柽柳(Tamarix spp.)和梭梭(Haloxylonammodendron)的"肥岛"效应

灌丛"肥岛"是全球干旱生态系统中的普遍现象,其发生和发展对干旱灌木、草原生态系统的结构和功能都具有重要影响,但其物种效应容易得到忽视.对准噶尔盆地南缘柽柳(Tamarix spp.)和梭梭(Haloxylon ammodendron)这两种不同地表形态灌木的冠下、冠缘和灌丛间地3种生境的土壤进行了采样、分析,结果表明:(1)柽柳和梭梭都存在"肥岛"现象,主要表现在土壤表层,其土壤性状与"岛"外土壤的差异随土壤深度增加而减弱;(2)生物性限制土壤养分由"岛"内向外梯度递减,而非生物性限制土壤要素可能高于、也可能低于"岛"外土壤,或者两者无显著差异;(3)从"肥岛"的空间尺度来看,柽柳"肥岛"的水平范围可能超出了本身冠幅覆盖区,而梭梭"肥岛"要小于本身冠幅覆盖区,其深度亦小于柽柳"肥岛";(4)相对于不同土壤要素而言,即使是同一物种,其"肥岛"也具有不同的空间范围.总的来看,研究区灌丛"肥岛"的发育具有明显的物种效应,相对梭梭而言,柽柳"肥岛"发育更广、更深,养分聚集更明显,其原因主要是柽柳的半球型树冠更利于保护和捕获凋落物,而较多的凋落物输入与土壤结构和土壤养分间的正反馈机制使柽柳冠下加速的生物地球化学循环能达到更广、更深的范围.灌丛"肥岛"的发育是干旱景观中生物过程与物理过程交互作用的产物,全面揭示其形成机理,探讨其对干旱生态系统结构、功能与动态的影响,需要更系统的研究.     

柽柳（Tamarix spp．ammodendron））和梭梭（Haloxylon的“肥岛”效应

灌丛“肥岛”是全球干旱生态系统中的普遍现象,其发生和发展对干旱灌木、草原生态系统的结构和功能都具有重要影响,但其物种效应容易得到忽视。对准噶尔盆地南缘柽柳（Tamarix spp．）和梭梭（Haloxylon ammodendron）这两种不同地表形态灌木的冠下、冠缘和灌丛间地3种生境的土壤进行了采样、分析,结果表明：（1）柽柳和梭梭都存在“肥岛”现象,主要表现在土壤表层,其土壤性状与“岛”外土壤的差异随土壤深度增加而减弱;（2）生物性限制土壤养分由“岛”内向外梯度递减,而非生物性限制土壤要素可能高于、也可能低于“岛”外土壤,或者两者无显著差异;（3）从“肥岛”的空间尺度来看,柽柳“肥岛”的水平范围可能超出了本身冠幅覆盖区,而梭梭“肥岛”要小于本身冠幅覆盖区,其深度亦小于柽柳“肥岛”;（4）相对于不同土壤要素而言,即使是同一物种,其“肥岛”也具有不同的空间范围。总的来看,研究区灌丛“肥岛”的发育具有明显的物种效应,相对梭梭而言,柽柳“肥岛”发育更广、更深,养分聚集更明显,其原因主要是柽柳的半球型树冠更利于保护和捕获凋落物,而较多的凋落物输入与土壤结构和土壤养分间的正反馈机制使柽柳冠下加速的生物地球化学循环能达到更广、更深的范围。灌丛“肥岛”的发育是干旱景观中生物过程与物理过程交互作用的产物,全面揭示其形成机理,探讨其对干旱生态系统结构、功能与动态的影响,需要更系统的研究。     

柽柳（Tamarix spp.）和梭梭（Haloxylon ammodendron）的“肥岛”效应

灌丛“肥岛”是全球干旱生态系统中的普遍现象,其发生和发展对干旱灌木、草原生态系统的结构和功能都具有重要影响,但其物种效应容易得到忽视。对准噶尔盆地南缘柽柳（Tamarix spp.）和梭梭（Haloxylon ammodendron）这两种不同地表形态灌木的冠下、冠缘和灌丛间地3种生境的土壤进行了采样、分析,结果表明：(1）柽柳和梭梭都存在“肥岛”现象,主要表现在土壤表层,其土壤性状与“岛”外土壤的差异随土壤深度增加而减弱;(2）生物性限制土壤养分由“岛”内向外梯度递减,而非生物性限制土壤要素可能高于、也可能低于“岛”外土壤,或者两者无显著差异;(3）从“肥岛”的空间尺度来看,柽柳“肥岛”的水平范围可能超出了本身冠幅覆盖区,而梭梭“肥岛”要小于本身冠幅覆盖区,其深度亦小于柽柳“肥岛”;(4）相对于不同土壤要素而言,即使是同一物种,其“肥岛”也具有不同的空间范围。总的来看,研究区灌丛“肥岛”的发育具有明显的物种效应,相对梭梭而言,柽柳“肥岛”发育更广、更深,养分聚集更明显,其原因主要是柽柳的半球型树冠更利于保护和捕获凋落物,而较多的凋落物输入与土壤结构和土壤养分间的正反馈机制使柽柳冠下加速的生物地球化学循环能达到更广、更深的范围。灌丛“肥岛”的发育是干旱景观中生物过程与物理过程交互作用的产物,全面揭示其形成机理,探讨其对干旱生态系统结构、功能与动态的影响,需要更系统的研究。     

模拟氮沉降对荆条灌木“肥岛”土壤养分的影响

氮沉降的增加,可能会对土壤养分造成更为显著的影响,目前关于大气氮沉降对植物"肥岛"效应中土壤养分的影响鲜有报道。于河南省太行山南麓地区,以NH_4NO_3为供施氮源,按土层深度采集土样,以模拟氮沉降方法(3个水平,无氮CK、低氮2g N m~(-2)a~(-1)处理、中氮12g N m~(-2)a~(-1)处理和高氮24g N m~(-2)a~(-1)处理),分析了氮沉降对太行山荆条灌木(Vitex negundo L.var.)"肥岛"土壤中有机质、全氮和速效磷含量的影响。结果表明:灌木"肥岛"中全氮和速效磷含量,总体表现出随氮沉降量增长而增加的趋势;氮沉降显著增加了土壤表层有机质、氮、磷的含量;高氮沉降与CK相比引起的各土层间养分差异更显著;随着氮沉降水平的增加,冠幅内外和土层间养分差异增大,土壤养分的增长率随之加大;氮沉降在一定程度内加剧了"肥岛"的富集效应,且氮沉降量越大,这种富集效应越显著。这些研究结果可为研究灌木"肥岛"对外源氮的响应机制及保育作用提供参考。     

几种灌木、半灌木对沙地土壤肥力影响机制的研究

研究了科尔沁地广泛分布的几种灌木和半灌木的“肥岛”和根际效应。结果表明,在灌丛下土壤有机C、全N和全P分别比灌丛间地高56％、51％和37％,土壤电导率（EC）提高了56％,但pH值并无明显变化;灌木根际土壤较非根际土壤有机C和全N分别高76％和54％,根际土壤pH降低0．19个单位,EC提高了2－3倍,但土壤全P并无显著变化,灌丛下土壤发和根际中土壤养分含量显著相关,表明丛肥岛的利于根系的生长,导致更多的根际沉积;而根系的活动又促进了肥岛的发育,灌丛对沙地土壤肥力的影响机制在于：灌丛对土壤风蚀物质、降尘和凋落物等的截获,形成灌丛“肥岛”;并通过发达的根系以根际沉积的形式向土壤输入大量的有机物质,从而使周围土壤的肥力性关得以改善。     

树干径流对梭梭"肥岛"和"盐岛"效应的作用机制

为探明荒漠灌木个体周围土壤养分和盐分的空间分布及其成因,以荒漠灌木梭梭(Haloxylon ammodendron Bge.)为研究对象,对其周围土壤pH值,电导率,有机碳,全氮和有效磷的空间异质性以及树干径流的化学性质进行了研究。结果表明:树干周围出现显著的"肥岛"效应,且土壤有机碳,全氮和有效磷的"肥岛"作用范围发生在距主根大约20—40 cm以内。土壤pH值和电导率在主根周围25 cm以内的值却显著低于外围,而在离主根25 cm处出现了"盐岛",即在梭梭主根中心形成了一种高养分、低盐和低pH值的环境。树干径流和自然降雨化学性质的对比研究表明:除pH值和CO23-外,树干径流中其他化学离子的含量均显著高于自然降雨中的含量,说明这种高养分、低盐分的环境是由树干径流引起的,也就是树干径流带给土壤养分的同时将盐分带走。     

古尔班通古特沙漠西南缘柽柳沙包的土壤化学计量特征

柽柳沙包作为沙漠地区一种特殊的生物地貌景观，在维持区域生态环境稳定中发挥着极为重要的作用。以古尔班通古特沙漠西南缘的典型柽柳沙包为研究对象，通过对土壤含水量、pH值、电导率、粒径及土壤有机碳（SOC）、总氮（TN）、总磷（TP）含量的分析，探讨了古尔班通古特沙漠柽柳沙包中土壤C、N、P的化学计量特征、垂直变化规律及影响因素。结果表明：（1）随着土层深度增加，SOC和TN均呈先升高后降低的变化，且C、N在表层土壤含量最高，具有"肥岛效应"；总磷（TP）含量总体变化幅度较小，呈弱变异。随着土层深度增加，土壤C/N呈先降低后升高再降低的变化，C/P和N/P呈先降低后升高的变化。（2）与全球及中国平均值相比，古尔班通古特沙漠柽柳沙包土壤C、N、P、C/N、C/P及N/P均相对较低，而C/N相对较高，土壤养分缺乏程度表现为N > C > P。土壤养分元素及化学计量比多呈显著的线性关系，且土壤化学计量比在0-200 cm层主要受C、N的制约，在200-500 cm层不仅受C、N的制约，也受P的限制。（3）土壤C、N、P化学计量特征在0-200 cm层主要受降水、温度及蒸发等气候因素的影响，而在200-500 cm层易受土壤含水量的影响；此外，粘、粉、沙粒含量在整个土壤剖面中对土壤C、N、P化学计量特征也具有明显的影响。     

盐碱地柽柳“盐岛”和“肥岛”效应及其碳氮磷生态化学计量学特征

为了探讨"盐岛"和"肥岛"效应影响下盐碱土的养分特征,对黄河三角洲盐碱地柽柳植株周围不同土层的pH值、电导率和碳氮磷含量及其生态化学计量学特征进行了研究.结果表明:土壤pH和电导率均随土层的加深而升高,0~20 cm土层土壤电导率随离植株距离的增加而降低,全磷含量则升高.20~40 cm土层土壤有机碳、全氮、N/P和C/P随离柽柳植株距离的增加而降低,C/N则升高.随着土层的加深,有机碳和全氮均呈降低趋势,而全磷则先降低后升高.土壤pH与电导率呈显著正相关,且二者与土壤碳氮磷及其生态化学计量比之间均呈显著负相关.     

黄河三角洲滨海滩涂不同密度柽柳林的土壤盐碱与养分特征

为探讨黄河三角洲滨海滩涂不同密度柽柳林的土壤盐碱和养分特征，明确不同密度柽柳林的“盐谷”及“肥岛”效应，以黄河三角洲山东省滨州市北海新区滨海滩涂的低密度（1100 株/hm2）、中密度（4100 株/hm2）和高密度（7100 株/hm2）柽柳林为研究对象，测定分析不同密度柽柳林及柽柳植株周边不同位置的土壤pH、电导率、速效氮、速效磷、速效钾、有机碳等指标。结果表明：（1）土壤电导率随林分密度增大表现为逐渐减小，在中、高密度柽柳林，土壤电导率分别比低密度降低28.39%、55.74%；随距离柽柳植株远近不同，中、高密度柽柳林土壤电导率表现为根部<冠幅中心<冠幅边缘<株间空地，即中、高密度柽柳林出现“盐谷”效应，而低密度林分未出现。（2）土壤速效氮、速效磷和有机碳含量随林分密度增大表现出先增大后减小，在中、高密度柽柳林，柽柳植株周边不同位置的速效氮、速效磷和有机碳含量存在显著差异（P<0.05），表现为根部>冠幅中心>冠幅边缘>株间空地，而低密度柽柳林差异不显著（P>0.05）；即中、高密度柽柳林出现“肥岛”效应，而低密度林分未出现。（3）中密度柽柳林在养分含量、养分富集率方面高于高密度，在盐分富集率方面低于高密度，具有更强的“肥岛”、“盐谷”效应。（4）不同密度柽柳林以及柽柳植株周边不同位置的土壤pH差异均不显著（P>0.05）。林分密度显著影响土壤盐分及养分含量，中密度柽柳林具有显著提高土壤肥力的作用，高密度次之，而低密度较差。不同密度柽柳林的降盐作用表现为中、高密度较好，低密度较差。基于柽柳林改良土壤盐碱与养分的作用，建议黄河三角洲滨海滩涂柽柳合理的初植密度为4100 株/hm2。     

盐碱地柽柳“盐岛”和“肥岛”效应及其碳氮磷生态化学计量学特征

为了探讨“盐岛”和“肥岛”效应影响下盐碱土的养分特征,对黄河三角洲盐碱地柽柳植株周围不同土层的pH值、电导率和碳氮磷含量及其生态化学计量学特征进行了研究.结果表明: 土壤pH和电导率均随土层的加深而升高,0～20 cm土层土壤电导率随离植株距离的增加而降低,全磷含量则升高.20～40 cm土层土壤有机碳、全氮、N/P和C/P随离柽柳植株距离的增加而降低,C/N则升高.随着土层的加深,有机碳和全氮均呈降低趋势,而全磷则先降低后升高.土壤pH与电导率呈显著正相关,且二者与土壤碳氮磷及其生态化学计量比之间均呈显著负相关.     

Rhombomys opimus contribution to the “fertile island” effect of tamarisk mounds in Junggar Basin

Fertile islands are created and maintained by a combination of physical and biologically mediated processes. Plants have been shown to be very important in the formation of fertile islands, and recent research indicates that the activities of burrowing animals have a significant influence on the physiochemical properties of soil that can promote the development of fertile islands. In this paper, we chose tamarisk (Tamarix spp.)??a constructive species that grows in the oasis-desert ecotone, and the great gerbil (Rhombomys opimus)??a widely distributed rodent in Central Asia to study the influence of great gerbils on soil nutrient dynamics in tamarisk mounds. Results indicate that fertile islands exist in tamarisk mounds without burrows of the great gerbil. However, the great gerbil??s burrowing activities promote the fertile island effect in tamarisk mounds: soil nutrients under shrubs with great gerbil activity were significantly higher than inter-mound areas in both surface soil and deep soil from 15 to 50?cm. Available nitrogen in mounds with rodent burrows was over twice as high as in tamarisk mounds without burrows at the same depth. The great gerbil??s burrowing activities promote the concentration of soil nutrients in the tamarisk mounds.     

不同形成时间高原鼢鼠鼠丘土壤养分分配规律

高原鼢鼠(Myospalax baileyi)作为青藏高原唯一营地下生活的鼠类,其造丘活动不仅能影响草地群落演替的方向和进程,而且对鼠丘土壤养分含量和分配造成空间异质性。关于不同形成时期的高原鼢鼠鼠丘养分含量及在垂直高度的分配规律研究报道尚少。基于此本研究以不同形成时期的鼢鼠鼠丘为研究对象,对鼠丘土壤养分含量及空间分配规律进行探讨。结果表明:随着鼠丘形成时间的推移,土壤养分总体表现为:1年鼠丘多年鼠丘对照区;与非鼠丘区相比,随着土壤土层增加,土壤养分未呈现规律性的变化。其中,土壤全氮和速效氮含量表现为1年鼠丘3年鼠丘5年鼠丘对照区;0—10cm土壤全磷和速效磷含量变化总体表现为多年鼠丘1年鼠丘对照区,10—30cm土层1年鼠丘土壤中全磷和速效磷含量最高。土壤速效钾和有机质含量随着鼠丘形成时间推移总体表现为:1年鼠丘5年鼠丘3年鼠丘;其中在10—30cm土层,1年鼠丘速效钾和有机质含量显著高于多年鼠丘和对照区。由此可见,高原鼢鼠造丘活动能显著改变土壤养分分配格局,短期内形成养分富集的肥力岛,为鼠丘土壤种子库中种子的萌发和植被生长提供必需的养分保证。     

The impact of plateau zokor<Emphasis Type="Italic">Myospalax fontanierii</Emphasis> burrows on alpine meadow vegetation on the Qinghai-Xizang (Tibetan) plateau

The impact of burrows constructed by plateau zokorsMyospalax fontanierii (Milne-Edwards, 1867) on alpine meadow vegetation on the Qinghai-Xizang (Tibetan) plateau was investigated. Plant samples taken from quadrats directly over active zokor burrows, back-filled burrows, adjacent burrow controls, and random sites from a field, in which no burrows or mounds occurred were compared. The biomass of plants (below- and above-ground) directly over shallow active burrows was significantly lower than on control plots. This reduction in biomass was not significantly different than that between deep active burrows and control plots. There were no significant differences between above- and below-ground plant biomass on areas perpendicular to active burrows when compared to random sites. Back-filling soil in burrows could promote the growth of above-ground monocotyledonous plants. However, the burrowing activities of zokors had a negative effect on biomass of dicotyledonous plants.     

玛河流域扇缘带盐穗木土壤速效养分的"肥岛"特征

比较了玛河流域扇缘带盐穗木灌丛在单生条件下及与猪毛菜共生条件下的土壤速效养分的"肥岛"特征。结果表明,盐穗木灌丛周围土壤的"肥岛"现象主要体现在土壤表层,沿立地点向外每隔0.6m逐渐减弱,且沿土层深度增加逐渐减弱。盐穗木在单生条件下,灌丛土壤碱解氮和速效钾在立地中心有明显的富集现象。在从立地原点向外3m的表层土壤中,两种养分分别从 2.75 g/kg和56.67 mg/kg下降至1.66 g/kg和29.0 mg/kg,且沿土壤剖面向下呈现显著性降低趋势(P<0.05),但均显著性高于裸地的同类值。而速效磷含量整体呈现亏损状态,其平均值较裸地速效磷含量低25.33%,表明盐穗木种群具有促进氮和钾的富积、但消耗磷的生态功能。在盐穗木-猪毛菜共生条件下,无论是在土壤表层还是沿土壤剖面,3种速效养分的含量整体上显著性高于裸地。共生条件下土壤的碱解氮含量整体低于单生条件下的值,而速效磷和速效钾的含量则是共生大于单生。研究表明,盐穗木单一种群条件下土壤速效磷的亏损状态可在猪毛菜共生条件下出现逆转,两者具有互补效应。该结论为干旱盐碱化地区植物与土壤关系研究提供了新的理论潜力。     

高原鼠兔挖掘活动对土壤中氮素含量的影响

本文通过测定不同类型高原鼠兔鼠丘和鼠丘下0 ～ 10 cm 土壤中总氮、铵态氮和硝态氮的含量变化,分析了高原鼠兔挖掘活动对土壤中无机氮含量的影响,并通过测定高原鼠兔鼠丘密度,计算了每只高原鼠兔对氮素循环的贡献。研究结果表明:不同类型鼠丘土壤中总氮含量无明显变化,铵态氮、硝态氮和无机氮含量处理间变化趋势为当年鼠丘>两年鼠丘> 多年鼠丘> 对照。方差分析结果表明,硝态氮含量在5 月时差异显著,当年鼠丘和两年鼠丘显著大于多年鼠丘和对照,无机氮含量在5 月和9 月表现为当年鼠丘显著高于对照。在不同月份,铵态氮含量月间变化趋势为5 ～ 8 月逐渐降低,至9 月略有增加,硝态氮和无机氮含量呈现“高- 低- 高-低- 高”的“W”变化趋势。方差分析结果显示,铵态氮、硝态氮和无机氮含量月间变化显著。不同类型鼠丘下0 ～ 10 cm 土壤中铵态氮、硝态氮和无机氮含量处理间和月份间变化趋势与鼠丘土壤中变化趋势基本一致,但硝态氮和无机氮含量在当年鼠丘中均显著高于对照,且不同月份间铵态氮、硝态氮和无机氮的含量差异显著(P
< 0.05)。每只高原鼠兔挖掘活动所形成的鼠丘土壤中的铵态氮、硝态氮和无机氮分别增加了162.6 mg/ kg、355.1 mg/kg 和497.7 mg/ kg。     

Islands of Fertility: A Byproduct of Grazing?

Empirical work in arid shrubland systems has documented a distinct spatial pattern of soil nutrient distribution, with higher concentrations of nutrients under shrub canopies compared to bare ground interspaces between shrubs. This “fertile island” pattern is considered characteristic of arid ecosystems. However, recent work at a desertified shrubland site reported no island of fertility pattern for nitrogen inside a long-term grazing exclosure despite a strong fertile island pattern outside the exclosure, leading to a hypothesis that the pattern may be associated with grazing. In this paper we examine this hypothesis in two ways. First, we collected soil nitrogen data inside and outside two long-term livestock exclosures. Second, we examined published work on the fertile island pattern for nitrogen, phosphorus and carbon, and its association with livestock grazing. At the field sites, there was a strong fertile island pattern for soil nitrogen in the grazed area outside each exclosure but no fertile island pattern in the ungrazed area inside the fence. From the literature, we identified 49 studies, which represent 99 cases that examine differences in soil nutrients under and between shrubs (that is, tests of the fertile island pattern). In 92 cases, fertile islands were present for at least one of the nutrients. All cases where livestock grazing was present exhibited fertile island patterns for nitrogen and most did so for carbon and phosphorus. In contrast, fertile islands were less consistent where livestock grazing was absent; all nine cases that had been ungrazed for more than 30 years did not exhibit fertile islands for nitrogen. Our empirical data and literature review suggest that the fertile island pattern may be an artifact of grazing rather than an inherent property of arid shrublands. Further, we suggest that the grazing history of a site needs to be explicitly considered when documenting spatial patterns of soil nutrients in arid systems. This has significant implications for our understanding of soil nutrient dynamics in arid systems, the management of rangelands, and the potential for reversal of desertification.     

Spatial heterogeneity of soil chemical properties at fine scales induced by <Emphasis Type="Italic">Haloxylon ammodendron</Emphasis> (Chenopodiaceae) plants in a sandy desert

Spatial heterogeneity is considered a ubiquitous feature in natural ecosystems. Fertile islands represent a typical example for such heterogeneity in desert ecosystems. The soil pH and salinity also show significant heterogeneity in fertile islands. To investigate the distribution of soil salinity and nutrients around individual shrubs and the major factors influencing their distribution, an experiment was conducted at the scale of the rhizosphere, root system, and individual for Haloxylon ammodendron (C. A. Mey.) Bunge (Chenopodiaceae) shrub in the Gurbantünggüt Desert. Specifically, the heterogeneity of the following soil chemical parameters was evaluated: pH, electrical conductivity (EC), soil organic carbon (SOC), total nitrogen (TN), and available phosphorus (AP). The chemical properties of the shrub stemflow were also evaluated to determine its contribution to the formation of fertile islands and the distribution of soil salinity. The results revealed great variance in the soil pH and EC at the rhizosphere and root system scales, indicating that a single root or root system exerts a great effect on soil pH and salinity. At the individual scale, the content of SOC, TN, and AP was significantly enriched in the layers adhering to the taproot, and this enrichment extended 20–40 cm from the taproot. Conversely, the soil pH and EC were significantly lower from the taproot to 10–25 cm away from the root, indicating that the fertile island is also an island of low alkalinity/salinity. Comparison of the chemical properties of stemflow and bulk precipitation revealed a higher content of chemical elements (except pH and CO₃ ²⁻) in the stemflow, indicating that the fertile island and lower pH and EC in this island were likely formed by the effects of stemflow. Specifically, stemflow brings in water and nutrients, while reducing the salt levels. Overall, the high nutrients and low alkalinity/salinity island created around the taproot favor the growth of the plants.