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胡杨(Populus euphratica)幼苗根系生长特征及影响因素研究
王丽娟
学位类型博士
导师赵成义 ; 刘志辉
2015
学位授予单位中国科学院大学
学位授予地点北京
学位专业自然地理学
关键词根系生长 表型可塑性 生物量分配 潜水埋深 基质
摘要胡杨(Populus euphratica)作为塔里木河流域荒漠河岸林的优势建群种,为其他物种提供重要的栖息地,其幼苗定居和群落自然更新能力与根系是否能接触到潜水埋深和毛管上升区边缘有直接关系,而洪水漫溢区胡杨根系的生长发育过程对水分的响应与适应机制在认知上的薄弱已成为荒漠河岸林生态恢复的瓶颈。这主要是由于植物根系形态结构的复杂性以及其隐藏于地下难于直接观测,使得对根系的研究仅限于其生物量、分布特征以及根的穿透深度等方面的研究,很少涉及到植物根系形态结构与功能及其对环境的响应与适应机制的研究,使干旱地区植物地下部分的研究大大滞后于地上部分。水分和基质是河岸林生态系统中最重要的环境因子。关于潜水埋深或基质单一因素对河岸林树种的影响,前人已做了大量研究,综合考虑潜水埋深和基质对河岸林树种影响的研究却很少。本文以胡杨实生幼苗为研究对象,设计了4个水分梯度(洪水、30 cm潜水埋深、50 cm潜水埋深和70 cm潜水埋深)和不同基质(粘土和粘土/沙土)控制试验,通过人工栽培控制试验,研究了不同潜水埋深和基质类型与胡杨幼苗的生长特征、生物量分配、根系特征之间的关系,分析了胡杨幼苗生长与环境之间的关系,阐明了胡杨幼苗生长策略、生物量分配模式及表型可塑性对异质性生境的响应。主要结论如下: 1. 不同处理下胡杨幼苗株高和基径均呈“S”型生长曲线,相同基质下,不同潜水埋深处的胡杨幼苗株高生长差异不显著(P<0.05);不同基质条件下,胡杨幼苗株高和基径均随潜水埋深增加而增加;潜水埋深对胡杨幼苗的节间距影响不显著。 洪水显著降低了胡杨幼苗根系生物量的分配比例,粘土和粘土/沙土基质条件下的根冠比均 < 0.5,二者的根冠比分别为0.45和0.37。而其他三个潜水埋深处理的根冠比呈30 cm < 50 cm < 70 cm的趋势,且根冠比均 > 1。这种根冠比随潜水埋深增大而增加的策略符合植物生长最优分配理论。 2. 不同潜水埋深下,基质对根系特征均无显著性影响。洪水显著降低了根系相对生物量,粘土基质和粘土/沙土基质条件下根系相对生物量分别为31.43%和26.28%。其余潜水埋深处理的根系相对生物量呈30 cm < 50 cm < 70 cm的趋势,且根系相对生物量均 > 50%。这种生物量随潜水埋深增大,根系相对生物量增大的分配策略与最优配理论相一致。不同基质下,胡杨幼苗主根长均在各潜水埋深附近,这是一种植物生长过程中的权衡,是对植物生长过程中权衡理论的印证。 3. 相同潜水埋深条件下,胡杨幼苗根系在不同基质间的修正拓扑指数qa和qb存在显著性差异(p < 0.05)。潜水埋深处理对胡杨幼苗根系拓扑结构无显著性影响(p < 0.05),与所提出的假说一(不同潜水埋深处理下,胡杨幼苗根系拓扑结构存在差异)不一致。 基质对胡杨幼苗拓扑结构影响显著(p < 0.05),与所提出的假说二(不同基质下,胡杨幼苗根系拓扑结构存在差异)一致。在粘土基质条件下,生长在洪水和30 cm潜水埋深的胡杨幼苗根系的拓扑指数相对较小(TI < 0.7),生长在50 cm和70 cm潜水埋深条件下的胡杨幼苗根系拓扑指数相对较大(TI > 0.7)。说明粘土基质下根系随着潜水埋深的增加,逐渐由二叉鲱骨型拓扑结构向鲱骨型拓扑结构转变;粘土/沙土基质条件下,随着潜水埋深的增加,胡杨幼苗根系修正拓扑指数qa呈现出洪水> 30 cm > 50 cm > 70 cm;拓扑指数(TI)也呈现出与qa相同的规律,TI值也由洪水处理下的0.733下降到70 cm潜水埋深处理下的0.621,说明粘土/沙土基质下根系随着潜水埋深的增加,由鲱骨型拓扑结构逐渐向二叉鲱骨型拓扑结构过渡。 结果与所提出的假说二(不同基质下,胡杨幼苗根系拓扑结构存在差异)一致。说明,在相似的水分环境中,生长在不同基质上的胡杨幼苗具有不同的根系生长适应策略。 4. 洪水处理虽然显著降低了胡杨幼苗的生长。但相对于遵循相对固定生长的策略和分配模式而言,幼苗通过产生不定根和压缩根系生物量分配比例(粘土基质:31.43%;粘土/沙土基质:26.28%)等适应机制,增加了胡杨幼苗在洪水生境中的适合度。 胡杨幼苗通过增加总根长和提高根系生物量分配比例的方式来响应较深的潜水埋深。粘土基质和粘土/沙土基质下,70 cm潜水埋深处理下幼苗总根长分别为29.56 m和43.80 m,是洪水处理下胡杨幼苗总根长的1.61倍和2.15倍。粘土基质和粘土/沙土基质下,70 cm潜水埋深处理下幼苗根系相对生物量分别为55.45%和67.83%,是洪水处理下胡杨幼苗根系相对生物量的1.76倍和2.58倍。这种形态可塑性和生物量分配调整符合最优分配理论。 基质对胡杨幼苗根系特征具有显著影响,即使在相同潜水埋深条件下,在不同基质中,胡杨幼苗表现出完全不同的根系特征:幼苗根系在潜水埋深较浅的粘土中具有较多一级根,而在较深粘土/沙土中幼苗具有较长的主根。潜水埋深较深的粘土基质中,幼苗通过增加根系总长来获取水分,而在粘土/沙土基质中,幼苗响应较深潜水埋深是由总根长的增加引起根系表面积增加来实现的,说明在根系并非总是通过增加其根系表面积来获取更多水分。 试验结果表明,胡杨幼苗能够通过根系特征和生物量分配的可塑性来适应一定范围水分生境,与所提出的假说三(适应性表型可塑性可能对该生境中木本植物的生长有利)一致。
其他摘要Populus euphratica is an ecological pioneer and a dominant tree of riparian floodplain in semi-arid environments, the success of seedling establishment is challenged by the ability of their roots to maintain contact with the water table depth and associated capillary fringe. However, the response of the root systems of riparian plants to hydrological fluctuations at the seedling stage has not been fully elucidated. Investigation of tree roots is laborious and time consuming. As soil heterogeneity and the difficulty in extracting integrity tree root systems without damaging them, seedlings root system structure and development are difficult to assess and are poorly understood in field environments. For this reason, the study of root topology and function in response to environmental fluctuations has been lagged behind the study of aboveground. Water table depths and sediment types are the most important environmental factors. Many studies have investigated the individual effects of water table depths or sediment types on the performance of wetland plants, but few have examined the combined influence of these processes. We conducted an experiment in which P. euphratica seedlings, grown in both clay and clay/sandy sediments, were subjected to a range of hydrological conditions over a period of 75 days. We compared the root traits, biomass allocation and growth of P. euphratica. We hypothesized that adaptive phenotypic plasticity is likely to develop or be advantageous in seedlings of this species to allow them to adapt desert floodplain environments. Topological analysis was carried out to investigate branching patterns as basic determinants of root architecture. The main results were as following: 1. P. euphratica seedlings growth characteristics Both the plant height and diameter cumulative growth curve of P. euphratica seedlings under both sediment types in the whole growth stage presented a “S” curve and showed a same trend: substantial increase at the begaining, linear decrease after that, then increase slightly. Water table depths have no significant effects on internode. In both sediment types, inundation significantly reduced seedling biomass partitioning to the roots at the end of the experiment (p < 0.05), and the seedlings subjected to inundation therefore showed a significantly lower root/shoot ratio than the other three treatments. In particular, the seedlings subjected to the inundation treatment allocated less biomass to the roots than to the shoots in clay sediment (R/S = 0.45) and in clay/sand sediment (R/S = 0.37), R/S ratio in both sediment types are less than 0.5, while the seedlings subjected to the remaining three treatments concentrated more resources in the root system (root/shoot >1) (R/S ratio: 30 cm < 50 cm < 70 cm). In both sediment types, the R/S ratio increased as water table depth decreased, which consistent with optimal partitioning theory. 2. Root growth characteristics of P. euphratica seedlings Sediments types had no effects on all root traits we measured in the same water table depth (p < 0.05). Inundation significantly reduced seedling biomass partitioning to the roots and the relative root biomass allocation increased as water table depth decreased (p < 0.05). Relative biomass of root in clay sediment and clay/sand sediment were 31.43% and 26.28%, respectively. While the relative biomass of root subjected to the remaining three treatments were more than 50% (relative biomass of root: 30 cm < 50 cm < 70 cm), consistent with optimal partitioning theory. The tap root depths were all around its water table depths, which was a trade-off in growth process. 3. Root topological characte ristics of P. euphratica seedlings responsed to different treatments The value of qa and qb were significant different at the same water table depth, (p < 0.05). Water table depth had no effects on root topological structure of P. euphratica seedlings (p < 0.05), which was inconsistent with our hypotheses 1. Sediment types had significant effects on P. euphratica seedlings root topological structure (p < 0.05), which was consistent with our hypotheses 2. In contrast with the 50 cm and 70 cm water table depth (TI > 0.7), topological index (TI) of inundation and 30 cm water table depth are relatively small (TI < 0.7). The TI increased as water table depth decreased, which means the root topological structure changes from dichotomous to herringbone branching. Inundation had the biggest TI in clay/sand sediment (TI=0.733), TI for the treatments were all less than 0.7, TI increased as water table depth decreased, which meant the root topological structure changes from herringbone to dichotomous branching. And this trend was comsistent with our hypothesis 2 (there were some significantly differences of root topological plasticity in contrasting sediment types), which meant that P. euphratica seedlings root had different adaptive strategies under same water table depth. 4. Root plasticity adaption of P. euphratica seedlings Growth was significantly reduced by inundation. However, rather than following relatively fixed trait and allocation patterns, the seedlings displayed adaptive mechanisms involving the development of adventitious roots to enhance plant stability and oxygen obtainment, together with a lower proportion of root biomass. At the whole-plant level, at deeper water table depths, seedlings allocated more biomass to the roots. And total root length increased with decreasing water table depths, regardless of the sediment, which was consistent with optimal partitioning theory. The sediment type had a significant effect on seedling root traits. The root traits of P. euphratica was very different in different sediment types under the same hydrological conditions, showing much greater first-order root number in clay sediment under shallower water table conditions, whereas rooting depth was greater in clay/river sand sediment under deep water table conditions. In clay sediment, seedlings responded to lower water availability via greater root elongation, while the root surface area was increased through increasing the total root length in clay/river sand sediment, suggesting that seedlings facing deeper water tables were not always likely to increase their root surface area to obtain more water. Our results indicated that P. euphratica seedlings were able to adapt to a range of water table conditions through plastic responses in root traits and biomass allocation.
学科领域自然地理学
语种中文
文献类型学位论文
条目标识符http://ir.xjlas.org/handle/365004/14627
专题研究系统_荒漠环境研究室
作者单位1.中科院新疆生态与地理研究所
2.新疆大学
推荐引用方式
GB/T 7714
王丽娟. 胡杨(Populus euphratica)幼苗根系生长特征及影响因素研究[D]. 北京. 中国科学院大学,2015.
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