基于稳定氧同位素确定植物水分来源不同方法的比较

利用稳定同位素技术确定植物水分来源,对提高生态水文过程的认识和对干旱半干旱区的生态管理至关重要。目前基于稳定同位素技术确定植物水分来源的方法众多,但不同方法之间对比的研究较少。本研究基于原位样品采集,室内实验测试,利用直接对比法、多元线性混合模型(IsoSource)、贝叶斯混合模型(MixSIR、MixSIAR)和吸水深度模型分析植物水分来源,并对比各方法的优缺点。结果表明:相对于多元线性混合模型(IsoSource)而言,贝叶斯混合模型(MixSIR、MixSIAR)具有更好的水源区分性能,但对数据要求较高,且植物木质部水和潜在水源同位素组成的标准差越小,模型运行结果的可信度更高。本研究中贝叶斯混合模型(MixSIR)为最优解。在利用稳定氢氧同位素技术确定植物水分来源时,可先通过直接对比法定性判断植物可能利用的潜在水源,然后再用多元线性混合模型(IsoSource)、贝叶斯混合模型(MixSIR、MixSIAR)计算出各潜在水源对植物的贡献率和贡献范围,必要时可评估模型性能,选择出最优模型,定量分析植物的水分来源。若植物主要吸收利用不同土层深度的土壤水,可结合吸水深度模型计算出植物吸收土壤水的平均深度。本研究为干旱半干旱地区利用同位素技术确定植物水分来源方法的选择提供了理论依据。     

箱式通量观测技术和方法的理论假设及其应用进展

碳(CO₂、CH₄)、氮(N₂O)和水汽(H₂O)等温室气体的交换通量是生态系统物质循环的核心, 是地圈-生物圈-大气圈相互作用的纽带。稳定同位素光谱和质谱技术和方法的进步使碳稳定同位素比值(δ ¹³C)和氧稳定同位素比值(δ ¹⁸O)(CO₂)、δ ¹³C (CH₄)、氮稳定同位素比值(δ ¹⁵N)和δ ¹⁸O (N₂O)、氢稳定同位素比值(δD)和δ ¹⁸O (H₂O)的观测成为可能, 与箱式通量观测技术和方法结合可以实现土壤、植物乃至生态系统尺度温室气体及其同位素通量观测研究。该综述以CO₂及其δ ¹³C通量的箱式观测技术和方法为例, 概述了箱式通量观测系统的基本原理及分类, 阐述了系统设计的理论要求和假设, 综述了从野外到室内土壤、植物叶-茎-根以及生态系统尺度箱式通量观测研究的应用进展及问题, 展望了气体分析精度和准确度、观测数据精度和准确度以及观测数据的代表性评价在箱式通量观测研究中的重要性。     

基于功能性状的水杉原生母树种群生境适应策略

植物的功能性状变异和表型可塑性是其应对异质生境的主要机制, 对植物的生长和分布有重要贡献。本文以湖北星斗山国家级自然保护区的水杉(Metasequoia glyptostroboides)原生母树为研究对象, 分析了母树种群功能性状对树木形态、地形因子及人为干扰的响应机制。结果表明: 水杉原生母树叶面积、叶干重和比叶面积的变异幅度大, 可塑性较强, 而枝和叶的干物质含量稳定性最高。人为干扰和4个地形因子均对每个功能性状变异方差有5%-20%的解释度, 冠幅对枝、叶干物质含量的变异方差有高达38%和76%的解释度。5个功能性状主要受海拔、坡位和人为干扰影响, 其中, 比叶面积对环境因子和干扰的响应规律不明显, 叶面积和叶干重在强烈人为干扰的环境中普遍增大, 枝和叶的干物质含量对坡向的变化最敏感。总之, 水杉原生母树种群通过功能性状变异对环境能产生一定的可塑性响应, 但人为干扰对母树生长影响较大, 建议人工辅助更新, 并适度减少农业和建筑对现存母树的影响。     

救护白鹤与野生白鹤迁徙路线和活动规律差异分析

受伤和体弱白鹤的救护及放归是白鹤保护的重要方式之一。2014—2016年间,先后对8只救护白鹤和2只野生白鹤进行环志并安装卫星跟踪器,根据所获得的卫星跟踪数据来分析比较救护白鹤与野生白鹤在秋季迁徙路线和在重要中途停歇地的最大日活动距离、活动区分布和面积、生境类型等方面的异同。结果显示,救护白鹤放归当年与放归次年以及救护白鹤放归当年与野生白鹤的秋季迁徙路线和活动规律之间存在明显差异,但救护白鹤放归次年与野生白鹤之间差异不明显。(1)放归当年,4只救护白鹤在农田和水塘停歇1个月左右,停歇时长明显高于野生白鹤和放归次年的救护白鹤。(2)救护白鹤放归当年在跨海方式、登陆地点、停歇地点以及登陆后的迁徙方向上表现出多样性和不确定性,其中部分个体在迁徙过程中有停顿徘徊、迷失迁徙方向的现象,且跨越渤海和大别山的距离大于放归次年的救护白鹤和野生白鹤。(3)救护白鹤放归后4天内每日最大活动距离小,而后高低分化明显,无明显规律,而救护白鹤放归次年的每日最大活动距离规律变化与野生白鹤较一致。(4)与救护白鹤放归次年以及野生白鹤的活动规律相比,救护白鹤放归当年的栖息地位点变化频繁,具体表现为生境类型选择的多样化,且无明显规律,同时活动区面积较小。探索救护白鹤放归野外后与野生白鹤迁徙路线和活动规律的差异,对救护白鹤的科学放归具有指导意义。     

柔鱼科近缘种茎柔鱼与鸢乌贼营养生态位及相互关系

同域近缘种由于进化选择的压力,会形成不同的行为适应策略。研究同域近缘种生态位格局,有助于理解近缘物种的竞争和共存机制,是深入了解种群动态变化的基础性问题。选取东太平洋赤道海域的柔鱼科头足类近缘种茎柔鱼和鸢乌贼为研究对象,利用生物地球化学示踪物(稳定同位素和脂肪酸)分析两种头足类的营养生态位及相互关系。结果显示,茎柔鱼和鸢乌贼肌肉的部分必需脂肪酸(C18∶2n6、C20∶2n6、C20∶3n3、C20∶4n6和C20∶5n3)含量存在差异,说明二者食物来源不同,但其碳、氮稳定同位素比值无显著差异,可能是因为相同个体大小的茎柔鱼和鸢乌贼营养级相近,且摄食空间相似。这些结果在营养生态位的分析结果中也得到了验证,稳定同位素营养生态位的重叠程度高于脂肪酸营养生态位,表明脂肪酸组成更能体现同域近缘种的食性差异。本研究可加深对头足类进化过程中摄食行为适应机制的理解,并为评估同域近缘种的营养生态位关系提供有益参考。     

休眠卵孵化对策与食物浓度对萼花臂尾轮虫(Brachionus calyciflorus)两品系干雌体种群增长的影响

周期性孤雌繁殖的轮虫靠休眠卵度过不良环境,等环境适宜时休眠卵孵化出干雌体,再次通过孤雌繁殖建立种群。通常休眠卵要经历一段休眠期再孵化,但也有些休眠卵生成后很快孵化,称为早孵化现象。有关休眠卵不同孵化对策如何影响其干雌体克隆种群的增长,目前尚不清楚。分别观测了萼花臂尾轮虫（Brachionus calyciflorus）的两个品系H1（窄温度生态位）和D1（宽温度生态位）的休眠卵在不同孵化对策和不同食物浓度下所生产的干雌体克隆群的种群增长差异。孵化对策包括早孵化（early hatching,EH）和晚孵化（late hatching,LH）;食物浓度包括高食物浓度（high food concentration,HF：2×10⁶个细胞/mL）和低食物浓度（low food concentration,LF：5×10⁵个细胞/mL）,每个品系下各设置4个实验组（LH-HF、LH-LF、EH-HF、EH-LF）,每组10个重复。结果发现,对D1品系来说：孵化对策和食物浓度对最大种群数量具有显著的综合影响（P=0.002）,但两因素间不存在交互作用（P=0.911）;早孵化的干雌体种群在最大种群数量上显著高于晚孵化的干雌体种群（P=0.001）。对H1品系：孵化对策和食物浓度对最大种群数量综合影响显著（P<0.001）,且两个因素之间存在交互作用（P<0.001）;高食物浓度下,EH干雌体克隆群的最大种群数量显著低于LH干雌体克隆群（P<0.001）。高食物浓度下干雌体克隆群开始有性生殖的密度阈值,D1品系EH组显著高于LH组（P=0.041）;而H1品系EH组却显著低于LH组（P=0.022）。最高种群密度下,H1品系的有性生殖率在两种孵化对策之间存在显著差异（P=0.044）,EH种群的有性生殖率低于LH种群,而D品系却未见有性生殖率在不同孵化对策间存在明显差异。本研究结果显示休眠卵的孵化对策会影响其后代干雌体种群的增长特性,其影响的结果可能与种群的生境适应相关。     

Raman-based dynamic feeding strategies using real-time glucose concentration monitoring system during adalimumab producing CHO cell cultivation

The use of Process Analytical Technology tools coupled with chemometrics has been shown great potential for better understanding and control of mammalian cell cultivations through real-time process monitoring. In-line Raman spectroscopy was utilized to determine the glucose concentration of the complex bioreactor culture medium ensuring real-time information for our process control system. This work demonstrates a simple and fast method to achieve a robust partial least squares calibration model under laboratory conditions in an early phase of the development utilizing shake flask and bioreactor cultures. Two types of dynamic feeding strategies were accomplished where the multi-component feed medium additions were controlled manually and automatically based on the Raman monitored glucose concentration. The impact of these dynamic feedings was also investigated and compared to the traditional bolus feeding strategy on cellular metabolism, cell growth, productivity, and binding activity of the antibody product. Both manual and automated dynamic feeding strategies were successfully applied to maintain the glucose concentration within a narrower and lower concentration range. Thus, besides glucose, the glutamate was also limited at low level leading to reduced production of inhibitory metabolites, such as lactate and ammonia. Consequently, these feeding control strategies enabled to provide beneficial cultivation environment for the cells. In both experiments, higher cell growth and prolonged viable cell cultivation were achieved which in turn led to increased antibody product concentration compared to the reference bolus feeding cultivation.     

Reductions in the dietary niche of southern sea otters (Enhydra lutris nereis) from the Holocene to the Anthropocene

The sea otter (Enhydra lutris) is a marine mammal hunted to near extinction during the 1800s. Despite their well‐known modern importance as a keystone species, we know little about historical sea otter ecology. Here, we characterize the ecological niche of ancient southern sea otters (E. lutris nereis) using δ¹³C analysis and δ¹⁵N analysis of bones recovered from archaeological sites spanning ~7,000 to 350 years before present (N = 112 individuals) at five regions along the coast of California. These data are compared with previously published data on modern animals (N = 165) and potential modern prey items. In addition, we analyze the δ¹⁵N of individual amino acids for 23 individuals to test for differences in sea otter trophic ecology through time. After correcting for tissue‐specific and temporal isotopic effects, we employ nonparametric statistics and Bayesian niche models to quantify differences among ancient and modern animals. We find ancient otters occupied a larger isotopic niche than nearly all modern localities; likely reflecting broader habitat and prey use in prefur trade populations. In addition, ancient sea otters at the most southerly sites occupied an isotopic niche that was more than twice as large as ancient otters from northerly regions. This likely reflects greater invertebrate prey diversity in southern California relative to northern California. Thus, we suggest the potential dietary niche of sea otters in southern California could be larger than in central and northern California. At two sites, Año Nuevo and Monterey Bay, ancient otters had significantly higher δ¹⁵N values than modern populations. Amino acid δ¹⁵N data indicated this resulted from shifting baseline isotope values, rather than a change in sea otter trophic ecology. Our results help in better understanding the contemporary ecological role of sea otters and exemplify the strength of combing zooarchaeological and biological information to provide baseline data for conservation efforts.     

Trophic level and basal resource use of soil animals are hardly affected by local plant associations in abandoned arable land

Plants provide resources and shape the habitat of soil organisms thereby affecting the composition and functioning of soil communities. Effects of plants on soil communities are largely taxon‐dependent, but how different functional groups of herbaceous plants affect trophic niches of individual animal species in soil needs further investigation. Here, we studied the use of basal resources and trophic levels of dominating soil meso‐ and macrofauna using stable isotope ratios of carbon and nitrogen in arable fallow systems 3 and 14–16 years after abandonment. Animals were sampled from the rhizosphere of three plant species of different functional groups: a legume (Medicaco sativa), a nonlegume herb (Taraxacum officinale), and a grass (Bromus sterilis). We found virtually no consistent effects of plant identity on stable isotope composition of soil animals and on thirteen isotopic metrics that reflect general food‐web structure. However, in old fallows, the carbon isotope composition of some predatory macrofauna taxa had shifted closer to that of co‐occurring plants, which was particularly evident for Lasius, an aphid‐associated ant genus. Trophic levels and trophic‐chain lengths in food webs were similar across plant species and fallow ages. Overall, the results suggest that variations in local plant diversity of grassland communities may little affect the basal resources and the trophic level of prey consumed by individual species of meso‐ and macrofauna belowground. By contrast, successional changes in grassland communities are associated with shifts in the trophic niches of certain species, reflecting establishment of trophic interactions with time, which shapes the functioning and stability of soil food webs.     

Age‐related variation in the trophic characteristics of a marsupial carnivore,the Tasmanian devil Sarcophilus harrisii

Age‐related changes in diet have implications for competitive interactions and for predator–prey dynamics, affecting individuals and groups at different life stages. To quantify patterns of variation and ontogenetic change in the diets of Tasmanian devils Sarcophilus harrisii, a threatened marsupial carnivore, we analyzed variation in the stable isotope composition of whisker tissue samples taken from 91 individual devils from Wilmot, Tasmania from December 2014 to February 2017. Both δ¹³C and δ¹⁵N decreased with increasing age in weaned Tasmanian devils, indicating that as they age devils rely less on small mammals and birds, and more on large herbivores. Devils <12 months old had broader group isotopic niches, as estimated by Bayesian standard ellipses (SEA_B mode = 1.042) than devils from 12 to 23 months old (mode = 0.541) and devils ≥24 months old (mode = 0.532). Devils <24 months old had broader individual isotopic niches (SEA_B mode range 0.492–1.083) than devils ≥24 months old (mode range 0.092–0.240). A decrease in δ¹⁵N from the older whisker sections to the more recently grown sections in devils <24 months old likely reflects the period of weaning in this species, as this pattern was not observed in devils ≥24 months old. Our data reveal changes in the isotopic composition of devil whiskers with increasing age, accompanied by a reduction in isotopic variation both among population age classes and within individuals, reflecting the effect of weaning in early life, and a likely shift from an initially diverse diet of small mammals, birds, and invertebrates towards increasing consumption of larger herbivores in adulthood.