木本植物对三峡库区消落带异质生境的响应及其适应性

At present, the large hydro-fluctuation belt around the Three Gorges Reservoir (TGR) and its fragile ecological environment have become a major focus of attention of the local and national governments. Ecological plant rehabilitation is one of the most viable management approaches for restoring injured ecosystems of riverside belts, and selecting suitable target plants is the primary problem that must be addressed. To this point, most of the research aimed at understanding the revegetation of this area has focused on studying the submergence tolerance of plants. However, research and practice have shown that in the hydro-fluctuation belt of the TGR vegetation restoration (especially of woody plants) is extremely difficult. This is in part because the hydro-fluctuation belt suffers not only counter-seasonal flooding but also frequent drought caused by the complex topography and harsh natural environment. Different kinds of plants have differing habitat requirements, especially with respect to the soil which is the foundation of plant survival. The proposed study is based on former research and will examine woody plants associated with the heterogeneous habitats of the TGR. The woody plant experimental materials will be selected according to the principle of "suitable trees". The responses and adaptability of these woody plants to habitat changes occurring in the hydro-fluctuation belt will be examined over the long-term in order to discover regulatory factors in the habitat of the hydro-fluctuation belt, especially soil physical and chemical properties. Mechanisms of physiological-ecological adaptation of woody plants will also be studied, with a view to providing scientific reference and theoretical support for the restoration of vegetation in the hydro-fluctuation belt of the TGR.

三峡库区大面积消落带及其脆弱的生态环境已经成为当地政府和国家关注的重大问题。对消落带和河岸带受损生态系统进行植物生态修复是非常有效的治理途径之一，而植物生态修复的首要问题是目标植物的筛选。对消落带植被恢复物种选择,目前绝大多数研究集中在植物耐反季节水淹方面, 即筛选适应长期、完全、深水淹没植物。然而，大量研究和实践证明，三峡库区消落带植被恢复尤其木本植物极其困难。究其原因，库区消落带不仅存在反季节水淹问题，还存在复杂的地质地貌以及自然干旱频繁等高度异质化生境问题。不同的植物对生境要求有所不同，尤其土壤是植被生存的基础。因此，本研究针对三峡库区异质生境，综合以往的研究，以木本植物为实验材料，依据"适地适树"原则，通过长期观察、比较研究一些木本植物对消落带生境变化的响应和适应性，探明消落带生境（尤其土壤理化性质）变化规律及适生植物的生长、生理生态适应机理，为三峡库区消落带植被恢复提供科学参考。

三峡库区消落带适生植物筛选中尤以适生木本植物难选。原因是该区域不仅存在反季节水淹问题，还存在土壤、夏季干旱频繁等高度异质化生境问题。.①木本植物对三种典型的库区消落带土壤的响应及适应性.消落带三种土壤类型中，种植在石灰性黄壤上的几种木本植物生长受阻，植株矮小，夏季干旱常出现萎蔫症状，导致长势弱，死亡率高（24%~56%），植株的平均株高、地径、生物量只相当于种植在紫色土、潮土上植株的20%~30%左右，对冬季水淹十分敏感，成活率均在10%以下（其余2种土壤平均成活率>50%）。可见，消落带土壤类型是影响木本植物存活及生长的关键因子。.②三峡库区消落带土壤理化性质动态.消落带上种植木本植物后，能逐渐改善消落带土壤理化性质，2017年与2014年相比部分指标趋于好转，但短期内对土壤整体质量的改善效果有限。同时，各消落带土壤理化指标与水位高程间无明显梯度关系，175m水位高程（库区水位调度上限）的土壤结构性质比170m和178m水位高程更不稳定。.③木本植物对三峡库区夏季干旱的响应及适应性.在同一土壤类型上对消落带夏季干旱的适应性（成活率+生物量）为桑树>水桦>落羽杉>秋华柳>池杉>水松>中华蚊母。.④木本植物对三峡库区消落带冬季水淹的响应及适应性.水淹时间长短是影响木本植物成活率及生长的又一关键生态因子。.即使是在消落带适生性较强的桑树、水桦和落羽杉，在173米高程以下（水淹时间两到四个月左右），成活率也较低：桑树41%、落羽杉45%，水桦60%，且生长发育较173米高程以上差。其余树种仅在174米以上能存活，但成活率均在10%以下。.本试验初步筛选出落羽杉、桑树、水桦3种木本植物（170米~175米高程种植4年后的平均成活率分别为54%、63%、78%），兼具耐干旱和水淹特性（其中水桦、桑树主要是通过形态和生理适应，而落羽杉则主要是生理适应），可以作为消落带170米以上高程紫色土、潮土植被恢复树种，有助于构建消落带上乔灌草稳定植物群落，有助于保水固土、消浪护岸，进而保护和恢复消落带生态环境。