海拔是重要的地理因素, 不同海拔梯度的局部环境因子会发生改变, 植物的性状和功能也会随之发生变异(Kergunteuil et al, 2018; Borghi et al, 2019)。与低海拔分布的植物相比, 分布在高海拔的植物倾向于更加矮小(Körner et al, 1989; Kappelle et al, 1995; Soethe et al, 2008; Brunet & Holmquist, 2009)。海拔异质性对不同植物繁殖器官的大小和雌雄资源投入的影响是不一致的。如甘青铁线莲(Clematis tangutica)花的大小及雌雄蕊的长度随着海拔的升高而增大(屈博, 2017①(①屈博 (2017) 甘青铁线莲花部特征的海拔变异及其繁殖适应. 硕士学位论文, 西北师范大学, 兰州.)); 唐古特雪莲(Saussurea tangutica)对雌雄蕊的资源分配随着海拔升高显著增加(杨亚军等, 2018); 金莲花(Trollius ranunculoides)分布在亚高山居群的花瓣数目少、花较大, 而分布在高山居群的花瓣数目多、花较小(Zhao & Huang, 2013)。
除了植物表型特征, 环境异质性也会导致植物次生代谢物成分和含量(化学性状)的变化, 不同环境中非生物因子(如温度、光照、水分等)的差异会对植物的生理代谢产生不同的影响, 植物的次生代谢物也会因为环境的差异而变化(阎秀峰等, 2007; Mullin et al, 2021)。温度是调节植物代谢的重要环境因子, 例如在非最佳温度条件下, 玉米(Zea mays)向光面的叶片中积累更多的花青素(Pietrini et al, 2002)。光照也会影响植物次生代谢产物的成分和含量, 例如光照不足会增加喜树(Camptotheca acuminata)叶片中喜树碱的含量(Wang et al, 2004)。在干旱胁迫下, 植物会产生更多的次生代谢物, 如氰苷、萜类物质、生物碱、丹宁和有机酸等, 例如干旱条件下喜树叶片中喜树碱的含量增加(Liu, 2000)。对十字花科碎米荠属草甸碎米荠(Cardamine pratensis)和车前科车前属大车前(Plantago major)的研究发现, 分布在低海拔的草甸碎米荠居群的脂肪族型芥子油甘的含量显著高于高海拔居群的个体, 而高海拔居群化学物质的多样性比低海拔居群要高25%; 分布在低海拔居群的大车前产生更多的总化合物、环烯醚萜苷类和咖啡酰苯乙醇苷(Bakhtiari et al, 2019)。随着海拔的升高, 美国松树韧皮部中单萜类和二萜类化合物的含量显著增多, 而可溶性糖(葡萄糖、果糖和蔗糖)的含量则显著降低, 而且淀粉、总萜烯以及二萜类化合物的含量具有显著相关性(Mullin et al, 2021)。随海拔梯度的变化, 环境中的非生物因子(主要是相对光照强度、温度和相对湿度)会产生变化, 它们如何影响植物的表型以及次生代谢物的成分和含量? 植物不同组织器官的次生代谢物是否存在差异? 相关研究还较少。
杜鹃属(Rhododendron)是中国被子植物中最大的木本植物属, 是世界著名的观赏植物, 有1,000多种, 主要分布在亚洲(Chamberlain et al, 1996)。中国-喜马拉雅地区既是杜鹃属的分布中心, 又是其多样化中心(方瑞征和闵天禄, 1995; 庄平, 2012)。不同海拔杜鹃花的形态、大小、颜色等特征有很大差异(Huang et al, 2017), 是研究海拔梯度变异对植物表型性状及其化学成分影响的理想材料。本研究以分布海拔跨度大的柳条杜鹃(R. virgatum)、大白杜鹃(R. decorum) (大理苍山居群)和红棕杜鹃(R. rubiginosum) (丽江老君山居群)为研究对象, 测量和分析了3个不同海拔(海拔A、海拔B、海拔C)居群的环境因子, 以及同一种杜鹃属植物在不同海拔居群的14个表型性状(营养器官和繁殖器官), 花蜜特征(花蜜体积、糖浓度和糖分组成)及茎、叶、花瓣、花粉和花蜜的次生代谢物的成分和相对含量, 主要探讨以下3个问题: (1)同一物种在不同海拔高度居群的表型性状的变异式样; (2)同一物种在不同海拔高度居群的次生代谢物的成分和相对含量的差异; (3)海拔梯度变化以及环境因子差异对植物表型特征和次生代谢物的综合性影响。以期深入了解不同海拔梯度3种杜鹃的表型性状的适应模式及非生物环境因子对植物各部位代谢产物生产的影响, 同时从两个方面对其进行综合性探究, 以揭示海拔及其环境因子对杜鹃属植物表型特征和化学性状的影响, 为杜鹃属植物分布和适应性研究提供理论依据(严璧君, 2020①(①严璧君 (2020) 云南轿子雪山杜鹃属植物沿海拔梯度的营养器官解剖特征及其表型可塑性研究. 硕士学位论文, 云南大学, 昆明.))。
1 材料与方法
1.1 研究地点与材料
研究对象为云南大理市苍山应乐峰东坡(25°41′ N, 100°5′ E)的杜鹃居群A (海拔高度约2,000 m)、居群B (海拔高度约2,500 m)、居群C (海拔约3,000 m)和丽江市老君山九十九龙潭保护区(26°38′ N, 99°4′ E)的居群A (海拔高度约3,400 m)、居群B (海拔高度约3,600 m)、居群C (海拔高度约3,800 m)。三个海拔跨度的设置是以物种分布的实际情况确定的, 苍山自然保护区柳条杜鹃和大白杜鹃分布的海拔范围大约是2,000-3,000 m, 老君山自然保护区红棕杜鹃分布的海拔范围大约是3,400-3,800 m。综合考虑物种的实际分布, 对老君山红棕杜鹃以200 m为间隔, 苍山以500 m为间隔进行梯度设置。根据对应的海拔间隔, 海拔A、B、C分别对应3种杜鹃由低至高的3个梯度。
苍山为云岭山脉主峰之一, 植被类型多样, 杜鹃物种多样性丰富, 我们选择分布海拔跨度大的柳条杜鹃(图1A)和大白杜鹃(图1B)为研究材料, 居群A和居群B生境为高山松(Pinus densata)林下灌木层, 居群C生长于林缘灌木层。柳条杜鹃为小灌木, 分布于1,700-3,000 m的山坡林缘、灌丛或湿润草地, 高1-2 m, 花序腋生, 每花序1-2朵花, 花冠钟状或漏斗状, 花色为淡红色, 偶有白色, 花期3-5月。大白杜鹃为常绿灌木或小乔木, 分布于1,000-3,300 m的灌丛中或森林下层, 高1-3 m, 顶生总状伞房花序, 有花8-10朵, 花冠宽漏斗状钟形、变化大, 花色为淡红色或白色, 花期4-6月, 果期9-10月。在老君山自然保护区, 我们选择红棕杜鹃(图1C)为研究材料, 居群A和居群B主要分布于林下或林缘灌木丛中, 居群C主要分布于路边、林缘灌木丛中。红棕杜鹃为常绿灌木, 分布在海拔2,500-4,200 m的云杉(Picea asperata)、冷杉(Abies fabri)、落叶松(Larix gmelinii)林林缘或林间间隙地, 高1-3 m, 花序顶生, 花冠宽漏斗状, 花色变异为淡紫色、紫红色、玫瑰红色、淡红色, 少有白色带淡紫色晕, 花期4-6月, 果期7-8月(严璧君, 2020①(①严璧君 (2020) 云南轿子雪山杜鹃属植物沿海拔梯度的营养器官解剖特征及其表型可塑性研究. 硕士学位论文, 云南大学, 昆明.))。
图1
图1
柳条杜鹃(A)、大白杜鹃(B)和红棕杜鹃(C)的花序以及杜鹃的花部特征测量(D, 以大白杜鹃为例)。a: 花冠长; b: 花冠宽; c: 花筒开口直径; d: 花筒深; e: 花筒直径; f: 雌蕊长; g: 最高雄蕊长; h: 最低雄蕊长。
Fig. 1
The inflorescence of Rhododendron virgatum (A), R. decorum (B), and R. rubiginosum (C) and measurement of floral characteristics of Rhododendron (D, R. decorum as example). a, Corolla length; b, Corolla width; c, Tube opening diameter; d, Floral tube length; e, Tube diameter; f, Pistil length; g, The longest stamen length; h, The shortest stamen length.
1.2 环境因子测量
为了探究不同海拔居群环境因子(温度、相对湿度和相对光照强度)的差异, 在每一个选定的杜鹃居群, 在距离地面1.5 m的枝干上悬挂DHM2机械通风干湿温度计(上海隆拓), 使用蒸馏水润湿湿球温度表下的纱套, 拧动通风器发条, 静置10 min后读取其干球、湿球温度表, 其中干球温度为空气实际温度(℃), 再根据气象常用表查得空气相对湿度(%)。使用数字照度计(CA1110型)测量杜鹃居群林下和裸地光照强度(lux), 相对光照强度(%) = 林下光照强度/裸地光照强度 × 100% (皮华强等, 2016; Quan, 2018)。每个居群每种环境因子测量15次。为了减少时间和天气造成的误差, 对于不同海拔环境因子的测量均是选择晴朗的天气进行, 测量时间固定在上午10:00-10:30。
1.3 杜鹃营养器官和繁殖器官特征测量
为了探究不同海拔居群同一种杜鹃的营养器官和繁殖器官特征是否存在差异, 对于3个不同海拔高度分布的苍山的柳条杜鹃和大白杜鹃以及老君山的红棕杜鹃, 分别随机选择30个植株, 测量成年植株的高度(精确到1 cm)、花枝直径(野外实验中均统一选择距离花序较近的枝条进行测量, 精确到0.01 mm)、叶片长度和宽度(均统一随机选择距离花序较近的健康完好的叶片, 精确到0.01 mm); 每个植株随机选择1朵处于盛花期、长势健康且完整的花, 测量其花冠长度和宽度、花筒开口直径、花筒深、花筒直径、雌蕊长、雄蕊长、花药的长度(a), 宽度(b), 高度(c)及柱头直径(d) (精确到0.01 mm)。因单花内雄蕊长度不一, 故我们分别测量最长和最短雄蕊的长度(图1D); 将花药近似为椭球体, 花药体积为πabc/6; 柱头表面近似为圆形, 则柱头表面积为π(d/2)2。为了统计不同海拔居群植株单花的花粉数和胚珠数, 在每一个海拔居群选定的30个植株上随机摘取1个即将开放的花苞, 将其保存于福尔马林-醋酸-酒精固定液(FAA, formalin-acetic acid-70% alcohol, 体积比为5 : 5 : 90)。在实验室将每朵花的花药和子房分离并一一对应做好标记。用钝头镊子充分研磨花药并定容至4 mL, 充分摇匀后取20 μL在光学显微镜下观察统计花粉数, 每朵花的花粉溶液随机取两次进行统计, 计算每朵花的花粉总数。在解剖镜下解剖每朵花的子房结构, 统计每朵花的胚珠数量。
1.4 杜鹃的花蜜特征测量
为了探究不同海拔居群同一种杜鹃的花蜜特征(花蜜的体积、糖浓度、糖成分)是否存在差异, 在每一个海拔居群选定的30个植株随机选择2个即将开放的花苞, 标记并套上尼龙网袋(隔绝访花者), 直至花朵完全盛开, 打开套袋, 在上午9:30-10:30用毛细吸管(圆柱形, 直径0.3 mm)吸取其中一朵花中的花蜜, 使用游标卡尺测量花蜜所占毛细吸管的长度(length, L), 花蜜体积(volume, V)的计算方法为V = π × 0.152 × L; 用手持折光测糖仪(Eclipse 0-85%, 购买于贝林汉姆斯坦利有限公司)测量花蜜的糖浓度。
对于每个居群的每一株套袋中的另外一朵花, 使用毛细吸管吸取花蜜, 测量其花蜜所占长度后将其全部吹至滤纸片上, 保存于1.5 mL离心管中置于冰盒保存, 带至室内于-20℃冰箱中保存。用高效液相色谱法(high performance liquid chromatography, HPLC)检测分析花蜜糖成分(葡萄糖、果糖、蔗糖)的含量。样品前处理: 在每一个花蜜样品中加入100 µL去离子水(保证载有花蜜的滤纸片被完全淹没), 室温下溶解48 h。检测条件为柱温35℃, 流速1 mL/min, 流动相80%乙腈, 单次进样量20 µL, 检测信号为示差检测器。同时配制葡萄糖、果糖和蔗糖的标准液, 并设置5个浓度梯度进行上机检测分析, 根据标准品的峰面积和糖质量拟合各个糖成分标准品的线性回归方程。最后计算每个花蜜样本中葡萄糖、果糖和蔗糖的含量(mg/mL) (Sun et al, 2017)。由于柳条杜鹃的花较小, 花蜜量也较少, 为了更有效地收集其花蜜, 我们在上午9:30-10:30采集高、中、低海拔居群的柳条杜鹃花并置于冰盒中, 在室内台灯下进行细致地吸取花蜜操作, 并测量花蜜的体积和糖浓度, 同时收集花蜜样本并冷冻保存, 带回学校进行花蜜糖成分的分析。
1.5 杜鹃不同组织中次生代谢物的成分和含量测定
为了探究不同海拔居群同一种杜鹃次生代谢物的成分和含量是否存在变异, 在选定的每一个居群随机选取5个植株, 每个植株上随机选择3-5个即将开放的花苞进行套袋, 直到花朵花药成熟且分泌花蜜, 收取其花瓣、花药和花蜜, 并摘取叶子(随机选择距离花序最近的1个叶片)和茎(截取约3 cm长)。由于杜鹃属植物花粉粒间有粘丝将花粉串联起来, 野外使用镊子挑取花粉并收集在1.5 mL离心管中; 使用毛细吸管量取花蜜体积并移置1.5 mL离心管中。花粉、花蜜样品均使用冰盒保存带回并储存于-20℃的冰箱中。野外采集的茎、叶、花瓣使用硅胶进行干燥并保存于塑封袋中, 在室内使用简仪便携电热鼓风干燥箱(101-2AB型, 天津市泰斯特仪器有限公司)烘干(70℃, 24 h)。
样品制备: 茎、叶、花瓣使用破壁机(耐欧AQ-180E-X, 中国浙江省慈溪市耐欧电器有限公司)进行充分打磨破碎, 经筛子反复过筛至样品无大颗粒物质。茎、叶、花瓣和花蜜样本分别称重(约0.01 g), 置于装有1 mL甲醇(色谱级)的离心管中。每个花药样品称重约0.01 g, 并置于1 mL甲醇的离心管中, 使用超声波细胞粉碎仪(Ultrasonic Homogenizer, JY92-IIDN)破碎花粉, 使花粉粒呈匀浆状; 处理后样品在室温下静置24 h (Wang et al, 2019), 然后10,000 rmp离心5 min, 取上清液并定容至750 μL。
使用超高效液相色谱(Ultra Performance Liquid Chromatography, ACQUITY UPLCH-class, Waters)和四极杆飞行时间串联质谱(Quadrupole/time- of-flight mass spectrometers, Xevo G2-XS QTof, Waters)分析花粉、花蜜、花瓣、茎、叶提取物中的次生代谢物。每一个样品的进样量为20 μL。色谱分析柱为C18 (ACQUITY UPLC BEH, 1.7 μm, 2.1 × 100 mm), 柱温设置为40℃。质谱条件: 采集模式为ESI+, ESI-; MS采集范围为50-1,500 Da, 扫描时间为0.1 s。检测条件参数: 溶解液流动相A为H2O (加有0.01%的甲酸); 流动相B为乙腈(加有0.01%的甲酸), 两种流动相浓度随洗脱时间而呈梯度变化。在0 min时A = 95%, B = 5%; 2 min时A = 95%, B = 5%; 17 min时A = 2%, B = 98%; 20 min时A = 2%, B = 98%。流速是 0.4 mL/min。数据的获取是在UNIFI科学信息系统中进行, 通过跟系统自带的中华药典数据库(Waters)进行最佳匹配比对, 确定化学物质的种类、化学式以及响应值。因样本中化学物质的含量越高其响应值就越大, 因此我们使用响应值代表某化学物质的相对含量。样本中各化学物质的响应值除以样本的质量(g), 即可代表每克样本中各化学物质的相对含量。使用SPSS 20.0和Excel 2010进行数据整理和分析。
1.6 数据分析
根据数据的类型选择相应的分布函数进行分析。为了比较不同海拔居群的环境因子、同一种杜鹃在不同海拔下植物的营养器管和繁殖器官的特征、花蜜特征以及植物各组织中次生代谢物的成分和含量的差异, 采用广义线性模型(generalized linear model, GLM)中的正态分布恒等关联函数(identity-link function)进行分析, 表型性状、花蜜特征、植物各组织中次生代谢物的成分和含量作为因变量, 不同海拔梯度作为自变量。为了比较同一种杜鹃的单花花粉数和胚珠数在不同海拔居群是否有差异, 采用广义线性模型中的泊松分布对数关联函数(loglinear-link function)进行分析, 其中花粉数和胚珠数作为因变量, 不同海拔梯度作为自变量。采用Pearson相关性分析同一种杜鹃的形态特征、次生代谢物的成分和含量、海拔及环境因子的相关性(苏应雄等, 2017)。在R软件中, 采用prcomp函数对不同海拔杜鹃的10个表型特征和含量最高的前5类次生代谢物进行主成分分析(principal component analysis, PCA), 并加载factoextra和ggplot2对数据进行可视化处理(Amato & Petit, 2017)。所有的统计分析在SPSS 26.0和R.4.1.1中完成。
2 结果
2.1 不同海拔居群环境因子的比较
居群A、B、C的环境因子沿海拔梯度存在不同程度的差异(表1)。整体上, 随着海拔的升高, 温度下降, 相对湿度增加。对于苍山居群, 海拔C中林下光照强度为1.13 ± 0.71 lux, 裸地光照强度为8.52 ± 4.21 lux; 海拔B中林下光照强度12.22 ± 9.19 lux, 裸地光照强度为29.31 ± 8.71 lux; 海拔A中林下光照强度6.07 ± 3.70 lux, 裸地光照强度为13.55 ± 9.66 lux。海拔C的相对光照强度(0.18% ± 0.04%)显著低于海拔B (0.40% ± 0.07%)和海拔A (0.52% ± 0.07%) (Wald χ2 = 14.105, df = 2, P = 0.001)。对于老君山居群, 海拔C的林下光照强度为1.00 ± 0.80 lux, 裸地光照强度为3.73 ± 3.26 lux; 海拔B的林下光照强度4.33 ± 3.41 lux, 裸地光照强度为21.32 ± 8.45 lux; 海拔A的林下光照强度6.67 ± 3.36 lux, 裸地光照强度为20.86 ± 9.51 lux; 3个海拔间的相对光照强度没有显著差异(表1)。
表1 不同海拔杜鹃居群环境因子(相对光照强度、温度和相对湿度)的比较(广义线性模型)。不同字母表明同一环境因子在不同海拔居群有显著性差异。加粗表示最大值。
Table 1
| 居群 Population | 海拔 Elevation (m) | 相对光照强度 Relative light intensity (%) | 温度 Temperature (℃) | 相对湿度 Relative humidity (%) | |
|---|---|---|---|---|---|
| 苍山 Cangshan Mountain | 海拔A Altitude A | 2,199.20 ± 7.96c | 0.52 ± 0.07a | 16.08 ± 0.28b | 57.17 ± 2.82b |
| 海拔B Altitude B | 2,511.20 ± 10.18b | 0.40 ± 0.07a | 18.92 ± 0.20a | 60.50 ± 1.93b | |
| 海拔C Altitude C | 2,809.00 ± 6.94a | 0.18 ± 0.04b | 12.88 ± 0.34c | 74.42 ± 2.47a | |
| Wald χ² | 2,593.848 | 14.105 | 234.227 | 28.222 | |
| P | < 0.001 | 0.001 | < 0.001 | < 0.001 | |
| 老君山 Laojun Mountain | 海拔A Altitude A | 3,398.20 ± 9.66c | 0.34 ± 0.04a | 12.39 ± 0.84a | 66.67 ± 2.17a |
| 海拔B Altitude B | 3,606.20 ± 8.80b | 0.25 ± 0.05a | 13.64 ± 1.33a | 70.33 ± 5.65a | |
| 海拔C Altitude C | 3,796.00 ± 10.40a | 0.28 ± 0.03a | 7.73 ± 1.17b | 72.11 ± 4.19a | |
| Wald χ² | 851.739 | 3.296 | 11.876 | 0.768 | |
| P | < 0.001 | 0.192 | 0.003 | 0.681 |
2.2 3种杜鹃不同海拔居群的营养器官和繁殖器官特征
对于柳条杜鹃, 分布在海拔A的植株个体的株高和叶长显著大于海拔B和海拔C (P < 0.05), 海拔C的植株个体的雌蕊和雄蕊长、花粉数显著大于海拔A和海拔B (P < 0.05)。对于大白杜鹃, 海拔A的植株个体的花药体积显著大于海拔B和海拔C (Wald χ2 = 9.624, df = 2, P = 0.008), 海拔B的花筒深、花筒直径、花筒开口直径和胚珠数均显著大于海拔A和海拔C (P < 0.05)。对于红棕杜鹃, 海拔A的株高、枝条直径、叶宽、花筒直径和胚珠数均显著大于海拔B和海拔C (P < 0.05), 海拔C的花粉数显著多于海拔A (Wald χ2 = 7.724, df = 2, P = 0.021) (表2)。随着海拔升高, 3种杜鹃的植株高度均降低, 除红棕杜鹃外, 花药体积与海拔呈负相关。
表2 柳条杜鹃、大白杜鹃和红棕杜鹃在腹痛还把居群营养器官和繁殖器官的比较(广义线性模型)(平均值±标准误)。不同字母表示同一杜鹃的特征在不同海拔居群间有显著性差异。加粗表示最大值。
Table 2
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2.3 不同海拔居群3种杜鹃化学性状的比较
2.3.1 花蜜体积、糖浓度和糖成分的比较
海拔C的杜鹃花蜜体积显著高于海拔A (Wald χ2 = 4.482, df = 1, P = 0.034), 海拔C的杜鹃花蜜浓度显著高于海拔A和海拔B (Wald χ2 = 19.051, df = 2, P < 0.001) (图2A)。柳条杜鹃海拔A (1.19 ± 0.18 μL)、海拔B (0.93 ± 0.10 μL)、海拔C (1.10 ± 0.10 μL)的花蜜体积不存在显著差异(Wald χ2 = 1.977, df = 2, P = 0.372); 大白杜鹃海拔A (3.22 ± 0.33 μL)、海拔B (3.98 ± 0.27 μL)和海拔C (4.47 ± 0.39 μL)的花蜜体积间差异不显著(Wald χ2 = 5.979, df = 2, P = 0.050)。红棕杜鹃海拔C的花蜜体积(1.94 ± 0.13 μL)显著高于海拔B (1.45 ± 0.08 μL)和海拔A (1.63 ± 0.19 μL) (Wald χ2 = 9.804, df = 2, P = 0.007)。柳条杜鹃和红棕杜鹃海拔C的花蜜糖浓度(80.47% ± 0.20%, 54.85% ± 1.38%)均显著高于海拔A (57.75% ± 2.74%, 33.08% ± 1.83%) (P < 0.05), 大白杜鹃的花蜜糖浓度在海拔A (30.27% ± 1.01%)、海拔B (28.51% ± 0.78%)和海拔C (30.91% ± 0.78%)之间没有显著差异(Wald χ2 = 4.985, df = 2, P = 0.083)。
图2
图2
不同海拔杜鹃花蜜体积(Ai)、花蜜糖浓度(Aii)和花蜜糖成分含量(B)的比较(柳条杜鹃、大白杜鹃和红棕杜鹃的数值合并分析) (平均值 ± 标准误)。不同字母表示不同海拔间差异显著(P < 0.05)。
Fig. 2
Comparison of nectar volume (Ai) and nectar concentration (Aii) and nectar sugar content (B) of three species of Rhododendron at different altitudes (mean ± SE). Different letters indicate significant differences between different altitudes (P < 0.05).
3种杜鹃花的糖成分中蔗糖含量(12.43 ± 0.91 mg/mL)最高, 其次为葡萄糖(7.38 ± 0.58 mg/mL)和果糖(1.76 ± 0.15 mg/mL), 其中, 海拔C的蔗糖含量(19.70 ± 2.68 mg/mL)显著高于海拔A (9.90 ± 1.14 mg/mL)和海拔B (11.00 ± 0.83 mg/mL) (Wald χ2 = 23.424, df = 2, P < 0.001), 海拔A的葡萄糖含量(8.82 ± 0.96 mg/mL)显著高于海拔C (5.55 ± 1.20 mg/mL) (Wald χ2 = 4.007, df = 1, P = 0.045), 与海拔B的葡萄糖含量(6.84 ± 0.86 mg/mL)差异不显著(Wald χ2 = 4.732, df = 2, P = 0.094)。果糖含量在海拔A、B、C间(2.05 ± 0.26、1.62 ± 0.20、1.54 ± 0.32 mg/mL)无显著性差异(Wald χ2 = 3.092, df = 2, P = 0.213) (图2B)。
2.3.2 各器官次生代谢物成分和含量的比较
整体上, 不同海拔柳条杜鹃、大白杜鹃和红棕杜鹃含量最高的前5类次生代谢物为黄酮类、甾体类、萜类、苯丙素类和生物碱类化学物质(按照相对含量从高到低排列)。将同一种杜鹃在同一海拔的茎、叶、花瓣、花粉和花蜜的这5类次生代谢物的相对含量的数据合并, 仅把海拔作为自变量, 比较同一种杜鹃在不同海拔次生代谢物的相对含量的差异, 结果发现杜鹃中含量最高的前5类次生代谢物在不同海拔间不存在显著性差异(P > 0.05) (图3)。花瓣中黄酮类物质的相对含量显著高于茎、叶、花粉和花蜜(Wald χ2= 47.829, df = 4, P < 0.001)。茎中甾体类物质的相对含量显著性高于叶、花瓣、花粉和花蜜(Wald χ2 = 12.052, df = 4, P = 0.017), 花粉中萜类物质的相对含量显著高于茎、叶、花瓣和花蜜(Wald χ2 = 10.584, df = 4, P = 0.032)。叶和花瓣中苯丙素类的相对含量边缘显著地高于茎、花粉和花蜜(Wald χ2 = 9.556, df = 4, P = 0.049)。植物的叶、花瓣中生物碱的相对含量显著高于花粉(P < 0.05) (图3)。黄酮类物质草棉黄素和5,7,8,4′-四羟基黄酮是杜鹃植物组织中最常见的化合物。茎中5-脱氢栝楼仁二醇(14.88%-18.18%)、双氢槲皮素(7.14%-11.24%)和5,7,8,4′-四羟基黄酮(7.23%-12.59%)各海拔均有存在且含量较高。不同海拔叶中常见物质是草棉黄素(15.49%-19.69%)和杨梅树皮素(5.34%-8.76%)。不同海拔花瓣中常见物质是草棉黄素(21.82%-27.99%)和5,7,8,4′-四羟基黄酮(13.37%-14.38%)。杜鹃的花粉和花蜜中次生代谢物种类数(分别为526和291)少于茎(875)、叶(1,080)和花瓣(975)。不同海拔花粉中常见物质包括5,7,8,4′-四羟基黄酮(37.23%-38.94%)和草棉黄素(17.16%-20.66%), 花蜜常见物质包括荆芥苷(14.15%-19.89%) (附录1)。
图3
图3
不同海拔杜鹃中黄酮类、甾体类、萜类、苯丙素类和生物碱类相对含量的比较(柳条杜鹃、大白杜鹃和红棕杜鹃的数值合并分析) (平均值 ± 标准误)。不同字母表示不同器官间同一类别物质具有显著性差异(P < 0.05)。
Fig. 3
Comparison of flavonoid, steroid, terpenoid, phenylpropanoid and alkaloid contents among Rhododendron at different altitudes (mean ± SE). Different letters indicate significant differences among different organs (P < 0.05).
2.3.3 3种杜鹃的表型和次生代谢物特征及环境因子与海拔的相关性
对同一种杜鹃不同海拔居群的环境因子(温度、相对湿度、相对光照强度)、植物表型(营养器官和繁殖器官)、次生代谢物特征(含量最高的前5类化学物质相对含量)的相关性分析发现, 3种环境因子与海拔间均存在显著的负相关关系(P < 0.05), 植株高度、花冠大小和花药体积与海拔呈显著负相关关系(P < 0.05), 雌蕊和雄蕊长度与海拔呈显著正相关关系(P < 0.05)。相对光照强度、植株高度、花筒体积与温度呈显著正相关关系(P < 0.05), 相对湿度、枝条直径与温度呈显著负相关关系(P < 0.05)。相对光照强度、植物高度和叶片面积与相对湿度呈显著负相关关系(P < 0.05)。花冠大小与相对湿度呈显著正相关关系(P < 0.05)。植物营养器官与繁殖器官结构的相关性见表3。
表3 杜鹃不同海拔居群的营养器官、繁殖器官、5类含量最高的次生代谢物与海拔、环境因子(温度、相对湿度、相对光照强度)的Pearson相关性分析。表格中灰色分割线左下方的数值表示相关性(r), 右上方的数值表示显著性(P)。P < 0.05时加粗表示, 且相应的相关性r值加粗并标注为蓝色, 浅蓝色表示P < 0.05, 蓝色表示P < 0.01, 深蓝色表示P < 0.001。
Table 3
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黄酮类、甾体类、萜类、苯丙素类、生物碱类物质的成分和含量随着海拔高度的变化并没有显著性差异(表3)。5类次生代谢物两两之间均存在极显著的正相关关系(P < 0.001)。黄酮类、甾体类和生物碱类化学物质的相对含量与温度呈显著正相关关系(P < 0.05), 甾体类物质与花筒体积、生物碱类与花筒体积和雌蕊长具有显著的正相关关系(P < 0.05)。
2.3.4 不同海拔杜鹃表型特征和次生代谢物的差异
为进一步分析不同海拔杜鹃植物表型和化学物质的差异, 对3个海拔杜鹃的10个表型性状和5类次生代谢物进行主成分分析, 结果见图4。其中第一主成分特征值和贡献率分别是4.67%和31.15%, 对应特征向量较大的包括甾体类、生物碱类、黄酮类、萜类和苯丙素类, 主要为次生代谢物。第二主成分特征值和贡献率分别为3.44%和22.92%, 特征向量较相关的指标除黄酮类之外, 还包括花筒体积、花筒开口直径、雌蕊长和雄蕊长以及柱头表面积和叶面积等表型特征, 这两个主成分的累计贡献率为53.07%, 已包括所测大部分信息, 具有一定代表性。中、低海拔杜鹃的特征组成存在重叠, 较为相似。
图4
图4
不同海拔杜鹃的10个表型特征和5种次生代谢物含量的主成分分析(PCA)
Fig. 4
Principal component analysis (PCA) of ten phenotypic characteristics and five secondary material components (flavonoid, steroid, terpenoid, phenylpropanoid and alkaloid) of Rhododendron at different altitudes
3 讨论
杜鹃属植物的营养器官和繁殖器官在不同海拔中存在不同程度的变异, 且不同物种间的变异程度有显著差异。柳条杜鹃、大白杜鹃和红棕杜鹃的植株高度、叶片大小均与海拔呈负相关关系。低海拔地区的低光强度有利于枝条的节间伸长, 在遮阴条件下更利于植株高度的增加(Botto, 2015)。随海拔升高, 这3种杜鹃的雄蕊长、单花花粉数在增加, 且单花花粉数增加显著, 而花粉数量的增加提高了传粉的成功率; 柳条杜鹃、大白杜鹃的雌蕊长显著增加, 红棕杜鹃的雌蕊长度没有显著性变异, 这可能与苍山和老君山的海拔跨度不同有关。植物的表型变异可分为趋势一致的适应性变异分化和多样趋势的随机性变异分化两种形式(Singh & Roy, 2017)。杜鹃属植物营养器官的资源投入随海拔的升高在减小, 但是雌雄蕊资源投入的总量随着海拔的升高在增加, 体现趋势一致的适应性变异分化模式。说明在高海拔的胁迫环境中, 3种杜鹃属植物获取的资源有限, 植株高度和花型的优化及植物对雌性繁殖的投入都有利于其在不同海拔环境下优化分配资源, 提高其繁殖成功率。植物表型的适应并不是单一性状主导, 高海拔植物因为温度限制导致生长受限, 矮小的姿态可以减少消耗, 维持生存, 同时它们增加花型表现和雄配子的数量, 这些性状以叠加的形式综合表现, 调节植物在生存繁殖中的权衡选择(Fabbro & Körner, 2004; Pacheco et al, 2016)。
本研究发现柳条杜鹃、大白杜鹃和红棕杜鹃的花大小(花冠以及花筒)表现为多样趋势的随机性变异分化形式。相较于海拔A, 海拔B和海拔C居群的柳条杜鹃和大白杜鹃花筒相对深而宽, 同时其雌雄蕊长度也随海拔上升而伸长。通常植株高度随着海拔的升高而减小, 而花大小随着海拔的升高而增大, 将有限的资源更多地分配给繁殖器官(何亚平等, 2005)。而对于红棕杜鹃, 其花冠和花筒随海拔升高而减小, 但其雌雄蕊长度在不同海拔间差异并不显著, 这可能是因为老君山的海拔在3,300 m以上, 前人的研究也表明海拔越高的地区, 温度低、辐射强, 昼夜温差大, 植物可获取的资源更少(Guo et al, 2016; Feng et al, 2022), 整体上红棕杜鹃的花大小随着海拔升高在变小, 且老君山居群海拔跨度仅200 m, 可能不足以引起其雄蕊长度的变异。3种杜鹃的花大小随海拔的变化与前人对杜鹃属等植物表型特征随海拔变化的研究结果相似, 例如分布在弓杠岭居群的陇蜀杜鹃(Rhododendron przewalskii), 其高海拔居群的花冠管直径、花冠管长、子房、花柱和雌蕊长显著大于中、低海拔居群, 但是在斗鸡台样地和卡卡山样地, 陇蜀杜鹃在各海拔的花部特征没有一致性的变化规律, 例如在卡卡山居群, 陇蜀杜鹃高海拔居群的花冠管直径、花冠管长较大, 但是花柱长和子房长度随着海拔的升高呈现先减少再增大后减少的变化趋势(何家莉, 2021①(①何家莉 (2021) 岷江源区陇蜀杜鹃(Rhododendron przewalskii)花部特征的时空变化及传粉生态学初探. 硕士学位论文, 四川师范大学, 成都.))。二型花柱植物海仙报春花(Primula poissonii)的花冠管开口大小、花药高度以及短柱型的柱头高度跟海拔呈显著正相关关系, 而花冠大小、长柱型花瓣长度、柱头到花冠管开口的距离及短柱型的花冠管长度与海拔呈显著负相关关系, 其他的性状与海拔无显著相关性(李海东等, 2015)。花大小的变异表明3种杜鹃具有较大可塑性, 也更有助于它们对不同环境的适应。
3种杜鹃属植物花蜜的糖浓度约为40%-50%, 富含蔗糖。这3种杜鹃的花蜜特征可能是对传粉者的适应。黄至欢等连续5年对横断山区15种杜鹃传粉生态学的研究表明, 鸟类和蜂类是该区域主要的传粉者(黄至欢, 2015; Huang et al, 2017)。Song等(2019)进一步研究确认柳条杜鹃和红棕杜鹃的主要传粉者是蜂类, 大白杜鹃的主要传粉者为鳞翅目昆虫如蛾蝶类等。蜂鸟传粉植物和蜂类传粉植物的花蜜主要以蔗糖为主(Martínez del Rio et al, 2001; Nicolson, 2002; Ornelas et al, 2002), 而雀形目鸟类传粉的植物花蜜则是以己糖为主(Baker et al, 1998; Nicolson, 2002), 在杜鹃中, 熊蜂等的访问频率与花蜜中蔗糖的糖浓度成正相关(黄至欢, 2015)。蛾蝶类等鳞翅目昆虫传粉的植物也富含蔗糖(Goodwin et al, 2011; 胡德美, 2021)。高海拔居群环境更为恶劣, 杜鹃属植物中生产蜜量更大、糖浓度更高的花蜜, 糖成分中蔗糖的组成比例含量更高, 便于蜂类等传粉者在更短时间内获取更高的能量报酬, 从而维持正常的生命活动。
次生代谢物作为植物化学防御的物质基础, 在协调植物与环境因子、生物因子相互作用关系中起着重要作用。在本研究中, 柳条杜鹃、大白杜鹃和红棕杜鹃中次生代谢物的相对含量并不随着海拔的变化而呈显著差异。然而前人的研究发现, 有些植物的次生代谢物随海拔升高呈显著升高或者降低的趋势。例如对高、中、低海拔居群的云南红豆杉(Taxus wallichiana)的研究发现, 针叶中黄酮类和酚类物质的含量与海拔呈显著正相关, 黄烷醇含量在不同海拔居群间没有显著性差异, 而总丹宁含量在中海拔居群最高, 黄酮类和酚类物质可增强植物应对辐射的能力(Adhikari et al, 2020)。随着海拔的升高, 这3种杜鹃中主要次生代谢物的含量没有显著性变化, 可能是杜鹃属植物次生代谢物的特征不易受到环境因子变化的影响。对杜鹃属植物化感作用的研究发现, 杜鹃产生的化学物质能够抑制自身或者林下伴生物种的种子萌发和幼苗的生长, 从而使得杜鹃属植物占优势的居群生物多样性降低(李朝婵等, 2018; Li et al, 2019)。柳条杜鹃、大白杜鹃和红棕杜鹃植株中富含黄酮类、甾体类、苯丙素类、萜类和生物碱类等次生代谢物, 可能是杜鹃属植物发挥化感作用的重要物质基础, 它们的含量变化与环境关系不大。
同一物种不同组织器官含有不同的化合物种类或者含量(Palmer-Young et al, 2019)。杜鹃属植物不同组织器官次生代谢物的种类和含量有显著差异, 茎中甾体类物质的含量最高, 叶片和花瓣中苯丙素类物质、生物碱类物质的含量显著高于其他类物质, 同时花瓣中还富含黄酮类物质, 而花蜜和花粉中次生代谢物的含量要少于茎、叶、花瓣部位, 花蜜中萜类物质和生物碱类物质含量较高。对川续断属(Dipsacus)植物根、茎、叶、花瓣、花粉、花蜜中次生代谢物川续断皂苷Ⅵ的检测分析发现, 根中川续断皂苷Ⅵ含量最高, 花粉中较低, 而花蜜中未检测出该物质(Wang et al, 2019)。不同组织器官化学物质种类和含量的差异可能与植物不同部位的主要功能存在差异有关联, 例如杜鹃属花瓣中同时富含黄酮类、苯丙素类和生物碱类物质, 因为花瓣是重要的繁殖器官, 不仅要应对变化的气候环境因子, 还要面对多变的生物因子(传粉者、啃食者、微生物等), 为了尽可能提高繁殖成功, 植物倾向把更多的资源投入到繁殖器官中。而花粉和花蜜作为植物主要的花报酬, 其一方面要吸引传粉者来访问进行传粉, 同时又要减少啃食者或者低效的传粉者对花粉、花蜜的浪费, 因此花粉和花蜜中含有一定类别的次生代谢物, 但是相对其他器官来说, 其次生代谢物含量较低。
附录 Supplementary Material
附录1 杜鹃茎、叶、花瓣、花粉和花蜜部位在不同海拔居群含量最高的前5种次生代谢物
Appendix 1 The top 5 secondary metabolites in stem, leaf, petal, pollen and nectar tissues of three species of Rhododendron at different altitudes
致谢
感谢云南省大理市马明永先生和老君山九十九龙潭自然保护区李正宏先生对野外实验的协助和支持, 感谢贵州师范大学生命科学学院本科生杨廷海和欧晓恒对本实验的帮助。
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DOI:10.17520/biods.2015171
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植物的花部性状在异质环境中表现出不均一的适应性进化, 其自然变异可能在时空格局上呈现一定的规律性。选择同一物种的不同地理居群进行花部表型变异分析, 能揭示花部性状随地理梯度的变异模式。海仙花报春(Primula poissonii)属于典型的二型花柱植物, 依赖昆虫传粉实现严格的型间异交。该物种广布于横断山地区亚高山-高山草甸, 其分布海拔跨度大且花部性状在种内具有较高变异, 但这些变异在不同地理梯度(海拔梯度和经纬度梯度)的特定选择因子作用下的变化规律尚不清楚。本研究选择海仙花报春16个居群, 对8个花部关键性状和二型花柱繁殖器官的互补度与海拔和经纬度的关系进行研究, 探究花部性状随地理梯度变异的模式及其潜在的选择因素。研究表明, 海仙花报春两种花型的花冠管开口大小、花药高度以及短柱花柱头高度与海拔均呈正相关, 但两种花型的花冠大小, 长柱花的花瓣长度、柱头到花冠管开口的距离, 以及短柱花的花冠管长度与海拔高度间均呈负相关, 其余性状与海拔无显著相关性。除短柱花中柱头高度以外的性状均随着纬度升高而逐渐减小。长柱花中除花药和柱头间的距离以及柱头到开口的距离外, 其余性状均随着经度的增加而减小; 短柱花的花瓣长度、花药高度以及花药和柱头间的距离随着经度的增加而变大, 其余性状均随着经度的增加而减小。繁殖器官间的互补度并不随地理环境的变化而变化。花部性状的地理变异可能受访花昆虫组成的地理变化驱动。繁殖器官间互补程度的高度保守表明非选型交配在居群二态性的维持和稳定过程中起关键作用。本研究为进一步深入开展报春花属(Primula)花部性状及其选择压力的地理变异研究奠定了基础。
Advance in the study on mechanism of tree resistance to insect
林木抗虫机制研究进展
Drought-induced in vivo synthesis of camptothecin in Camptotheca acuminata seedlings
Intake responses in nectar feeding birds: Digestive and metabolic causes, osmoregulatory consequences, and coevolutionary effects
Primary and secondary metabolite profiles of lodgepole pine trees change with elevation, but not with latitude
DOI:10.1007/s10886-021-01249-y
PMID:33651224
[本文引用: 2]
Climate change has a large influence on plant functional and phenotypic traits including plant primary and secondary metabolites. One well-established approach to investigating the variation in plant metabolites involves studying plant populations along elevation and latitude gradients. We considered how two space-for-time climate change gradients (elevation and latitude) influence carbohydrate reserves (soluble sugars, starches) and secondary metabolites (monoterpenes, diterpene resin acids) of lodgepole pine trees in western Canada. We were particularly interested in the relationship of terpenes and carbohydrates with a wide range of tree, site, and climatic factors. We found that only elevation had a strong influence on the expression of both terpenes and carbohydrates of trees. Specifically, as elevation increased, concentrations of monoterpenes and diterpenes generally increased and soluble sugars (glucose, sucrose, total sugars) decreased. In contrast, latitude had no impact on either of terpenes or carbohydrates. Furthermore, we found a positive relationship between concentrations of starch and total terpenes and diterpenes in the elevation study; whereas neither starches nor sugars were correlated to terpenes in the latitude study. Similarly, both terpenes and carbohydrates had a much greater number of significant correlations to site characteristics such as slope, basal area index, and sand basal area, in the elevational than in the latitude study. Overall, these results support the conclusion that both biotic and abiotic factors likely drive the patterns of primary and secondary metabolite profiles of lodgepole pine along geographical gradients. Also, presence of a positive relationship between terpenes and starches suggests an interaction between primary ad secondary metabolites of lodgepole pine trees.
Pollination by passerine birds: Why are the nectars so dilute?
DOI:10.1016/S1096-4959(02)00014-3 URL [本文引用: 2]
Low flower-size variation in bilaterally symmetrical flowers: Support for the pollination precision hypothesis
DOI:10.3732/ajb.1500371
PMID:26656130
[本文引用: 1]
The evolutionary shift from radial to bilateral symmetry in flowers is generally associated with the evolution of low flower-size variation. This phenomenon supports the hypothesis that the lower size variation in bilateral flowers can be attributed to low pollinator diversity. In this study, we propose two other hypotheses to explain low flower-size variation in bilateral symmetrical flowers. To test the three hypotheses, we examined the relative importance of pollinator diversity, composition, and bilateral symmetry itself as selective forces on low flower-size variation.We examined pollinator diversity and composition and flower-size variation for 36 species in a seminatural ecosystem with high bee richness and frequent lepidopteran visitation.Bilateral flowers were more frequently visited than radial flowers by larger bees, but functional-group diversity of the pollinators did not differ between symmetry types. Although bilateral flowers had significantly lower flower-size variation than radial flowers, flower-size variation did not vary with pollinator diversity and composition but was instead related to bilateral symmetry.Our results suggest that the lower size variation in bilateral flowers might have evolved under selection favoring the control of pollinator behavior on flowers to enhance the accurate placement of pollen on the body of the pollinator, independent of pollinator type. Because of the limited research on this issue, future work should be conducted in various types of plant-pollinator communities worldwide to further clarify the issue.© 2015 Botanical Society of America.
Nectar oasis produced by Agave marmorata Roezl. (Agavaceae) lead to spatial and temporal segregation among nectarivores in the Tehuacán Valley, México
DOI:10.1016/S0140-1963(02)90971-7 URL [本文引用: 1]
Plastic responses contribute to explaining altitudinal and temporal variation in potential flower longevity in high Andean Rhodolirion montanum
DOI:10.1371/journal.pone.0166350 URL [本文引用: 1]
Chemistry of floral rewards: Intra- and interspecific variability of nectar and pollen secondary metabolites across taxa
Climate drives plant-pollinator interactions even along small-scale climate gradients: The case of the Aegean
DOI:10.1111/plb.12593 URL [本文引用: 1]
Pollination biology of Caragana sinica (Buchoz) Rehd
锦鸡儿(Caragana sinica (Buchoz) Rehd.)传粉生物学研究
Anthocyanin accumulation in the illuminated surface of maize leaves enhances protection from photo-inhibitory risks at low temperature, without further limitation to photosynthesis
Influence of stigma colors on reproductive success of Epimedium pubescens
High altitude population of Arabidopsis thaliana is more plastic and adaptive under common garden than controlled condition
DOI:10.1186/s12898-017-0149-5 URL [本文引用: 2]
Plant growth along the altitudinal gradient—Role of plant nutritional status, fine root activity, and soil properties
Pollen aggregation by viscin threads in Rhododendron varies with pollinator
DOI:10.1111/nph.2019.221.issue-2 URL [本文引用: 1]
Are pollinators the agents of selection on flower colour and size in irises?
DOI:10.1111/oik.2017.v127.i6 URL [本文引用: 1]
Potential distribution of Impatiens davidii and its pollinator in China
DOI:10.17521/cjpe.2021.0108 URL [本文引用: 1]
牯岭凤仙花及其传粉昆虫在中国的潜在分布区域分析
DOI:10.17521/cjpe.2021.0108
[本文引用: 1]
牯岭凤仙花(Impatiens davidii)为中国特有的珍稀观赏花卉, 野生种群较小, 同时依赖特殊的传粉者三条熊蜂(Bombus trifasciatus)授粉, 为特化传粉植物, 传粉资源为限制其种群扩散的重要因素。该研究基于63条牯岭凤仙花分布数据、54条三条熊蜂分布数据、19个环境气候因子, 运用最大熵(MaxEnt)模型模拟预测当前及未来(2050s、2070s) 3种气候代表性浓度路径情景RCP2.6、RCP4.5、RCP8.5下牯岭凤仙花和三条熊蜂的潜在分布区域。结果表明: 影响牯岭凤仙花分布的主要环境因子为最暖季度降水量。当前气候条件下, 牯岭凤仙花与三条熊蜂具有较高的地理分布重合度、生态位宽度、生态位重合度, 共同分布区域占比高达99.09%, 较大程度上保证了牯岭凤仙花的传粉资源; 在未来3种气候情景下, 牯岭凤仙花分布区域向东北、华北扩张, 适生面积增加6.60-22.19万km<sup>2</sup>; 三条熊蜂适生区整体略微北移, 适生面积增加4.48-15.50万km<sup>2</sup>; 两者共同分布区域占牯岭凤仙花适生区域比例降低1.40%-9.00%, 表明未来牯岭凤仙花适生区可能受到气候变化和传粉资源缺失共同影响。
Phenotypic diversity of Rhododendron rubiginosum populations at different altitudes
红棕杜鹃不同海拔种群的表型多样性研究
Nectar properties and the role of sunbirds as pollinators of the golden-flowered tea (Camellia petelotii)
DOI:10.3732/ajb.1600428 URL [本文引用: 1]
Bumblebee rejection of toxic pollen facilitates pollen transfer
DOI:10.1016/j.cub.2019.03.023 URL [本文引用: 2]
Effects of light intensity on secondary metabolite camptothecin production in leaves of Camptotheca acuminata seedlings
Spatiotemporal evolution of the global species diversity of Rhododendron
Plant secondary metabolism and its response to environment
植物次生代谢及其与环境的关系
Discrepancy caused by various altitudes in both floral traits and reproductive allocation of Saussurea tangutica
唐古特雪莲花部特征及生殖分配的海拔差异
Differentiation of floral traits associated with pollinator preference in a generalist- pollinated herb, Trollius ranunculoides (Ranunculaceae)
DOI:10.1086/669910 URL [本文引用: 1]
