Joe E. Brummer

A footprint of past climate change on the diversity and population structure of Miscanthus sinensis

BACKGROUND AND AIMS Miscanthus is a perennial C4 grass that is a leading potential feedstock crop for the emerging bioenergy industry in North America, Europe and China. However, only a single, sterile genotype of M. × giganteus (M×g), a nothospecies derived from diploid M. sinensis (Msi) and tetraploid M. sacchariflorus (Msa), is currently available to farmers for biomass production. To facilitate breeding of Miscanthus, this study characterized genetic diversity and population structure of Msi in its native range of East Asia. METHODS A total of 767 accessions were studied, including 617 Msi from most of its native range in China, Japan and South Korea, and 77 ornamental cultivars and 43 naturalized individuals from the USA. Accessions were evaluated with 21 207 restriction site-associated DNA sequencing single nucleotide polymorphism (SNP) markers, 424 GoldenGate SNPs and ten plastid microsatellite markers. KEY RESULTS Six genetic clusters of Msi from geographically distinct regions in Asia were identified. Genetic data indicated that (1) south-eastern China was the origin of Msi populations found in temperate eastern Asia, which is consistent with this area probably having been a refugium during the last glacial maximum (LGM); (2) Msi migrated directly from south-eastern China to Japan before migrating to the same latitudes in China and Korea, which is consistent with the known sequence of warming post-LGM; (3) ornamental Msi cultivars were derived from the southern Japan population, and US naturalized populations were derived from a sub-set of the ornamental cultivars; and (4) many ornamental cultivars previously described as Msi have hybrid ancestry from Msa and Msi, whereas US naturalized populations of Msi do not. CONCLUSIONS Population structure of Msi was driven by patterns of warming since the LGM, and secondarily by geographical barriers. This study will facilitate germplasm conservation, association analyses and identification of potential heterotic groups for the improvement of Miscanthus as a bioenergy crop.

Tiller defoliation patterns under short duration grazing in tallgrass prairie.

Simulated 8-pasture short duration grazing systems were studied in 1985-86 to determine the effect of grazing schedule and stocking rate on defoliation patterns of individual grass tillers of big bluestem (Andropogon gerardii Vitman) and little bluestem (Schizachyrium scoparium (Michx.) Nash). Treatments consisted of 3 grazing schedules (2,3, or 4 rotation cycles per 152-day grazing season) and 2 stocking rates (1.3 and 1.8 times the recommended normal). Grazing schedule and stocking rate did not affect the percent tiller height reduction per grazing period except for the combination of 2-cycle grazing and heavy stocking which increased percent height reduction. Percent tiller height reduction per grazing period decreased over the grazing season for the 3 and 4-cycle grazing schedules. Grazing schedule and stocking rate had little effect on the height at which tillers were defoliated. Increasing the number of grazing periods reduced the percentage of tillers defoliated per grazing period but increased the cumulative defoliation frequency over the grazing season. Grazing schedule did not affect the percentage of tillers ungrazed over the entire grazing season. Big bluestem was consistently defoliated more intensely and frequently than little bluestem.

Grazing date and frequency effects on prairie sandreed and sand bluestem.

A 5 year study was conducted during 1988-1992 to quantify the effects of grazing date and frequency on total organic reserves of prairie sandreed [Calamovilfa longifolia (Hook.) Scribn.] and sand bluestem (Andropogon hallii Hack.). Treatments consisted of mid-month grazing periods in (1) June, (2) July, (3) August, (4) October, (5) June and July, (6) June and August, (7) July and August, or (8) June, July, and August. Seasonal stocking rates were equal among treatments and divided equally over multiple grazing periods. Grazing treatments were applied to the same pastures during 4 consecutive years with yearling cattle and 4-7 day grazing periods. Mean tiller weight of etiolated initial-spring growth was used to estimate total organic reserves in the fifth year. Dormant season grazing in October was not different from 4 years of rest for either species. Total organic reserves in prairie sandreed decreased when paddocks were grazed in June or July regardless of the number of grazing periods per treatment. Reserves in sand bluestem were maintained by grazing once in June or August. Rotationally grazing pastures 2 or more times during June-August is least likely to maintain or increase total organic reserves in either species. Multiple grazing periods initiated in June reduced reserves by about 38% in prairie sandreed and 30% in sand bluestem. When stocking rates are similar to this study, deferment periods should be longer than 60 days after grazing in June to avoid measurable reductions in total organic reserves in both species. Periodic deferment of grazing until mid-August or later will be required to maintain simultaneously high levels of reserves in prairie sandreed and sand bluestem.

Plant community responses to short duration grazing in tallgrass prairie.

A key to management of short duration grazing systems is maintaining proper rest periods for individual pastures, but information on the necessary length of rest periods for tallgrass prairie is limited. Research hypotheses for this study were that tallgrass prairie plant communities would respond differently to grazing schedules incorporating rest periods of varying lengths and that this response would be dependent on stocking rate. Treatments consisted of 3 grazing schedules (2, 3, or 4 rotation cycles per 152 day grazing season) and 2 stocking rates (1.6 and 2.2 times the moderate continuous rate). Plant frequency, standing crop, species composition, and forage utilization were sampled from 1985 to 1989. Precipitation was above average in 4 of the 5 study years. Grazing schedule did not affect any vegetation parameter over time. Stocking rate did not affect plant frequency or species composition. Standing crop was reduced and forage utilization increased at the higher stocking rate but these effects were consistent over time. Frequency of western ragweed [Ambrosia psilostachya DC.] and the relative species composition of the forb component increased in all grazed pastures compared to ungrazed pastures. The overall lack of major treatment effects was attributed to favorable precipitation, spring burning, and the initial high-seral successional stage of the experimental pastures.

Manganese and Zinc Toxicity Thresholds for Mountain and Geyer Willow

Information on the heavy metal toxicity thresholds of woody species endemic to the western United States is lacking but critical for successful restoration of contaminated riparian areas. Manganese (Mn, 50–10,000 mg l−1) and zinc (Zn, 100–1000 mg l−1) toxicity thresholds were determined for Geyer (Salix geyeriana Anderss.) and mountain (S. monticola Bebb) willow using a sand-culture technique. The lethal concentration (50%) values were 3117 and 2791 mg Mn l−1 and 556 and 623 mg Zn l−1 for Geyer and mountain willow, respectively. The effective concentration (50%) values for shoots were 2263 and 1027 mg Mn l−1 and 436 and 356 mg Zn l−1 for Geyer and mountain willow, respectively. Shoot tissue values did not increase with increasing treatment concentrations. However, metals in the roots did increase consistently in response to the treatments. Metal levels in the shoot tissues were low for Zn (65–139 mg kg−1) and moderate for Mn (1300–2700 mg kg−1). Geyer and mountain willow have good resistance to Mn, possibly due to evolution in hydric soils with increased Mn availability, and may be useful for phytostabilization of soils with high levels of available Mn. Both species were affected to a greater degree by Zn as compared to Mn, but still exhibited good resistance and should be useful in remediating sites with at least moderate levels of available Zn. Based on the thresholds evaluated, Geyer willow had greater resistance to both Mn and Zn as compared to mountain willow, especially at lower concentrations in which growth of Geyer willow was actually stimulated.

Establishment and Growth of Two Willow Species in a Riparian Zone Impacted by Mine Tailings

A field study was initiated to determine survival, growth characteristics, and metal uptake of two montane riparian willow species, Geyer (Salix geyeriana Andersson) and mountain (S. monticola Bebb) willow, grown in amended fluvial mine tailing deposits. Revegetation was done with staked and previously rooted cuttings to determine if planting method had an effect on successful establishment of willows. A second planting was done the following growing season which tested cuttings of different ages. The addition of lime increased the soil pH from 5.0 to 6.5 and effectively reduced bioavailability of most heavy metals below phytotoxic levels. However, both willow species, regardless of planting method, concentrated Cd, Mn, Pb, and Zn in their leaf tissue above levels considered toxic to agronomic plants. Over the course of four growing seasons, prerooted mountain willows had a consistently higher survival rate compared to staked willows. At the end of the fourth growing season, mountain willow had a higher survival rate and produced greater aboveground growth for both planting methods, irrespective of year planted, compared with Geyer willow. Based on growth characteristics, the use of prerooted mountain willows would be recommended for successful revegetation of amended fluvial mine tailing deposits in riparian zones. However, because of the high Cd uptake into aboveground tissues, care should be taken in restoration efforts where wildlife and domestic livestock are likely to browse on the willows.

Canopy analysis as a technique to characterize defoliation intensity on Sandhills range.

Characterization of relationships between grazing and vegetation responses is difficult. Rapid and accurate measurement of pasture canopy characteristics would help clarify these relationships if canopy changes are directly related to grazing variables. The objectives of this study were (1) to evaluate use of the LI-COR LAI-2000 for quantification of changes in canopy density and architecture in response to defoliation by cattle, (2) to determine if changes in leaf area index (LAI) measured with the LAI-2000 are related to stocking rate, and (3) to determine advantages and drawbacks of the LAI-2000 for monitoring grazing impacts on canopy density and architecture. Leaf area index and mean foliage tilt angle were measured before and after defoliation by cattle (Bos taurus L.) in June, July, and August under 9 grazing treatments on Nebraska Sandhills range. Differences in LAI could be attributed to certain grazing treatments at various points throughout the season. Grazing treatment had little impact on mean foliage tilt angle. Change in LAI (delta LAI) had a significant negative relationship with stocking rate (P < or = 0.0001). The relationship detected for delta LAI versus stocking rate predicted LAI reductions of between 0.14 and 0.40 for the range of stocking rates studied; stocking rate accounted for 62% of the decrease in LAI caused by grazing. When configured for the Sandhills canopy, the LAI-2000 provided a rapid and precise method for quantification of the degree of defoliation associated with grazing.

Herbage dynamics of tallgrass prairie under short duration grazing.

Simuiated &pasture short duration graaing systems were studied in 1985-86 to determine the effect 01 timing and intewdty of graaing on seasonai herbage dynamics. Treatments consisted of 3 grazing scbeduiea (2,3, or 4 rotation cycles per 152 day grazing season) and 2 stoching rates (1.3X and 1.8X the recommended normal). Average ttatonal standing crop increased from 4-cycie to 2-cycie grazing at the iight stoching rate but did not respond to grazing schedule at the heavy stocking rate. Within the graaing season, babage standing crop was affected by graaing schedule in late summer in 1985 but not in 1986. Favorable growhtg conditions redted in Ugbt forage utiiiaation which averaged 39% over all treatments. Net berbap l ccmmdation rates were not affected by any experimentai factor and averaged 34 kg ha-r d-r over all treatments. Time trends for net herbage accumulation rate from May to September were aiso simiiar across treatments. Total herbage disappearance and herbage disappearance per animal-uuitday (AUD) were significantly higher under 4-cycle graaing at the heavier stoching rate than under all other treatments.

Interactions Among Western Ragweed and Other Sandhills Species After Drought

Abstract Interannual differences in yield and species composition of herbaceous vegetation on semiarid rangelands are common and often related to variations in precipitation regime. Interspecific interactions that occur after drought-induced population fluxes of western ragweed (Ambrosia psilostachya D.C.) were evaluated by removing western ragweed or associated species from 1-m2 quadrats at weekly intervals beginning in early May, June, or July 1991 or 1992 on high-seral sandhills prairie in Nebraska. The composite of peak standing crops for ragweed and each group of associated species was 77% greater during May–October 1991 (2 252 kg·ha−1) compared with 1992 (1 275 kg·ha−1) when April and May precipitation was 98 mm below average and a late frost occurred. Mean levels of western ragweed herbage up to 436 kg·ha−1 had no effect on associated species in 1991 when above average precipitation occurred throughout the growing season. In contrast, when an unusually dry spring occurred in 1992, relatively small mean levels of ragweed (189 kg·ha−1) reduced end-of-season standing herbage of rhizomatous C4 grasses on control plots by about 21% (137 kg·ha−1) with little effect on other associated species, regardless of when treatments were initiated. Within a given year, western ragweed density was seasonally constant, similar among treatments, and independent of preceding-year species composition. Severe defoliation of western ragweed had little effect on subsequent-year populations, indicating an ability to maintain primordia for several years with limited plant growth. Because western ragweed is not a strong competitor in the presence of vigorous graminoids, deferring use of June- or July-grazed pasture until after July in the subsequent year can minimize increases in western ragweed.

Cattle diet quality under short duration grazing on tallgrass prairie.

Paddocks of tallgrass prairie were grazed at intervals similar to 8-paddock short duration grazing. Two replicates of a 2 X 3 factorial treatment design were evaluated to determine the influence of stocking rate and grazing schedule on crude protein and digestible organic matter content of cattle diets. Stocking rates were 1.3 or 1.8 multiples of the rates recommended by the Soil Conservation Service for the study site. Grazing schedules were 2, 3, or 4 complete cycles during a 152-day grazing season. Grazing and rest periods were lengthened as the season progressed and forage accumulation rate slowed. Masticate samples were collected from the experimental paddocks on alternate days during the grazing periods in 2 consecutive years. No stocking rate by grazing schedule interactions were observed (P > 0.10). Diet crude protein was depressed (P 0.20). In vitro digestibility was not influenced by stocking rate but tended (P < 0.13) to be higher for the 3- and 4-cycle grazing schedules. The balance of crude protein and digestible organic matter was most favorable (P < 0.05) for the 3-cycle diets. Based on diet composition, more frequent grazing periods appeared to maintain a higher, more stable plane of nutrition than the slower rotation schedules.