黄河源区人工草地植被群落和土壤养分变化

[目的]研究黄河源区不同年限人工草地植被群落特征和土壤养分的动态变化,揭示高寒地区人工草地稳定机制与演替规律,为退化高寒草甸(湿地)的近自然恢复和缩短退化草地恢复时间提供理论依据。[方法]选择黄河源区青海省玛沁县3,11,17 a单播垂穗披碱草人工草地,对植被与土壤养分特征进行调查。[结果]随着种植年限增加,人工草地优势种垂穗披碱草盖度降低,植物总盖度、生物结皮盖度、杂类草盖度以及生殖枝数量呈倒"V"型变化,而原生植被莎草科植物盖度、物种多样性逐渐增加,17 a人工草地中莎草科植物的盖度是3,11 a的10倍;人工草地土壤养分中全氮、全钾、速效氮、速效钾以及有机质随年限增加呈现积累趋势,土壤pH值逐渐趋于中性。土壤全氮含量在不同恢复年限之间差异最大,平均准确率降低度为25.71,有机质含量次之,其平均准确率降低度为18.55,而全钾含量及均匀度指数最小,平均准确率降低度均小于5。[结论]高寒地区人工草地群落结构和土壤营养随着建植时间的延长在逐渐恢复,建植17 a的人工草地土壤全氮、有机质含量仅是原生高寒草甸土壤的50%左右,因此,17 a人工草地土壤养分完全恢复还需要较长时间。     

生物土壤结皮对荒漠区土壤微生物生物量的影响

为探明生物土壤结皮对土壤微生物生物量碳和氮的影响,以腾格里沙漠东南缘的人工植被固沙区生物土壤结皮覆盖的沙丘土壤为研究对象,根据固沙时间的不同将样地分为4个不同的区进行采样(55、47、30和20 a固沙区),以流沙区(0 a)和天然植被区(100 a)为对照。研究表明:人工植被固沙区的藻-地衣结皮和藓类结皮均可显著提高土壤微生物生物量碳(SMBC)和氮(SMBN)含量(p0.05),且固沙年限与SMBC和SMBN含量存在显著的正相关关系(p0.05);结皮类型显著影响土壤微生物生物量,藓类结皮下SMBC和SMBN含量显著高于藻-地衣结皮下SMBC和SMBN含量(p0.05);此外,生物土壤结皮可显著提高0~20 cm土层SMBC和SMBN含量(p0.05),且这种影响随土层的增加而减弱。而且,生物土壤结皮下SMBC和SMBN含量表现明显的季节变化,表现为夏季春季秋季。水热因子是决定土壤微生物生物量季节变化的主要因子,而生物土壤结皮通过调节土壤温度和湿度而影响土壤微生物生物量的季节变化。     

库布齐沙漠植被恢复对风沙土壤碳通量与碳储量的影响

为阐明库布齐沙漠植被恢复过程中土壤碳通量的时空动态特征及主控因子，明确土壤有机碳含量和储量的变化趋势，本研究以流动沙地、半固定沙地、藻结皮固定沙地和地衣苔藓混合结皮固定沙地为研究对象，运用静态暗箱–气相色谱法对风沙土壤碳通量及水热因子进行观测，并对土壤有机碳含量和密度进行测定和计算。结果表明，生长季内风沙土壤碳通量变异较大，季节动态与土壤温度基本一致，且随植被恢复碳通量呈递增趋势：混合结皮固定沙地(210.28 mg/(m~2·h))>藻结皮固定沙地(177.45 mg/(m~2·h))>半固定沙地(117.34 mg/(m~2·h))>流动沙地(65.61mg/(m~2·h))；土壤碳通量与各层土壤温度均显著正相关，除流动沙地土壤碳通量与深层土壤含水量显著负相关外，其余样地碳通量均与表层土壤含水量显著负相关；风沙土壤有机碳含量和密度随植被恢复而递增：混合结皮固定沙地(1.32 g/kg,0.94 kg/m~2)>藻结皮固定沙地(1.03 g/kg,0.74 kg/m~2)>半固定沙地(0.45 g/kg,0.36 kg/m~2)>流动沙地(0.27...     

人工藻结皮对旱区农田土壤风蚀的防控效应

[目的]分析人工藻结皮对土壤起沙风速和风蚀速率的影响及其风蚀防控效果,探索人工藻结皮在农田土壤风蚀防控中的可行性,为农田土壤风蚀防控提供新思路。[方法]研究了400,600,800,1 000,1 200 ml/m²共5个藻液接种量对农田土壤藻结皮形成的影响,进而采用风洞试验,研究人工藻结皮对土壤风蚀的防控效应,探讨了该技术应用于农田土壤风蚀防控的可行性。[结果]在室外自然环境条件下,通过接种藻液可形成不同盖度的藻结皮。藻接种量为1 200 ml/m²时,培养14 d盖度可达30%,50 d后,其盖度可达60%以上,藻生物量、结皮厚度是对照的52和9倍,均有显著差异(p<0.05)。人工藻结皮可显著提高农田土壤的起沙风速,降低风蚀速率。当藻结皮盖度为30%左右,起沙风速(9 m/s)较裸土增加44%,风蚀速率较裸土降低80%以上。[结论]通过在农田土壤接种藻液形成藻结皮,可显著改变土壤物理属性,增强土壤抗风蚀性。农田土壤接种藻液形成藻结皮可以作为一种快速、有效的方法应用于农田土壤风蚀防控。     

流动沙地建植人工固沙梭梭林的土壤演变过程

梭梭是西北干旱区人工固沙植被建设的主要树种,人工固沙梭梭林建植后植被系统的演变受土壤发育的影响。在河西走廊中段临泽平川绿洲边缘选择0、3、6、9、16和40 a时间序列的固沙梭梭林地,研究人工固沙植被建植后的土壤发育过程,探讨梭梭植物与土壤反馈作用及其对植被系统演变的影响。结果表明,随着梭梭种植年限的增加,土壤黏粉粒、有机碳(SOC)和全氮(TN)含量逐渐增加,但显著变化发生在种植9 a以后的0~20 cm表层土壤,而盐分的积累发生在0~100 cm整个土层,20~80 cm土层的盐分积累量高于表层0~20 cm;盐分组成中,24 SO-、Ca2+和Na+含量随着梭梭种植年限的增加而增加,在16 a和40 a梭梭林土壤剖面中有显著积累。梭梭种植16 a和40 a后,0~10 cm土层SOC含量较未造林沙地分别增加3.3倍和5.7倍、0~100 cm土壤剖面盐分含量分别增加5.4倍和6.5倍,表明梭梭生长发育过程中土壤盐分积累较SOC和养分积累更为显著。盐分的积累可能对草本植物的生长发育产生负效应,进而影响人工植被系统的稳定性。在流动沙地建植人工梭梭林40 a的时间序列上,土壤从干旱砂质新成土向干旱正常新成土发育;随着盐分的进一步积累和干旱区钙化过程,最终可能演变为钙积正常干旱土,但需更长时间尺度的观测研究。     

黄土区边坡陡坡段植被建植技术及应用效果

[目的]研究高陡边坡区存在植被退化、植被建植困难、保水性能差、水土流失等问题,为半干旱区高陡边坡生态修复提供新的思路和借鉴作用。[方法]提出了3种建植技术——锚索框架植生袋平铺法建植技术(A区)、锚索框架植生袋梯田法建植技术(B区)和锚索框架梯田法(C区),以解决该区建植中存在的问题,维护工程建设和运营安全。[结果]①A区植被覆盖度最高(85%),且植物种类和株数最多;B区和C区盖度分别为60%和12%。②0—20 cm土层间,土壤含水量表现为:B区(7.72%)A区(7.20%)C区(4.03%);0—2 cm土层间土壤含水率:A区(5.82%)B区(3.95%)C区(2.88%);2—10 cm和10—20 cm间:B区A区C区。③0—20 cm土层间土壤容重表现为:A区(1.18 g/cm~3)B区(1.24 g/cm~3)C区(1.25 g/cm~3);0—10 cm间:B区(1.23 g/cm~3)C区(1.19 g/cm~3)A区(1.15 g/cm~3),且容重均处于适宜状态;10—20 cm土层间:A区(1.21 g/cm~3)B区(1.25 g/cm~3)C区(1.31 g/cm~3),C区处于偏紧状态;④土壤侵蚀模大小为:A区(3 078 t/km~2·a)B区(3 579 t/km~2·a)C区(4 556 t/km~2·a)。[结论]利用锚索框架植生袋平铺法建植技术可显著提高植被生长状况,减少土壤侵蚀,生态修复效果显著。     

长江口典型湿地植被储碳、固碳功能研究——以崇明东滩芦苇带为例

湿地生态系统具有很强的储碳、固碳能力,在全球碳循环中占有重要地位.为了解长江口典型湿地芦苇(Phragmites australis)的储碳、固碳情况,通过实地调研与实验室测定相结合的方法,研究了崇明东滩芦苇带湿地植被的生物量和初级生产力,并测算了其碳储量和固碳能力.结果表明:长江口典型芦苇带湿地植被的碳储量较大,为2.66～5.74 kg·m-2,平均4.02 kg·m-2,且地下部分的生物现存量大于地上部分,地下/地上生物量比率为2.33～3.64,平均2.96,碳储量是地上部分的近3倍;长江口典型芦苇带湿地具有很强的固碳能力,达1.11～2.41 kg·m-2·a-1,是全国陆地植被平均固碳能力的2.3～4.9倍,全球植被平均固碳能力的2.7～5.9倍.     

植被重建下露天煤矿排土场边坡土壤碳储量变化

植被重建是治理排土场边坡水土流失最直接也是最有效的生物措施,研究不同植被重建模式下土壤有机碳(SOC)和全氮(TN)含量的空间分布规律是筛选适宜排土场边坡生长的植被模式的重要条件。选取内蒙古黑岱沟露天煤矿治理15年的排土场边坡中4种植被重建模式(自然恢复地、草地、灌木林、乔木林),采集270个土壤剖面(0~100 cm)样品,研究不同重建模式下SOC储量的变化。结果表明:(1)植被重建模式显著影响剖面SOC、TN含量及分布(p0.05),0~10 cm和10~20 cm SOC、TN均呈草地灌木乔木自然恢复地,20 cm以下各土层SOC、TN虽然也表现相似的特征,但差异随土层深度增加越来越小。(2)剖面SOC密度和储量表现为原地貌区治理排土场新建排土场。经15年植被重建后,排土场边坡表现出巨大的固碳能力,1 m深度的林地和草地碳储量分别增加了5.38、11.85 t hm-2,但仅原地貌水平的1/2和3/5。(3)林地和草地的固碳速率分别为35.87、79.01 g m-2a-1,草地的固碳速率是林地的2.2倍,从土壤固碳及水土流失防治的角度考虑,建议矿区排土场边坡植被重建优先选择草地,其次灌木。     

秦岭山区不同闭矿年限尾矿库植被恢复调查

[目的]对秦岭山区不同闭矿年限尾矿库植被恢复情况进行调查研究,可为矿区植被恢复与重建提供理论依据。[方法]以秦岭山区4个不同闭矿年限(2,3,6和14 a)的金尾矿库为研究对象,在尾矿库的库顶和边坡设置样方,对样方内植被种类、高度、密度、盖度、优势度进行调查。[结果]闭矿6 a的尾矿库植被种类最多,其次是闭矿14,3和2 a的植被种类;闭矿14 a的尾矿库植被相对高度最高,其次是闭矿6,3和2 a的植被相对较高;闭矿6 a的尾矿库植被相对密度最高,其次是闭矿14,3和2 a的植被相对密度;闭矿14 a的尾矿库植被盖度最高,其次是闭矿6,3和2 a的植被盖度;尾矿库植被主要为菊科植物和禾本科植物,闭矿6 a的尾矿库植被优势度最高,其次是闭矿14,3和2 a的植被优势度。[结论]金尾矿库区自然恢复植被生长情况与闭矿年限有密切关系;人工覆土可以显著增加尾矿库区自然恢复植被种类的多样性。     

黄土丘陵区人工柠条林土壤有机碳组分和碳库管理指数演变

采用时空替代法,探讨了黄土丘陵区人工柠条林地在10,17,30,34,40,50 a时间序列上0-40 cm土层内土壤碳组分和碳库管理指数的演变特征.结果表明:(1)随着林龄的增加,柠条林地中土壤总有机碳和活性有机碳含量增加,均为10 a时含量最低,40～50 a时趋于稳定.但二者出现的峰值年限不同,总有机碳在34 a时含量最高,达4.29 g/kg,而活性有机碳含量在40 a时最高,为0.83 g/kg;(2)柠条林地碳库管理指数随林龄增加整体呈上升趋势,在0-20 cm土层随生长年限的增加明显提高,比10 a柠条林地高出54.2％～153.0％,而在20-40 cm土层其增幅不明显,甚至在17～30 a期间比10a时下降了8.0％～16.9％;(3)相关分析表明,活性有机碳与总有机碳之间存在极显著正相关关系,并且与土壤肥力指标也呈显著或极显著相关;碳库指数和碳库管理指数与土壤碳组分、其他主要肥力指标之间也显著相关.研究表明,在黄土丘陵区植被恢复过程中,柠条种植可增加土壤的有机碳含量,改善土壤肥力.碳库指数与碳库管理指数可以作为反映黄土丘陵区植被恢复的监测因子.     

CARBON FIXATION OF CYANOBACTERIAL–ALGAL CRUSTS AFTER DESERT FIXATION AND ITS IMPLICATION TO SOIL ORGANIC CARBON ACCUMULATION IN DESERT

Enhanced carbon fixation in soil crusts may facilitate the restoration of damaged ecosystems, but this requires greater knowledge of carbon fixation patterns and mechanisms. We measured the net photosynthetic rate (P_n) and estimated annual carbon fixation (ACF) in cyanobacterial–algal crusts after desert fixation in the Tengger Desert, northwestern China. The accumulated carbon fixation since the establishment of a restoration site was also calculated. In addition, stepwise regression analysis was used to study the relation between P_n and ACF and the physicochemical properties of crusts. Results showed that P_n was significantly higher at a more established 51‐year‐old restoration site (1·57 µmol m⁻² s⁻¹) than at a younger 15‐year‐old site (0·92 µmol m⁻² s⁻¹). The ACF also increased significantly with restoration time, but in two temporal phases, a slower ACF phase between 15 and 26 years of restoration (0·28–0·7 gC m⁻² y⁻¹) and a high ACF phase after 43–51 years of restoration (3·3 gC m⁻² y⁻¹). Stepwise regression analysis revealed that P_n was significantly correlated with chlorophyll a and crust cover, whereas ACF was only correlated with crust cover. Accumulated carbon fixation increased from 2·9 gC m⁻² after 15 years to 35·4 gC m⁻² at 51 years following establishment of the restoration site. The accumulated carbon fixation was positively correlated with soil organic carbon content. This study demonstrated that carbon fixation by cyanobacterial–algal crusts increased progressively after desert fixation. Artificial measures, like the establishment of these restoration zones, can facilitate the colonization and development of biological soil crusts and are an effective biological tool for desert soil restoration. Copyright © 2011 John Wiley & Sons, Ltd.     

干旱与重吸水对人工藻结皮光合特性的影响

通过接种蓝藻构建人工藻结皮促进荒漠地区生物结皮的生长发育以及整个荒漠生态系统的恢复,被认为是一种行之有效的荒漠化控制方法。在构建藻结皮过程中,接种的蓝藻以及形成的藻结皮,经常遭受干旱等环境条件的胁迫。本研究通过室内人工构建藻结皮,对形成的藻结皮进行干旱及重吸水处理,在此过程中监测结皮光合生物量、多糖含量以及结皮光合特性的变化规律。结果发现,干旱处理1d后,结皮蓝藻胞外多糖的分泌明显增加(p0.05);当结皮完全进入干燥状态后,结皮蓝藻停止所有代谢活动,结皮生物量及胞外多糖含量保持在一个相对稳定的水平。在结皮重吸水后,结皮初始荧光Fo能够迅速恢复,并在10 min内达到最大;之后Fo逐渐下降,同时结皮光合活性(Fv/Fm)按照函数y=ax/(b+x)逐渐上升并达到稳定。此外,在不同水分条件下,结皮光合活性随着水分的增加逐渐增加;然而结皮净光合速率(Pn)却随着水分的增加先增加后又下降,呈现单峰变化模式。该研究表明结皮蓝藻的代谢调节在人工藻结皮适应荒漠干旱环境中具有重要的作用,这对于进一步理解蓝藻乃至蓝藻结皮对干旱胁迫的适应,以及荒漠化防治中人工藻结皮的构建、维护、管理具有重要的理论与实践意义。     

Effects of drought and salt stresses on man-made cyanobacterial crusts

As a primary successional stage of biological soil crusts (BSCs), cyanobacterial crusts form firstly in the arid and semiarid areas. At the same time, they suffer many stress conditions, such as drought, salt, etc. In this study, we constructed man-made cyanobacterial crusts with Microcoleus vaginatus Gom. and comparatively studied the effects of drought and salt stresses on the crusts. The results showed that crust growth and photosynthetic activity was significantly inhibited by the stress conditions (P < 0.05), and inhibitory effect increased with the increasing stress intensity and treated time. Compared with salt stress, drought completely stopped crust metabolic activity, so the crust biomass was conserved at a higher level, which meant that drought itself might provide the crusts some protection, especially when the crusts simultaneously suffered drought and salt stresses. That is very important for the survival of crusts in the high-salt areas. In addition, to some extent the crusts could adapt to the stress conditions through metabolic adjustment. In our experiment, we found the accumulation of exopolysaccharides (EPS) increased under stress conditions within a certain threshold.     

Carbohydrates in cyanobacterial soil crusts as a source of carbon in the southwest Kalahari, Botswana

Semiarid ecosystems, also known as drylands, contain small amounts of carbon (C). To date only few studies have evaluated soil C dynamics in these ecosystems. Cyanobacterial soil crusts are considered a major source of organic C in semiarid ecosystems through photosynthesis, increasing soil organic C (SOC) pool as carbohydrates. This study considers cyanobacterial soil crusts as a source of C in the southwest Kalahari. Cyanobacterial soil crusts are well adapted to drylands because extracellular polysaccharide (EPS) secretions provide stabilization of soil and resistance to desiccation. The carbohydrate and chlorophyll a content were evaluated in the upper soil profile on Kalahari Sands and pan soils. Topsoil carbohydrate concentration decreased exponentially with depth. The carbohydrate content produced in cyanobacterial soil crusts in the southwest Kalahari represents up to 75% of the total SOC and is thus an essential component for the fertility of Kalahari Sand soils.     

Feasibility of cyanobacterial inoculation for biological soil crusts formation in desert area

Practical testing of the feasibility of cyanobacterial inoculation to speed up the recovery of biological soil crusts in the field was conducted in this experiment. Results showed that cyanobacterial and algal cover climbed up to 48.5% and a total of 14 cyanobacterial and algal species were identified at the termination of inoculation experiment; biological crusts' thickness, compressive and chlorophyll a content increased with inoculation time among 3 years; moss species appeared in the second year; cyanobacterial inoculation increased organic carbon and total nitrogen of the soil; total salt, calcium carbonate and electrical conductivity in the soil also increased after inoculation. Diverse vascular plant communities composed of 10 and 9 species are established by cyanobacterial inoculation on the windward and leeward surface of the dunes, respectively, after 3 years. The Simpson index for the above two communities are 0.842 and 0.852, while the Shannon-Weiner index are 2.097 and 2.053, respectively. In conclusion, we suggest that cyanobacterial inoculation would be a suitable and effective technique to recover biological soil crusts, and may further restore the ecological system.     

库布齐沙漠不同发育类型人工结皮对露水凝结作用的比较研究

露水的形成是干旱、半干旱地区生态系统中重要的环境因子.以库布齐沙漠不同发育类型的人工结皮为研究对象,通过每天野外跟踪观测人工结皮的露水凝结量,比较人工结皮露水凝结量的大小及其凝结能力的差异性.试验以人工蓝藻结皮(ACC)、人工藻结皮(AAC)、人工苔藓结皮(AMC)以及自然苔藓结皮(NMC)和流沙(SS)为材料,并以绒布-平板露水测定法(CPM)为参照,试验时间为42 d.结果表明,CPM法测定的日平均露水凝结量为0.02～0.35 mm,ACC露水凝结量为0.012～0.191 min,AAC为0.032～0.230 mm,AMC为0.048~0.274 mm,NMC为0.056～0.304 mm,SS为0.003～0.083 mm.露水凝结量随结皮的发育状况而存在显著差异,露水凝结量大小依次为NMC>AMC>AAC>ACC>SS.结果还发现.人工结皮的形成明显促进了荒漠地表对露水的吸收和保持,结皮能够比沙表面凝结更多的露水,且结皮的露水千化过程比沙表面更慢.推测结皮藻丝体的发育及其胞外分泌物是结皮凝结较多露水的重要原因,同时依赖于结皮表面的微气候环境.本研究揭示了露水在维系结皮生存中的生态学意义,表明人工结皮具有较好的水土保持功能,同时有利于更好地理解生物结皮对露水的凝结机制与吸收利用情况,并为荒漠化地区有限水源条件下人工结皮利用露水等非降雨型水分进行野外生存提供重要的理论支持和试验依据.     

Nitrogen fixation in biological soil crusts from southeast Utah,USA

Biological soil crusts can be the dominant source of N for arid land ecosystems. We measured potential N fixation rates biweekly for 2 years, using three types of soil crusts: (1) crusts whose directly counted cells were >98% Microcoleus vaginatus (light crusts); (2) crusts dominated by M. vaginatus, but with 20% or more of the directly counted cells represented by Nostoc commune and Scytonema myochrous (dark crusts); and (3) the soil lichen Collema sp. At all observation times, Collema had higher nitrogenase activity (NA) than dark crusts, which had higher NA than light crusts, indicating that species composition is critical when estimating N inputs. In addition, all three types of crusts generally responded in a similar fashion to climate conditions. Without precipitation within a week of collection, no NA was recorded, regardless of other conditions being favorable. Low (<1°C) and high (>26°C) temperatures precluded NA, even if soils were moist. If rain or snow melt had occurred 3 or less days before collection, NA levels were highly correlated with daily average temperatures of the previous 3 days (r²=0.93 for Collema crusts; r²=0.86 for dark crusts and r²=0.83 for light crusts) for temperatures between 1°C and 26°C. If a precipitation event followed a long dry period, NA levels were lower than if collection followed a time when soils were wet for extended periods (e.g., winter). Using a combination of data from a recording weather datalogger, time-domain reflectometry, manual dry-down curves, and N fixation rates at different temperatures, annual N input from the different crust types was estimated. Annual N input from dark crusts found at relatively undisturbed sites was estimated at 9 kg ha^-1 year^-1. With 20% cover of the N-fixing soil lichen Collema, inputs are estimated at 13 kg ha^-1 year^-1. N input from light crusts, generally indicating soil surface disturbance, was estimated at 1.4 kg ha^-1 year^-1. The rates in light crusts are expected to be highly variable, as disturbance history will determine cyanobacterial biomass and therefore N fixation rates.     

Biological soil crust development affects physicochemical characteristics of soil surface in semiarid ecosystems

Water and nutrients are scarce resources in arid and semiarid ecosystems. In these regions, biological soil crusts (BSCs) occupy a large part of the soil surface in the open spaces surrounding patches of vegetation. BSCs affect physicochemical soil properties, such as aggregate stability, water retention, organic carbon (OC) and nitrogen (N) content, associated with primary ecosystem processes like water availability and soil fertility. However, the way BSCs modify soil surface and subsurface properties greatly depends on the type of BSC. We hypothesised that physicochemical properties of soil crusts and of their underlying soils would improve with crust development stage. Physicochemical properties of various types of soil crusts (physical crusts and several BSC development stages) and of the underlying soil (soil layers 0–1 cm and 1–5 cm underneath the crusts) in two semiarid areas in SE Spain were analysed. The properties that differed significantly depending on crust development stage were aggregate stability, water content (WC) (at −33 kPa and −1500 kPa), OC and N content. Aggregate stability was higher under well-developed BSCs (cyanobacterial, lichen and moss crusts) than under physical crusts or incipient BSCs. WC, OC and N content significantly increased in the crust and its underlying soil with crust development, especially in the first centimetre of soil underneath the crust. Our results highlight the significant role of BSCs in water availability, soil stability and soil fertility in semiarid areas.     

Biological and microbial activity in biological soil crusts from the Tabernas desert,a sub-arid zone in SE Spain

The ecology and functional role of biological soil crusts (BSCs) in arid and semi-arid zones have been extremely well studied. However, little is known about the biochemical properties related to the number and activity of the microbiota that form the crusts, even though information about these properties is very important for understanding many of the processes that affect the formations. In this study, several properties related to the activity and number of microorganisms (biomass-C, basal respiration, dehydrogenase activity and nitrogen mineralization potential) were determined at different depths (crusts, 0–0.5 cm; middle, 0.5–3 cm and deep, 3–5 cm layers) in two types of crusts (predominated by cyanobacteria and by lichens) in the Tabernas desert (Almeria, SE Spain). The absolute values of the above-mentioned properties and the values expressed relative to the total organic carbon (TOC) content were both much higher in the crust layers than in the surface horizons of soils under Mediterranean or Atlantic climates. A large part of the TOC in the BSCs was contained in the microbiota and another large part was readily metabolized during incubation of the crusts for 10 days at 25 °C. The net nitrogen mineralization rate was also high, and ammonification predominated in the crust layers, whereas nitrification predominated in the middle and deep layers. In all types of BSCs, the microbiota colonized the deep layers, although with greater intensity in the lichen-dominated BSCs than in the cyanobacterial BSCs. The results also indicate that hydrolytic enzymes are not stabilized on soil colloids and their activity depends only on the active microbiota.     

新疆棉田小区域碳变化量研究

为研究膜下滴灌条件下棉田小区域碳变化量,在棉花生长期内采用Li-8100A土壤碳通量自动测定仪和LCpro+光合仪连续观测不同样地土壤呼吸速率和净光合速率。结果表明:不同样地的土壤呼吸速率日变化均表现为单峰型曲线,峰值出现在16:00;而棉田净光合速率日变化则表现为单双峰曲线交替变化规律。两者月变化均呈现先升高后降低的趋势,7月土壤呼吸速率和净光合速率达到最大值。不同样地间土壤呼吸速率和净光合速率存在差异,土壤呼吸速率表现为垄间>垄上>裸地,净光合速率表现为垄间>垄上。棉田小区域在棉花整个生育期内均表现为碳汇,6-9月棉田净固碳总量为2 203.7 C g/m^2,光合作用固碳量为土壤呼吸排碳量的2.67倍。