沙坡头人工植被固沙区天然降水的入渗和分配研究

土壤、植被冠层与大气界面间(SVAT)物质传输过程日益成为水文学研究最感兴趣的领域,降水量的迁移与转换是非灌溉区SVAT主要的物质传输过程.干旱半干旱区稀疏灌丛蒸散量占降水量的90%以上,因此对降水入渗与水分在土壤内植物根际区再分配的研究显得十分重要.试验于2001年8月17日至9月30日在中国科学院沙坡头试验站进行,主要观测人工植被荒漠灌木柠条(Caragana korshinskii) 灌丛固定沙丘降水入渗与再分配过程.结果表明:在7次不连续降水过程中,土壤入渗深度与降水强度呈简单线性相关关系,土壤入渗速率约为降水强度的10倍.当次降水过程中降水强度小于0.46 mmh-1时,土壤入渗速率约为0 cm*h-1,此时的降水对沙区土壤基本上没有水分补给作用.受荒漠灌木柠条根系吸水作用的影响,其根系密集剖面深度40～140 cm内降水水分入渗积累不明显.降水入渗速率及入渗深度受土壤剖面初始含水率多寡而变化,干燥土壤剖面有助于提高瞬时入渗速率.降水以后随着时间的推移,人工固沙区微环境内空气温度、湿度等气象条件适宜,柠条生长进入相对旺盛阶段,其根系密集层140 cm深度处土壤含水率在总体上下降的过程中,表现出昼消夜长的趋势,试验期间翌日 8:00时土壤含水率值略高于前一日20:00时水分值 0.1%～0.3%.     

沙坡头没蒿和柠条叶片δ13C 和 N 含量的季节变化特征

通过对腾格里沙漠东南缘沙坡头人工固沙区油蒿和柠条叶片稳定碳同位素分辨率（△）和N 含量的测定，研究了不同种植方式下油蒿和柠条叶片△ 和 N 含量的季节变化及其关系。结果表明：在不同种植方式下，两种植物的△ 与 N 含量在不同月份之间均存在显著差异。油蒿叶片 △ 极显著高于柠条的：在不同种植方式下，油蒿单种下 △ 显著高于混种，柠条则反之。 油蒿叶片 N 含量极显著低于柠条的：不同种植方式下柠条叶片 N 含量无显著差异，而单种油蒿叶片 N 含量则显著低于混种。在 △ 与 N 含量的关系中，柠条叶片 △ 与 N 在两种生境、单种和混种下均极显著正相关，雨明柠条叶片 N 含量可以作为其 △ 与 N 含量的季节变化及其关系在不同微生境有所差异。     

湿润条件下几种锦鸡儿属灌木的气体交换特征及调节机制

土壤水分充足时柠条、中间锦鸡儿和小叶锦鸡儿的Pn、E和Gs均大幅度提高,Pn和Gs值的大小顺序为:中间锦鸡儿>小叶锦鸡儿>柠条,E值的大小顺序为:柠条>中间锦鸡儿>小叶锦鸡儿。柠条一日内的Fv/Fo、Fm/Fo和Fv/Fm值最高,日间没有明显的降低;中间锦鸡儿的上述各项荧光参数值最低,且在13:00~ 17:00出现"低谷",说明发生了明显的光合作用光抑制;小叶锦鸡儿各项测值的大小和波动幅度居于两者之间;3种灌木的光抑制均可在黄昏得到恢复。3种灌木的Chl以中间锦鸡儿为高,柠条和小叶锦鸡儿相近;Car的日均值仍以中间锦鸡最高,柠条和小叶锦鸡儿则相近。一日内以柠条的水势最低且波动平缓;中间锦鸡儿和小叶锦鸡儿的水势较高,日间降幅较大,在15:00~ 17:00降至最低。柠条脯氨酸含量在日间明显增加,中间锦鸡儿稍有增加,小叶锦鸡儿则不明显;3种灌木的脯氨酸含量依次为柠条>中间锦鸡儿>小叶锦鸡儿。     

Effects of Vegetation Restoration on Soil Physical Properties in the Wind–Water Erosion Region of the Northern Loess Plateau of China

In the northern Loess Plateau that has been severely affected by wind–water erosion, shifts from arable land to forest or grasslands have been promoted since 1998, using both native and introduced vegetation. However, there is little knowledge of the ecological consequences and effectiveness of the vegetation restoration in the region. Therefore, relationships between watershed‐scale soil physical properties and plant recovery processes were analyzed. The results show that soil physical properties such as bulk density, hydraulic conductivity, mean weight diameter, and the stability of >1 mm macro‐aggregates have been significantly ameliorated in the 0–20 cm soil layer under secondary natural grasslands. In contrast, re‐vegetation with introduced species such as Caragana korshinskii or Medicago sativa had adversely affected the soil physical properties, probably due to the deterioration of soil water conditions and lower organic matter inputs resulting from severe erosion. Reductions in bulk density and increases in saturated hydraulic conductivity could be used as indicators of soil structure amelioration since they are closely related to most other measured properties. Practical considerations for future re‐vegetation projects are suggested, particularly that native species with lower water consumption rates than the introduced species should be used to avoid further soil degradation.     

荒漠灌丛降雨再分配对土壤pH值的影响

对腾格里沙漠东南缘沙坡头地区1989年建植人工植被区优势固沙灌木柠条（Caragana korshinskii）和半灌木油蒿（Artemisia ordosica）树干茎流及穿透雨的pH值,以及灌丛基部、灌丛下和灌丛外裸地0～10 cm和10～20 cm剖面深度土壤pH值分别进行测定,并与大气降雨pH值进行比较,以探讨荒漠灌丛降雨再分配对土壤pH值空间变异的影响。结果表明:大气降雨pH值最高,穿透雨pH值次之,树干茎流pH值最低,三者之间具有显著差异（p<0.05）。灌丛外裸地土壤pH值最高,灌丛下次之,树干基部最低。总体而言,0～10 cm剖面深度土壤pH值小于其下方10～20 cm剖面深度土壤pH值。柠条灌丛产生的树干茎流对土壤的酸化作用强于油蒿灌丛。树干茎流和穿透雨的酸化作用是导致土壤pH值从灌丛间裸地到灌丛基部方向上降低的一个重要原因。     

高寒沙地人工植被恢复区地表沉积物粒度特征

共和盆地位于青藏高原东北部,是典型的高寒干旱、半干旱荒漠区.青海省治沙试验站经过近50年的发展,形成以封沙育草区、固沙造林区和农田林网区为一体的绿洲防护体系,成为中国高寒沙地土地沙漠化综合整治的典型示范.本文选择典型固沙植物柠条(Caragana korshinskii)和乌柳(Salix microstachya),针对不同治理年限的沙丘和丘间地,探讨治理50年后人工植被恢复区地表60 cm深度土壤粒度的时空变化.结果表明:直播柠条能促进沙丘地表60 cm土层沉积物的细化,尤以地表5 cm更甚.土壤颗粒的变化与植被生长状况及物质来源有关.     

荒漠灌丛树干茎流及其入渗、再分配特征

运用铝箔收集法测定了荒漠灌木柠条（Caragana korshinskii Kom.）树干茎流;利用时域反射仪连续测量土壤剖面水分含量,分析树干茎流影响下柠条根际区水分入渗与再分配过程。结果表明,柠条灌丛产生树干茎流需要2.2 mm的前期降雨量,树干茎流占降雨量的7.9%,平均汇流率是89.8。土壤表层含水率对降雨过程响应明显; 当降雨量达到6 mm时,树干茎流有利于增加根际区土壤水分增量,补充深层土壤水分,对荒漠植被在干旱条件下存活起着重要作用。     

Effects of Caragana Korshinskii Kom. Cover on runoff,sediment yield and nitrogen loss

Soil erosion is serious in the Loess Plateau of China. Deposition of the eroded sediment in lakes or rivers may lead to eutrophication, because the sediment carries a lot of nutrients. Field experiments were conducted to study soil erosion and loss of nitrogen (N) from a 15o hillslope with 30% (low) or 80% (high) coverage of the shrub Caragana korshinskii Kom. A bare soil plot was used for the comparison. The results showed that Caragana korshinskii cover significantly reduced runoff and soil erosion. In comparison to the bare soil plot, the vegetation covered plots had about 20% less runoff and 65% less sediment. In general, the concentration of N in both runoff water and the eroded sediment decreased with time and approached a steady value. However, the species of nitrate nitrogen (NO3) was exceptional which increased with time slightly. The soil erosion caused an N loss of about 250 mg/m2 for the bare soil plot, the low coverage of Caragana korshinskii reduced the N loss by 20% and the high coverage of Caragana korshinskii reduced the N loss by 40%. Moreover, the amount of total N in eroded sediment was 2 to 3 times higher than the value in runoff water. In the total N loss, the organic N was about 75-80%. Nevertheless, inorganic N in runoff water was 5 to 10 times higher than the value in eroded sediment. The species of NO3 was obviously higher than the species of ammonium nitrogen (NH4). NO3 was the main species of inorganic N loss and was about two thirds of total. The organic N was the main species of N in the eroded sediment.     

不同生长季节光照强度和温度对柠条叶片光合作用和呼吸作用的影响

表观光合速率在夏季高于秋季并随光照强度增加递增，光饱和点、光补偿点和饱和光下的ＣＯ２补偿点夏季高于秋季，而呼吸作用和叶绿素的含量则较低。这表明秋季叶片光合速率降低与叶绿素含量无关，除部分受呼吸作用影响外，可能还受其它因素的影响。表观光合速率和真光合速率在２５℃时最高，随处理温度升高迅速递降，而呼吸速率则递增。延长温度的处理时间，光合作用和呼吸作用的变幅增大，秋季比夏季明显。这些结果表明，柠条叶片的光合作用和呼吸作用对温度敏感而不耐高温。     

非结构糖在柠条(Caragana korshinskii K.)再生生长和持续生存中的作用

 柠条在地上组织破坏后从根颈处萌蘖出大量的一年生枝，根系储存的碳水化合物将供应地上生长。但连续刈割后根系储存物质如何变化，储存物质在柠条生长和维持存活中的作用仍须研究。本文在不同时间段内对柠条新萌蘖枝进行连续去除（处理1：对照，3月28日刈割1次后不再处理；处理2：从萌芽到6月9日，每3 d去除一次新萌发枝；处理3：从萌芽到6月24日，每3 d去除一次新萌发枝；处理4：从萌芽到7月15，每3 d去除一次新萌发枝）。结果表明：处理3和4在7月非结构糖含量显著高于处理1和2，说明处理1和2将根系储存的非结构糖用于地上生物量的恢复。连续刈割处理（处理3和4）导致柠条根系非结构糖含量持续下降，这主要是由根系呼吸作用引起。秋末对当年生枝统计结果表明，各处理之间当年生枝数/刈割枝在各处理间差异不显著，说明柠条对外界的破坏具有极强的忍耐能力。