Loss of functionally important and regionally endemic species from streams forced into intermittency by global warming

Climate change is altering hydrological cycles globally, and in Mediterranean (med-) climate regions it is causing the drying of river flow regimes, including the loss of perennial flows. Water regime exerts a strong influence over stream assemblages, which have developed over geological timeframes with the extant flow regime. Consequently, sudden drying in formerly perennial streams is expected to have large, negative impacts on stream fauna. We compared contemporary (2016/17) macroinvertebrate assemblages of formerly perennial streams that became intermittently flowing (since the early 2000s) to assemblages recorded in the same streams by a study conducted pre-drying (1981/82) in the med-climate region of southwestern Australia (the Wungong Brook catchment, SWA), using a multiple before-after, control-impact design. Assemblage composition in the stream reaches that remained perennial changed very little between the studies. In contrast, recent intermittency had a profound effect on species composition in streams impacted by drying, including the extirpation of nearly all Gondwanan relictual insect species. New species arriving at intermittent streams tended to be widespread, resilient species including desert-adapted taxa. Intermittent streams also had distinct species assemblages, due in part to differences in their hydroperiods, allowing the establishment of distinct winter and summer assemblages in streams with longer-lived pools. The remaining perennial stream is the only refuge for ancient Gondwanan relict species and the only place in the Wungong Brook catchment where many of these species still persist. The fauna of SWA upland streams is becoming homogenised with that of the wider Western Australian landscape, as drought-tolerant, widespread species replace local endemics. Flow regime drying caused large, in situ alterations to stream assemblage composition and demonstrates the threat posed to relictual stream faunas in regions where climates are drying.     

新疆短命植物小拟南芥(Arabidopsis pumila)种子萌发特性及其生态适应性

通过显微结构及不同处理条件下种子萌发率的观察,对早春短命植物小拟南芥(Arabidopsis pumila)种子萌发特性及影响因素进行了研究,并对其生态适应性进行了讨论。结果表明:(1)温度和光照变化对自然生境和温室收获种子的萌发率影响均不显著,说明此种群在前期萌发阶段对光、温不敏感;(2)自然生境中采收的小拟南芥种子萌发率显著低于温室收获种子,说明环境条件的变化对短命植物种子的发育具有重要作用,可显著改变种子的萌发行为;(3)赤霉素使自然生境收获种子胚活性增强从而对萌发有较大促进作用,可使萌发率增加50%以上;(4)对种皮进行各种机械损伤处理使得种皮松弛或透气,可以显著提高自然生境种子的萌发率(超过70%);(5)盐和干旱胁迫对种子萌发均具有明显的抑制作用,但复水后部分被抑制种子可重新萌发,显示盐和干旱胁迫可导致种子产生浅度休眠。结合小拟南芥自然生存环境及本研究的结果,显示其种子萌发特性与生境具有高度适应性。     

Leaf litter decomposition in an ephemeral karst lake (Chaney Lake,Kentucky, U.S.A.)

Litter decomposition in temporary aquatic environments has not been experimentally studied as much as it has in perennial systems. However, litter is likely a critical resource for organisms inhabiting ephemeral aquatic habitats. In this study, we used litterbags under different conditions of submergence and water physical and chemical properties/characteristics to study mass and nutrient losses of terrestrial materials in an ephemeral karst lake in south-central Kentucky (USA). In the first experiment, which was designed to compare decomposition rates in submerged and dry sites, total mass and carbon declined more rapidly in the litter at fully submerged sites than in dry sites. In the second experiment, which was designed to compare decomposition rates in two different submerged environments, total mass and carbon showed similar decomposition trends between the two submerged areas with different seasonal temperature patterns. Nitrogen patterns were variable but in general nitrogen levels increased in the litter in both experiments over a period of several months. These results are similar to those found in some perennially inundated systems and indicate that litter decomposition dynamics in this temporary lake can be greatly affected by lake hydrology. Year-to-year variations in hydrology may thus have strong impacts on nutrient and energy release within this system, which may affect the organisms within this karst lake and in other areas of the karst ecosystem that are ecologically connected to it.     

Island biogeography of temporary wetland carabid beetle communities

Aim The study tests if island biogeography is applicable to invertebrate communities of habitat islands in the agricultural landscape that are not fragments of formerly larger habitats. Location Thirty temporary wetlands in the agricultural landscape of northeast Germany. Methods The composition and species richness of carabid beetle communities was analysed. Habitat area, isolation, the density of temporary wetlands in the landscape, land‐use intensity and the maximum duration of flooding were recorded as independent variables. Overall species richness and wetland species richness were studied in independent regression analyses. The community composition was analysed by means of a Canonical Correspondence Analysis (CCA). A partial CCA was used to analyse the effect of the distance to the edge of the field after removing impacts of other independent variables. Results The area of the habitats and various measures of isolation (mean distances = 81–240 m) did not influence species richness or wetland species richness. The community composition was mainly determined by the land‐use intensity, habitat area did not have significant effects, and the distance to the edge of the field was the only effective isolation parameter. Short‐winged species were more often affected by the distance to the edge of the field than full‐winged species. Main conclusion There is evidence that the distances between the wetlands do not provide an effective barrier to the species dispersal and, therefore, metapopulation structures including subpopulations of multiple temporary wetlands might counteract local area effects on subpopulations. Short‐winged species, however, might be more affected by isolation than full‐winged species. As carabid beetle community structure in most early successional habitats is similar, these results may be representative of many agricultural landscape habitats. Nature conservancy concepts that aim to increase habitat area and habitat connectivity have successfully been applied to fragmented late‐successional habitats. The present study indicates that such concepts do not necessarily result in higher diversity or larger populations in early successional habitats.     

The effects of an unpredictable precipitation regime on vernal pool hydrology

1. Vernal pools are small precipitation‐fed temporary wetlands once common in California. They are known for their numerous narrowly endemic plant and animal species, many of which are endangered. These pools experience the typical wet season/dry season regime of Mediterranean climates. Their hydrological characteristics are determined by a complex interaction between the highly variable climate and topographic relief. 2. Hypotheses regarding the effects on ponding of total precipitation, storm intensity and pattern were examined using long‐term weather records combined with two decades of data on the length and depth of inundation in 10 individual pools. Similarly, data on pool landscape position and microtopography allowed examination of the interactions between topography and rainfall amount and pattern. 3. The total amount of precipitation and length of inundation were strongly correlated. Landscape position affected ponding duration, with collector pools holding water longer than headwater pools. Basin microtopography interacted with climatic variability to determine the nature and extent of within‐basin microhabitats sufficiently different in hydrological and/or soil conditions to support or exclude individual species. The effect on hydroperiod of precipitation concentrated in a few months rather than spread more evenly over the season depended on total precipitation. 4. Changes in climate, the mound‐and‐depression landscape or pool microtopography could have profound impacts on the hydrology of individual pools as well as the array of hydrological conditions in the system. Given the individualistic responses of the numerous endemic species supported by vernal pools, any of these environmental changes could diminish their sustainability and increase the risk of species extinction. Conservation, restoration and management decisions should take these factors into account.     

荒漠短命植物不同生长期化学计量特征与生境土壤因子关系分析

深入了解荒漠短命植物的化学计量特征,有助于更好地理解生境土壤因子与植物生存策略的关系。以古尔班通古特沙漠广泛分布的尖喙牻牛儿苗（Erodium oxyrrhynchum）、假狼紫草（Nonea caspica）、琉苞菊（Hyalea pulchella）、飘带果（Lactuca undulata）为植物材料,测定不同深度（0~5、5~10、10~15 cm）的土壤理化性质,野外原位多时段采样比较分析4种植物化学计量特征与土壤因子的动态变化及其耦合关系。结果表明：①4种短命植物碳（C）、氮（N）、磷（P）含量普遍较低,化学计量特征存在物种间差异,但在不同生长期内变化规律大致相似。N、P含量从幼苗期到结实期逐渐减少,而C含量则长期趋于稳定。整个生长期内,P、C∶P的变异幅度较大,相反,C、N∶P的变异幅度较小。4种植物在不同生长期的化学计量特征差异与生长期、植物种类存在显著相关性。②0~5 cm土层有机碳（SOC）、总氮（TN）、总磷（TP）含量最高,且随土层的加深逐渐减少。随着植物的生长,0~5 cm土层中SOC和TN含量呈明显增加的趋势,而TP含量却呈现抛物线状变化趋势。在植物不同生长期内,土壤TP含量稳定性最强,SOC、TN的变异性较强,较低的N含量及TN∶TP比显示出该区域土壤属于N素缺乏类型。3个土层土壤在不同生长期的化学计量特征差异受土层、生长期的影响显著。③4种植物与各层次土壤化学计量特征的相关性无一致规律。植物化学计量指标仅与0~10 cm土层SOC、SOC∶TP相关性较强,而大部分化学计量特征间未显示出相关性。上述结果说明植物化学计量特征并非全部由土壤养分特征直接决定,其明显的种间差异显示了植物自身遗传特性在土壤—植物计量特征耦合关系的重要性。     

荒漠短命植物地上和地下生产力对极端干旱和降水的响应

在古尔班通古特沙漠南缘沙垄4个坡位和坡向,设置减少65%和增加65%生长季降水量以模拟极端干旱和极端降水事件,研究极端干旱和极端降水事件对沙垄不同坡位和坡向短命植物层片生产力的影响。结果表明: 极端干旱使地上净初级生产力和地下净初级生产力分别显著降低48.8%和13.7%,极端降水使地上净初级生产力和地下净初级生产力分别显著增加37.9%和23.2%。地上净初级生产力对极端干旱和极端降水的敏感性(0.26和0.21 g·m^-2·mm^-1)显著强于地下净初级生产力的敏感性(0.02和0.03 g·m^-2·mm^-1)。沙垄东坡地上净初级生产力(24.22 g·m^-2)和地下净初级生产力(5.77 g·m^-2)与西坡相比显著增大29.7%和71.7%,而地上净初级生产力和地下净初级生产力对降水变化的敏感性在不同坡位和坡向之间差异不显著。     

十字花科植物PEBP基因家族的分子进化

近年来植物基因组测序物种数量的指数增长, 为我们对植物环境适应性状的遗传和变异的全面理解提供了保障。磷脂酰乙醇胺结合蛋白(phosphatidylethanolamine-binding protein, PEBP)在植物的开花转变和株型建立中起着重要作用, 一直是植物生物学研究关注的热点领域之一。然而对该家族并没有利用新近测序的基因组数据进行比较基因组分析, 制约了对其在分子水平上的进化研究。为了确定PEBP基因家族的分子进化机制, 本研究利用生物信息学方法开展了7种十字花科植物拟南芥(Arabidopsis thaliana)、琴叶拟南芥(A. lyrata)、小鼠耳芥(A. pumila)、亚麻荠(Camelina sativa)、甘蓝(Brassica oleracea)、白菜(B. rapa)和油菜(B. napus)的PEBP基因家族成员的全基因组鉴定、结构特征和比较进化分析。从7个物种中共鉴定出91个PEBP基因, 系统进化分析表明它们分属5个亚家族: MFT、FT/TSF、TFL1、CEN和BFT。基因结构分析发现甘蓝、白菜和油菜的CEN基因内含子明显比其余4个物种的内含子长。蛋白结构域分析表明MFT比其他4个亚家族成员少了一个motif 2, TFL1比其他亚家族多了motif 8。选择压力分析发现7个物种PEBP同源基因均受到较强的纯化选择, 其中TFL1亚家族受到的纯化选择最弱。共线性分析表明十字花科植物PEBP基因家族随古代多倍体事件发生不同程度的扩张, TSF在甘蓝、白菜和油菜中丢失。非生物胁迫下, 在拟南芥中过量表达小鼠耳芥的一个MFT基因, 转基因拟南芥种子的萌发率明显低于野生型, 暗示MFT基因在调控种子萌发上的功能保守。本研究为深入研究十字花科植物PEBP基因的进化特征和生物学功能奠定了基础。