不同碳源及浓度对草原樱桃组培苗繁育的影响

为降低草原樱桃组培苗生产的成本,加快组培苗推广,本试验研究了不同碳源对草原樱桃增殖和生根的影响。结果显示,蔗糖和白砂糖为草原樱桃组培快繁的最佳碳源,当浓度为20g·L-1和30g·L-1时,草原樱桃组培苗的繁殖系数和生根均较好,而从经济角度考虑,可用白砂糖代替蔗糖,白砂糖浓度为20g·L-1。     

Rainfall,evapotranspiration, and soil moisture as herbage production predictors for Wyoming rangelands

Rangelands are an important ecosystem in the western US, and herbage and livestock production are important issues throughout the western states. Making stocking rate decisions early in the growing season is difficult because of high variation in annual herbage production. In this study, regression analysis was used to relate herbage biomass to monthly and growing season predicator variables (rainfall, actual evapotranspiration, and soil moisture) using data collected from fifteen Wyoming rangeland sites. Both predictor and response variables were scaled before regression to correct for different physical and environmental conditions between sites. Growing season precipitation was the strongest predictor of herbage biomass production (r² = 0.79), followed by growing season actual evapotranspiration (r² = 0.69), and growing season profile-average soil water content (r² = 0.59). April profile-average (0–90 cm) and April surface (0–30 cm) soil moisture also predicted herbage biomass (r² = 0.53–0.54), indicating that early growing season soil moisture can be used to inform stocking rate and grazing management decisions as it provides information at the onset of the growing season.     

Soil organic C in the tallgrass prairie-derived region of the corn belt: effects of long-term crop management

Concerns with rising atmospheric levels of CO₂ have stimulated interest in C flow in terrestrial ecosystems and the potential for increased soil C sequestration. Our objectives were to assess land management effects on soil organic carbon (SOC) dynamics and SOC sequestration for long-term studies in the tallgrass prairie region of the US. Major losses of SOC following conversion of native prairie to arable agriculture at Sanborn Field and the Morrow Plots were rapid (20 to 40 yr), occurred in response to greatly reduced C inputs and accelerated C decay rates, and had largely abated by the mid-1900s. Losses of SOC occurred mainly in easily decomposable, labile C fractions. At Sanborn Field, modeled labile SOC was reduced to 4% of native prairie levels for treatments with low C inputs. A large capacity for soil C sequestration likely exists in the tallgrass prairie region, if labile C pools can be replenished. This agroecosystem has a strong C decomposition regime and increased sequestration of labile C will rely on management practices that increase C inputs (i.e., fertilization, returning crop residues) and stabilize labile C (i.e., perennial cropping, reduced tillage). The capacity for soil C sequestration, however, will vary considerably among sites and be dependent on initial levels of labile SOC and the ability of management practices to stabilize greater inputs of labile C.     

Control of one invasive plant species allows exotic grasses to become dominant in northern Great Plains grasslands

Decline of leafy spurge (Euphorbia esula) in the northern Great Plains of the US is generally viewed as a success story for biological control, but quality of the vegetation that survived the infestation is key to recovery of ecosystem function. In addition, effects of other invasive species, notably cool-season exotic grasses, must be taken into account. Objectives of this study were (1) to evaluate direction and significance of changes in biomass of native and exotic grasses, forbs, and leafy spurge and in plant species composition following control of leafy spurge by flea beetles and (2) to evaluate the relative effects of leafy spurge and exotic grasses on biomass of native grasses, biomass of forbs, and richness of native species. We monitored species composition (1998-2003 and 2008) and biomass (2000, 2002, 2003 and 2008) of these groups on spurge-infested and noninfested permanent plots at three sites with unbroken prairie sod in North Dakota, USA. We found little evidence, in terms of species richness or biomass of native grasses or forbs, that leafy spurge was being replaced by desirable native species, although desirable as well as weedy and exotic species were characteristic of 2008 vegetation at all three sites. Structural equation models revealed that leafy spurge had temporally intermittent negative effects on forb biomass and species richness, but no effects on native grasses. In contrast, exotic grass had consistently strong, negative effects on native grass biomass, as well as stronger negative effects than leafy spurge on native species richness. Although substantial native plant diversity remains at these sites, exotic grasses pose an important threat to these crucial building blocks of native prairie ecosystems.     

Natural N abundances in a tallgrass prairie ecosystem exposed to 8-y of elevated atmospheric CO2

After 8-y of elevated CO₂, we previously detected greater amounts of total soil nitrogen, suggesting that rates of ecosystem N flux into or out of tallgrass prairie had been altered. Denitrification and associative N fixation rates are the two primary biological processes that are known to control N loss and accumulation in tallgrass prairie soil. Therefore, our objective was to assess the natural abundance of plant and soil ¹⁵N isotopes as a cumulative index of potential change in efflux or influx of N into and out of the tallgrass prairie after 8-y of exposure to elevated CO₂. Aboveground plant delta ¹⁵N values of Andropogon gerardii were close to zero and more positive as a result of elevated CO₂, but whole-soil values at the 5-30 cm depth were significantly reduced (6.8 vs 7.3; P<0.05) under elevated CO₂-chamber (EC) relative to ambient CO₂- chamber (AC). Total, aboveground plant biomass, root-in-growth, extractable N, microbial biomass N, and soil pools collectively exhibited a range of delta ¹⁵N values from −2.8 to 7.3. Measurements of surface soil ¹⁵N indicate that a change in N inputs and outputs has occurred as a result of elevated atmospheric CO₂. In addition to possible changes in denitrification and N₂ fixation, other sources of N such as the re-translocation of N to the surface from deeper soil layers are needed to explain how soil N accrues in surface soils as a consequence of elevated CO₂. Our results support the notion that C accrual may promote N accrual, possibly driven by high plant and microbial N demand amplified by soil N limitation.     

Terrestrial vertebrate communities at black-tailed prairie dog (Cynomys ludovicianus) towns

We capitalized on a regional-scale, anthropogenic experiment—the reduction of black-tailed prairie dog (Cynomys ludovicianus) towns across the Great Plains of North America—to test the hypothesis that decline of this species has led to declines in diversity of native grassland vertebrates of this region. We compared species richness and species composition of non-volant mammals, reptiles and amphibians at 36 prairie dog towns and 36 paired sites in the Panhandle Region of Oklahoma during the summers and falls of 1997, 1998 and 1999. We detected 30 species of mammals, 18 species of reptiles and seven species of amphibians. Comparisons between communities at prairie dog towns and paired sites in the adjacent landscape indicated that while richness per se was not necessarily higher in towns, they did harbor significantly more rare and imperiled species. Species that were positively associated with prairie dog towns during one or both seasons (summer and fall) included badgers (Taxidea taxus), eastern cottontails (Sylvilagus floridanus), coyotes (Canis latrans), grasshopper mice (Onychomys leucogaster), swift fox (Vulpes velox), pronghorn antelopes (Antilocapra americana), striped skunks (Mephitis mephitis), white-tailed deer (Odocoileus virginianus), cattle, thirteen-lined ground squirrels (Spermophilus tridecemlineatus), black-tailed jackrabbits (Lepus califonicus), barred tiger salamanders (Ambystoma tigrinum), plains spadefoot toads (Scaphiopus bombifrons), Great Plains toad (Bufo cognatus), Woodhouse's toad (Bufo woodhousii), prairie rattlesnakes (Crotalis viridis), western plains garter snakes (Thamnophis radix), Texas horned lizards (Phrynosoma cornutum), and ornate box turtles (Terrapene ornata).     

Establishing Wyoming Big Sagebrush in Annual Brome-Invaded Landscapes with Seeding and Herbicides

Seeding native plants into degraded grasslands presents major challenges. Often, seeded species fail to establish and areas become/remain dominated by unwanted plants. We combined herbicides and seeding in former coal mining fields dominated by exotic winter annual grasses (downy brome [Bromus tectorum L.] and Japanese brome [Bromus arvensis L.], hereafter “annual bromes”). The main interest was restoring Wyoming big sagebrush (Artemisia tridentata spp. wyomingensis [Beetle & A. Young] S.L. Welsh, hereafter “big sage”), a very difficult species to restore to North American grasslands. We tested the nonselective herbicide glyphosate and the grass-specific herbicide quizalofop. The summer following herbicide applications and seeding, annual brome cover in controls 22% (CI_95% 13%, 36%) was significantly greater (P < 0.03) than in glyphosate 11% (CI_95% 5%, 25%) and quizalofop 16% (CI_95% 7%, 35%) treatments. At Decker mine, glyphosate increased seeded big sage density (P < 0.04) from 0.76 (CI_95% 0.27, 2.11) to 3.05 (CI_95% 1.42, 6.56) plants ? m^-2 the second summer after seeding. Corresponding increases for Spring Creek mine were from 0.11 (CI_95% 0.03, 0.43) to 0.43 (CI_95% 0.13, 1.40) plants ? m^-2 (P < 0.04). These results were consistent across two experiments initiated in different years. In addition to big sage, our study’s seed mixes contained native grasses and forbs, and herbicide treatments tended to promote establishment of these plant groups. In annual brome-dominated areas of the northern Great Plains, conditions amenable to big sage seedling establishment do not appear entirely uncommon, and herbicides can increase establishment.     

Assessing wind and mammals as seed dispersal vectors in an invasive legume

While some plants have modified seed structures to facilitate dispersal, many lack such specialised adaptations, making their mode of dispersal unclear. This can be particularly problematic for predicting shifts in species ranges or tracking the spread of invasive plants. As an example, the seed size and shape of the invasive legume, Lespedeza cuneata, suggest that wind and attachment to animals are not important for dispersal, yet populations can spread surprising distances within a few years. Using a series of experiments conducted in the laboratory and field, we tested wind and mammal fur as mediators of seed dispersal. To test wind dispersal, seed traps were arranged radially around a patch of L. cuneata and seeds were collected following dispersal. Attachment to mammal fur was tested by fitting pelts of a deer, coyote and raccoon to artificial torsos and determining seed retention in both the field and the laboratory. Laboratory trials also examined the influence of wet versus dry conditions. Our results showed that wind direction strongly influenced dispersal distance and seeds were readily dispersed by mammal fur. The number of seeds retained was species specific, depending on fur depth and mammal size, with seed retention increasing under wet conditions. Together, these results suggest that both wind and mammal fur contribute to the movement of L. cuneata across grasslands. Consequently, both dispersal vectors should be considered when designing and implementing control strategies.     

黑马河草原4种植物茎的解剖结构研究

利用常规石蜡切片的方法对黑马河草原上的4种植物茎的解剖结构观察比较,结果表明：这4种植物茎的基本结构具有相似性,均由表皮、皮层、维管柱3部分组成;它们的共同显著特征都具有较发达的髓部及皮层厚角组织;茎中维管组织与基本组织（皮层和髓）的比值较低。综合植物茎的解剖结构说明,这4种植物都具有适应寒、旱生环境的典型结构特征。     

Disturbances in tallgrass prairie: local and regional effects on community heterogeneity

Community heterogeneity in tallgrass prairie was analyzed at regional and local levels to assess the effects of disturbances on community structure at different spatial scales. The sites were part of NASA's First ISLSCP Field Experiment (FIFE) in Kansas, and were located on grassland treatments that were undisturbed, and burned-only on Konze Prairie Research Natural Area, and grazed-only and grazed + burned on adjacent ranch land. Sites in grazed-only or grazed + burned treatments were less similar to each other, on a regional scale (15 × 15 km), than were burned-only or undisturbed sites. Grazing reduced the cover of dominant species, making space available for the establishment of immigrants from the region. Each site was different because of establishment by different species from the large regional species pool. At the local scale (0.1 ha), the most homogeneous treatments were those that were most heterogeneous at the regional scale. Undisturbed treatments at the local scale were the most heterogeneous compared to sites under other treatments. Therefore, regional responses to disturbances were more variable than local responses, and were not predictable from within-site analyses.