不同供水条件下侧柏和刺槐幼树的蒸腾耗水与土壤水分应力订正

采用旱棚人工控水,对侧柏、刺槐不同水量全生长期均衡供水条件下,2～3年生幼树的生理需水规律、蒸腾耗水与土壤水分的关系进行了研究.结果表明,刺槐蒸腾耗水量随土壤供水能力的增大而增加.其中以生长前期和生长盛期耗水为主,约占年蒸腾耗水量的80.5%;刺槐年均生理需水量是侧柏的5.13倍.侧柏蒸腾耗水量在土壤相对含水率为40%～100%有一峰值.当土壤相对含水率≤87.84%时,蒸腾耗水量随土壤相对含水率增加而增大;反之则减小.侧柏蒸腾耗水量以生长盛期最大,约占年蒸腾量的46.27%,生长后期次之,生长前期较小.并求出了两树种蒸腾耗水的土壤水分应力订正函数及在非充分供水条件下实际蒸腾耗水的时间-水分函数.     

半干旱区旱地不同覆盖种植方式玉米田的土壤水分和产量效应

为探讨半干旱区旱地不同种植方式玉米(Zea mays)田的土壤水分动态特征, 测定了全膜双垄沟播(PMF)、全沙覆盖(SM)和裸地(CK) 3种不同处理0-200 cm土壤水分季节变化、垂直变化及年际变化。结果表明: PMF明显改善玉米拔节前0-200 cm土壤的水分条件, 有利于玉米前期生长; 随着玉米生育进程的推进, 3种处理的耗水量依次为: PMF﹥SM﹥CK, 而土壤贮水量表现为CK﹥SM﹥PMF; 在相同降雨条件下, PMF处理0-200 cm土壤水分降雨入渗补给深度最大, SM次之, CK最小。随着种植年限增加, PMF的耗水量和耗水深度增加, 两年种植期间耗水深度从20-120 cm向120-200 cm推移; 连续种植两年后, 3种处理40-120 cm土壤含水量下降至9.0%以下, 其中PMF下降最快(7.9%), 土壤含水量接近萎蔫系数7.2%, 玉米只能靠当年降水生长, 如种植年限继续增加, 土壤极有可能形成干层。3种处理之间耗水量、产量、水分利用效率都存在显著差异, PMF最高, SM次之, CK最低。因此, 在半干旱区采用全膜双垄沟播种植玉米可显著提高产量, 但连续种植可导致土壤贮水量显著降低, 对农田可持续生产能力造成不利影响。     

永定河沿河沙地杨树人工林蒸腾耗水特征及其环境响应

杨树是我国北方最常见的人工造林树种之一。一直以来在干旱、半干旱地区,速生杨树用材林和生态防护林的耗水问题备受关注。研究不同生长发育阶段杨树人工林蒸腾耗水及其对各环境因子的响应对于实现杨树人工林可持续经营具有重要价值。采用树干液流法结合微气象观测系统和土壤水分观测,在2010—2011年对位于北京南郊大兴林场、林龄为13a的杨树人工林林分蒸腾耗水和环境因子进行了同步观测,以期能够探究该林分的蒸腾耗水及其对环境因子的响应。结果表明,树干液流密度(Js)日变化呈明显的单峰曲线,单株样木耗水量随着胸径的增加而增大。在半小时尺度上,单株树木Js与浄辐射(Rn)、饱和水气压差(VPD)存在时滞,这种时滞现象随土壤水分条件不同而变化。林分蒸腾耗水总量在2010和2011年生长季内分别为113.7 mm和174.8 mm,占同期降雨的30.2%和36.9%,与该杨树人工林前期研究相比,随着林龄的增长2010—2011年的蒸腾量呈减小趋势。日尺度上,该人工林蒸腾耗水与净辐射(Rn)、饱和水汽压差(VPD)和土壤体积含水率(SWC)显著相关,在不同土壤水分条件下Rn与林分蒸腾的相关关系发生变化,而VPD过高会对林分蒸腾产生抑制。林分月蒸腾和年总蒸腾主要取决于同期降雨量,因此,降雨年际差异较大时,蒸腾的年际变化也相应较大。     

不同干旱土壤条件下杨树的耗水规律及水分利用效率研究

 在适宜土壤水分（70%θf）,中度干旱（55%θf）和严重干旱（40%θf）3种土壤水分条件下研究杨树（Populus simonii）的耗水特性和水分利用特征。结果表明,随着土壤含水量的下降,杨树叶水势、相对含水量(RWC)、生长速率、光合速率及单叶水分利用效率（WUE）显著下降;在适宜水分和中度干旱条件下,杨树的快速生长和干物质迅速积累时期主要集中在5～6月,严重干旱下快速生长时期和干物质积累主要集中在5月;杨树总耗水量和总生物量的大小顺序为：适宜水分＞中度干旱＞严重干旱;WUE则表现出中度干旱下最高,严重干旱下最低;杨树在适宜水分下的日、旬、月耗水量明显高于中度干旱和严重干旱处理;杨树在适宜水分、中度干旱和严重干旱条件下的最高耗水月分别在6～7月,最高旬耗水量分别在7月中旬、上旬和6下旬;在中度水分亏缺和严重水分亏缺下的最高耗水日出现的时间比适宜水分下的最高耗水日提前1～2个月以上。一天中的最大耗水高峰随着杨树生育期和土壤含水量的不同而有明显差异。研究结果表明,杨树不具备耐旱植物的特征,因此在黄土高原缺水地区不适宜大面积栽植,只能用于水分条件较好的立地条件下造林。     

基于稳定同位素和热扩散技术的张北杨树水分关系差异

利用稳定氢同位素和热扩散技术研究张北防护林杨树的水分来源和蒸腾耗水,分析确定未退化与退化杨树的水分关系差异.结果表明:在生长季节中退化杨树主要利用0～30 cm土壤水分,未退化杨树主要利用30～80 cm土壤水分,两者的水分来源不同.旱季时,未退化杨树利用深层土壤水分和地下水的比例明显高于退化杨树.雨季中,杨树对0～30 cm土壤水分的利用比例增加,退化杨树增加幅度明显高于未退化杨树,对30～180 cm土壤水分的利用比例均减少.未退化杨树的液流速率大于退化杨树,不同天气中液流速率表现出相似的变化趋势,但未退化杨树液流的启动时间比退化杨树早.相关分析表明,未退化和退化杨树液流速率与土壤温度、风速、太阳辐射、相对湿度、空气温度均呈极显著的相关关系.退化杨树液流速率与土壤温度和空气相对湿度呈极显著负相关,与其他因素呈显著正相关,而未退化杨树仅与空气相对湿度呈极显著负相关,与其他因素均呈显著正相关关系,表明退化和未退化杨树蒸腾耗水易受环境条件的影响.退化杨树液流日累计量明显小于未退化杨树,表明其蒸腾耗水量较少;退化杨树水分来源浅,蒸腾耗水的减少并不能阻止林分退化.     

梨枣花果期耗水规律及其与茎直径变化的相关分析

设置4个水分处理,研究了4年生梨枣2010年及2011年花果期不同供水条件下土壤水分动态和耗水规律,分析了梨枣日耗水量与茎直径变化间的相关性,建立回归模型.结果表明:(1)2a内各处理梨枣耗水量随土壤供水量的增加而增大,其日耗水量最大值均出现在灌水后1周内;各处理果实膨大期日耗水强度大于开花坐果期.(2)2a内各处理茎直径日变化平均值(MTD)、茎直径日最大值(MXTD)均符合Logistic函数关系,MXTD与MTD在表征梨枣茎秆生长规律方面效果一致,各处理茎直径变化指标(MTD、MXTD)增长率因水分处理的不同而存在差异.(3)高水分(T1处理)条件下茎直径变化指标(MTD、MXTD、MDS(茎直径日最大收缩量)、DG(茎直径日生长量))在表征枣树耗水状况方面不敏感;在低水分(T4处理)条件下,日耗水量与茎直径日最大收缩量(MDS)相关系数较其他3个茎直径变化指标(MTD、MXTD、DG)高且达极显著水平,说明MDS能够更好的表征低水分处理的梨枣耗水规律.在此基础上建立耗水量与茎直径变化回归模型,为评价梨枣耗水状况提供依据.     

不同覆盖方式对旱地马铃薯耗水特性和产量的影响

在陇中半干旱区设置玉米整秆带状覆盖(ST)、地膜覆盖(PT) 2种覆盖方式,以露地平作为对照(CK),研究了不同覆盖方式对马铃薯田土壤水分、耗水规律、产量及水分利用效率的影响。结果表明:与CK相比,覆盖处理显著(P<0.05)提高了马铃薯播种至收获期0～200 cm土壤贮水量,ST和PT处理土壤贮水量较CK的增幅分别以收获期(12.3%)和淀粉积累期(9.1%)最大;覆盖处理降低了马铃薯全生育期耗水量,以ST处理的降幅最大(23.4%);与CK相比,ST处理显著降低了生育前期(播种-块茎形成期)和后期(淀粉积累期-收获期)的耗水量,显著增加了生育中期(块茎形成期-淀粉积累期)耗水量,并增加了深层土壤水分,而PT处理主要降低了生育前期和中期耗水,显著增加了生育后期耗水; ST和PT处理分别使马铃薯产量较CK显著增加32.4%和32.9%,水分利用效率提高73.8%和48.8%。综上可知,玉米整秆带状覆盖处理能显著改善马铃薯生育中后期0～200 cm土壤水分状况,使马铃薯关键生长阶段耗水增多,能显著提高马铃薯产量和水分利用效率。     

不同小麦品种耗水特性和籽粒产量的差异

在田间试验条件下,采用10个小麦品种,设全生育期不灌水(W0)、灌底墒水+拔节水(W1)、灌底墒水+拔节水+开花水(W2)3个处理,每次灌水量60 mm,研究不同小麦品种不同生育阶段的耗水特点和籽粒产量的差异.结果表明:以W0、W1和W2处理的小麦籽粒产量和水分利用效率(WUE)2因子为指标进行聚类分析,可将10个品种分为3组:高产高水分利用效率组(组Ⅰ)、高产中水分利用效率组(组Ⅱ)和中产低水分利用效率组(组Ⅲ).在W0处理下,组Ⅰ小麦品种的总耗水量、开花至成熟期的耗水量和耗水模系数均低于组Ⅱ和组Ⅲ,籽粒产量最高;在W1处理下,组Ⅰ小麦品种拔节至开花期的耗水量和耗水模系数均低于组Ⅱ和组Ⅲ,开花至成熟期的耗水量和耗水模系数在组Ⅰ、组Ⅱ和组Ⅲ间无显著差异;在W2处理下,组Ⅰ小麦品种的土壤供水量、拔节至开花期的耗水量和耗水模系数均低于组Ⅱ和组Ⅲ,开花至成熟期的耗水量和耗水模系数为组Ⅰ和组Ⅲ低于组Ⅱ.表明组Ⅰ高产高水分利用效率品种为最适宜品种,而底墒水和拔节水各灌60 mm的W1处理是兼顾高产与节水的最佳处理.     

宁夏河东沙区刺槐和丝绵木水分利用策略

刺槐和丝绵木混交林是宁夏河东沙区防护林建设的主要模式,了解刺槐和丝绵木的水分利用策略,能为区域植被恢复和防护林林分结构调整提供科学依据。以宁夏河东沙区刺槐(Robinia pseudoacacia)和丝绵木(Euonymus bungeanus)混交林为研究对象,通过监测微气象、树干液流和土壤质量含水量,结合大气降水、土壤水、植物木质部水同位素组成,采用Granier及其校正公式,运用贝叶斯混合模型(MixSIAR)和相似性比例指数(PS)研究2个树种的蒸腾耗水、水分来源和水分利用关系。结果表明：刺槐和丝绵木的蒸腾耗水量在生长季中期较高,前期和后期较小,刺槐的蒸腾耗水量是丝绵木的1.55倍;影响刺槐蒸腾耗水的主要环境因子为饱和水汽压差、太阳辐射、0—40 cm土壤质量含水量和40—120 cm土壤质量含水量;影响丝绵木蒸腾耗水的主要环境因子为饱和水汽压差、太阳辐射、平均气温、0—40 cm土壤质量含水量和40—120 cm土壤质量含水量;蒸腾耗水较高时,刺槐主要吸收利用中层土壤水,丝绵木主要吸收利用浅层土壤水,蒸腾耗水较低时,刺槐主要吸收利用浅层土壤水,丝绵木主要吸收利用中层土壤水;在...     

水蚀风蚀交错区典型植被土壤水分消耗和补充深度对比研究

研究了黄土高原水蚀风蚀交错区六道沟小流域8种植被类型条件下植物消耗土壤水分深度与降水对应的补充深度。结果表明:裸地、农地、撂荒地、人工草(灌)地(苜蓿地、柠条地、沙打旺地)、当地典型草地(荒草地、长芒草地)在平水年及干旱年,土壤水分均表现为负平衡;丰水年部分样地土壤水分得到补充。平水年以及干旱年(2010—2011年)植物耗水深度依次为:柠条地撂荒地沙打旺地苜蓿地≈长芒草地≈荒草地农地裸地,降水补充深度为农地裸地撂荒地荒草地长芒草地沙打旺地苜蓿地柠条地。丰水年(2012年)裸地、苜蓿地、荒草地与沙打旺地土壤水分并未显示出明显负平衡过程,但柠条地耗水深度依然达到260 cm,其它样地依次为撂荒地农地长芒草地;降水入渗深度排序:农地裸地撂荒地=柠条地荒草地=苜蓿地长芒草地沙打旺地。水蚀风蚀交错区土壤蒸发(裸地蒸发)以及降水补充深度一般为0—120 cm范围内,丰水年土壤水分能得到恢复。农地的土壤水分消耗与补充深度略有增加。农地撂荒后耗水深度与撂荒地植被类型有密切联系,随植被盖度与丰度的增加,耗水有进一步加深的趋势,撂荒地土壤水分补充深度小于等于消耗深度。农地退耕还草所种植的深根性植被(苜蓿、沙打旺、柠条等)不仅会迅速消耗当季降水,同时会进一步消耗土壤深层储水,致使120 cm以下观测土层土壤含水量较低,造成土壤水分消耗深度较浅的假象。除撂荒地外,高生物产量的人工草(灌)耗水量高,耗水深度也深,因此在退耕还林(草)过程中,应该充分考虑不同植被类型的年度水分交换深度,采取措施降低消耗深度,增加入渗深度。     

柴达木盆地蒸散发遥感估算与耗水有效性评价

陆面蒸散发(ET)是自然生态系统水分耗散的主要方式,准确把握其时空变化特征,对于区域水资源合理利用与生态环境保护具有重要意义。针对我国西北干旱内陆区实测资料匮乏的现状,基于MODIS产品,构建了具有时空二维属性的地表温度-植被指数特征空间,实现了柴达木盆地陆面蒸散发的时空连续估算;在此基础上,进一步分离土壤蒸发与植被蒸腾,开展研究区自然生态系统耗水有效性评价。结果表明:(1)柴达木盆地近九年多年平均ET为188.75 mm,受降水空间分布格局影响,ET具有明显的从东南向西北减少趋势;(2)土壤蒸发与植被蒸腾多年平均值为171.06 mm和14.26 mm,后者年内峰值出现时间总体比前者晚1个月,具有滞后效应;(3)盆地陆地生态系统多年平均耗水总量为430.94亿m³,其中高效、中效和低效耗水的占比分别为6.55%、52.57%和40.88%。在区域尺度以时空连续的方式揭示了ET水分消耗的有效性,可为基于ET水资源管理目标的实现提供重要科学支撑。     

西北黑河中游荒漠绿洲农田作物蒸腾与土壤蒸发区分及作物耗水规律

利用中国生态系统研究网络临泽内陆河流域研究站绿洲农田2009年小气候、湍流交换、土壤蒸发和叶片气孔导度等综合观测试验数据,应用Shuttleworth-Wallace(S-W)双源模型以半小时为步长估算了绿洲农田玉米生长季实际蒸散量,并利用涡动相关与微型蒸渗仪实测数据对田间蒸散发量和棵间土壤蒸发量计算结果进行了检验。结果表明:S-W模型较好地估算研究区的蒸散量,并能有效区分农田作物蒸腾和土壤蒸发;全生育期玉米共耗水640 mm,其中作物蒸腾累积量为467 mm,土壤蒸发累积量为173 mm,分别占总量的72.9%和27.1%;日时间尺度上,作物蒸腾和土壤蒸发分别在0—6.3 mm/d和0—4.3 mm/d之间变化,其日平均分别为2.9和1.0 mm/d;田间供水充足,作物蒸腾与土壤蒸发比值明显受作物生长过程影响,播种—出苗期、出苗—拔节期、拔节—抽雄期、抽雄—灌浆期、灌浆—成熟期,其比值分别为0.04、0.8、7.0、5.2和1.4,不同阶段的比值差异主要受叶面积指数影响。     

Physiological mechanism for the reduction in soil water in poplar (Populus deltoides) plantations in Dongting Lake wetlands

The use of large-scale tree plantations has provoked increasing concern regarding the negative effects on local environments in different ecosystems. However, the physiological mechanism underlying the reduction in soil water by tree plantations in wetlands is not clear. The aims of this study were to investigate the effects of poplar (Populus deltoides) plantations on soil water content and to elucidate the underlying physiological mechanisms. To this end, we conducted a 1-year fixed-plot investigation of soil water content (SWC), plant photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and water-use efficiency (WUE) of individual leaves of 11- and 5-year-old poplars and of reed (Triarrherca sacchariflora, a native herbaceous plant) in the Dongting Lake wetlands, China. SWC was highest in reed, intermediate in 11-year-old poplar, and lowest in 5-year-old poplar, suggesting that poplar plantations produce a lower soil water content in wetlands. From May to July, Pn was significantly higher in reed than in the two poplar stands, but did not differ between the different-aged poplars. As a whole, Gs and Tr were higher, but WUE was lower, in the poplar stands than in reed during the growing season, indicating that Gs and Tr are the key physiological mechanisms associated with the lower soil water in poplar stands. Relationships among Pn, Gs, and Tr showed positive correlations (P < 0.01) for each type of vegetation. These data suggest that poplar plantations may cause the transformation of wetlands into dry land due to a lower WUE leading to a massive water loss from soil. This, in turn, would have an influence on community composition and ecosystem function after establishment of the plantations.     

Ecohydrology and the Partitioning AET Between Transpiration and Evaporation in a Semiarid Steppe

Water availability defines and is the most frequent control on processes in arid and semiarid ecosystems. Despite widespread recognition of the importance of water in dry areas, knowledge about key processes in the water balance is surprisingly limited. How water is partitioned between evaporation and transpiration is an area about which ecosystem ecologists have almost no information. We used a daily time step soil water model and 39 years of data to describe the ecohydrology of a shortgrass steppe and investigate how manipulation of soil and vegetation variables influenced the partitioning of water loss between evaporation and transpiration. Our results emphasize the overwhelming importance of two environmental factors in influencing water balance processes in the semiarid shortgrass steppe; high and relatively constant evaporative demand of the atmosphere and a low and highly variable precipitation regime. These factors explain the temporal dominance of dry soil. Annually and during the growing season 60–80% of the days have soil water potentials less than or equal to −1.5 MPa. In the 0–15 cm layer, evaporation accounts for half of total water loss and at 15–30 cm it accounts for one third of the loss. Annual transpiration/actual evapotranspiration (T/AET) ranged from 0.4–0.75 with a mean of 0.51. The key controls on both T/AET and evaporation/actual evapotranspiration in order of their importance were aboveground biomass, seasonality of biomass, soil texture, and precipitation. High amounts of biomass and late timing of the peak resulted in the highest values of T/AET.     

不同退化红砂荒漠草地的水分分配格局

研究了内蒙古阿拉善盟不同过牧退化红砂草地的土壤 植物 大气系统的水分分配格局、不同退化草地和主要植物种的水分利用效率 .2 0 0 1年降雨量 12 4 .3mm ,其中试验期 119.4mm .1m深土壤水分结果表明 ,10～ 4 0cm土层受蒸散影响最大 ;由于主要共存种红砂和无芒隐子草根系分布和蒸腾强度不同等 ,含水量在 10～ 2 0cm土层以中度退化区显著低于其它样区 (P <0 .0 5 ) ,而 2 0～ 4 0cm土层以轻度退化区较低 .样地年均蒸发量为 30 .6mm ,红砂种群的年均蒸腾量为 11.9mm .随着草地退化加剧 ,裸地的蒸发量和退化指示种匍根骆驼蓬种群的蒸腾量增加 ,而红砂种群的蒸腾量降低 .与较轻度退化区比 ,中度和重度退化区的水分利用率分别下降了 14 .6 %和 4 6 .1% ,红砂水分利用率分别下降了 37.8%和 73.8% .     

Influence of mulching on the pattern of growth and water use by spring wheat and moisture storage on a fine textured soil

Eight tonnes ha^–1 of stubble were used to mulch spring wheat (Triticum aestivum) on a fine textured soil with the aim of controlling both transpiration and soil evaporation during the wet pre-anthesis phase to increase moisture supply during grain filling in the eastern wheatbelt of Western Australia. Mulching reduced leaf area per plant by reducing the culm number; consequently the green area index was reduced. Reduced culm number was associated with low soil temperature which at 50 mm depth averaged 7°C lower under the mulched crop relative to the control crop in mid-season. The smaller canopies of the mulched crop used 15 mm less water than those of the control before anthesis; this difference in water-use was due equally to reduced transpiration and soil evaporation. However, the mulched crop was unable to increase ET during grain filling, a response associated with the persistence of low soil temperature for most of the growth period. Hence, total ET for the season was significantly lower (18 mm) under the mulched crop than the control crop. At harvest, mulching did not have significant effects on total above-ground dry matter and grain yields, but it increased water use efficiency for grain yield by 18%, grain weight by almost 17% and available moisture in both uncropped and cropped plots by an average of 43 mm.To determine whether there was any residual effects of soil treatment on moisture storage during the summer fallow period, soil moisture was monitored both in cropped plots and uncropped plots, that were either mulched or unmulched during the growing season, from harvest in October 1988 until next planting in June 1989. Available moisture at next planting was correlated with moisture storage at harvest despite the differences in run-off, soil evaporation and fallowing efficiency (increase in moisture storage as a percentage of rainfall) between treatments during fallowing. Therefore, the mulched treatments had more moisture available (30 mm), mostly as a result of less water use during cropping in the previous growing season, than the unmulched treatment.The study shows that mulching may be used to restrain both transpiration and soil evaporation early in the season to increase availability of soil moisture during grain filling. Secondly, mulching during the previous growing season had little effect on soil moisture during the summer fallow period, however, the moisture saved by mulching during cropping was conserved for the following season. These results indicate the importance of evaluating mulching of winter crops in terms of crop yield in the subsequent growing season as well as in the current season in which the soil was treated.Abbreviations D through drainage - DAS days after sowing of the crop on 31 May 1988 - DM dry matter produced in the above-ground portion of the crop (kg ha^–1) - E₀ evaporation from Class A pan (mm) - E_s evaporation from uncropped soil (mm) - E_sc evaporation from soil beneath the wheat canopy (mm) - ET evapotranspiration (mm) - FE fallowing efficiency (gain in soil moisture storage/rainfall) - GAI green area index (area of green vegetation per unit land area) - GWUE water-use efficiency for grain production (grain yield/total ET, kg ha^–1mm^–1) - K extinction coefficient (see equation 1) - RO run-off of moisture from soil surface during/following rainfall (mm) - SM available soil moisture (mm) at harvest (SMh) or at planting (SMp) - WUE water-use efficiency for total above-ground dry matter yield (see GWUE)     

辽宁章古台樟子松人工林水分动态的研究

 本文根据1979—1985年的观测资料,对辽宁省彰武县章古台沙地樟子松人工林水分因子的分布与变化规律及其数量关系进行了分析。结果表明,樟子松人工固沙林的土壤含水率逐渐降低,25年生林分比无林对照区低1.08%。樟子松的蒸腾耗水量占同期降水量的34.7一71.4%,占林地水分输出总量的60.8—71.7%,是水分输出的主要途径,也是发生水分亏缺的主要因素。林分进行适当的疏伐和中耕,对改善水分状况,调整水分关系起一定作用。试验的结果还表明,章古台地区干旱年的降水量大致相当于科尔沁沙地其它地区正常年的降水量。因此,在这些地区大面积营造片状人工林,会导致水分亏缺问题。但若空留沙丘的中上部不营造乔木林,而利用水分条件比较好的沙丘下部、丘间低地进行带状造林或块状造林,则可能保持水分平衡,促进成林。     

Ecohydrological effects of grazing‐induced degradation in the Patagonian Monte,Argentina

Water‐limited ecosystems have undergone rapid change as a consequence of changing land use and climate. The consequences of these changes on soil quality and vegetation dynamics have been documented in different regions of the world. In contrast, their effects on soil water, the most limiting resource in these environments, have received less attention, although in recent years increasing efforts have been made to relate grazing, soil water and vegetation functioning. In this paper, we present the results of field observations of plant phenology and soil water content carried out during two successive years at four sites along a degradation gradient caused by grazing in the Patagonian Monte, Argentina. We also developed a simplified soil water balance model to evaluate how changes in plant cover could affect water balance. Our field observations showed that the soil water content in the soil layer where roots of grasses are abundant (0–25 cm) was higher and the growing cycles were longer in degraded than in preserved sites. Similarly, our modelling approach showed that the deep soil (depth > 10 cm) was wetter in the degraded than in the preserved situation. Simulation also suggested a switch from transpiration to a direct evaporation dominance of water losses with degradation. Although reductions in plant cover related to grazing degradation were associated with a decrease in annual transpiration, the simulated soil water loss by transpiration was higher during summer in the degraded than in the well preserved situation. Thus, our field observations seem to be a consequence of ecohydrological changes causing an accumulation of water in the soil profile during the cold season and its transpiration during summer. In conclusion, our results showed that changes in plant cover caused by grazing disturbance can alter the soil water balance, which in turn can affect vegetation function.