Spotted Knapweed Utilization by Sequential Cattle and Sheep Grazing

Prescribed (or targeted) sheep grazing can effectively suppress the invasive perennial forb spotted knapweed (Centaurea stoebe L. ssp. micranthos [Gugler] Hayek). Some ranchers and other natural resource managers, however, resist using this weed management tool over concerns that sheep may consume too much of the graminoid standing crop, thereby decreasing its availability to cattle and wildlife and possibly harming graminoids with excessive defoliation. One potential approach to address these concerns is to graze spotted knapweed infestations first with cattle, immediately followed by sheep. We evaluated this sequential grazing strategy on foothill rangeland in western Montana, comparing sequential grazing at a moderate stocking rate in mid June (spotted knapweed in bolting stage) vs. mid July (spotted knapweed in late-bud/early flowering stage). Pastures (0.81 ha) were grazed with three yearling cattle for 7 d, immediately followed with 7 d of grazing by seven yearling sheep. Combined relative (i.e., utilization) of graminoids by cattle and sheep averaged 40% in June and July, safely within sustainable grazing use levels recommended for the site. Combined relative use of spotted knapweed by cattle and sheep also did not differ between June and July, averaging 62%. Previous research indicates that this degree of use is sufficient to suppress spotted knapweed. Our results indicate that prescribed sheep grazing can be applied immediately following cattle grazing in either June or July to suppress spotted knapweed without overusing desirable graminoids. Cattle and sheep will eat less graminoids and more spotted knapweed if cattle and sheep graze sequentially when spotted knapweed is in its late-bud/early flowering stage (mid July) rather than its bolting stage (mid June).     

Bluebunch Wheatgrass Response to Spring Defoliation on Foothill Rangeland

Spring elk grazing may reduce forage availability for wildlife or livestock in summer and may harm forage resources on foothill rangeland. We quantified bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love) response to spring defoliation on foothill rangeland in southwestern Montana. Two experiments were conducted simultaneously on a foothill grassland site and a foothill sagebrush steppe site. Bluebunch wheatgrass plants (n = 800) were selected and excluded from wild and domestic ungulates. Clipping treatments were applied in either early spring (mid- to late April) or late spring (mid- to late May), and plants were clipped to 1 of 3 residual heights (3, 6, or 9 cm) for 1, 2, or 3 successive years. Unclipped plants served as controls. Plant response was measured in late June and late July on both sites. April clipping for 3 successive years did not adversely affect bluebunch wheatgrass in June or July (P > 0.05) at either site. On foothill grassland, May defoliation to 3 cm for 2 consecutive years reduced leaf height (P = 0.04) in July. May defoliation for 3 successive years to 3 or 6 cm reduced plant yield (P < 0.05) and leaf height (P < 0.05) in June, and May defoliation for 3 successive years to 3 cm reduced leaf height (P = 0.02) in July. On foothill sagebrush steppe, 3 successive years of May defoliation to ≤ 9-cm stubble heights decreased leaf height in June (P < 0.05). We conclude that foothill rangelands where bluebunch wheatgrass receives moderate or light defoliation (6–9-cm residual stubble heights) in mid- to late May should be limited to no more than 2 successive years of mid- to late May grazing, whereas sites that receive heavy to severe defoliation (≤ 3-cm residual stubble heights) in mid- to late May should not be grazed for 2 successive years during mid- to late May.     

Defoliation Effects On Bromus Tectorum Seed Production: Implications For Grazing

Cheatgrass (Bromus tectorum L.) is an invasive annual grass that creates near-homogenous stands in areas throughout the Intermountain sagebrush steppe and challenges successful native plant restoration in these areas. A clipping experiment carried out at two cheatgrass-dominated sites in eastern Oregon (Lincoln Bench and Succor Creek) evaluated defoliation as a potential control method for cheatgrass and a seeding preparation method for native plant reseeding projects. Treatments involved clipping plants at two heights (tall = 7.6 cm, and short = 2.5 cm), two phenological stages (boot and purple), and two frequencies (once and twice), although purple-stage treatments were clipped only once. Treatments at each site were replicated in a randomized complete block design that included a control with no defoliation. End-of-season seed density (seeds · m⁻²) was estimated by sampling viable seeds from plants, litter, and soil of each treatment. Unclipped control plants produced an average of approximately 13 000 and 20 000 seeds · m⁻² at Lincoln Bench and Succor Creek, respectively. Plants clipped short at the boot stage and again 2 wk later had among the lowest mean seed densities at both sites, and were considered the most successful treatments (Lincoln Bench: F_6,45 = 47.07, P < 0.0001; Succor Creek: F_6,40 = 19.60, P < 0.0001). The 95% confidence intervals for seed densities were 123–324 seeds · m⁻² from the Lincoln Bench treatment, and 769–2 256 seeds · m⁻² from the Succor Creek treatment. Literature suggests a maximum acceptable cheatgrass seed density of approximately 330 seeds · m⁻² for successful native plant restoration through reseeding. Thus, although this study helped pinpoint optimal defoliation parameters for cheatgrass control, it also called into question the potential for livestock grazing to be an effective seed-bed preparation technique in native plant reseeding projects in cheatgrass-dominated areas.     

Biomass Production and Net Ecosystem Exchange Following Defoliation in a Wet Sedge Community

Riparian ecosystems provide many ecosystem services, including serving as an important forage resource for livestock grazing operations. We evaluated defoliation impacts on above- and belowground production, and net ecosystem exchange of CO₂ (NEE), in a wet sedge (Carex nebrascensis Dewey)-dominated plant community. In June or July of 2004–2005, experimental plots were clipped to 10 cm stubble height and paired control plots left unclipped. All plots were clipped to 2.5 cm in mid-September, and end-of-season and season-long aboveground production calculated. Root ingrowth cores were used to estimate annual root production and root length density (RLD). A portable gas exchange system and plexiglass chamber were used to measure NEE in 2005. An elevated water table in 2005 vs. 2004 was associated with higher (P &spilt; 0.001) season-long aboveground production (about double), but lower (P ≤ 0.05) belowground production (about half). Total productivity did not differ between years, but below-:aboveground ratios were 3× higher in 2004 vs. 2005. RLD was not different between years (P &spigt; 0.05). Clipping reduced (P ≤ 0.05) end-of-season aboveground standing crop by 33% to 73% depending on clipping month and year. Effects of clipping month on season-long aboveground production were inconsistent between years; June clipping decreased (P ≤ 0.05) production (-10%) in 2005 and July clipping decreased (P ≤ 0.05) production (-25%) in 2004. NEE for June-clipped plots recovered within 1 mo of clipping, whereas NEE for plots clipped in July remained below unclipped levels at the end of the growing season. Water table levels strongly influenced below-:aboveground ratios, although total production was relatively stable between years. Year effects overwhelmed clipping effects on season-long aboveground production. Defoliation after mid-summer did not allow recovery of photosynthetic capacity by the end of the growing season, suggesting the potential for long-term impact with regular late-season defoliation.     

Above-Ground Net Primary Production for Elymus lanceolatus and Hesperostipa curtiseta After a Single Defoliation Event

Above-ground net primary production (ANPP) of northern wheatgrass (Elymus lanceolatus [Scribn. & J. G. Sm.] Gould) and western porcupine grass (Hesperostipa curtiseta [Hitchc.] Barkworth) was determined after defoliation to a 7.5 cm stubble height on five landform elements in the Northern Mixed Prairie that had been ungrazed for > 25 yr. Landform elements included north aspect–concave slopes, north aspect–convex slopes, south aspect–concave slopes, south aspect–convex slopes, and level uplands. ANPP was determined for 2 yr after defoliating plots once in May, June, July, August, September, October, November, or April. Northern wheatgrass and western porcupine grass ANPP varied among landform elements (P < 0.01), but not with the month of defoliation × landform element interaction (P ≥ 0.22). Month of defoliation did not influence ANPP of northern wheatgrass (P ≥ 0.69), but that of western porcupine grass was reduced by August and September defoliations (P < 0.01). ANPP of both grasses was insensitive to landform element in terms of defoliation responses. Northern wheatgrass ANPP was not responsive to temporal aspects of a single defoliation. With the exception of August and September defoliations, western porcupine grass also was insensitive to a single defoliation in different months. Land managers should consider rest (1 yr nongrazing) following grazing of western porcupine grass in August or September, whereas responses to defoliation in different months suggest northern wheatgrass can be grazed annually.     

Summer and Winter Defoliation Impacts on Mixed-Grass Rangeland

Combined growing- and dormant-season pasture use has potential to increase herbage harvest without causing the undesirable shift in species composition that occurs with excessive utilization. The objective of this study was to determine the effect of summer clipping on winter pastures and winter clipping on summer pastures regarding standing crop, plant community composition, and forage quality. The study was conducted from 2003–2006 at the Antelope and Cottonwood Research Stations located in the mixed-grass prairie of western South Dakota. At each location, the experimental design was a randomized complete block with three replications that included 18 clipping treatments arranged as a split-split plot. Whole plots consisted of four summer clipping dates (May–August). Subplot treatments were two clipping intensities (clipped to residual height to achieve 25% or 50% utilization). Sub-subplots consisted of two winter clipping intensities (unharvested or clipped to a residual height to achieve a total utilization of 65%). Two winter control treatments were arranged in the subplot and split into two clipping intensities of 50% and 65% utilization. Winter biomass for the May 25% clipping treatment was similar to winter biomass for winter-only clipping. No increase in forage quality resulted from summer clipping compared with winter clipping. Three consecutive yr of combined growing-season and dormant-season defoliation to 65% utilization resulted in no change in functional group composition compared with ≤ 50% utilization treatments. Clipping in June resulted in reduced midgrass biomass at both stations and increased shortgrass biomass at Cottonwood. Results suggest that producers could combine growing and dormant-season grazing to increase the harvest of herbage on mixed-grass prairie, but should change season of use periodically to avoid an undesirable shift in plant composition.     

宁夏南部山区苜蓿褐斑病田间发生及流行动态

根据不同地带、田块和不同的刈割期,针对目前宁夏南部山区栽植的国外引进品种、地方品种进行了褐斑病Pseudopeziaz medicaginis田间发生及流行动态调查。结果表明,不同苜蓿Medicago sativa品种上褐斑病的发生程度不同,18个调查品种中,加拿大DY和耐寒苜蓿发病重,其次是美国杂花苜蓿、WL323、中首1号,固原苜蓿发病最轻,但是不同品种上病害的发生和发展趋势是相同的;褐斑病的季节消长曲线呈“S”型,5月底、6月初为病害的始发期,7、8月为盛发期,9月进入衰退期,整个生长季节中病害的增长速度以8月上中旬最快,7月下旬和8月下旬次之,7、8月是褐斑病发展的关键期。刈割措施影响病害的发生和发展。适时、合理应用刈割措施是延缓、减轻和控制褐斑病危害的有效措施。     

Medusahead Dispersal and Establishment in Sagebrush Steppe Plant Communities

Medusahead (Taeniatherum caput-medusae [L.] Nevski) is an invasive annual grass that reduces biodiversity and production of rangelands. To prevent medusahead invasion land managers need to know more about its invasion process. Specifically, they must know about 1) the timing and spatial extent of medusahead seed dispersal and 2) the establishment rates and interactions with plant communities being invaded. The timing and distance medusahead seeds dispersed from invasion fronts were measured using seed traps along 23 35-m transects. Medusahead establishment was evaluated by introducing medusahead at 1, 10, 100, 1 000, and 10 000 seeds · m⁻² at 12 sites. Most medusahead seeds dispersed less than 0.5 m from the invasion front (P < 0.01) and none were captured beyond 2 m. Medusahead seeds dispersed from the parent plants from early July to the end of October. More seeds were trapped in August than in the other months (P < 0.01). Medusahead establishment increased with higher seed introduction rates (P < 0.01). Medusahead density was negatively correlated to tall tussock perennial grass density and positively correlated to annual grass density of the preexisting plant communities (P = 0.02). Medusahead cover was also negatively correlated with tall tussock perennial grass density (P = 0.03). The results suggest that containment barriers around medusahead infestations would only have to be a few meters wide to be effective. This study also suggests that promoting or maintaining tall tussock perennial grass in areas at risk of invasion can reduce the establishment success of medusahead. Tall tussock perennial grass and annual grass density, in combination with soil data, may be useful in predicting susceptibility to medusahead invasion.     

刈割对香根草生长发育的影响

在香根草快速生长期间,适时适度的刈割有利于促进香根草的地上部和地下部健康、协调地生长。研究了不同频度和不同时间刈割处理,对香根草发育的影响,结果显示:刈割可以促进茎叶的伸长,茎叶含水量升高;适当频度的刈割可以有效地控制香根草的高度,茎叶变宽厚,延长香根草绿期,保持良好的景观效果,但过度刈割(处理Ⅰ)会使相应的效应下降;在7月中旬至9月中旬香根草快速生长期间刈割1次,不但可以明显增加地上部茎叶的产量,促进地上部分蘖的发生,同时也有利于地下部根系的生长发育,提高根茎比,但不刈割(对照处理Ⅷ)、刈割不及时(处理Ⅶ)或频繁刈割均不利于香根草的健康生长。     

不同放牧强度下绵羊采食方式的变化特征

本研究将绵羊对禾本科植物的采食方式主要分为摘叶、拔芯和去顶3种类型.研究发现采食方式受植物种类、季节和放牧压的影响.对羊草(Leymus chinensis)的采食方式以去顶和摘叶为主, 对芦苇(Phragmites communis)的采食方式以去顶和拔芯为主.具体表现为,羊草的去顶率,8月以前随放牧强度减小、季节推移而降低,8月后则相反;摘叶率随放牧压增加和时间推移大致是先增加后减少;拔芯率随放牧压的增加而增大,6月最高,9月最低;总体上,未被采食的羊草比例随放牧压降低而增大,在生长季后期相应增加.芦苇去顶率随时间推移先降低后增加;拔芯率在6月随放牧压减小而降低,其它月份里主要随放牧压减小而升高,从整个生长季看,芦苇拔芯率在6月初最大;芦苇摘叶率的变化受前2种采食方式制约;未被采食的芦苇比例随放牧压降低而增加,但在7月后中牧要比轻牧和重牧低,在放牧干扰下,生长季里未被采食的芦苇比例在8月达最大.     

Yield Response of Needle-and-Thread and Threadleaf Sedge to Moisture Regime and Spring and Fall Defoliation

Little information is available to help managers of cool-season dominated semiarid rangelands determine when to begin and end grazing in the spring and fall. Therefore, we evaluated the effects of clipping spring and fall growth on subsequent-year yield of needle-and-thread (Hesperostipa comata [Trin. & Rupr.] Barkworth) and threadleaf sedge (Carex filifolia Nutt.) (USDA-NRCS 2012) using a randomized complete block, split-plot experimental design with fall moisture regimes (ambient or supplemental water) applied to main plots and defoliation treatments applied to subplots. Two combinations of spring defoliation, one for each fall moisture regime, were composed of a factorial array of three spring clipping dates (early May, late May, mid-June) and three levels of defoliation (0%, 40%, 80%). A third combination of treatments was composed of the supplemental water regime and an array of a single spring clipping date (late May), a single fall clipping date (late September, after regrowth), and three levels of defoliation (0%, 40%, 80%) in the same year. Ambient fall moisture was low, leading to continued senescence of needle-and-thread and threadleaf sedge, whereas the application of 10 cm of supplemental water in mid-August stimulated fall growth. The study was replicated with two sets of main plots at four sites in consecutive years, 2002 and 2003. Yield data were collected in mid-June of the year following treatment. Subsequent-year yield of needle-and-thread was not affected by defoliation under average plant-year precipitation conditions (2003) (P > 0.05); however, it was reduced following heavy (80%) late spring (late May or June) defoliation during a drought year (2002) (P > 0.05). Subsequent-year yield of threadleaf sedge was not affected by defoliation in either year (P > 0.05). Because it is difficult to predict when drought will occur, avoiding heavy late-spring grazing in needle-and-thread–dominated pastures in consecutive years would be prudent.     

Diet Quality Modifies Germination of Dichrostachys cinerea and Acacia nilotica Seeds Fed to Ruminants

The pods of many woody plants form an important part of the diet of livestock during the dry season due to their high nutritive value. However, the dispersal of seeds that remain intact and can potentially germinate after excretion is of particular concern when animals consume seeds of encroaching or invasive woody plants. The objectives of this study were to determine the effects of animal species in two experiments (experiment 1: goats, sheep; experiment 2: goats, cattle), diet quality (Medicago sativa hay, Digitaria eriantha hay) and seed characteristics (size, hardness) on the effectiveness of animal seed dispersal and germination of Dichrostachys cinerea and Acacia nilotica seeds. Owing to a limitation on the availability of seeds, the two experiments were done separately at different times. Each animal in both experiments received 1 000 A. nilotica seeds and 1 000 D. cinerea seeds mixed with either a low-quality diet (D. eriantha hay) or a high-quality diet (M. sativa hay). In experiment 1, we found a significant interaction effect of animal species (goats, sheep), diet (high-quality hay, low-quality hay), and seed species (A. nilotica seeds, D. cinerea seeds) on germination (P < 0.0001). There was also a higher seed recovery (P < 0.009) when animals were offered high-quality hay (47.4% ± 4.65) compared to low-quality hay (30.2% ± 3.24). In experiment 2, animal species affected seed recovery (P < 0.0325; goats 32.0% ± 6.44; cattle 50.3% ± 4.27) and germination percentage (P < 0.055; goats 14.1% ± 1.48; cattle 9.3% ± 0.94). The diet quality fed to the animals may affect dispersal and germination. However, animal species and seed characteristics also had important effects on germination of D. cinerea and A. nilotica seeds. Thus, all three of these factors play a major role in dissemination of viable seeds.     

不同刈割频度对大针茅草原土壤呼吸及其土壤因子的影响

通过对大针茅草原土壤呼吸特性及影响因子的测定,研究3种不同刈割方式天然草地土壤呼吸特性及其影响因子,为典型草原刈割对碳收支研究提供基础理论依据。大针茅草原是亚洲中部草原亚区特有的一种草原类型。研究区设置在内蒙古锡林浩特市东部以大针茅建群的典型草原;在2009-2013年进行不同频度的刈割处理,一年两次、一年一次、两年一次(割一年休一年)、围封,在2013年8月采集测定土壤养分样品,在2013年生长季的6、7、8月进行土壤呼吸速率的测定及土壤微生物数量的测定。结果表明,围封处理下土壤含水量要高于其他刈割处理。6与8月时,围封处理下的细菌和微生物总数均显著高于刈割处理。不同频度刈割下群落的土壤呼吸速率有显著的差异,割一年休一年与围封处理显著高于其他刈割处理,且不同处理的土壤呼吸速率均在7月初为最低;土壤呼吸速率在内蒙古干旱半干旱地区与土壤含水量呈极显著正相关关系,受土壤含水量影响显著。结合生物多样性及生产利用的角度,割一年休一年为最合理的刈割频度。     

Microbial Composition before and after Conservation of Grass-Dominated Haylage Harvested Early,Middle, and Late in the Season

Haylage for horses is often harvested in late plant maturity, which could be associated with an increased risk of impaired hygienic quality in the forage and short aerobic storage stability after bale opening, but knowledge in this area is scant. An experiment was conducted in which the microbial composition was analyzed before and after conservation of primary growth haylage harvested early (June), middle (July), and late (August) in the season during 1 year. The counts of yeast, enterobacteria, and lactic acid bacteria (LAB) in preconserved herbage increased with the advancing harvest time (P ≤ .02). After conservation, the August haylage had increased counts of enterobacteria (log 4.3 colony-forming unit [CFU]/g) and LAB (log 6.5 CFU/g), compared with the June and July haylage (log ≤1.7 CFU/g for enterobacteria and ≤5.7 CFU/g for LAB, P < .001). The yeast counts were the lowest in the June haylage (log 5.0 CFU/g) compared with the July and August haylage (log ≥6.3 CFU/g, P < .001). After conservation, the mold counts were lower in the June haylage and greater in the August haylage (P = .01). In the preconserved herbage, Cladosporium cladosporioides was the most common mold species in June but Fusarium poae was in July, and Mucor fragilis in August. After conservation, Penicillium carneum was the only species found in the June haylage, with M. circinelloides most frequently found in the July haylage and M. hiemalis and M. circinelloides found at similar frequencies in the August haylage. An advanced harvest time resulted in greater counts of enterobacteria, yeast, and LAB and an increased number of mold species in the conserved haylage. The aerobic storage stability of the opened haylage bales measured by temperature was similar among the harvests.     

The Effect of Targeted Grazing and Biological Control on Yellow Starthistle (Centaurea solstitialis) in Canyon Grasslands of Idaho

Yellow starthistle (Centaurea solstitialis L.) is an invasive weed of significant importance on rangelands in the western United States. Field experiments were conducted in 2003 and 2004 to determine the effect of targeted grazing on yellow starthistle growth and bud production, and on the efficacy of four established biological control seed-head–feeding insects, which included three species of weevils and one fly species. We tested sheep and cattle grazing at three yellow starthistle growth stages—rosette, bolting, and late bud—at a site where all four biocontrol agents were established. The timing of grazing had a greater impact on yellow starthistle growth and bud production than the type of grazing animal. In comparison to the control, grazing at the rosette and bolting stage resulted in shorter plants both years of the study, but increased the number of buds following grazing at the bolting stage and at the rosette stage in 2003. Negligible seed production across treatments, in 2003, precluded detection of treatment effects. However, in 2004, grazing at the rosette and bolting stages resulted in a greater number of seeds per plant compared to the control and the late bud stage, which were similar. Results indicated that the timing of grazing did not negatively impact biocontrol efficacy. Eustenopus villosus adult injury and total insect larval damage were similar to control plants following each grazing treatment both years, indicating potential compatibility between targeted grazing and biocontrol for integrated management of yellow starthistle.     

Knapweed Hay as a Nutritional Supplement for Beef Cows Fed Low-Quality Forage

Advancing our ability to use invasive plants for producing commodities is central to the agricultural industry. Our objective was to evaluate Russian knapweed (Acroptilon repens &lsqb;L.] DC.) as a winter feed supplement for ruminant livestock. In Experiment 1, we utilized three ruminally cannulated steers in a completely randomized design to compare the ruminal degradation characteristics of alfalfa and Russian knapweed. In the second experiment, Russian knapweed and alfalfa were compared as protein supplements using 48 midgestation, beef cows (530 ± 5 kg) offered ad libitum hard fescue (Festuca brevipila Tracey) straw in an 84-d study. Treatments included an unsupplemented control and alfalfa or Russian knapweed provided on an iso-nitrogenous basis. In Experiment 1, the rate and effective degradability of neutral detergent fiber was greater for alfalfa compared with Russian knapweed (P ≤ 0.02). Ruminal lag time for NDF (period before measurable disappearance began) was greater for knapweed (P = 0.03). Soluble nitrogen, rate of N degradation, rumen degradable N, and effective degradability of N were all greater for alfalfa compared with Russian knapweed (P &spilt; 0.01). In Experiment 2, supplementation increased (P &spilt; 0.01) cow weight gain and BCS compared to the unsupplemented control with no difference between alfalfa and Russian knapweed (P = 0.47). There was no difference (P = 0.60) in the quantity of straw offered between the unsupplemented cows and supplemented groups, but alfalfa fed cows were offered approximately 11% more (P = 0.03) than Russian knapweed-fed cows. Total DM offered to cows was greater (P &spilt; 0.01) for supplemented compared with unsupplemented cows with no difference noted between alfalfa and Russian knapweed (P = 0.79). Russian knapweed is comparable to alfalfa as a protein supplement for beef cows consuming low-quality forage. Using Russian knapweed as a nutritional supplement can help solve two major production problems; managing an invasive weed, and providing a feedstuff that reduces an impediment in livestock production systems.     

Trait Response and Change in Genetic Variation upon Selection for Spike Number in Salina Wildrye

Salina wildrye (Leymus salinus [M.E. Jones] Á. Löve) is a perennial cool-season grass that potentially could become an important restoration species in the Colorado Plateau. However, its seed production has never been commercially viable due to sparse heading. We compared a 4x ssp. salmonis population, Lakeside C₃, to an 8x ssp. salinus population, 9043501, for seed production ? related traits and measured the response of 9043501 to 2 cycles of selection for increased spike number over a 4-yr period at Millville, Utah. Seed yield of Lakeside and 9043501 was similar (P > 0.10) in 2013, but seed yield of 9043501 was 81% greater (P < 0.10) than Lakeside in 2014 and 191% greater (P < 0.01) in 2015. Lakeside spike number was 99% greater (P < 0.0001) than 9043501 in 2013, but they were similar (P > 0.10) in 2014 and 2015. Seeds per spike of 9043501 were 71% (P < 0.05), 80% (P < 0.05), and 209% (P < 0.01) greater than Lakeside in 2013, 2014, and 2015, respectively. Selection in 9043501 increased (P < 0.05) spike number by 4.3 spikes per plant (19.8%) per cycle of selection in the first seed-production yr (2013), but no change was seen in 2014 or 2015 (P > 0.10). Selection did not change (P > 0.10) seeds per spike or individual seed mass. Consequently, seed yield increased (P < 0.05) 0.32 g per plant per cycle (36.8%) in 2013, with no increase (P > 0.10) in 2014 or 2015. Dry matter per plant across the 4 yr increased (P < 0.01) 10.3 g per plant per cycle (9.3%), and canopy height increased (P < 0.01) 3.9 cm per cycle (6.6%) in 2013. AFLP DNA primers detected a 1.7% loss of genetic variation per cycle, presumably due to a combination of selection and genetic drift, but no plant traits were diminished as a result.     

野生高乌头开花习性及种子灌浆特性研究

利用甘肃永登县野生高乌头植株为研究材料,标记初花期一致的植株,每天测定单株开花数和蓇葖果数,并每隔3 d测定蓇葖果种子数、粒重和体积,对其开花结果动态和种子灌浆特性系统研究,旨在揭示其开花结果习性及其种子灌浆规律,为探寻高乌头种子发育规律及适宜采收期提供科学依据。结果表明,野生高乌头植株主花序花蕾自下而上依次开放。单花开放后第3天形成蓇葖果,第15天种子成形,并开始脱水形成干物质积累。单株开花数等于蓇葖果数,基本不落花,但仅主花序中部及以下部位蓇葖果具成熟种子。在种子整个灌浆过程中,百粒鲜重和干重的变化动态均呈“S”型曲线,符合Logistic方程。籽粒鲜重快增期在花后7～21 d,最大增长速率出现在花后14 d,在花后27 d达到最大,而干物质积累快增期在花后16～30 d,最大积累速率出现在花后23 d。开花36 d后蓇葖果脱落,种子灌浆和株上脱水中断,导致种子含水量达50%以上,采收后种子在快速脱水过程中可能形成深休眠特性,说明高乌头种子适宜采收期为开花后第36天左右(8月中下旬),蓇葖果尚未开裂时及时分批采收为宜。     

Spring Clipping,Fire, and Simulated Increased Atmospheric Nitrogen Deposition Effects on Tallgrass Prairie Vegetation

Defoliation aimed at introduced cool-season grasses, which uses similar resources of native grasses, could substantially reduce their competitiveness and improve the quality of the northern tallgrass prairie. The objective was to evaluate the use of early season clipping and fire in conjunction with simulated increased levels of atmospheric nitrogen deposition on foliar canopy cover of tallgrass prairie vegetation. This study was conducted from 2009 to 2012 at two locations in eastern South Dakota. Small plots arranged in a split-plot treatment design were randomized in four complete blocks on a warm-season grass interseeded and a native prairie site in east-central South Dakota. The whole plot consisted of seven treatments: annual clip, biennial clip, triennial clip, annual fire, biennial fire, triennial fire, and undefoliated control. The clip plots consisted of weekly clipping in May to simulate heavy grazing. Fire was applied in late April or early May. The subplot consisted of nitrogen applied at 0 or 15 kg N · ha^?1 in early June. All treatments were initially applied in 2009. Biennial and triennial treatments were reapplied in 2011 and 2012, respectively. Canopy cover of species/major plant functional groups was estimated in late August/early September. Annual clipping was just as effective as annual fire in increasing native warm-season grass and decreasing introduced cool-season grass cover. Annual defoliation resulted in greater native warm-season grass cover, less introduced cool-season grass cover, and less native cool-season grass cover than biennial or triennial defoliation applications. Low levels of nitrogen did not affect native warm-season grass or introduced cool-season cover for any of the defoliation treatments, but it increased introduced cool-season grass cover in the undefoliated control at the native prairie site. This study supports the hypothesis that appropriately applied management results in consistent desired outcomes regardless of increased simulated atmospheric nitrogen depositions.