青土湖不同年限退耕地植被物种多样性及土壤酶活性研究

采用时空替代法,对甘肃省民勤县青土湖不同年限退耕地(退耕1 a、2 a、4 a、8 a、13 a、20 a、30 a、40 a)的植被演替特征、土壤酶活性进行调查,以耕地为对照(CK),分析植被群落与土壤酶活性的相关性,以揭示其变化规律及其驱动机制,为青土湖区及其相似地区退耕地生态系统修复及生态环境建设提供理论基础。结果表明：(1)青土湖在退耕40 a自然恢复过程中,9个样方中共出现16科32属42种植物,物种构成表现为：多数种归于少数科,大部分植物种为单属单科。(2)随着退耕年限的增加,群落优势种由草本植物逐渐转化成灌木植物,植物种由退耕初期(1 a或2 a)的19种降低到退耕4 a的14种、退耕20 a的13种、退耕30 a的5种;退耕30 a时耐盐碱灌木植物盐爪爪成为该地的优势种,其重要值达到52.862,但退耕40 a时优势种盐爪爪的重要值降为36.008。(3)随着退耕年限增加,植物Margalef丰富度指数呈波动式下降的趋势;Shannon多样性指数和Pielou均匀度指数总体趋势呈先增加后减小,再逐渐趋于稳定;Simpson优势度指数整体变化幅度较小,最终呈稳定的趋势。(4)在不同土层(0~20 cm和20~40 cm)中,4种土壤酶活性随退耕年限增加总体表现出先升高后下降再逐渐趋于稳定的趋势,均在退耕8 a后显著下降,且磷酸酶和脲酶活性均显著低于蔗糖酶和过氧化氢酶活性;与对照样地(CK)相比,磷酸酶活性与脲酶活性均随退耕年限增加而下降;土壤磷酸酶、蔗糖酶和脲酶活性均随土层加深而降低。(5)相关分析结果显示,0~20 cm土层中,物种数与土壤蔗糖酶活性、磷酸酶活性以及脲酶活性均呈显著正相关关系;20~40 cm土层中,物种数与土壤脲酶活性呈极显著正相关关系,与土壤过氧化氢酶活性呈显著负相关关系;Margalef丰富度指数与0~20 cm土层的磷酸酶活性和蔗糖酶活性均呈显著正相关关系,与脲酶活性呈极显著正相关关系;20~40 cm土层中,Margalef丰富度指数与脲酶活性呈极显著正相关关系;Shannon多样性指数、Pielou均匀度指数和Simpson优势度与4种土壤酶活性间相关性较低且均不显著。研究认为,在青土湖区退耕地植被自然演替过程中,植物群落变得比较单一,物种多样性逐年降低,脲酶活性对物种多样性起着关键性作用。     

浅层滑坡多发区典型灌木根系对边坡土体抗剪强度的影响

生态建设是"一带一路"可持续发展的基础,甘肃省陇南市位于"一带一路"核心区域,地处浅层滑坡多发区,地质灾害频发。通过单根抗拉试验和重塑土直接剪切试验对该区域四种典型灌木杠柳、胡枝子、酸枣和石榴的土壤及根系进行研究,探讨灌木根系对土壤物理性质和浅层滑坡的改善效应。结果表明,灌木根系能显著提高土壤含水率,改善孔隙结构;抗拉强度与根径间存在显著幂函数关系(P0.01),根径1 mm的毛细根抗拉强度最强,单根抗拉强度依次为胡枝子石榴酸枣杠柳;重塑土抗剪强度随土壤含水率升高而降低,土壤粘聚力(C)和内摩擦角(φ)均随含水率增加而减小,在10%的最优含水率下,抗剪强度依次为石榴酸枣杠柳胡枝子;随根系密度增加,杠柳和胡枝子的根-土复合体抗剪强度减小,酸枣和石榴在1.5倍天然根系密度下对土壤抗剪强度增强效果最强。通过评价浅层滑坡多发区不同灌木护土固坡效应,为"一带一路"沿线展开生态修复提供理论依据。     

Plant-Herbivore Interaction and Its Consequences for Succession in Wetland Ecosystems: A Modeling Approach

Herbivore grazing is increasingly used as a management tool to prevent the dominance of vegetation by tall grasses or trees. In this report, a model is described that is used to analyze plant-herbivore interactions and their scaling up to landscape scale. The model can be used to predict effects of herbivory on vegetation development. The model is an ecosystem model including modules for carbon and nitrogen cycling through plants, soil organic matter, and atmosphere. Plants compete for light and nitrogen. An herbivory module is included that implements selective foraging by a herbivore in a spatially heterogeneous area. Simulations were done to analyze the effects of herbivore density on vegetation dynamics, to analyze the impact of soil fertility on maximum herbivore density, and to analyze effects of herbivore density on landscapes. Two important points come forward from the model. Maximum herbivore abundance shows a hump-shaped curve along a soil fertility gradient. At higher soil fertility, light competition becomes more important. Herbivory interferes with plant competition, giving the tall, less palatable species a competitive advantage and thereby reducing the food quality and availability and hence the carrying capacity of the area. At a landscape scale, herbivory leads to increased heterogeneity. This increased heterogeneity may increase carrying capacity. The implications of these points for nature management are discussed. Received 13 May 1998; accepted 23 November 1998.     

Gene Flow and its Consequences in Sorghum spp.

Gene flow between crops and their weedy or wild relatives can be problematic in modern agricultural systems, especially if it endows novel adaptive genes that confer tolerance to abiotic and biotic stresses. Alternatively, gene flow from weedy relatives to domesticated crops may facilitate ferality through introgression of weedy characteristics in the progeny. Cultivated sorghum (Sorghum bicolor), is particularly vulnerable to the risks associated with gene flow to several weedy relatives, johnsongrass (S. halepense), shattercane (S. bicolor ssp. drummondii) and columbusgrass (S. almum). Johnsongrass and shattercane are common weeds in many sorghum production areas around the world. Sorghum varieties with adaptive traits developed through conventional breeding or novel transgenesis pose agronomic and ecological risks if transferred into weedy/wild relatives. Knowledge of the nature and characteristics of gene flow among different sorghum species is scarce, and existing knowledge is scattered. Here, we review current knowledge of gene flow between cultivated sorghum and its weedy and wild relatives. We further discuss potential avenues for addressing gene flow through genetic, molecular, and field level containment, mitigation and management strategies to facilitate successful deployment of novel traits in this economically important crop species.     

陆面模式中根系参数的改进及其对模拟结果的影响

为改进陆面模式中根系的参数化,本文在陆面模式SSiB2玉米农田参数本地化的基础上,将CERES-Maize的根系子模型嵌套到SSiB2模式中,研究2种改进的根系参数化方案对陆气通量模拟结果的影响.结果表明： 当根系模型只为SSiB2模式提供根系深度参数（方案1）时,陆气通量的模拟精度有所提高：整个生育期内,感热通量、潜热通量等的模拟值与观测值的相关系数增大,线性拟合的均方根误差减小;播种后121天 成熟,CO₂通量的模拟精度也有所提高.当根系模型为SSiB2模式同时提供根系深度和根长密度两种参数（方案2）时,上述通量的模拟精度较原SSiB2模式同样得以提高.与方案1相比,方案2考虑因素更为复杂、全面,但陆气通量的模拟效果却反而有所下降.改进的根系参数化方案较原SSiB2模式的根系参数化方案更接近实际,这使陆气通量的模拟精度提高;方案2过分夸大了表层土壤的相对根量,使其模拟效果逊色于方案1.     

西南地区松属侧根的强度特征对其防护林固土护坡作用的影响

森林植被固土护坡的机械效应主要源于树干和根系与斜坡土壤间的机械作用 ,具体包括土壤加强作用、锚固作用、斜向支撑作用、坡面负荷作用等。乔木根系的土壤加强作用是植被稳定土壤的最有效的机械途径 ;根系可以加强土壤颗粒对根的粘聚力和根际土层的聚合力 ,在土壤本身内摩擦角度不变的情况下 ,提高土层对滑移的抵抗力。加强作用可分为侧根的斜向加强作用 (或侧根牵引效应 )和垂直根的垂向加强作用[1,2 ] ,前者指侧向伸延的根系以侧根牵引阻力的形式提高根际土层斜向抗张强度从而提高土体抗滑力的作用。通常情况下 ,土壤滑动和蠕移首先在坡…     

Genetic diversity of Astragalus nitidiflorus, a critically endangered endemic of SE Spain,and implications for its conservation

Inter-simple sequence repeats (ISSR) markers were used to assess the genetic diversity and population structure in five populations of Astragalus nitidiflorus, a critically endangered species endemic to southeast Spain. Eight primers amplified 78 bands with 40 (51.3%) being polymorphic. Statistical results indicated a low genetic diversity at the population and species level, with percentages of polymorphic bands (PPB) ranging from 28.2 to 37.2% (an average of 31.8%), and means of gene diversity (H_E) of 0.129 and 0.171 respectively. The Shannon’s index (SI) ranged from 0.160 to 0.214 at the population level and was 0.260 at the species level. A low level of genetic differentiation among populations was detected, based on the Shannon’s information index (0.297), the coefficient of genetic differentiation between populations (G_ST = 0.2418) and AMOVA analysis (Φ_ST = 0.255). The estimated gene flow (Nm) was 0.789. The high genetic connectivity found among populations of A. nitidiflorus is an evidence of a recent habitat fragmentation. In addition, a bottleneck event in the past has been revealed, with a subsequent reduction of population size and a loss of genetic variation. Based on these results, the conservation strategy of A. nitidiflorus was proposed.     

Impact of cadmium and zinc on growth and water status of Zygophyllum fabago in two contrasting metallicolous populations from SE Spain: comparison at whole plant and tissue level

Cadmium and zinc accumulation and toxicity were assessed in whole plants and callus culture of two Zygophyllum fabago populations originating from two metallicolous sites in Murcia (southeast Spain), La Peña and Mazarrón, the first containing 2.8‐times more Cd and five‐times more Zn than the second. Seedlings from both ecotypes were exposed for 3 weeks to 1 or 10 μm Cd, and to 10 or 100 μm Zn in nutrient solution in a controlled environment. Calli from both ecotypes were exposed to 0.01, 0.1 or 1 mm Cd, and to 0.1, 1 or 5 mm Zn. Plants from both populations exhibited similar tolerance to Zn, while tolerance to Cd appeared more important in plants from La Peña than those from Mazarrón. Only minor differences were recorded in final Cd accumulation, with higher Cd retention in roots and stems of plants from La Peña. In both populations, transient decreases in the rate of Zn intake and translocation from root to shoot were recorded. This reduction in ion uptake was not more efficient for the population from the most contaminated area compared to the less contaminated area. Similar concentrations of Cd were found in cotyledon‐derived calli from the two populations, but absorbed Cd induced conspicuous water stress in calli issues from Mazarrón but not in those from La Peña. It is concluded that, beside comparable levels of heavy metal concentration in tissues, the physiological strategy of tolerance may differ according to the metal and according to the considered population.     

Re-sorption of organic compounds by roots of Zea mays L. and its consequences in the rhizosphere

The influx and efflux of sugar-C and the cycling of C within intact maize roots (Zea mays L.) was studied in sterile solution culture. Using metabolic inhibitors it was shown that roots could take up sugars against the concentration gradient probably via H⁺-ATPase dependent plasmalemma proton cotransporters. In contrast to this, no evidence was found for an ATPase mediated efflux of sugars from the root. All parts of the root were capable of taking up exogenous sugars. Examination of sugar exudation sites along the root slowed efflux at all locations, with the amount of efflux linearly correlated with internal cellular concentration. The results clearly indicated that the influxefflux mechanisms are linked both spatially, temporally and with respect to the sugars capable of transportation. The turnover of C within the root was found to be extremely rapid with turnover of the soluble sugar pool being 0.8 to 15 times daily depending on root spatial location. The results strongly suggest that the recapture of sugars from outside the root plays an important role in regulating the amount of C lost to the soil which in turn will reduce both pathogen attraction and the size of the rhizosphere microbial population and will also increase the plant's C efficiency.     

Relationships between soil parameters and vegetation in abandoned terrace fields vs. non-terraced fields in arid lands (Lanzarote,Spain): An opportunity for restoration

Over 90% of terraced fields have been abandoned on the island of Lanzarote in the last 40 years. The present work analyses the effects of abandonment on the soil and vegetation recovery of terraced field agroecosystems by comparing them with adjacent non-terraced fields in Lanzarote, Canary Islands (Spain). This information is necessary to take the appropriate management actions to achieve goals such as soil protection and biodiversity conservation. Results indicate that terraced fields display better soil quality than non-terraced ones, as shown by the significant differences found in parameters such as SAR, exchangeable Na, CaCO₃, B content, moisture content or soil depth. Moreover, the terraced fields' plant community has more species similarities with the native plant community when compared with non-terraced areas. Owing to characteristics such as deeper soils, more water capacity, lower salinity and less sodic soils, terraced soils provide better conditions for passive restoration of both soil and vegetation. Therefore, the recovery and maintenance of wall structures and revegetation with native/endemic species are proposed to promote the restoration of native systems and preserve a landscape with cultural and aesthetic value.     

Significance and limits in the use of predawn leaf water potential for tree irrigation

Research in estimating the water status of crops is increasingly based on plant responses to water stress. Several indicators can now be used to estimate this response, the most widely available of which is leaf water potential (Ψ_LWP) as measured with a pressure chamber. For many annual crops, the predawn leaf water potential (Ψ_PLWP), assumed to represent the mean soil water potential next to the roots, is closely correlated to the relative transpiration rate, RT. A similar correlation also holds for young fruit trees grown in containers. However, exceptions to this rule are common when soil water content is markedly heterogeneous. Two experimental conditions were chosen to assess the validity of this correlation for heterogeneous soil water content: 1) young walnut trees in split-root containers. The heterogeneity was created by two unequal compartments (20% and 80% of total volume), of which only the smaller was irrigated and kept at a moisture content higher than field capacity (permanent drainage). 2) adult walnut trees in an orchard. In this case, soil water heterogeneity was achieved by limiting the amount of localised irrigation (20% of the irrigated control) which was applied every evening. Values of sap flux and of minimum and predawn leaf water potentials with homogeneous and heterogeneous soil water content were compared for trees grown in the orchard and in containers. In spite of intense drought reflected by very low RT or stem water potential, Ψ_PLWP of trees under heterogeneous moisture conditions remained high (between -0.2 and -0.4 MPa) both in the orchard and in containers. These values were higher than those usually considered critical under homogeneous soil conditions. A semi-quantitative model, based on the application of Ohm's analogy to split-root conditions, is proposed to explain the apparently conflicting results in the literature on the relation between Ψ_PLWP and soil water potential. This revised version was published online in August 2006 with corrections to the Cover Date.     

Consequences of phenotypic plasticity vs. interspecific differences in leaf and root traits for acquisition of aboveground and belowground resources

Trade-offs between acquisition capacities for aboveground and belowground resources were investigated by studying the phenotypic plasticity of leaf and root traits in response to different irradiance levels at low nutrient supply. Two congeneric grasses with contrasting light requirements, Dactylis glomerata and D. polygama, were used. The aim was to analyze phenotypic covariation in components of leaf area and root length in response to above- and belowground resource limitation and the consequences of this variation for resource acquisition and plant growth. At intermediate shading (30 and 20% of full sunlight) the plants were able to maintain their total root length, despite a strongly increased total leaf area and a reduced biomass allocation to roots. This was associated with an unaltered or slightly increased nutrient uptake and growth. At 5.5% relative irradiance, growth was severely reduced, especially in the shade-tolerant D. polygama. The results show that constraints on acquisition capacities for aboveground and belowground resources, caused by biomass allocation, may be alleviated by plasticity in other traits such as tissue-mass density and thickness of roots and leaves. The results also suggest different adaptive constraints for phenotypic plasticity and for genetically determined interspecific variation. Phenotypic plasticity tends to maximize resource acquisition and growth rate in the short term, whereas the higher tissue-mass density and the longer leaf life-span of shade-tolerant species indicate reduced loss rates as a more advantageous species-specific adaptation to shade in the long term.     

Aerobiology of Artemisia airborne pollen in Murcia (SE Spain) and its relationship with weather variables: annual and intradiurnal variations for three different species. Wind vectors as a tool in determining pollen origin

Detailed results from a 2-year survey of airborne pollen concentrations of Artemisia in Murcia are presented. Three consecutive pollen seasons of Artemisia occurring each year, related to three different species (A. campestris, A. herba-alba and A. barrelieri), were observed. A winter blooming of Artemisia could explain the incidence of subsequent pollinosis in the Murcia area. With regard to meteorological parameters, mathematical analyses showed relationships between daily pollen concentrations of Artemisia in summer–autumn and precipitations that occurred 6–8 weeks before. The cumulative percentage of insolation from 1 March seemed to be related to blooming onsets. Once pollination has begun, meteorological factors do not seem to influence pollen concentrations significantly. Intradiurnal patterns of pollen concentrations were similar for late summer and winter species (A. campestris and A. barrelieri). During autumn blooming (A. herba-alba), the intradiurnal pattern was particularly erratic. Theoretical values of wind run were obtained for each pollen season by the graphical sum of hourly wind vectors. When theoretical wind run was mapped onto the vegetation pattern, supposed pollen source locations were obtained for each hour. By comparing supposed hourly pollen origins with the intradiurnal patterns of pollen concentrations, it can be seen that this simple model explains variations in mean pollen concentrations throughout the day. Received: 6 May 1998 / Revised: 24 February 1999 / Accepted: 12 March 1999     

The relationships between static and dynamic variables in the description of root growth. Consequences for field interpretation of rooting variability

Field root investigations are often limited by the static nature of classical observations, resulting in the need to develop alternative methodologies that allow dynamic interpretation of root architecture variability on the basis of static measurements. The objectives of this work were (i) to evaluate the use of selected morphological indicators, namely root apical diameter (Da) and the length of the apical unbranched zone (LAUZ), in predicting primary and lateral root growth patterns in banana trees, (ii) to propose a field methodology for the assessment of root dynamics based on static measurements. Banana trees (Musa acuminata cv `Grande Naine') were grown in 5 rhizotrons as well as in field conditions, respectively on pouzzolane and Mollic Andosols. In rhizotrons, root growth analysis was carried out by reporting root elongation, Da and LAUZ, three times a week. In field conditions, 4 series of excavations were made at three-week intervals. Apart from root growth rate, measurements were the same as those in the rhizotrons. LAUZ was confirmed as a stable and good predictor of root growth rate for the different types of roots. In the rhizotrons, the root growth of lateral roots was found to be well correlated to the product of Da and the growth rate of the bearing root. Evaluation in field conditions from static observations attested consistent relationships between measured and predicted root length for lateral roots (slopes close to 1:1). The apical diameter can be considered as a good indicator of root growth potential, while actual lateral root growth depends on the bearing root elongation rate. Morphological static indicators calibrated from growth dynamics in rhizotrons are of major interest in explaining growth variability in field conditions. Especially the `growth rate-LAUZ' relationship can be considered a useful tool in interpreting field patterns of growing roots in relation to various soil conditions.     

Growth of Anacystis in the Presence of Thiosulphate and its Consequences for the Architecture of the Photosynthetic Apparatus

With the aim of obtaining information on the degree of flexibility maintained in cyanobacteria in context with their phylogenetic position, Anacystis was grown in the presence of thiosulphate, oxidized in a photosystem I (PSI) dependent reaction (K_M 7.4 × 10^?3 M thiosulfate). Besides DBMIB, only o-phenanthroline and p-hydroxymercuribenzoate blocked thiosulphate-dependent PSI activity to some extent; iodonitrothymol, DCMU and cyanide had no influence. Growth of Anacystis in the presence of thiosulphate induced a reorganization of the photosynthetic apparatus characterized by a shift in the PSII/PSI ratio in favor of PSI, comparable to low light conditions. Capability for oxygenic photosynthesis never completely disappeared; structural elements of PSII were retained in the membrane to a certain degree. The antenna pigment system signalled high light under conditions of thiosulphate oxidation as judged from the ratio of phycocyanin to chlorophyll. Besides a shift in the ratio of PSII to PSI components, the polypeptide pattern of thylakoids from thiosulphate grown cells shows several additional components compared to the controls and, moreover, higher concentrations of some polypeptides present in the controls, particularly a M_r 41000 polypeptide. The process of thiosulphate oxidation appears bound to the thylakoid membrane.     

四川九顶山西坡红桦林天然种群空间格局及更新研究

用T-square距离方法,通过空间格局的T形指数C及其检验值Z₁,对九顶山西坡红桦种群中选取的3块样地6条样线进行了研究.结果表明,该区红桦种群空间分布格局以随机型分布为主,如样地支部牛场、十二河等,少数地区由于遭到人类的严重干扰和破坏,形成了集聚型分布格局,如样地上堰.通过分布距离指数I的进一步对照分析得出,在样线L4中,在主要的随机格局中也有少部分表现出了集聚型.本区红桦树种按其年龄段的不同分为3个年龄级:幼树、成年树、老年树.红桦幼树比较缺乏,仅占红桦树种的12%,而老年树种占24%,年龄结构为衰老型.在九顶山西坡,红桦种群已开始老化,幼树又相当缺乏,使红桦种群的自我更新面临极大威胁,建议加强对红桦林的保护和种群自我更新能力的研究.