Edge effects on fauna in fragmented seagrass meadows

Abstract Fragmented habitats are a common occurrence in many marine systems, but remain poorly studied in comparison to their terrestrial counterparts. Here, I show that crustaceans inhabiting fragmented Zostera seagrass meadows show a dramatic response (change in abundance) to patch edges, with 11 out of 12 tests showing greatest abundance at the boundary between sand and seagrass. These patterns occurred on a scale of 0.25–1 m around the patch edge. Changes in seagrass biomass are unlikely to explain this pattern, as seagrass biomass increased smoothly at the patch edge, and did not decline towards patch interiors. In contrast to crustaceans, only a few polychaete taxa responded to the patch edge (9 of 25 tests), and bivalves generally did not show a response (1 of 5 tests). These latter groups are predominantly infaunal, and their lack of response may be partly due to the presence of substantial quantities of seagrass root and rhizome material in the sand habitat, which was defined visually based on the lack of above‐ground seagrass components only.     

Changes in plant species richness over the last century in the eastern Swiss Alps: elevational gradient, bedrock effects and migration rates

Areas of 2,800–3,000 m a.s.l. represent the alpine-nival ecotone in the Alps. This transition zone connecting the closed swards of the alpine belt and the scattered vegetation of the nival belt may show particularly strong climate warming driven fluctuations in plant species richness compared to the nival belt. To test this hypothesis, 12 summits within this range were investigated in the canton of Grisons, Switzerland in 2004. Complete lists of vascular plant species consisting of 5–70 species were collected on each summit and the elevation of the uppermost occurrence of each species was recorded. These data were compared to historical records over 120 years in age. Within this time, vascular plant species richness increased by 11% per decade on summits in the alpine-nival ecotone. Despite this considerable change, a comparison with nival summits did not support the hypothesis that species richness increase at the alpine-nival ecotone is higher than in the nival belt. A general trend of upward migration in the range of several metres per decade could be observed. Anemochorous species were more often found to be migrating than zoochorous or autochorous species and migration was higher on calcareous than on siliceous bedrock. A comparison between the summits with the adjacent slopes in our study revealed that changes in species number could be used as an indicator for climate-induced changes—if at all—only for the narrow summit areas.     

Transport of groundwater-borne phosphorus to Lake Bysjön,South Sweden

Lake Bysjön is a hypertrophic seepage lake, with groundwater as a main external source of phosphorus. Twelve groundwater samples from the vicinity of the lake were high in phosphate (0.4 to 11 mg l^–1, mean value 2.57 mg l^–1 PO₄-P), both within the riparian zone and in two shallow wells located upstreams the lake in the nearby village. Phosphorus sorption capacity of four sand samples measured with the Langmuir isotherm method was low (7.3 to 121,1 mg kg^–1 PO₄-P), with the lowest values found within the riparian zone. It is suggested that the phosphorus originates from garden fertilizers and other human sources, and that the low absorption capacity of the soils is caused by the leaching of calcium from the watershed, a process which started some 3000 years ago. Riparian zone itself has almost no retention capacity, and processes within it (e.g., redox-related) have only secondary importance for the transport of phosphorus to the lake.     

影响阜康荒漠-绿洲过渡带荒漠植物数量特征的土壤驱动力分析

荒漠-绿洲过渡带是绿洲向沙漠系统的过渡地带,荒漠植物是绿洲扩展或荒漠化加速的缓冲器,土壤环境是影响植物演变的重要影响因素,土壤环境因素是整个过渡带演化的重要驱动力。通过对阜康荒漠-绿洲过渡带荒漠植物群落实地调查,利用通用植物数量分析软件CANOCO 5.0中冗余度分析(RDA),探讨过渡带影响荒漠植物群落数量特征指标的土壤驱动因子。结果表明:(1)土壤含水量、全N、全P和有机质是影响荒漠植物群落数量特征的主要驱动力因子,环境解释量累计达到69%,而总盐、p H和全K对荒漠植物群落数量特征影响较弱;(2)4个土壤主要驱动力对荒漠植物群落数量特征重要性大小顺序:土壤含水量有机质全N全P;(3)荒漠植物群落数量特征与土壤含水量、有机质和全P呈正相关,但与全N为负相关关系,揭示了土壤含水量、有机质和全P是利于荒漠植物群落稳定的正驱动力,而全N为抑制荒漠植物生长的负驱动力。综上所述,土壤各因子的驱动力作用不尽相同,存在正、负差异,协同维护荒漠植物群落数量特征的稳定和发展。     

岷江干旱河谷-山地森林交错带震后生态恢复的关键科学技术问题

作为典型的生态过渡区，岷江干旱河谷-山地森林交错带不仅是藏羌居民生活的重要区域，而且在抑制干旱河谷上延和延伸亚高山森林生态系统的功能等方面具有十分重要的作用。但这种脆弱生态系统极易受到人类活动干扰和自然灾害的损害，使其成为“5．12”汶川大地震中受损程度较高、灾后生态恢复与重建的重点区域之一。基于岷江干旱河谷-山地森林交错带受汶川大地震破坏的特点以及该区的生态重要性和本身的脆弱性，损毁生态系统的快速评估与生态重建规划、生产与生态双赢共建关键技术、震后残存植被保育、水源涵养地植被保护与恢复、震毁植被恢复与重建、耕地生产恢复与重建、边坡综合治理、低效薪炭林改良以及居民聚居点风景林营造等被认为是震后生态恢复的关键科学技术问题。震毁生态系统的生态恢复过程监测与评估、干旱河谷-山地森林交错带生态系统的脆弱性机制及生态学过程、震后生态系统对变化环境的响应与适应机制等可能是未来的重点研究领域。     

塔克拉玛干沙漠南缘荒漠绿洲过渡带不同土地利用影响下土壤化学计量特征

荒漠绿洲过渡带在维护绿洲生态安全和绿洲稳定上具有重要作用。垦荒等土地利用的增强使得荒漠绿洲过渡带的健康稳定受到了巨大的挑战。以塔克拉玛干沙漠南缘典型荒漠绿洲过渡带为研究对象,系统分析了不同土地利用方式(桑田、半自然柽柳林、瓜地、棉花-玉米地)对土壤养分化学计量特征的影响。土壤取样沿农田到荒漠方向进行,分5层进行。研究发现,土壤各养分指标均受土地利用方式(4种)、土层(5层)和与农田边缘垂直距离(4梯度)的显著影响,且存在一定的交互作用。土地利用方式显著影响土壤各养分元素含量。随土层由浅到深,有机碳(C)、有效氮(N)和有效磷(P)基本呈下降趋势,全N具有波动变化,而全P变化不显著。随与农田边缘垂直距离的增加,各养分含量基本呈递减趋势。对同一土层(共选择三层)不同土地利用方式下土壤养分具体分析表明,棉花-玉米地这一利用方式在农田内部具有最高的土壤有机C和全N含量,其次为桑田。随着与农田边缘垂直距离的增加,土壤C、N含量优势减弱。除农田内部样地(0 m)外,三层土壤全P含量基本呈桑田柽柳林棉花-玉米地趋势。表层有效N含量在农田内部样地(0 m)瓜地最高,其他距离处(大于等于20 m)棉花-玉米地高,下层土壤有效氮含量在农田内部各土地利用方式间无差异。在各距离样点处不同土地利用类型间土壤有效P含量的变化无明显规律,在农田内部以瓜地有效P含量最高。棉花-玉米地土壤全量N/P在农田内部和与农田边缘垂直距离20 m处含量最高。三土层土壤有效N/P在农田内部以柽柳林最高,随着与农田边缘垂直距离增加,土壤有效N/P显著改变。综合来看,土地利用对荒漠绿洲过渡带土壤营养含量的增加具有正向作用,由土壤养分变化带来的生态效应值得关注。     

Distributional dynamics of a specialized subterranean community oppose the classical understanding of the preferred subterranean habitats

Troglobionts are organisms that are specialized for living in a subterranean environment. These organisms reside prevalently in the deepest zones of caves and in shallow subterranean habitats, and complete their entire life cycles therein. Because troglobionts in most caves depend on organic matter resources from the surface, we hypothesized that they would also select the sections of caves nearest the surface, as long as environmental conditions were favorable. Over 1 year, we analyzed, in monthly intervals, the annual distributional dynamics of a subterranean community consisting of 17 troglobiont species, in relation to multiple environmental factors. Cumulative standardized annual species richness and diversity clearly indicated the existence of two ecotones within the cave: between soil and shallow subterranean habitats, inhabited by soil and shallow troglobionts; and between the transition and inner cave zones, where the spatial niches of shallow and deep troglobionts overlap. The mean standardized annual species richness and diversity showed inverse relationships, but both contributed to a better insight into the dynamics of subterranean fauna. Regression analyses revealed that temperatures in the range 7–10°C, high moisture content of substrate, large cross section of the cave, and high pH of substrate were the most important ecological drivers governing the spatiotemporal dynamics of troglobionts. Overall, this study shows general trends in the annual distributional dynamics of troglobionts in shallow caves and reveals that the distribution patterns of troglobionts within subterranean habitats may be more complex than commonly assumed.     

高山林线交错带高山杜鹃的凋落物分解

凋落物分解是维持生态系统生产力、养分循环、土壤有机质形成的关键生态过程。高山林线交错带是陆地生态系统中对气候变化响应的敏感区域。季节变化和海拔梯度上的植被类型差异可能会影响该区域凋落物的分解,进而对高山生态系统的碳氮循环产生重要影响。采用凋落物分解袋的方法,研究了川西高山林线交错带优势种高山杜鹃(Rhododendron lapponicum)凋落叶在雪被期和生长季的分解特征。结果显示:(1)季节变化和植被类型对高山杜鹃凋落物的分解均具有显著影响(P0.05),凋落叶的质量损失主要发生在生长季且在高山林线最大,暗针叶林中雪被期的质量损失略高于生长季,但差异不显著;(2)林线交错带上高山杜鹃凋落叶分解缓慢,一年干物质失重率为9.62%,拟合分解系数k为0.145;(3)高山杜鹃凋落叶的质量变化主要体现在纤维素降解显著且集中在雪被期,木质素无明显降解,在高山林线上C/N、C/P、木质素/N变化幅度较小且C、N、P的释放表现得稳定而持续。结果表明,季节性雪被对林线交错带内高山杜鹃分解的影响不仅局限在雪被期内,雪被融化期间频繁的冻融作用和雪融水淋洗作用可能会促进高山杜鹃凋落物在生长季初期的分解。总的来看,在气候变暖的情景下,雪被的缩减、生长季的延长和高山杜鹃群落的扩张可能加速高山林线交错带高山杜鹃凋落物的分解。