“微观繁殖体”溯源

通过查阅"微观繁殖体"相关文献,对其概念进行溯源追踪并据以总结归纳。笔者认为"微观繁殖体"这个概念不应该作为放散的孢子、配子、合子、不同生长阶段的显微个体及有生长能力的大型海藻碎片的统称,而应只是泛指那些肉眼不可见的只进行营养繁殖的二倍体细胞团、脱落下来的组织块和"色素体"(有色藻段)等碎片,即是一个或者多个二倍体的藻类细胞。并以石莼属绿藻浒苔(Ulva prolifera)为例,简述浒苔微观繁殖体在其生活史中的主要作用,为浒苔"微观繁殖体"的理论研究和实际利用奠定基础。     

青海湖湖陆风的数值研究

用一个含植被参数化的二维中尺度模式研究青海湖夏季的湖陆风,模拟结果再次表明该模式具有重现局地中尺度环境特征,如冷（热）岛环境和湿岛等。同时表明,模式对植被覆盖度是敏感的,即有稀疏植被覆盖（σ＝３０％）情况的湖陆风白天比裸地情况要小,夜间则大,湖岸水平温度（或湿度）梯度随植被覆盖度增加而减小。     

Fragmentation as a Strategy for Caulerpa Species: Fates of Fragments and Implications for Management of an Invasive Weed

Abstract. The successful growth of fragments to full size macroalgal clones is well known for many taxa in mariculture. From an ecological context, however, few studies relate success by invasive species to the ability to fragment readily, disperse widely or re-attach rapidly - obvious hallmarks of weedy species. This study compares morphologically and ecologically distinct species of the green alga Caulerpa : in the Mediterranean, Caulerpa taxifolia is well known as an invasive weed; Caulerpa prolifera grows around or inside seagrass beds and is not apparently invasive; Caulerpa verticillata is among the most diminutive species, with potentially the most restricted reef distribution. We tested three hypotheses: (i) fragment success is independent of size, (ii) fragment success is independent of position within the plant and (iii) fragments from all species will be equally successful in establishing rhizoids, the first step to re-attachment. The success of small fragments (5–40 mm lengths) cut from distinct locations within replicate plants was scored for survival and establishment of rhizoids in bioassays. Additionally, for C. taxifolia , estimates were made of the force needed to puncture upright and prostrate axes, thereby estimating forces required to generate fragments from these two sources. Among the three species, only upright axes of C. taxifolia readily recovered from fragmentation stress for fragment sizes > 10 mm. The forces required to fragment upright axes were substantially less than for comparable rhizome portions. Fragments of C. prolifera were viable only for rhizome portions; fragments of C. verticillata were not viable at any size examined in this study. Estimates of viable fragment size, origin and force required to fragment axes for C. taxifolia support existing field data suggesting that fragmentation is the effective propagation mechanism underlying the spread of this invasive weed.     

Sediment particle selectivity and its response to overland flow hydraulics within grass strips

Particle selectivity plays an important role in clarifying sediment transport processes in vegetative filter strips (VFS). 10-m long grass strips at slopes of 5° and 15° were subjected to a series of sediment-laden inflows experiments with different particle sizes to investigate the sediment transport and its response to overland flow hydraulics. The inflow sediments came from local soil, river-bed sand, and mixed, with median particle size d₅₀ of 39.9, 207.9 and 77.4 μm, respectively. Three independent repeated experiments were carried for each treatment. The results show that when the sediment trapping lasted for a certain length of time, the re-entrainment of some small-sized particles was greater than the deposition; that is, net loss occurred, which was not erosion of the original soil. Net loss of particles is mainly determined by the particle diameter. The coarser the inflow sediment particles and/or the steeper the slope, the coarser the particles can be net lost. Deposited sediment causes the VFS bed surface to become smooth and hydraulic resistance decrease exponentially. Unit stream power P is more suitable than shear stress τ of overland flow to be used to describe the process of sediment particle transport in VFS. The relationship between P and d₅₀ of outflow sediment is very consistent with the form of power function with a constant term. These results are helpful to understand the physical process of sediment transport on vegetation hillslopes.     

Development of a simplistic vegetative filter strip model for sediment and nutrient retention at the field scale

Vegetative filter strips (VFSs) are a commonly used conservation measure to remove pollutants from agricultural runoff. The effectiveness of VFSs has been widely studied at the plot scale, yet researchers generally agree that field scale implementations are far less effective. The purpose of this research was to develop a field scale VFS submodel for the Soil and Water Assessment Tool (SWAT). A model for the retention of sediments and nutrients in VFSs was developed from experimental observations derived from 22 publications. A runoff retention model was developed from Vegetative Filter Strip MODel (VFSMOD) simulations. This model was adapted to operate at the field scale by considering the effects of flow concentration generally absent from plot scale experiments. Flow concentration through 10 hypothetical VFSs was evaluated using high resolution (2 m) topographical data and multipath flow accumulation. Significant flow concentration was predicted at all sites, on average 10% of the VFS received half of the field runoff. As implemented in SWAT, the VFS model contains two sections, a large section receiving relatively modest flow densities and a smaller section treating more concentrated flow. This field scale model was incorporated into SWAT and verified for proper function. This model enhances the ability of SWAT to evaluate the effectiveness of VFSs at the watershed scale. Published in 2009 by John Wiley & Sons, Ltd.     

鄂尔多斯半日花居群间营养器官的解剖学研究

对鄂尔多斯半日花不同居群间营养器官进行解剖学比较和分析,发现它们都具明显的旱生植物特征。但是由于其生境不同,叶表现为宽叶与细叶两种类型生长于沟边坡下较湿润环境的植株的叶较宽,一般不反卷,称其为宽叶型;生长于干燥阳坡上较干旱环境的植株的叶较窄,常反卷为针形,称其为细叶型。宽叶型的叶比细叶型的叶宽、长、厚,但角质层比细叶型薄,表皮毛比细叶型少,外切向壁不加厚,叶肉有栅栏组织和海绵组织的区别,上表皮气孔不下陷,由大型薄壁细胞形成维管束鞘。细叶型的叶上表皮气孔强烈下陷,叶肉无栅栏组织和海绵组织的区别,由木质化或栓质化细胞形成维管束鞘。同时,将鄂尔多斯半日花与其他几种旱生、中生植物叶的解剖特征进行了比较,其解剖学特征基本同其他几种旱生植物。     

Channel and vegetation recovery from dredging of a large river in the Gulf coastal plain,USA

Anthropogenic impacts in large rivers are widely studied, but studies of recovery once a disturbance has stopped are uncommon. This study examines the biogeomorphic recovery of a 40-km river corridor on the mid-Apalachicola River, Florida following the cessation of dredging, disposal, and snag removal in 2002. This failed navigation project resulted in vegetation losses (~166 ha between 1941 and 2004), river widening, and increased point bar areas. We used paired sets of imagery for a 10-year period during the recovery process at two different flow levels to assess sand bar change, land cover change, and their spatial variations. Most large sand bars decreased significantly in area due to growth of pioneer species, typically from the bankside of the bar. Mean bar area shrank 0.17 and 0.20 ha for the 30th and 1st percentile flows, respectively. For the entire study area, both water-level comparisons showed gains in vegetation (23.36 and 15.83 ha), compensated by losses in the extent of water (16.83 and 8.55 ha) and sand bar losses (6.53 and 7.28 ha). Overall, these gains during the 10-year passive recovery period are equivalent to ~15% of the vegetation losses that resulted from the navigational dredging. As found in other studies, most of the pioneer vegetation grew approximately 2 m relative elevation above the low-water surface. The initial length of the tree line and the area of herbaceous growth both had a significant and positive relationship with the area of new vegetation growth over the study interval. As parts of the river are healing, reduced channel capacity from narrowing and tree growth will benefit the floodplain. As elsewhere, understanding of a river's biogeomorphology, hydrology, and disturbance history can help in selecting appropriate recovery metrics to further advance the understanding and management of disturbed floodplains. © 2020 John Wiley & Sons, Ltd.     

Spatial variation of the vegetative roughness in Mediterranean torrential streams affected by check dams

This study focuses on the spatial variations in vegetative roughness associated with morphological channel adjustments due to the presence of check dams in Mediterranean torrential streams. Manning’s n values were estimated using methods established by previous studies of submerged and non-submerged vegetation in laboratory flume experiments and field work. The results showed a linear decrease in shrub density and rate of variation of the roughness coefficient versus degree of submergence with increasing distance upstream from the check dam, while downstream, the filling of the check dam and the bed incision had the most influence. A regression analysis was applied by fitting the data to different models: relationships between Manning’s n and the flow velocity were found to be of the power type for shrubs in all upstream sections, while relationships of flow velocity versus hydraulic radius in the sections closest to check dams showed a good fit to second-order polynomial equations.     

Vegetative reproduction by multicellular propagules in Rhodophyta: an overview

This paper deals with vegetative reproduction by multicellular propagules in Rhodophyta. An extensive examination of the relevant literature shows that this phenomenon in Rhodophyta is not well known. A propagule is here defined as a vegetative multicellular structure which spontaneously detaches from the parent thallus and gives rise to a new individual. The origin and morphological features of multicellular propagules are examined in the various known propagule‐forming species. The importance of multicellular propagules as both overwintering and resting organs and as a taxonomic feature is also shown. Their role in increasing local populations and/or for long‐distance dispersal is discussed. The relative abundance of vegetative reproduction by multicellular propagules versus sexual reproduction, as well as the advantages of this additional mode of reproduction, are shown and discussed. The production of multicellular propagules may contribute to the capacity of species to increase populations, to weather unpredictable environmental changes, to survive in conditions that would be lethal for entire thalli, and to reach new habitats. As resting organs, they may also be responsible for long‐distance dispersal and may account for the introduction of some alien species. Accordingly, propagule‐forming species are probably more competitive than taxa that do not produce such propagules. These considerations should be taken into account in future studies of the biology, ecology and demography of Rhodophyta.     

Two‐dimensional flow patterns near contour grass hedges

Grass hedges are narrow strips of stiff‐stemmed vegetation used to control erosion and sediment delivery. When planted on the contour, the hydraulic resistance of the vegetation slows runoff, creates ponding, and promotes sediment deposition. When tillage is performed between grass hedges, soil may be thrown against the vegetation, where it settles to form a berm within the hedge. Tillage‐induced berms divert part of runoff, causing it to flow alongside the hedge without crossing it. Such flow partitioning created by grass hedges was measured on experimental plots located on silt loam loess soil near Holly Springs, Mississippi, USA, where hedges planted at the bottom of 5%, 22.1‐m‐long slopes evolved berms averaging 0.13 m in height. They diverted about 80% of the runoff for events smaller than 5 mm and about 50% for large events. A two‐dimensional model was developed to determine overland flow patterns over complex terrains, accounting for oriented roughness created by tillage corrugations, crop rows, and larger features such as berms and vegetative barriers. The model was used to reproduce the flow partition observed in the field experiments and to determine how berm height and slope steepness and length affected runoff redistribution. Numerical simulations indicated that for most runoff events, ponded runoff depths were not high enough to overtop the berm but rather crossed the berms through cracks and gaps, represented in the model as small triangular weirs. The model also was applied to a 6.0‐ha watershed in Western Iowa, USA, where nine grass hedges were planted across 12–16% slopes. Computed dynamic flow properties showed that berms increased the amount of runoff flowing laterally upslope of the hedges and that a large portion of the runoff crossed the vegetative strips at a few locations and with high flow depths, increasing the risk of development of ephemeral gullies. Copyright © 2011 John Wiley & Sons, Ltd.