Root proliferation in native perennial grasses of arid Patagonia,Argentina

Pappophorum vaginatum is the most abundant C4perennial grass desirable to livestock in rangelands of northeastern Patagonia,Argentina.We hypothesized that(1)defoliation reduce net primary productivity,and root length density and weight in the native species,and(2)root net primary productivity,and root length density and weight,are greater in P.vaginatum than in the other,less desirable,native species(i.e.,Aristida spegazzinii,A.subulata and Sporobolus cryptandrus).Plants of all species were either exposed or not to a severe defoliation twice a year during two growing seasons.Root proliferation was measured using the cylinder method.Cylindrical,iron structures,wrapped up using nylon mesh,were buried diagonally from the periphery to the center on individual plants.These structures,initially filled with soil without any organic residue,were dug up from the soil on 25April 2008,after two successive defoliations in mid-spring 2007.During the second growing season(2008–2009),cylinders were destructively harvested on 4 April 2009,after one or two defoliations in midand/or late-spring,respectively.Roots grown into the cylinders were obtained after washing the soil manually.Defoliation during two successive years did reduce the study variables only after plants of all species were defoliated twice,which supported the first hypothesis.The greater root net primary productivity,root length density and weight in P.vaginatum than in the other native species,in support of the second hypothesis,could help to explain its greater abundance in rangelands of Argentina.     

Impacts of livestock grazing on a savanna grassland in Kenya

The dynamics of most rangelands in Kenya remain to be poorly understood.This paper provides baseline information on the response of a semiarid rangeland under different livestock grazing regimes on land inhabited by the Massai people in the east side of Amboseli National Park in Kenya.The data were collected from grasslands designated into four types:(1) grassland from previous Massai settlements that had been abandoned for over twenty years;(2) grassland excluded from livestock grazing for eight years;(3) a dry season grazing area;and (4) a continuous grazing area where grazing occurred throughout all seasons.Collected data included grass species composition,grass height,inter-tuft distance,standing grass biomass and soil characteristics.The results indicated that continuous grazing area in semiarid rangelands exhibited loss of vegetation with negative,long-term effects on grass functional qualities and forage production,whereas grassland that used traditional Maasai grazing methods showed efficiency and desirable effects on the rangelands.The results also showed that abandoned homestead sites,though degraded,were important nutrient reservoirs.     

Productivity and persistence of perennial grass mixtures under competition from annual weeds in the alpine region of the Qinghai-Tibetan Plateau

In the alpine region of the Qinghai-Tibetan Plateau four indigenous perennial grass species Bromus inermis (BI), Elymus sibiricus (ES), Elymus nutans (EN) and Agropyron cristatum (AC) were cultivated as three mixtures with different compositions and seeding rates, BI + EN, BI + ES + AC and BI + ES + EN + AC. From 1998 to 2001 there were three different weeding treatments: never weeded (CK); weeded on three occasions in the first year (1-y) and weeded on three occasions in both the first and second year (2-y) and their effect of grass combination and interactions on sward productivity and persistence was measured. Intense competitive interference by weedy annuals reduced dry matter (DM) yield of the swards. Grass combination significantly affected sward DM yields, leaf area index (LAI) and foliar canopy cover and also species composition DM and LAI, and species plant cover. Interaction between weeding treatments and grass combination was significant for sward DM yield, LAI and canopy cover, but not on species composition for DM, LAI or species plant cover. Grass mixture BI + ES + EN + AC gave the highest sward DM yield and LAI for both weeding and non-weeding treatments. Species ES and EN were competitively superior to the others. Annual weedy forbs must be controlled to obtain productive and stable mixtures of perennial grasses, and germination/emergence is the most important time for removal. Weeding three times (late May, late June and mid-July) in the establishment year is enough to maintain the production and persistence of perennial grass mixtures in the following growing seasons. Extra weeding three times in the second growing year makes only a slight improvement in productivity.     

乌拉特荒漠草原群落物种多样性和生物量关系对放牧强度的响应

以内蒙古乌拉特荒漠草原灌丛和草本植物群落为对象,研究这2种植物群落的物种组成、物种多样性及其与地上生物量关系对不同放牧处理(对照、中牧、重牧)的响应。结果表明:①随着放牧强度的增加,灌丛群落中红砂(Reaumuria songarica)和碱韭(Allium polyrhizum)的优势度增大,沙生针茅(Stipa glareosa)的优势度减小;重牧降低草本群落中沙生针茅的优势度,增加了蒙古韭(Allium mongolicum)和碱韭的优势度。②不同放牧处理显著降低了灌丛和草本群落的盖度、高度以及灌丛群落的密度,消除了灌丛和草本群落之间盖度的差异(P> 0. 05)。中牧降低灌丛群落的Pielou均匀度指数,重牧降低灌丛群落的物种丰富度,灌丛和草本群落的其他多样性指数在放牧处理之间无显著差异(P> 0. 05)。除物种丰富度外,其他多样性指数在灌丛和草本群落之间差异显著(P <0. 05)。③不同放牧处理降低了灌丛和草本群落的地上生物量和凋落物量,导致灌丛和草本群落之间地上生物量的显著差异(P <0. 05)。④地上生物量与Simpson优势度指数负相关,与Shannon-Wienner多样性指数和Pielou均匀度指数正相关;放牧处理下地上生物量与密度、物种丰富度正相关。放牧处理改变了荒漠草原植物群落组成、结构和功能,进而改变了群落结构和功能的重要关系。     

Competition between palatable and unpalatable prairie grasses under selective and non-selective herbivory in semi-arid grassland

In a small plot study we used a systematic additive design to evaluate at what severity and frequency of defoliation sideoats grama (Bouteloua curtipendula) would remain competitive and recover from defoliation while growing with meadow dropseed (Sporobolus compositus). In the 3-year study plants were transplanted from pots into the experimental design when equal in size. When B. curtipendula was selectively defoliated moderately or severely, at both 30- and 60-day intervals, it still produced as much as when undefoliated growing with undefoliated S. compositus. Moderately defoliated B. curtipendula did not reduce biomass yield of S. compositus growing with it compared to when S. compositus was growing alone. When both plants were non-selectively defoliated severely, S. compositus responded very weakly and B. curtipendula recovered at the same rate as it had under the other defoliation treatments. The total biomass produced by both species growing together was highest when B. curtipendula was moderately defoliated. As soil moisture was not limited in this experiment we do not believe our results refute the hypothesis that selective grazing by livestock in these ecosystems has contributed to a reduction of B. curtipendula relative to S. compositus. Although S. compositus was reduced more than B. curtipendula by heavy nonselective defoliation this treatment is unlikely to produce desirable results in the long term as the highest total vegetation production occurred when B. curtipendula was moderately defoliated.     

Effects of grassland management on the community structure,aboveground biomass and stability of a temperate steppe in Inner Mongolia,China

Plant community structure responds strongly to anthropogenic disturbances, which greatly influence community stability. The changes in community structure, aboveground biomass(AGB), biodiversity and community stability associated with different management practices were studied with a three-year field investigation in a temperate steppe of Inner Mongolia, China. The species richness, Shannon-Wiener index, evenness, plant functional type abundance, AGB, temporal community stability, summed covariance, scaling coefficient and dominant species stability were compared among areas subjected to long-term reservation(R), long-term grazing(G), mowing since enclosure in 2008(M) and grazing enclosure since 2008(E). Site R had higher perennial grass abundance and lower species richness than sites G, M and E, although the AGB was not significantly different among the four sites. The species structure varied from a single dominant species at site R to multiple dominant species at sites G, M and E. The long-term reservation grassland had lower biodiversity but higher stability, whereas the enclosed grassland with/without mowing had higher biodiversity but lower stability. Different stability mechanisms, such as the compensatory dynamics, mean-variance scaling and dominant species stability were examined. Results showed that community stability was most closely related to the relative stability of the dominant species, which supports the biomass ratio hypothesis proposed by Grime.     

Effects of warming and clipping on plant and soil properties of an alpine meadow in the Qinghai-Tibetan Plateau,China

Climate warming and livestock grazing are known to have great influences on alpine ecosystems like those of the Qinghai-Tibetan Plateau(QTP) in China. However, it is lacking of studies on the effects of warming and grazing on plant and soil properties in these alpine ecosystems. In this study, we reported the related research from manipulative experiment in 2010–2012 in the QTP. The aim of this study was to investigate the individual and combined effects of warming and clipping on plant and soil properties in the alpine meadow ecosystem. Infrared radiators were used to simulate climate warming starting in July 2010, while clipping was performed once in October 2011 to simulate the local livestock grazing. The experiment was designed as a randomized block consisting of five replications and four treatments: control(CK), warming(W), clipping(C) and warming+clipping combination(WC). The plant and soil properties were investigated in the growing season of the alpine meadow in 2012. The results showed that W and WC treatments significantly decreased relative humidity at 20-cm height above ground as well as significantly increases air temperature at the same height, surface temperature, and soil temperature at the depth of 0–30 cm. However, the C treatment did not significantly decrease soil moisture and soil temperature at the depth of 0–60 cm. Relative to CK, vegetation height and species number increased significantly in W and WC treatment, respectively, while vegetation aboveground biomass decreased significantly in C treatment in the early growing season. However, vegetation cover, species diversity, belowground biomass and soil properties at the depth of 0–30 cm did not differ significantly in W, C and WC treatments. Soil moisture increased at the depth of 40–100 cm in W and WC treatments, while belowground biomass, soil activated carbon, organic carbon and total nitrogen increased in the 30–50 cm soil layer in W, C and WC treatments. Although the initial responses of plant and soil properties to experimental warming and clipping were slow and weak, the drought induced by the downward shift of soil moisture in the upper soil layers may induce plant belowground biomass to transfer to the deeper soil layers. This movement would modify the distributions of soil activated carbon, organic carbon and total nitrogen. However, long-term data collection is needed to further explain this interesting phenomenon.     

Compensation in seasonal leaf area dynamics and leaf longevity after defoliation in Buddleja davidii

Buddleja davidii is a major invasive weed and its success is attributed to its ability to recover rapidly following defoliation. To quantify the impacts of defoliation on seasonal leaf area dynamics, we measured rates of leaf area growth and loss on cohorts of leaves on control plants and on plants that were defoliated by 66% repeatedly at monthly intervals throughout two growing seasons. The rate of leaf area growth was closely related to cumulative air temperature, but the maximum rate for the defoliated plants in the first season was 2.2 times that of the control plants. This compensational leaf growth resulted in 52% greater total emergent leaf area, attributable to increased node production (34%) and leaf size (35%), compared with control plants. Leaf longevity during the first growing season in the defoliated plants was 12% greater than that in the control plants. During the second season, the degree of compensation was greatly reduced, attributable to reduced leaf size in defoliated plants compared with the control. Total emergent leaf area over both seasons in the defoliated treatment exceeded control values by only 15%. The impact of leaf loss on the vigour in this invasive shrub may, in the short term, be less significant than would be predicted. However, the impacts of continued defoliation are likely to increase markedly in subsequent years. The study provides the basis for modelling leaf area dynamics and plant growth in response to defoliation associated with biocontrol release programmes.     

Site‐related set‐back by weeds on the establishment of 12 biomass willow clones

Ten commercial clones of willow and two breeding clones were studied for their ability to compete with weeds during the establishment year at three different sites in southern Sweden. Cuttings were planted according to commercial practice in April, and the two treatments, ‘Weeded’ and ‘Unweeded’, were laid out in a strip‐plot design. Weeds in the ‘Weeded’ treatment were removed mechanically and by hand hoeing. Willow plant shoot weight and plant mortality were measured after the first growing season to evaluate the initial effect of weeds. In addition, weed flora, weed aboveground biomass, soil properties, shoot damage and soil moisture were assessed during the growing season. Plant mortality was <1% in the ‘Weeded’ treatment at the three study sites, while in ‘Unweeded’ it was significantly higher, 2.7%, 24.6% and 37.4%. Weeds reduced willow plant shoot weight by 93.4%, 94.0% and 96.1% at the three sites. Only one site showed clonal differences in shoot growth reduction, as well as in plant mortality. These results show the importance of weed control in willow plantations, as growth of all clones tested were dramatically hampered by weeds during the first growing season, regardless of trial site conditions. Moreover, conditions at certain sites, such as soil properties in combination with weed cover, may cause high plant mortality during the establishment year in this perennial biomass crop.     

Rangeland Monitoring and Fire: Wildfires and Prescribed Burning,Nutrient Cycling,and Plant Succession

Prescribed fires are used to manipulate and manage rangelands, but effective monitoring techniques are needed to ensure that management goals and objectives are being met. The application of an effective fire program on rangelands is not a simple task. Overgrazing by livestock since the early development of the livestock industry has altered the vegetative complex on most rangelands with an increase in woody plants. Because of its relatively low cost, prescribed fire, both cool and warm season, are sustainable practices if proper grazing management is part of the management scheme. Grazing management and prescribed fire have often been treated as separate issues by rangeland managers; however, development and application of an effective prescribed burning program requires an understanding of the relationship between fire and grazing. Ranchers need fuel (grass) to burn and they also need income from livestock, which requires forage (grass, a major part of forage). In the short-term, fire reduces carrying capacity for livestock but, in the long-term, fire increases grass production, resulting in increased carrying capacity. Therefore, some monitoring technique is needed that will allow the manager to budget grass for both fuel and forage. The Grazing Manager (TGM) is a software program that projects both forage production (expressed as animal unit days) and, animal demand (expressed as animal unit days) for each forage year. TGM has been successfully used on the Texas A&M University Research Station at Sonora as a tool to integrate prescribed fire and grazing management.     

Developing a prescription for brush control in the Chaco region,effects of combined treatments on the canopy of three native shrub species

Shrub encroachment is frequent in grazing lands in the Chaco region, Argentina. Fire is used by cattlemen to reduce the dominance of the shrub stands, improve forage standing biomass and quality, and enhance grazing accessibility. In this research, we assessed the combined effect of roller chopping?+?fire on the plant canopy of three native shrub species, Acacia gilliessi, Celtis ehrenbergiana, and Schinus bumelioides. We used a randomized design, with three factors, year, burn dates, and fine fuel load. Before the burn, the area received a roller-chopping treatment. Canopy volume reduction was assessed using, DifV?=??1*(V_i???V_a) and DifS?=??1*(S_i???S_a), respectively, where V?=?plant volume and S?=?sprout number. Suffixes i and a represent measurements taken before the roller-chopping treatment and one growth season after the fire, respectively. Fire intensity, headfire residence time, woody residues, and initial plant volume were evaluated as covariates. Results indicate a negative fire effect on canopy volume and sprouting. A. gilliesi was more susceptible to fire than the other two species. High fine fuel load and high fire intensity generated a severe effect on sprout number. The same trend was observed for coarse fuels. The canopy volume reduction was greater in A. gilliesi than the other species, reaffirming its high susceptibility to fire. Head fires were faster in 2009 than in 2008 and in the late than in the early burn dates. These results suggest that mechanical?+?fire treatments can be useful management tools for controlling shrub encroachment in the western Chaco.     

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.     

不同干扰对高寒草原群落物种多样性和生物量的影响

通过对新疆巴音布鲁克高寒草原天然草地进行灌溉、围栏(2年、7年、13年)和自由放牧处理,探讨不同干扰类型对草地植物多样性和生物量的影响。结果表明:灌溉使草地植物群落的高度、盖度和地上、地下生物量达到较高的水平,物种多样性也有一定程度的增加;而在自由放牧制度下,由于干扰过于剧烈,草地已呈退化趋势,物种多样性和生物量均较低;在围栏草地中,随着围封年限的增加,群落高度、盖度、地上、地下生物量逐渐增加,物种丰富度、多样性指数、均匀度指数呈现先增加后减小的趋势。在5种干扰类型中,物种丰富度、Shannon-W iener指数(H′)的排列顺序为:放牧草地<围栏2年草地<灌溉草地<围栏13年草地<围栏7年草地;P ielou均匀度指数的排列顺序为:围栏2年<放牧<灌溉<围栏13年<围栏7年;地上生物量的变化趋势为:放牧草地<围栏2年草地<围栏7年草地<围栏13年草地<灌溉草地;地下生物量的变化趋势为:放牧草地<围栏2年草地<灌溉草地<围栏7年草地<围栏13年草地。     

How precipitation and grazing influence the ecological functions of drought-prone grasslands on the northern slopes of the Tianshan Mountains,China?

Drought-prone grasslands provide a critical resource for the millions of people who are dependent on livestock for food security.However,this ecosystem is potentially vulnerable to climate change(e.g.,precipitation)and human activity(e.g.,grazing).Despite this,the influences of precipitation and grazing on ecological functions of drought-prone grasslands in the Tianshan Mountains remain relatively unexplored.Therefore,we conducted a systematic field investigation and a clipping experiment(simulating different intensities of grazing)in a drought-prone grassland on the northern slopes of the Tianshan Mountains in China to examine the influences of precipitation and grazing on aboveground biomass(AGB),soil volumetric water content(SVWC),and precipitation use efficiency(PUE)during the period of 2014–2017.We obtained the meteorological and SVWC data using an HL20 Bowen ratio system and a PR2 soil profile hydrometer,respectively.We found that AGB was clearly affected by both the amount and seasonal pattern of precipitation,and that PUE may be relatively low in years with either low or excessive precipitation.The PUE values were generally higher in the rapid growing season(April–July)than in the entire growing season(April–October).Overall,moderate grazing can promote plant growth under water stress conditions.The SVWC value was higher in the clipped plots than in the unclipped plots in the rapid growing season(April–July),but it was lower in the clipped plots than in the unclipped plots in the slow growing season(August–October).Our findings can enhance the understanding of the ecological effects of precipitation and grazing in drought-prone grasslands and provide data that will support the effective local grassland management.     

准噶尔瓣囊顶冰花物候及地下鳞茎形态变化观察

鳞茎植物是生存于干旱荒漠环境中的一类重要生活型类群。鳞茎植物以地下鳞茎作为营养贮存器官,鳞茎内的芽以休眠状态渡过不利季节,而在水份与温度等环境条件适宜时的迅速反应,很快完成一年的生活周期。近几年B.Boenken等人对以色列内格夫荒漠的几种鳞茎植物进行了生态与生物学方面的研究,目前国内还未见有这方面的研究报道。本文对分布于准噶尔盆地荒漠的瓣囊顶冰花的物候学特征进行了野外观察,并解剖和观察了地下鳞茎在更替过程中的形态发育变化。     

Ecophysiological factors contributing to the invasion of Panicum maximum into native Miscanthus sinensis grassland in Taiwan

Panicum maximum (guinea grass), a native grass of Africa, has invaded and displaced the native Miscanthus sinensis grassland at Dadu terrace in central Taiwan. The Dadu terrace has distinct wet and dry seasons and is prone to fire during the dry seasons. We compared photosynthesis and growth, as well as the growth response to two water treatments, between P. maximum and M. sinensis plants to understand ecophysiological factors contributing to the successful invasion of the grass. In comparison with M. sinensis, P. maximum had a significantly higher photosynthetic rate, larger specific leaf area and a higher leaf area/total biomass ratio, and thus grew faster and higher, and accumulated more biomass under well‐watered conditions. The growth of P. maximum was more susceptible than M. sinensis to drought stress. Faster growth of seedlings and more biomass accumulation of mature plants would give P. maximum a highly competitive advantage over M. sinensis for resource acquisition in the Dadu terrace during the wet season, which might contribute to the successful invasion of P. maximum into the grassland of M. sinensis.     

Interacting effects of soil degradation and precipitation on plant productivity in NE Patagonia,Argentina

Our objective was to examine the effects of inter-annual variation of precipitation on productivity of two dominant species (Chuquiraga avellanedae, an evergreen shrub, and Nassella tenuis, a perennial grass) in two communities of contrasting soil degradation: a herbaceous steppe with shrubs (HSS) and a degraded shrub steppe (SS). Data were collected during two consecutive years with different annual precipitation. Aboveground productivity was determined nondestructively using a double sampling approach. The number of inflorescences per plant was recorded too. Perennial grass productivity was lower in SS than in HSS in both years, while shrub productivity was lower in SS only during the year of below average precipitation. With rising precipitation the perennial grass increased the number of inflorescences while the evergreen shrub augmented vegetative biomass. In summary, the effects of precipitation on plant productivity are community dependent; abiotic factors, such as superficial and sub-superficial soil characteristics, and biotic factors, such as leaf area index (LAI) or tussock sizes, may interact to influence the responses of species to precipitation. Our results suggest that if precipitation increased, this would favor the dominance of shrubs over grasses.     

陇东苹果园生草复合体系土壤水分季节动态

陇东黄土高原半干旱区降雨年际变化较大,且年内分布不均,果园种草实践的优化不仅有助于减少干旱季节牧草对果园土壤水分过度消耗,还会促进其生态涵养效应的更好发挥。为探究种植不同牧草对旱作果园土壤水分季节动态的影响。试验设置4个处理,分别为在苹果园行间种植鸭茅、白三叶和混播牧草(鸭茅和白三叶)及清耕果园。结果表明:春季轻度干旱条件下,种植鸭茅和豆-禾混播牧草会降低果园土壤水分,但种值白三叶对果园土壤水分影响不显著;在夏季经历长期干旱之后,种植牧草显著降低了果园各土层的水分含量;整个生长季种植鸭茅、混播牧草和白三叶果园的蒸散量分别比清耕果园高45.3 mm、55.4 mm和0.7 mm,由此可知,在陇东黄土高原半干旱区苹果园内,不宜种植鸭茅等高耗水的禾本科植物,但可以种植白三叶等耗水少的豆科植物来改善果园环境。该研究结果对于陇东黄土高原旱作果园生草实践的改进具有一定的指导意义。     

科尔沁沙地70种草本植物个体和构件生物量比较研究

比较分析了科尔沁沙地70种草本植物盛花期时的个体和构件生物量特性。结果表明:43种植物个体生物量小于5.0 g,大部分物种根、茎、叶、花等构件的生物量均小于2.0 g,62种植物的根冠比小于1,说明70种草本植物中的大部分物种以地上生物量为主,只有少数物种具有较发达的地下根系。植物各构件生物量之间呈显著正相关,对个体生物量的贡献率为:茎>叶>根>花。多年生和1~2年生物种的个体生物量以及各构件生物量均无显著差异,但1~2年生物种的茎和地上生物量对个体生物量的贡献率显著高于多年生物种,而多年生物种的地下生物量对个体生物量的贡献率显著高于1~2年生物种,不同构件对生物量贡献率的差异有利于不同生活型植物的种群扩散和繁衍。     

基于MapReduce模型的生物量遥感并行反演方法研究

MapReduce模型是一种基于云计算平台下新型的并行编程模型。文中将MapReduce并行编程模型应用到遥感影像并行化处理中,以2005-2009年5a生长季期(5-10月)MODIS13Q1数据产品为数据源,对青海省三江源地区的生物量(草地总生物量和可食草量)进行并行化反演,研究基于该模型的生物量遥感并行反演方法。实验分析结果表明:基于该模型的并行生物量遥感反演结果与经过精度验证的串行反演结果一致,并行化反演结果准确、可信;并行化反演效率较串行化反演效率有大幅提高,并随着计算节点的增加,并行效率不断提高。