【作者】 郝文芳；

【导师】 陈存根；

【作者基本信息】 西北农林科技大学 ， 生态学， 2010， 博士

【摘要】 本文以陕北黄土丘陵区撂荒地为研究对象,通过野外调查和室内分析相结合,研究撂荒地恢复演替过程中群落的结构特征、物种多样性及生态位演变,结合土壤物理、化学、生物学性质动态的变化,分析撂荒地恢复演替的规律及土壤质量对植被恢复的响应,探索群落结构与环境因子的关系,进而分析植被恢复的机理。主要结论如下:①撂荒演替过程中群落的动态特征在整个演替阶段,植物群落以双子叶植物(Dicotyledons)为主,其次为单子叶植物(Monocotyledons),再次为裸子植物(Gymnosperm)和蕨类植物(Pteridophyte)。研究区大类群结构相对简单,植物类群相对少。菊科(Compositae)、禾本科(Gramineae)、豆科(Leguminosae)的物种在研究区植被恢复过程中所起的作用最大。达乌里胡枝子(Lespedeza dahurica)、长芒草(Stipa bungeana)、铁杆蒿(Artemisia sacrorum)和白羊草(Bothriochloa ischaemum)贯穿演替的始终,它们在群落演替中占据着重要的地位,对群落的稳定性有重要的价值。撂荒演替优势种更替出现反复,群落的演替有趋同效应。物种的生活型是以多年生草本为主,半灌木和小灌木占据一定的比例,灌木和乔木占比例很少。生活型的改变主要体现在繁殖对策上,1-2年生的草本植物,其生活史对策以r-对策为主,多年生草本、半灌木和灌木,生活史对策上倾向于k-对策。群落的数量特征随着演替时间的延长呈现增加的趋势,生物量随着撂荒时间的延长呈现减少的趋势。地下生物量主要集中在0-60cm土层,100cm以下为零。随着土层深度的加深,根系生物量逐渐减少。群落丰富度随撂荒时间的延长变化幅度较小;群落的Simpson多样性指数变化趋势表明撂荒演替使物种相对集中,撂荒演替不利于物种多样性的增加;撂荒初期群落的优势度较大,随着植被恢复演替时间的延长,呈下降趋势;在撂荒演替过程中,群落中物种分布均匀,优势种的地位不突出;群落的Shannon-Wiener指数呈现增加的趋势,随着撂荒时间的延长,群落的稳定性呈现增加的趋势;群落的Peilou均匀度指数表明前期随着撂荒年限的增加群落的多样性逐渐增大,并稳定在一个较高的水平,后期多样性有降低的趋势。在演替过程中,虽然前期和后期的时间相隔较长,群落的微生境被隔离了,但是群落中物种被隔离的程度却不很明显。②撂荒地土壤性质对植被恢复的响应在垂直剖面上,随着土层深度的加深,土壤含水量呈现逐渐增加的趋势。立地间土壤含水量从大到小的趋势是:阴坡>半阴坡>半阳坡>阳坡。土壤含水量的月变化受诸多因素的限制,没有统一的规律。土壤含水量的年际动态趋势表明,撂荒演替没有使土壤含水量恢复。本研究中土壤含水量的年际间、月变化、立地间以及土层间的变化规律不尽一致,但是总的趋势是撂荒演替过程中,土壤水分的恢复效果不甚明显。撂荒演替使得土壤的容重变小。土壤养分的变化主要集中在表层,深层变化微弱,上层养分含量大于下层。土壤有机质、全氮、速效氮、速效钾、速效磷和有机碳含量在撂荒初期的群落里比较高,随着弃耕时间的延长其含量呈现增加的趋势,但各样地土壤养分的绝对增加量比较少。随着撂荒地演替时间的延长,土壤微生物碳、微生物氮含量增加,土壤微生物氮与全氮之比、土壤基础呼吸强度、土壤代谢熵随着撂荒时间的延长呈现增大的趋势。在撂荒演替过程中,土壤尿酶、碱性磷酸酶的活性呈现跳跃式的变化。土壤微生物碳与有机碳之比的动态变化趋势表明:晚期土壤质量和前期相比有所退化,但并不是无限制的退化下去,而是稳定在一定的范围;同时随着演替时间的延长,土壤微生物总数有趋于稳定的趋势。③撂荒演替的方向群落的数量特征、群落结构的动态分析表明:随着撂荒时间的延长,群落逐渐得到恢复。土壤的物理性质、化学性质和大部分微生物学指标随着演替的进行,呈现增加的趋势。结合群落结构动态趋势、土壤性质等方面,初步总结出黄土丘陵区弃耕演替为进展演替。④撂荒演替植被恢复的机理大部分样地中生态位最宽的物种是优势种或者亚优势种,这些优势种在控制群落性质和环境方面起着主导作用,他们对资源环境利用较为充分,对环境的适应能力强,在竞争中处于优势地位。各主要种群之间的生态位重叠程度较高,尤其是优势种和亚优势种间重叠较多,这种重叠使得物种之间相互竞争,在竞争中为取得更多资源,群落必然朝着有利于资源利用的方向发展,导致了物种生态位的分化,这是弃耕地植被恢复过程中物种相互替代的主要驱动力,也是植被演替的生态学机理所在。植物群落演替过程,是植物群落与土壤相互影响和相互作用的过程,土壤性质影响优势种的拓殖和更替,植被的恢复又促进土壤的发展。在这个协同进展演替过程中,土壤性质的各指标所起的作用不同,土壤全氮、有机质、土壤呼吸量和碱性磷酸酶是影响撂荒地演替的关键因子,土壤微生物量氮和土壤呼吸熵对植被恢复的作用也较强,这些指标是衡量土壤性质的主要指标。植物群落的演替是对其初始状态的异化过程,不但体现在种类组成和结构的改变上,也体现在环境的改变上,植物演替过程,是物种对土壤肥力不断适应和改造及不同物种在不同肥力梯度下相互竞争和替代的过程,土壤肥力是植物演替的重要驱动力之一。更多还原

【Abstract】 Taking the abandoned farmland in the hilly and gully Region of North Shaanxi as its subject, the study investigated the variations in the structural characteristics, species diversities and niches of communities on abandoned farmland during its recovering successions by the substitution method of time sequence for space sequence and the field survey and lab combined analysis, and examined the responses of recovering succession patterns and soil qualities of abandoned farmland to vegetation recoveries in combination with the dynamic variation in its soil physical chemical and biological properties so as to probe into the relations between community structure and environmental factors and then the mechanisms of vegetation recoveries. Its main conclusions are as follows:1.Dynamic characteristics of the communities on abandoned farmland during its recovering successionDuring the whole succession, the plant communities were dominated mainly by dicotyledons, secondarily by monocotyledons, and thirdly by gymnosperms pteridophytes. In the region under study, the large plant classes and groups had relatively simple structures and relatively small numbers of plant species. Composite, Gramineae and Leguminosae species played the most important role in the vegetation recoveries. L.davurica, Stipa bungeana, Artemisia gmelinii and Bothriochloa ischaemum existed through the whole succession, occupying an important position in the community successions and being of great value in maintaining the communities stable. During the succession of abandoned farmland, the dominant species alternatively and repeatedly appeared and the community successions tended to conform. The life types of the species were perennial herbs in most cases, the sub-shrubs and under-shrubs occupied certain proportions, and the shrubs and arbors occupied very small proportions. The life types of the species were perennial herb dominated and contained certain proportions of sub-shrubs and under-shrubs.The life types mainly embodies their variations in their reproduction strategies, 1-2 year old herbs taking R-strategy during their life history and perennial herbs, sub-shrubs and under-shrubs basically taking K-strategy during their life history.The numbers of the communities tended to increase as their successions prolonged, but their biomasses tend to decline with the farmland-abandoning time. The underground biomasses mainly distributed in 0-60cm soil and no longer distribute below 100cm deep. As the soil depth increased, the root biomasses gradually decreased.During the vegetation recoveries, the species diversities presented different patterns. Some communities hadα-species diversity indexes tending to increase with the farmland-abandoning time, some hadα-species diversity indexes tending to stabilize within certain limits and others hadα-species diversity indexes tending to rise. The analysis of theβ-species diversity indexes showed that although the quadrats under study were far away from one another in time sequence and thus their communities were isolated in microhabitat and lie differently in space sequence, their species isolations appeared not remarkable. Therefore, the species diversity variations were dynamic during the recovering succession of abandoned farmland and their mechanisms of the variations need to be further studied.2. Responses of soil properties of abandoned farmland to its vegetation recoveriesIn the vertical soil profile, as the soil depth increased, the soil water contents tended to gradually increase. The soil water contents of the different sites ranked in the decreasing order of north-facing slopeland > semi-north facing slopeland > south-facing slopeland >semi-south-facing slopeland. The monthly soil water contents were limited by many factors and thus did not presented a consistent pattern. The year to year variations of the soil water contents showed that farmland abandoning did not recover soil water content.According to the study, the variations of the soil water contents between the different years, months and the sites did not present very consistent patterns, but their general tendencies were that during the succession of abandoned farmland, the soil water content did not evidently recover. The succession of abandoned farmland rendered its soil bulk weight to decrease.The soil nutrients mainly distributed in topsoil, thus varying only slightly in deeper soil and having higher contents in upper soil than in lower soil. in the early farmland abandoning period the soil organic matter contents, nitrogen totals, available nitrogen, potassium and phosphorous contents, and organic carbon contents of the communities were higher and with the farmland-abandoning time they tended to increase but their absolute contents increased slightly .The soil biological properties presented following several tendencies: with the succession time, some of the soil microbial parameters tended to increase, some of them tended to stabilize, and several of them tended to decline, and some of them tended to fluctuate.Because soil biological properties sensitively indicated soil quality variations, they performed better than soil chemical and physical properties in indicating soil quality responses to dynamic succession of abandoned farmland. Thus it was proposed that soil chemical, physical and biological properties be employed as the indicators for assessing soil quality responses in research.3. Succession direction of abandoned farmlandThe dynamic analysis of the numbers and structures of the communities showed that with the time, the structures of the communities became complicated and their natural resource-exploiting capacities gradually increased. With the succession, the soil physical and chemical indicators and some microbial indicators tended to increase. Ecological recovery involves two respects, vegetation recovery and soil recovery, and taking into account a full range of all its relevant respects, the succession of abandoned farmland in the hilly and gully loess region was concluded as a progressive succession.4. Vegetation-recovering mechanism of the succession of abandoned farmlandIn most of the quadrats, the species with the widest niches were dominant or subdominant species, which played a dominant role in determining the natures and environments of the communities to which they belonged, so that they could more fully exploit their environmental resources, better adapt themselves to their environments and take advantageous positions in competition. The different major populations had highly overlapped niches and the dominant and subdominant species in particular had highly overlapped niches; and these overlaps made the different species compete with one another for more resources and as a result the communities inevitably succeeded towards the directions in favor of their resource exploitations, thus resulting in their niches differentiating. This was the driving force of the species replacement in the vegetation-recoveries of abandoned farmland as well as the ecological mechanism of its vegetation successions.The successions of the plant communities were the processes whereby the plant communities and soils mutually interacted with and acted on each other, the soil fertilities affecting the colonization and replacement of the dominant species and the vegetation recovery promoting the soil development. In this co-succession, the different soil property indicators took different effects and among them, the farmland-abandoning times, slope aspects and gradients, nitrogen totals, organic matter contents, soil respirations and phosphatase activities were the key factors that affected the vegetation successions, and the microbial-biomass nitrogen contents and soil respiration quotients had stronger effects on the vegetation recoveries.The successions of the plant communities were the dissimilating processes of their original forms whereby they embodied their variations not only in their species compositions but also in their environments, and the plant successions were the processes whereby the species continuously adapted themselves to and improved the soil fertilities, and the different species competed and replaced one another at different fertility gradients, so that the soil fertilities were the driving force of the plant succession.更多还原