Perceptions of Landowners Concerning Conservation,Grazing, Fire,and Eastern Redcedar Management in Tallgrass Prairie

Successful prairie restoration will depend in part on convincing private landowners with agricultural and recreational use goals to implement appropriate rangeland management practices, such as prescribed burning and cattle grazing, to control invasive species and encroachment of woody plants. However, landowners have been slow to adopt appropriate practices in the US Midwest. The purpose of this study was to explore attitudes and behaviors of private landowners toward prescribed burning and moderate stocking as rangeland management tools. A survey was mailed to 193 landowners (response rate 51%) in the Grand River Grasslands region of southern Iowa and northern Missouri. While 68% of landowners viewed grazing as a legitimate land management tool, only half of landowners thought of fire as a legitimate tool. Over 75% of respondents believed that the increase in eastern redcedar and other trees in grasslands was a problem, with 44% considering it a major problem. Although 84% of landowners said that they had taken action to control eastern redcedar, only 25% had participated in a prescribed burn. Income from agriculture and recreational goals were negatively and significantly correlated (-0.252, P = 0.035). While holding recreational goals constant in the analysis, landowners reporting income from agriculture goals as very or extremely important were negatively and significantly associated with reporting environment and grassland factors as very or extremely important. Adoption of prescribed burning by private landowners might be more widespread if proponents focus on the effectiveness of fire for controlling eastern redcedar, which is viewed as a problem by most landowners in the region. Intervention efforts must include landowners with different goals as part of the promotion and educational process.     

模拟降水和氮沉降增加对草地生物量影响的研究进展

研究降水和氮沉降增加对草地生态系统生物量的作用机制及其适应特征,有助于深刻理解气候变化对草地生态系统生产力和各项服务功能的影响,对草地生态系统的可持续发展具有重要意义。本文综述了模拟降水和氮沉降增加对草地植物生物量的改变及其可能的机制分析,探讨了植物对环境的适应特征,并在此基础上提出了未来气候变化条件下草地生态系统所面临的挑战和当前研究中主要存在的问题。     

模拟氮沉降对高寒湿地土壤理化性质和酶活性的影响

为研究氮沉降对土壤酶和土壤理化性质的影响,本研究在青海湖东岸开展野外控制试验,设计4个施氮水平0 g·m^-2,2 g·m^-2,5 g·m^-2和10 g·m^-2(分别为N0,N2,N5和N10),测定土壤养分和土壤酶活性。结果表明：氮沉降对土壤pH值和全磷含量无显著影响,硝态氮在浅层土中含量随施氮量的增加而逐渐下降,铵态氮在10 g·m^-2浅层土中含量显著高于其它处理,有机碳含量在2 g·m^-2处理下显著高于其它处理;酸性磷酸酶和脲酶随施氮量的增加活性显著升高,氮沉降抑制过氧化氢酶活性,碱性蛋白酶对氮沉降不敏感;相关分析表明,酸性磷酸酶、脲酶活性与铵态氮含量呈显著正相关关系,过氧化氢酶活性与硝态氮含量呈显著正相关关系,碱性蛋白酶活性与有机碳含量呈极显著正相关关系。本研究表明氮沉降影响高寒湿地碳、氮含量及其计量比,进而影响土壤酶活性。     

Burning and Climate Interactions Determine Impacts of Grazing on Tallgrass Prairie Systems

Tallgrass prairie may respond differently to prescribed burning and subsequent preferential grazing, termed pyric herbivory, under variable climate conditions. This 6-yr study (2011−2016) compared tallgrass prairie pastures that were subjected to burned and unburned conditions while exposed to grazing under differing climate conditions in the Southern Great Plains of the United States. The study area consisted of six pastures, three burned and three unburned. Each burned pasture was further divided into three patches and subjected to a 3-yr rotational burning cycle. The Enhanced Vegetation Index (EVI) derived from Landsat 7/8 (EVI_LS) and Moderate Resolution Imaging Spectroradiometer (MODIS, EVI_MOD) was used to indicate vegetation production depending on size of pastures. On the basis of EVI_LS, most burned patches (11 of 18) had lesser production (overall difference of 3%) than unburned patches within the same pasture. The differences were larger (13%) in a drought yr (2011) compared with normal (3% in 2013) and wet (<1% in 2015) yrs. The distribution of precipitation controlled EVI_LS for periods during and after grazing. The burned patches tended to have lower EVI_LS during grazing periods than the unburned patches within the same pasture, probably because of selective grazing of newly grown grass in recently burned patches. In contrast, the differences in EVI_LS between during and after grazing periods were mostly (78%) smaller in burned than unburned patches. However, more variations in EVI_LS existed among pasture comparisons due to landscape heterogeneity. Similar results were observed with EVI_MOD. Overall, results demonstrated that pyric herbivory management and climate determine the impacts of grazing on tallgrass prairie systems. The contrasting seasonal forage availabilities in burned and unburned patches, indicated by different seasonality of EVI, also suggests that patch burning might better balance the quantity and quality of the grass available for cattle grazing.     

Fire and Nitrogen Effects on Purple Threeawn (Aristida purpurea) Abundance in Northern Mixed-Grass Prairie Old Fields

Purple threeawn (Aristida purpurea Nutt. varieties) is a native grass capable of increasing on rangelands, forming near monocultures, and creating a stable state. Productive rangelands throughout the Great Plains and Intermountain West have experienced increases in purple threeawn abundance, reducing overall forage quality. Our objectives were to 1) reveal the effects of prescribed fire and nitrogen amendments on purple threeawn abundance and 2) assess nontarget plant response posttreatment. Season of fire (no fire, summer fire, fall fire) and nitrogen addition (0 kg N · ha^?1, 46 kg N · ha^?1, and 80 kg N · ha^?1) were factorially arranged in a completely randomized design and applied to two similar sites in southeastern Montana. We evaluated fire and nitrogen effects on purple threeawn basal cover, relative composition, and current-year biomass one growing season postfire at two sites treated during different years. Spring weather following fire treatments was very different between years and subsequently impacted community response. Initial purple threeawn biomass at both sites was 1 214 ± 46 kg · ha^?1 SEc. When postfire growing conditions were wet, current-year biomass of purple threeawn was reduced 90% and 73% with summer and fall fire, respectively. Under dry postfire growing conditions, purple threeawn current-year biomass was reduced 73% and 58% with summer and fall fire, respectively. Nitrogen additions had no effect on purple threeawn current-year biomass at either site. Current-year biomass of C₃ perennial grass doubled with nitrogen additions and was not impacted by fire during a wet spring. Nitrogen additions and fire had no effect on C₃ perennial grass current-year biomass following a dry spring. Prescribed fire appears to be a highly effective tool for reducing purple threeawn abundance on semiarid rangelands, with limited detrimental impacts to nontarget species.     

模拟干旱和氮沉降对唐古特白刺根系生长特征的影响

为深入了解氮沉降和干旱胁迫对植物生长特征的影响,本试验选择荒漠植物唐古特白刺（Nitraria tangutorum）,设置对照（田间最大持水量）与干旱（田间最大持水量的20%~40%）两个水分梯度以及0,6,36,60 mmol·L^-1 4个氮素浓度处理,研究模拟干旱和氮沉降对其根系生长特征的影响。结果表明：正常水分条件下唐古特白刺根系生长状况均优于干旱条件（P<0.05）;根直径和根尖数随着氮素浓度的增加而增加（P<0.05）;当氮素浓度为36 mmol·L^-1时,唐古特白刺的各项生长指标均表现为最佳状态。白刺各根系生长指标间相关分析表明,白刺总根长、根系平均直径、总表面积和总体积之间在水分和氮素交互作用下互相呈极显著正相关关系（P<0.01）。因此,本试验得出干旱胁迫抑制了氮素对根系生长的促进作用,而氮素的增加在一定程度上可缓减干旱对唐古特白刺的影响;在乌兰布和沙漠,干旱条件下氮沉降可能对唐古特白刺存在一定的补偿作用。     

模拟氮沉降和收获期对秋萌东方旱麦草生长与饲用品质的影响

短命植物东方旱麦草(Eremopyrum orientale)广泛分布于新疆北部,适时萌发,有助于缓解春季饲草短缺。为探究氮沉降和收获期对秋萌东方旱麦草生长与饲用品质的影响,本试验采用人工模拟方式,设置0 kg·ha^-1·a^-1,30 kg·ha^-1·a^-1,60 kg·ha^-1·a^-13个氮添加处理和2个收获时期(拔节孕穗期和开花期),分析不同处理下秋萌东方旱麦草生长指标和饲用品质指标变化。结果表明：在30 kg·ha^-1·a^-1,60 kg·ha^-1·a^-1氮添加条件下,秋萌东方旱麦草的株高、叶长、叶宽、分蘖数、茎粗、平均地上鲜重、粗蛋白和粗脂肪含量均高于0 kg·ha^-1·a^-1;同时,中性洗涤纤维、酸性洗涤纤维含量降低。与第一收获期相比,第二收获期东方旱麦草粗蛋白含量显著降低,中、酸性洗涤纤维与粗脂肪含量升高,平均地上生物量无差异。综合考虑东方旱麦草秋萌株的生长与饲用品质,在第一收获期(拔节孕穗期)和60 kg·ha^-1·a^-1氮添加下可获得最优饲草,但30 kg·ha^-1·a^-1较低水平氮沉降也能显著提升其生产力与饲用品质。     

Performance and Economic Returns of Stocker Cattle on Tallgrass Prairie Under Different Grazing Management Strategies

A 4-yr study was conducted to determine performance of stocker calves on tallgrass prairie under three grazing management strategies. Pastures were assigned to one of three grazing treatments. Grazing was initiated in June, and pastures were grazed only during the summer months for 57 to 104 d (79.5 ± 20.7 d). Two of the pastures were grazed season-long. Calves in one of the season-long treatments were fed a protein supplement during the second half of the grazing season; calves in the other season-long treatment were not supplemented (control group). The third pasture, an intensive early stocking (IES) treatment, was grazed at twice the stocking rate used in the season-long pastures for the first half of the grazing season (40 ± 11 d) and rested for the second half (39.5 ± 10 d). Individual stocker performance during the first half of the summer was similar among grazing treatments. Providing supplemental protein during the second half of the grazing season increased BW gain by 30 kg/ha during the last 40 d of the 80-d grazing season and increased BW gain by 12 kg/ha for the entire summer. Over the summer, IES stocker calves produced 24% more gain/ha than season-long stocked calves. Nonetheless, IES management was not more profitable than season-long grazing with or without protein supplementation. Under short-term ownership of calves in the IES system, fixed costs represented a large portion of the total cost.     

Plant Community and Soil Microbial Carbon and Nitrogen Responses to Fire and Clipping in a Southern Mixed Grassland

Disturbances, such as fire and grazing, play important roles in determining grassland plant community composition and soil microbial dynamics, as well as regulating the flows of carbon (C) and nitrogen (N) between the two groups of organisms. In a mixed grassland of the southern Great Plains, we tested the hypotheses that spring-season fire would increase the absolute biomass and relative proportion of C₄ grasses in the plant community, and decrease soil microbial biomass N, thereby increasing microbial C∶N ratios. We also tested the hypothesis that clipping (to simulate grazing) would reduce effects of fire, with a greater reduction of fire effect corresponding to an increased frequency of clipping. Contrary to our hypothesis, C₄ grasses showed no significant treatment responses. Treatment effects were limited to C₃ grasses, and clipping was more important than fire in terms of effects on plant community composition. However, because of its greater capacity to reduce aboveground litter, fire had the greater impact on soil microbial C. Contrary to the hypothesized outcome, no significant effects of disturbance on soil microbial N were observed. This suggests that control of N cycling in this ecosystem is primarily microbial in nature, though dependent on inputs of plant C via litter. Interactions between fire and clipping were observed in litter mass, highlighting the importance of litter inputs for plant–soil nutrient feedbacks.     

施肥和刈割对新麦草产草量影响的研究

本文研究氮肥,磷肥,钾肥和刈割次数的交互作用与新麦草人工草地产草量的动态关系。结果表明,氮肥,磷肥,钾肥和刈割次数间存在一定的交互作用。其中以氮肥与磷肥,氮肥与刈次间的交互作用较大;而钾肥与刈次间的交互作用较小。在试验范围内,氮肥,磷肥,钾肥和刈次的最佳组合为：每公顷施氮３１２千克,磷１７１千克,钾１２５千克,刈割２次。利用频数分析法给出产草量维持在一定水平的具体调控措施。     

羊草草原火烧效应的模拟实验研究

用控制火烧和模拟实验的方法研究了内蒙古羊草草原的火烧效应及其作用机理。实验结果表明,火烧对个别植物更新芽的伤害、火烧后土壤有效氮的变化和枯落物的移走是造成植物种 群及群落发生变化的重要原因,尤其是建群种羊草的显著增加更与火烧后优势种大针茅的受害和土壤有效氮的增加密切相关;而土壤有效氮的增加和羊草优势度的提高,则可能是群落内物种多样性发生变化的重要原因。     

模拟氮沉降对克氏针茅和碱韭种间竞争的影响

以克氏针茅和碱韭为研究对象,分析单播和混播种植方式下,氮沉降对两种植物地上生物量、地下生物量的影响,比较两种植物的竞争能力。结果表明:单播时,克氏针茅的株高随着施氮浓度的增加而上升且在施氮20 g/(m^2·yr)时显著高于其他处理(P<0.05),碱韭的株高在施氮20 g/(m^2·yr)时显著低于其他处理(P<0.05)。氮素对克氏针茅种群和碱韭种群都具有显著的调节效应,随着氮素梯度的增加,克氏针茅与碱韭的地上生物量、地下生物量、总生物量均有增加的趋势。克氏针茅对氮素添加的响应相比碱韭更明显,在单播时,克氏针茅在施氮10 g/(m^2·yr)时地上、地下及总生物量显著高于其他处理(P<0.05),混播时,克氏针茅在施氮20 g/(m^2·yr)时地上、地下及总生物量最大;在模拟氮沉降的过程中,克氏针茅与碱韭的种内竞争大于种间竞争,说明氮沉降对两者之间的竞争关系影响较小。     

Short-term Effects of Nitrogen Deposition on Soil Enzyme Activities in Tibet Grasslands

[Objective] The paper was to study the effects of nitrogen deposition on enzyme activity in different layers of soil. [Method] With grassland located in Zhuqudeng Village, Bujiu Township, Linzhi City, the Tibet Autonomous Region, as the object, nitrogen deposition was simulated from July 2014 to August 2015. Four N addition treatments were established: control(0 kg·hm2/a), low N(LN, 25 kg·hm2/a), medium N(MN, 50 kg·hm2/a) and High N(HN, 150 kg·hm2/a), aiming at measuring enzyme activity(invertase, catalase, urease, amylase, cellulase, polyphenol oxidase and β-glucosidase) in different layers of grassland soil(0-20 cm and 20-40 cm). [Result](1) Different levels of simulated nitrogen deposition had significant impact on invertase and β-glucosidase at the soil depth of 0-20 cm(P0.05), but no significant impact on catalase, urease, amylase, cellulase and polyphenol oxidase(P0.05); invertase, polyphenol oxidase and β-glucosidase had significant response to nitrogen deposition at the soil depth of 20-40 cm(P0.05), while catalase, urease, amylase and cellulose had no significant response( P0.05).(2) The activities of invertase and polyphenol oxidase were enhanced at the soil depth of 0-20 cm, and that of β-glucosidase was inhibited.(3) With the deepening of nitrogen deposition, the ac-tivities of invertase and cellulose were enhanced at the soil depth of 20-40 cm; the activity of polyphenol oxidase was reduced in LN treatment, but increased in HN treatment; the activity of β-glucosidase was increased in LN treatment, but decreased in MN treatment.(4) With the deepening of soil layers, invertase and polyphenol oxidase responded similarly to simulated nitrogen deposition. [Conclusion] The results provide certain scientific basis and fundamental data for better understanding and evaluating the effects of nitrogen deposition on enzyme activity in grassland soil.     

降水、氮沉降及放牧对草地生态系统凋落物分解的影响研究进展

草地生态系统对我国建设生态文明、提供生态系统服务、保障食品安全和维护边疆稳定有举足轻重的作用。全球气候变化和过度的人为干扰打破了草地生态系统原有的平衡及稳定性,造成草地退化、沙化和盐渍化现象严重。草地生态系统结构、功能与过程的稳定是保证草地生态系统稳定的基础。凋落物分解过程是草地物质循环的重要环节,对维持草地生态系统稳定性具有重要作用。草地生态系统凋落物分解对降水格局变化、大气氮沉降增加及放牧干扰的响应已有较多的研究。对目前国内外相关研究进行了梳理和总结,发现降水、氮沉降和放牧对草地生态系统凋落物分解的影响,因地理位置和气候变化以及草地类型的异质性而不同,也有针对同一地区开展的研究呈现不同结果的现象。目前对这三种干扰因素中的两因素或三因素交互作用对草地生态系统凋落物分解过程的影响研究较少,而研究气候变化及人为干扰对草地生态系统凋落物的影响对正确理解草地生态系统结构与功能,以及可持续利用与保护草地生态系统具有重要的意义。     

添加氮素对退化高寒草地植被及营养品质的影响

施肥是众多草地恢复措施中提高草地肥力的主要方式之一,为了探讨高寒退化草地适宜的氮(N)添加量,以高寒退化草地为研究对象,设置不同施氮水平N1(10 kg· hm-2),N2(20 kg·hm-2),N3(30 kg·hm-2),N4(40 kg·hm-2),分析添加氮素对高寒退化草地群落物种多样性,生产力及牧草品质的影...     

氮沉降对贝加尔针茅草原土壤真菌群落结构的影响

以贝加尔针茅草原为研究对象,采用高通量测序技术,研究连续6年模拟8个氮沉降水平（0,15,30,50,100,150,200,300 kg N·hm^-2·a^-1）对贝加尔针茅草原0~10 cm、10~20 cm土层土壤真菌群落结构的影响。结果表明,氮沉降显著影响真菌群落结构,0~10 cm土层与10~20 cm土层各氮沉降处理相对丰度在门、纲、属水平上均存在明显差异;且0~10 cm土层与10~20 cm土层土壤真菌群落对氮沉降的响应存在明显差异,存在明显的土层梯度效应。典范对应分析表明,土壤pH、有机碳、硝态氮和速效磷含量是影响贝加尔针茅草原土壤真菌群落结构变化重要因素。以上结果表明,氮沉降通过改变草原土壤的化学性质,影响了土壤真菌群落结构。     

春季禁牧对内蒙古草原植被的影响

2002年春季进行禁牧与自由放牧的对比研究。结果表明,春季禁牧对草原植被的群落特征具有十分显著的影响;在禁牧区,植被产草量、盖度、高度和密度等与自由放牧区之间差异显著(P<0.05)。春季禁牧有利于草原植被的可持续利用。同时,禁牧期的长短对草原植被也有一定的影响,但是不显著。     

Interactive Effects of Nitrogen Deposition and Grazing on Plant Species Composition in a Serpentine Grassland

The interaction of resource availability and disturbance can strongly affect plant species richness and the spread of exotic plants. Several ecological theories posit that disturbance mediates the richness-reducing effects of increased competition as resource levels rise. In the low-nutrient serpentine grasslands of the San Francisco Bay Area, the fertilizing effects of atmospheric nitrogen (N) deposition may threaten native species by promoting nitrophilic exotic grasses. Attempts to mitigate these N deposition effects have focused on cattle grazing as a strategy to reduce exotic grass cover. We simulated realistic N deposition increases with low-level fertilization, manipulated grazing with fencing, and monitored grazing intensity using camera traps in a 4 yr factorial experiment to assess the effects of grazing and N deposition on several measures of native and exotic species dynamics in California's largest serpentine grassland. Our results suggest that native species diversity may increase slightly under low-level N deposition with moderate grazing in this system. However, grazing may not be effective at limiting exotic cover as N accumulates in the future. Examination of treatment trajectories using principal response curves indicated that responses to grazing might be determined more by functional group (forb or grass) than origin (native or exotic). Grazing intensity varied dramatically within the single stocking rate used to manage this ecosystem. Given this variation and the contrasting effects of grazing on different functional groups, more targeted management may be required to improve conservation outcomes.     

CO2浓度升高、干旱胁迫和氮沉降对白羊草光响应曲线的影响

为揭示白羊草(Bothriochloa ischaemum (L.) Keng.)对全球气候变化的光合生理特征响应规律,采用盆栽控制试验,研究了白羊草在不同CO₂浓度、水分条件和施氮水平下叶片的叶绿素含量和光响应曲线特征。结果表明:随CO₂浓度升高和施氮量增加,白羊草叶片SPAD值,最大净光合速率(P_max),表观量子效率(AQE)和光饱和点(LSP)均呈增加趋势;干旱胁迫降低了SPAD值,P_max和LSP。多因素方差分析表明,CO₂浓度,水分处理和施氮水平对SPAD值,P_max和LSP有极显著影响,施氮水平对AQE有极显著影响。CO₂浓度和水分处理对P_max,AQE和LSP有显著的交互作用;CO₂浓度和施氮水平对P_max,AQE和光补偿点(LCP)有极显著的交互作用;水分处理和施氮水平对P_max,AQE和LSP有极显著的交互作用。RDA分析表明氮素是影响白羊草光合特征的最重要因素。全球CO₂浓度升高和氮沉降增加对干旱胁迫引起的白羊草光合速率下降有显著的缓解作用。