兰州大学机构库 >生命科学学院
风沙环境下沙拐枣(Calligonum mongolicum)自然更新策略研究
Alternative TitleNatural regeneration strategies of Calligonum mongolicum under different aeolian environments
樊宝丽
Thesis Advisor赵长明
2017-04-02
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name博士
Keyword风沙环境 沙拐枣 自然更新 繁殖策略 固沙造林
Abstract

沙拐枣(Calligonum mongolicum Turcz.)是一种优良的防风固沙先锋种,生长于流动、半流动沙丘,是干旱区沙地植被的重要建群种和人工固沙造林的优选物种,在保障西部生态安全中发挥了极其重要的作用。针对沙拐枣在荒漠区流沙生境上自然更新能力强,而在沙丘固定后自然更新下降的生态现象,本文以干旱荒漠区(民勤西沙窝)不同风沙环境上的沙拐枣为研究对象,较为系统地从种子生产、扩散、种子库、种子萌发、幼苗更新、克隆生长等方面开展其繁殖特性、自然更新策略研究,以期揭示不同生境下沙拐枣自然更新的策略,并解析沙丘固定后人工林自然更新受限原因。主要结果如下:

(1)沙拐枣采取多种繁殖策略来适应荒漠区多变的风沙环境。首先,沙拐枣具有一年多次(2~3次)开花结实策略,不同成熟期对果实重量有明显影响,果实单粒重9月<8月<6月。其次,种子主要靠风力扩散,扩散方向与风沙流活动密切关联;种子具有长距离和短距离扩散两种策略,为其开辟新的定居生境和形成土壤种子库创造了可能;种子寿命较长,可形成持久土壤种子库,当年生和保存3年的种子活力均高于90%,且出苗率差异不显著。最后,种子萌发率较低(最高45%),首次出苗时间约14d,部分春季未萌发的种子可推迟至秋季出苗,沙拐枣采取谨慎型和两头下注型的萌发策略来应对荒漠环境的不确定性;种子萌发和出苗对干旱、盐胁迫耐性较强,模拟干旱(PEG-6000最高浓度20.3%)和盐胁迫(NaCl最高浓度0.8%)对其出苗率影响不大。(2)不同流沙环境下沙拐枣种群自然更新策略明显不同。首先,风蚀区全部以克隆繁殖更新,沙埋区以克隆繁殖为主兼有种子更新,而丘间地仅以种子更新;风蚀区和沙埋区每年仅开花结实2次,而丘间地每年开花结实3次。其次,沙埋区种子雨季节动态变化曲线呈单峰,风蚀区变化平缓,而丘间地呈双峰;在0-10cm土层中,风蚀区土壤浅层种子库密度远低于深层,而沙埋区都较高,丘间地土壤浅层远高于深层;2-5cm土壤层种子库密度与样地内当年生实生苗幼苗密度显著正相关。再者,沙埋区幼苗出土率在6月和8月都较高(分别为2300和1300株/ha),而风蚀区分别仅为2株和75株/ha且无法存活;当年生幼苗高度、幼苗基茎、幼苗的比叶重在三种风沙环境下无显著差异,幼苗通过增加同化枝的节数和长度以及具有较高的持水力来抵抗流沙胁迫。最后,克隆苗不仅比实生苗生长迅速,且可通过与生长良好沙埋子株的连接,使严重风蚀胁迫下的子株能够存活、生长并完成整个生活史,对风蚀环境表现出了较强的适应性。(3)沙丘固定后人工沙拐枣种群自然更新策略发生了显著变化。人工造林形成了固定沙丘后,沙拐枣不仅无克隆更新,而且种子更新的实生苗密度仅67株/ ha,显著低于流沙区的310株/ha。沙丘固定后地表风沙流活动降低、土壤紧实度增加限制了沙拐枣水平根的发育,使得固定沙丘无克隆繁殖。固定沙丘的土壤种子库密度和分布模式与流沙区无差异,说明土壤种子库不是其自然更新的限制因素;但沙丘固定后土壤紧实度的增加导致了很低的幼苗出土率和幼苗存活率。因此,土壤物理属性的改变是导致沙丘固定后沙拐枣更新策略变化的主要原因。

综上,沙拐枣在自然更新过程中采取一年多次开花结实、长距离种子扩散模式、形成持久土壤种子库、以及两头下注的萌发策略,并借助克隆性去适应荒漠区恶劣多变的环境,不同风沙环境对沙拐枣自然更新过程有重要的影响。该研究不仅系统地揭示了固沙先锋植物沙拐枣的自然更新策略,而且对荒漠区沙拐枣人工林的科学管理具有重要指导意义。

Other Abstract

Calligonum mongolicum, a great windbreak and sand-fixation pioneer species occurred in mobile and semifixed dunes, is regarded as one of the most important building groups of sandy vegetation, and most suitable afforestation species for sand-fixation in arid areas, which plays an extremely important role in protecting the ecological security in Western China. C. mongolicum shows a strong ability of natural regeneration in desert mobile sand dune, but this ability is sharp decline when the sand dune is getting fixed. The ecological and physiological mechanisms which behinds this phenomenon is still poorly known. In this thesis, we investigated reproductive features and natural regeneration strategies of C. mongolicum in three different aeolian environments from various of aspects including the number of seeds, the pattern of seed dispersal, the density of seeds in soil seed banks, seed germination rate, seedling emergence rate and clonal growth to reveal the factors resulted in weak natural regeneration after sand dune were fixed. The results are shown as following:

1)C. mongolicum had several reproductive strategies to adapt to various aeolian environments in deserts. First, it flowered and produced seeds 2-3 times a year. The phenology played an important role in seed production. The seed mass of matured seeds is: September2)C. mongolicum took different strategies to power population natural regeneration in the three aeolian environments. First, the regeneration in the wind erosion plot and the sand accumulation plot is mainly relied on clonal reproduction with plants flowered and produced seeds twice a year while there is no clonal reproduction in the intersand dune plot with plants flowered and produced seeds three times a year. Second, the vertical distribution of soil seed bank was related with the soil texture and the aeolian environment. The high soil compaction in intersand dune resulted in the seeds hardly deep into the soil seed bank, leading that seeds only just settled in the shallow soil layer. However, the strong sand movement in wind erosion plot resulted in a much lower seed bank density at shallow than deep soil layer, and a relative higher soil seed bank at 0-10cm depth in sand accumulation plot. There was significant difference for the seedling emergence rate and the seedling survival rate among the three different aeolian environments, and the soil seed bank at 2-5cm depth was significantly and positively correlated with seedling emergence rate. Third, the sand accumulation plot showed much higher density of seedlings in both spring and autumn (2300/ha and 1300/ha, respectively) than the wind erosion plot (2/ha and 30/ha, respectively). The height, the basal stem diameter and leaf area of seedling were similar in all the three aeolian environments and seedlings were resistant to mobilesand by increasing the number and the length of assimilation branches to maintain a higher water holding capacity. Fourth, clonal seedlings with connections with their maternal plants were growing faster than seedlings generated from soil seed banks, which was beneficial to the survival and growth under wind stress to complete the whole life history, suggesting a better ability to adapt to the wind erosion environment.3)After the dune fixation, the natural regeneration strategy of C. mongolicum have changed significantly. When the afforestation area formaed the fixed dune, the seedlings were only generated by seeds, and the seedling density was only 67 plants/ha, which was significantly lower than that of the mobilesand area (310 plants/ha). After the dune fixation, the surface sandstorm activity decreased and the aeration porosity of soil increased, which limited the development of the root of seedlings, and resulted in the fixed dune with no clonal reproduction. The density and distribution pattern of seeds in the soil seed bank of fixed dune did not differ from those in mobilesand, indicating that soil seed bank was not a limiting factor of natural regeneration in afforestation. However, the increase of soil aeration porosity after dune fixation resulted in a low seedling unearthed rate and massive decease of the survival rates of seedlings. Therefore, the change of soil physical features is the main reason for the change of the natural regeneration strategy after sand dune fixation.

In conclusion, C. mongolicum was benefited from multiple life cycles per year, the long-distance dispersal, the formation of a persistent soil seed bank, and the seed germination in both spring and autumn, for its local adaptation to the harsh environments in the desert area. The natural regeneration strategies changed at the three different aeolian environments. This study not only systematically revealed the natural regeneration strategies for the sand-fixation pioneer species C. mongolicum, but also has important guiding significance for the management and plantation of Calligonum acerata in the desert area.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/221474
Collection生命科学学院
Recommended Citation
GB/T 7714
樊宝丽. 风沙环境下沙拐枣(Calligonum mongolicum)自然更新策略研究[D]. 兰州. 兰州大学,2017.
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