【作者】 王宁；

【导师】 李靖； 焦菊英；

【作者基本信息】 西北农林科技大学 ， 水土保持与荒漠化防治， 2008， 硕士

【摘要】 土壤侵蚀可造成表层土壤种子库的流失,同时影响土壤养分水分条件,进而影响种子的萌发、建植以及植被的生长和繁殖。而在土壤侵蚀非常严重的黄土高原地区,关于土壤侵蚀对植被繁殖策略、土壤种子库运移、幼苗建植影响的研究至今还未见到报道。为此,研究黄土丘陵沟壑区坡沟侵蚀过程对土壤种子运移与幼苗建植以及繁殖策略的影响就显得十分重要,可为该区植被的自然恢复与重建提供一定的科学理论依据。本研究在黄土丘陵沟壑区安塞纸坊沟选取三个代表性侵蚀单元,即短坡面深沟谷自然恢复侵蚀单元(侵蚀单元Ⅰ),长坡面浅沟谷自然恢复侵蚀单元(侵蚀单元Ⅱ)和坡面治理侵蚀单元(侵蚀单元Ⅲ),按照分水岭——沟间地坡面——沟沿线——沟谷坡面的顺序沿流水方向布设共20个5m×5m样地,分别以植被下、植被间、淤积微地形分0-2cm、2-5cm、5-10cm三层采样,用萌发法鉴定土壤种子库组成与密度,并跟踪调查幼苗库和营养繁殖体库,进而较为全面地分析土壤侵蚀、立地条件与土壤种子库组成与分布,营养繁殖及幼苗建植的关系。主要取得以下研究结果:(1)研究区3个侵蚀单元20个样地的土壤样品中,共有6597棵幼苗萌发并得以鉴定,分属于17个科50个种;在恢复时间较短、植被稀疏、土壤侵蚀较为强烈的样地,土壤种子库中一、二年生物种所占比例较大,而在植被恢复较好且盖度较大的样地多年生物种占有较大比例。(2)土壤侵蚀对土壤种子库的次分布具有一定的影响,表现为淤积微地形的种子库密度显著高于侵蚀微地形的种子库密度,具体表现为淤积地形〉植被下〉植被间。淤积地形种子库密度为1585-21585seed/m2,植被下为2170-10736seed/m2,植被间为1129-6585seed/m2。治理的侵蚀单元Ⅲ内总体种子库密度较低,分布在2007-9381seed/m2之间。(3)土壤侵蚀对种子库的物种组成也具有一定的影响,植被群丛能够有效拦截较多的物种的种子,其次是淤积微地形,而在侵蚀微地形种子库的物种数量最低。(4)研究区共有9个科的35个物种具有营养繁殖策略,其中菊科和禾本科占到77%。营养繁殖物种数在植被恢复较好,侵蚀微弱的单元Ⅲ内最多,而自然恢复的单元Ⅰ与Ⅱ内营养繁殖物种较少,且主要分布在沟谷坡地。(5)研究区具有营养繁殖能力的主要物种铁杆蒿、茭蒿、山苦荬、裂叶堇菜,分布样地主要处在自然恢复的沟谷坡面,坡面较陡,侵蚀强烈,土壤水分含量较低,但是土壤有机质、全氮、有效氮、速效钾含量较高。另一些主要物种白羊草、长芒草、中华隐子草、赖草、二裂委陵菜、阿尔泰狗哇花等,分布样地主要处于沟间地坡面,土壤面蚀普遍,土壤水分、养分均较低。主要靠种子繁殖的物种猪毛蒿、苦卖菜、黄鹌菜、地锦、菊叶委陵菜、狗尾草、达乌里胡枝子、鸦葱、狭叶米口袋、糙叶黄耆、硬质早熟禾、二色棘豆等,主要分布在植被条件较差、面蚀较强的样地。(6)样地内跟踪调查的幼苗属于56个物种,其中60%的物种是依靠种子繁殖。幼苗库密度随时间的变化表现为7月31日> 9月11日> 10月13日> 6月27日,且7月31日调查密度远远高于其它时期的幼苗库密度。侵蚀单元Ⅰ、Ⅱ均表现为沟沿线上样地幼苗库密度较高,沟谷坡面较低,沟间地坡面居中。(7)幼苗库密度远远低于土壤种子库密度,但幼苗库的物种数却大于种子库的物种数。幼苗库与种子库物种相似性系数在侵蚀单元Ⅰ、Ⅱ内的侵蚀部位较低,而在有植被拦截和淤积部位相似性较高;侵蚀单元Ⅲ内相似性均较低。幼苗库和种子库中均有且出现频率较高的物种有猪毛蒿、铁杆蒿、阿尔泰狗哇花、达乌里胡枝子、香青兰、菊叶委陵菜、地锦、中华隐子草、白羊草。同时种子库密度大小制约着幼苗库密度的大小。(8)研究区主要物种幼苗建植特点表现为铁杆蒿、茭蒿、阿尔泰狗哇花、柠条、扁核木、杠柳的幼苗要求养分条件好,植被盖度高,侵蚀受到抑制的生境;香青兰、白羊草、中华隐子草、狼牙刺、牻牛儿苗、猪毛蒿、达乌里胡枝子、地锦、猪毛菜、紫筒草、角蒿、长芒草幼苗对养分条件和表层水分条件要求不高,在植被稀疏、面蚀强烈的部位也能萌发并部分成功建植。更多还原

【Abstract】 Soil erosion can result in seed loss in the surface soil seed bank, and also affects soil nutrients and water conditions, thus has impacts on seed germination and establishment, growth and reproduction of the vegetation. Soil erosion is frequent and serious in the the hill-gullied area on the Loess Plateau. However, there has been no report about the interaction between slope-gully erosion and plant reproductive strategy, soil seed bank removal and seedlings establishment. So it is important to study this problem to provide some theories for the vegetation restoration and rebuilding in this area.The study area is based in Zhifanggou Ansai, the typical hill-gully area on the Loess Plateau. Three representative slope-gully erosion units were selected: short slope and deep gully erosion unit with natural restoration (UnitⅠ), long slope and shallow gully erosion unit with natural restoration (UnitⅡ), managed slope and deep gully erosion unit (UnitⅢ). The plots were selected along the route of runoff by the order: watershed divide, slopes of inter-gullies, the margin between gully and inter-gully, and slope of gully. Totally 20 plots with area of 5m×5m were arranged. The soil cores were collected from soil layer 0-2cm, 2-5cm, and 5-10cm to indentify the seed density and species composition of the soil seed bank in three different microinstructions (the area under shrub/herbosa, the gap between shrub/herbosa, and the silted area). The density and composition of species of soil seed bank were detected by germination method in laboratory, and tracking investigation on the seedling bank and clone propagulum bank were also conducted to analyze the interaction of soil erosion and seedling establishment and vegetation reproduction. The main results were obtained as follows:(1) 6597 seedlings belonging to 50 species were germinated in the soil samples from the 20 sampled plots, which belong to 17 families. The annual species takes up larger proportion in the plots with sparse vegetation and serious soil erosion. While the perennial species takes up larger proportion in the plots which has been restoring for long period with slight soil erosion. (2) The density and species composition of soil seed bank are affected by the surface soil erosion. The result shows that the density of soil seed bank in the lower silted place is significantly larger than that in the gap between shrub/herbosa with the sequence of the silted area > the area under shrub/herbosa > the gap between shrub-herbosa. The density of soil seed bank in silted area is 1585-21585 seed/m2, under the shrub/herbosa is 2170-10736 seed/m2, and in the gap between shrub/herbosa is 1129-6585 seed/m2, the density of seed bank in the UnitⅢwith managed slope is 2007-9381 seed/m2.(3) The species of soil seed bank is affected by the soil erosion too. The vegetation tussock can hold up the seed of most species efficaciously, and then is the silted area, while the gap between the shrub/herbosa loss the seed of many species.(4) 35 species belong to 9 families have the ability of clone regeneration. About 77% of them are belonged to composite and gramineous grass. UnitⅢhas the largest number of this kind of species. In the UnitⅠand UnitⅡthis kind of species are mainly growing in the gully slope, where has been restoring for a long period.(5) Some of the main species with the ability of clone regeneration such as Artemisia gmelinii, Artemisia giraldii, Ixeris Chinensis, Viola dissecta mainly grow in the gully slope in the natural restoring unit with steep slopes, intense erosion, low soil moisture content, but higher content of organic matter, total N, available N and available K. The other clone species such as Bothriochloa ischcemum, Stipa bungeana, Cleistogenes chinensis, Leymus scalinus, Potentilla bifurca, Heteropappus altaicus mainly grow in inter-gully slopes, where has the high frequency of surface erosion, lower soil nutrient and soil moisture. The species reproduction only by seed such as Artemisia scoparia, Ixeris denticulate, Youngia japonica, Euphorbia humifusa, Potentilla tanacetifolia, Setaria viridis, Lespedeza davurica, Scorzonera divarieata, Gueldenstaedtia stenophylla, Astragalus scaberrimus, Oxytropis discolor, Poa sphondylodes grow in the plot with serious erosion, sparse vegetation.(6) There are 56 species in the seedling bank, 60% of them reproduced only by seed. The density of seedling bank is changing with time, i.e. 31st July >> 11th September > 13th October > 27th June. The margin area between gully and inter-gully has larger density of seedling bank, but the gully slope has lower density.(7) The density of seedling bank is less than the seed bank, but there are more species in the seedling bank. The species similarity coefficient of seedling bank and seed bank is lower in the eroded area but higher in the place with covered vegetation in the UnitⅠand UnitⅡ. But in the UnitⅢwith planted Caragana intermedia in inter-gully slope, has the lower similarity coefficient. The species both in the seed bank and seedling bank with high frequency are Artemisia scoparia, Artemisia gmelinii, Heteropappus altaicus, Lespedeza davurica, Dracocephalum moldavica, Potentilla tanacetifolia, Euphorbia humifusa, Cleistogenes chinensis, and Bothriochloa ischcemum.(8) The establishment of the seedling of the main species shows that the seedling of Artemisia gmelinii, Artemisia giraldii, Heteropappus altaicus, Caragana intermedia, Periploca sepium need the habitat with higher nutrient and covered vegetation. Dracocephalum moldavica, Bothriochloa ischcemum, Cleistogenes chinensis, Sophora viciifolia, Artemisia scoparia, Lespedeza davurica, Euphorbia humifusa, Salsola collina Pall, Stipa bungeana can grow in the habitat with sparse vegetation and erious erosion, and some seedlings can established successfully.更多还原