塔里木河下游河岸带植被的空间结构特征

揭示我国内陆河流域下游河岸带植被的空间结构特征, 对于了解我国西北干旱区荒漠河岸带植被的空间分布规律、指导荒漠化治理和内陆河水资源管理具有重要意义。该研究基于野外大范围植被调查数据支持下的遥感监督分类方法, 利用Landsat-8 OLI遥感数字图像, 辨识了塔里木河下游柽柳(Tamarix spp.)灌丛、胡杨(Populus euphratica)疏林和芦苇(Phragmites australis)草地3类主要的河岸带植被, 并利用建立的叶面积指数(LAI)遥感反演经验模型反演了研究区柽柳灌丛和胡杨疏林的叶面积指数, 旨在从区域尺度和总体趋势上分析荒漠河岸带植被的空间结构和分布特征。结果表明: 在有详细地物资料的基础上, 遥感监督分类可以作为一种干旱区荒漠河岸带植被分类的有效方法; 遥感分类结果显示塔里木河下游胡杨疏林分布面积约336.4 km², 柽柳灌丛约为405.3 km², 胡杨疏林总体更靠近河道, 柽柳灌丛分布范围更广; 河岸带植被LAI整体很低, 柽柳灌丛和胡杨疏林平均LAI值分别为0.253和0.252, LAI小于0.5的植被对应面积分别占柽柳灌丛和胡杨疏林总面积的92.4%和90.1%, 表明了塔里木河下游荒漠河岸植被空间上稀疏分布的特征; 统计结果显示, 河岸带植被结构存在巨大的空间变异性, 其中胡杨疏林比柽柳灌丛的空间变异性更大; 河岸带植被LAI随距河道距离呈现显著负指数分布规律, 在离河道1 km范围内LAI随离河道距离快速下降, 而1 km外区域叶面积指数普遍低于0.1, 表明植被主要分布在河道两侧1 km范围内。整体稀疏的空间分布、显著的空间变异性, 以及由LAI体现的植被盖度随距河道距离的负指数下降规律是荒漠河岸带植被空间结构的3个基本特征。     

Water sources of Populus euphratica and Tamarix ramosissima in Ejina Delta,the lower reaches of the Heihe River,China

Aims We aim to evaluate the water sources of typical riparian arbor species (Populus euphratica) and shrub species (Tamarix ramosissima), and analyze the spatial and temporal dynamics of plant water source in Ejina Delta, the lower reaches of the Heihe River, China.Methods Eight sampling sites were selected in the riparian zones along the East River and West River in Ejina. The plant xylem water, soil moisture, rainwater, stream water and groundwater were taken and pretreated during the growing season in 2015-2016, and the stable oxygen isotope ratio (δ¹⁸O) for each water sample was measured. The δ¹⁸O of plant xylem water and soil moisture were compared to estimate the dominant depth of root water uptake, and the linear-mixed model called “IsoSource” were applied to determine plant water sources and quantify their proportions.Important findings This study indicated that the main recharge sources for P. euphratica and T. ramosissima were stream water and groundwater. The contributions of rain water to them was negligible due to the limited amount and the shallow infiltration depth of local rainfall. As affected by groundwater level fluctuation, soil physical properties, as well as lateral and vertical recharge of stream water on soil moisture, the dominant depth of root water uptake spatially varied. However, the relative contributions of stream water or groundwater to plant water sources did not change significantly across space. Populus euphratica used more stream water (68%), while T. ramosissima used more groundwater (65%). Plant water sources were sensitive to environmental flow controls. The contributions of stream water to the water sources of the two species went up to 84% and 48% for P. euphratica and T. ramosissima respectively during the discharge period, but dropped to 63% and 30% during the non-discharge period. On the other hand, the contributions of groundwater decreased to 16% and 52% during the discharge period, but increased to 37% and 70% during non-discharge period. It is noteworthy that the high similarity of δ¹⁸O between stream water and groundwater due to extensive water exchange in the riparian zone made increase the uncertain in quantifying plant water sources.     

塔里木河下游胡杨空心特征

本文选取塔里木河下游阿拉干断面胡杨林长期监测样地,分析胡杨林空心率、树洞特征及其在不同胸径和树高组间的分布特点。结果表明: 研究区胡杨种群具有较高的空心现象,空心胡杨占调查胡杨总数量的56%,约159株·hm^-2;胡杨空心率在不同胸径和树高组间呈显著差异,其与胸径呈显著正相关,与树高呈显著负相关。该监测样地胡杨树洞密度约560个·hm^-2,平均每株2个;所调查的胡杨树洞大部分出现在树干上(57.1%),均以树干中部洞口为主(31.3%);直径为5~15 cm的树洞(38.2%)所占比例最大。总树洞数量、单株树洞数量、树洞直径等特征与胸径呈显著正相关,与树高呈显著负相关,而各树洞类型在不同胸径和树高组间的分布不同,变化趋势不一致。胡杨树洞在各方位上的分布差异显著,树洞集中分布在正西方向上。胡杨荒漠河岸林的空心发生率较为严重,且胸径越大其空穴化程度越明显。加强保育幼龄胡杨和修复退化荒漠河岸林具有重要意义。     

沙漠腹地天然绿洲不同林龄胡杨水分利用来源

了解干旱荒漠绿洲区主要植被的水分利用来源,能为该区域植被保护和水资源的合理分配提供科学依据.本研究以达里雅布依天然绿洲胡杨幼龄木(胸径DBH≤10 cm)、成熟木(10 cm＜DBH≤40 cm)和过熟木(DBH＞40 cm)为对象,测定不同林龄胡杨木质部水和潜在水源(地表水、0～3m土层土壤水、地下水)的氧同位素,运...     

腾格里沙漠东南缘不同植被类型土壤种子库多样性

为探究荒漠地区不同植被类型土壤种子库动态与分布规律,揭示不同植被类型群落的植被演替趋势与多样性特征,以腾格里沙漠东南缘胡杨群落、柠条群落、赖草群落和沙蓬群落为对象,采集0～2、2～5、5～10、10～20 cm土层土样,研究土壤种子库特征及其与地上植被的关系。结果表明: 4个植被类型的土壤种子库中共发现13种植物,隶属于3科12属,1、2年生草本植物种子占多数,藜科植物较多;土壤种子库密度较低,呈现柠条群落＞赖草群落＞胡杨群落＞沙蓬群落;种子库密度和植物种类整体随土壤剖面的加深而降低;综合Shannon指数、Simpson指数、Pielou指数和Patrick丰富度指数进行分析,土壤种子库物种多样性呈现胡杨群落＞赖草群落＞柠条群落＞沙蓬群落,柠条群落土壤种子库与地上植被相似性系数最高,沙蓬群落次之,胡杨群落和赖草群落最低。总体上,以胡杨群落为代表的乔木林较为稳定,以沙蓬群落为代表的沙地生态系统最为脆弱。     

林分、土壤及空间因子对谷地云冷杉林叶面积指数空间异质性的影响

叶面积指数(LAI)的空间异质性对研究植物的生长状况、分布格局及其对气候变化的响应机制至关重要, 然而关于不同因素对解释LAI空间变异相对贡献率的报道尚少。该研究依托小兴安岭9.12 hm ² (380 m × 240 m)谷地云冷杉林固定样地, 采用LAI-2200植物冠层分析仪测定了228个小样方(20 m × 20 m)的LAI, 基于地统计学方法分析了LAI的空间异质性; 测定了每个小样方的28个林分因子和10个土壤因子, 利用主轴邻距法(PCNM)量化了空间因子, 并采用方差分解的方法解析了林分、土壤、空间因子及其相互作用对LAI空间变异的相对贡献率。结果表明: LAI在37 m尺度内具有强烈的空间自相关, 且在不同方向上LAI呈现相异的空间格局; 3种因子及其相互作用共同解释了LAI空间变异的50.4%, 其中空间因子的贡献率最大, 单独解释了LAI空间变异的25.5%; 中等树(5 cm <胸径≤ 10 cm)的密度和主要树种(冷杉(Abies nephrolepis)和云杉(Picea spp.))的胸高断面积均与LAI显著正相关, 质量含水率与LAI显著负相关。总体来看, 空间自相关对小兴安岭谷地云冷杉林LAI空间异质性的决定作用明显强于林分因子和土壤因子。     

Distribution pattern and influencing factors of soil salinity at Tamarix cones in the Taklimakan Desert

柽柳(Tamarix chinensis)沙包是塔克拉玛干沙漠特殊的生物地貌景观, 对维持区域生态环境的稳定具有极其重要的作用。该研究采用野外调查与室内分析相结合的方法, 选取且末、阿拉尔、策勒、塔中4个典型区域的柽柳沙包为研究对象, 对柽柳沙包0-500 cm土壤垂直剖面进行采样, 测定土壤pH值、枯落物含量、电导率及HCO₃ ^-、Cl ^-、SO₄ ^2-、Ca ²⁺、Mg ²⁺、K ⁺、Na ⁺含量, 分析柽柳沙包中土壤盐分的空间变化规律及其影响因素。结果表明: 1)从且末、阿拉尔、策勒到塔中, 土壤pH值总体呈升高趋势, 土壤电导率及Na ⁺、Ca ²⁺、Mg ²⁺、SO₄ ^2-含量总体呈降低趋势, K ⁺、Cl ^-、HCO₃ ^-含量没有明显的变化规律。2)盐分在4个样区的垂直分布主要表现为: 且末和策勒样区柽柳沙包的土壤盐分呈表层聚集现象; 阿拉尔和塔中样区柽柳沙包的土壤盐分呈深层聚集现象。随着土层深度的增加, 土壤pH值总体呈升高的趋势, 土壤枯落物含量总体呈降低趋势; 土壤电导率在且末和策勒样区总体呈降低趋势, 阿拉尔样区呈先降低后升高再降低的变化趋势, 而塔中样区呈先升高后降低再升高的变化趋势。3)根据相关性分析和主成分分析, 且末样区土壤枯落物含量、SO₄ ^2-、Na ⁺、K ⁺为影响土壤盐分含量的主要因子, 且土壤盐分以硫酸盐为主; 阿拉尔样区影响土壤盐分组成的主要因子为Cl ^-、Na ⁺; 策勒样区为Cl ^-、K ⁺、Na ⁺; 塔中样区为Cl ^-、Na ⁺、Ca ²⁺、SO₄ ^2-, 且土壤盐分均以氯化物为主。综合分析表明, 不同区域柽柳沙包中土壤盐分存在空间变异性, 柽柳沙包土壤盐分的变化与干旱沙漠地区强烈的蒸发作用、地表风蚀强度、地下水埋深、土壤中枯落物及柽柳的生物积盐效应等因素密切相关, 是影响不同区域土壤盐分分布的关键因子。     

Exploring the influence of soil types underneath the canopy in winter wheat leaf area index remote estimating

Aims Remote sensing is an effective and nondestructive way to retrieve leaf area index (LAI) from plot, regional and global range. Soil background is one of the confounding factors limiting remotely estimating LAI. And soil type contains a large proportion of soil background information, which can influence the optical properties of vegetation canopy and soil. However, our knowledge on the effects stemmed from soil types underneath the canopy on LAI remote estimating have been in shortage. Thus, this study aims to explore the influences of soil types underneath the canopy on winter wheat LAI remote estimating. Methods We analyzed the sensitivity variation of eight spectral indices, named normalized difference vegetation index (NDVI), modified soil-adjusted vegetation index (MSAVI), modified chlorophyll absorption ratio index 2 (MCARI₂), red edge inflection point (REIP), red edge amplitude (Dr), red edge area (SDr), red edge symmetry (RES), normalized difference spectral index (NDSI), to LAI in different soil types, and then we identified some spectral intervals or parameters that were insensitive to soil type variations underneath the canopy. We also compared the accuracy of two commonly used regression models, partial least squares regression (PLSR) and random forest regression (RFR), in estimating LAI for different soil types. We also explored the problems arising from applying the regression model developed in single soil type area to complex soil types area in retrieving LAI. Important findings This paper demonstrates the effects of soil types underneath the canopy on LAI retrieving. 1) The sensitivity of spectral indices to LAI is significantly different due to the soil type variation, but REIP has the least effects from soil type variation among the eight spectral indices. Meanwhile, the band selection algorithm of lambda-by-lambda not only chooses the most sensitive spectral interval for LAI, but also provides a feasible way to construct the spectral index that exhibits strong resistances to the effects of soil types underneath the canopy. 2) The accuracy of LAI estimation by regression models differs under soil type considered or not. So we suggest that in small scale researches, especially in a field scale, the ability of regression models in explaining variables is the priority consideration, while the PLSR is superior to RFR in this respect. Under the premise of unknown priori knowledge of land surfaces, the RFR is more suitable for retrieving LAI than PLSR, but land surface priori knowledge is still necessary. These findings provide the theoretical basis and methods for developing remotely sensing estimating LAI models adapted to various land surfaces. Further analysis is needed in applying the findings in more crop types, cultivars and growth stages.     

Functional diversity of soil microorganisms in Casuarina equisetifolia woodlands of different stand ages in Hainan Island

为研究不同林龄木麻黄(Casuarina equisetifolia)林地土壤微生物功能多样性的动态变化, 通过Biolog系统对海口市桂林洋开发区滨海不同林龄(幼龄林(林龄5-8年)、中龄林(林龄15-20年)和成熟林(林龄30年及以上))的木麻黄林地土壤微生物的功能多样性进行了分析。结果表明: (1)对照裸地和成熟林林地土壤微生物对所使用的Biolog-ECO微孔板中的31种碳源的利用率和对这31种碳源的各分类碳源的利用率高于中龄林与幼龄林林地; (2) Shannon-Wiener指数(H′), McIntosh、Simpson多样性指数随着林龄增大而增大, 不同林龄林地间的H′差异显著, 幼龄林和中龄林的McIntosh、Simpson多样性指数无显著差异; (3)主成分分析结果表明, 在主成分分离中起分异作用的主要碳源为单糖和氨基酸。林地土壤微生物群落多样性随着林龄增加而增高, 这可能是林分凋落物、植物根系分泌的次生代谢物、土壤养分、林地土壤特异性微生物等共同作用的结果。     

Measuring seasonal dynamics of leaf area index in a mixed conifer-broadleaved forest with direct and indirect methods

利用光学仪器法能够快速、高效地测定森林生态系统的叶面积指数(leaf area index, LAI)。然而, 评估该方法测定针阔混交林LAI季节动态准确性的研究较少。该研究基于凋落物法测定了小兴安岭地区阔叶红松(Pinus koraiensis)林LAI的季节动态, 其结果可代表真实的LAI。参考真实的LAI, 对半球摄影法(digital hemispherical photography, DHP)和LAI-2000植物冠层分析仪测定的有效叶面积指数(effective LAI, L_e)进行了评估。首先对DHP测定LAI过程中采用的不合理曝光模式(自动曝光)进行了系统校正。同时, 测定了光学仪器法估测LAI的主要影响因素(包括木质比例(woody-to-total area ratio, α)、集聚指数(clumping index, Ω_E)和针簇比(needle-to-shoot area ratio, γ_E))的季节变化。结果表明: 3种不同方法测定的LAI均表现为单峰型的季节变化, 8月初达到峰值。从5月至11月, DHP测定的L_e比真实的LAI低估50%-59%, 平均低估55%; 而LAI-2000植物冠层分析仪测定的L_e比真实的LAI低估19%-35%, 平均低估27%。DHP测定的L_e 经过自动曝光, α、Ω_E和γ_E校正后, 精度明显提高, 但仍比真实的LAI低估6%-15%, 平均低估9%; 相对而言, LAI-2000植物冠层分析仪测定的L_e经过α、Ω_E和γ_E校正后, 精度明显提高, 各时期与真实的LAI的差异均小于9%。研究结果表明, 考虑木质部和集聚效应对光学仪器法的影响后, DHP和LAI-2000植物冠层分析仪均能相对准确地测定针阔混交林LAI的季节动态, 其中, DHP的测定精度高于85%, 而LAI-2000植物冠层分析仪的测定精度高于91%。     

Carbon density characteristics of sparse Ulmus pumila forest and Populus simonii plantation in Onqin Daga Sandy Land and their relationships with stand age

Aims
Sparse Ulmus pumila forest is an intrazonal vegetation in Onqin Daga Sandy Land, while Populus simonii has been widely planted for windbreak and sand dune stabilization in the same region. Our objective was to compare the differences in carbon (C) density of these two forests and their relationships with stand age.
Methods
We measured the C content of tree organs (leaf, twig, stem, and root), herb layers (above ground vegetation and below ground root) and soil layers (up to 100 cm) in sparse Ulmus pumila forests and Populus simonii plantations of different stand ages, and then computed C density and their proportions in total ecosystem carbon density. In addition, we illustrated the variation in carbon density-stand age relationship for tree layer, soil layer and whole ecosystem. We finally estimated the C sequestration rates for these two forests by the space-for-time substitution approach.
Important findings
The average C contents of tree layer and soil layer for sparse Ulmus pumila forests were lower than those for Populus simonii plantations. The total C density of sparse Ulmus pumila forests was half of that of Populus simonii plantations. The carbon density of soil and tree layers accounted for more than 98% of ecosystem C density in the two forests. Irrespective of forest type, the C density ratios of soil to vegetation decreased with stand age. This ratio was 1.66 for sparse Ulmus pumila forests and 1.87 for Populus simonii plantations when they were over-matured. The C density of tree layer, soil layer, and total ecosystem in both forests increased along forest development. There were significantly positive correlations between tree layer’s C density and stand age in both forests and between the total ecosystem C density of sparse Ulmus pumila forests and stand age. The C sequestration rate of tree layer was 5-fold higher in Populus simonii plantation than in sparse Ulmus pumila forest. The ecosystem-level C sequestration rate was 0.81 Mg C·hm^-2·a^-1 for sparse Ulmus pumila forest and 5.35 Mg C·hm^-2·a^-1 for Populus simonii plantation. These findings have implications for C stock estimation of sandy land forest ecosystems and policy-making of ecological restoration and C sink enhancement in the studied area.     

Eurasian badger habitat selection in Mediterranean environments: Does scale really matter?

It is widely believed that spatial scale affects habitat selection, and should influence management options, especially for species with wide geographic distribution or large territories. Eurasian badger habitat selection has been well studied throughout most of its European distribution range, but never at multiple spatial scales. We used compositional analysis to assess habitat selection of Eurasian badgers in southern Portugal at four spatial scales (1, 4, 25, and 100 km²). We assessed habitat use from setts, latrines and footprints presence, and road kills. Oak woodlands with understorey were selected at all scales, being the most preferred habitat at 3 scales (1, 4, and 100 km²). Pastures were most selected at the scale of the 25 km² cell, but their use was not significantly different from oak woodland with understorey. Shrubs and pastures were also secondly important at the majority of scales. Contrary to findings at northern latitudes, deciduous forests decreased in importance as cell size increased. In the highly humanized and fragmented landscape of southern Portugal, Eurasian badgers are selecting the matrix of oak woodlands interspersed with patches of pastures, shrubs and riparian vegetation. In these oak woodlands, scale does not have a marked effect. Management for badgers should provide, for at least, 30% of oak woodland cover at all scales. Our study illustrates the across-scale importance of maintaining the historically human altered, sustainable and unique landscape and land use system – the montado.     

Main plant communities and characteristics of Kalamaili Ungulate Nature Reserve in east Junggar Basin

The main vegetation types of Kalamaili Nature Reserve in east Junggar Basin were investigated in this paper, and based on the data from 54 plot samples, the characteristics of the main desert plant communities from the main vegetation types were quantitatively described. And the results showed that, the vegetation in this reserve can be divided in to 9 major desert plant community types were recognized: Form. Haloxylon ammodendron, Form. Krascheninnikovia ceratoides, Form. Atraphaxis spinosa, Form. Reaumuria songarica, Form. Artemisia songarica, Form. Convolvulus tragacanthoides, Form. Anabasis salsa, Form. Stipa glareosa and Form. Seriphidium terrae-albae, and then, 16 associations were divided from these 9 major community types.     

Spatiotemporal variation and scale effect of canopy leaf area index of larch plantation on a slope of the semi-humid Liupan Mountains,Ningxia, China

Aims Leaf area index (LAI) is an important canopy structure parameter characterizing ecological and hydrological processes, such as forest growth, canopy interception and transpiration. Forest LAI is limited by both light and soil water availability, thus may vary with slope position and seasonality. This study is aimed at the spatiotemporal variation of LAI and its relationship with environmental variables. Methods A 34-years-old Larix gmelinii var. principis-rupprechtii planted forest situated on a typical slope located in a small watershed of Xiangshuihe within Liupan Mountains was selected for LAI observations. Sixteen plots along a 30 m wide transect along the slope was surveyed from May to October of 2015 to measure the monthly canopy LAI. Important findings It showed there was a remarkable difference of LAI among slope positions. The LAI in May decreased toward downslope direction with a scale effect of -0.02/100 m. Whereas for the period from June to August, LAI showed a nonlinear variation along slope positions: increasing from to top slope downward, reaching its maximum at the middle slope, and then decreasing to the slope foot. The scale effect of LAI was +0.15/100, +0.16/100, and +0.18/100 m in the slope range (downward positive) of 0-244.2 m, but -0.09/100, -0.08/100, and -0.07/100 m in the slope range of 244.2-425.1 m for June, July and August, respectively. The LAI increased toward downslope in September and October, with a slope scale effect of +0.03/100 m and +0.09/100 m, respectively. The seasonal variation of LAI-slope relationship showed a shift from the light and temperature control in the early growing season, to the soil water resources control in the mid growing season, and then to an integrated control of many factors in the late growing season. In the early growing season when soil moisture and nutrients were abundant, terrain shading limited the leaf growth in middle and downslope. From early to the mid growing season, the soil moisture on the slope was quickly depleted due to fast evapotranspiration and poor moisture retention of the coarse soil. On the other hand, average solar height increased, and allowed direct light radiation to penetrate to the middle then downslope. The result is that the leaf growth in the middle slope was the strongest in the mid growing season. During the late growing season, the temperature decreased fast in the mountain top to incur earlier leaf fall than the mountain foot. Thus the LAI exhibited the increasing trend toward the downslope.     

胡杨组织培养叶片及插穗毛状根发生

胡杨(Populus euphratica)是唯一分布在干旱沙漠地区的高大乔木, 根蘖能力强, 但自然条件下插穗难以生根, 扦插繁殖困难。该文研究发根农杆菌菌株ATCC11325诱导胡杨发根, 菌液浓度为OD₆₀₀=0.4, 添加100 mg·L^-1乙酰丁香酮, 叶片切段划伤预培养后侵染10分钟, 培养20天, 在叶片创伤部位诱导发生无向性的健壮毛状根; 浸染肉质根插穗, 须根发生和植株成活率从20%提高到60%, 且地上部分分枝多, 生长茂盛。该发根农杆菌菌株显著促进胡杨插穗生根成活。     

基于稳定同位素技术的塔里木河下游不同林龄胡杨的水分利用来源

水分是制约很多陆地生态系统植物生长和繁殖的重要因素, 在干旱地区尤为明显。利用稳定同位素技术探究塔里木河下游不同林龄胡杨(Populus euphratica)的水分来源情况, 了解生态输水背景下荒漠河岸林的水分利用循环与利用策略, 可为生态输水提供科学依据, 同时也可对同类地区的生态恢复提供借鉴。本研究通过测定塔里木河下游胡杨茎干水和各潜在水源(土壤水、地下水)的稳定氢氧同位素值(δD、δ¹⁸O), 应用多源线性混合模型(IsoSource)分析了各潜在水源对不同林龄胡杨的贡献比例, 并结合3种林龄胡杨不同土壤深度含水量的变化, 分析了胡杨的主要吸水层位。结果表明: (1)不同林龄胡杨样地的不同深度区间上的土壤水δ¹⁸O值存在显著差异(P < 0.05): 胡杨幼龄木、成熟木、过熟木木质部δ¹⁸O分别为-7.83 ± 0.07‰、-8.53 ± 0.11‰、-9.36 ± 0.21‰; 而δD值不存在显著差异(P > 0.05)。可据此来推断胡杨的主要吸水层位。(2)总体上, 三种林龄胡杨土壤水δ¹⁸O值随土壤深度增加而减小, 并趋于接近地下水的δ¹⁸O值。其中, 0-60 cm土壤水受蒸发影响比较大, 其同位素组成经历了强烈的蒸发分馏过程, 土壤含水量极少, 土壤水δ¹⁸O值偏正。(3)不同林龄胡杨所利用的水分来源不同: 胡杨幼龄木对于地表80 cm以下的土壤水以及地下水均有一定程度的利用, 对80-140 cm、140-220 cm和220-340 cm的土壤水平均利用比率依次为16.2%、21.4%和24.6%, 对地下水平均利用比率为24.5%; 成熟木主要利用220-340 cm的土壤水及地下水, 平均利用比率分别为36.9%和42.3%; 过熟木主要利用140-340 cm的土壤水及地下水, 平均利用比率分别为32.8%和49.3%。     

Improving the accuracy of indirect methods in estimating leaf area index using three correction schemes in a Larix gmelinii plantation

Aims Woody materials and clumping effects are key error sources in estimating leaf area index (LAI) by optical methods. However, how to correct the error caused by woody materials has not reached consensus. The aims of this study are (1) to evaluate the accuracy of optical methods for estimating effective LAI (L_e) in a deciduous needle leaf forest stand, and (2) to develop a practical correction scheme to improve the accuracy of optical methods in estimating LAI.Methods L_ewas estimated by two indirect methods (i.e., digital hemispherical photography (DHP) and LAI-2000 plant canopy analyzer method (LAI-2000 method) in an annual maximum leaf area period in a Larix gmelinii plantation. Then, we developed three correction schemes to improve the accuracy of indirect methods in estimating LAI. Meanwhile, two direct methods (i.e., litter collection and allometry methods) were used to estimate LAI. Taking LAI from litter collection as a reference, we evaluated the effectiveness of three correction schemes and tested the influence of zenith angle ranges on the correction results.Important findings With zenith angle ranges of 0-45° (rings 1-3), 0-60° (rings 1-4), 45°-60° (ring 4) and 0-75° (rings 1-5), L_eobtained from DHP underestimated LAI from both litter collection and allometry by 19%-32% and 18%-29%, respectively. L_efrom LAI-2000 method with four zenith angles also underestimated LAI from both litter collection and allometry by 9%-30% and 8%-28%, respectively. Although the contribution of woody materials to LAI was overestimated in correction scheme A, it was effective in correcting L_efrom DHP with zenith angles of 45º-60º (ring 4), and also effective for L_efrom LAI-2000 method with zenith angles of rings both 1-3 and 1-4. Correction scheme B was all effective in correcting L_efrom DHP with four zenith angle ranges. Generally, correction scheme C was more effective than other two schemes in correcting L_efrom both DHP and LAI-2000 method with four zenith angle ranges. These results indicate that the zenith angle range is a key factor for determining the accuracy of optical methods in estimating LAI besides woody materials and clumping effects.     

中国典型陆地生态系统波文比特征及影响因素

波文比(β)是陆面过程中的重要参数, 影响着地表和大气间的能量交换, 明确β的空间变异规律和影响因素有助于对地表能量平衡和气候间反馈关系的预测。该研究收集了在中国不同生态系统类型开展的用涡度相关法(EC)测量地表能量平衡的公开发表文献, 构建了β和气象环境因子数据库, 分析了β在生态系统之间的差异、空间变异特征及影响因素。主要结果: (1)所有生态系统β平均值为0.95 ± 0.64, 变异系数67%, 偏度1.58, 峰度3.07, 整体服从对数正态分布, β平均值最高为灌木生态系统(1.26), 最低为湿地生态系统(0.49)。(2) β在生态系统类型间差异显著: 森林和湿地生态系统β无显著差异, 灌木生态系统β >草地生态系统 β >森林和湿地生态系统 β, 农田生态系统β介于草地生态系统与森林和湿地生态系统之间。(3) β随着纬度的增加而增加, 不随经度和海拔变化。纬度每增加1°,β增加0.038。(4) β随着年降水量(MAP)、年平均气温(MAT)、净辐射(R_n)、当年降水量(PPT)、当年平均气温(T_a)和叶面积指数(LAI)的增加而降低。(5)不同生态系统中β对生物和非生物因素的响应存在显著差异: 草地、森林和灌木生态系统的β对生物和非生物因素变化较为敏感, 而农田和湿地生态系统的β与所有生物和非生物因素均无显著相关关系。(6) MAP和R_n是β变化的直接影响因素, LAI通过影响R_n间接影响β。结果表明了植被类型与气候因素之间具有交互作用, 能量分配最主要的影响因素是降水, 叶面积对能量分配的调节作用并不显著。     

Temporal areal changes of wetlands in the lower reaches of the Tarim River and their responses to ecological water conveyance

及时了解和定量分析荒漠区河岸带湿地月度时序变化趋势及对生态输水过程的响应, 对认识湿地生态修复过程, 改进生态输水策略, 维护湿地生态系统稳定具有重要意义。该文基于Landsat ETM+/TM/OLI和Sentinel 2形成的月尺度的密集长时序遥感数据, 分析2000-2018年塔里木河下游英苏-阿拉干之间的湿地时序变化特征, 并评估湿地变化对生态输水过程的响应。结果表明: 近19年来湿地面积持续增加, 其中2011-2013年和2017-2018年是面积快速增加的时段。不同的单、双通道输水方式和输水量大小解释了喀尔达依湿地与博孜库勒湿地在不同时段增长的快慢。对湿地面积与生态输水量、地下水埋深关系的分析表明, 累计生态输水量的持续增加是近20年来塔里木河下游河岸带湿地扩张的重要因素, 每年大于3.5亿m ³的双通道生态输水, 地下水埋深维持在-5.0- -3.5 m是湿地持续稳定增长的关键。     

塔里木河干流胡杨径向生长对地表径流变化的响应

以塔里木河干流荒漠河岸胡杨(Populuseuphratica)为研究对象,在塔里木河干流河道上游和中游选择帕满水库和坎白尔吾斯坦2个断面,分析胡杨径向生长的特点。根据不同断面的河道径流数据,采用小波分析和相关性分析方法研究塔里木河胡杨径向生长随径流动态变化的响应。结果表明,帕满水库-新其满断面,胡杨基部断面生长增量(BAI)与径流在15–24年时间尺度上都发生震荡,且径流震荡年份要早于基部断面生长增量震荡年份。坎白尔吾斯坦-英巴扎断面,胡杨BAI与径流在10–20年时间尺度上都发生震荡,BAI震荡周期出现时间较晚。在塔里木河干流沿岸,径流是胡杨径向生长的主要限制因素之一。上游帕满水库断面,胡杨BAI与前一年11月至当年3月的径流量呈显著相关;中游坎白尔吾斯坦断面,胡杨BAI与前一年12月至当年3月的径流量呈显著相关。塔里木河不同河段胡杨BAI对径流变化响应的敏感度存在差异。研究表明,塔里木河上游采样区胡杨生长良好,所对应的最佳径流达1.3340×10~8 m~3;塔里木河中游采样区胡杨径向生长的最合理径流量的范围为0.380 3×10~8–1.205 6×10~8 m~3。