Water inputs across a tropical montane landscape in Veracruz,Mexico: synergistic effects of land cover,rain and fog seasonality,and interannual precipitation variability

Land‐cover change can alter the spatiotemporal distribution of water inputs to mountain ecosystems, an important control on land‐surface and land‐atmosphere hydrologic fluxes. In eastern Mexico, we examined the influence of three widespread land‐cover types, montane cloud forest, coffee agroforestry, and cleared areas, on total and net water inputs to soil. Stand structural characteristics, as well as rain, fog, stemflow, and throughfall (water that falls through the canopy) water fluxes were measured across 11 sites during wet and dry seasons from 2005 to 2008. Land‐cover type had a significant effect on annual and seasonal net throughfall (NTF <0=canopy water retention plus canopy evaporation; NTF >0=fog water deposition). Forest canopies retained and/or lost to evaporation (i.e. NTF<0) five‐ to 11‐fold more water than coffee agroforests. Moreover, stemflow was fourfold higher under coffee shade than forest trees. Precipitation seasonality and phenological patterns determined the magnitude of these land‐cover differences, as well as their implications for the hydrologic cycle. Significant negative relationships were found between NTF and tree leaf area index (R²=0.38, P<0.002), NTF and stand basal area (R²=0.664, P<0.002), and stemflow and epiphyte loading (R²=0.414, P<0.001). These findings indicate that leaf and epiphyte surface area reductions associated with forest conversion decrease canopy water retention/evaporation, thereby increasing throughfall and stemflow inputs to soil. Interannual precipitation variability also altered patterns of water redistribution across this landscape. Storms and hurricanes resulted in little difference in forest‐coffee wet season NTF, while El Niño Southern Oscillation was associated with a twofold increase in dry season rain and fog throughfall water deposition. In montane headwater regions, changes in water delivery to canopies and soils may affect infiltration, runoff, and evapotranspiration, with implications for provisioning (e.g. water supply) and regulating (e.g. flood mitigation) ecosystem services.     

模拟穿透雨减少对锐齿栎(Quercus aliena var. acuteserrata)树干液流密度的影响

降水格局变化是全球气候变化的重要特征之一,未来气候变化下,较为频繁和严峻的干旱将威胁地球中纬度部分地区的森林,但森林植被如何响应季节性干旱胁迫及其机制尚不清楚。北亚热带-暖温带过渡区分布着以锐齿栎(Quercus aliena var.acuteserrata)为优势树种的落叶阔叶林,研究其水分蒸腾代谢过程对干旱的响应是评估气候变化对过渡区天然落叶阔叶林生态系统水碳影响的关键科学问题。在典型的锐齿栎天然林中通过开展模拟穿透雨减少大型野外实验,采用Granier热扩散式探针技术监测锐齿栎树干液流密度的动态变化,研究了不同径级锐齿栎树干液流密度对模拟干旱的响应规律。结果表明:(1)穿透雨减少对树干液流密度的影响呈现季节变异。在7月份,林内穿透雨减少显著降低了锐齿栎的树干液流密度,但生长季后期的10月份林内穿透雨减少反而使锐齿栎树干液流密度显著升高。(2)不同径级的锐齿栎树干液流密度在生长季内对干旱有不同的响应,特别是小径级的树干液流密度与其他径级有较多的不同。小径级的锐齿栎树干液流密度在5、7月份表现为减雨样地显著小于对照样地,在9、10月份则表现为减雨样地显著大于对照样地。中径级的锐齿栎树干液流密度在5、10月份表现为减雨样地显著大于对照样地,在7月份则表现为减雨样地极显著小于对照样地。大径级的锐齿栎树干液流密度在6、7月份表现为减雨样地显著小于对照样地,在10月份则表现为减雨样地显著大于对照样地。     

北京西山地区油松林水文过程中营养元素迁移特征

对北京西山地区31a油松林降水化学进行定位监测与分析.结果表明：（1）大气降水流经油松林过程中,其营养元素（除Na^＋外）的浓度出现梯度变化：树干茎流高于穿透雨高于大气降水,并且有明显的月际变化,表明从林冠、树干淋洗大量的营养元素,林冠和树干中养分元素迁移是森林生态系统养分循环重要的组成部分.（2）营养元素变化中,浓度差异变化较大的元素是NO3^--N和K^＋,NO3^--N在穿透雨和树干茎流的浓度分别是大气降水的4.4倍、9.9倍,它们中的K^＋浓度分别为大气降水的4.1倍和8.1倍.（3）降水经过油松林,养分淋溶总量为54.12kg hm^-2,淋溶量较多的元素是Ca和K,淋溶强度最大的元素是K^＋.（4）北京西山地区大气降水输入林地的养分66.38kg hm^-2,较多的元素是Ca、N.降水经过油松林输入林地养分总量为120.50kg hm^-2,Ca元素最高,为61.22kg hm^-2,其次是N元素（NH4^＋-N＋N3^--N）,为31.34kg hm^-2,K元素为16.49kg hm^-2,Mg元素为8.11kg hm^-2,Na元素最少,为3.34kg hm^-2.     

Exchange of Proton and Major Elements in Two-Layer Canopies Under Acid Rain in a Subtropical Evergreen Forest in Central-South China

Canopy exchanges of H^＋ and N （NH4^＋-N, NO3^--N） and other major ions were evaluated and quantified In twolayer canopies based on throughfall measurements in Shaoshan Forest during the period 2000-2002, central-south China, The collected annual rainfall, throughfall, and sub-throughfall were 1 401, 1 191, and 1 084 mm/year, respectively. Fifteen percent and 8% of rainfall （or 9% of throughfall） were intercepted by the top canopy and sub-canopy layers, respectively, The foliar leaching of base cations from the top canopy was significantly higher than that from the sub-canopy, and the latter accounted for 25% of the former. The uptake of H^＋ and NH4^＋ was significantly higher in the top canopy than in the sub-canopy, indicating that the canopy buffering capacity in the top canopy was stronger than the sub-canopy; Mg^2＋ can be absorbed from water flux on the sub-canopy foliar surfaces to compensate for the Mg deficit in the forest soil during the growing season,     

大兴安岭北部兴安落叶松林穿透雨延滞效应

以黑龙江漠河生态站兴安落叶松天然林为研究对象,对林外雨、穿透雨和树干茎流进行定位观测,分析大兴安岭北部兴安落叶松林穿透雨延滞效应.结果表明： 穿透雨量、树干茎流量和林冠截留量分别占同期降雨总量的76.5%、2.6%和20.9%.降雨发生后,穿透雨与林外雨在产生和终止时间上均存在一定延滞性;随降雨量级增大,穿透雨滞后时间表现出逐渐缩短的趋势,变动范围为（67.8±7.8）～（17.2±3.9） min（穿透雨）和（112.0±38.8）～（48.3±10.6） min（树干茎流）;相同降雨量级下,穿透雨滞后时间随降雨强度增大而逐渐降低,且降雨强度>2 mm·h^-1时延滞时间显著缩短,同时随雨前干燥期的增加而增长,而当雨前干燥期≥48 h时,降雨量则是影响滞后时间的主要因素;降雨终止时,降雨量>5.0 mm,穿透雨终止时间也存在延滞性,且随降雨强度增加而增大,但与雨前干燥期关系不明显;树干茎流终止时间先于林外雨终止时间,且主要与降雨量级有关,降雨量级越小,终止时间越早.     

岷江冷杉针叶林下穿透雨空间分布特征

森林对降水的截留作用、林下穿透雨的水文学及生态学意义一直是生态水文学研究中的热点 ,但是关于林下穿透雨空间分布特征的研究还比较少。在四川西部的卧龙自然保护区研究了岷江冷杉林下穿透雨的空间分布特征。在岷江冷杉针叶林下布设了 8个雨量筒用以测量林下穿透雨 ,对两年共 35次降雨的穿透雨研究结果表明 ,林下各观测点的穿透雨率同林外降雨量之间的关系都可以用逻辑斯谛曲线方程较好地模拟 ,与传统的对数方程模拟相比 ,前者的相关程度显著高于后者 ,而且用逻辑斯谛方程进行模拟时 ,方程中的各参数具有一定的生态学意义。此外 ,研究发现林下各点的穿透雨率具有显著的差异 ,位点 4下的穿透雨存在着明显的聚集效应 ,此处的平均穿透雨率达到了 10 3.2 %。对林下 8个点穿透雨进行聚类分析表明 ,林下位点 4和位点 8的穿透雨特征与其余 6个点的穿透雨特征有显著的差异。对影响岷江冷杉林下穿透雨空间分布的因素分析表明 ,观测点上方的冠层覆盖度、枝叶层厚度与降雨量之间均有一定的负相关关系 ,但其影响未达到显著水平 ;观测点到树干的距离与林下的穿透雨之间的关系可以较好地用二次多项式方程模拟 ,方程的相关程度很高 (R=0 .94 91) ;各观测点正上方的冠层以及枝叶性质也对穿透雨的空间分布特征有一定的     

The response of an Eastern Amazonian rain forest to drought stress: results and modelling analyses from a throughfall exclusion experiment

Warmer and drier climates over Eastern Amazonia have been predicted as a component of climate change during the next 50–100 years. It remains unclear what effect such changes will have on forest–atmosphere exchange of carbon dioxide (CO₂) and water, but the cumulative effect is anticipated to produce climatic feedback at both regional and global scales. To allow more detailed study of forest responses to soil drying, a simulated soil drought or 'throughfall exclusion' (TFE) experiment was established at a rain forest site in Eastern Amazonia, Brazil, for which time-series sap flow and soil moisture data were obtained. The experiment excluded 50% of the throughfall from the soil. Sap flow data from the forest plot experiencing normal rainfall showed no limitation of transpiration throughout the two monitored dry seasons. Conversely, data from the TFE showed large dry season declines in transpiration, with tree water use restricted to 20% of that in the control plot at the peak of both dry seasons. The results were examined to evaluate the paradigm that the restriction on transpiration in the dry season was caused by limitation of soil-to-root water transport, driven by low soil water potential and high soil-to-root hydraulic resistance. This paradigm, embedded in the soil–plant–atmosphere (SPA) model and driven using on-site measurements, provided a good explanation ( R ² > 0.69) of the magnitude and timing of changes in sap flow and soil moisture. This model-data correspondence represents a substantial improvement compared with other ecosystem models of drought stress tested in Amazonia. Inclusion of deeper rooting should lead to lower sensitivity to drought than the majority of existing models. Modelled annual GPP declined by 13–14% in response to the treatment, compared with estimated declines in transpiration of 30–40%.     

鼎湖山季风常绿阔叶林某些沉积元素转移过程中的浓度分析

对鼎湖山大气降水、季风常绿阔叶林林冠穿透水、土壤水(30cm和80cm深)以及溪水中某些沉积元素进行了系统连续的观测研究,从沉积元素的转移过程阐明了鼎湖山自然保护区和季风常绿阔叶林所承受的环境压力,通过分析沉积元素在这些水文学过程中的浓度变化和相互联系,试图揭示该生态系统相应功能过程变化的规律。得到如下结果：(1)大气降水中的Pb含量远远高于穿透水、土壤水(30cm和80cm深)以及溪水中的含量,随着水分由输入向输出流动,Pb的浓度逐渐降低;(2)在大气降水、林冠穿透水、土壤水(30cm和80cm深)以及溪水中,Al离子的浓度逐步增加;(3)除Pb外,所有其他元素(Al、Mn、sr、Mg、Na、K和Ca)在土壤溶液中的浓度都高于5个水文过程的平均值;(4)Mn、K、Ca的输入和输出的浓度都不高;(5)Na和Mg在土壤水和溪水中的浓度超过5个水文过程的平均值。这表明：(1)鼎湖山的大气具有高浓度的Pb含量,而且Pb在季风常绿阔叶林系统中处于一个持续的积累过程;(2)酸性降水不仅活化了土壤中的Al元素,对各个水文学过程中的离子浓度也有增大的作用;(3)Na和Mg在当前的大气环境下有可能加速地从季风常绿阔叶林生态系统中淋洗出来。总之,由于酸雨和大气污染的影响,鼎湖山森林生态系统将处于不稳定状态。     

亚热带常绿阔叶林和杉木人工林茎流与穿透雨的养分特征

亚热带常绿阔叶林和杉木人工林树干茎流和穿透雨养分含量均表现季节动态变化。养分含量中,K^ 、Ca^2 、NO3%-浓度高,Na^ 、Mg^2 居中,HPO4^2-含量低,相对于林外雨,养分均出现富集化,但树干茎流养分富集化高于穿透雨。树干茎流出现强烈的酸化,而穿透雨酸化现象不明显。树种之间的茎流养分特征表现不一样,樟树和枫香总的养分浓度较高,其次为刨花楠,最后为青冈和红栲。     

第2代杉木幼林生态系统水化学特征

对第 2代杉木幼林生态系统的降雨、穿透水、茎流、地表和地下径流等水文过程中 N、P、K、Ca、Mg、Cu、Fe、Zn和 Mn9种养分元素含量进行了连续 5 a的测定 ,结果表明 :降雨通过林冠后其化学特性发生明显变化 ,p H值出现酸化现象 ,穿透水中 Zn和 Org-N为负淋溶 ,其余各元素浓度有所增加。树干茎流的富集作用比穿透水强 ,其中 Zn为负 ,其它元素的浓度均比林外降雨的高。地表径流中 Zn>Org-N>NO3 -N,与降雨中含量相比较为淋失迁移型 ,Ca>K>Cu>Mg>P>NH4 -N>Mn>Fe为内贮型 ,p H值增大。地下径流中 Zn>Org-N>NH4 -N>K>Mn为淋失迁移型、Ca>Mg>Cu>NO3 -N>P>Fe为内贮型。该系统的水循环中 Ca>Mg>Fe>P为净损失、Zn>K>Org-N>NH4 -N>Mn>NO3 -N>Cu为净积累 ,与第 1代杉木林相比 ,第 2代杉木幼林水化学过滤与吸贮功能较差 ,系统稳定性也较弱 ,生态功能的恢复需要一定的时间