生物结皮对5种不同形态的荒漠植物种子萌发的影响

生物结皮广泛分布于干旱、半干旱区, 强烈影响着土壤表层理化特性, 进而对种子散布、萌发和定居产生影响。目前关于生物结皮与植物种子萌发关系的研究结论存在争议。该文通过室内人工控制实验, 研究了生物结皮对古尔班通古特沙漠5种具不同种子形态特征的荒漠植物白梭梭(Haloxylon persicum)、蛇麻黄(Ephedra distachya)、角果藜(Ceratocarpus arenaarius)、涩芥(Malcolmia africana)和狭果鹤虱(Lappula semiglabra)的种子萌发的影响。结果表明, 在干燥和湿润两种条件下, 生物结皮对不同形态植物种子萌发均具有不同的作用。在干燥条件下, 生物结皮显著抑制了角果藜和涩芥种子的萌发(p<0.05), 对其它3种植物无显著影响; 而湿润条件下, 生物结皮显著抑制了白梭梭、角果藜和狭果鹤虱种子的萌发(p<0.05), 对蛇麻黄、涩芥则无显著影响。     

Effects of biological soil crusts on emergence of desert vascular plants in North China

Biological soil crusts are a universal and common feature in arid and semi-arid regions and their appearance profoundly affects soil surface properties which may greatly change the seed dispersal, germination and establishment. To date, only a handful of experiments have exerted to investigate the effects of crusts on vascular plants and the conclusions from these studies are variable. In this study, we investigate the influences of two different crusts universally spreading in southeastern part of the Tengger Desert with four chronosequences (24, 41, 50 years old in artificial vegetation area and natural vegetation crusts) on vascular plants. Crusts were placed at three different sites to simulate different environmental factors (wind velocity and soil crust moisture), we set two soil moisture regimes for crusts to investigate how vascular plants respond under different moisture regimes in crusts. Emergence densities of vascular plants were significantly higher in moss crust than in algae crust. With the development of crusts, seed emergence increased in moss crust while decreased in algae crust. As for effects of moisture, our results showed that soil moisture had a significant effect on seed emergence in both types of crusts at all developing phases. Crusts with higher moisture had more seedlings than those with lower moisture. The above results indicated that the appearance of crusts changed the surface soil properties, which had greatly influenced the entrapment and lodgement of seeds in the study area, thus subsequently influence seed emergence through affecting natural factors.     

实验室条件下两种生物土壤结皮对荒漠植物种子萌发的影响

生物土壤结皮广泛分布在干旱、半干旱区,深刻影响着土壤表层特性,进而对植物种子散布、萌发和定居产生极大的影响。到目前为止,生物土壤结皮与植物关系的研究很少见到,并且这些有限的研究所得出的结论存在着争议。研究了不同年龄的两种生物土壤结皮（苔藓结皮和藻类结皮）对油蒿（Artemisia ordosica）和雾冰藜（Bassia dasyphylla）种子萌发的影响,同时也研究了这两种结皮在失去活性前后对油蒿、雾冰藜和小画眉草（Eragrostis poaeoides）种子萌发的影响。苔藓和藻类结皮的出现对油蒿和雾冰藜种子的萌发均有显著的促进作用,而结皮年龄对植物种子的萌发没有显著的差异。对于不同的植物种,结皮类型和活性对种子的萌发具有不同的作用。雾冰藜在两种结皮上的萌发有显著的差异而油蒿和小画眉草在两种结皮上的萌发没有显著差异。活藻类显著地增加了三种植物的种子萌发,活苔藓仅增加了油蒿和雾冰藜种子萌发量而对小画眉草种子的萌发没有作用,研究表明,生物土壤结皮对一些植物种子萌发具有明显的促进作用。     

Effects of Biological Soil Crusts on Seed Bank, Germination and Establishment of Two Annual Plant Species in the Tengger Desert (N China)

The presence of biological soil crusts can affect the germination and survival of vascular plants, but the reasons are not well investigated. We have conducted a field investigation and greenhouse experiments to test the effect of crusts on two desert annual plants, which occur on the stabilized dunes of the Tengger Desert in N China. The results showed that biological soil crusts negatively influenced the seed bank of Eragrostis poaeoides and Bassia dasyphylla. The important effect of biological soil crusts on seed germination and establishment were performed indirectly through reducing the amount of germinating seeds. Field investigation and experimental results with regard to the seed bank indicated that higher seedling density was found in disturbed crust soil and bare soil surface than in intact crust soils. Greenhouse experiments showed that the effects of biological soil crusts on germination and establishment of the two plants are not obvious in moist condition, while disturbed crusts are more favorable to seed germination in dry treatment. Significant differences in biomass were found between disturbed crust soil and bare soil. Survival and growth of the two annual plants were enhanced in both algal and moss crusts during the season of rainfall or in moist environment, but crusts did not affect seedling survival in the dry period. The small seeded E. poaeoides has higher germination than larger-seeded B. dasyphylla in crust soils, but B. dasyphylla has a relatively higher survival rate than E. poaeoides in crust soils.     

腾格里沙漠固定沙丘藓类植物结皮层的自然恢复及人工培养试验研究

 通过藓类结皮层的自然恢复和人工培养藓类植物促进结皮层形成试验,研究了腾格里沙漠固定沙丘生物结皮层形成过程中优势成分真藓 （Bryum argenteum） 的繁殖生物学特性,结果表明：藓类结皮层人工去除后在3～4年内70%的样方基本恢复,在此过程中真藓主要靠茎叶碎片传播和繁殖;通过分株法、撒茎叶法培养的真藓在1个月后长满整个样地, 主要通过如下方式繁殖——茎的碎片连续分枝可产生小植株,茎、叶均可产生原丝体,由原丝体发育产生小植株,小植株又可再生原丝体,如此反复产生新植物体,这一过程是野外人工促进生物结皮层形成过程中真藓主要的繁殖途径。与室内培养中真藓的繁殖特性相比较,野外培养的真藓在繁殖过程中产生的原丝体较粗壮,分枝多,但在两种条件下的繁殖特性相同,能够揭示该地区自然条件下藓类植物萌发和定居的繁殖机理。该研究为人工促进生物结皮层形成及治理受损结皮层提供了实验依据。     

模拟降水对古尔班通古特沙漠生物结皮表观土壤碳通量的影响

水分是控制干旱区生态过程的重要环境因素,在水分受限制的生态系统中,降水通过改变土壤的干湿状态直接控制地下生物过程。生物结皮作为干旱区主要的地表覆盖物,能利用空气中有限的水分进行光合作用,其自身的碳交换是干旱区土壤碳通量的重要组成部分。通过模拟0(对照)、2、5 mm和15 mm 4个降水梯度,利用红外气体分析仪,对古尔班通古特沙漠中部生物结皮以及裸地表观土壤碳通量进行测量,探讨不同强度降水条件下生物结皮对表观土壤碳通量的影响,结果表明:(1)降水增加了生物结皮表观土壤碳释放量,2、5 mm和15 mm 3种降水处理累积碳释放量分别是对照的151.48%、274.97%、306.44%,并且随着降水后时间的延长,表观土壤碳通量逐渐减小直至达到降水前的水平;(2)生物结皮与裸地的表观土壤碳通量对降水的响应不同,对照和最大降水量下,生物结皮表观土壤碳通量大于裸地,但是2 mm和5 mm降水后,生物结皮表观土壤碳通量小于裸地,并且二者在2 mm降水时差异显著(P<0.05),而在其它降水处理下无显著差异;(3)连续两次降水事件,活性碳在初级降水后的大量释放使得二次降水后释放量下降,其中裸地碳释放量下降速率与降水强度正相关。本研究说明,在探求荒漠地区土壤碳交换对降水的响应规律时,应该考虑生物结皮的影响以及连续降水事件的差异。     

Seed characteristics and soil surface patch type interact to affect germination of semi-arid woodland species

Biological soil crusts are common in many arid and semi-arid regions and they can alter microenvironments which are likely to directly and indirectly influence vascular plant establishment. The effect of biological soil crusts on germination is also influenced by the biological characteristics of the seeds themselves but rarely have the effects of both crust type and seed morphology on germination been examined in the same study. In this study, seed of five semi-arid woodland species with contrasting seed morphology were sown on top of patch types that commonly occur in natural woodlands (foliose lichen, short-turf moss, tree leaf litter, disturbed crust) and their emergence was followed. Percent germination varied between patch types and, for the largest-seeded species (Maireana excavata), final germination was significantly lower on the biological soil crust and litter patch types because they strongly acted as a physical barrier to seed penetration into the soil. The remaining four species showed no significant differences in final percent germination with patch type because most seeds either completely or partially penetrated the surface layer. Germination time courses, however, showed that biological soil crusts delayed the timing of germination of these species. Hence, soil crusts might differentially affect the spatial patterning of species in semi-arid woodlands by their subtle influence on seedling emergence that is determined by differences in seed morphology and subsequent positioning within crusts.     

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.     

Population dynamics of Echinops gmelinii Turcz. at different successional stages of biological soil crusts in a temperate desert in China

• The effects of biological soil crusts (BSC) on vascular plant growth can be positive, neutral or negative, and little information is available on the impacts of different BSC successional stages on vascular plant population dynamics.
• We analysed seedling emergence, survival, plant growth and reproduction in response to different BSC successional stages (i.e. habitats: bare soil, cyanobacteria, lichen and moss crusts) in natural populations of Echinops gmelinii Turcz. in the Tengger Desert of northwest China. The winter annual E. gmelinii is a dominant pioneer herb after sand stabilisation.
• During the early stages of BSC succession, the studied populations of E. gmelinii were characterised by high density, plant growth and fecundity. As the BSC succession proceeded beyond moss crusts, the fecundity decreased sharply, which limited seedling recruitment. Differences in seedling survival among the successional stages were not evident, indicating that BSC have little effect on survival in arid desert regions. Moreover, E. gmelinii biomass allocation exhibited low plasticity, and only reproductive allocation was sensitive to the various habitats. Our results further suggest that the negative effects of BSC succession on population dynamics are primarily driven by increasing topsoil water‐holding capacity and decreasing rain water infiltration into deeper soil.
• We conclude that BSC succession drives population dynamics of E. gmelinii, primarily via its effect on soil moisture. The primary cause for E. gmelinii population decline during the moss‐dominated stage of BSC succession is decreased fecundity of individual plants, with declining seed mass possibly reducing the success of seedling establishment.

     

生物土壤结皮对准噶尔盆地5种荒漠植物幼苗生长与元素吸收的影响

生物土壤结皮广泛分布于许多干旱和半干旱地区, 它影响土壤物理过程、水文、侵蚀和养分循环过程, 从而影响植物种子萌发与生长发育。该文以新疆准噶尔盆地腹地的古尔班通古特沙漠的生物土壤结皮为研究对象, 分析了生物土壤结皮对准噶尔盆地5种荒漠植物(白梭梭(Haloxylon persicum)、蛇麻黄(Ephedra distachya)、角果藜(Ceratocarpus arenaarius)、涩芥(Malcolmia africana)和狭果鹤虱(Lappula semiglabra))的生长及其对元素吸收的影响。结果表明: 1)相对于裸沙而言, 生物土壤结皮显著促进了荒漠植物的生长速率, 并增加了草本植物地上和地下的生物量, 但对灌木的生物量无显著影响; 2)生物土壤结皮使部分一年生草本植物的开花和结实期提前, 这可能有利于荒漠植物在有限的环境资源下快速完成生活史, 并繁衍后代; 3)生物土壤结皮能够影响荒漠植物对土壤中营养元素的吸收, 具体表现在生物土壤结皮显著促进了5种植物对N的吸收, 增加了荒漠植物在N贫乏的荒漠生态系统的适应能力, 而对P和K的吸收均没有影响。生物土壤结皮对荒漠植物对元素吸收的影响因种而异, 对不同的植物有不同的影响。荒漠植物对Mg、Mn和Cu的吸收受生物土壤结皮的影响最小。     

Dispersal strategies and spatial organization of vegetation in arid ecosystems

Seed dispersal and establishment are critical stages for plants in arid environments, where vegetation is spatially organized in patches with suitable and unsuitable sites for establishment. Theoretical studies suggest that the ability of vegetation to self‐organize in patchy spatial patterns is a critical property for plant survival in arid environments, and is a consequence of a scale‐dependent feedback between plants and resource availability. Field observations show that plants of arid environments evolved towards short dispersal distance (proxichory) and that the investment in reproduction increases along an aridity gradient. Here, we investigated how plant dispersal strategies affect spatial organization and associated scale‐dependent feedback in arid ecosystems. We addressed this research question using a model where the spatio‐temporal vegetation patterns were driven by scale‐dependent feedbacks between plants and soil water availability. In the model, water availability limited vegetation growth, seed production and establishment ability. Seed dispersal was modelled with an integrodifferential equation that mimicked important plant dispersal characteristics (i.e. fecundity, mean dispersal distance and establishment ability). Results showed that, when the investment in fecundity was relatively high, short seed dispersal helped maintaining higher mean biomass in the system, improving the vegetation efficiency in water use. However, higher fecundity induced a large cost, and high mean biomass could be sustained only with high establishment ability. Considering low establishment ability, intermediate fecundity was more efficient than low fecundity in maintaining high plant biomass under the most arid conditions. Consistently, plant dispersal strategies that maintained more biomass were related to a vegetation spatial organization that allowed the most efficient soil water redistribution, through the strengthening of the scale‐dependent feedback. The efficient dispersal strategies and spatial patterns in the model are commonly observed in plants of arid environments. Thus, dispersal strategies in arid environments might contribute to a favourable spatial organization and associated scale‐dependent feedback.     

Experimental Studies on the Natural Restoration and the Artificial Culture of the Moss Crusts on Fixed Dunes in the Tengger Desert,China

Soil microbiotic crusts cover extensive portions of the arid and semiarid regions of the world and play an important ecological role.Moss is one of the major components in the crusts.The reproduction and establishment of the mosses are crucial to the formation of moss crusts.Bryum argenteum is the dominant species of moss crusts in the Shapotou region (104°57'E,37°27'N) of the Tengger Desert.In search for the characteristics of natural reproduction and establishment of the mosses,10 quadrates (10×10 cm for each) were obtained by removing the moss crusts in different positions of fixed dunes.These 10 quadrates were observed for 3 years depending on the species' components and coverage.Meanwhile,in the third year,two quadrates (1×1 m for each) were set up in a crustabsent area and two different experiments of the asexual reproduction (broadcast planting and offshoots) were conducted,respectively.The reproductive process was observed under the microscope,and the morphological indicators of the new individuals were measured.The results were compared with the ones from indoor experiments using the same methods.All the results showed the following:(1) 70% of the quadrates (i.e.,7 of the 10 quadrates) were recovered within 3-4 years;thus,the quick recovery might be due to the dispersal and reproduction of the fragments of stems and leaves of B.argenteum;(2) as for the two quadrates in the artificial reproduction test,the new plants occupied the uncovered space of the quadrates in 1 month,and there were two main reproduction approaches,one of which was that the stems continually branched and produced young plants,and the other was that the young plants and the fragments of the stems and leaves repeatedly and extensively reproduced protonema,which finally developed into a large number of new plants;(3) the reproductive characteristics were identical,though the protonema in the field was more robust and had more branches than the ones indoors.     

Disturbance of biological soil crust increases emergence of exotic vascular plants in California sage scrub

Biological soil crusts (BSCs) are comprised of soil particles, bacteria, cyanobacteria, green algae, microfungi, lichens, and bryophytes and confer many ecosystem services in arid and semiarid ecosystems worldwide, including the highly threatened California sage scrub (CSS). These services, which include stabilizing the soil surface, can be adversely affected when BSCs are disturbed. Using field and greenhouse experiments, we tested the hypothesis that mechanical disturbance of BSC increases emergence of exotic vascular plants in a coastal CSS ecosystem. At Whiting Ranch Wilderness Park in southern California, 22 plots were established and emergence of exotic and native plants was compared between disturbed and undisturbed subplots containing BSC. In a separate germination study, seed fate in disturbed BSC cores was compared to seed fate in undisturbed BSC cores for three exotic and three native species. In the field, disturbed BSCs had significantly (>3×) greater exotic plant emergence than in undisturbed BSC, particularly for annual grasses. Native species, however, showed no difference in emergence between disturbed and undisturbed BSC. Within the disturbed treatment, emergence of native plants was significantly, and three times less than that of exotic plants. In the germination study, seed fates for all species were significantly different between disturbed and undisturbed BSC cores. Exotic species had greater emergence in disturbed BSC, whereas native plants showed either no response or a positive response. This study demonstrates another critical ecosystem service of BSCs—the inhibition of exotic plant species—and underscores the importance of BSC conservation in this biodiversity hotspot and possibly in other aridland ecosystems.     

Biological soil crusts determine the germination and growth of two exotic plants

In arid and semiarid ecosystems, the potential threats of exotic invasive species are enhanced due to increasing human activities. Biological soil crusts (BSCs), acting as arid ecosystem engineers, may play an important role in preventing the establishment of exotic invasive plants. Our goal was to examine whether BSCs could inhibit the establishment of probable exotic plant species originating from adjacent grasslands located along the southeast edge of the Tengger Desert. In our study, we investigated the effects of three BSC types (cyanobacteria, lichen, and moss crusts) under two disturbance conditions (intact and disturbed) on the establishment of two exotic plant species (Ceratoides latens and Setaria viridis) using indoor experiments. We found both negative and positive effects of BSCs on the establishment of the two exotic plant species. Compared with the disturbed BSCs, the germination percentages of C. latens and S. viridis were reduced by 54% to 87% and 89% to 93%, respectively, in intact BSCs. In contrast, BSCs significantly promoted the height growth and aboveground biomass of the two exotic plant species (p < .05) by enhancing the soil water and nutrient availability for the exotic plants. Our results confirm that BSCs strongly suppress the rapid expansion of exotic plant populations by inhibiting germination of seed with big size or appendages and have a weak inhibitory effect on exotic plant with small and smooth seeds. This may decrease the threat of propagation of exotic species. In the meantime, BSCs promote the growth of a few successful engraftment seedlings, which increased the beta diversity. Our work suggests that better understanding the two opposing effects of BSCs on the establishment of exotic plant species in different growth stages (germination and growth) is important for maintaining the health and stability of revegetated regions.     

生物土壤结皮对种子萌发和幼苗建植的影响研究进展

生物土壤结皮（BSC）在陆地生态系统中具有重要的生态地位,尤其是旱地生态系统中,BSC占据了种子植物之间的广阔地面。因此,BSC的发展必然影响种子植物更新过程与植被空间格局;但其作用方式、影响程度等因相关研究涉及多气候要素、土壤类型、BSC组成物种和种子植物物种的差异及其不同组合,导致目前的研究结论存在广泛争议。研究综合论述了BSC改变地表微形态对种子传播过程的影响;BSC改变土壤特性（物理、化学、生物学）对种子萌发和幼苗存活与建植等关键环节的影响;并结合种子形态特征及种子萌发、幼苗建植的性状等,综合分析了BSC对种子传播、种子萌发与幼苗建植等更新过程的潜在影响机理;探讨了目前研究矛盾性结论产生的原因。总体来说,深入研究并全面揭示BSC对种子植物更新过程的影响,应加强学科交叉,将分子生物学、植物生理学、生物化学等微观研究,与遥感、野外生态因子过程监测、控制实验等宏观、中观研究结合,从机理到过程方面动态研究BSC对种子植物更新过程的影响,并引入水文模型、气候模型、种群动态模型等模型预测方法,研究气候变化、各类干扰频发的情景下,BSC对种子传播、萌发及幼苗建植过程的潜在影响,以期促进对BSC与种子植物间相互关系的研究,加深对干旱脆弱生态系统植被发展规律的认识。     

Progress in the study of algae and mosses in biological soil crusts

Algae and mosses are not only two of the familiar communities in the process of desert vegetational succession, but also have the highest biomass in biological soil crusts. Meanwhile, being the pioneer plants, algae and mosses are involved in the establishment of biological soil crusts, which have great importance in arid environments and play a major role in desert ecosystems, such as being the indicator of the vegetation type, soil-holding, preventing erosion by water and wind, and sand fixation. This paper reviews the advances in the study of algae and mosses in arid and semi-arid areas. It mainly describes the ecological functions of algae and mosses including their influences on water cycle, circulation of substances, and community succession. In addition, the relationships between algae and mosses are discussed. Finally, some suggestions are proposed for the research orientations of algae and mosses in biological soil crusts. Ecologically, algae and mosses have significant ecological importance in arid areas, especially in those areas where environmental problems are becoming increasingly serious.     

Progress in the study of algae and mosses in biological soil crusts

Algae and mosses are not only two of the familiar communities in the process of desert vegetational succession,but also have the highest biomass in biological soil crusts.Meanwhile,being the pioneer plants,algae and mosses are involved in the establishment of biological soil crusts,which have great importance in arid environments and play a major role in desert ecosystems,such as being the indicator of the vegetation type,soil-holding,preventing erosion by water and wind,and sand fixation.This paper reviews the advances in the study of algae and mosses in arid and semi-arid areas.It mainly describes the ecological functions of algae and mosses including their influences on water cycle,circulation of substances,and community succession.In addition,the relationships between algae and mosses are discussed.Finally,some suggestions are proposed for the research orientations of algae and mosses in biological soil crusts.Ecologically,algae and mosses have significant ecological importance in arid areas,especially in those areas where environmental problems are becoming increasingly serious.     

Recovery of lichen-dominated soil crusts in a hyper-arid desert

Soil crust lichens can be the dominant vegetation in desert regions that are unsuitable for higher plants, and are vital to soil stabilization and primary production. Biological soil crusts are vulnerable to disturbance and there is little evidence of the lichen components achieving full recovery following human disturbances in semi-arid to arid environments, and no records of recovery in hyper-arid deserts. Eight sites with varying anthropogenic, mechanical disturbance regimes were assessed in the hyper-arid Namib Desert for levels of recovery and successional convergence, based on a comparative analysis of overall lichen cover and community composition in disturbed and control locations. Recovery time estimations ranged from 5 to 530 years, with no detected linear relationship to impact gradient (low to high impact). Variables that were found to most strongly influence recovery rates were the overall cover of lichen growth and total number of lichen species in the bordering undisturbed areas, followed by the extent of soil compaction in the disturbed area, altered soil surface microrelief and vitality of subsurface soil crust components. An assessment of pioneering species demonstrated a link between increased soil depressions, i.e. track ruts, and the occurrence of fragmenting, wind-dispersing species. Track ruts in hype-arid deserts are not as vulnerable to the water erosion found in less arid deserts, and may be advancing recovery by trapping fragments. However, the lichen community structure was significantly different between all of the disturbed and control areas, regardless of the recovery phase, suggesting that while the lichen community composition may not. The ecological consequences of such disturbances may be far reaching in hyper-arid deserts where lichens are primary heterotrophs soil stabilizers. Given the economic development occurring within coastal hyper-acid deserts of the world, these impacts undoubtedly call for conservation attention.     

Experimental Studies on the Natural Restoration and the Artificial Culture of the Moss Crusts on Fixed Dunes in the Tengger Desert, China

Soil microbiotic crusts cover extensive portions of the arid and semiarid regions of the world and play an important ecological role. Moss is one of the major components in the crusts. The reproduction and establishment of the mosses are crucial to the formation of moss crusts. Bryum argenteum is the dominant species of moss crusts in the Shapotou region (104°57′E, 37°27′N) of the Tengger Desert. In search for the characteristics of natural reproduction and establishment of the mosses, 10 quadrates (10×10 cm for each) were obtained by removing the moss crusts in different positions of fixed dunes. These 10 quadrates were observed for 3 years depending on the species’ components and coverage. Meanwhile, in the third year, two quadrates (1×1 m for each) were set up in a crust-absent area and two different experiments of the asexual reproduction (broadcast planting and offshoots) were conducted, respectively. The reproductive process was observed under the microscope, and the morphological indicators of the new individuals were measured. The results were compared with the ones from indoor experiments using the same methods. All the results showed the following: (1) 70% of the quadrates (i.e., 7 of the 10 quadrates) were recovered within 3–4 years; thus, the quick recovery might be due to the dispersal and reproduction of the fragments of stems and leaves of B. argenteum; (2) as for the two quadrates in the artificial reproduction test, the new plants occupied the uncovered space of the quadrates in 1 month, and there were two main reproduction approaches, one of which was that the stems continually branched and produced young plants, and the other was that the young plants and the fragments of the stems and leaves repeatedly and extensively reproduced protonema, which finally developed into a large number of new plants; (3) the reproductive characteristics were identical, though the protonema in the field was more robust and had more branches than the ones indoors. Translated from Acta Phytoecologica Sinica, 2005, 29(1) (in Chinese)     

干旱沙区生物土壤结皮发育对红砂形态及干物质积累的影响

为了探讨干旱沙区生物土壤结皮发育对红砂形态及干物质积累的影响,以巴丹吉林沙漠南缘已发育不同类型生物土壤结皮并有红砂种群成功定居的区域为研究场所,通过野外监测与室内测定的方法对藻类-地衣、地衣、地衣-藓类结皮上的红砂（当年生、幼株、成株）形态特征及生物量进行了调查研究。结果表明：（1）藻类-地衣结皮演替到地衣-藓类结皮的过程中,当年生红砂形态差异不显著,但5 a以上植株基部分枝长、树冠/侧冠投影面积、主根长均显著减小;同时,地衣-藓类结皮的3-5 a植株基部分枝数明显减少,且5 a以上植株明显矮化。（2）生物土壤结皮发育不仅降低了红砂幼株或成株生物量积累能力,还减小了植株根冠比,且降低/减小程度随结皮演替或株龄的增大逐渐增大。（3）红砂形态、生物量指标与物理或藻类结皮面积百分比呈极显著正相关关系,与藓类结皮面积百分比呈极显著的负相关关系。因此认为,生物土壤结皮的演替导致土壤关键生态因子（如土壤水分）发生变化,进而影响红砂植株生长发育能力,从而使得不同发育阶段结皮上的同龄红砂形态特征及生物量存在差异性。