Moss-covered Soil Research Articles

Mosses stimulate soil carbon and nitrogen accumulation during vegetation restoration in a humid subtropical area

Mosses form a ground layer with a thickness of nearly 1 cm during the first decade of vegetation restoration, but their effects on the belowground microbial community and soil properties and the associated soil carbon (C) and nitrogen (N) accumulation in subtropical areas are unclear. Here, we measured soil C and N variables (soil organic C [SOC], total N [TN], dissolved organic C, ammonium [NH4+-N] and nitrate [NO3−-N]), soil microbial community and soil properties (soil water content [SWC] and pH) under four treatments (bare soil [BS], bare soil with transplanted moss, moss-covered soil [MS] and moss-covered soil with moss removed) in three vegetation types (forest plantations, forage grasslands and mixed plantations and forage grasslands) in a subtropical climate. We analyzed the effects of native mosses, moss transplantation and removal using BS and MS as references. One year post-treatment, moss transplantation increased NO3−-N and NH4+-N in the 0–5 cm and 2–5 cm soil layers, respectively. Conversely, moss removal decreased SOC and TN in the 0–2 cm soil layer and SWC in the 0–5 cm soil layer. Compared to BS and MS, native moss presence, moss transplantation and removal decreased the total microbial, bacterial and fungal biomass and altered the soil microbial community composition (ratios of fungi and bacteria and Gram-positive bacteria to Gram-negative bacteria) to varying degrees. Moss properties (biomass, C and N concentrations, C:N ratio and saturated water absorption content), as well as SWC, soil microbial biomass and community composition regulated by mosses affected soil C and N. These findings underscore the crucial role of mosses in facilitating soil C and N accumulation during vegetation restoration.

Bacterial Diversity Analysis and Screening for ACC Deaminase-Producing Strains in Moss-Covered Soil at Different Altitudes in Tianshan Mountains-A Case Study of Glacier No. 1.

The elevation of the snowline of the No. 1 Glacier in the Tianshan Mountains is increasing due to global warming, which has created favorable conditions for moss invasion and offers an opportunity to investigate the synergistic effects of incipient succession by mosses, plants, and soils. In this study, the concept of altitude distance was used instead of succession time. To investigate the changes of bacterial-community diversity in moss-covered soils during glacial degeneration, the relationship between bacterial community structure and environmental factors was analyzed and valuable microorganisms in moss-covered soils were explored. To do so, the determination of soil physicochemical properties, high-throughput sequencing, the screening of ACC-deaminase-producing bacteria, and the determination of ACC-deaminase activity of strains were performed on five moss-covered soils at different elevations. The results showed that the soil total potassium content, soil available phosphorus content, soil available potassium content, and soil organic-matter content of the AY3550 sample belt were significantly different compared with those of other sample belts (p < 0.05). Secondly, there was a significant difference (p < 0.05) in the ACE index or Chao1 index between the moss-covered-soil AY3550 sample-belt and the AY3750 sample-belt bacterial communities as the succession progressed. The results of PCA analysis, RDA analysis, and cluster analysis at the genus level showed that the community structure of the AY3550 sample belt and the other four sample belts differed greatly and could be divided into two successional stages. The enzyme activities of the 33 ACC-deaminase-producing bacteria isolated and purified from moss-covered soil at different altitudes ranged from 0.067 to 4.7375 U/mg, with strains DY1-3, DY1-4, and EY2-5 having the highest enzyme activities. All three strains were identified as Pseudomonas by morphology, physiology, biochemistry, and molecular biology. This study provides a basis for the changes in moss-covered soil microhabitats during glacial degradation under the synergistic effects of moss, soil, and microbial communities, as well as a theoretical basis for the excavation of valuable microorganisms under glacial moss-covered soils.

Effects of moss-dominated biocrusts on soil detachment by overland flow in the Three Gorges Reservoir Area of China

Biological soil crusts (biocrusts) are important landscape components that exist in various climates and habitats. The roles of biocrusts in numerous soil processes have been predominantly recognized in many dryland regions worldwide. However, little is known about their effects on soil detachment process by overland flow, especially in humid climates. This study quantified the effects of moss-dominated biocrusts on soil detachment capacity (Dc) and soil erosion resistance to flowing water in the Three Gorges Reservoir Area which holds a subtropical humid climate. Potential factors driving soil detachment variation and their influencing mechanism were analyzed and elucidated. We designed five levels of coverage treatments (1%–20%, 20%–40%, 40%–60%, 60%–80%, and 80%–100%) and a nearby bare land as control in a moss-dominated site. Undisturbed soil samples were taken and subjected to water flow scouring in a hydraulic flume under six shear stresses ranging from 4.89 to 17.99 Pa. The results indicated that mean Dc of moss-covered soil varied from 0.008 to 0.081 kg m−2 s−1, which was 1.9 to 21.0 times lower than that of bare soil (0.160 kg m−2 s−1). Rill erodibility (Kr) of moss-covered soil ranged from 0.0095 to 0.0009 s m−1, which was 2 to 20 times lower than that of bare soil (0.0187 s m−1). Both relative soil detachment rate and Kr showed an exponential decay with increasing moss coverage, whereas the critical shear stress (τc) for different moss coverage levels did not differ significantly. Moss coverage, soil cohesion, and sand content were key factors affecting Dc, while moss coverage and soil bulk density were key factors affecting Kr. A power function of flow shear stress, soil cohesion, and moss coverage fitted well to estimate Dc (NSE=0.947). Our findings implied that biocrusts prevented soil detachment directly by their physical cover and indirectly by soil properties modification. Biocrusts could be rehabilitated as a promising soil conservation measure during ecological recovery to enhance soil erosion resistance in the Three Gorges Reservoir Area.

The mechanism of soil nitrogen transformation under different biocrusts to warming and reduced precipitation: From microbial functional genes to enzyme activity

Soil nitrogen (N) mineralization is a microbially-mediated biogeochemical process that is strongly influenced by changing climates. However, little information is available on the mechanisms behind the response of N mineralization to prolonged warming coupled with drought in soils covered by biocrusts. We used open top chambers to investigate the rate of soil N transformation (ammonification, nitrification and mineralization), enzyme activity and gene abundance in response to warming coupled with reduced precipitation over three years (2016–2018). Warming and drought significantly reduced the N transformation rate, extracellular enzyme activity, and gene abundance in moss-covered soil. For cyanobacteria-covered soil, however, it inhibited enzyme activity and increased the abundance of the nitrification-related genes and therefore nitrification rate. Our treatments had no obvious effects on N transformation and enzyme activity, but reduced gene abundance in bare soil. Biocrusts may facilitate N transformation while the degradation of moss crust caused by climate warming will dampen any regulating effect of biocrusts on the belowground microbial community. Furthermore, belowground microbial communities can mediate N transformation under ongoing warming and reduced precipitation by suppressing ammonification- and nitrification-related gene families, and by stimulating nitrification-related gene families involved in cyanobacteria-covered soil. This study provides a basis for identifying the functional genes involved in key processes in the N cycle in temperate desert ecosystems, and our results further highlight the importance of different biocrusts organisms in the N cycle in temperate deserts as Earth becomes hotter and drier.

Post-wildfire moss colonisation and soil functional enhancement in forests of the southwestern USA

Fire mosses, including Ceratodon purpureus, Funaria hygrometrica and Bryum argenteum, can achieve high cover within months to years after high-severity fire, but do so heterogeneously across space and time. We conducted a survey of moss cover and erosion-related functions after 10 wildfires in Pinus ponderosa and mixed-conifer forests of the southwestern USA. We sampled 65 plots in high-severity patches, stratifying by elevation and insolation over each fire. Using three landscape-scale predictor variables and one temporal predictor, we explained 37% of the variance in fire moss cover using a random forest model. The predictors in order of importance were: equinox insolation (sunlight/day), pre-fire vegetation type, pre-fire soil organic carbon and time since fire. Within each plot we examined differences between bare and moss-covered soil surface microsites and found moss-covered microsites had a mean increase of 55% water infiltration, 106% shear strength, 162% compressive strength and 195% aggregate stability. We tested a suite of nutrients, finding 35% less manganese in the moss-covered soil. This research demonstrated that post-fire colonisation by moss is predictable and that colonisation improves soil surface erosion resistance and hydrological function, with implications for managing severely burned landscapes.

腾格里沙漠东南缘不同类型生物土壤结皮对土壤有机碳矿化的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 腾格里沙漠东南缘不同类型生物土壤结皮对土壤有机碳矿化的影响 DOI: 10.5846/stxb201902220317 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41671111，41530746） Carbon mineralization of soil covered by different types of biological crusts in the southeastern fringe of the Tengger Desert Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:生物土壤结皮（BSCs）是荒漠生态系统的重要组成部分，是该区土壤碳循环及碳平衡的关键影响因素。研究了腾格里沙漠东南缘不同类型生物土壤结皮覆盖下土壤碳矿化过程及其对温度（10℃、25℃和35℃）和水分（土壤含水量10%和25%）变化响应特征，分析了土壤碳矿化过程与土壤理化性质的关系。结果表明：（1）结皮的形成和发育显著影响土壤有机碳矿化过程，藻类、地衣和藓类结皮覆盖的土壤碳矿化速率和CO2-C累积释放量均显著高于去除结皮的土壤，不同类型BSCs覆盖土壤和去除结皮土壤之间均表现为藓类结皮土壤 > 地衣结皮土壤 > 藻类结皮。（2）含结皮层土壤的平均和最大矿化速率均随温度升高和水分增加而逐渐增大，有结皮覆盖的土壤和去除结皮的土壤对温度和水分变化的响应规律相同。（3）有结皮土壤和去除结皮土壤碳矿化速率的温度敏感性（Q10）与结皮类型密切相关，均表现为藓类结皮 > 地衣结皮 > 藻类结皮。结果表明生物土壤结皮由以藻类为主向以藓类为主的演变进一步促进了土壤碳矿化过程，结皮对土壤碳循环的调控作用受水热等环境因子的共同影响。 Abstract:Biological soil crusts (BSCs) are the association of soil organisms including algea, cyanobacteria, bacteria, fungi, lichen and moss and soil particles, which cover as much as 70% of the interspaces between vegetation and are the key component of arid and semiarid ecosystems. They play a significant role in the process of soil formation and biogeochemical cycling of carbon and nitrogen. Although the functions of BSCs in soil carbon cycling in drylands have been extensively described in the literature, previous research has primarily focused on the effects of BSCs on soil carbon sequestration and respiration. Knowledge is rather poor regarding their effects on soil organic carbon mineralization which is the major part of global carbon cycling and an important process of carbon loss from soils in terrestrial ecosystem. Consequently, understanding the effects of BSCs on soil organic mineralization and their regulating factors is crucial to thoroughly addressing their contribution to the soil carbon budget and balance in drylands.In this study, both intact soil (IS) and BSC-being-removed soil (BRS) samples were collected from algae-, lichen-, and moss-covered soil plots in the southeastern fringe of the Tengger Desert. Carbon mineralization rates of different types of soils and their responses to soil moisture and temperature were investigated by dark incubation. The relationships between soil mineralization rates and soil physicochemical factors were also analyzed. The results showed that (1) SOC mineralization rates and cumulative CO2-C release from IS were significantly higher than those from BRS. These two parameters for both IS and BRS were in the order moss crust > lichen crust > algae crust. (2) The average and maximum soil carbon mineralization rates increased with increasing magnitude of incubation temperature and soil water content, and the dynamic patterns of their response both were similar. (3) Temperature sensitivity (Q10) of the three intact soils and their respective subsoils were closely linked to BSC types, with the highest value for moss-covered soil and the lowest for algae-covered soil. Our understanding of the effects of on soil carbon mineralization suggests that the evolution of BSCs from algae-dominated to moss-dominated soil promoted carbon mineralization, and their regulation of soil carbon cycling was strongly controlled by environmental factors, such as temperature and soil moisture. 参考文献 相似文献 引证文献

Effects of biocrusts and rainfall characteristics on runoff generation in the Mu Us Desert, northwest China

AbstractHow the presence of biocrusts regulates runoff generation in the Mu Us Desert is not well known. Runoff experiments under natural and artificial rainfalls and numerical simulations were conducted in semiarid environments to evaluate the effects of biocrust type and rainfall characteristics on runoff. The experimental results showed that the water drop penetration time (WDPT) of the moss-dominated biocrusts was 68.7% higher than that of lichen-dominated biocrusts. Nevertheless, the saturated hydraulic conductivity (Ks) for moss-dominated biocrusts was 72.7% lower than that for the lichen-dominated biocrusts. Runoff yield for moss-dominated biocrusts was significantly higher than that for lichen-dominated biocrusts. Runoff yield was mainly explained by rainfall amount (or maximum 5-min rainfall intensity, I5max) (P &amp;lt; 0.001) and WDPT (P = 0.001). The influences of biocrust type, rainfall intensity, and their interaction on runoff coefficient were significant at the probability level of 0.01. The results of numerical simulations concluded that surface runoff was generated for lichen- and moss-dominated biocrusts when rainfall intensity reached 73.5 and 49 mm h–1, respectively. Runoff coefficient in the moss-covered soil increased obviously when rainfall intensity changed from 49 to 73.5 mm h–1. The results suggest that runoff could be changed substantially under increasing trends in rainfall intensity in the Mu Us Desert.

Temporal variations in infiltration properties of biological crusts covered soils on the Loess Plateau of China

Biological soil crusts (BSCs) are widespread in abandoned farmlands over the Loess Plateau after the “Grain for Green” project was implemented in 1999. However, few studies have been carried out to quantify the effects of BSCs on temporal variations of soil infiltration properties. This study was conducted to investigate the effects of two typical BSC (moss and cyanobacteria) on the temporal variations of soil infiltration properties reflected by soil sorptivities under different pressures of 0 (S0) and −3 (S3) cm, saturated hydraulic conductivity (Ks), and wetting front depth (WFD) on the Loess Plateau. Two BSC-covered sites and one bare soil site (as control) were selected to measure soil infiltration properties using a disc infiltrometer under two consecutive pressure heads of 0 and −3cm, and then the S0, S3, and Ks were calculated. The WFD was measured quickly by a ruler after the measurement of soil infiltration. The experiments started from May 9 to October 8, 2015 for 7 times at approximately 3weeks interval. Soil physicochemical properties and BSC thickness were also measured to explain the temporal variations of soil infiltration properties. The results showed that the thickness of moss and cyanobacteria crusts increased continually during the experimental period. BSC affected top-soil (0–5cm) properties (soil water content, bulk density, texture, and organic matter content) significantly, and the effects of moss were greater than those of cyanobacteria. BSC was effective to impede soil infiltration. Compared to the control, the mean S0, S3, Ks, and WFD of moss-covered soil reduced by 31.4%, 25.2%, 39.0%, and 22.7%. While, S0, S3, Ks, and WFD of cyanobacteria-covered soil declined by 21.5%, 18.2%, 29.3%, and 11.9%, respectively. The temporal variations in infiltration properties of both moss- and cyanobacteria-covered soils were similar. S0, S3, Ks, and WFD generally decreased over time. However, the related infiltration properties of bare soil fluctuated over time with no distinguish trend. The temporal variations in infiltration properties were closely related to the seasonal variations in BSC thickness and soil water content.

Seasonal variation of net N mineralization under different biological soil crusts in Tengger Desert, North China

Biological soil crust (BSC) is a key biotic factor in desert areas and can significantly alter nutrient cycling. The interaction between seasonal climatic change and BSC can further modify nutrient cycling. Thus far, limited information has been provided regarding the effect of BSC on net soil nitrogen (N) transformation and their seasonal pattern in temperate desert areas. Therefore, we assessed the seasonal patterns of net soil N mineralization and nitrification in three microhabitats (moss-covered, cyanobacteria–lichen-covered, and bare soils) from October 2011 to September 2012 by using an intact soil core in situ incubation method. Seasonal variations in inorganic N pools, net N mineralization, and nitrification rates were observed. The seasonal patterns of net N transformation rates were greatly modified by soil temperature and moisture (highest in August and lowest in January). During non-growing season, net N immobilization was observed in the three microsites; a higher inorganic N content was observed in the moss-covered soil than in other soils. BSC increased the net soil N transformation rates during the early growing season but reduced the inorganic N content during the peak growing season. On the basis of these findings, we concluded that seasonal variation in climate significantly affected N transformation. The colonization and the development of BSC stimulated N cycling and storage in arid desert systems.

The response mechanisms of soil N mineralization under biological soil crusts to temperature and moisture in temperate desert regions

Soil nitrogen (N) mineralization is an important component of the N cycling process in desert ecosystems. However, the effects of biological soil crust (BSC), especially different patterns of BSCs (i.e. moss, algae-lichen), on net nitrification and N mineralization rates under climate-change conditions are still largely unexplored. To investigate the effects of temperature and moisture on net nitrification and N mineralization rates in BSC-dominated desert soils, and to highlight the regulatory role of BSC on N availability in the Tengger Desert, China, intact soil cores from three microhabitats (moss-covered, algae-lichen-covered, and bare soil) were incubated at six temperatures (−10, 5, 15, 25, 35, and 40 °C) and four moisture levels (29, 58, 85, and 170% field water content, FWC). Generally, moss-covered soil exhibited the highest net N transformation rate, whereas, algae-lichen-covered soil inhibited the nitrification process. Incubation temperature and moisture significantly affected net nitrification and N mineralization rates in all three microhabitats, in general that values were higher at the higher temperature (i.e. 25, 35, and 40 °C) compared to lower temperature (i.e. −10, 5, 15 °C). The net N mineralization rate for the three microhabitats peaked at 85% FWC. Overall, results indicated that BSCs, especially moss-dominated soils, increase net N transformation rate and N availability. Thus, they can make a contribution to plant growth and play a positive role in primary productivity under climate change in arid areas.

Leifsonia psychrotolerans sp. nov., a psychrotolerant species of the family Microbacteriaceae from Livingston Island, Antarctica

A cold-tolerant, yellow-pigmented, Gram-positive, motile, facultatively anaerobic bacterial strain, LI1(T), was isolated from a moss-covered soil from Livingston Island, Antarctica, near the Bulgarian station St. Kliment Ohridski. Comparative 16S rRNA gene sequence-based phylogenetic analysis placed the strain in a clade with the species Leifsonia kafniensis KFC-22(T), Leifsonia pindariensis PON10(T) and Leifsonia antarctica SPC-20(T), with which it showed sequence similarities of 99.0, 97.9 and 97.9 %, respectively. DNA-DNA hybridization revealed a reassociation value of 2.7 % with L. kafniensis LMG 24362(T). The DNA G+C content of strain LI1(T) was 64.5 mol%. The growth temperature range was -6 to 28 °C, with optimum growth at 16 °C. Growth occurred in 0-5 % NaCl and at pH 4.5-9.5, with optimum growth in 1-2 % NaCl and at pH 5.5-6.5. The predominant fatty acids were anteiso-C(15 : 0), C(18 : 0) and iso-C(15 : 0). The polar lipids were phosphatidylglycerol and diphosphatidylglycerol. Physiological and biochemical tests clearly differentiated strain LI1(T) from L. kafniensis. Therefore, a novel cold-tolerant species within the genus Leifsonia is proposed: Leifsonia psychrotolerans sp. nov. (type strain LI1(T) = DSM 22824(T) = NCCB 100313(T)).

Arthrobacter livingstonensis sp. nov. and Arthrobacter cryotolerans sp. nov., salt-tolerant and psychrotolerant species from Antarctic soil

Two novel cold-tolerant, Gram-stain-positive, motile, facultatively anaerobic bacterial strains, LI2(T) and LI3(T), were isolated from moss-covered soil from Livingston Island, Antarctica, near the Bulgarian station St Kliment Ohridski. A rod-coccus cycle was observed for both strains. 16S rRNA gene sequence analysis revealed an affiliation to the genus Arthrobacter, with the highest similarity to Arthrobacter stackebrandtii and Arthrobacter psychrochitiniphilus for strain LI2(T) (97.8 and 97.7 % similarity to the respective type strains) and to Arthrobacter kerguelensis and Arthrobacter psychrophenolicus for strain LI3(T) (97.4 and 97.3 % similarity to the respective type strains). The growth temperature range was -6 to 28 °C for LI2(T) and -6 to 24 °C for LI3(T), with an optimum at 16 °C for both strains. Growth occurred at 0-10 % (w/v) NaCl, with optimum growth at 0-1 % (w/v) for LI2(T) and 0.5-3 % (w/v) for LI3(T). The pH range for growth was pH 4-9.5 with an optimum of pH 8 for LI2(T) and pH 6.5 for LI3(T). The predominant fatty acids were anteiso-C(15 : 0), C(18 : 0) and anteiso-C(17 : 0) for LI2(T) and anteiso-C(15 : 0) and C(18 : 0) for LI3(T). Physiological and biochemical tests clearly differentiated strain LI2(T) from A. stackebrandtii and A. psychrochitiniphilus and strain LI3(T) from A. kerguelensis and A. psychrophenolicus. Therefore, two novel species within the genus Arthrobacter are proposed: Arthrobacter livingstonensis sp. nov. (type strain LI2(T) = DSM 22825(T) = NCCB 100314(T)) and Arthrobacter cryotolerans sp. nov. (type strain LI3(T) = DSM 22826(T) = NCCB 100315(T)).

Frequency and distribution patterns of zoosporic fungi from moss-covered and exposed forest soils

Uniflagellate zoosporic “fungi” (=Chytridiomycota and the zoosporic protista Hyphochytriomycota) are common inhabitants of soil. However, at what scale differences in their spatial distribution can be detected is poorly known. The first objective of this study was to assess the association of organismal distribution and frequency with two microhabitats: moss-covered and exposed forest soils, at four macroscopically similar but spatially separate sites in the Blue Ridge and Allegheny Mountains of Virginia. The second objective was to provide statistically either acceptance or denial of inferences derived from sampling regimes involving a more limited number of samples. To evaluate the scale where distributional differences may occur within a site, protocols involved four collection regimes and random point and linear transect sampling. Chytrid frequency on thalli of two moss genera was greatest in the soil surrounding and under the moss rhizoids. Random point sampling methods suggested differences in zoosporic fungal frequency between moss-covered soil and the exposed soil adjacent to mosses, as well as between two moss taxa. Linear transect sampling methods also suggested differences in zoosporic fungal frequencies between moss-covered soil and soil proximal to mosses. However, statistical analysis of random point samples using a goodness-of-fit test demonstrated that there was no significant difference in frequency of zoosporic fungi from moss-covered soil and exposed soil proximal to mosses. More importantly, there was a significant difference in the frequency of ubiquitous and common zoosporic fungal species between different moss/soil complexes. This study demonstrates that differences in chytrid distribution can be detected at a microscale while at a larger scale, similarity in frequency and distribution was found.

Breeding Sites of Snipe Flies (Rhagionidae) and Other Diptera in Woodland-Grass Soils

During terrestrial surveys for immature and adult rhagionids in northern California (Mendocino Co.), USA, woodland-grass soils were found to be a breeding source for 8 species of snipe flies: Chrysopilus , 2; Ptiolina , 1; Rhagio , 1; and Symphoromyia , 4. Immatures of a Ptiolina sp. near zonata obtained by hand sorting moss-covered soil samples from 1978–1980 yielded 2 adults. This is apparently the first time that Ptiolina has been reported from the state and that Ptiolina immatures have been successfully reared in the Nearctic Region. Adults of 8 rhagionid species were collected in emergence traps from April to July and in December 1980, with emergence densities ranging from 0.04 individuals/m2 for S. inconspicua to 1.30/m2 for Ptiolina sp. Emergence traps also captured miscellaneous dipterans belonging to ca. 48 species in 20 families. Incidental to other studies, a single male of an undescribed species of Symphoromyia near truncata was taken in an emergence trap in Contra Costa Co.

Recruitment and survival of seedlings of a perennial Hieracium species in a patchy environment

Observations on a population of Hieracium piloselloides Vill. in an old-field habitat revealed two distinct microsites on which seeds might land, bare soil and moss-covered areas. Regular monitoring of newly emerged seedlings on both microsites revealed that the seeds could germinate as soon as they are shed and that emergence of the seedlings coincided with rainfall, forming distinct emergence flushes. The number of emergences and losses recorded on the bare soil sites always exceeded those which occurred on the moss-covered microsites. The greatest losses of seedlings from the population occurred in periods of low rainfall. The mortality in six seedling cohorts was also followed on these plots. Similar patterns of survival were shared by most of the bare soil cohorts and by all cohorts of moss-covered soil, but the decline in the bare soil cohorts was always more rapid. The number of seeds available in the natural seed rain is estimated to be 40 190 seeds/m2. To this, a total of 120 000 seeds/m2 were added artificially in marked plots, and from the recorded emergences, the establishment success of seedlings was estimated at less than 1%. It is suggested that in terms of monthly microclimatic variation, both types of microsite may be of value in contributing to the apparent stability of the population.