不同重金属污染水平下生物结皮及下层土壤细菌群落的差异性分析

为了探究生物结皮及下层土壤细菌群落多样性及结构在不同重金属污染水平下的差异及其影响因素,以宁夏东部工矿区和封育草地内广泛分布的两类生物结皮为研究对象,采用高通量测序技术,分析结皮层(A层)和结皮下层(B层)土壤细菌群落结构和多样性差异。采用相关分析、冗余分析探讨两个生境生物结皮各层次细菌群落与土壤环境因子的关系。结果表明：(1)相较于封育区,工矿区2类生物结皮对源自大气降尘的重金属元素具有更显著的表层富集作用,并表现出显著的种间差异：苔藓结皮>藻结皮。污染负荷指数评价结果显示：工矿区生物结皮各层次重金属污染程度更高,且均表现为A层污染程度高于B层。(2)两个生境的优势细菌门组成基本一致,均为放线菌门、变形菌门、酸杆菌门。受生物结皮类型、重金属污染程度的影响,细菌群落结构差异显著,主要表现为：工矿区藻结皮A、B层的α多样性指数均大于封育区,而苔藓结皮A、B层的细菌多样性指数高于封育区,丰富度指数低于封育区。主坐标分析结果显示,不同生境的生物结皮细菌群落结构差异明显,而同一生境的生物结皮细菌群落结构相似。重金属As、Pb、土壤黏粒含量和pH是影响生物结皮细菌群落结构的主要土壤环境因子...     

混合生物结皮对土壤养分的影响与群落结构之关联——以黄土丘陵区的生物结皮为例

自然条件下生物结皮是藻、藓及地衣等结皮类型以不同比例组成的混合群落，显著影响土壤养分含量，目前混合生物结皮对土壤养分的影响与其群落结构的关系尚不清楚，限制了混合生物结皮土壤养分的评估。为此，研究通过测定单一组成的藻结皮、藓结皮以及80%藻+20%藓、60%藻+40%藓、40%藻+60%藓和20%藻+80%藓4个不同藻藓比例的混合生物结皮土壤有机碳、全氮、全磷、速效磷、铵态氮和硝态氮含量，研究了混合生物结皮土壤养分与其群落结构之间的关联。结果显示：(1)藓结皮层土壤有机碳、全氮、速效磷、铵态氮和硝态氮含量显著高于藻结皮，分别高出166.4%、77.2%、55.1%、56.2%和42.2%。(2)藻藓混合生物结皮土壤有机碳、全氮、速效磷和铵态氮含量与组成和盖度等结构特征有关，可以通过单一类型生物结皮土壤养分含量与盖度加权预测混合生物结皮土壤养分储量。(3)混合生物结皮土壤有机碳、全氮、速效磷和铵态氮储量实测值(x)与预测值(y)拟合的线性函数分别为y=0.97x、y=0.96x、y=1.18x和y=0.92x。(4)混合生物结皮对全磷和硝态氮含量的影响与群落结构无关。生物结皮对下层0—5 ...     

巴丹吉林沙漠东南缘沙米群落分布与土壤因子的关系北大核心CSCD

基于野外样地调查资料,运用数量分类与排序的方法,对巴丹吉林沙漠东南缘沙米群落分布与土壤因子的关系进行探讨,以期为沙米人工驯化栽培提供理论支撑。结果表明:沙米群落共包括植物种21个,其中苋科8个种,禾本科、菊科各3个种,柽柳科2个植物种,蒺藜科、豆科、茄科、蓼科、白花丹科各1个植物种。双向指示种分析(TWINSPAN)将沙米群落分为7个群丛。群丛Ⅰ到群丛Ⅶ的变化过程中,土壤水分由5.12%逐渐降低至1.01%;土壤粘粒含量由6.32%逐渐降低至2.53%。群丛Ⅰ土壤砂粒含量由78.25%逐渐增大至群丛Ⅵ的89.84%和群丛Ⅶ的87.78%。各群丛土壤有机质、全氮、速效磷、pH、电导率呈波动变化。典范对应分析(CCA)结果表明,土壤因子解释30.8%的沙米群丛总变差,解释贡献率大小排序为土壤水分(6.8%)>pH(5.3%)>速效磷(4.4%)>有机质(4.4%)>全氮(3.6%)>土壤粉粒(2.3%)>土壤电导率(2.2%)>土壤砂粒(1.9%)。其中,土壤水分、pH、有机质、速效磷是影响沙米群落分布的重要环境调控因子。沙米人工栽培过程除了保证正常的水分供应外,还应注重土壤有机质和速效磷的补充。     

火电厂周边不同生物结皮细菌群落特征差异及其影响因素

为探究大气降尘重金属污染对矿区周边不同类型生物结皮细菌群落结构的影响,利用高通量测序技术分析位于宁东能源化工基地典型火电厂周边的3类生物结皮(藻结皮ZB、混生结皮HB、苔藓结皮TB)和对照(CK,裸土)的细菌丰度和群落结构,并探讨了影响细菌群落结构的环境因子。结果表明: 不同类型生物结皮的理化性质和重金属含量存在差异,且由于生物结皮对大气降尘重金属的富集作用造成各类结皮均达重度污染级别。在相对丰度排名前10的优势细菌门中,芽单胞菌门、蓝细菌门在不同类型生物结皮之间差异显著。细菌群落α多样性由高到低排序依次为CK>TB>HB>ZB。非度量多维排序(NMDS)结果显示,裸土细菌群落与其他3种生物结皮存在明显差异。相关性分析表明,生物结皮演替对细菌群落组成具有显著影响,细菌多样性和组成与pH、养分、重金属含量等密切相关。放线菌门、绿弯菌门相对丰度与pH值呈显著正相关关系,而与全氮(TN)、全磷(TP)、Pb、Zn、Cd均呈显著负相关关系;冗余分析结果表明,TN、pH、TP、有机碳(SOC)是影响3种生物结皮细菌群落α多样性以及一些优势菌群相对丰度的主要土壤环境因子,而重金属Pb、Zn、Cd是影响细菌群落结构的主要重金属元素,对细菌群落数量和多样性有抑制或刺激作用。说明pH、重金属和养分是影响结皮细菌群落组成的关键因子。总体而言,长期的重金属富集作用会对生物结皮的细菌多样性和群落组成产生影响。     

封育对高寒草甸植物群落构成及生态位特征的影响

封育是天然草地管理的一种有效措施,利于草地生产力提高和退化草地恢复。该研究通过对青藏高原高寒草甸放牧和封育草地物种多样性、植被构成、植物种生态位特征、草地演替度等分析,解析高寒草甸植物种间关系及草地演替方向。结果表明:(1)封育显著降低了草地群落植物物种数以及α和β多样性指数,显著增加了草地1年生植物种数、地面芽植物种数和地上生物量。(2)放牧草地地上生物量以莎草科(59.7%)和禾本科(23.9%)为主,封育草地地上生物量以禾本科(85.0%)为主;放牧草地优势种为矮嵩草(Kobresia humilis)和线叶嵩草(K.capillifolia),封育草地优势种为垂穗披碱草(Elymus nutans)和早熟禾(Poasp.)。(3)放牧和封育草地的群落植物种重要值均与各自的生态位宽度变化规律一致。(4)草地植物种间竞争主要发生在不同科属植物种之间,封育增加了群落植物种整体生态位重叠值和植物种间竞争。(5)草地群落演替度为封育地放牧地,封育群落处于较稳定状态。研究认为,封育促进了高寒草甸由莎草+杂类草群落向禾草+杂类草群落演替。     

模拟放牧干扰对黄土丘陵区生物结皮坡面土壤水分入渗的影响

水分是黄土高原地区植被恢复的关键影响因子,该区广泛分布的生物结皮显著影响土壤水分入渗。干扰影响生物结皮土壤水分入渗,但目前不同强度的干扰对生物结皮土壤水分入渗的影响仍不明确。本研究以黄土丘陵区吴起县合沟小流域的生物结皮坡面为对象,模拟羊蹄踩踏干扰,研究10%、20%、30%和40%干扰强度(以生物结皮破损度表征)对生物结皮坡面地表覆被的影响,采用线源入流入渗法观测了不同强度干扰后土壤水分入渗特征,通过结构方程模型和相关性分析,探索了干扰对生物结皮坡面土壤水分入渗的影响机制。结果表明:与对照(不干扰)相比,10%干扰强度下藻结皮盖度显著增加33.6%,20%干扰强度对藻结皮盖度无显著影响,30%和40%干扰强度下藻结皮盖度分别显著降低了36.1%和75.0%;40%干扰强度显著增加了枯落物盖度(34.3%),其他处理无显著影响;10%、20%和30%干扰强度下地表粗糙度分别显著降低了22.3%、11.1%和5.6%,40%干扰强度下增加了8.2%;40%干扰强度下初始入渗率显著增加了77.1%,其他干扰强度无显著影响;不同干扰对土壤稳定入渗率和平均入渗率无显著影响。可见,干扰主要通过降低藻结皮盖度,增加枯落物盖度和改变地表粗糙度,进而促进了土壤水分初始入渗。本研究可为黄土高原退耕地生物结皮管理提供科学依据。     

黄土丘陵区生物结皮群落组成与水分入渗的关系

黄土丘陵区坡面尺度生物结皮多是由藻、藓和地衣等以不同比例、不同方式组合的一个复杂群落结构,显著影响水分入渗,但目前混合生物结皮水分入渗与其群落结构之间的关系仍不清楚,妨碍了对坡面尺度生物结皮土壤渗透性的评估。本研究测定了藻结皮、藓结皮及藓结皮盖度分别为<15%、15%～30%、30%～45%、45%～60%、＞60% 5个不同藻藓比例的混合生物结皮的稳定入渗速率,采用主成分分析和通径分析揭示混合生物结皮水分稳定入渗速率的影响因素,明确混合生物结皮水分稳定入渗速率与群落结构之间的关系。结果表明: 藻结皮和藓结皮土壤饱和导水率分别为0.66和2.40 mm·min^-1。藓结皮盖度从<15%到>60%的混合生物结皮的稳定入渗速率为0.80～2.30 mm·min^-1。混合生物结皮水分稳定入渗速率主要与藓结皮盖度和藓结皮改善的土壤孔隙结构密切相关,相关系数分别为0.636(P=0.011)和0.835(P=0.000)。通过藻结皮和藓结皮土壤饱和导水率与盖度加权预测的混合生物结皮水分入渗量(y)与混合生物结皮实测水分入渗量(x)具有极显著相关关系(r=0.945),二者拟合的线性函数为y=0.85x(R²=0.98,P<0.05)。本研究明确了混合生物结皮水分入渗与单一组成生物结皮水分入渗之间的关系,为准确评估该区生物结皮水文过程提供了科学依据。     

基于CCA的坡面尺度生物结皮空间分布

生物结皮是干旱半干旱地区普遍存在的活地被物,在该区生态系统中具有重要的生态功能。探讨生物结皮的空间分布规律是科学管理该资源的理论基础。选择黄土高原水蚀风蚀交错区六道沟小流域内的典型坡面,通过全面调查并应用GS+和CANOCO统计软件进行分析,探讨了坡面尺度上生物结皮的空间分布特征及其影响因子。结果表明:(1)生物结皮的分布具有明显的空间分异性。沙土区生物结皮以大面积连续分布为主,平均结皮盖度在30%以上;在黄土区则以零星分布为主,结皮盖度大都在20%以下,主要分布在坡的边缘和末端。而生物结皮厚度和抗剪强度的空间变异不大,说明其主要与生物结皮的发育年限有关。(2)典范对应分析(CCA)表明:生物结皮的空间分布与土壤、植被、地表湿度、坡度坡向等有密切关系。其中,土壤类型和生物结皮的空间分布关系最大,可以解释生物结皮空间变异的20%。其次是植被群落类型和地形湿度指数,沙蒿(Artemisia desertorum Spreng.Syst.Veg.)地和小叶杨(Populus simonii Carr.)林地是其最理想的生长环境;其他如坡度、坡向、太阳辐射等也都对生物结皮的分布有一定的影响。总体上,生物结皮具有明显的地形、土壤和植被群落的选择性,偏向于生长在较湿润的沙生植被群落当中。     

不同干扰对黄土区典型草原物种多样性和生物量的影响

对黄土区典型草原进行封育+施肥(EF)、封育+火烧(EB)、封育(E)和放牧(G)处理,实地调查分析群落盖度、高度、密度、地上现存量和物种多样性,以研究不同干扰对黄土区典型草原群落物种多样性和生物量的影响.结果表明:在4种干扰类型中,施肥+封育草地群落盖度和地上生物量最高,且优势度指数最高,这与禾本科草占优势地位有关,群落均匀度指数和多样性指数最低,符合“生态位理论”;放牧地群落高度、盖度、密度和地上现存量最低,群落丰富度指数和多样性指数最高,支持“中度干扰理论”;封育地密度和均匀度指数最高;具体表现为:4种干扰类型地上生物量的变化趋势为封育+施肥＞封育+火烧＞封育＞放牧;说明长时间的封育对草地是一种严重干扰.群落丰富度指数(R和Ma)的排列顺序为放牧＞封育+施肥＞封育+火烧＞封育,群落物种多样性指数(H'和D)的排列顺序为放牧＞封育＞封育+火烧＞封育+施肥,优势度指数与多样性指数相反,群落均匀度指数(Jsw和Ea)的排列顺序为封育＞放牧＞封育+火烧＞封育+施肥.不同干扰样地群落生产力与Shannon-Wiener和Simpson 多样性指数间呈负相关关系,这个结论可以用地上/地下竞争的相互作用来解释.     

三峡库区苔藓生物结皮对土壤水分入渗的影响

在三峡库区王家桥小流域选取以苔藓为优势种的生物结皮样地,以附近无结皮发育的裸地为对照,设计5个盖度水平(1%～20%、20%～40%、40%～60%、60%～80%和80%～100%),采用环刀法测定土壤入渗过程,研究生物结皮盖度对入渗过程的影响。结果表明: 与裸地相比,生物结皮发育可显著提高表层土壤粘结力、孔隙度、黏粒含量、水稳性团聚体和有机碳含量,显著降低土壤容重和砂粒含量。生物结皮促进了土壤水分入渗,初始入渗率、稳定入渗率、平均入渗率和累积入渗量可达裸地的2.0倍及以上,土壤入渗性能随结皮盖度的增大呈先增加后减小的变化规律,在40%～60%盖度下最大。通径分析显示,土壤初始入渗率主要受结皮盖度、土壤容重和有机碳含量的影响,稳定入渗率主要受结皮盖度和土壤容重的影响。Horton模型对三峡库区生物结皮覆盖土壤的水分入渗过程拟合效果最佳。     

Exclusion effects on vegetation characteristics and their correlation to soil factors in the semi-arid rangeland of Mu Us Sandland,China

Exclusion has been applied as a main measure for re-vegetation all over the world.This paper,by comparing the results of year-round exclusion,seasonal exclusion,and non-exclusion,quantified the vegetation variations under three different exclusion measures and their correlation to soil factors.The analysis results for community species component and plant diversity using multi-response permutation procedures (MRPPs)showed that exclusion did change the species component and increase plant diversity remarkably,while the period of exclusion had no significant influence on these two community features.The indicator species analysis and calculation of similarity indices indicated that community for year-round exclusion were becoming xerophytization and unpalatability,and showed highly spatial heterogeneity of plant species distribution,whereas community for seasonal exclusion was under stable non-equilibrium condition.Detrended correspondence analysis (DCA)and detrend canonical correspondence analysis (DCCA)results of relationship between plant species and soil variables demonstrated that soil moisture was a controlling factor for plant species component,microbiotic soil crust cover,soil organic matter,and soil bulk density had significant effects on soil moisture,among which microbiotic soil crust was a leading factor owing to its limitation to rainfall infiltration on the one hand,and its constraints to entrance of herbaceous seeds into soil or to germination of soil seeds on the other hand.As a result of long-term removal of animal grazing,crust kept intact in year-round exclusion community,which was a main reason of community xerophytization.It was also obvious from ordination results that some important environmental factors,such as tempo-spatial change of rainfall and corresponding tempo-spatial change of soil moisture,were neglected during direct gradient analysis.In addition,biodiversity was close related to soil nutrients as well as to soil moisture condition (soil water content and crust cover),and it had positive relation to available N,and negative relation to available P.Higher soil N had advantage to non-leguminous plants growth on nutrition-poor sand land definitely.The impact of P to community component was unclear and should be studied from plant physiology.Further researches on nonequilibrium theory in semi-arid rangeland will provide a scientific and flexible animal development paradigm for being implementing livestock fen-raising and grazing-forbidden policies in China.     

Exclusion effects on vegetation characteristics and their correlation to soil factors in the semi-arid rangeland of Mu Us Sandland, China

Exclusion has been applied as a main measure for re-vegetation all over the world. This paper, by comparing the results of year-round exclusion, seasonal exclusion, and non-exclusion, quantified the vegetation variations under three different exclusion measures and their correlation to soil factors. The analysis results for community species component and plant diversity using multi-response permutation procedures (MRPPs) showed that exclusion did change the species component and increase plant diversity remarkably, while the period of exclusion had no significant influence on these two community features. The indicator species analysis and calculation of similarity indices indicated that community for year-round exclusion were becoming xerophytization and unpalatability, and showed highly spatial heterogeneity of plant species distribution, whereas community for seasonal exclusion was under stable non-equilibrium condition. Detrended correspondence analysis (DCA) and detrend canonical correspondence analysis (DCCA) results of relationship between plant species and soil variables demonstrated that soil moisture was a controlling factor for plant species component, microbiotic soil crust cover, soil organic matter, and soil bulk density had significant effects on soil moisture, among which microbiotic soil crust was a leading factor owing to its limitation to rainfall infiltration on the one hand, and its constraints to entrance of herbaceous seeds into soil or to germination of soil seeds on the other hand. As a result of long-term removal of animal grazing, crust kept intact in year-round exclusion community, which was a main reason of community xerophytization. It was also obvious from ordination results that some important environmental factors, such as tempo-spatial change of rainfall and corresponding tempo-spatial change of soil moisture, were neglected during direct gradient analysis. In addition, biodiversity was close related to soil nutrients as well as to soil moisture condition (soil water content and crust cover), and it had positive relation to available N, and negative relation to available P. Higher soil N had advantage to non-leguminous plants growth on nutrition-poor sand land definitely. The impact of P to community component was unclear and should be studied from plant physiology. Further researches on non-equilibrium theory in semi-arid rangeland will provide a scientific and flexible animal development paradigm for being implementing livestock fen-raising and grazing-forbidden policies in China. __________ Translated from Acta Ecologica Sinica, 2005, 25(12): 3212–3219 [译自: 生态学报]     

干旱半干旱地区人工固沙灌木林生态系统演变特征

应用实验生态学方法分析了沙坡头地区栽植于1956、1964、1981、1987年的无灌溉人工植被固沙群落浅层土壤分形特征、植被盖度、物种特征、生物量、土壤水分、土壤微生物,以及群落土壤物理和土壤养分特征,并与流动沙丘进行比较。结果表明,在干旱半干旱的草原化荒漠地区,首先利用半隐蔽式草方格沙障对流动沙丘进行固定,然后栽植灌木柠条、花棒等和半灌木油蒿,经过40多年的稳定演变,该区域逐渐形成由矮灌木与草本植物覆盖,以及隐花植物与微生物土壤结皮复合的固定沙丘景观。在人工植被固沙防护体系稳定演变过程中,浅表层土壤的细粒化和养分富集化特征,微生物土壤结皮与亚表层土壤厚度,以及浅表层土壤体积含水率均随固沙年限的延长趋于显著增加。而土壤微生物数量、植被盖度、植物种数等生物群落学属性在固沙年限达40a左右时,已趋于最大,尔后呈缓慢下降趋势。随着固沙年限的增加,灌木树种不断衰退减少,当固沙年限逾17a之后,群落生物量增至峰值后略有下降。土壤分形维数与土壤粘粒含量呈显著正相关关系,流动沙丘被人工植被固定年代越久远,浅表层(0~3cm)土壤粘粒含量(4.50%)越高,其分形维数越大(D=2.4083),表明人工植被固沙防护体系浅表层土壤结构变得越紧实,流动沙丘(D=2.0484)在人工植被的固定作用下,发生逆转的趋势越显著,沙丘日趋固定。     

Microbiotic Crusts and Ecosystem Processes

Microbiotic crusts are biological soil crusts composed of lichens, cyanobacteria, algae, mosses, and fungi. The biodiversity of these crusts is poorly understood; several cosmopolitan species dominate in most areas, but many species are confined to one or a few sites. Nitrogen fixation by organisms within the crust can be the dominant source of nitrogen input into many ecosystems, although rates of nitrogen input are limited by water availability, temperature, and nitrogen loss from the crust. Photosynthetic rates of the microbiotic crust can be 50% of those observed for higher plants, but the contribution of crusts to carbon cycling is not known. The microbiotic crust binds soil particles together, and this significantly increases soil surface stability and resistance to erosion. Greenhouse studies have found that crusts can enhance seed germination, seedling survivorship, and plant nutrient status, but further experiments are needed under field conditions. Crusts are extremely susceptible to surface disturbance and fire, and disruption of crusts can decrease soil fertility and stability resulting in lower nutrient availability for vascular plants and significant soil loss from the ecosystem.     

生物土壤结皮——荒漠化地区研究的热点问题

生物土壤结皮在荒漠化地区广为分布。从结皮的概念、结皮对生态系统和景观变化的影响（包括水文循环、土壤侵蚀、土壤养分循环、维管植物的萌发和生长、动物多样性、景观异质性以及生态系统和景观变化监测和评价等）以及生物土壤结皮对干扰的反应及其恢复机理等方面详细地论述了生物结皮在荒漠化发生发展及其防治中所起的重要作用,并提出了今后生物土壤结皮研究的方向和着眼点。     

Patterns of seed germination in Californian serpentine grassland species

Summary Germination of nine Californian serpentine annual species and one perennial grass was examined as a function of soil and litter cover and seasonal timing of rainfall. Germination responses varied with the date of moisture application, and the patterns of variation differed among species. Germination occurred in waves over time, but in most of the species, virtually all the seeds had germinated by December. These results indicate that yearly climatic variation can affect species composition and competitive relationships among species through the germination process. Soil and litter cover produced little or no effect except for the smallest-seeded species.     

Structure of biological soil crust communities in Callitris glaucophylla woodlands of New South Wales,Australia

Question: What is the nature of the relationships between cover, diversity and abundance of biological soil crusts, cover and diversity of vascular plants, and annual rainfall, soil texture and forestry practices in Callitris glaucophylla woodlands? Location: Arid and semi‐arid Callitris glaucophylla‐domi‐nated woodlands of eastern Australia. Methods: We documented soil crust‐forming mosses, lichens and liverworts at 83 woodland sites along a gradient of declining rainfall. Linear and non‐linear regression were used to examine relationships between soil crust species and attributes of vascular plant communities, and a similarity matrix (species abundance X sites) was subjected to Non‐metric Multi‐Dimensional Scaling (MDS), and Analysis of Similarities (ANOSIM) to show the degree of association between groups of taxa, and soil texture, rainfall classes and forestry practices. Results : We collected 86 taxa. Mosses were dominated by the family Pottiaceae, and lichens were dominated by squamulose forms. Average annual rainfall was highly correlated with soil crust community composition, and loamy soils supported a greater cover and diversity of taxa compared with sandy soils. Increases in tree cover were associated with significant, though weak, increases in abundance, but not diversity, of crusts. Crusts tended to be more diverse in areas that (1) had a sparse cover of ground‐storey plants; (2) were relatively stable ‐ as indicated by the proportion of perennial and/or native plants; (3) had more stable soil surfaces; and (4) were unlogged. Litter cover, overstorey thinning, and livestock grazing had no appreciable effect on crust diversity or cover. Conclusions : Callitris glaucophylla woodlands provide substantial habitat for soil crust organisms, and the dense tree cover and closed canopies of Callitris do not appear to have a major influence on the structure of biological crust communities. Unlike other woodland systems, relatively few patches would be required to reserve a high diversity of crust species.     

黄土丘陵区地形、土壤水分与草地的景观格局

在黄土丘陵区,地形因素和土壤水分是决定草地景观格局的主要因素,同时草地景观格局在不同尺度上影响着景观中的流.地形因素、土壤水分和草地结构在不同尺度上有着密切的联系,研究它们之间的关系对于了解生态系统的过程十分重要.针对黄土高原异质化的草地群落结构,选取黄土丘陵区经过20多年自然封育形成的天然草地,从坡面尺度对景观格局进行了调查研究,在地形因素、土壤水分和草地结构中选取了有代表性的指标14个,用多元统计分析对选取的指标进行了主成分分析和聚类分析.聚类分析将样方分成3种植被类型,不同植被类型的海拔、坡度、20～140cm土壤含水量以及物种丰富度和生物多样性存在显著性差异.相关分析表明：海拔对0～300cm土壤含水量影响显著;海拔对草地群落盖度,坡位、坡向对草地群落的物种丰富度和生物多样性有着重要影响;而草地群落的物种丰富度和生物多样性与0～100cm土层的含水量关系密切.     

Prediction of neotropical tree and liana species richness from soil and climatic data

We present an analysis of local species richness in neotropical forests, based on a number of 0.1 ha samples of woody plants collected by the late Alwyn Gentry. For each of 69 forests, soils were analysed and climatic data were collated. Using transformed independent variables and interaction terms, multiple regression equations were developed that explained the greatest possible amount of variation in species richness, and the best equations were selected on the basis of regression diagnostics. The best models are presented for (a) all neotropical forests, (b) forests west of the Andes (transandean) and (c) east of the Andes (cisandean), and for various subsets based on elevation and annual rainfall. For the whole dataset, and for most subsets, annual rainfall and rainfall seasonality were the most important variables for explaining species richness. Soil variables were correlated with precipitation — drier forests have more nutrient-rich soils. After the inclusion of rainfall variables, available soil nutrient concentrations contributed little to explaining or accounting for additional variation in species numbers, indicating that tropical forest species richness is surprisingly independent of soil quality. The results are consistent with the hypothesis that plants in mature tropical forests may obtain nutrients through the process of direct cycling, in which mineral nutrients are extracted from litterfall before they enter the soil. The strong relationship between community species richness and rainfall patterns has implications for biodiversity conservation. Wet forests with an ample year-round moisture supply harbour the greatest number of woody plant species and should be a focus of conservation efforts.Died 3 August 1993.     

Fine roots of <Emphasis Type="Italic">Prosopis flexuosa</Emphasis> trees in the field. Plant and soil variables that control their growth and depth distribution

Fine root growth in natural vegetation is difficult to predict due to its regulation by soil and plant factors. Field studies in arid ecosystems show a variety of root responses to soil resources and to plant aboveground phenology that sometimes differ from root responses predicted by controlled experiments. There is a pressing need to cover a greater diversity of plant species and ecological scenarios in field studies. In this paper, we have studied fine roots of Prosopis flexuosa trees living with or without access to phreatic water in an inter-dune valley and a dune flank, respectively, in the Central Monte Desert, Argentina. We have described fine root growth over time and at different depths by rhizotron observations and soil core auger samples in relation to soil water and nutrients, tree crown phenology, plant water and nutrient status. We have found that surface soil moisture from rainfall is the variable that best predicts seasonal topsoil fine root growth. Access to groundwater advanced leaf sprouting with respect to rainfall, but did not advance root growth that stayed linked to rainfall in valley and dune flank trees. Trees without access to phreatic water produced deeper and thicker or denser roots, which is consistent with the poor soil resource content of dunes. Variations in rainfall dynamics due to global climate change may have a particular impact on fine roots and ecosystem processes such as biogeochemistry and carbon budget in dune flank trees as well as in valley trees.