【作者】 梁爱华；

【导师】 杨改河；

【作者基本信息】 西北农林科技大学 ， 植物资源学， 2015， 博士

【摘要】 退耕还林(草)工程是植被恢复的有效措施,在退化和脆弱生态系统的恢复与重建中起着重要的作用。黄土高原作为我国水土流失与生态退化的典型区域,已成为我国实施生态恢复工程的重点,揭示和阐释生态恢复过程中生态效应规律及关键驱动因素,对该区域植被恢复建设、脆弱生态系统功能修复以及生态环境改善具有重要的科学价值和实践指导意义。因此,本文以黄土高原丘陵沟壑区为研究区域,基于恢复生态学理论与生态学研究法,选取陕北纸坊沟流域恢复植被为研究对象,探讨在当地立地条件下植被恢复模式(人工恢复和自然恢复)、植被类型(人工乔木、灌木和草地)、树种(油松、刺槐)、林分组成(纯林和混交林)、退耕年限下群落多样性、土壤质量、碳、氮、水效应及其互作关系、局地小气候等生态效应与功能的整体变化效应,以期为退耕还林(草)综合生态效应的评价与调控,以及生态工程的实施提供科学指导。主要研究结果如下:1.退耕地植被恢复群落结构和物种多样性变化效应退耕地人工植被恢复过程中,群落物种组成丰富,共包括23科63属73种,草本群落中禾本科、菊科和豆科植物占主要地位,其中阿尔泰狗娃花、稗草、败酱、铁杆蒿、猪毛草和达乌里胡枝子等林下草本物种重要值和生态位宽度较大,重叠指数较高,成为群落的优势种。不同林分组成以混交林的物种丰富度和多样性指数较高,群落内部异质性随之增加,而纯林群落结构相对简单,物种多样性低。在不同恢复年限的刺槐群落中,低林龄群落可利用资源丰富,物种多样性较高,高林龄的物种经过长期竞争,群落结构趋于稳定,物种多样性随之降低。可见,在退耕还林过程中选择混交林的造林模式,能优化群落结构,形成空间复合式立体配置,有利于黄土丘陵区退耕区生态效应的最大化。2.退耕地植被恢复下土壤质量的提升效应与农地相比,植被恢复使退耕地土壤大团聚体含量和团聚体稳定性均显著增加。不同退耕还林地与年限下土壤团聚体稳定性顺序为:油松35a>撂荒地35a>柠条26a>刺槐12a>刺槐35a>撂荒地12a>沙打旺6a>刺槐26a>撂荒地26a>农地。同时,植被恢复减小了表层土壤的容重,相应地增加了土壤孔隙度,使土壤透气性增强,土壤物理性质得到改善。同时,植被恢复亦显著增加了退耕地土壤有机质、全氮、碱解氮、速效钾的含量以及土壤脲酶和蔗糖酶的活性。在土壤剖面上,土壤有机质和养分元素含量不仅在土壤表层极显著增加,并且在深层土壤亦有显著增加。说明退耕还林从土物理、化学、生物学性质上综合改良了土壤质量。3.植被恢复对退耕地土壤碳固存及碳-氮关系的影响植被恢复显著增加了退耕地土壤总有机碳和全氮及其活性组分含量(活性有机碳和碱解氮),并且碳氮库增加效应表现为乔木>灌木>撂荒。土壤总碳与全氮亦在植被恢复过程中呈显著地线性正相关关系。并且在土壤剖面上,碳氮库间的线性关系随着土层深度的增加而渐次降低,深层土壤的碳氮库及二者的比值增加的潜能都随着恢复年限的增加而增大。与自然恢复相比,在短期内人工林对固存碳氮效应及相互关系均具有优越性,表现出人工植被恢复措施有效、快速提升土壤固定碳氮效应的巨大潜力。4.植被恢复对退耕地土壤含水量及碳-水关系的影响无论是退耕还林人工恢复植被还是撂荒自然恢复植被,农地转变后初期都使土壤含水量降低,而到26a后出现拐点,此后土壤含水量开始恢复,但恢复速率较缓慢。无论是不同季节(月份)、不同土层深度、退耕模式(人工恢复与自然恢复),退耕地的土壤碳汇效应与土壤含水量间成反比关系,即植被恢复的碳封存功能是以消耗土壤水分为代价。在土壤剖面上,0-20cm土层土壤碳汇-含水量相关性最大,随土层加深依次递减。不同季节中7月份土壤碳汇与土壤含水量间显著相关,4月份相关性小。随恢复年限的增加,土壤碳汇-含水量关系趋于互惠,26a(拐点)以后由负相关性变为正相关,35a时具有显著的正相关关系。人工恢复的土壤碳汇-含水量相关性大于自然恢复。土壤碳汇-含水量关系具有重要的应用价值,当有机碳积累超过30Mg?ha-1时,土壤含水量降到了6%以下,接近于当地土壤的萎蔫系数。因此在实践上,要通过适当的人工干扰,如控制群落的密度等途径使土壤碳库维持在一定的水平以下,以利于林内土壤的碳-水平衡。5.退耕地植被恢复的局地小气候变化效应与裸地相比,混林、纯灌木林和撂荒地一天的平均光照强度分别降低3.39×104lx,3.4×104lx和0.9×104lx;平均空气温度分别降低了5.3℃、1.3℃和0.5℃;土壤温度分别降低了14.9℃、16.8℃和10.7℃;但是大气相对湿度分别增加了8.4%、7.3%和2.0%;150cm冠层内风速平均分别减小了97.2%、87.5%和22.2%。可见,退耕地植被恢复产生了显著的局地小气候效应,即降温、增湿、捕光和挡风效应。在较短恢复时间内,人工辅助恢复优于自然恢复,混林的小气候效应优于纯灌木和草地,即群落结构越复杂,小气候效应越明显。但是退耕林地植被生长耗水也引起土壤含水量呈现降低趋势。更多还原

【Abstract】 Grain for green project is an effective measure of vegetation restoration, which plays an important role in the restoration and reconstruction of degradation and fragile ecosystem. The Loess Plateau, as a typical area of soil and water loss and ecological degradation in China, has become the focus site for the implementation of ecological restoration engineering in this country. Revealing and interpretation of the ecological effect laws as well as its driving factors during the process of ecological restoration has important scientific value and practical guiding significance for re-construction of the regional vegetation, repair fragile ecosystem function and improve the ecological environment. Based on the restoration ecology theory, and also using ecosystem positioning method, the present study designed to investigate the influence of restoration approach(artificial or natural),conversion type(forestland or grassland), plantation type(woodland or shrubland) as well as conversion period(time since conversion) on community biodiversity, soil quality, carbon sequestration, nitrogen cycle, soil water content and microclimate in Zhifanggou watershed of Ansai country, a classic deeply incised hilly-gully place in loess plateau region. We aimed to provide theoretical basis for controlling and interferencing the ecological effect of ‘Grain for Green’ project, and also provide direction for policy-making. The results are as following:1. Effect of vegetation restoration on community structure and biodiversity.Through quadrate investigation and static analysis, we found that there is abundant species that belong to 23 families, 63 genera and 73 species. Among the understory communities, the dominant families include Gramineae, Compositate and Leguminosae; there is an obvious floristic characteristics, in which the world distribution has an absolute advantage. The mix forest has a relative great species richness and diversity index which increased the heterogeneity inside community, whereas the community structure of pure thrubland is simple and also with a lower biodiversity. Among the communities with various conversion times from cropland, the young plantations have a higher biodiversity while the elder plantation has a lower one because of their stable community structure derived by long term competition. During the community succession, the understory grass plants, including Heteropappus altaicus, Barnyard grass, Patrinia scaniosaefolia, Artemisia vestita, Salsola and Lespedeza daurica, have a bigger important value and species riche breadth, as well as a higher overlap index. This is resulted from their acclimated to local water deficiency conditions, and which guarantee them advantage than others in competition for resource, so become the dominant species.2. Effect of grain for green project on soil quality.Compared with cropland, vegetation restoration significantly increased the content of >0.25 mm aggregate(macro-aggregate), and also increased soil aggregate stability. Vegetation restoration decreased bulk density of surface soil, increased soil porosity and gas permeability, and at last improved soil physical quality.Vegetation restoration also significantly increased the content of soil organic matter, total nitrogen, available nitrogen and available potassium, so enhanced soil fertility and improved soil chemical quality.Compared with cropland, vegetation restoration greatly increased the activity of soil urease and sucrase, that as the well indicators of soil biological quality. There is present a season specificity for those enzymes activity. For urease, the ensyme activity is pixed in spring, followed by summer, and with the smallest activity in autumn. For sucrase, there is also a pix in spring, followed by the smallest value in summer, and then rised in autumn,but still lower than the spring’ value. These ensyems activity decreased along with soil depth, but we have not find an obvious difference among the community with a various restoration time.3. Vegetation restoration on soil carbon sequestration and carbon- nitrogen relationship.Vegetation restoration not only significantly increased soil organic C(SOC) and soil total N(STN), but also greatly improved labile organic C(LOC) and soil labile N(SLN). In 0-60 cm soil profile, compared with both 20~40 cm depth and 40~60 cm soil depth, there is a significant change of the organic matter(C and N) in 0~20 cm soil depth, which indicated that the shallow soil is more sensitive to land use change. Whereas both SOC and LOC present a nonlinear accumulation characteristics across time,both STN and SLN increased linearly with the restoration time increasing. We also found the increase of both SOC and STN in 0~20cm soil depth is mainly relevant with restoration time, however, both in 20~40 cm and 40~60 cm soil depth, it is significantly related with re-vegetation mode. As for SOC increasing and activation among different vegetation type, there is a trends of woodland, then shrubland, followed by abandoned land. Whereas abandoned land is benefit of STN restoration,artificial highwood and shrubbery accelerate SLN, means available N restoration in degraded and barren soil. Finally, compared with field, vegetation restoration significantly increased the correlation between SOC and STN. Among the same vegetation type, the related coefficient(r2) between SOC and STN increased with restoration time below 26 yr, while above 26 yr, it maintain constant. As for the similar restoration time but different vegetation type, the positive effect of woodland is bigger than shrubland, while the latter is bigger than abandoned land. In a word, vegetation restoration on degenerated farmland significantly increased CO2 sequestration, restored soil nutrition availability, and improved the relationship between soil C and N. In a short revegetation time, artificial restoration is superior to natural restoration.Afforestation of degraded cropland significantly promoted CO2 sequestration and restored soil N availability, which consequently reduced N limitation and sustained C sequestration. Above a vegetation age threshold, i.e. 26 yr, afforestation significantly improved the linear correlation relationship between soil organic C(SOC) and total N(TN) stocks in the 0–60 cm soil profile. This linear SOC-TN stock nexus decreased with increasing soil depth, and the potential of having improved SOC stock, TN stock and the ratio between them in deeper soil layers increased with increasing time after afforestation. Managed plantations provide superior CO2 sequestration and improvement in the SOC-TN correlation only for a short period after afforestation when compared to natural restoration where trees establish by natural colonization.4.Effect of vegetation restoration on soil water content and carbon-water relationship.Disregard to artificial or natural approach, vegetation restoration commonly make soil water content decreased in the initial stage, but after 26 yr, soil water content start rise though with a low rate. In correspondence, there is an inverse relationship between SOC stocks and soil water content disregard to season, soil depth and restoration approach, which means carbon sequestration derived by vegetation restoration is at the expense of the consumption of soil moisture.Through soil profile, the relationship between SOC stocks and water content is significant, at 0-20 cm soil depth, then with the soil depth deeper, the relationship gradually become insignificant. There is a significant relationship between SOC storks and water content in summer(July) than in spring(April). With the restoration time increasing, SOC stocks and water content gradually become mutual benefit, and after restoration 26 yr, the reverse relationship changed to positive relationship.The SOC stocks-water content relationship has an important application in field, that is when the SOC accumulated over 30 mg?ha-1, the water content decreased close to wilt coefficient of 6%. So in practice, people should maintain the SOC sequestration rate below this value through some disturbance method, such as controlling community density, planting more thrub and grass rather than forest etc., thus make the carbon and water balance inside the plantation soil.5.Effect of Grain for Green project on microclimate.Compared with cropland, the average light intensity within a day for mixed forest, pure shrubbery and abandoned land has decreased by 3.9×104lx, 3.4×104 lx, and 0.9×104lx, respectively, and the mean air temperatures of them decreased by 5.3℃, 1.3 ℃and 0.5℃, respectively. Our results also revealed that the highest temperatures on soil surface of them have decreased by 14.9℃, 16.8 and 10.7℃ ℃, respectively, but the corresponding air relative humidity has increased by 8.4%, 7.3% and 2.0 %, respectively. It is evident that vegetation restoration is capable of producing significant microclimate effects on temperature-reduction, air humidification, light-harvesting and wind-resistance. In addition, in a short-term scale, artificial-assistant restoration is more favorable than natural restoration in microclimate improving. And with the community architecture more complex, the positive effects on micro-climate become more significant. However, these effects were obtained at the expense of soil moisture, especially for the artificial forest. Although mixed forest relative to pure forest has better soil moisture, it still can not escape soil water conditions deterioration. On practice, adjusting the critical point with the minimum water consumption to obtain the biggest local microclimate effect, is privotal to the success of vegetation construction in arid and semi-arid areas of Loess Plateau.更多还原