陕北毛乌素沙地生物结皮发育特征的初步研究

通过野外采样和室内分析相结合,掌握了陕北毛乌素沙地不同采样点生物结皮层的理化性质以及该地区生物结皮的发育特征,为以后进一步研究毛乌素沙地生物结皮的防风固沙效应奠定了理论基础.结果表明:随着生物结皮的发育,结皮层厚度增加.最大值为11.82 mm;土壤颗粒细化,0.02～0.05 mm之间的颗粒含量为7.3%～27.7%,高于流沙中的颗粒含量;由于颗粒的细化,结皮层容重增加,其抗剪强度明显提高,且抗剪强度与厚度和容重之间存在一定的相关性.生物结皮层pH值为7.23～7.81,低于流动沙地的pH值;有机质、N和K含量明显高于流沙的含量;P含量有所增加但不明显.研究表明,各个样点的生物结皮效应表现有所不同,原因有多方面.主要是结皮的发育程度、植被盖度以及采样点地形地貌之间的差异所引起.     

黄土丘陵区垂直陡壁表面不同类型生物土壤结皮养分与微生物养分限制特征

生物土壤结皮的发育类型对土壤养分和微生物代谢起着重要作用。为进一步明确在生物结皮发育过程中微生物的限制性养分与影响因素,研究选择黄土丘陵区垂直陡壁表面上的裸土(CK)、浅色藻结皮(LA)、深色藻结皮(DA)、藻藓混合结皮(AM)和藓结皮(M)为研究对象,分析了不同生物土壤结皮类型下碳(C)、氮(N)、磷(P)养分状况与胞外酶活性,并通过胞外酶化学计量来量化微生物的代谢限制。结果表明:LA,DA,AM和M这4种类型生物土壤结皮C,N,P养分含量和微生物生物量C,N,P均显著高于CK(p<0.05),并且SOC,TN,TP和微生物生物量C,N,P随CK,LA,DA,AM和M的顺序逐渐增大,藓结皮微生物量C,N,P分别是CK处理的18.3,27.6,14.1倍。生物土壤结皮的发育显著提高了C,N,P循环酶的活性,冗余分析结果表明土壤养分与酶活性密切相关。此外,通过酶计量的矢量模型结果来看,生物土壤结皮的发育造成微生物相对碳限制的增大与相对磷限制的减小,并受到速效养分含量的影响。偏最小二乘路径模型结果也表明生物土壤结皮的类型会间接影响微生物的代谢限制。总的来说,生物土壤结皮类型的变化会改善土壤养分状况与微生物量等性质,养分资源的供应状况会造成微生物养分代谢的变化。     

丹江口库区典型小流域生物结皮驱动土壤性质变化及分离响应

为探究生物结皮发育驱动下土壤水蚀特征及机理,选取苔藓发育为优势种的退耕样地,设计5个盖度等级(1%～20%,20%～40%,40%～60%,60%～80%,80%～100%),以裸地为对照,在不同水流剪切力(6.12～19.64 Pa)下进行冲刷试验。结果表明：结皮发育显著影响土壤养分含量,且高盖度结皮覆盖下养分表聚效应更加明显。生物结皮发育显著影响土壤分离能力,裸地土壤分离能力[1.465 6 kg/(m²·s)]为生物结皮[0.004 2～0.468 2 kg/(m²·s)]的3.58～348.95倍,裸地细沟可蚀性(0.293 5 s/m)为生物结皮(0.001 0～0.082 2 s/m)的3.57～293.50倍。相对土壤分离能力及细沟可蚀性均随结皮盖度增加呈指数函数衰减,结皮冲破时间随结皮盖度增加呈指数函数增长;非线性回归分析表明,土壤分离能力可用水流剪切力、生物结皮盖度和土壤黏结力进行模拟(NSE=0.749)。综上,生物结皮发育显著提升土壤抗侵蚀性能,研究结果可为半湿润区水土流失防治及生物结皮管理利用提供理论参考。     

黄土丘陵区不同盖度生物结皮土壤抗冲性研究

按藓类植物所占结皮面积比例为盖度划分标准,采用变坡度水槽研究了不同盖度生物结皮对土壤抗冲性及黏结力、有机质、容重等理化属性的影响,探索了生物结皮理化属性与抗冲性之间的关系。结果表明:结皮容重随结皮盖度的增加呈不断减小的变化趋势4,盖度(苔藓盖度>80%)平均结皮容重比1盖度(苔藓盖度<20%)减小了16%;土壤黏结力、有机质、>5 mm水稳性团聚体百分比均随着结皮盖度的增加而增大。生物结皮通过本身分泌的有机凝胶体和多聚糖等胶结物质及菌丝之间的缠绕、包裹等作用,不但改善了土壤本身的理化属性,而且增强了松散土粒与土粒之间的黏结作用;结皮土壤抗冲刷时间随着结皮盖度的增加而延长,土壤侵蚀率随着结皮盖度的增加而减少,证实了结皮的形成和发育减少或避免了土壤侵蚀的发生与发展;生物结皮提高土壤抗冲性的作用主要表现在生物结皮提高了土壤黏结力与团聚体含量上。     

侵蚀条件下生物结皮对坡面土壤碳氮的影响

 为了探讨侵蚀条件下生物结皮对坡面土壤碳氮的影响,通过野外小区对比试验与室内分析相结合,研究有、无生物结皮坡面土壤有机质、全氮、硝态氮和铵态氮的分布特征。结果表明：生物结皮对坡面土壤碳氮积累具有重要意义,同一坡位下,土壤有机质、全氮和硝态氮含量在0～20cm剖面上均明显表现为生物结皮大于无结皮。总体来看,生物结皮对土壤碳氮的影响主要集中在0～10cm土层,与无结皮相比,土壤有机质、全氮、硝态氮和铵态氮平均储量分别增加了44.7%、18.2%、39.2%和4.33%。生物结皮能显著增加0～2和2～5cm土壤硝态氮含量（P<0.05）,这除了生物结皮对土壤养分的保蓄效应外,还可能与生物结皮向土壤释放硝态氮有关。由于铵态氮流失特征不同于硝态氮,加之生物结皮可能会利用或释放铵态氮,使生物结皮对其影响表现出无明显规律性。相关分析表明,土壤有机质与全氮、硝态氮和铵态氮均达到了极显著或显著的正相关关系（P<0.01或P<0.05）。综上所述,侵蚀环境下生物结皮发挥着重要的固土蓄肥功能,这对研究区退化生态系统的恢复和重建具有积极的意义。     

流沙固定过程中土壤性质变异初步研究

植被的分布格局与土壤性质空间异质性密切相关。对降水小于200mm地区的沙坡头无灌溉条件下流沙固定过程中土壤性质的空间变化进行了研究。结果表明,随固沙植物群落的演变和土壤成土环境的改善与生物地球化学循环过程的加强,土壤性质发生了显著的变化:(1)固沙区土壤机械组成中粘粒(<0.001mm)含量、土壤水溶性盐(EC电导率)、pH、有机质和全氮含量都较流沙区有很大提高,且差异显著(p<0.05);固沙区土壤剖面性质的改变主要发生在结皮层和0～5cm的表层(topsoil),受表层土壤发育的影响5～30cm土层有所改变,但差异性不显著(p>0.05)。(2)土壤质地相对均一的流沙区土壤剖面性质无变异(p>0.05)。(3)不同年限固沙区间土壤性质变异差异性不显著(p>0.05);而表层(0～5cm)与结皮层土壤性质变化趋势一致,且相关性显著(r>0.807,p<0.05)。     

冻融交替对不同生物结皮土壤饱和导水率的影响

  目的  生物土壤结皮在干旱、半干旱地区分布广泛,能显著影响土壤饱和导水率的大小,为探明冻融交替对不同类型生物结皮土壤饱和导水率的变化。  方法  以神木六道沟流域混合结皮（藻结皮 + 苔藓结皮）和苔藓结皮土壤为研究对象,采用室内模拟冻融实验的方法,测定不同冻融交替次数和初始含水率共同作用下生物结皮土壤饱和导水率（Ks）的变化。  结果  （1）冻融条件下,苔藓结皮和混合结皮的存在相比裸土均降低了土壤Ks。（2）同一冻融次数下,苔藓结皮和混合结皮土壤Ks随初始含水率增加总体呈现先增大后减小的趋势;同一初始含水率下,两种结皮土壤Ks随冻融次数增加呈现逐渐增大的趋势。（3）冻融后苔藓结皮土壤Ks显著大于混合结皮土壤,在同一冻融条件下,初始含水率为8%时,冻融3次和7次后两种结皮土壤Ks相差最大,表现为苔藓结皮土壤Ks分别是混合结皮土壤的2.1和2.3倍。（4）冻融通过影响结皮层容重和结皮厚度及结皮下层土壤有机质和 > 0.25 mm团聚体含量进而影响Ks,冻融次数对结皮厚度及有机质含量有极显著影响（P < 0.01）,对结皮容重有显著影响（P < 0.05）,初始含水率对 > 0.25 mm团聚体含量有极显著影响（P < 0.01）。（5）冻融环境下苔藓结皮和混合结皮土壤的Ks均与冻融次数呈极显著正相关（P < 0.01）,与结皮容重呈极显著负相关（P < 0.01）。并对两种结皮Ks与其他因子进行偏最小二乘回归分析,结果表明苔藓结皮土壤Ks的主要影响因子依次为结皮容重 > 冻融次数 > 结皮厚度,而混合结皮土壤Ks的主要影响因子为冻融次数 > 结皮容重。  结论  冻融交替对生物结皮土壤饱和导水率有较显著影响,且冻融作用主要是通过影响结皮厚度、结皮容重及结皮下层土壤大团聚体颗粒及有机质含量来影响生物结皮土壤饱和导水率。     

黄土丘陵区影响生物结皮退化因素的初步研究

通过植被-枯落物-生物结皮的样方调查,分析植被、枯落物及结皮自身生长状况与结皮退化的关系。结果表明：1）植被盖度和基盖度的变化对生物结皮退化影响较大,而对枯落物下结皮退化度和枯落物下结皮盖度的影响不明显,说明高等植物对植物间空地生物结皮退化的影响不明显;2）生物结皮的自身生长状况与其退化过程的关系不明显,其退化主要是受到其他因素的作用影响;3）枯落物的厚度和盖度是枯落物下结皮退化的重要影响因素,也是影响结皮退化盖度的重要因素。     

不同生境对人工结皮发育及表土氮、磷含量及其代谢酶活性的影响

土壤生物结皮对于改善荒漠地区的生态环境和土壤的增肥改良具有重要作用.本研究以库布齐沙漠固定沙丘(迎风坡、坡顶、背风坡和丘间地)披碱草和沙蒿群落下长期发育(8年生)的人工藻结皮为研究对象,测定不同生境下人工结皮对表层土壤氮、磷元素含量以及相关土壤酶活性的影响.结果表明,在不同立地条件下,沙丘顶部结皮叶绿素a和土壤可溶磷含量最高,分别为4.24 mg/g和2.926 mg/kg.丘间地结皮层土壤碱性磷酸酶活性、总磷含量及脲酶活性为最高,迎风坡结皮生物量和土壤碱解氮、速效磷含量以及土壤酶活性明显高于背风坡结皮层土壤.在相同立地条件下,披碱草下结皮生物量、碱解氮、速效磷含量和脲酶及碱性磷酸酶活性显著高于沙蒿下的结皮土壤.本研究表明生境的差异性导致人工结皮发育程度不同,进而对表土氮、磷含量及其代谢酶产生不同影响,人工生物结皮的发育程度与表土氮磷素含量及其代谢酶活性之间存在显著相关性.不同植被群落对生物结皮发育具有不同的作用,披碱草对人工生物结皮影响的正效应高于沙蒿.     

毛乌素沙地生物土壤结皮与沙化土地的关系研究

生物土壤结皮在荒漠地区广泛分布,是固沙和促进沙地生态恢复的重要生物因子。利用1989,2002和2006年的Landsat遥感影像,分别通过生物土壤结皮指数和NDVI阈值法,提取了毛乌素沙地生物土壤结皮和沙化土地的空间分布,并分析了二者之间联系。结果表明:(1)研究区1989,2002和2006年结皮面积所占比例分别为54.77%,55.72%和64.29%,表现为持续增加趋势,结皮斑块间连接度在增强,结皮的稳定性进一步巩固。(2)1989—2006年区内沙化土地的程度逐渐减弱,沙化程度综合指数由1989年的3.24下降到2006年的2.65。(3)1989—2006年,中度和重度沙化土地结皮分布范围最为广泛,均在70%以上;极重度沙化土地内的结皮面积表现为持续下降,1989,2002和2006年分别为19.40%,5.76%和2.80%。(4)以1989年沙化土地的格局为基础,1989,2002和2006年极重度沙化土地内生物结皮的数量比例分别为19.40%,33.18%和45.21%,处于上升趋势。     

Biological soil crust and surface soil properties in different vegetation types of Horqin Sand Land,China

Physical and chemical properties (including coverage, thickness, hardness, moisture, particle size distribution, organic matter and nutrient contents etc.) of biological soil crust and 0–5.0 cm surface soil under the crust in three types of vegetation (semi-shrub Artemisia frigida, shrub Salix gordejevii and tree Populus simonii) were surveyed in 2005 and 2006 in Horqin Sand Land to understand the effects of different vegetation types on development of soil crust and surface soil properties under crust. The results showed that 1) no physical soil crust or biological soil crust (BSC) formed on mobile dunes without vegetation, though most ground surface in originally mobile dunes had been covered by BSC fifteen years after planted vegetation was established; 2) BSC development was best in shrub S. gordejevii sites, second in semi-shrub A. frigida sites, and weakest in tree P. simonii sites; 3) development of BSC was better in moss crust distributed mainly beneath or near plant canopies than in lichen crust distributed mainly between plant canopies in all three vegetation types; 4) surface soil properties 0–5.0 cm under BSC were improved significantly in all three vegetation types compared to those in mobile sand land. The magnitude of improvement was greater in S. gordejevii sites than in A. frigida and P. simonii sites, and greater in moss crust sites than lichen crust sites, but the magnitude of improvement decreased significantly with increasing surface soil depth; 5) based on the above-mentioned results, we suggest that S. gordejevii should be favored in future planting in Horqin Sand Land.     

藻菌混合结皮对土壤水肥保持及玉米幼苗生长的影响

[目的] 研究藻菌混合结皮对土壤水肥保持及玉米幼苗生长的影响,为土壤治理与改良策略提供理论依据。[方法] 使用来自内蒙古翁牛特沙漠的2种产胞外多糖的细菌（Sphingomonas sp.D3-1和Massilia armeniaca sp.ZMN-3）和2种藻类（Cladophora aegagrophila D3-a和Nostoc sphaeroides0 D3-25）制备成藻菌混合剂后,喷洒至土壤表面,形成土壤结皮。研究藻菌混合结皮与土壤水肥保持、微生物数量及酶活性的关系,及其对玉米幼苗的影响。[结果] 与对照相比,藻菌混合结皮明显延缓了土壤水分的流失速度,并使氮、磷和钾的平均淋失效率分别减少了76.9%,64.4%和47.8%,土壤中的细菌、真菌和放线菌数量分别增加了8.3,1.8和3.1倍,芽孢杆菌的数量下降了12.4%。另外,在玉米盆栽中,藻菌混合结皮使玉米幼苗的地上部鲜/干重、根部鲜/干重和地上/下部长度分别提升30.0%/55.6%,55.4%/38.5%和16.5%/18.0%,叶绿素含量增加15.0%。[结论] 藻类与产胞外多糖的细菌共同形成的藻菌混合结皮,明显改善了土壤的水肥保持效果,可作为治理土壤的新途径加以推广。     

Differential wind tolerance of soil crust mosses explains their micro-distribution in nature

Wind has extensive effects on biological and ecological performances of organisms throughout the world. However, the responses of desert biological soil crusts to wind are still largely unexplored. Bryum argenteum and Didymodon vinealis are two predominant soil crust mosses that exhibit restricted, contrasting microhabitats with B. argenteum being excluded from higher wind speed microsites in the windward slopes of fixed sand dunes in the Tennger Desert, Northern China. We conducted this study to determine if wind has negative effects on the ecophysiological variables of the two soil crust mosses and whether D. vinealis possesses greater resistance to high wind speed than B. argenteum. The results showed that photosynthesis, respiration, PSII photochemical efficiency, photosynthetic pigments, shoot upgrowth, productivity and regeneration potential of the two soil crust mosses were all drastically inhibited due to the rapid drying, prolonged drought period and unfavorable coupling of moisture and temperature under high wind speed conditions. In addition, D. vinealis displayed stronger resistance to wind than B. argenteum based on all of the aspects mentioned above. Overall, the negative effects of wind on the physiology of soil crust moss and the differential resistance to wind observed in this study suggest that wind is an important determinant regulator influencing ecological micro-distribution patterns of soil crust moss in desert ecosystems.     

沙漠生物结皮土壤发育特征的研究

通过对沙漠生物结皮层相关的土壤特性研究表明,结皮层不仅具有明显的养分富集和细粒物质的聚集作用,而且结皮层腐殖质成份的含量以及其分子结构和复杂程度也在增加。腐殖质光学特性的变化趋势明显反映了不同地区结皮层土壤发育的地带性特征。结皮层持水量明显高于沙层,并对降水再分配有一定影响。     

干旱胁迫对沙枣幼苗根茎叶生长及光合色素的影响

干旱半干旱地区水分是植被恢复和演替的限制性生态因子,沙土生物结皮能降低水分入渗,造成土壤水分浅层化和加剧土壤水分时空分异,因此有必要采取措施进行适度干扰,以促进生态恢复和重建。土壤蒸发是天然降水无效损失的一个重要途径,研究生物结皮对土壤蒸发的影响十分必要。以陕北水蚀风蚀交错区沙土生物结皮为研究对象,分析了移除生物结皮和沙埋2种干扰下生物结皮类土壤水分蒸发特性。结果表明,移除生物结皮并不能起到显著地抑制土壤蒸发的作用(p>0.05),而沙埋对土壤蒸发具有显著地抑制作用(p<0.01),且随沙埋厚度的增加,蒸发抑制率提高。20mm沙埋的抑制蒸发作用最大,蒸发抑制率达到了58.15%。5mm和10mm沙埋的蒸发抑制率则分别为25.20%和28.29%,二者之间的差异未达到显著水平(p>0.05)。可见,沙埋对于改善土壤水分状况具有极积意义,但应控制沙埋的厚度。     

Soil microbial activity and a free-living nematode community in the playa and in the sandy biological crust of the Negev Desert

The effect of environmental factors and soil properties on microbial and soil free-living nematode communities was investigated in two desert soil formations, a playa and sandy biological crust. Soil samples were collected from October 2007 to September 2008 from the upper (0–10 cm) soil layers in the Negev Desert area. Unlike microorganisms, soil free-living nematodes were found to be negatively dependent on monthly rain and positively dependent on water evaporation. We suggest that water evaporation from pore caves in both soil formations increases the predation success of soil free-living nematodes, while daily rain increases the survival potential of soil microorganisms since the predators require more time to find their prey. Soil properties were found to have a different influence on microbial and soil free-living nematode communities in the two soil formations. Microbial respiration and biomass were negatively correlated with calcium and potassium in the playa area and with sodium in the sandy biological crust area. The free-living nematode community exhibited a negative correlation with electrical conductivity and sodium and a positive correlation with potassium in the playa samples, while no dependence on soil properties was found in the sandy biological crust samples. It can, therefore, be concluded that soil properties affect predation rate in the playa samples through changes in porosity. Generally accepted ecological indices such as trophic diversity (T), Simpson’s dominance (λ), Shannon–Weaver (H′), maturity (MI), and basal (BI) indices pointed to specific ecological conditions at the two observed soil formations.     

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.     

Application of an electronic micropenetrometer to assess mechanical stability of biological soil crusts

An in situ determination of biological soil‐crust stability was carried out in two study sites along a sharp rainfall gradient. Penetration resistance (PR) of the crusts was measured using a newly developed light‐weight needle‐type electronic micropenetrometer. The depth‐related PR data revealed two sections possessing different structures and stability. The topcrust (0–2 mm) had significantly higher amounts of N, organic C, carbonates, and salts as compared to the underlain subcrust. The mean PR of the topcrust was 0.68 MPa for the southern study site, Nizzana‐South (≈ 100 mm annual rainfall), and it increased significantly for the northern study site, Nizzana‐69 (≈ 170 mm annual rainfall), with a mean of 1.11 MPa. A subcrust (2–30 mm) was identified that was characterized by a high amount of carbonates and a PR > 2 MPa. The electronic micropenetrometer system is a promising device for identifying areas of changing crust stability in relation to biological soil‐crust properties. The overall stability of biological soil crusts depends on the topcrust and subcrust structure. This structure is linked to abiotic and biotic factors and likely in relation to the amount of annual precipitation.     

南方山区花岗岩风化壳崩岗侵蚀及其防治对策——以广东省五华县新一村为例

崩岗侵蚀是我国南方山区最重要的水土流失形式,崩岗侵蚀的治理是水土流失治理的关键。本文以广东省韩江上游五华县新一村为例,论述了我国南方山区花岗岩风化壳崩岗侵蚀的特点,分析了花岗岩风化壳崩岗侵蚀特别发育与花岗岩风化壳——土壤性质的关系。并探讨了采用生物措施和工程措施相结合的方法治理花岗岩崩岗侵蚀的效果。     

Distribution and activity of hypolithic soil crusts in a hyperarid desert (Baja California, Mexico)

Widespread and ecologically important, biological soil crusts include those microbial communities living on the surface of the soil and those that live beneath semitranslucent rocks (a.k.a. hypolithic crusts). We examined the distribution, abundance, physiology, and potential soil N contributions of hypolithic, biological crusts in hyperarid ecosystems of the Baja California peninsula and islands in the midriff region of the Gulf of California, Mexico (Sonoran desert). Crusts were limited in distribution to areas with translucent quartz rocks less than 3 cm thick, were not found on areas of islands with seabird guano deposition, but covered as much as 1% (12,750 m²) of the surface area of one island. The percent of available rocks colonized by crusts was similar between the mainland (38%) and islands without seabird guano (26%). Carbon fixation rates in the field, which have not been previously reported, ranged between 0 and 1.23 μmol m⁻² s⁻¹, and in the lab ranged between 0.66 and 0.94 μmol m⁻² s⁻¹. Evidence of low rates of N fixation was inferred from δ ¹⁵N values of crust and soil. Hypolithic crusts were found to have minimal, if any, influence on soil salinity, pH, and , but may represent up to 14% of the biomass of primary producers on these islands and provide C and N to the belowground and possibly aboveground heterotrophic communities where crusts exist. The results of this study suggest a limited but potentially important contribution of hypolithic soil crusts to hyperarid ecosystems.