Endophyte Infection May Affect the Competitive Ability of Tall Fescue Grown with Red Clover

Cool-season grasses infected with Neotyphodium endophytes may be more persistent and competitive than non-infected plants. In a greenhouse experiment, two tall fescue ( Festuca arundinacea Schreb.) cloned genotypes (DN2 and DN11) with different growth characteristics and endophyte status (E−, non-infected; E+, infected) were grown in monocultures and in full competition with red clover ( Trifolium pratense L.) cv. Reddy Red for 20 weeks. When grown in monoculture, endophyte infection reduced the root dry matter (DM) of DN2 (16 %) and DN11 (5 %) when compared to E− plants, while shoot DM was not affected. In full competition with red clover, root and shoot DM of tall fescue were not influenced by endophytes, but cumulative herbage DM yield was less in E+ than in E− plants. Root growth of red clover was significantly depressed (22 %) in competition with E+ plants of DN2 compared to E− plants, but was not affected when plants were grown in competition with DN11. The relative yield total (RYT) did not differ from 1.0 in red clover mixtures with E− plants of DN2 and DN11, and with E+ plants of DN11, indicating competition between the competitors for the same resources. In contrast, RYT was less than 1.0 in the red clover/DN2 E+ mixture, suggesting a negative interaction between the competitors. Endophyte infection increased the competitive ability of DN2 but reduced that of DN11 when compared to E− plants. Because the concentration of pyrrolizidine alkaloids in roots of E+ plants of DN2 was twice that found in roots of DN11 (1083 and 536 μg g⁻¹, respectively), we suggest that pyrrolizidine alkaloids might influence the competitive ability of some endophyte–tall fescue associations through a possible allelopathic effect on companion species.     

关于竞争市场意识与建筑师的职能

市场导致竞争,建筑师的创作必须与市场经济相结合,市场经济改变了过去对于建筑师职能的理解,给建筑师提示了新要求。     

Nutrient Use Efficiency as a Factor Determining the Structure of Herbaceous Plant Communities in Low-Nutrient Environments

We tested the hypothesis that, in competition for nutrients, the plant species using more efficiently the limiting nutrient will tend to dominate in plant communities. Two experiments were conducted. In the first, plant communities consisting of perennial herbaceous species were grown in large boxes filled with soil enriched with all necessary nutrients, except for nitrogen (N) in half of the boxes and phosphorus (P) in the other half. It was expected that N or P, respectively, would become progressively limiting. In the second experiment, five perennial species, in monocultures and in mixtures of the five species, were grown in nutrient solutions of the combination of 3 levels of potassium (4, 16 and 64 µg ml⁻¹) × 2 levels of phosphorus (1 and 4 µg ml⁻¹) with all the other necessary nutrients at adequate concentrations for plant growth. In the first experiment, changes of the proportions of species biomass duration to community biomass duration between the second and the third years of the experiments were negatively related to species P shoot concentrations, but they were not related to species N shoot concentrations, probably because N did not become limiting. The second experiment showed that the species use efficiency of a particular nutrient (measured as the quantity of dry matter produced per g nutrient) was highest when the availability of this nutrient was lowest; the species with the highest use efficiency of a particular nutrient tended to have the highest relative abundance when this nutrient was limiting. The results of both experiments suggest that nutrient competition is important in low-nutrient environments and the species that use more efficiently the limiting nutrients have a competitive advantage and tend to dominate in the plant community.     

鄱阳湖生态经济区返乡农民工创业优势分析

从环境、竞争和产业3个方面分析了鄱阳湖生态经济区返乡农民工创业的优势,结果表明:鄱阳湖生态经济区返乡农民工在创业环境、创业竞争能力、产业竞争能力等方面占据优势,在现代生态农业、新型工业、休闲农业、现代农产品流通等领域发展过程中,返乡农民工具有得天独厚的优势,是建设鄱阳湖生态经济区的宝贵人力资源。     

四川王朗国家级自然保护区大熊猫与家畜竞争关系

基于四川王朗国家级自然保护区2009年的野生动物生境监测数据,利用列联表法、生态位重叠法和分布频率法,研究了大熊猫与家畜的竞争关系.结果表明:四川王朗国家级自然保护区的大熊猫与家畜竞争的主要环境条件是,海拔(A)为2500 m≤A＜3 000m的针阔混交林中,乔木特征是高度(D)为20 m≤D＜30 m、郁闭度(E)为...     

Balanced designs for two-component competition experiments

Summary Many two-variety competition experiments have plants of the two varieties systematically arranged on a triangular lattice of hill plots. Designs, balanced in a certain sense, are introduced and their advantages explained. An example of such a design is presented and compared with one of a more conventional nature.     

The Conductance model of plant growth and competition in monoculture and species mixtures: a review

Over the past two decades, an ecophysiological model has been developed for annual horticultural crops and weeds, which has the powerful ability to predict the growth of plants in monoculture and mixed species stands from parameter values derived from plants grown in isolation, even if the species display contrasting canopy architecture. The model can also simulate the effects of different spatial arrangements on plant growth. The purpose of the model is to describe, in simple yet mechanistically‐based terms, the effects of contrasting environments and competitive interactions on the growth of individual plants. In the simplest form of the model, growth is described by an empirical growth equation, using time calculated from an integration of the growth‐promoting effects of environmental factors. More complex versions of the model include a self‐shading component, which provides an algorithm for inter‐plant competition based on crown zone areas. This model is termed the ‘Conductance model’ and this article outlines its development, applications to date, goodness of fit to experimental data, and discusses its strengths and weaknesses and scope for further testing and application. This article, which is dedicated to the late David Aikman, also sets out how the model can be applied to simulating weed–crop competition from simple data sets.     

小麦不同类型品种混种竞争效应分析

采用生态学中的de Wit替代系列法研究了多穗型品种济南17和大穗型品种烟辐188两个优质小麦品种在混播条件下的竞争效应,并对产量构成要素进行比较分析。试验结果表明,在一定的密度变化范围内,济南17较烟辐188表现出较强的自身调节能力。混播条件下,烟辐188干物质积累速率明显低于播种比例的增加幅度,说明济南17具有更强的占有和利用共同资源的能力。     

不同类型猴樟混交林种间关系和冠层结构

以贵州人工栽培的猴樟纯林和3种类型的混交林为研究对象,采用Hegyi单木竞争指数模型对其种内、种间及全林分竞争强度进行定量研究,分析了不同混交组成树种的生态位宽度、生态相似系数和生态位重叠并测定了林分的冠层结构参数。结果表明:猴樟纯林的竞争最强,猴樟×杜英×楠木混交林是一个生态相似性较大、生态位重叠较高的混交组合,但目前竞争最小;猴樟×广玉兰×女贞混交林则是一个生态相似性小、生态位重叠较低且竞争比较强的混交组合,需要进行结构调整。研究结果反映出了不同混交组合中物种生态位宽度、生态位重叠和种间竞争关系的复杂性。混交林的冠层结构参数因树种组成、混交比例不同而异,总体上混交林的冠层参数空间异质性大于纯林。     

Effects of planting spacing and site quality on 25-year growth and mortality relationships of Douglas-fir (Pseudotsuga menziesii var. menziesii)

Growth and mortality of coast Douglas-fir (Pseudotsuga menziesii var. menziesii) were studied for 25 years after planting seedlings at 1–6-m spacings on a site of moderate quality in the western Cascade Mountains of Washington. Responses were compared to those from two other studies representing high and low site qualities. Third-year height did not differ among spacings (P = 0.80), providing no evidence that close spacing stimulated early growth. Piecewise regression identified the onset of competition-induced mortality when stand density index (SDI [Reineke, L.H. 1933. Perfecting a stand density index for even-aged forests. Journal of Agricultural Research 46, 627–638]) exceeded 52% (S.E. = 4.6) of the species’ maximum or when average crown ratio (CR) declined below 52% (S.E. = 0.9). For a range of SDI values, CR averaged 2–7% points greater at the high-quality site than at the moderate-quality site. In a regression analysis of combined data from the moderate- and high-quality sites, relative values of average stem diameter and stand volume (% of maximum values observed per site) 23–25 years after planting increased and decreased with planting spacing, respectively (R² = 0.97 and 0.91, respectively). Intersection of these relationships at 3-m spacing indicated a point of equivalent relative development of tree size and stand yield. For a range of site qualities, stands planted at 3-m spacing: (1) maintained tree vigor (CR ≥ 50%) and stability (average height:dbh ratio <90), (2) experienced little or no competition-induced mortality through age 25 years, and (3) allocated 25-year growth equitably to development of tree size and stand yield, thereby providing a desirable starting point for subsequent management.