually, a diverse mixture of native forbs could be incorporated in permanent pastures by means of rotational grazing by cattle. An experiment was established on a farm in northeastern Iowa on a pasture that had never been plowed but had been grazed since the 1880s. One treatment was protected from grazing to test for the presence of remnant vegetation. Andropogon gerardii, Sorghastrum nutans, Panicum virgatum, and Desmanthus illinoensis were introduced in plots first treated with glyphosate; seeds were either drilled (DR) or hand-broadcast and incorporated by controlled cattle trampling (BT). Seedling establishment and aboveground biomass were followed over 3 years. There was no evidence for remnant native plants on uplands, but seven species of native forbs and four native graminoids flowered in exclosures erected within waterways. D. illinoensis initially established up to 12 seedlings/m² but had disappeared from all but one plot by the third year. Variation in native grass establishment among replicate plots within treatments was very high, ranging initially from 0.2 to 9.9 plants/m². In August of the second year, native grasses made up only 8% of the available forage in DR plots and 1% of BT plots. One year later, however, native grasses made up 56% of the available forage in DR plots and 37% of BT plots, and these differences were significant (p = 0.05). A pilot study seeded in late winter (frost seeding) suggested that seeds spread after cattle trampling produced five times more seedlings (2.5/m²) than seeds spread before cattle trampling (0.5/m²). Frost seeding had advantages because it did not require herbicide for sod suppression or tractor access to the site. New plantings could be safely grazed in early spring and late fall, before and after most native grass growth, to offset the negative economic impact of protecting new plantings from burning during the growing season. But this practice precluded subsequent prescribed burning. I propose a strategy for incorporating native wildflowers into the pasture over time with minimum cost.     

NATURE OF THE PLANT COMMUNITY. V. VARIATION WITHIN THE TRUE PRAIRIE COMMUNITY-TYPE

Mc Millan , C. (U. Texas, Austin.) Nature of the plant community. V. Variation within the true prairie community-type. Amer. Jour. Bot. 46(6): 418–424. Illus. 1959.—Population samples of grass species were transplanted to Lincoln, Nebraska, from two grassland communities within the general distribution of the true prairie community-type. These represented extensive grassland areas near Watertown, South Dakota, and Manhattan, Kansas. True prairie relicts near Colorado Springs, Colorado and in the Black Hills of southwestern South Dakota were also studied in the transplant garden. Only in one species, Stipa spartea Trin., were the transplanted populations essentially similar in behavior. In 8 of the species, Koeleria cristata (L.) Pers., Bouteloua gracilis (H.B.K.) Lag., B. curtipendula (Michx.) Torr., Schizachyrium scoparium Nash, Andropogon gerardi Vitman, Panicum virgatum L., Sorghastrum nutans (L.) Nash, and Sporobolus heterolepis (A. Gray) A. Gray, the Manhattan populations were the latest flowering. In Elymus canadensis L., the Manhattan population was the earliest flowering. The abstraction of two communities into a true prairie type of community with other communities of similar species-populations is a convenient method for discussing distributional phenomena. However, extreme caution must be used in generalizing about characteristics other than distributional. If the 10 species in the present study were designated by letters, the Watertown and Manhattan communities could be compared ecologically as a b' c d e f g h i j and a b c' d' e' f' g' h' i' j'. The use of taxonomic relationship in vegetational studies is convenient for the reduction of sample size, but the vital aspect of studying variation within the species is in the determination of harmony between vegetation and its habitat. The relict communities are in adjustment with their habitats and represent the results of natural selection in favoring early-flowering variants within a number of different species. The key to distribution of the true prairie vegetation, widespread or relict, lies in the harmony between a habitat variable and a vegetation variable. Through natural selection, each stand of true prairie may be fundamentally different from any other stand.