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常绿阔叶林因人类不合理利用,遭到严重破坏,其残存的母桩、根茎、种子等地下繁殖体会因为亚热带地区有利的水热条件而由残存体发展成为大面积的次生林、次生灌丛和灌草丛[1]。自然条件下,属于退化生态系统的亚热带次生灌丛经过长时间的逐步恢复形成针叶树先锋群落[2-3],但仍有大面积的次生灌丛群落存在着演替更新困难的问题[1]。顺从生态系统的演替规律进行的人为干扰演替是促进次生灌丛正向演替最有效和最省力的办法[4]。一般地,非耐荫种会逐渐地被中度耐荫种和更耐荫种取代,从而演替成为顶极种。近年来,人为干扰演替成为生态方面研究的热点,选取更多的功能组树种,借助荧光技术,从光合生理特征和可塑性大小角度进行研究将成为今后的趋势,而这对生态恢复和近自然林业建设具有重要的意义[5]。植物的耐荫性(shaded-tolerance或shade-adapted)是由植物的遗传特性和外部光环境变化的适应性共同决定的[6-8]。通过植物耐荫性可判断适宜其生长的演替阶段。遮光条件下,植物一般通过减小比叶质量、增大比叶面积、增加叶绿素质量分数以及降低叶绿素a与叶绿素b比值等进行光合作用和光形态建成[9]。近年来,关于遮光对植物影响的研究得到重视,例如对遮光条件下植物的光合特性、叶绿素荧光特性以及其他的生理特性响应的研究[8-12]。这些研究有利于理解植物对不同光环境的响应机制,为叶片特征、叶绿素荧光和净光合速率作为指标判断植物耐荫性提供依据,但这些实验大多是针对园林树种的盆栽实验,缺乏实地验证。天然次生灌丛中由于缺乏乔木层,光照充足,自然条件下演替中后期树种更新困难[1]。如果通过人工设置遮光条件能够成功补植中后期树种,将对加快次生灌丛的演替起重要的作用。木荷Schima superba和枫香Liquidambar formosana是中国亚热带重要的优良乡土速生阔叶树种[13],是近些年来浙江省喜闻乐见的针叶林阔叶化改造混交树种。本研究通过在天然次生灌丛群落种植常绿阔叶树木荷(演替中后期代表种)和落叶阔叶树枫香(演替早期代表种),并设置人工控制光照实验,探讨它们在不同光环境下叶片光合指标方面的响应差异,为把握次生灌丛的近自然演替规律及生态恢复和人工管理提供理论指导和实践参考,对加速次生灌丛群落演替及生态恢复具有重要意义。
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由表 1可知:木荷叶片比叶面积随遮光程度升高而增大,于70%遮光处理达到最大值,比全光照处理增加了46.15%,与全光照处理有显著性差异(P < 0.05);比叶干质量和比叶鲜质量均随遮光率增加而降低,在遮光率70%处理下最小,相较于全光照,分别降低了31.93%和25.08%,与全光照处理差异显著(P < 0.05)。
表 1 遮光对木荷和枫香叶片特征的影响
Table 1. Effect of shade on leaf morphography of Schima superba and Liquidambar formosana
遮光
率/%木荷 枫香 比叶面积/
(cm2·mg-1)比叶干质量/
(mg·cm-2)比叶鲜质量/
(mg·cm-2)相对含水量/% 比叶面积/
(cm2·mg-1)比叶干质量/
(mg·cm-2)比叶鲜质量/
(mg·cm-2)相对含水量/% 0 0.143±0.007 a 7.030±0.354 a 15.699±0.507 a 0.551±0.037 a 0.137±0.007 a 7.307±0.352 a 15.525±0.696 a 0.529±0.002 a 50 0.193±0.018 ab 5.214±0.483 b 12.836±0.622 b 0.595±0.018 b 0.213±0.009 b 4.706±0.201 b 11.259±0.195 b 0.582±0.025 b 70 0.209±0.005 b 4.785±0.114 b 11.761±0.070 b 0.593±0.012 b 0.180±0.006 c 5.566±0.181 b 13.750±0.734 ab 0.595±0.008 ab 说明:同列字母表示处理间差异显著(P < 0.05)。表中数据为平均值±标准误。 枫香叶片比叶面积随遮光率增加先增大后减小,于全光照处理取得最小值,50%遮光处理达到最大值,比全光照条件增加了55.47%,且3个不同处理间差异显著(P < 0.05);比叶干质量和比叶鲜质量均随遮光率增加先下降后上升,均在50%遮光处理取得最小值,相较于全光照条件,分别减小了35.60%和27.48%;比叶干质量在全光照与遮光处理间差异显著(P < 0.05);比叶鲜质量在50%遮光与全光照处理差异显著(P < 0.05)。全光照条件下木荷叶片和枫香叶片的相对含水量均显著小于遮光条件(P < 0.05)。
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如表 2所示:遮光处理下相同质量(0.1 g)木荷叶片和枫香叶片的叶绿素a(Chl a),叶绿素b(Chl b),以及叶绿素总量(Chl a+b)均高于全光照处理,且随遮光率增加而增加,均在遮光率70%处理下取得最大值,与全光照相比分别增加66.92%,119.35%,79.95%和120.37%,171.56%,133.76%。木荷叶片叶绿素a与叶绿素b之比(Chl a/b)随遮光率增加先下降后保持稳定。枫香叶片Chl a/b随光荫梯度增加呈现下降趋势。枫香叶片和木荷叶片均在全光照条件下获得最大Chl a/b,遮光处理与全光照处理均有显著性差异(P < 0.05)。遮光处理木荷Chl a/b值约为2.3,而枫香大于2.3。从不同遮光处理木荷叶片和枫香叶片的叶绿素变化量看,不同遮光处理对木荷叶绿素质量浓度各个指标值的影响并不大,而枫香叶绿素质量浓度变化剧烈。
表 2 不同遮光处理下2种植物叶片光合色素质量浓度
Table 2. Comparison of pigment contents in ieaves of two species under different shading treatments
树种 遮光率/% 叶绿素a/(mg·L-1) 叶绿素b/(mg·L-1) 叶绿素总量/(mg·L-1) 叶绿素a/b 木荷 0 6.56±1.09 a 2.17±0.18 a 8.73±1.28 a 3.00±0.25 a 50 8.62±1.08 b 3.76±0.34 ab 12.38±1.43 b 2.28±0.08 b 70 10.95±1.64 c 4.76±0.61b 15.71±2.25 c 2.29±0.05 b 枫香 0 6.48±0.05 a 2.11±0.08 a 8.56±0.03 a 3.08±0.14 a 50 12.41±3.12 b 4.79±1.37 b 17.20±4.49 b 2.62±0.10 b 70 14.28±1.36 b 5.73±0.98 b 20.01±2.34 c 2.52±0.19 b 说明:同列字母表示处理间差异显著(P < 0.05)。表中数据为平均值±标准误。 -
由图 1可得:3个不同光环境枫香叶表光强均呈先上升后下降趋势,且具相似的变化趋势,均于12:00取得峰值。全光照条件枫香叶表光强变化呈现“单峰型”,且10:00和14:00,8:00和16:00分别具有相近的光照强度,近似“对称结构”;而遮光条件下叶表光强的日变化不具“对称结构”。木荷叶表光强也呈先上升后下降趋势,且均于12:00取得1天中叶表光强最大值,12:00至14:00时间段的叶表光强下降幅度较大,木荷叶表光强均小于枫香叶表光强。
图 1 不同遮光下枫香和木荷叶表光合有效辐射日变化
Figure 1. Diumal variation of photosynthetically active radiation (PAR) on leaf surface of Liquidambar formosana and Schima superba
全光照下枫香叶片和木荷叶片净光合速率均呈“双峰型”(图 2),分别于1 d中的10:00和14:00取得峰值,1 d中的12:00取得最低值,而遮光处理净光合速率变化呈“单峰型”,均于12:00取得峰值。2个不同遮光梯度枫香叶片净光合速率具有相似的变化趋势;1 d中3个不同光环境枫香净光合速率为全光照 > 50%遮光 > 70%遮光。70%遮光下木荷净光合速率日变化趋势较平缓,而50%遮光变化剧烈,尤其是10:00-14:00时间段;50%遮光处理木荷叶片净光合速率在12:00时间段明显大于全光照条件。
图 2 不同遮光条件下枫香和木荷净光合速率日变化
Figure 2. Diumal variation of net photosynthetic rate of Liguidamar formosana and Schima superba in different treatments
由图 3所示:木荷叶片Fv/Fm值随遮光率增加无明显变化,3个不同处理组均为0.79,且各处理均无显著性差异(P > 0.05)。枫香叶片Fv/Fm值均低于全光照条件,且随着遮光梯度增加呈现减小趋势,于70%遮光条件达到最小值,与全光照条件相比减少2.97%;70%遮光处理与全光照处理有显著性差异(P < 0.05),其余各处理无显著性差异(P > 0.05)。不同遮光处理下,木荷叶片Fv/Fm值均位于0.75~0.85,而枫香叶片的Fv/Fm值在70%遮光处理下为0.74,其变化趋势比木荷叶片明显,且均小于木荷叶片Fv/Fm值。
Photosynthetic characteristics with shading for Schima superba and Liquidambar formosana
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摘要: 在浙江临安次生灌丛群落中设置3种不同遮光率的光环境(0%,50%,70%),观测及比较不同光环境中木荷Schima superba和枫香Liquidambar formosana部分叶片特征、光合色素质量浓度、叶绿素荧光和净光合速率,探讨遮光处理对木荷和枫香生理生态的影响。结果表明:遮光处理下木荷叶片和枫香叶片比叶面积、相对含水量以及光合色素质量浓度均显著增大(P < 0.05);不同光照条件下木荷叶片比叶质量和叶绿素a/b均比枫香小,而比叶面积较大;遮光处理枫香叶片Fv/Fm均低于全光照,且70%遮光条件下Fv/Fm为0.74;木荷叶片Fv/Fm值均为0.75~0.85;50%遮光程度下,12:00时间段木荷叶片净光合速率高于全光照条件。综上所述,木荷较枫香耐荫,能适应更宽的光照幅度。在亚热带次生灌丛演替进程中,木荷不同于枫香,在森林演替上属于中间性类型,在强光条件下适度遮光可促进其生长。Abstract: The area of evergreen broad-leaf forest reversely evolved into the secondary brush community which was lower yields, weaker resistance ability and less diversity. So it was important to investigate that if it is helpful for trees growth to decrease the light intensity for sapling trees in the secondary brush stand which had a stronger light than evergreen broad-leaf forest. Schima superba and Liquidambar formosana were used in this experiment as materials to study the effects of three different shading levels (shading of 0%, 50%, and 70%) on their photosynthetic characteristics. The experiment was set in a secondary bush community in Lin'an, Zhejiang. Some of the leaf characteristics, photosynthetic pigment content, chlorophyll fluorescence parameters, and net photosynthetic rate were measured. Each species were selected 10 trees as samples in every shading level, and 5 trees were chosen to measure the indicators mentioned above. Results showed that compared to the full light treatment, specific leaf area (SLA), relative water content, and photosynthetic pigment content in the shade treatments of both species increased significantly (P < 0.05). The Fv/Fm value of L. formosana under shading was lower than that in full lightreaching 0.74 at 70% shading; whereas, Fv/Fm values of S. superba were in the range of 0.75-0.85 in three different treatments. The net photosynthetic rate of S. superba with 50% shading (8.11 μmol·m-2·s-1) was higher than the full light treatment (4.64 μmol·m-2·s-1) at 12:00. Thus, S. superba which was more shade-tolerant than L. formosana could live in a wider range of light intensities including secondary bush community succession stages in the subtropics where it belonged to intermediate forest succession.
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表 1 遮光对木荷和枫香叶片特征的影响
Table 1. Effect of shade on leaf morphography of Schima superba and Liquidambar formosana
遮光
率/%木荷 枫香 比叶面积/
(cm2·mg-1)比叶干质量/
(mg·cm-2)比叶鲜质量/
(mg·cm-2)相对含水量/% 比叶面积/
(cm2·mg-1)比叶干质量/
(mg·cm-2)比叶鲜质量/
(mg·cm-2)相对含水量/% 0 0.143±0.007 a 7.030±0.354 a 15.699±0.507 a 0.551±0.037 a 0.137±0.007 a 7.307±0.352 a 15.525±0.696 a 0.529±0.002 a 50 0.193±0.018 ab 5.214±0.483 b 12.836±0.622 b 0.595±0.018 b 0.213±0.009 b 4.706±0.201 b 11.259±0.195 b 0.582±0.025 b 70 0.209±0.005 b 4.785±0.114 b 11.761±0.070 b 0.593±0.012 b 0.180±0.006 c 5.566±0.181 b 13.750±0.734 ab 0.595±0.008 ab 说明:同列字母表示处理间差异显著(P < 0.05)。表中数据为平均值±标准误。 表 2 不同遮光处理下2种植物叶片光合色素质量浓度
Table 2. Comparison of pigment contents in ieaves of two species under different shading treatments
树种 遮光率/% 叶绿素a/(mg·L-1) 叶绿素b/(mg·L-1) 叶绿素总量/(mg·L-1) 叶绿素a/b 木荷 0 6.56±1.09 a 2.17±0.18 a 8.73±1.28 a 3.00±0.25 a 50 8.62±1.08 b 3.76±0.34 ab 12.38±1.43 b 2.28±0.08 b 70 10.95±1.64 c 4.76±0.61b 15.71±2.25 c 2.29±0.05 b 枫香 0 6.48±0.05 a 2.11±0.08 a 8.56±0.03 a 3.08±0.14 a 50 12.41±3.12 b 4.79±1.37 b 17.20±4.49 b 2.62±0.10 b 70 14.28±1.36 b 5.73±0.98 b 20.01±2.34 c 2.52±0.19 b 说明:同列字母表示处理间差异显著(P < 0.05)。表中数据为平均值±标准误。 -
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