毛乌素沙地优势植物对全球气候变化的响应研究

毛乌素沙地是中国半干旱地区典型沙地，这里的干旱生态系统对全球的水热配合格局的变化具有很灵敏的响应。随着未来全球气候变化，如温度和降水量变化，将给这里的陆地生态系统分布格局和生产力以及水分平衡带来巨大影响。故本文人工控制157. 5mm、315. Omm、472. 5mm和630. Omm4种施水量水平以及25/20℃和28/23℃（白天／晚上）两种温度，来研究与模拟毛乌素沙地优势植物对水分和温度变化的响应。 以沙柳、杨柴和油蒿幼苗为研究对象，人工控制4种降水量水平来探讨它们的水分平衡对全球变化中降水量变化的响应。结果表明，随着施水量的增加，沙地贮水量及其它的变化量、湿度、蒸发量和蒸腾量均逐渐增大。并且157. 5mm和315. Omm施水量的植物沙地出现水分亏缺现象。相同施水量下，沙地蓄水量和湿度均杨柴沙地>沙柳沙地>油蒿沙地，而植物蒸腾量却油蒿>沙柳>杨柴。 以沙柳和油蒿幼苗为研究对象，人工控制4种降水量水平来探讨植物气体交换过程对全球变化中降水量变化的响应。结果表明，施水量的增加显著提高了两种植物的净光合速率、蒸腾速率、气孔导度和光能利用效率，并且显著降低了叶片温度。同时，157. 5mm施水量造成沙柳和油蒿的净光合速率和蒸腾速率具有显著的“午睡”现象，而充足施水却有效的解除或缓解这种“午睡”现象。 以沙柳、杨柴、油蒿和柠条幼苗为研究对象，人工控制4种降水量水平来探讨植物叶绿素荧光对全球变化中降水量变化的响应。结果表明，不同施水量对这4种植物的初始荧光、最大荧光、可变荧光和PSII光化学效率均具有显著影响。157. 5mm施水量的沙柳、杨柴、油蒿和柠条以及630. Omm施水量的柠条出现明显的光抑制现象。 以沙柳、杨柴、油蒿和柠条幼苗为研究对象，人工控制4种降水量水平来探讨植物生长对全球变化中降水量变化的响应。结果表明，施水量的增加对沙柳、油蒿和杨柴枝叶形态和生物量等都具有显著正效应。而157. 5mm和630. Omrn的施水量对柠条生长具有负作用。另外，沙柳、杨柴和油蒿根冠生物量比随着施水量增加均逐渐减小，而不同施水量的油蒿根冠生物量比之间差异不显著。 以柠条、杨柴和油蒿幼苗为研究对象，人工控制两种温度水平来探讨植物形态、生物量和气候交换特征对增温的响应。结果表明，增温显著提高了柠条和杨柴株高、叶数、叶面积、生物量、净光合速率、蒸腾速率和气孔导度，却显著降低了水分利用效率。增温对油蒿叶数、叶大小、叶面积、生物量、蒸腾速率和气孔导度没有显著影响，却显著提高了油蒿的树高和净光合速率。柠条、杨柴和油蒿之间的种间生长和生理特征均有显著差异。

不同保水剂对宁南山区马铃薯生长发育和产量的影响

为促进宁南半干旱山区产业支柱作物马铃薯的生产,解决马铃薯生产、特别是苗期的干旱缺水问题,采用田间试验方法,进行PAM保水剂、多功能保水剂与一定配方尿素+过磷酸钙的施用对马铃薯生长发育、产量及效益的试验。结果表明,两种保水剂均能促进马铃薯生长发育,增加干物质积累,但是在不同生育时期促进作物生长的效果有所不同。1%PAM保水剂浸种2~3 min处理在前期效果显著,多功能保水剂在后期效果突出。马铃薯以施用多功能保水剂30 kg/hm2效果最好,其产量和商品薯分别比对照高出52.33%、138.29%,增收5 356.8元/hm2。研究表明,施用30 kg/hm2多功能保水剂比用1%PAM保水剂浸种2~3min更适宜宁南半干旱区及其同类地区旱地种植马铃薯。

半干旱区施氮和灌溉条件下覆膜对春玉米产量及氮素平衡的影响

以典型半干旱区干湿砂质新成土(Ust-Sandic Entisols)为供试土壤进行田间试验,研究地膜覆盖、施氮及补充灌水量对春玉米(Zea maysL.)产量、土壤矿质氮(NO3--N和NH4+-N)及氮素平衡的影响。结果表明,0—100 cm土体范围内,随着土层加深,播前和收获后土壤NO3--N含量呈降低趋势,NH4+-N有所增加,但变幅不大;总矿质氮量(NO3--N和NH4+-N)表现为下降。说明地膜覆盖和施氮并没有使NO3--N深层累积量增加,这可能与土壤本身供氮能力严重不足有关。与不施氮相比,施氮各处理氮肥表观损失量增加;与不覆膜相比,作物氮素累积量比不覆膜显著增加(P<0.05)。在低灌(80 mm)覆膜和高灌(160 mm)覆膜条件下,玉米的氮肥利用率均比不覆膜提高了18.8%,说明覆膜低灌在相同施氮条件下,可节约80 mm灌水。但低灌(80 mm)与高灌(160 mm)不覆膜间氮肥利用率差异不显著,表明在相同施氮条件下,覆膜可有效提高氮肥利用率,减少氮素损失。综合考虑子粒产量和氮肥利用率,"覆膜+补灌80 mm+施氮90 kg/hm2"可能为本试验条件下较优的栽培模式。

丘陵半干旱区春小麦耗水特征与水分高效利用

该文利用Penman-Monteith公式和田间灌溉试验，对丘陵半干旱区春小麦的需水耗水特征进行了计算分析，并利用旱棚和田间试验、数理统计和系统分析等方法，对冬灌和涌流灌溉的节水效果、喷灌制度和喷灌水量分布、水肥耦合互馈作用、有限水量的最优分配等进行了综合研究.通过模拟寻优得出了春小麦不同产量水平下的水肥管理优化方案.以Jensen模型为基础，利用动态规划确定了不同初始土壤含水量和可利用灌溉水量下的最优分配决策.

丘陵半干旱区小流域雨水集蓄与高效利用

探索基于小流域土壤侵蚀治理基础上的雨水集蓄利用模式和技术，是解决丘陵半干旱区水资源短缺，实现生态环境良性循环和农业可持续发展的重要途径，也是雨水集蓄利用研究的热点。本文运用水土保持、径流叠加与异地利用理论和方法，在小流域入渗产流特征及雨水资源潜力分析基础上，开展了小流域坡耕地集流梯田工程和沟壑荒地窖棚工程雨水集蓄利用试验，对小流域雨水集蓄利用工程设计、集流蓄水与高效利用效果进行了系统研究。利用Philip入渗理论和逐步回归分析方法对人工降雨和自然降雨结果处理分析，建立了小流域坡耕地、林地和荒地土壤的入渗产流及其相关因子数学模型。雨水潜力分析表明，该地区典型小流域水资源供需态势基本上都处于用水高度紧张状态，而且生态需水比重最高，占总需水量的69．29％。研究建立了小流域坡耕地—集流梯田雨水集蓄叠加利用模式和技术，确定了集流梯田工程的平坡比、田面宽度和田坎高度等断面参数。集流梯田和坡耕地相比土壤含水量提高16.61％-25.87％，增加产值70.98％-114.30％；该区坡耕地适宜修建1: 1平坡比的集流梯田，集流坡面种植矮秆作物和林果。研究建立了小流域沟壑荒地—窖棚雨水集蓄异地利用模式和技术，确定了坡面窖群集蓄型、沟道坝窖结合型和山泉窖池长蓄短用型等雨水集蓄工程及其断面参数。窖棚模式渗灌比畦灌节水50.0％以上，灌溉效率提高19.01kg·m-3·hm-2，单位水产值增加 107.1％-143.2％，而且较好地改善了大棚内的环境条件。

丘陵半干旱区春小不知所云水肥耦合效应

采用312-D最优饱和设计，在丘陵半干旱区开展了连续4年的田间试验，深入地研究了春小麦水肥祸合效应。水肥单因子对产量和水分利用效率（WUE）有显著影响，大小顺序为：水＞磷＞氮，其中三个因子对产量的提高均是正效应，而对WUE的提高，氮、磷施用量是正效应，过量灌溉是负效应；两因子间祸合作用的强弱顺序为：氮与水祸合＞氮与磷祸合＞磷与水祸合，其中氮与磷祸合，以及氮与水祸合对提高产量和认心E均表现为极显著相互促进作用，而磷与水祸合表现为不显著的相互替代作用。水肥祸合通过提高气孔导度（Gs）、蒸腾速率（Tr）、叶表面相对湿度（RH）、叶内水浓度（Hi）和降低胞间COZ浓度（Ci），来提高叶片光合速率（Pn）。氮素营养缺乏引起叶片“光合午休”现象的发生，增加施氮量可以避免“光合午休”现象的发生。籽粒产量与灌浆期叶片Pn呈正相关。水肥单因子对叶片Pn影响的大小顺序是：氮＞磷＞水；因子间藕合作用强弱顺序为：氮与水棍合＞磷与水祸合＞氮与磷祸合。水肥优化管理是提高产量、叶片Pn及WUE的重要途径。中等用量的氮、磷、水藕合可以达到高产、高效，获得较高的WUE和叶片Pn，实现节水高产高效与较高叶片Pn的统一，为春小麦科学灌溉施肥提供了理论依据。

遮荫与外源脱落酸喷施对粗枝云杉(Picea asperata Mast.)不同种群抗旱性的影响

本研究通过粗枝云杉不同种群进行的温室半控制试验，采用植物生态学、生理学和生物化学的研究方法，系统地研究了粗枝云杉不同种群抗旱性的生长、形态、生理和生化机理，并结合有关研究进行综合分析，得出主要研究结论如下： 1.粗枝云杉对干旱胁迫的综合反应 粗枝云杉在干旱胁迫下的适应机制为：（1）相对生长速率及植株结构的调整：干旱胁迫下虽然植株相对生长速率显著降低，且有相对较多的生物量向根部分配，但并未发现细根/总根比增加。（2）粗枝云杉对干旱胁迫的光合作用表现为：干旱胁迫显著地降低了控制的理想条件下的气体交换，但干旱胁迫对PSII最大光化学效率（Fv/Fm）没有影响，表明干旱并未影响到光合机构。（3）干旱还影响了很多生理生化过程，包括渗透调解物质（游离脯氨酸）、膜脂过氧化产物、脱落酸（ABA）含量的增加，以及保护酶活性的升高。这些结果证明植物遭受干旱胁迫后发生了一系列的形态、生理和生化响应，这些变化能提高干旱时期植物的存活和生长能力。 2.粗枝云杉不同种群对干旱胁迫反应的种群差异 粗枝云杉三个种群－干旱种群（四川丹巴和甘肃迭部）和湿润种群（四川黑水）对干旱适应不同，这种不同应归因于它们采用的用水策略不同：在水分良好和干旱胁迫条件下，受试种群在相对生长速率和水分利用效率（WUE）方面都表现出显著的种群间差异。与湿润种群相比，干旱种群在两种水分条件下有更高的WUE。粗枝云杉不同种群的碳同位素组分（δ13C）只在干旱胁迫下有显著差异，并且这种差异在水分良好时比干旱胁迫条件下小，说明生理响应和干旱适应性之间的关系受植物内部抗旱机制和外部环境条件（如水分可利用性）或两者互作效应的影响。这些结果说明干旱种群和湿润种群所采用的用水策略不同。干旱种群有更强的抗旱能力，采用的是节水型的用水策略，而湿润种群抗旱能力较弱，采用的是耗水型的用水策略。 3. 遮荫对粗枝云杉不同种群抗旱性影响 干旱胁迫显著降低了全光条件下叶相对含水量（RWC）、相对生长速率、气体交换参数、PSII的有效量子产量（Y），提高了非光化学猝灭效率（qN）、水分利用效率、脯氨酸（PRO）积累、脱落酸（ABA）含量及保护酶活性。然而这种变化在遮荫条件下不明显。我们得出结论适度遮荫降低了干旱对植物的胁迫作用。另一方面，在干旱条件下，与湿润种群相比，干旱种群抗旱性更强，表现在干旱种群净光合速率与单位重量上叶氮含量（Nmass）降低较少。另外，干旱种群表现出更为敏感的气孔导度，更高的热耗散能力（qN）能力、用水效率、ABA积累、保护酶活性，以及更低的总用水量、相对生长速率。这一结果表明这两种群采用不同的生理策略对干旱和遮荫做出反应。许多生长和生理反应差异与这两个种群原产地气候条件相适应。 4. 外源脱落酸(ABA)喷施对粗枝云杉不同种群抗旱性影响 外源ABA喷施在干旱和水分良好条件下均不同程度地提高了根/茎比，表明根和茎对ABA敏感程度不同。实验结果还表明，外源ABA喷施对这两个种群在干旱胁迫期间影响不同。干旱胁迫期间，伴随着ABA喷施，湿润种群净光合速率(A)显著降低，而干旱种群净光合速率变化不明显。另一方面，外源ABA喷施显著提高了干旱条件下干旱种群的单位叶面积重（LMA）、根/茎比、细根/总根（Ft）比、水分利用效率（WUE）、ABA含量, 以及保护酶活性。然而，外源ABA喷施对湿润种群的上述测定指标没有显著影响。这一结果表明干旱种群对外源ABA喷施更为敏感, 反应在更大的气孔导度降低，更高的生物量可塑性，及更高的水分利用效率、ABA含量和保护酶活性。综上所述，我们得出结论，粗枝云杉对外源ABA敏感性因种群的不同而不同。该研究结果可为两个明显不同种群在适应分化方面提供强有力的证据。 Arid or semi-arid land covers more than half of China's land territory. In arid systems, severe shortages of soil water often coincide with periods of high temperatures and high solar radiation, producing multiple stresses on plant performance. Protection from high radiation loads in shaded microenvironments during drought may compensate for a loss of productivity due to reduced irradiance when water is available. Additionally, ABA, a well-known stress-inducible plant hormone, has long been studied as a potential mediator for induction of drought tolerance in plants. Picea asperata Mast., which is one of the most important tree species used for the production of pulp wood and timber, is a prime reforestation species in western China. In this experiment, different population of P. asperata were used as experiment material to study the adaptability to drought stress and population differences in adaptabiliy, and the effects of shade and exogenous abscisic acid (ABA) application on the drought tolerance. Our results cold provide a strong theoretical evidence and scientific direction for the afforestation, and rehabilitation of ecosystem in the arid and semi-arid area, and provide a strong evidence for adaptive differentiation of different populations, and so may be used as criteria for species selection and tree improvement. The results are as follows: 1. A large set of parallel response to drought stress Drought stress caused pronounced inhibition of the growth and increased relatively dry matter allocation into the root; drought stress also caused pronounced inhibition of photosynthesis, while drought showed no effects on the maximal quantum yield of PSII photochemistry (Fv/Fm) in dark-adapted leaves, indicating that drought had no effects on the primary photochemistry of PSII. However, in light-adapted leaves, drought reduced the quantum yield of PSII electron transport (Y) and increased the non-photochemical quenching (qN). Drought also affected many physiological and biochemical processes, including increases in superoxide dismutase (SOD), ascorbate peroxidase (APX) activities, malondialdehyde and ABA content. These results demonstrate that there are a large set of parallel changes in the morphological, physiological and biochemical responses when plants are exposed to drought stress; these changes may enhance the capability of plants to survive and grow during drought periods. 2. Difference in adaptation to drought stress between contrasting populations of Picea asperata There were significant population differences in growth, dry matter allocation and water use efficiency. Compared with the wet climate population (Heishui), the dry climate population (Dan ba and Jiebu) showed higher LMA, fine root/total root ratio and water use efficiency under drought-stressed treatments. The results suggested that there were different water-use strategies between the dry population and the wet population. The dry climate population with higher drought tolerance may employ a conservative water-use strategy, whereas the wet climate population with lower drought tolerance may employ a prodigal water-use strategy. These variations in drought responses may be used as criteria for species selection and tree improvement. 3. The effects of shade on the drought tolerance For both populations tested, drought resulted in lower needle relative water content (RWC), relative growth rate (RGR), gas exchange parameters and effective PSII quantum yield (Y), and higher non-photochemical quenching (qN), water use efficiency (WUE), proline (PRO) and abscisic acid (ABA) accumulation, superoxide dismutase (SOD), ascorbate peroxidase (APX) activities as well as malondialdehyde (MDA) levels and electrolyte leakage in sun plants, whereas these changes were not significant in shade plants. Our study results implied that shade, applied together with drought, ameliorated the detrimental effects of drought. On the other hand, compared with the wet climate population, the dry climate population was more tolerant to drought in the sun treatment, as indicated by less decreases in A and mass-based leaf nitrogen content (Nmass), more responsive stomata, greater capacity for non-radiative dissipation of excitation energy as heat (analysed by qN), and higher WUE，higher level of antioxidant enzyme activities，higher ABA accumulation as well as lower MDA content and electrolyte leakage. Many of the differences in growth and physiological responses reported here are consistent with the climatic differences between the locations of the populations of P. asperata. 4. The effects of exogenous abscisic acid (ABA) application on the drought tolerance For both populations tested, exogenous ABA application increased root/shoot ratio (Rs) under well-watered and drought-stressed conditions, indicating that there was differential sensitivity to ABA in the roots and shoots. However, it appeared that ABA application affected the two P. asperata populations very differently during drought. CO2 assimilation rate (A) was significantly decreased in the wet climate population, but only to a minor extent in the dry climate population following ABA application during soil drying. On the other hand, ABA application significantly decreased stomatal conductance (gs), transpiration rate (E) and malondialdehyde (MDA) content, and significantly increased leaf mass per area (LMA), Rs, fine root/total root ratio (Ft), water use efficiency (WUE), ABA contents, superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT) activities under drought condition in the dry climate population, whereas ABA application did not significantly affect these parameters in the wet population plants. The results clearly demonstrated that the dry climate population was more responsive to ABA application than the wet climate population, as indicated by the strong stomata closure and by greater plasticity of LMA and biomass allocation, as well as by higher WUE, ABA content and anti-oxidative capacity to defense against oxidative stress, possibly predominantly by APX. We concluded that sensitivity to exogenous ABA application is population dependent in P. asperata. Our results provide strong evidence for adaptive differentiation between populations of P. asperata.

遮荫与外源脱落酸喷施对青杨(Populus cathayana Rehd.)不同种群抗旱性的影响

杨树具有分布广、适应性强的特征，在生态环境治理和解决木材短缺方面均占有重要位置。青杨(Populus cathayana Rehd.)是青杨派树种的重要成员之一，也是生长较迅速、易繁殖的重要杨树资源。本研究选取了来自不同气候地区的青杨两种群为材料，采用植物生态学、生理学和生物化学的研究方法，系统地研究了青杨对干旱与遮荫、干旱与外源脱落酸(ABA)喷施的生长、形态、生理和生化响应及种群间差异，研究成果可为我国干旱半干旱地区的造林以及生态恢复提供理论依据和科学指导。主要研究结论如下：1.青杨在干旱胁迫下的适应机制为：生长性状及生物量的分配变化：干旱胁迫下虽然植株生长受抑，株高、基茎及各部分生物量都显著减小，但有相对较多的生物量向根部分配，根/冠比以及细/粗根比增加。青杨对干旱胁迫的光合作用表现为：干旱胁迫降低了青杨的净光合速率、蒸腾速率、气孔导度以及光合氮利用效率，提高了瞬时用水效率。干旱还引起了活性氧的产生，使得膜脂过氧化产物丙二醛(MDA)增加，同时也增强了植物抗氧化酶系统(如超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)活性的增加)及非酶系统的能力(如抗坏血酸(AsA)含量的增加)。干旱降低了植物叶片的相对含水量，而促进了渗透调节物质(游离脯氨酸及可溶性糖)的积累，增加了植物的渗调能力。干旱下青杨两种群的内源ABA含量显著增加，碳同位素组分(δ13C)也显著提高。这些结果证明植物遭受干旱胁迫后发生一系列的形态、生理和生化响应，这些变化能提高植物在干旱下的存活和生长能力。2.青杨两种群对干旱胁迫反应的种群差异：与来自湿润地区的汉源种群相比，来自干旱地区的乐都种群在干旱条件下生物量向根系分配的可塑性更强，同时具有更强的抗氧化系统能力，所受到活性氧的伤害也更少，并且累积更多的脯胺酸和ABA，具有更高的δ13C。这些都说明了乐都种群对干旱的适应性比汉源种群更强。两种群对干旱的响应差异应归于它们的用水策略的不同：汉源种群来自湿润地区，采用了耗水型的用水策略，抗旱能力较弱；而乐都种群，来自干旱地区，通常采用节水型的用水策略，有更强的抗旱能力。3.遮荫对青杨两种群抗旱性的影响：遮荫对青杨抗旱性的影响决定于遮荫程度的不同，我们的结果表明中度的遮荫可以有效的提高干旱下植物的生长，对干旱胁迫有明显的缓解作用，具体体现在中度遮荫下受旱植物的叶片相对含水量得到提高，使得植物体内水分状况得到了改善；光合速率并未降低，植物光合氮利用效率增加，说明中度的遮荫并未明显限制植物的碳获得；抗氧化酶活性与膜脂过氧化产物MDA含量的同时降低，说明中度遮荫下所受到的活性氧伤害减少；中度遮荫下的ABA及δ13C的变化也不如在全光下变化明显，这也说明中度遮荫缓解了干旱胁迫。但是重度的遮荫却对干旱胁迫有明显的加剧作用，主要表现在重度遮荫降低了植物的光合速率，严重抑制了植物的生长；同时重度遮荫下脯胺酸含量和抗氧化酶活性的急剧下降，导致了植物渗调能力的下降及膜脂过氧化产物MDA的显著升高；重度遮荫还显著降低了内源ABA的累积和δ13C，降低了植物的抗旱能力。此外，青杨两种群在对干旱和遮荫的响应中，也表现出种群差异。汉源种群，来自湿润且年日照辐射较少的地区，表现出相对更强的耐荫性和需水性。而乐都种群，来自干旱且年日照辐射丰富的地区，表现出相对更强的耐旱性和需光性。这说明了植物对环境胁迫的耐受性是其长期适应原生境的结果，并且来自不同气候地区的两种群在面临环境胁迫时会采取不同的生存策略。4. 外源ABA喷施对青杨两种群抗旱性的影响：外源ABA的喷施可以提高两种群的抗旱性，具体表现为外源ABA喷施促进了青杨根系的生长，显著提高了干旱下植物的根/冠比和细/粗根比，减少了比叶面积；在生理生化方面，外源ABA降低了干旱下植物叶片的气孔导度，降低了蒸腾速率和净光合速率，但提高了瞬时用水效率，提高了叶片的相对含水量，增加了干旱下植物的保水能力。外源ABA进一步增加了干旱下植物内源ABA的积累，促进了植物渗调物质如脯胺酸和可溶性糖的积累，增加了抗氧化酶系统(如SOD、APX、CAT)的活性和非酶系统AsA的含量，降低了活性氧(如超氧阴离子(O2和过氧化氢(H2O2))对植株的伤害。此外，外源ABA还进一步提高了干旱下植物的δ13C，提高了植物的长期用水效率，由此提高了植物的抗旱能力。另一方面，两种群对外源ABA和干旱的响应也有所差别。来自湿润地区的汉源种群，对干旱较为敏感，所受干旱的影响也较大，而外源ABA的喷施对汉源种群抗旱性的提高作用也更为突出。乐都种群，由于其长期适应干旱地区的生长，本身已具有较强的抗旱能力，因此外源ABA喷施对其抗旱性的提高不如对汉源种群的效果明显。由此我们可以得出对于一些抗性弱或干旱敏感的物种或者种群，可以采用外施ABA的方法来提高其抗性。Poplars play an important role in lumber supply, and are important component ofecosystems due to their wide distribution and well adaptation. Populus cathayana Rehd.,which belongs to Populus Sect. Tacamahaca Spach, is one of the most important resources ofpoplars for its fast growth and reproductive. In this study, different populations of P.cathayana were used as experiment material to investigate the adaptability to drought stressand population differences in adaptability, and the effects of shade and exogenous abscisicacid (ABA) application on the drought tolerance. Our results could provide a strongtheoretical evidence and scientific direction for the afforestation, and rehabilitation ofecosystem in the arid and semi-arid area, and provide a strong evidence for adaptivedifferentiation of different populations, and so may be used as criteria for species selectionand tree improvement. The results are as follows:1. A large set of parallel response to drought stress: Drought stress caused pronouncedinhibition of the growth and increased relatively dry matter allocation into the root. For thetwo populations, the shoot height, basal diameter and total biomass were decreased but theroot/shoot ratio and fine root/coarse root ratio were increased under drought conditions；Drought stress caused pronounced inhibition of photosynthesis, decreased the stomatalconductance, transpiration rate, and photosynthetic nitrogen-use efficiency (PNUE) butincreased the instantaneous water use efficiency. Drought significantly improved the levels ofreactive oxygen species and malondialdehyde (MDA) and to induce the entire set ofantioxidative systems including the increase of activities of superoxide dismutase (SOD),ascorbate peroxidase (APX), catalase (CAT) and ascorbate (AsA) content. Drought decreased the leaf relative water content (RWC) but improved the capability of osmotic adjustmentindicated by the higher proline accumulation. Drought also increased the ABA content andcarbon isotope composition (δ13C), which indicating the long period water use efficiency wasimproved under drought. These results demonstrate that there are a large set of parallelchanges in the morphological, physiological and biochemical responses when plants areexposed to drought stress; these changes may enhance the capability of plants to survive andgrow during drought periods.2. Difference in adaptation to drought stress between contrasting populations of P.cathayana: Compared with the Hanyuan population (wet climate), the Ledu population (dryclimate) showed higher root/shoot ratio and water use efficiency, exhibited higherantioxidative systems capability thus resulting in less oxidative damage, accumulated moreABA and free proline content under drought conditions. The results suggested that there weredifferent water-use strategies between the two populations. The Ledu population, whichcomes from dry climate region, with higher drought tolerance, may employ a conservativewater-use strategy, whereas the Hanyuan population, which comes from wet climate, withlower drought tolerance, may employ a prodigal water-use strategy. These variations indrought responses may be used as criteria for species selection and tree improvement.3. The effects of shade on the drought tolerance: The reduction in the availability of lightand water affected the morphological and physiological responses of the two P. cathayanapopulations. In addition, the light environment modified the growth responses of P.cathayana seedlings to varying water environments in different ways depending upon theintensity of the light levels considered. There is an apparent alleviation to drought effects bymoderate shade in P. cathayana seedlings, as indicated by the higher leaf RWC, and unchanged net photosynthesis and PNUE, as well as by the lower antioxditative enzymeactivity, MDA, ABA and δ13C levels, which implied moderate shade did not significantlylimited the carbon acquisition or inhibited the plant growth, but ameliorated the detrimentaleffects of drought. On the other hand, an apparent aggravation to drought effects by severeshade was also observed, as indicated by the pronounced decrease of plant growth and net photosynthesis, the lower total biomass, ABA level, δ13C, free proline content andantioxditative enzyme activity and higher MDA accumulation. By contrast, the twopopulations showed different responses to shade and drought. The Hanyuan population,which comes from a riparian basin having a relatively wet climate and less annual solarradiation, is more sensitive to drought but more tolerant to shade. The Ledu population, whichcomes from a mountainous plateau with less rainfall and with more annual solar radiation, ismore tolerant to drought but more sensitive to shade. The results demonstrated that theendurance of plants to stress is a result of long-term evolution and adaptation to theenvironment, as suggested by the different strategies employed by the P. cathayanapopulations originating from contrasting habitats when they were exposed to drought andshade.4. The effects of exogenous ABA application on the drought tolerance: For bothpopulations under drought conditions tested, exogenous ABA application significantlyimproved the root/shoot ratio, fine root/coarse root ratio, and decreased the specifical leaf area.On the physiological and biochemical traits, exogenous ABA application significantlydecreased stomatal conductance, transpiration rate and net photosythesis but increased theinstance water use efficiency and leaf RWC. On the other hand, exogenous ABA applicationsignificantly increased endogenous ABA, proline, solube sugar and AsA content, as well asSOD, APX and CAT activities, thus reduced the damage of reactive oxygen species. Moreover,the long period water use efficiency as indicated by δ13C was also improved by exogenousABA application. In additionally, there was different responsive between the two populationsto drought and exogenous ABA application. The Hanyuan population, which comes from wetclimate region, is more sensitive to drought, and the effect of exogenous ABA is moreobviously than that in the Ledu population, which comes from dry climate region and is moredrought-responsive. Therefore, we can use exogenous ABA application to improve theresistance of plants, especially for the drought- sensitive species or populations.

黄土高原土壤水分与水土保持措施相互作用

土壤水是重要的生态水源和水文要素之一 ,黄土高原位于干旱半干旱地区 ,降水量的年际变化大和季节分配极不均匀 ,土壤水资源对植物生长发育的影响尤为重要。同时 ,土壤水的数量及其分布也受人类活动影响。水土保持措施是黄土高原人类改造下垫面过程之一 ,这种改造会影响土壤水分的静态分布和动态过程。水土保持坡面工程措施能有效地提高土壤含水率。深根系人工林草植被使土壤含水率降低 ,甚至造成利用性土壤干层 ,影响人工植被的永续发展。尽管天然植被也有较高的生产力水平 ,但并未引起土壤水分状况的恶化 ,这是黄土高原植被营造及规划中值得注意和进一步研究的问题

Seasonal and interannual variation in water vapor and energy exchange over a typical steppe in Inner Mongolia, China

In this study, we conducted eddy covariance (EC) measurements of water vapor exchange over a typical steppe in a semi-arid area of the Inner Mongolia Plateau, China. Measurement sites were located within a 25-year-old enclosure with a relatively low leaf area index (similar to 1. 5 m(2) m(-2)) and dominated by Leymus chinensis. Energy balance closure was (H + LE) = 17.09 + 0.69 x (Rn - G) (W/m(2); r(2) = 0.95, n = 6596). Precipitation during the two growing seasons of the study period was similar to the long-term average. The peak evapotranspiration in 2004 was 4 mm d(-1), and 3.5 mm d(-1) in 2003. The maximum latent heat flux was higher than the sensible heat flux, and the sensible heat flux dominated the energy budget at midday during the entire growing season in 2003; latent heat flux was the main consumption component for net radiation during the 2004 growing season. During periods of frozen soil in 2003 and 2004, the sensible heat flux was the primary consumption component for net radiation. The soil heat flux component was similar in 2003 and 2004. The decoupling coefficient (between 0.5 and 0.1) indicates that evapotranspiration was strongly controlled by saturation water vapor pressure deficit (VPD) in this grassland. The results of this research suggest that energy exchange and evapotranspiration were controlled by the phenology of the vegetation and soil water content. In addition, the amount and frequency of rainfall significantly affect energy exchange and evapotranspiration upon the Inner Mongolia plateau. (c) 2007 Published by Elsevier B.V.

Main ecological gradients and landscape matrix affect wild rabbit Oryctolagus cuniculus (Linnaeus, 1758) (Mammalia: Leporidae) abundance in a coastal region (South-East Spain)

Landscape analysis with transects, in the Marina Baja area (province of Alicante, Spain), has contributed to establish the influence of different landscape matrices and some environmental gradients on wild rabbit Oryctolagus cuniculus (Linnaeus, 1758) (Mammalia: Leporidae) abundance (kilometric abundance index, KAI). Transects (n = 396) were developed to estimate the abundance of this species in the study area from 2006 to 2008.Our analysis shows that rabbits have preferences for a specific land use matrix (irrigated: KAI = 3.47 ± 1.14 rabbits/km). They prefer the coastal area (KAI = 3.82 ± 1.71 rabbits/km), which coincides with thermo-Mediterranean (a bioclimatic belt with a tempered winter and a hot and dry summer with high human density), as opposed to areas in the interior (continental climate with lower human occupation). Their preference for the southern area of the region was also noted (KAI = 8.22 ± 3.90 rabbits/km), which coincides with the upper semi-arid area, as opposed to the northern and intermediate areas (the north of the region coinciding with the upper dry and the intermediate area with the lower dry). On the other hand, we found that the number of rabbits increased during the 3-year study period, with the highest abundance (KAI = 2.71 ± 1.30 rabbits/km) inMay. Thus, this study will enable more precise knowledge of the ecological factors (habitat variables) that intervene in the distribution of wild rabbit populations in a poorly studied area.

Cutting management of multipurpose tree legumes: effects on green herbage production, leaf retention and water-use-efficiency during the dry season in Timor, Indonesia

Edible herbage production and water-use-efficiency of three tree legumes (Leucaena leucocephala cv. Tarramba, L. pallida x L. leucocephala (KX2) and Gliricidia sepium), cut at different times of the year (February, April, June and uncut) were compared in a semi-arid area of Timor Island, Indonesia. Cutting in the early and mid dry-season (April and June) resulted in higher total leaf production (P< 0.05) and water-use-efficiency (P< 0.05), than cutting late in the wet-season (February) or being left uncut. For the leucaena treatments removing leaf in the early to mid dry-season reduced transpiration, saving soil water for subsequent regrowth as evidenced by the higher relative water contents of leaves from these treatments. This cutting strategy can be applied to local farming conditions to increase the supply of feed for livestock during the dry season.

Bridging Perspectives

People’s ability to change their social and economic circumstances may be constrained by various forms of social, cultural and political domination. Thus to consider a social actor’s particular lifeworld in which the research is embedded assists in the understanding of how and why different trajectories of change occur or are hindered and how those changes fundamentally affect livelihood opportunities and constraints. In seeking to fulfill this condition this thesis adopted an actor-oriented approach to the study of rural livelihoods. A comprehensive livelihoods study requires grasping how social reality is being historically constituted. That means to understand how the interaction of modes of production and symbolical reproduction produces the socio-space. Research is here integrated to action through the facilitation of farmer groups. The overall aim of the groups was to prompt agency, as essential conditions to build more resilient livelihoods. The smallholder farmers in the Mabalane District of Mozambique are located in a remote semi-arid area. Their livelihoods customarily depend at least as much on livestock as on (mostly) rain-fed food crops. Increased climate variability exerts pressure on the already vulnerable production system. An extensive 10-month duration of participant observation divided into 3 periods of fieldwork structured the situated multi-method approach that drew on a set of interview categories. The actor-oriented appraisal of livelihoods worked in building a mutually shared definition of the situation. This reflection process was taken up by the facilitation of the farmer groups, one in Mabomo and one in Mungazi, which used an inquiry iteratively combining individual interviews and facilitated group meetings. Integration of action and reflection was fundamental for group constitution as spaces for communicative action. They needed to be self-organized and to achieve understanding intersubjectively, as well as to base action on cooperation and coordination. Results from this approach focus on how learning as collaboratively generated was enabled, or at times hindered, in (a) selecting meaningful options to test; (b) in developing mechanisms for group functioning; and (c) in learning from steering the testing of options. The study of livelihoods looked at how the different assets composing livelihoods are intertwined and how the increased severity of dry spells is contributing to escalated food insecurity. The reorganization of the social space, as households moved from scattered homesteads to form settlements, further exerts pressure on the already scarce natural resource-based livelihoods. Moreover, this process disrupted a normative base substantiating the way that the use of resources is governed. Hence, actual livelihood strategies and response mechanisms turn to diversification through income-generating activities that further increase pressure on the resource-base in a rather unsustainable way. These response mechanisms are, for example, the increase in small-livestock keeping, which has easier conversion to cash, and charcoal production. The latter results in ever more precarious living and working conditions. In the majority of the cases such responses are short-term and reduce future opportunities in a downward spiral of continuously decreasing assets. Thus, by indicating the failure of institutions in the mediation of smallholders’ adaptive capabilities, the livelihood assessment in Mabomo and Mungazi sheds light on the complex underlying structure of present day social vulnerability, linking the macro-context to the actual situation. To assist in breaking this state of “subordination”, shaped by historical processes, weak institutions and food insecurity, the chosen approach to facilitation of farmer groups puts farmer knowledge at the center of an evolving process of intersubjective co-construction of knowledge towards emancipation.

Production of Syrah wines in tropical conditions of Northeast Brazil.

Twenty years ago, in the Northeast Brazil, a tropical semi-arid area, the production of tropical wines from some Vitis vinifera L. cultivars started. In this region, it is possible to harvest two times a year, between April and December, and nowadays Syrah is the most cultivated wine grape. Research works about irrigation rnanagement in Syrah started in 2000 at Brazilian Agricultural Research Corporation (Embrapa). The aim of this paper is to introduce some characteristics about the region where Syrah grapevines is being cultivated under irrigation in Northeast Brazil, and to present some results obtained from field experiments as well as some grape and wine charcteristics already determined.

Profiles of illicit drug use during annual key holiday and control periods in Australia: Wastewater analysis in an urban, a semi-rural and a vacation area

AIMS: To examine changes in illicit drug consumption between peak holiday season (23 December-3 January) in Australia and a control period two months later in a coastal urban area, an inland semi-rural area and an island populated predominantly by vacationers during holidays. DESIGN: Analysis of representative daily composite wastewater samples collected from the inlet of the major wastewater treatment plant in each area. SETTING: Three wastewater treatment plants. PARTICIPANTS: Wastewater treatment plants serviced approximately 350, 000 persons in the urban area, 120,000 in the semi-rural area and 1100-2400 on the island. MEASUREMENTS: Drug residues were analysed using liquid chromatography coupled to a tandem mass spectrometer. Per capita drug consumption was estimated. Changes in drug use were quantified using Hedges' g. FINDINGS: During the holidays, cannabis consumption in the semi-rural area declined (g = -2.8) as did methamphetamine (-0.8), whereas cocaine (+1.5) and ecstasy (+1.6) use increased. In the urban area, consumption of all drugs increased during holidays (cannabis +1.6, cocaine +1.2, ecstasy +0.8 and methamphetamine +0.3). In the vacation area, methamphetamine (+0.7), ecstasy (+0.7) and cocaine (+1.1) use increased, but cannabis (-0.5) use decreased during holiday periods. CONCLUSIONS: While the peak holiday season in Australia is perceived as a period of increased drug use, this is not uniform across all drugs and areas. Substantial declines in drug use in the semi-rural area contrasted with substantial increases in urban and vacation areas. Per capita drug consumption in the vacation area was equivalent to that in the urban area, implying that these locations merit particular attention for drug use monitoring and harm minimisation measures.