【作者】 王轶浩；

【导师】 王彦辉；

【作者基本信息】 中国林业科学研究院 ， 生态学， 2012， 博士

【摘要】 酸沉降对森林生态系统的长期影响还未消除，然而以极端干旱事件频发为代表的全球气候变化对酸雨区的受害森林又带来新的挑战，研究变化环境下的生态水文过程和功能响应已成为21世纪生态环境与水资源管理的热点。为全面深入理解气候变化背景下酸害森林的健康变化，丰富森林生态水文学的理论内容和专业视角，并为受害森林的生态水文服务功能评价和管理提供理论指导和决策支持，本文在重庆铁山坪酸雨区调查了受害马尾松林（林龄40-60年）的结构特征和定位监测了其水文过程，并参考国内健康森林（马尾松林）的结构特征和水文功能文献数据，对比分析了酸害马尾松林的结构特征变化和其生态水文特征。主要结论如下：1．受害马尾松林的林分结构特征变化明显在所研究的马尾松林中，以马尾松为主构成了主林冠层，且在下木层中几乎没有马尾松分布；研究林分的树种组成较简单（4-9种），其多样性指数（Simposon）较低，变化在0.23-0.69。香樟、木荷、楠木等阔叶树种主要分布在下木层，并开始进入被压木优势度等级，它们与马尾松的种间竞争将日趋激烈。马尾松林的冠层郁闭度较高（0.87），但因大量针叶凋落造成冠层稀疏，不能构成对林下灌木、草本分布的影响。林下灌木层的盖度为63.95%、草本层的盖度为48.62%；草本分布受到灌木层盖度的显著影响。与健康马尾松林相比，受害马尾松林的根系生物量减小和分布变浅（主要在0-40cm），尤其是细根生物量减少和集中分布在表层（0-10cm），并随土深而快速减小。2．受害马尾松林针叶变小变少和枯落物分解变慢与健康马尾松相比，受害马尾松的枯死叶和青黄叶的单叶长（15.10和12.83cm）和单叶重（0.024和0.019g）都较小；枯死针叶的比叶面积要大（35.12cm2/g），说明受害马尾松的针叶变小变薄了。受害马尾松林的叶面积指数年均值为1.25（0.92-1.83），远低于其它地点健康马尾松林的3.76-3.94。它的年内动态变化为从年初开始到4、5月份逐渐减小，然后到9、10月份之前缓慢增大，之后又逐渐减小，这是马尾松针叶生长和凋落节律共同影响的结果。与其它地点马尾松林相比，受害马尾松林的未分解层枯落物的分解速率较慢，年失质率为35.62%；分解半衰期和全衰期（分解至95%时）分别为1.3和2.5年。3．受害马尾松林的土壤水文物理性质变差受害马尾松林的土壤水文物理性质以表层（0-10cm）最好，10-20cm土层居中，20cm以下土层相对较差，其中，非毛管孔隙度和渗透性随土深明显地减小，但健康马尾松林的土壤非毛管孔隙度随土深的变化比较缓和。受害马尾松林土壤的水源涵养功能和同一地点的针阔混交林相差不大，但明显差于阔叶林和好于毛竹林。与其它地点土壤酸化较轻的马尾松林相比，酸害马尾松林的土壤水文物理性质明显变差，表现为各土层的密度较大、渗透性和贮水能力下降、土壤孔隙度（包括毛管孔隙度、非毛管孔隙度和总孔隙度）较小。4．受害马尾松林的年凋落量增大但针叶减少和枝条增多且更集中在伏旱期与健康或酸害较轻的马尾松林相比，受害马尾松林的年凋落物量（5.96t/hm2）增大但组成有差别，表现为针叶减少但枝条增多，各组分比例顺序为针叶＞树枝＞有机碎屑＞树皮（球果）＞阔叶。受害马尾松林的凋落物量变化对干旱胁迫更敏感，除阔叶凋落物外，其它凋落物组分的数量变化均不同程度受到土壤水分含量影响，尤其是30-40和40-50cm土层的水分含量。受干旱影响，马尾松林的年凋落格局发生重大变化，主要集中在夏季伏旱时期，但阔叶树种还能维持正常凋落节律（主要发生在4-5月份和11-12月份），说明阔叶树种在该酸雨区的适应性好于马尾松林。5．土壤缺水胁迫导致的受害马尾松林健康退化是因其根系吸水能力下降受害马尾松林的土壤含水量具有明显的时空变化，与同一研究地点的其它森林类型（针阔混交林、阔叶林和毛竹林）相比，其土壤含水量因冠层蒸散耗水较少而较高，且与毛竹林比较接近。田间持水量（或毛管孔隙度）和田间持水量的82%（毛管孔隙度的80%）是影响受害马尾松健康变化的两个重要阈值，低于此阈值时就会发生大量落叶，这主要是受害马尾松林的细根减小和分布变浅导致的吸水能力下降，造成相对土壤干旱，这在濒死马尾松衰亡过程的液流密度与土壤水分的关系中得到佐证。因此，受害马尾松林极易遭受缺水胁迫，特别是伏旱时期，无论少水年、平水年还是丰水年都存在，说明缺水胁迫已成为除酸害外影响森林健康的又一重要因素。6．受害马尾松林因针叶和细根减少而导致蒸腾耗水降低受害马尾松的树干液流密度的个体差异更多受叶面积指数影响，而不是树木相对高度所决定的优势度。正如3号优势木在其叶面积指数较小（0.68）时的月液流密度低于叶面积指数较大（1.46）的4号亚优势木，但其叶面积指数增大后的月液流密度又能超过4号木。受害马尾松林一般表现为大量针叶脱落，林冠叶面积指数降低，这使得其树木蒸腾耗水降低，因此，在同一地点的4种森林类型中，受害马尾松林的土壤含水量最高。受害马尾松林的月蒸腾耗水量变化在10.19-48.89mm之间，平均为27.24mm，其年内动态为先增加后减小，在夏季（7-8月份）达到高峰，月蒸腾量基本维持在40mm左右。树木蒸腾量与土壤水分条件也密切相关，受害马尾松因根系吸水能力下降引起的可利用水分减少也是导致其蒸腾量降低的重要原因。7．受害马尾松林的水文过程与功能特征受害马尾松林林冠稀疏致使其冠层截留容量较低（1.54mm），穿透雨率较高（84.66%）、树干茎流率（0.26%）和产生茎流的临界降雨量（5mm）以及林冠截留率（15.07%）较低。受害马尾松林的枯落物储量为11.06t/hm2；分别测定的未分解层、半分解层、总枯落物层的饱和持水率为195.54、214.48和197.61%，对应的最大持水深为0.71、0.82和1.46mm，均明显低于其它地点的健康马尾松林（15.7-32.20t/hm2，203-277%，3.40-5.12mm），说明受害马尾松林的枯落物水文功能下降。研究期间受害马尾松林的蒸散率减少，为67.38%；但产流率增大，为33.51%。更多还原

【Abstract】 Until now, the effect of acid deposition on forest ecosystem has not been removed, but theglobal climate change with increasingly frequent extreme drought events brings newenvironmental challenge for the damaged forests in acid rain region. Understanding theeco-hydrological processes and functional responses in a changing environment becomes anew hot spot for managing the eco-environment and water resources in21stcentury. In order tocomprehensively and further understand the health changes of forests damaged by acid rainunder the background of climate change, to enrich the theory of forest eco-hydrology, and alsoto provide theoretical guidance and policy-making support for the evaluation and managementon eco-hydrological services of damaged forests, the stand structure of damaged Masson pine(Pinus massoniana) forests (40-60a) were investigated, and its hydrological processes werepermanently monitored in the acid rain region of Tieshanping, Chongqing. Further, the studyresults were compared with the stand structure and hydrological function of healthy (Massonpine) forests reported in literature. Then, the change of stand structure of Masson pine forestsand the eco-hydrological characteristics caused by acid rain were identified. The mainconclusions are as follows:1. Remarkable changes of stand structure of damaged Masson pine forestsThe tree canopy layer of studied stands was mainly composed of Masson pines, but nearlyno Masson pine was found in the underwood layer. The tree species in the stand were fewer(only4-9), and biodiversity (Simposon) index was low and varied from0.23to0.69. Thebroad-leaves tree species (Cinnamomum camphora, Schima superba, Phoebe zhennan, et al)were mainly distributed in the underwood layer, but they begin to access the retarded tree layer,and their competition with the currently dominant Masson pines became to be intensive. Thecanopy density of Masson pine stand was as high as0.87. However, the high defoliation causedby acid rain led to a sparse canopy, which can not restrict the existence of shrub layer and herb layer. The coverage of shrub layer was63.95%and the coverage of herb layer was48.63%.However, the shrub layer affected the distribution of herb layer significantly. Compared withhealthy Masson pine stand, the root biomass of damaged Masson pine stand was decreased andits depth distribution became shallower (mainly with0-40cm), especially the fine root biomasswas decreased and mainly distributed in the soil layer of0-10cm and decreased rapidly withincreasing soil depth.2. Smaller needle size and slower litter-fall decomposition of damaged Masson pineforestsCompared with healthy Masson pine stands, the dead needles and green needle inlitter-fall of damaged stand were smaller, with a length of15.10cm and12.83cm, respectively;their weight of single needle was also lower, with the value of0.024g and0.019g, respectively;and the specific leaf area (SLA) of dead needles was higher (35.12cm2/g). This means that theneedles of damaged Masson pine stands became smaller and thinner. The canopy LAI ofdamaged Masson pines was as low as only1.25, much lower than that of healthy Masson pinestands (of3.76-3.94) located in other places. The LAI of the damaged Masson pine standsdecreased slowly from the beginning of a year until to April-May, and then gradually increaseduntil September-October, afterwards it decreased again gradually. This was an integrated resultof needle growth and litter-fall rhythm. The decomposition rate of un-decomposed litter waslower than that of other healthy Masson pine stands, with an annual quality loss rate of35.62%,a half-decomposition period of1.3years and a fully-decomposition (95%) period of l2.5years.3. Worse soil hydrological properties of damaged Masson pine forestsThe soil hydrological properties of0-10cm soil layer were the best in the damagedMasson pine stands; and they were moderate in the10-20cm soil layer and worse in deeper soillayers. The non-capillary porosity and infiltration rate decreased sharply with increasing soildepth; as a contrast, the non-capillary porosity in healthy Masson pine stands at other placesdecreased slowly with increasing soil depth. The water-retention functions of the soil ofdamaged Masson pine stands were pretty much the same with broadleaved-coniferous mixed forest, but significant worse than the broad-leaf forests and better than the bamboo forests inthe same study site. Compared with the healthy Masson pine stands of other places, the soilhydrological properties of damaged Masson pine stands were obviously worse, presenting by ahigher bulk density of each soil layer, lower infiltration rate and water-holding capacity of soil,and smaller porosity (including the capillary, non-capillary and total porosity).4. Increased annual litter-fall with less needles and more twigs and mainly concentrated indry-summer periodCompared with healthy or less damaged Masson pine stands, the annual litter-fall amountof damaged Masson pine stands was increased, but with changed composition, representing bya decreased needles and increased twigs. The order of weight percentage of litter-fallcomponents was: needles> twigs> debris> bark and cones> broad leaves. The variation oflitter-fall became quite sensitive to drought stress. The amount of all components of litter-fall,but except the broad leaves, was affected by the soil moisture, especially in the soil layers of30-40cm and40-50cm. Because of the drought stress, the pattern of litter-fall of damagedMasson pine stands has significantly changed, with more distributed in the dry-summer period.However, the litter-fall rhythm of broad-leaves tree species was not changed (by maintainingthe two litter-fall peaks in April-May and November-December), this shows that broad-leavestree species have a stronger adaptability than Masson pine in the acid rain region.5. The health decline of damaged Masson pines related with water deficit was caused bythe reduced water-absorbing abilityAn obvious patio-temporal variation of soil moisture was observed in the damagedMasson pine stands. Compared with other forest types at the same study sites, such as thebroadleaved-coniferous mixed forest, broad-leaf forest and bamboo forest, the soil moisture ofdamaged Masson pine stands was higher as a result of less canopy evapotranspiration and itwas pretty much the same of bamboo forest. The field capacity (or the capillary porosity) and82%of field capacity (or80%of capillary porosity) are two important thresholds of soilmoisture to affect the health condition of damaged Masson pines; the soil moisture lower than these thresholds will lead to a high defoliation. This was mainly caused by a relative soildrought due to the declined capacity of absorbing water as the result of the quantity reductionof fine root and its shallower distribution. This was confirmed by the observed relationbetween sap flow density of a nearly-dead Masson pine and soil moisture. Therefore, thedamaged Masson pines become very easily to suffer from water deficit stress, especially in thedry-summer period, regardless if the annual precipitation is abundant, normal or less thanaverage. This means that the water deficit has become a new stress besides the acidificationstress affecting the forest health condition.6. Reduced needles and fine-roots caused lower transpiration of damaged Masson pinesThe difference of sap flow density between individual sample trees of Masson pine wasmore directly affected by their difference in leaf area index, rather than by their dominancedetermined by their relative height in canopy. For example, when the dominant tree of No.3had a low LAI of0.68, its monthly sap flow density was lower than that of the co-dominanttree of No.4which has a higher LAI of1.46; but the monthly sap flow density of tree No.3washigher after its LAI surpassed the tree No.4. Generally, damaged Masson pine suffered fromhigh needle defoliation and this resulted to a reduced LAI of canopy. This caused a reduction oftree transpiration. Therefore, the soil moisture of damaged Masson pine stands was the highestamong the four forest types invested in the same study site. The monthly transpiration variedfrom10.19to48.89mm for the damaged Masson pine stands, with an average of27.24mm. Ithad a seasonal variation of firstly increase and then decrease. It reaches a peak of about40mm/month in the period of July to August. The tree transpiration is closely related with soilmoisture, so the lower water-availability caused by the reduced fine roots is also an importantreason of the lower transpiration of damaged Masson pine stands.7. Characteristics of hydrological processes and functions in damaged Masson pine standsThe damaged Masson pine stands presented a sparse canopy and lower canopyinterception capacity of1.54mm. This led to a higher through-fall ratio (84.66%), lower stemflow ratio (0.26%) and canopy interception ratio (15.07%) and the critical rainfall depth (5mm) to form stem flow. The humus quantity on the floor of damaged Masson pine stands was11.06t/hm2; the separately measured water-holding capacity of un-decomposed, half-decomposedhumus layer and the total humus layer was195.54%,214.48%and197.61%, respectively; thecorresponding water-holding capacity in depth was0.71,0.82and1.46mm, respectively. Allof them were lower than those of healthy Masson pine stands in other places (15.7-32.20t/hm2,203-277%,3.40-5.12mm). This shows that the hydrological functions of humus layer indamaged Masson pine stands was declined. The ratio of evapotranspiration in damagedMasson pine stands was reduced (to67.38%) during the study, while the runoff ratio wasincreased (to33.51%).更多还原