植物功能性状是植物个体在生长发育过程中与外界环境相互作用而形成的植物性状, 它既能够响应外界环境的变化, 又能对生态系统过程和功能产生影响(刘晓娟和马克平, 2015; Kattge et al., 2020)。植物功能性状是目前生态学研究的热点, 通过对植物功能性状的测量, 可以了解植物在不同环境下的生存策略, 分析植物群落的构建机制, 探究生物多样性对生态系统功能的影响, 并为植被恢复中物种的选取提供理论依据(Kattge et al., 2020)。大量的研究表明, 植物功能性状的比较, 是分析同域或异域物种生长策略差异的有效手段(Díaz et al., 2016; 何念鹏等, 2018)。功能性状具有种内可塑性, 不考虑种内变异的同域物种功能性状比较, 将对物种生长策略分析产生显著的影响, 而相同条件下的种植实验是规避种内性状表型可塑性的有效手段。
叶是高等植物主要的同化器官, 叶性状是植物功能性状的重要组成部分, 叶性状分析对于了解物种的生长特性和生态学功能具有重要意义(Heilmeier, 2019; 李耀琪和王志恒, 2021)。叶的结构和化学组成变化造成的物种功能的差异是驱动物种共存和生态位分化的重要机制(Sack & Frole, 2006; Peppe et al., 2011)。Wright等(2004)建立了全球叶经济谱, 将“投资”和“收益”的概念融入生态学的研究中。外来种往往叶寿命较短, 采取资源快速投资收益方式, 具有高的比叶面积、叶绿素含量、叶氮含量、叶磷含量、光合速率和呼吸速率, 属于快速生长物种; 而本地种叶性状与外来种相反, 投资方式比较保守, 属于慢速生长物种(Wright et al., 2004; Lusk et al., 2019; Kumar et al., 2021)。一般来说, 相比于本地种, 采取积极资源获取策略的外来种在高资源栖息地更具有优势; 采取保守生长策略的本地种在低资源中更有优势(Funk, 2013)。此外, 除叶性状, 本地种和外来种在生物量分配与种子质量的适应策略方面也存在差异。在生物量分配方面, 外来种往往在叶和茎中分配的生物量更多(Wang et al., 2013), 而本地种则更倾向于将更多的生物量分配给地下部分。Poorter (2009)发现根生物量比等性状对于地下水和营养的获取具有重要的指示意义。在种子质量角度, 不同植物种子大小各不相同, 大的种子资源丰富, 存活率高, 以质量取胜; 小的种子则以数量取胜(Westoby et al., 1992)。
受人类活动的影响, 我国暖温带分布着大片的次生灌丛。在灌木层中, 荆条(Vitex negundo var. heterophylla)、酸枣(Ziziphus jujuba var. spinosa)和小花扁担杆(Grewia biloba var. parviflora)是常见的乡土树种。荆条是灌木层常见的优势种, 在海拔700 m以下的山地丘陵地区的阳坡和阴坡均有分布, 而酸枣和小花扁担杆多以伴生种出现, 其中小花扁担杆多生长于灌木层下层。而紫穗槐(Amorpha fruticosa)和火炬树(Rhus typhina)则是灌木层常见的外来种。在部分区域已形成生长优势, 两者都原产北美洲, 紫穗槐在20世纪20年代, 作为一种庭园观赏植物传入我国, 现在我国东北、华北、西北等地区均有栽培, 广泛栽植于河岸、河堤、沙地、山坡及铁路沿线。火炬树自1974年以来向全国各省区推广, 以黄河流域及其以北各省区栽培较多, 常分布于碱性土壤地区, 主要用于荒山绿化兼作盐碱荒地风景林树种(张川红等, 2005)。由于外来种的栽植和扩散, 以上几个物种常常在一个区域内共存, 存在竞争关系(Kunstler et al., 2016)。在山东灌丛的野外调查中也发现, 荆条是灌木层的优势物种, 分布广泛; 酸枣和小花扁担杆均为伴生物种, 但前者多分布在阳坡, 后者多分布在阴坡; 紫穗槐广泛应用于护坡等修复活动中, 而火炬树生长能力很强, 与本地种荆条竞争关系明显。尽管以上物种的功能性状及其对环境的响应策略已有研究报道(胡会峰等, 2006; 曹嘉瑜等, 2021), 但是不同物种在相同生境条件下的生长策略对比研究还较少, 本研究对灌木群落整体演变趋势具有重要意义。
本研究以中国暖温带本地灌木荆条、酸枣和小花扁担杆, 外来灌木紫穗槐和火炬树为研究对象, 通过对一年生幼苗功能性状的测量, 比较了它们生长策略的差异。旨在探讨: 本地种和外来种资源获取策略和适应对策有何不同? 外来种的竞争优势是如何通过功能性状体现出来的?
1 材料和方法
1.1 研究区域概况
本研究在山东大学莱芜房干生态实验站(36.43° N, 117.45° E)进行, 该生态站位于山东省济南市莱芜区西北部山区。该地区属于暖温带大陆性季风气候, 夏季高温多雨, 冬季寒冷干燥, 四季分明。年降水量600-800 mm, 年平均气温12.5 ℃ (Tan et al., 2018)。
1.2 实验设计
实验在房干生态实验站的大棚内进行, 将采集的荆条、酸枣、小花扁担杆、紫穗槐和火炬树种子在纱布上进行催芽, 等其发芽后播种在PVC塑料盆中, 塑料盆的上口直径、下口直径和高度分别为29、25、32 cm。待小苗生长到20 cm左右时进行间苗, 每盆保留1株长势一致且良好的小苗, 每个物种20盆重复。4个月后, 在植物生长旺盛的8月份进行功能性状指标的测定, 实验期间对小苗精心管理, 定期除虫, 保证适宜的水分和养分条件。
1.3 指标测定
叶结构性状: 每个物种选取生长健康的10片成熟叶(单叶或复叶), 各个物种的叶实物图见图1, 测量叶长度(L)、宽度(W)、叶柄长度(PL)、复叶柄长度(CPL), 叶扫描后用Image-Pro Plus 6.0图像处理软件测量叶周长(LP)、叶面积(Area)。将叶和叶柄分开后, 在85 ℃下烘干至恒质量, 分别记录单叶或复叶的叶干质量(LDWt)、叶柄干质量(PDWt)。根据以上的测量指标, 计算如下指标:叶散热能力γ′ (LP2/Area)、叶长叶宽比(L/W)、叶长叶柄长比(L/PL)、比叶质量(LMA = LDWt/Area)、叶生物量分配(LBP = LDWt/(LDWt + PDWt))。
图1
图1
暖温带5种灌木的叶形状实物图。A, 火炬树小叶。B, 火炬树羽状复叶。C, 紫穗槐小叶。D, 紫穗槐羽状复叶。E, 酸枣叶片。F, 小花扁担杆叶片。G, 荆条叶片。
Fig. 1
Pictures of five shrub leaves in warm temperate zone. A, Leaflet of Rhus typhina. B, Pinnately compound leaf of Rhus typhina. C, Leaflet of Amorpha fruticosa. D, Pinnately compound leaf of Amorpha fruticosa. E, Leaf of Ziziphus jujuba var. spinosa. F, Leaf of Grewia biloba var. parviflora. G, Palmately compound leaf of Vitex negundo var. heterophylla.
叶元素含量: 采集生长健康的成熟叶, 带回实验室烘干, 磨细过筛后的样品用H2SO4-H2O2消解后, 用蒸馏法测定全氮(N)含量, 钒钼黄比色法测定全磷(P)含量, 火焰光度法测定钾(K)含量。各指标均以单位质量含量表示, 每个物种4个重复。
叶绿素(Chl)含量: 每个物种选取6片叶, 进行Chl含量的测定, 叶用体积分数95%乙醇浸泡24 h后, 用722 s可见分光光度计(棱光科技有限公司, 上海)测定提取液在665和649 nm处的吸光度D665和D649, 通过以下公式计算Chl含量。
式中, C为色素浓度，即指Chl a或Chl b的浓度, 单位为mg·L-1, 样品鲜质量单位为g, V为提取液体积，为12.5 mL。
叶气体交换: 在实验末期, 选取晴朗的天气, 利用便携式光合仪CI-340 (CID Bio-Science, Camas, USA)测定光合作用, 测量时间在9:30-11:30之间, 实验过程中光强均高于1 200 μmol·m-2·s-1, 此光强已达到C3木本植物的光饱和点(蒋高明, 2004)。最大净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)、胞间CO2浓度(Ci)等指标被记录的同时, 同步记录光合有效辐射(PAR)和大气CO2浓度(Ca)等环境参数。计算瞬时水分利用效率(WUE) = Pn/Tr和表观光能利用效率(LUE) = Pn/PAR。
叶绿素荧光: 在实验末期, 选取晴朗的天气, 利用便携式调制叶绿素荧光仪Mini-PAM (Walz, Effeltrich, Germany)测定荧光日变化, 从4:30到19:30, 每隔1 h测定一次, 测定黎明前的最小荧光值(Fo)和最大荧光值(Fm), F′m为光照下的最大荧光, Ft为瞬时荧光, 每个物种重复测定6次。据此计算光系统II实际量子产量(Yield)、电子传递速率(ETR)、光化学淬灭系数(qP)、非光化学淬灭系数(NPQ), 其中0.5是假设吸收的光被两个光系统均分, 0.84是叶的吸光系数(张守仁, 1999)。
生物量: 在实验前期, 测量每个物种的种子百粒质量(HSM); 在实验末期, 每个物种选取5株进行生物量测定, 小心地从盆中取出植株, 用自来水将根冲洗干净, 然后分为根、茎、叶, 其中根分为主根和侧根, 茎分为主茎和分枝, 叶分为叶和叶柄, 在85 ℃下烘干至恒质量后称质量, 根据各部分的生物量计算生物量分配指标。
1.4 数据处理
采用单因素方差分析检验不同物种功能性状间是否有显著差异, 当数据不满足正态性和方差齐性的要求时, 首先对数据进行对数转换, 方差分析的结果存在显著差异时用邓肯方法进行多重比较。采用Spearman系数进行叶性状间的相关性分析, 显著性检验均是在α = 0.05的水平上进行的, 使用SPSS 23.0软件进行统计分析, 使用OriginPro 2017软件包作图。
2 结果和分析
2.1 不同灌木叶特征、结构和物质含量的比较
表1 5个暖温带灌木物种叶特征、结构和物质组成性状的比较(平均值±标准误)
Table 1
| 性状 Trait | 荆条 Vitex negundo var. heterophylla | 酸枣 Ziziphus jujuba var. spinosa | 小花扁担杆 Grewia biloba var. parviflora | 紫穗槐 Amorpha fruticosa | 火炬树 Rhus typhina |
|---|---|---|---|---|---|
| Area (cm2) | 9.261 ± 1.045c | 4.652 ± 0.410c | 54.529 ± 3.560a | 4.509 ± 0.314c | 22.574 ± 0.817b |
| L/W | 2.380 ± 0.126b | 2.142 ± 0.052b | 1.476 ± 0.053c | 3.157 ± 0.165a | 3.296 ± 0.117a |
| L/PL | 6.088 ± 0.555c | 27.319 ± 2.846a | 8.940 ± 0.215c | 19.041 ± 0.811b | - |
| γ′ | 48.389 ± 5.577a | 21.526 ± 0.981c | 20.755 ± 0.430c | 20.438 ± 0.708c | 36.152 ± 1.332b |
| LMA (g·m-2) | 48.094 ± 0.611bc | 49.303 ± 1.698ab | 44.539 ± 1.513c | 53.040 ± 1.342a | 46.389 ± 1.397bc |
| x(c) (cm·cm-1) | 0.417 ± 0.006c | 0.447 ± 0.006b | 0.402 ± 0.004d | 0.483 ± 0.004a | 0.392 ± 0.003d |
| N (g·kg-1) | 32.825 ± 0.581c | 42.105 ± 0.768a | 37.878 ± 1.221b | 36.800 ± 1.158b | 27.073 ± 1.103d |
| P (g·kg-1) | 3.540 ± 0.186b | 5.968 ± 0.111a | 5.593 ± 0.462a | 5.208 ± 0.548a | 5.793 ± 0.284a |
| K (g·kg-1) | 12.015 ± 0.889b | 15.040 ± 0.142a | 12.478 ± 0.514b | 9.895 ± 0.368c | 10.073 ± 0.540c |
| N:P | 9.371 ± 0.632a | 7.068 ± 0.236b | 6.908 ± 0.586b | 7.274 ± 0.689b | 4.710 ± 0.309c |
| Chl a (mg·g-1) | 1.565 ± 0.060c | 2.316 ± 0.112a | 2.055 ± 0.085b | 2.013 ± 0.040b | 1.771 ± 0.064c |
| Chl b (mg·g-1) | 0.667 ± 0.043c | 0.878 ± 0.057ab | 0.938 ± 0.064a | 0.812 ± 0.027abc | 0.726 ± 0.037bc |
| Chl a/b | 2.384 ± 0.156 | 2.658 ± 0.076 | 2.215 ± 0.081 | 2.494 ± 0.096 | 2.446 ± 0.035 |
| LBP | 0.878 ± 0.004b | - | 0.965 ± 0.001a | 0.790 ± 0.006c | 0.764 ± 0.007d |
Area, 叶面积; Chl a, 单位质量叶绿素a含量; Chl b, 单位质量叶绿素b含量; Chl a/b, 叶绿素a、b含量比值; K, 叶全钾含量; LBP, 所有叶干质量/(所有叶干质量+所有叶柄干质量); LMA, 比叶质量; L/PL, 叶长/叶柄长; L/W, 叶长/叶宽; N, 叶全氮含量; N:P, 叶氮磷比; P, 叶全磷含量; x(c), 重心到基部距离与叶长比值; γ′, 周长2/面积。不同小写字母表示物种之间存在显著差异(p < 0.05)。
Area, leaf area; Chl a, chlorophyll a content per unit mass; Chl b, chlorophyll b content per unit mass; K, leaf potassium content; LBP, leaf dry mass (LDWt)/(LDWt + petiole dry mass (PDWt)); LMA, LDWt/Area; L/PL, leaf length to petiole length; L/W, leaf length to width; N, leaf nitrogen content; N:P, leaf nitrogen content to phosphorus content ratio; P, leaf phosphorus content; x(c), ratio of distance from center of gravity to base to leaf length; γ′, leaf perimeter (LP)2/Area. Different lowercase letters indicate significant differences among different species (p < 0.05).
对于不同灌木叶的N、P、K含量来讲, 酸枣叶中N、P、K含量最高, 火炬树叶的N含量最低, 荆条叶的P含量最低, 紫穗槐叶的K含量最低。单位质量的叶绿素含量与叶N含量有着良好的相关性(表2), 但是Chl a/b在不同物种间没有显著差异。
表2 5个暖温带灌木物种叶性状的Spearman相关性分析
Table 2
| LMA | γ′ | L/W | L/PL | LBP | N | P | K | N:P | Chl a | Chl b | Chl a/b | Chl t | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Area | -0.048 | 0.168 | 0.525** | -0.027 | -0.700** | -0.600** | 0.096 | -0.814** | -0.573** | -0.172 | -0.089 | -0.134 | -0.146 |
| LMA | 0.071 | 0.425** | 0.281 | -0.243 | 0.269 | 0.116 | 0.098 | 0.170 | -0.083 | -0.210 | 0.232 | -0.078 | |
| γ′ | 0.386** | -0.486** | -0.199 | -0.635** | -0.400 | -0.140 | 0.081 | -0.650** | -0.575** | -0.035 | -0.671** | ||
| L/W | 0.293 | -0.787** | -0.367 | -0.050 | -0.490* | -0.155 | -0.263 | -0.414* | 0.340 | -0.305 | |||
| L/PL | -0.446* | 0.579* | 0.424 | 0.135 | -0.262 | 0.557** | 0.425* | 0.302 | 0.564** | ||||
| LBP | 0.582* | -0.131 | 0.715** | 0.491 | 0.142 | 0.361 | -0.473* | 0.199 | |||||
| N | 0.387 | 0.638** | 0.280 | 0.722** | 0.418 | 0.325 | 0.689** | ||||||
| P | 0.118 | -0.704** | 0.480* | 0.316 | 0.097 | 0.423 | |||||||
| K | 0.281 | 0.242 | 0.189 | 0.203 | 0.236 | ||||||||
| N:P | -0.078 | -0.156 | 0.156 | -0.051 | |||||||||
| Chl a | 0.796** | 0.166 | 0.970** | ||||||||||
| Chl b | -0.378* | 0.895** | |||||||||||
| Chl a/b | -0.013 |
粗体表示相关具有显著性; *, p < 0.05; **, p < 0.01。Chl t，单位质量总叶绿素含量，其他性状的简称同
Bold indicates significant correlation; *, p < 0.05; **, p < 0.01. Chl t, the total chlorophyll content per unit mass, other abbreviations for traits see
2.2 不同灌木叶生理性状的比较
图2
图2
5种暖温带灌木叶气体交换参数比较(平均值±标准误)。n = 4-8, 不同小写字母表示差异显著(p < 0.05)。
Fig. 2
Gas exchange parameters of the five shrub species in warm temperate zone (mean ± SE). n = 4-8, different lowercase letters indicate significant differences (p < 0.05). Ci, substomatal CO2 concentration; Gs, stomatal conductance; LUE, apparent light use efficiency; Pn, net photosynthesis rate; Tr, transpiration rate; WUE, water use efficiency.
图3
图3
5种暖温带灌木的叶绿素荧光日变化(平均值±标准误, n = 6)。ETR, 电子传递速率; NPQ, 非光化学淬灭系数; PAR, 光合有效辐射; T, 气温; Yield, 实际量子产量。
Fig. 3
Diurnal courses of chlorophyll fluorescence of the five shrub species in warm temperate zone (mean ± SE, n = 6). ETR, electron transport rate; NPQ, non photochemical quenching; PAR, photosynthetically active radiation; T, air temperature; Yield, actual quantum yield.
2.3 不同灌木生物量分配的比较
表3 暖温带5个灌木物种的各器官生物量分配(平均值±标准误)
Table 3
| 性状 Trait | 荆条 Vitex negundo var. heterophylla | 酸枣 Ziziphus jujuba var. spinosa | 小花扁担杆 Grewia biloba var. parviflora | 紫穗槐 Amorpha fruticosa | 火炬树 Rhus typhina |
|---|---|---|---|---|---|
| HSM (g) | 0.947 ± 0.013c | 17.095 ± 0.119a | 4.605 ± 0.025b | 0.833 ± 0.007c | 0.919 ± 0.010c |
| RMR | 0.295 ± 0.015a | 0.187 ± 0.014bc | 0.162 ± 0.020c | 0.218 ± 0.017b | 0.181 ± 0.018bc |
| SMR | 0.284 ± 0.014b | 0.328 ± 0.020 a | 0.328 ± 0.012a | 0.340 ± 0.005a | 0.179 ± 0.005c |
| LMR | 0.420 ± 0.008c | 0.485 ± 0.012b | 0.510 ± 0.009b | 0.442 ± 0.021c | 0.639 ± 0.019a |
| R/S | 0.422 ± 0.031a | 0.231 ± 0.020b | 0.196 ± 0.030b | 0.281 ± 0.027b | 0.224 ± 0.027b |
| BR/AR | 5.051 ± 0.209a | 1.184 ± 0.121b | 1.629 ± 0.329b | 1.842 ± 0.248b | 5.485 ± 0.596a |
| B/MS | 0.266 ± 0.053c | 0.772 ± 0.080b | 1.109 ± 0.103a | 0d | 0d |
| P/L | 0.094 ± 0.006c | - | 0.038 ± 0.003d | 0.271 ± 0.013b | 0.308 ± 0.016a |
| STMR | 0.320 ± 0.016b | 0.328 ± 0.020b | 0.346 ± 0.012b | 0.434 ± 0.004a | 0.329 ± 0.010b |
B/MS, 分枝生物量/主茎生物量; BR/AR, 侧根生物量/主根生物量; HSM, 种子百粒质量; LMR, 叶生物量/总生物量; P/L, 叶柄生物量/叶生物量; RMR, 根生物量/总生物量; R/S, 根生物量/(叶生物量+茎生物量); SMR, 茎生物量/总生物量; STMR, 支撑结构比例。不同小写字母表示物种之间存在显著差异(p < 0.05)。
B/MS, branch mass/main stem mass; BR/AR, branch root mass/axial root mass; HSM: mass of 100 seeds; LMR, leaf mass/total mass; P/L, petiole mass /lamina mass; RMR, root mass/total mass; R/S, root mass/shoot mass; SMR, stem mass/total mass; STMR, supporting structure mass ratio. Different lowercase letters indicate significant differences among different species (p < 0.05).
3 讨论
3.1 本地种和外来种的生长策略
本地种将更多的生物量分配给地下, 资源获取策略相对保守。这种缓慢投资方式使得本地种在资源贫瘠的生境中更具有优势。从气体交换特征来看, 荆条和酸枣属于低光合低蒸腾的物种, 这主要归结于两者的气孔导度比较低。气孔是植物体进行气体交换和水分进出的通道, 气孔导度对于CO2的扩散具有很强的限制作用, 进而对光合作用起到限制作用(Drake et al., 2017; 叶子飘等, 2021), 同时也限制了蒸腾失水(Flexas et al., 2016), 说明荆条和酸枣对于资源的利用保守。叶片的结构性状与生理性状往往具有良好的对应关系。比如具有高比叶质量的物种叶氮含量和相对生长速率一般比较低(Poorter et al., 2009; 张泽文等, 2021), 本地物种酸枣和荆条具有较高的比叶质量, 导致它的生长速率相对较慢。具有叶齿的叶片具有生长上的优势, 特别是当处于不利的环境中时(Xu et al., 2008), 因为它对热量具有高的传导能力, 从而使叶片温度降低保持生理活性(Xu et al., 2008), γ′用来表示叶片的分裂程度, 而本地种荆条的γ′要远高于其他物种。在生物量分配方面, 广泛分布的本地种荆条的根生物量比显著高于外来种火炬树和紫穗槐。本地种荆条较高的根冠比使其具有很强的抗干扰能力和干扰后的恢复能力(戴晓兵, 1989; Naidu & Delucia, 1997; 赵思金等, 2008), 这是其分布范围广的重要原因, 赵思金等(2008)对灌木与草混播的灌木根系分布的研究发现, 荆条在群落中根系分布量的平均值最大; 戴晓兵(1989)对怀柔山区荆条的研究也发现, 其根系的生物量占总生物量的55%以上，且发现荆条根系的最高生长速度出现在5-7月, 而枝条的最高生长速度在7-10月, 这说明荆条首先长根占据有利的地下空间, 这有利于当雨季到来气候转暖以后充分吸收养分供给地上部分的生长, 这种对根的优先分配也是植物一项重要的储存策略。种子质量能够反应植物的生殖策略, 不同植物的种子质量能够相差到11个数量级(Moles et al., 2005), 大的种子以质量取胜, 小的种子以数量取胜, 并且更有利于随风传播。这就涉及生态学中不同物种的生态对策问题, r对策者以提高增殖能力和扩散能力获得生存, 而K对策者以提高竞争能力获得优胜(孙儒泳等, 1993)。本研究发现, 本地种酸枣和小花扁担杆更倾向于K对策(表3), 而荆条更倾向于r对策。
相对于本地种, 大多数的外来种具有积极的生长策略和资源获取策略。外来种一般具有较高的比叶面积、叶片养分(如N和P)含量和叶绿素含量, 从而提高自身的光合能力, 加快生物量的积累来适应外界环境(Kumar et al., 2021)。本研究发现外来种紫穗槐和火炬树具有很强的光合能力, 尤其对于瞬时变化的光照具有很强的适应能力。紫穗槐属于高光合高蒸腾的物种, 这尽管可以提高物种的光能利用效率, 但是水分利用效率不高是一大缺陷。火炬树属于高光合低蒸腾的物种, 其不仅具有高的光能利用效率而且具有高的水分利用效率, 在保持较低蒸腾作用的情况下, 利用有限水分进行较高程度的光合作用, 对树木的生长发育来说是一种最为经济有效的方式(郑淑霞和上官周平, 2006)。叶柄具有支撑叶片、传导水分的作用, 紫穗槐这种粗短的叶柄可能更有利于支撑运动的叶片, 而火炬树几乎没有叶柄, 这有利于水分的传输, 这点从叶长与叶柄长的比值也可以证实。高的叶长叶宽比可以减小叶片边缘距中脉的平均距离, 对于提高叶片水分传导的效率和机械支持力都具有重要的意义(Niinemets et al., 2007)。叶脉与叶柄相连, 在叶片内部起着支撑叶片和传导水分的作用, 发达的中脉及其维管组织不仅有利于提高水分的输导效率, 同时对叶片抵御干旱和大风也有着重要意义(史刚荣等, 2006; Scoffoni et al., 2017)。本研究中, 紫穗槐对支撑结构的较大投入既有叶片尺度上的(表1)也有整株个体尺度上的(表3)。从叶片的层面上来说, 具有复叶的物种对支撑结构的投入比较大, 尤其是火炬树和紫穗槐; 而从个体的层面上来说, 将叶柄、分枝、茎这些支撑结构都加和以后, 紫穗槐的支撑结构投入明显高于其他几个物种, 这样的分配对于维持水分的传导以及叶片的运动都有着重要的意义。外来物种凭借优越的光合能力, 促进了地上生物量的积累。与本地种相比, 外来种紫穗槐和火炬树地上生物量分配更多。且在种子质量方面, 外来种紫穗槐和火炬树为r对策者, 两者种子的扩散能力都比较强, 这对于外来种能够入侵林下非常重要。
随着物种的耐阴能力增加, 叶片的大小增加, 比叶质量减小(Niinemets, 1998; 张云舒, 2017), 在5个物种中, 小花扁担杆的叶面积最大, 比叶质量最小。另外, 本研究发现小花扁担杆叶片Chl a/b要比其他4种低一些, 这也是阴生叶片的特征, 因为Chl b是捕光天线复合物的主要色素成分, 因此Chl a/b间接反映了捕光复合物的大小, 林下植物反应中心复合物小而捕光复合物大, 阳生植物与之相反, 所以阴生植物比阳生植物具有更低的Chl a/b (Chow et al., 1990)。这有利于提高林下植物对红光的有效吸收, 以保持光合系统之间的能量平衡(蒋高明, 2004)。Chl a/b与环境因子尤其是光照的关系更大, 遮阴下Chl a/b的降低可使植物更好利用遮阴环境中的漫射光, 有利于适应弱光环境(李晓征等, 2006)。从叶片生理角度看, 小花扁担杆正午过后荧光日变化的实际量子产量恢复值也比较慢, 这也说明了其叶片可能对于高光强的适应能力有限, 其叶片体现出来一些阴生性。总之, 小花扁担杆具有较大的叶片面积、较低的比叶质量和Chl a/b、缓慢的实际量子产量恢复能力, 说明其具有阴生物种的特性。
3.2 灌木层的演替趋势
物种特性影响了群落演替的进程。荆条和酸枣都是暖温带的喜光本地种, 而荆条的分布范围更广, 这与它较强的种子传播能力有关, 同时荆条采取将更多的生物量优先分配在地下根中储存的策略, 这保证了其在植被受干扰, 植物地上部分受到破坏后可以继续生存, 抵抗干扰能力较强(Crow, 1988; Naidu & Delucia, 1997), 这也是荆条在人为干扰严重的华北山区能够在灌木层占据优势的重要原因。植物的耐阴性影响着森林演替动态中的物种组成(Poorter & Rozendaal, 2008), 演替早期低比叶质量的快速生长物种逐渐会被演替后期高比叶质量的缓慢生长物种所代替(Poorter, 2009)。演替早期植物或先锋植物被认为具有许多阳生植物的特征, 演替后期或顶极群落植物则是对遮阴条件具有较强忍耐力的类群(公绪云等, 2018)。本研究发现, 作为伴生种的小花扁担杆体现出了一定的阴生性, 其叶面积大且Chl a/b低, 因此随着群落演替的进行, 小花扁担杆在暖温带灌木层物种中可能会占据更大的优势。因为早期演替物种比晚期演替植物有更大的适应能力(史刚荣等, 2006; 公绪云等, 2018), 史刚荣等(2006)认为牡荆(Vitex negundo var. cannabifolia)和酸枣叶片结构会随着群落演替进程发生变化, 说明它们不仅对恢复演替早期的干旱生境具有较强的适应性, 而且对演替后期的阴蔽条件也具有一定忍受力, 在植被恢复演替中具有重要作用。外来物种在资源丰富的生境中具有生长和繁殖优势。火炬树克隆繁殖力极强(Wang et al., 2008; Tan et al., 2018), 种群迅速增长, 对本地种造成严重威胁(Yuan et al., 2013; Du et al., 2017), 这与火炬树克隆分株的枝叶侧向生长快于树高生长有关, 这可以促使火炬树克隆分株快速占据灌草丛上层, 利于火炬树单优群落不断的向外缘扩散(张明如等, 2008)。尽管火炬树在造林方面有优势, 在荒山植被修复中发挥着重要的作用, 但在中国已被列为入侵物种(Wang et al., 2008), 在种植火炬树时应该采取更加保守的策略。在经过近一个世纪的栽植驯化以后, 发现外来种紫穗槐并没有对本地生态环境造成入侵, 反而因其优良的耐寒、耐旱、耐湿、抗风沙、抗逆性等优良品质成为了防风固沙、水土保持的常用植物(闫永庆等, 2008; Zhang et al., 2013), 广泛地种植于铁路和公路两旁。关于暖温带的灌木层物种在未来气候变化的条件下如何演变, 值得进一步探究。
4 结论
中国暖温带灌木2个外来种和3个本地种体现出了不同的生长和资源利用策略: (1)外来种火炬树和紫穗槐表现出很好的光合优越性, 对于瞬时变化的光强具有很强的适应能力。(2)本地种荆条和酸枣对资源的利用比较保守。小花扁担杆具有阴生性, 在灌木层演替后期的阴蔽条件下更具有生长优势。(3)良好的种子扩散能力和叶散热能力、保守的光能利用策略、较强的干扰后恢复能力是荆条成为中国暖温带地区广布优势种的重要原因。
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PMID:30985943
[本文引用: 1]
Leaf size varies conspicuously along environmental gradients. Small leaves help plants cope with drought and frost, because of the effect of leaf size on boundary layer conductance; it is less clear what advantage large leaves confer in benign environments. We asked if large leaves give species of warm climates an advantage in seedling light interception efficiency over small-leaved species from colder environments. We measured seedling leaf, architectural and biomass distribution traits of 18 New Zealand temperate rainforest evergreens; we then used a 3-D digitiser and the Yplant program to model leaf area display and light interception. Species associated with mild climates on average had larger leaves and larger specific leaf areas (SLA) than those from cold climates, and displayed larger effective foliage areas per unit of aboveground biomass, indicating higher light interception efficiency at whole-plant level. This reflected differences in total foliage area, rather than in self-shading. Our findings advance the understanding of leaf size by showing that large leaves enable seedlings of species with highly conductive (but frost-sensitive) xylem to deploy large foliage areas without increasing self-shading. Leaf size variation along temperature gradients in humid forests may therefore reflect a trade-off between seedling light interception efficiency and susceptibility to frost.© 2019 The Authors. New Phytologist © 2019 New Phytologist Trust.
Structural characteristics and diversity of typical shrub communities in Qilian Mountains
祁连山典型灌丛群落结构特征及其多样性研究
A brief history of seed size
DOI:10.1126/science.1104863
PMID:15681384
[本文引用: 1]
Improved phylogenies and the accumulation of broad comparative data sets have opened the way for phylogenetic analyses to trace trait evolution in major groups of organisms. We arrayed seed mass data for 12,987 species on the seed plant phylogeny and show the history of seed size from the emergence of the angiosperms through to the present day. The largest single contributor to the present-day spread of seed mass was the divergence between angiosperms and gymnosperms, whereas the widest divergence was between Celastraceae and Parnassiaceae. Wide divergences in seed size were more often associated with divergences in growth form than with divergences in dispersal syndrome or latitude. Cross-species studies and evolutionary theory are consistent with this evidence that growth form and seed size evolve in a coordinated manner.
Growth, allocation and water relations of shade-grown Quercus rubra L. saplings exposed to a late-season canopy gap.
DOI:10.1006/anbo.1996.0446 URL [本文引用: 2]
Are compound-leaves woody species inherently shade-intolerant? An analysis of species ecological requirements and foliar support costs
DOI:10.1023/A:1009773704558 URL [本文引用: 1]
Leaf shape and venation pattern alter the support investments within leaf lamina in temperate species: a neglected source of leaf physiological differentiation?
Sensitivity of leaf size and shape to climate: global patterns and paleoclimatic applications
DOI:10.1111/j.1469-8137.2010.03615.x
PMID:21294735
[本文引用: 1]
• Paleobotanists have long used models based on leaf size and shape to reconstruct paleoclimate. However, most models incorporate a single variable or use traits that are not physiologically or functionally linked to climate, limiting their predictive power. Further, they often underestimate paleotemperature relative to other proxies. • Here we quantify leaf-climate correlations from 92 globally distributed, climatically diverse sites, and explore potential confounding factors. Multiple linear regression models for mean annual temperature (MAT) and mean annual precipitation (MAP) are developed and applied to nine well-studied fossil floras. • We find that leaves in cold climates typically have larger, more numerous teeth, and are more highly dissected. Leaf habit (deciduous vs evergreen), local water availability, and phylogenetic history all affect these relationships. Leaves in wet climates are larger and have fewer, smaller teeth. Our multivariate MAT and MAP models offer moderate improvements in precision over univariate approaches (± 4.0 vs 4.8°C for MAT) and strong improvements in accuracy. For example, our provisional MAT estimates for most North American fossil floras are considerably warmer and in better agreement with independent paleoclimate evidence. • Our study demonstrates that the inclusion of additional leaf traits that are functionally linked to climate improves paleoclimate reconstructions. This work also illustrates the need for better understanding of the impact of phylogeny and leaf habit on leaf-climate relationships.© 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.
Leaf traits show different relationships with shade tolerance in moist versus dry tropical forests
DOI:10.1111/j.1469-8137.2008.02715.x
PMID:19140935
[本文引用: 3]
Shade tolerance is the central paradigm for understanding forest succession and dynamics, but there is considerable debate as to what the salient features of shade tolerance are, whether adult leaves show similar shade adaptations to seedling leaves, and whether the same leaf adaptations are found in forests under different climatic control. Here, adult leaf and metamer traits were measured for 39 tree species from a tropical moist semi-evergreen forest (1580 mm rain yr(-1)) and 41 species from a dry deciduous forest (1160 mm yr(-1)) in Bolivia. Twenty-six functional traits were measured and related to species regeneration light requirements.Adult leaf traits were clearly associated with shade tolerance. Different, rather than stronger, shade adaptations were found for moist compared with dry forest species. Shade adaptations exclusively found in the evergreen moist forest were related to tough and persistent leaves, and shade adaptations in the dry deciduous forest were related to high light interception and water use.These results suggest that, for forests differing in rainfall seasonality, there is a shift in the relative importance of functional leaf traits and performance trade-offs that control light partitioning. In the moist evergreen forest leaf traits underlying the growth-survival trade-off are important, whereas in the seasonally deciduous forest leaf traits underlying the growth trade-off between low and high light might become important.
Leaf size and leaf display of thirty-eight tropical tree species
DOI:10.1007/s00442-008-1131-x
PMID:18719946
[本文引用: 1]
Trees forage for light through optimal leaf display. Effective leaf display is determined by metamer traits (i.e., the internode, petiole, and corresponding leaf), and thus these traits strongly co-determine carbon gain and as a result competitive advantage in a light-limited environment. We examined 11 metamer traits of sun and shade trees of 38 coexisting moist forest tree species and determined the relative strengths of intra- and interspecific variation. Species-specific metamer traits were related to two variables that represent important life history variation; the regeneration light requirements and average leaf size of the species. Metamer traits varied strongly across species and, in contrast to our expectation, showed only modest changes in response to light. Intra- and interspecific responses to light were only congruent for a third of the traits evaluated. Four traits, amongst which leaf size, specific leaf area (SLA), and leaf area ratio at the metamer level (LAR) showed even opposite intra- and interspecific responses to light. Strikingly, these are classic traits that are thought to be of paramount importance for plant performance but that have completely different consequences within and across species. Sun trees of a given species had small leaves to reduce the heat load, but light-demanding species had large leaves compared to shade-tolerants, probably to outcompete their neighbors. Shade trees of a given species had a high SLA and LAR to capture more light in a light-limited environment, whereas shade-tolerant species have well-protected leaves with a low SLA compared to light-demanding species, probably to deter herbivores and enhance leaf lifespan. There was a leaf-size-mediated trade-off between biomechanical and hydraulic safety, and the efficiency with which species can space their leaves and forage for light. Unexpectedly, metamer traits were more closely linked to leaf size than to regeneration light requirements, probably because leaf-size-related biomechanical and vascular constraints limit the trait combinations that are physically possible. This suggests that the leaf size spectrum overrules more subtle variation caused by the leaf economics spectrum, and that leaf size represents a more important strategy axis than previously thought.
Leaf structural diversity is related to hydraulic capacity in tropical rain forest trees
The hydraulic resistance of the leaf (R1) is a major bottleneck in the whole plant water transport pathway and may thus be linked with the enormous variation in leaf structure and function among tropical rain forest trees. A previous study found that R1 varied by an order of magnitude across 10 tree species of Panamanian tropical lowland rain forest. Here, correlations were tested between R1 and 24 traits relating to leaf venation and mesophyll structure, and to gross leaf form. Across species, R1 was related to both venation architecture and mesophyll structure. R1 was positively related to the theoretical axial resistivity of the midrib, determined from xylem conduit numbers and dimensions, and R1 was negatively related to venation density in nine of 10 species. R1 was also negatively related to both palisade mesophyll thickness and to the ratio of palisade to spongy mesophyll. By contrast, numerous leaf traits were independent of R1, including area, shape, thickness, and density, demonstrating that leaves can be diverse in gross structure without intrinsic trade-offs in hydraulic capacity. Variation in both R1-linked and R1-independent traits related strongly to regeneration irradiance, indicating the potential importance of both types of traits in establishment ecology.
Leaf vein xylem conduit diameter influences susceptibility to embolism and hydraulic decline
DOI:10.1111/nph.14256
PMID:27861926
[本文引用: 1]
Ecosystems worldwide are facing increasingly severe and prolonged droughts during which hydraulic failure from drought-induced embolism can lead to organ or whole plant death. Understanding the determinants of xylem failure across species is especially critical in leaves, the engines of plant growth. If the vulnerability segmentation hypothesis holds within leaves, higher order veins that are most terminal in the plant hydraulic system should be more susceptible to embolism to protect the rest of the water transport system. Increased vulnerability in the higher order veins would also be consistent with these experiencing the greatest tensions in the plant xylem network. To test this hypothesis, we combined X-ray micro-computed tomography imaging, hydraulic experiments, cross-sectional anatomy and 3D physiological modelling to investigate how embolisms spread throughout petioles and vein orders during leaf dehydration in relation to conduit dimensions. Decline of leaf xylem hydraulic conductance (K ) during dehydration was driven by embolism initiating in petioles and midribs across all species, and K vulnerability was strongly correlated with petiole and midrib conduit dimensions. Our simulations showed no significant impact of conduit collapse on K decline. We found xylem conduit dimensions play a major role in determining the susceptibility of the leaf water transport system during strong leaf dehydration.© 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.
Leaf anatomy of dominant plant species in the successional communities of Xiangshan Moutnain, Huaibei, China
淮北相山恢复演替群落优势树种叶片的生态解剖
DOI:10.17521/cjpe.2006.0042
[本文引用: 3]
对淮北相山混交林5个优势种叶片的生态解剖学观察表明，其叶片结构具有一定的旱生特征：表皮具发达的表皮毛或角质层，全栅等面叶或具发达的栅栏组织，维管组织发达。牡荆（Vitex negundo var. cannabifolia）和酸枣（Ziziphus jujuba var. spinosa）作为两个广布优 势树种，叶片结构表现出很大的可塑性：1）同一群落环境（混交林）中，叶片结构随着季节的变化表现出发育可塑性（5月初的叶片比9月中旬更具有阳生叶的特点）；2）不同恢复 演替阶段的群落中，叶片结构随着群落环境的变化表现出环境可塑性，其变化趋势为：灌草丛（旱生/阳生）灌丛（旱生/阳生）落叶疏林（中生/阳生）人工侧柏（Platyclad us orientalis）林（中生/阴生）。这种可塑性既是植物适应其异质生境的一种重要机制，同时又是不同群落环境的反映。非参数相关分析表明，牡荆和酸枣的叶片结构受多个生态因子综合影响，其中水分和风速是影响叶片结构的主导因子。叶片的上表皮角质层厚度、气孔器密度、栅栏组织厚度 、叶片厚度、木质部厚度、韧皮部厚度、维管束厚度等性状均与土壤含水量和空气相对湿度呈显著负相关，与风速呈显著正相关。
Invasive Rhus typhina invests more in height growth and traits associated with light acquisition than do native and non-invasive alien shrub species
DOI:10.1007/s00468-018-1698-8 URL [本文引用: 2]
Invasion possibility and potential effects of Rhus typhina on Beijing municipality
DOI:10.1111/j.1744-7909.2008.00660.x URL [本文引用: 2]
Comparative evolutionary ecology of seed size
DOI:10.1016/0169-5347(92)90006-W URL [本文引用: 1]
The worldwide leaf economics spectrum
DOI:10.1038/nature02403 URL [本文引用: 2]
Effect of salt stress on Amorpha fruticosa L. growth and physiological index
盐胁迫对紫穗槐生长发育及生理特性的影响
Investigation on CO2-response model of stomatal conductance for plants
DOI:10.17521/cjpe.2020.0326 URL [本文引用: 1]
植物气孔导度对CO2响应模型的构建
Competitive interaction between the exotic plant Rhus typhina L. and the native tree Quercus acutissima Carr. in Northern China under different soil N:P ratios
DOI:10.1007/s11104-013-1748-3 URL [本文引用: 1]
Dispersal of staghorn sumac in Beijing areas
北京地区火炬树的萌蘖繁殖扩散
Growth strategy of Rhus typhina clonal ramets in the hilly area of the Taihang Mountains
太行山低山丘陵区火炬树克隆分株的生长策略
A discussion on chlorophyll fluorescence kinetics parameters and their significance
叶绿素荧光动力学参数的意义及讨论
Effects of soil moisture and light intensity on ecophysiological characteristics of Amorpha fruticosa seedlings
DOI:10.1007/s11676-013-0352-y URL [本文引用: 1]
Study on Root distribution of four species of shrub in artificial shrub and grass mixture communities
不同人工灌木与草混播群落中4种灌木根系分布的研究
Comparison of leaf gas exchange and chlorophyll fluorescence parameters in eight broad-leaved tree species
8种阔叶树种叶片气体交换特征和叶绿素荧光特性比较
Canopy weight than leaf weight in young Larix olgensis plantations
人工长白落叶松幼龄林树冠比叶重
DOI:10.13287/j.1001-9332.202108.002
[本文引用: 1]
比叶重(LMA)是构建生态系统过程模型的重要参数之一,准确预测树冠比叶重的动态变化对提高模型精度有重要意义。本研究以黑龙江省尚志市帽儿山林场人工长白山落叶松为对象,分别在生长季针叶不同发育时期对树冠内不同垂直位置的针叶比叶重进行测量,分析针叶比叶重在树冠垂直方向及针叶不同发育时期的变化规律,探讨导致其时间和空间差异的主要因子,建立长白落叶松幼龄林比叶重动态预估模型。结果表明: 比叶重在树冠垂直方向表现为随着相对着枝深度(RDINC)的增加而减小,完全展叶后比叶重在垂直方向的变化幅度明显高于展叶初期。比叶重在不同发育时期表现为随发育进程先增大后趋于稳定,该趋势随着树冠深度的增加而逐渐减弱。分别以RDINC和年度积日(DOY)为单一变量预测比叶重时,模型的调整后决定系数(R<sub>a</sub><sup>2</sup>)低于0.6,当同时以RDINC和DOY为自变量构建比叶重预估模型时,R<sub>a</sub><sup>2</sup>提高0.19,且模型检验效果良好(ME=0.54 g·m<sup>-2</sup>, MAE=5.74 g·m<sup>-2</sup>)。研究表明长白落叶松比叶重在树冠不同轮层和不同针叶发育期间均存在显著差异,以RDINC和DOY为自变量构建的比叶重预测模型可以很好描述长白落叶松比叶重的空间及生长季针叶发育期变化,为阐明树冠发育机理提供理论依据,为提高生态过程模型精度奠定基础。
