基于根部年轮与导管特征的黄土高原苜蓿生长衰退分析

紫花苜蓿作为黄土高原退耕还林还草工程的重要人工草本物种,对控制水土流失、植被固碳和生态环境改善等方面都发挥着重要生态作用;但是苜蓿草地在黄土高原普遍出现生长不可持续的特征,在第6年左右植被出现明显生长衰退现象。本研究在黄土高原4个降水梯度(280、400、500 mm和550 mm)的地点采集紫花苜蓿和自然对照草本物种:委陵菜的根部年轮样品,并分析了紫花苜蓿与委陵菜的年轮宽度和导管大小随年龄的变化趋势特征及与气候要素的相关关系。研究结果表明:在气候暖干化环境下,紫花苜蓿和委陵菜的年轮宽度随年龄增加都有不断下降的趋势,且在降水量偏低样点下降更为显著,这是由于植株在降水量偏低地点易遭受严重水分胁迫,以致无法满足生长所需的水分而造成根部生长速率明显减缓。紫花苜蓿根部导管大小随年龄增加均有明显下降趋势,在降水量偏低的样点下降趋势更加显著;这表明水分胁迫随年龄增加逐渐加剧,紫花苜蓿导管大小逐年下降以致不能满足自身生长的水分需求,植被生长呈衰退趋势,且在降雨偏低地区,苜蓿生长衰退出现时间较早。自然草本委陵菜根部导管大小随年龄增加均有明显上升趋势且在降水量偏低样点上升趋势更显著,这表明委陵菜通过增大根部导管大小、增加输水能力来满足随年龄增加不断上升的水分需求,这也说明委陵菜导管结构特征较好的适应了黄土高原干旱半干旱环境,生长处于可持续发展状态。     

阈值温度和积温对川西高原林线岷江冷杉径向生长的影响

高山林线的形成机理一直是高山生态学讨论的一个焦点问题,其中林线树木生长的阈值温度一直是研究热点。利用川西高原九寨沟弓杠岭林线岷江冷杉(Abies faxoniana)树木径向生长数据,通过树轮宽度-气候因子关系分析,探讨阈值温度和积温对林线岷江冷杉径向生长的影响。结果表明:林线岷江冷杉径向生长主要受到温度限制,其中林线岷江冷杉径向生长与当年生长季(7、8和9月)、冬季(12、1和2)及上一年9、10月温度显著正相关(P0.05),但与降水的相关性较弱。林线岷江冷杉径向生长与不同起始温度的初日负相关,与不同起始温度的终日正相关,且与9.5℃阈值温度的初日负相关最强(P0.05),与6.5℃阈值温度的终日正相关最强(P0.05)。林线岷江冷杉径向生长还与7—9.5℃的积温及9.5℃持续天数显著正相关(P0.05),说明7—9.5℃可能是形成层活动的阈值温度,尤其7℃可能是林线岷江冷杉生长的起始温度。林线岷江冷杉生长期从4月中旬开始到10月初结束,随着1980年后温度的显著升高,生长期活动积温开始增加,生长期初日提前(4.6d/10a,r~2=0.19,P=0.01),生长期终日延后(1.8 d/10a),使得生长期延长(6.4 d/10a),进而对林线岷江冷杉径向生长有显著的促进作用。未来气候变暖可能会使川西林线树木生长增加,林线可能会上移。     

入侵植物加拿大一枝黄花根际解钾菌多样性及解钾活性

入侵植物加拿大一枝黄花(Solidago canadensis)具有较强的钾(K)富集能力, 这可能和其对土壤微生物群落的改变有关。根际解钾菌能够将植物难以利用的矿物态钾转化为植物可以利用的可溶性钾, 而加拿大一枝黄花如何影响根际解钾菌多样性和解钾活性尚未明了。该研究以浙江省杭州湾湿地围垦区内自然生长的加拿大一枝黄花和其伴生本地植物白茅(Imperata cylindrica)为研究对象, 比较了加拿大一枝黄花和白茅体内及土壤中的钾含量水平, 钾供给水平对生物量积累的影响, 以及根际解钾菌的数量、多样性和解钾活性的差异。结果表明, 加拿大一枝黄花茎、叶中的钾含量均显著高于白茅, 分别是白茅的1.59和7.33倍; 加拿大一枝黄花和白茅的土壤全钾含量差异不显著, 速效钾含量在0-10 cm土层中差异显著、在10-20 cm土层中差异不显著。随着钾供应水平提高, 加拿大一枝黄花和白茅的生物量均显著增加。利用解钾培养基计数培养后发现, 加拿大一枝黄花根际解钾菌的数量是白茅的3.51倍。分离培养后将出现解钾圈的菌株进行鉴定, 利用解钾液体培养实验测定其解钾量, 发现从加拿大一枝黄花根际土中分离得到的15个解钾菌株中, 有9个具有高效解钾能力, 其处理液中K ⁺含量较空白对照高出85.11%-192.54%, 其中菌株H2-20解钾能力最强, 解钾量为10.657 mg·L ^-1。加拿大一枝黄花根际解钾菌解钾作用显著高于白茅。经16S rDNA鉴定发现, 加拿大一枝黄花15个根际解钾菌株分属11个属, 其中有6个属已经被报道证实具有明显解钾能力。这些结果表明加拿大一枝黄花根际解钾菌数量较为丰富, 且大多具有较高解钾活性, 可能对其钾富集具有重要贡献。     

树鼩PSEN1全长编码序列的克隆及分子特征分析

目的 获取树鼩早老素蛋白-1(PSEN1)的全长编码序列并进行分子特征分析。方法 以树鼩脑组织总RNA为材料,通过RT-PCR、RACE-PCR扩增和序列拼接获得PSEN1基因全长编码序列,进而通过DNAMAN、MEGA等生物信息学软件对其序列和分子特征进行分析。qRT-PCR和Western Blot进一步分析PSEN1在树鼩各个组织的表达模式。结果 克隆鉴定了树鼩PSEN1基因,其cDNA的开放阅读框全长1128 bp,编码375个氨基酸。通过系统发育谱系树、氨基酸序列对比分析,发现树鼩PSEN1与小鼠、大鼠等相比更接近人类和非人灵长类动物。qRT-PCR和Western Blot的结果表明,树鼩PSEN1在脑组织的表达量明显高于其他脏器组织。结论 通过克隆树鼩PSEN1基因序列并进行分析,为今后进一步深入研究该基因功能和建立相关疾病动物模型提供理论基础。     

Niche‐based relationship between sympatric bark living insect pests and tree vigor decline of Pinus yunnanensis

Forest stands of Pinus yunnanensis Franch in southwestern China are seriously damaged by several bark living insect pests. These pests commonly exist in the same host tree and exploit limited phloem resources. In this study, we hypothesized that sympatric pests would occupy different ecological niches to reduce interspecific competition, and their coordinated attack would aggravate the tree vigor decline of P. yunnanensis. To quantify the ecological niches, we used a sampling method involving three dimensional divisions of tree resource states: (a) sample plot dimension (to evaluate the extent of pest colonization at plot scale), (b) trunk height dimension, and (c) tree vigor dimension. Those attacked pine canopies and colonized trunks were analysed in the field study. The results showed that Tomicus minor and Tomicus yunnanensis both widely and uniformly distributed in lightly, moderately and heavily damaged canopies while they aggregated on particular trunks of dying and withered trees. Lower and middle trunk sections (1–4 m) were mainly occupied by Monochamus alternatus and T. minor, yet T. yunnanensis dominated the upper parts (5–6 m). There was an overlap of the pine shoot beetles in the middle sections (2–4 m), whereas all three species were ecologically segregated in other trunk sections. During the shoot feeding phase, tree vigor declined with pine shoot beetles' increasing shoot feeding density. They coexisted in the same host tree, while M. alternatus only attacked dying and withered tree trunks, causing a greater infestation. Colonization of pine shoot beetle then followed by M. alternatus could be the major causes of tree mortality. This study highlights the resource utilization pattern of sympatric bark living insect pests corresponding with tree vitality. Those findings would help to understand the mechanisms of pest outbreak in P. yunnanensis ecosystem and provide potential guidance for developing an early monitoring pest warning system.     

Molecular phylogenetics of slit‐faced bats (Chiroptera: Nycteridae) reveal deeply divergent African lineages

The bat family Nycteridae contains only the genus Nycteris, which comprises 13 currently recognized species from Africa and the Arabian Peninsula, one species from Madagascar, and two species restricted to Malaysia and Indonesia in South‐East Asia. We investigated genetic variation, clade membership, and phylogenetic relationships in Nycteridae with broad sampling across Africa for most clades. We sequenced mitochondrial cytochrome b (cytb) and four independent nuclear introns (2,166 bp) from 253 individuals. Although our samples did not include all recognized species, we recovered at least 16 deeply divergent monophyletic lineages using independent mitochondrial and multilocus nuclear datasets in both gene tree and species tree analyses. Mean pairwise uncorrected genetic distances among species‐ranked Nycteris clades (17% for cytb and 4% for concatenated introns) suggest high levels of phylogenetic diversity in Nycteridae. We found a large number of designated clades whose members are distributed wholly or partly in East Africa (10 of 16 clades), indicating that Nycteris diversity has been historically underestimated and raising the possibility that additional unsampled and/or undescribed Nycteris species occur in more poorly sampled Central and West Africa. Well‐resolved mitochondrial, concatenated nuclear, and species trees strongly supported African ancestry for SE Asian species. Species tree analyses strongly support two deeply diverged subclades that have not previously been recognized, and these clades may warrant recognition as subgenera. Our analyses also strongly support four traditionally recognized species groups of Nycteris. Mitonuclear discordance regarding geographic population structure in Nycteris thebaica appears to result from male‐biased dispersal in this species. Our analyses, almost wholly based on museum voucher specimens, serve to identify species‐rank clades that can be tested with independent datasets, such as morphology, vocalizations, distributions, and ectoparasites. Our analyses highlight the need for a comprehensive revision of Nycteridae.     

云南蒙自钳嘴鹳夜栖地利用及夜栖树选择

动物对夜栖地选择的灵活程度是其分布和扩散的重要因素之一。钳嘴鹳(Anastomus oscitans)为中国新分布种,要了解其扩散趋势,掌握其夜栖地需求至关重要。2015年11月至2018年7月在云南蒙自坝区,使用卫星跟踪技术对6只钳嘴鹳进行了夜栖地利用和夜栖树选择研究,结果表明:(1)钳嘴鹳可以在多种生境中夜栖,包括林地、沼泽、岛屿等。从群体水平上分析,钳嘴鹳主要夜栖于沼泽中,利用率为(51.19±12.34)%,其次为林地(31.55±11.34)%和岛屿(17.26±5.70)%;从个体水平上来看,不同钳嘴鹳的夜栖地利用方式差异较大,其中4只主要利用沼泽,而另外2只主要利用林地;(2)随机森林分析表明:影响钳嘴鹳夜栖树选择的首要因子为距觅食地距离,其次为树高、地径和最低枝高度,而人为干扰因子的影响较弱。综合来看,钳嘴鹳对夜栖地类型以及夜栖树均表现出了极强的适应性和可塑性,这可能是其能够快速扩散的重要原因之一。同时也表明夜栖树并不能成为一个有力的限制因子,钳嘴鹳有可能继续向国内的南方湿地区扩散。     

大花杓兰亲环素基因(CmCyP)的克隆及生物信息学分析

亲环素是一个多基因家族,在植物生命活动中发挥着重要的作用。该研究以大花杓兰(Cypripedium macranthum)为材料,采用RT-PCR技术克隆到1个亲环素基因(CyP),并对其进行生物信息学分析。结果表明:大花杓兰CyP基因的开放阅读框序列为525 bp,命名为CmCyP(GenBank登录号为MH411125),编码174个氨基酸。预测CmCyP蛋白是一个位于细胞质、相对分子量约为18 kD、理论pI为8.73、无信号肽、跨膜结构域的亲水性蛋白质。磷酸化和糖基化位点预测分析发现,CmCyP蛋白存在18个潜在的磷酸化位点和2个潜在的糖基化位点。蛋白保守结构域预测分析发现,CmCyP蛋白包含一个高度保守的肽脯氨酰顺反异构酶结构域,属于单结构域亲环素。对二级结构进行预测分析发现,CmCyP蛋白中存在无规卷曲70个、延伸链56个、α-螺旋23个、β-折叠25个,这4种结构元件在三级结构中也有体现。系统进化树结果显示,大花杓兰CmCyP蛋白与铁皮石斛(Dendrobium catenatum)和万带兰(Vanda hybrid cultivar)的CyP蛋白的亲缘关系较近。该研究首次克隆了大花杓兰亲环素基因(CmCyP),为进一步探讨CmCyP基因的生物学功能奠定了基础。