中国东北部贝加尔针茅(Stipa baicalensis)草原生产量与生态因素的关系及其预测模型

 本文报道了贝加尔针茅(Stipa baicalensis)草原生产量与主要生态因素积温、降水和土壤有机质含量的关系。讨论了这些生态因素及其交互作用对草原生产量的影响。采用二次正交旋转回归设计和双重组合设计方法建立了贝加尔针茅草原生产量的预测模型,经对该模型的检验表明,所建模型可以在草原畜牧业生产中广泛应用．     

Vegetation gradient on the shores of Lake Nasser in Egypt

The paper, a synthesis based on data generated by our own investigation on Stipa baicalensis steppe for the period 1986–1988, deals with the relationships among biotic and abiotic factors at community ecology level. Analysis is placed on aboveground net primary production (ANPP), the energy source for livestock production process, and on accumulated temperature (5°C) (X₁), rainfall during the growing season of the steppe plants (X₂), and content of organic matter of surface soil (X₃), the abiotic variables most often used to explain variation in ANPP.The models predicting ANPP in Stipa baicalensis steppe were structured in terms of X₁, X₂, and X₃. The predictive power of the models was found to be very high, and the models were successfully validated in three cases with an independent data set.The prediction model that gave the best fitting in Stipa baicalensis steppe was% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbqfgBHr% xAU9gimLMBVrxEWvgarmWu51MyVXgaruWqVvNCPvMCG4uz3bqefqvA% Tv2CG4uz3bIuV1wyUbqee0evGueE0jxyaibaieYlf9irVeeu0dXdh9% vqqj-hEeeu0xXdbba9frFf0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea% 0dXdar-Jb9hs0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaacaqabe% aadaabauaaaOabaeqabaGaaeywaiaabIcacaWG4bGaaiykaiabg2da% 9iaaiwdacaaIYaGaaGioaiaac6cacaaIXaGaaG4maiaaikdacaaI4a% Gaey4kaSIaaGymaiaaikdacaGGUaGaaGymaiaaiMdacaaI0aGaaGio% aiaadIhadaWgaaWcbaGaaGymaaqabaGccqGHRaWkcaaI4aGaaGOmai% aac6cacaaI1aGaaG4naiaaicdacaaIXaGaaGimaiaaicdacaaIXaGa% amiEamaaBaaaleaacaaIYaaabeaakiabgUcaRiaaiwdacaaI3aGaai% OlaiaaigdacaaI5aGaaGioaiaaiEdacaWG4bWaaSbaaSqaaiaaioda% aeqaaOGaey4kaSIaaGymaiaaikdacaGGUaGaaGOnaiaaiodacaaI3a% GaaGynaiaadIhadaWgaaWcbaGaaGymaaqabaGccaWG4bWaaSbaaSqa% aiaaikdaaeqaaOGaeyOeI0IaaGOnaiaac6cacaaIXaGaaGOmaiaaiA% dacaaI1aGaamiEamaaBaaaleaacaaIXaaabeaakiaadIhadaWgaaWc% baGaaG4maaqabaaakeaacaqGGaGaaeiiaiaabccacaqGGaGaaeiiai% aabccacaqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabccacaqGRaGa% aeOmaiaabIdacaqGUaGaaeimaiaabIdacaqG3aGaaeynaiaadIhada% WgaaWcbaGaaGOmaaqabaGccaWG4bWaaSbaaSqaaiaaiodaaeqaaOGa% aeylaiaabodacaqG2aGaaeOlaiaabgdacaqG3aGaae4naiaabsdaca% WG4bWaa0baaSqaaiaaigdaaeaacaaIYaaaaOGaaeylaiaabccacaqG% ZaGaaeymaiaab6cacaqG0aGaaeinaiaabkdacaqG5aGaamiEamaaDa% aaleaacaaIYaaabaGaaGOmaaaakiaab2cacaqGYaGaaeOnaiaab6ca% caqGYaGaaeOnaiaabodacaqGZaGaamiEamaaDaaaleaacaaIZaaaba% GaaGOmaaaaaaaa!9ED0!\[\begin{gathered} {\text{Y(}}x) = 528.1328 + 12.1948x_1 + 82.5701001x_2 + 57.1987x_3 + 12.6375x_1 x_2 - 6.1265x_1 x_3 \hfill \\ {\text{ + 28}}{\text{.0875}}x_2 x_3 {\text{ - 36}}{\text{.1774}}x_1^2 {\text{ - 31}}{\text{.4429}}x_2^2 {\text{ - 26}}{\text{.2633}}x_3^2 \hfill \\ \end{gathered} \]We have also made, in detail, the analysis of the relationships among ANPP and 3 ecological factors above variables. ANPP was responsive to all of 3 ecological factors discussed in the paper. Action intensity, which has an effect upon ANPP, can be indicated by a contribution rate. The contribution rates of X₁, X₂, and X₃ were 1.069, 2.0513 and 1.8889, respectively.This paper not only discussed profoundly the relationships among ANPP and X₁, X₂, and X₃, but also studied exhaustively effects of the interactions X₁, X₂, and X₃, on ANPP.     

Comparison of some methods for collecting and analyzing data on aboveground net production and diversity of herbaceous vegetation in a northern Utah subalpine context

Our major objective was to compare methods of collecting and analyzing data on herbaceous aboveground net primary production and plant diversity in sequence of sites inferred to represent a meadow aspen fir spruce-sere in the middle Rocky Mountains. These comparisons should help us better interpret the literature and prepare for monitoring vegetation trends due to global climatic changes. Both absolute and relative values for above net primary production were highly dependent on methods used. The magnitude of differences in community diversity also varied greatly depending on the methods used to express plant richness, equitability, heterogeneity and dominance. We conclude that it is impossible to objectively test differences in production and diversity using data from single sampling dates and arbitrary choices of methods. In communities with great inter and intra-seasonal dynamics, an index of dominance that only measures magnitude (e.g. peak standing crop) was shown to have undesirable properties. We have demonstrated how average seasonal phytomass can overcome these problems by employing a measure of residence time as well as magnitude.Abbreviations ANPP = aboveground net primary production - ASP = average seasonal phytomass - NCSC = net aboveground community standing crop - PCSC = peak community aboveground standing crop     

Affinity analysis: methodologies and statistical inference

Affinity analysis (AA) is a group of methods for the study of the variation of degrees of compositional relatedness among all of the communities in a landscape. AA cab be used with statistical inference to compare mosaic diversities (89-1) among different landscapes, identify unusual sites within a landscape, and determine when a pair of sites are significantly different from each other. These procedures were done with a set of samples from meadows in the Danube River Valley near Ulm by using random simulations to provide expectations of the summary statistics. The sampling and statistical limitations of AA were discussed.     

Gradient analysis of reversed treelines and grasslands of the Valles Caldera,New Mexico

Objective: : Treeless meadows and parks are widespread but poorly understood features of the montane vegetation of the western USA. These communities frequently form reversed treelines where grassy valleys occur below forested slopes above. Our purpose was to assess the environmental correlates of such treelines, as well as patterns in the composition and diversity of grasslands and forest margins in the Valles Caldera National Preserve. Location: Valles Caldera National Preserve (35°50′‐36°00’ N, 106°24′‐106°37’ W, 2175–3150 m), Jemez Mountains, New Mexico, USA. Methods: We conducted a gradient analysis based on 200 nested quadrats on transects crossing reversed treelines and spanning the compositional heterogeneity of grasslands. We used cluster analysis and non‐metric multidimensional scaling to assess relationships between compositional variation and environmental variables. Results: We found strong, highly significant relationships of the vegetation to gradients in slope inclination, soil texture, moisture, nutrient availability, and nighttime minimum temperatures. Reversed treelines are most strongly associated with shifts in the thermal regime, exhibit weaker relationships with soil texture and nutrient content, and show no relationship with gravimetric soil moisture. Gradients in aspect, soil moisture, and annual mean temperature are associated with compositional variation within grasslands and forest margins. Conclusions: Lower nightly minimum temperatures and fewer consecutive frost‐free days resulting from cold‐air drainage may prevent tree seedling establishment in valley bottoms via photo‐inhibition, tissue damage, or frost heaving. Fine‐textured soils may also impede tree seedling establishment in valley bottoms. These findings lay the groundwork for experimental and physiological tests of these potential causes of these reversed treelines.     

Genetic diversity analysis and conservation implications for the Iberian threatened populations of the irano-turanian relict Krascheninnikovia ceratoides (Chenopodiaceae)

Krascheninnikovia ceratoides (L.) Gueldenst. (Chenopodiaceae) is an irano‐turanian steppe plant with a striking geographical vicariance between the western Mediterranean and the central Asian regions. Its westernmost populations are located in the north‐east part of the Iberian Peninsula, in the narrow middle Ebro and Alfambra valleys, where they are threatened and have been catalogued as ‘vulnerable’. Genetic diversity and structure was studied in 150 individuals from five populations of these two valleys using inter‐simple sequence repeats (ISSR). A total of 121 informative bands allowed the identification of 150 genotypes. Nei's genetic diversity found in all natural populations (h = 0.448) was higher than that of other geographical restricted species. Analysis of molecular variance and spatial correlations analyses showed a strong genetic differentiation among populations (35.88%) and among valleys (22.33%). The unweighted pair‐group method of arithmetical averages and Neighbour‐joining clusterings further demonstrated a substructure of two population cores within the Ebro valley. Our genetic data suggest that the high levels of genetic diversity and the strong genetic structure found among the northern Iberian populations and ranges of K. ceratoides might result from the summed effects of its tetraploidy, its outbreeding nature, and its success in colonizing newly altered areas. However, the ISSR data might also reflect the existence of an ancient wider distribution range of the plant in the Iberian Peninsula coupled with a more recent history of habitat fragmentation. Different management conservation guidelines are recommended for this plant after our genetic analysis: a microreserve of approximately 2 km² is proposed for the highly threatened population of Osera (Ebro valley), whereas seed collection strategies and occasional population reinforcements are suggested for the remaining populations. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92 , 419–429.     

Effects of simulated grazing on different genotypes of Bouteloua gracilis: how important is morphology?

Populations of grasses exposed to grazing by vertebrates often exhibit reduced stature, increased tillering, reduced flowering, and other morphological differences which distinguish them from ungrazed populations. These differences frequently are interpreted as an adaptive response that reduces grazing damage; however, there are few experimental tests of this hypothesis. This paper describes a field experiment designed to determine whether morphological variation among genotypes of the grass Bouteloua gracilis is related to variation in their responses to grazing. Eleven genotypes differing in morphological and reproductive characters were transplanted into a shortgrass steppe community near Fort Collins, Colorado. Replicates of each genotype were subjected to clipping treatments intended to realistically simulate three grazing intensities. After two growing seasons, different genotypes still maintained significant differences in a wide range of morphological and demographic characters. However, there were few significant effects of grazing treatment, and no significant genotype×treatment interactions. These results suggest that for B. gracilis clipped in simulation of natural grazing, defoliation has few short-term effects on fitness components, and intrapopulation morphological variation has few consequences for defoliation resistance. Received: 22 March 1999 / Accepted: 26 October 1999     

Neutral responses of plant community Ca concentration to nitrogen enrichment in a semiarid grassland

氮沉降对半干旱草原植物群落钙浓度的影响 钙(Ca)是植物生长所必需的营养物质,牧草中钙的含量对反刍动物的饲粮和健康具有重要意义。目前,关于氮沉降增加是否改变牧草的Ca浓度仍不是十分清楚。我们于2008–2015年在中国北方半干旱草原开展了氮沉降速率增加实验,测定了不同氮处理下每个样方内所有植物的Ca浓度,并且 根据各样方内每个物种的Ca浓度及其相对生物量,计算出功能群水平和群落水平的植物Ca浓度。研究结果表明,尽管物种水平和功能群水平的Ca浓度对氮沉降表现为负响应,但群落水平Ca浓度在整个氮添 加速率梯度上保持稳定。由于杂类草Ca浓度显著高于禾草,杂类草相对生物量的增加抵消了物种水平和功能群水平Ca浓度对氮沉降的负响应。另外,群落Ca库对氮添加速率表现为正饱和响应,且阈值为10 g N m−² yr−¹。本研究表明了氮沉降背景下植物相对生物量的变化对调控牧草Ca浓度和储量具有重要作用。     

Microbial N Turnover and N-Oxide (N<Subscript>2</Subscript>O/NO/NO<Subscript>2</Subscript>) Fluxes in Semi-arid Grassland of Inner Mongolia

Gross rates of N mineralization and nitrification, and soil–atmosphere fluxes of N₂O, NO and NO₂ were measured at differently grazed and ungrazed steppe grassland sites in the Xilin river catchment, Inner Mongolia, P. R. China, during the 2004 and 2005 growing season. The experimental sites were a plot ungrazed since 1979 (UG79), a plot ungrazed since 1999 (UG99), a plot moderately grazed in winter (WG), and an overgrazed plot (OG), all in close vicinity to each other. Gross rates of N mineralization and nitrification determined at in situ soil moisture and soil temperature conditions were in a range of 0.5–4.1 mg N kg⁻¹ soil dry weight day⁻¹. In 2005, gross N turnover rates were significantly higher at the UG79 plot than at the UG99 plot, which in turn had significantly higher gross N turnover rates than the WG and OG plots. The WG and the OG plot were not significantly different in gross ammonification and in gross nitrification rates. Site differences in SOC content, bulk density and texture could explain only less than 15% of the observed site differences in gross N turnover rates. N₂O and NO _x flux rates were very low during both growing seasons. No significant differences in N trace gas fluxes were found between plots. Mean values of N₂O fluxes varied between 0.39 and 1.60 μg N₂O-N m⁻² h⁻¹, equivalent to 0.03–0.14 kg N₂O-N ha⁻¹ y⁻¹, and were considerably lower than previously reported for the same region. NO _x flux rates ranged between 0.16 and 0.48 μg NO _x -N m⁻² h⁻¹, equivalent to 0.01–0.04 kg NO _x -N ha⁻¹ y⁻¹, respectively. N₂O fluxes were significantly correlated with soil temperature and soil moisture. The correlations, however, explained only less than 20% of the flux variance.