河西走廊沙丘活化过程中沙拐枣的自然更新及驱动机制

After several years growth,the shrubs or sub-shrubs will come to deterioration,if they can not achieve natural regenerations by themsleves, the sand dune will become dune-activation and once again threaten the ecological safety. As one of the most serious desertification area, Hosi Corridor has launched a large scale activities to plant forests for windbreak and sand-fixation since new China was established, however , when choose the forests species,they paid too much on the function benefits of fixing moving sand dune and drought resistance without considering their abilities of natural regenerations.Calligonum mongolicum, which is Widely distributed in most areas of Hosi Corridor, is a very excellent pioneer shrub on the shifting sand dune. During recent years monitoring, we found that Calligonum mongolicum has a strong natural regenerations and there are many natural updated seedings come up on moving or semi-mobile dunes where we took field investigation. How did they occupy the econiche and by what way then succeeded achieved their regeneration, study about this aspect is still not reported by now. So in this project we study about the natural regenerations of Calligonum mongolicum in different desertification land at the ecological regions of Hexi corridor:such as Linze, Gaotai and Minqin will be selected as research areas to carry out the whole process of natural regenation of Calligonum mongolicum from reproductive strategies, seed dispisal and seed soil bank ,seed germination mechanism, seeding establishing and physiological and biochemical characteristics, to reveal the capability and guiding of Calligonum mongolicum, exploring its natural regeneration mechenism during the process of desertification, which has important guidance significance for the vegetation restoration and reconstruction in the similar arid areas.

灌木生长到一定阶段会出现衰败，如果不能进行自然更新，沙丘就会重新活化形成新的沙源。以往在防风固沙林树种的选择上主要考虑防风固沙效益和耐旱性，而对物种的自然更新能力有所忽略。沙拐枣（Calligonum mongolicum）是一种自然更新能力很强的优良防风固沙灌木树种，广泛分布于河西走廊沙区。本项目选择分布在河西走廊不同生态条件下的沙拐枣为对象，采用时空替代方法，分别在个体和种群水平上研究它们在沙丘活化过程中的自然更新过程及其驱动机制，深入了解沙丘活化过程中沙拐枣的种群繁殖对策、种子扩散、种子雨和土壤种子库特征、种子及其幼苗对土壤水分、温度、沙埋等环境因子的生态适应对策，探讨沙拐枣种群在不同微生境条件下的自然更新能力和更新机理，为甘肃河西走廊防风固沙林树种的选择、生态林建设、绿洲边缘退化固沙植被的恢复和管理提供参考。

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。本项目以干旱荒漠区不同风沙环境上的沙拐枣为研究对象，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。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。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；种子寿命较长，可形成持久土壤种子库。最后，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，模拟干旱和盐胁迫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、土壤种子库密度及幼苗出土率在三种立地类型间差异显著；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。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，且可借助克隆整合作用，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。. 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。