Leguminosae plants play a key role in affecting soil physical-chemical and biological properties during grassland succession after farmland abandonment in the Loess Plateau,China

Leguminosae are an important part of terrestrial ecosystems and play a key role in promoting soil nutrient cycling and improving soil properties.However,plant composition and species diversity change rapidly during the process of succession,the effect of leguminosae on soil physical-chemical and biological properties is still unclear.This study investigated the changes in the composition of plant community,vegetation characteristics,soil physical-chemical properties,and soil biological properties on five former farmlands in China,which had been abandoned for 0,5,10,18,and 30 a.Results showed that,with successional time,plant community developed from annual plants to perennial plants,the importance of Leguminosae and Asteraceae significantly increased and decreased,respectively,and the importance of grass increased and then decreased,having a maximum value after 5 a of abandonment.Plant diversity indices increased with successional time,and vegetation coverage and above-and below-ground biomass increased significantly with successional time after 5 a of abandonment.Compared with farmland,30 a of abandonment significantly increased soil nutrient content,but total and available phosphorus decreased with successional time.Changes in plant community composition and vegetation characteristics not only change soil properties and improve soil physical-chemical properties,but also regulate soil biological activity,thus affecting soil nutrient cycling.Among these,Leguminosae have the greatest influence on soil properties,and their importance values and community composition are significantly correlated with soil properties.Therefore,this research provides more scientific guidance for selecting plant species to stabilize soil ecosystem of farmland to grassland in the Loess Plateau,China.

Asset specificity and farmers' intergenerational succession willingness of apple management

Understanding the factors behind apple farmers’willingness to pass on the management of their farms to their descendants is crucial to the continuity of apple production.Due to the high specificity of the human capital,physical assets,land assets,and geographical location in apple production,this study used a binary logistic regression and a mediating effect model to explore the impact of asset specificity on farmers’intergenerational succession willingness of apple management(FISWAM)and to examine the mediating effects of loss aversion in the impact of asset specificity on the FISWAM.The results showed that about 18.68%of the respondents expressed willingness to transfer their apple business between generations,and the FISWAM was generally weak.In addition to the negative impact of geographical location specificity(GLS),human capital specificity(HCS),physical assets specificity(PAS),and land assets specificity(LAS)can enhance the FISWAM.Loss aversion plays a partial mediating role in the impact of PAS,LAS,and GLS on the FISWAM.

Understorey species distinguish late successional and ancient forests after decades of minimum human intervention: A case study from Slovenia

The main species composition drivers in temperate deciduous forests are environmental conditions, a stand?s age and the site history, e.g., the succession stage and past land use, as well as disturbance regime and current management. We compared plant species diversity and composition in late successional and ancient forests, cooccurring on the same small river island applying species accumulation curves and nonmetric multidimensional scaling, respectively. Given the island?s geomorphological characteristics, we expected these to be very similar before human intervention in the past. The forests experienced differing disturbance regimes in the past, while over the last 30 years, human intervention has been the same and reduced to a minimum. The ancient forest in this study had two major characteristics defining it as old, mature forest: continuity of presence for more than 200years and specific composition. The late successional forest experienced major disturbance in the 20th century and was allowed natural regeneration by bordering on the ancient forest, representing a potential species pool,and by decades of minimum human intervention. Our results showed that, even though there was no difference in species richness, we could still detect differences between the forests, particularly in the abundance and species composition of the understorey, among which geophytes had the most indicative importance. To make our results useful on a broader scale, we composed from the literature a species list of plants indicative for ancient forest and tested its application. These results are important for distinguishing between old and mature secondary stands and particularly for identifying old forest stands, which should be conserved and, in the case of fragmented landscapes, included in a network connecting forest fragments.

Arbuscular Mycorrhizal Fungal Colonization at Different Succession Stages in Songnen Saline-Alkali Grassland

Arbuscular mycorrhizal(AM)fungi can form symbiosis with 90%of the vascular plants and play important roles in ecosystem.To realize the AM fungal colonization at different succession stages in saline-alkali land and screen AM fungi species with great functions,roots and soil samples were collected from the three succession stages of Songnen saline-alkali grassland.The soil properties and AM fungal colonization were measured,and the fungus distributed extensively in three stages was annotated by sequencing for AML1/AML2 target,subsequently,maize was selected as the host to verify its colonization.The results showed that the soil properties improved with the succession of saline-alkali grassland.The plants’communities of the three stages could be colonized by AM fungi,and the colonization rate of Leymus chinensis(the third stage)ranged from 66.67%to 100%,Puccinellia tenuiflora(the second stage)ranged from 50%to 80%,while the Suaeda glauca(the first stage)was only 35%–60%.Glomeraceae sp1 was identified as the dominant AM fungi species which occurred frequently in the succession of saline-alkali land with the isolation frequency,relative abundance,and importance value of 100%,18.1%,and 59.1%,respectively.The colonization rate of Glomeraceae sp1 in maize ranged from 80%to 87%and similar mycorrhizal characteristics were detected in the roots of P.tenuiflora,S.glauca,and L.chinensis,indicating that Glomeraceae sp1 colonized the samples in the field.The correlation matrix indicated that colonization rate,colonization intensity,and vesicle abundance were closely related to soil conditions most,and they were related significantly to all the soil properties except cellulase activity.Besides,redundancy analysis(RDA)showed that soil properties drove the changes of AM fungal colonization and sporulation.These results will provide theoretical support for realizing the relationship between AM fungal colonization and soil conditions,and also for the exploration of AM fungi species with great functions.

Changes in plant debris and carbon stocks across a subalpine forest successional series

Background:As a structurally and functionally important component in forest ecosystems,plant debris plays a crucial role in the global carbon cycle.Although it is well known that plant debris stocks vary greatly with tree species composition,forest type,forest origin,and stand age,simultaneous investigation on the changes in woody and non-woody debris biomass and their carbon stock with forest succession has not been reported.Therefore,woody and non-woody debris and carbon stocks were investigated across a subalpine forest successional gradient in Wanglang National Nature Reserve on the eastern Qinghai-Tibet Plateau.Results:Plant debris ranged from 25.19 to 82.89 Mg∙ha−1 and showed a global increasing tendency across the subalpine forest successional series except for decreasing at the S4 successional stage.Accordingly,the ratios of woody to non-woody debris stocks ranged from 26.58 to 208.89,and the highest and lowest ratios of woody to non-woody debris stocks were respectively observed in mid-successional coniferous forest and shrub forest,implying that woody debris dominates the plant debris.In particular,the ratios of coarse to fine woody debris stocks varied greatly with the successional stage,and the highest and lowest ratios were found in later and earlier successional subalpine forests,respectively.Furthermore,the woody debris stock varied greatly with diameter size,and larger diameter woody debris dominated the plant debris.Correspondingly,the carbon stock of plant debris ranged from 10.30 to 38.87 Mg∙ha−1 across the successional series,and the highest and lowest values were observed in the mid-coniferous stage and shrub forest stage,respectively.Most importantly,the carbon stored in coarse woody debris in later successional forests was four times higher than in earlier successional forests.Conclusions:The stock and role of woody debris,particularly coarse woody debris,varied greatly with the forest successional stage and dominated the carbon cycle in the subalpine forest ecosystem.Thus,preserving coarse woody debris is a critical strategy for sustainable forest management.

Rebirth after death: forest succession dynamics in response to climate change on Gongga Mountain, Southwest China

Global climate change is having long-term impacts on the geographic distribution of forest species. However, the response of vertical belts of mountain forests to climate change is still little known. The vertical distribution of forest vegetation(vertical vegetation belt) on Gongga Mountain in Southwest China has been monitored for 30 years. The forest alternation of the vertical vegetation belt under different climate conditions was simulated by using a mathematical model GFSM(the Gongga Forest Succession Model). Three possible Intergovernmental Panel on Climate Change(IPCC) climate scenarios(increase of air temperature and precipitation by 1.8℃/5%, 2.8℃/10% and 3.4℃/15% for B_1, A_1B and A_2 scenarios, respectively) were chosen to reflect lower, medium and higher changes of global climate. The vertical belts of mountainous vegetation will shift upward by approximately 300 m, 500 m and 600 m in the B_1, A_1B and A_2 scenarios, respectively, according to the simulated results. Thus, the alpine tree-line will move to a higher altitude. The simulation also demonstrated that, in a changing climate, the shift in the vegetation community will be a slow and extended process characterized by two main phases. During the initial phase, trees of the forest community degrade or die, owing to an inability to adapt to a warmer climate. This results in modest environment for the introduction of opportunistic species, consequently, the vegetation with new dominant tree species becomes predominant in the space vacated by the dead trees at the expense of previously dominated original trees as the succession succeed and climate change advance. Hence, the global climate change would dramatically change forest communities and tree species in mountainous regions because that the new forest community can grow only through the death of the original tree. Results indicated that climate change will cause the change of distribution and composition of forest communities on Gongga Mountain, and this change may enhance as the intensity of climate change increases. As a result, the alternation of death and rebirth would finally result in intensive landscape changes, and may strongly affect the eco-environment of mountainous regions.

Analysis on Vegetation Succession Model and Process under Groundwater Exploitation in Subei Lake Watershed

[Objective] The study aimed to analyze vegetation succession process under groundwater mining conditions in Subei Lake watershed. [ Method] A succession model for vegetation and burial depth of groundwater level was constructed based on field survey, and it was used to pre- dict the vegetation succession rules and process according to the changes in burial depth of groundwater level in Subei Lake watershed under groundwater exploitation. [ Result~ In Subei Lake watershed, aquatic vegetation was most closely related to burial depth of groundwater level, fol- lowed by mesophytic vegetation, while psammophilous and xerophytic vegetation did not have obvious relation with burial depth of groundwater lev- el. When burial depth of groundwater level was small, dominant plants grew well, but they grew worse or died with the increase in burial depth of groundwater level. As the groundwater level fell constantly, burial depth of groundwater level went up, and vegetation succession would occur grad- ually from aquatic vegetation to mesophytic and xerophytic vegetation, from Carex L. and Iris ensata Thunb shoaly land to Achnatherum splendens shoaly lands, from Salix psammophila shrubs to Artemisia desterorum Spreng and Caragana korshinskii shrubs, and from Populus simonii to Salix matsudana. [Condusion] The research could provide scientific references for studying the relationship between groundwater resources and ecological environment in Subei Lake basin.

Preliminary study on seasonal succession and development pathway of phytoplankton community in the Bohai Sea

Phytoplankton species composition and species succession were determined in 1998-1999 based on 2 nestle investigation cruises in the Bohai Sea and two monthly monitoring stations at Penglai and Changdao for 15 months. The seasonal succession and pathway of phytoplankton community in the Bohai Sea were discussed complementarily with history data. The main process of Phytoplankton community development in the Bohai Sea was controlled by temperature and nutrient replenishes. There were two cell abundance peaks in an annual variation, the main peak in April and the secondary peak in September. In winter, the cell abundance was low due to the low temperature, the phytoplankton community was mainly made up of small-celled diataoms. In spring, the phytoplankton community was developed very quickly by small-celled diatom in suitable conditions of temperature and nutrients. In summer, the cell abundance decreased and big-celled diatoms became predominated. In autumn, because of the replenish of nutrient, big-celled diatoms and dinoflagellates formed another cell abundance peak. during the annual variation of phytoplankton community in the Bohai Sea, species succession was the main process of community development, the species sequence just occur at special areas and special periods. The evolution of phytoplankton community in the Bohai Sea accords with the hypothesis of Margalef's phytoplankton community of four stages. But the size feature is contrary to the hypothesis, which may be caused by nutrient replenish in autumn in Bohai Sea and the top to down control.

Responses of soil nitrogen, phosphorous and organic matter to vegetation succession on the Loess Plateau of China

Revegetation is a traditional practice widely used for soil protection. We evaluated the effect of natural revegetation succession on soil chemical properties and carbon fractions （particulate organic carbon （POC）, humus carbon （HS-C）, humic acid carbon （HA-C） and fulvic acid carbon （FA-C）） on the Loess Plateau of China. The vegetation types, in order from the shortest to the longest enclosure duration, were： （a） abandoned overgrazed grassland （AbG3; 3 years）; （b） Hierochloe odorata Beauv. （HiO7; 7 years）; （c） Thymus mongoficus Ronnm （ThM15; 15 years）; （d） Artemisia sacrorum Ledeb （AtS25; 25 years）; （e） Stipa bungeana Trin Ledeb （StB36; 36 years） and （f） Stipa grandis P. Smirn （StG56; 56 years）. The results showed that the concentrations of soil organic carbon, total nitrogen and available phosphorus increased with the increase of restoration time except for ThM15. The concen- tration of NH4-N increased in the medium stage （for ThM15 and AtS25） and decreased in the later stage （for StB36 and StG56） of vegetation restoration. However, NO3-N concentration significantly increased in the later stage （for StB36 and StG56）. Carbon fractions had a similar increasing trend during natural vegetation restoration. The con- centrations of POC, HS-C, FA-C and HA-C accounted for 24.5%-49.1%, 10.6%-15.2%, 5.8%-9.1% and 4.6%-6.1% of total carbon, respectively. For AbG3, the relative changes of POC, HS-C and FA-C were significantly higher than that of total carbon during the process of revegetation restoration. The higher relative increases in POC, HS-C and FA-C confirmed that soil carbon induced by vegetation restoration was sequestrated by higher physical and chemical protection. The increases of soil C fractions could also result in higher ecological function in semiarid grassland ecosystems.

Implications of the Precambrian Non-stromatolitic Carbonate Succession Making up the Third Member of Mesoproterozoic Gaoyuzhuang Formation in Yanshan Area of North China

A particular non-stromatolitic carbonate succession making up the third member of the Mesoproterozoic Gaoyuzhuang （高于庄） Formation might demonstrate that a stromatolite decline of the Mesoproterozoic occurring at ca. 1 450 Ma besides other three events of the Proterozoic, respectively, occurred at ca. 2 000 Ma, ca. 1 000 Ma, and ca. 675 Ma. The forming duration of this non-stromatolitic carbonate succession can be generally correlative to that of a similar depositional succession in North America, i.e. a non-stromatolitic carbonate succession made up by the Helena Formation of the Belt Supergroup, which suggests that the stromatolite decline occurring at ca. 1 450 Ma may be a global event. This information endows the non-stromatolitic carbonate succession making up the third member of the Gaoyuzhuang Formation in the Yanshan （燕山） area with important significance for the further understanding of Precambrian sedimentology. The Mesoproterozoic Gaoyuzhuang Formation in Yanshan area is a set of more than 1 000 m thick carbonate strata that can be divided into four members （or subformations）. The first member （or the Guandi （官地） subformation） is marked by a set of stromatolitic dolomites overlying a set of transgressive sandstones; the second member （or the Sangshu＇an （桑树鞍） subformation） is a set of manganese dolomites with a few stromatolites; the third member （or the Zhangjiayu （张家峪） subformation） is chiefly made up of leiolite and laminite limestones and is characterized by the development of molar-tooth structures in leiolite limestone; the fourth member （or the Huanxiusi （环秀寺） subformation） is composed of a set of dolomites of stromatolitic reefs or lithoherms. Sequence-stratigraphic divisions at two sections, i.e. the Jixian （蓟县） Section in Tianjin （天津） and the Qiangou （千沟） Section of Yanqing （延庆） County in Beijing （北京）, demonstrate that a particularly non-stromatolitic succession making up the third member of the Mesoproterozoic Gaoyuzhuang Formation is developed in the Yanshan area of North China, in which lots of grotesque matground structures （wrinkle structures and palimpsest ripples） are developed in beds of leiolite limestone at the Qiangou Section and lots,of molar-tooth structures are developed in beds of leiolite limestone at the Jixian Section. The time scale of the Gaoyuzhuang Formation is deduced as 200 Ma （from 1 600 Ma to 1 400 Ma）. The duration of an obvious hiatus between the Gaoyuzhuang Formation and the underlying Dahongyu （大红） Formation is deduced as 50 Ma to 100 Ma, thus the forming duration of the Gaoyuzhuang Formation is thought as 100 Ma （1 500 Ma to 1 400 Ma）. Furthermore, the age of the subface of the third member of the Gaoyuzhuang Formation that is just in the mid position of the Gaoyuzhuang Formation can be deduced as about 1 450 Ma, which is the basis to infer a stromatolite decline of the Mesoproterozoic occurring at ca. 1 450 Ma. Importantly, several features of both the molar-tooth structure and the stromatolite, such as the particular forming environment, the important facies-indicative meaning, and the episodic distribution in the earth history, might express the evolutionary periodicity of the surface environment of the earth and can provide meaningful clues for the understanding of the Precambrian world, although their origin and forming mechanism is highly contentious. Therefore, like other three stromatolitic declines, respectively, occurring at ca. 675 Ma, ca. 1 000 Ma, and ca. 2 000 Ma, the identification of the stromatolite decline occurring at ca. 1 450 Ma during the Golden Age of stromatolites （2 800 Ma to 1 000 Ma） has important meaning for the further understanding of the evolving carbonate world of the Precambrian.

Roles of fishing and climate change in long-term fish species succession and population dynamics in the outer Beibu Gulf,South China Sea

A prevailing,controversial hypothesis is that fishing pressure has played a greater role than climatic and environmental drivers,in changing fish species succession and biomass fluctuation in the South China Sea(SCS).Based on otter trawl survey data from 1959 to 2010 in the outer Beibu Gulf(OBG),northern SCS,large seasonal and interannual variation is reported for fish species composition,the proportional abundances of dominant taxa,and fish biomass.Generalized additive models are developed to quantify relationships between fish biomass and the external factors of fishing pressure and climate change.Fishing pressure proved to be the main driver of sharp declines in demersal fish stocks,with high-value species being replaced by low-value ones over time.Abrupt decreases in fish biomass during the years of 1993 and 1998 correspond to El Nino events,with climate change possibly the main driver of proportional representation of pelagic species in fisheries trawl catch.The need to differentiate impacts of fishing and environmental drivers on fish species with different life history strategies is stressed to better understand fish community dynamics.

Genetic Types of Meter-Scale Cyclic Sequences and Fabric Natures of Facies Succession

Different genetic types of meter-scale cyclic sequences in stratigraphic records result from episodic accumulation of strata related to Milankovitch cycles. The distinctive fabric natures of facies succession result from the sedimentation governed by different sediment sources and sedimentary dynamic conditions in different paleogeographical backgrounds, corresponding to high-frequency sea-level changes. Naturally, this is the fundamental criterion for the classification of genetic types of meter-scale cyclic sequences. The widespread development in stratigraphic records and the regular vertical stacking patterns in long-term sequences, the evolution characters of earth history and the genetic types reflected by specific fabric natures of facies successions in different paleogeographical settings, all that show meter-scale cyclic sequences are not only the elementary working units in stratigraphy and sedimentology, but also the replenishment and extension of parasequence of sequence stratigraphy. Two genetic kinds of facies succession for meter-scale cyclic sequence in neritic-facies strata of carbonate and clastic rocks, are normal grading succession mainly formed by tidal sedimentation and inverse grading succession chiefly made by wave sedimentation, and both of them constitute generally shallowing upward succession, the thickness of which ranges from several tens of centimeters to several meters. The classification of genetic types of meter-scale cyclic sequence could be made in terms of the fabric natures of facies succession, and carbonate meter-scale cyclic sequences could be divided into four types: L-M type, deep-water asymmetrical type, subtidal type and peritidal type. Clastic meter-scale cyclic sequences could be grouped into two types: tidal-dynamic type and wave-dynamic type. The boundaries of meter-scale cyclic sequences are marked by instantaneous punctuated surface formed by non-deposition resulting from high-frequency level changes, which include instantaneous exposed punctuated surface, drowned punctuated surface as well as their relative surface. The development of instantaneous punctuated surface used as the boundary of meter-scale cyclic sequence brings about the limitations of Walter's Law on the explanation of facies distribution in time and space, and reaffirm the importance of Sander's Rule on analysis of stratigraphic records. These non-continuous surface could be traced for long distance and some could be correlative within same basin range. The study of meter-scale cyclic sequences and their regularly vertical stacking patterns in long-term sequences indicate that the research into cyclicity of stratigraphic records is a useful way to get more regularity from stratigraphic records that are frequently complex as well as non-integrated.

Soil water repellency and influencing factors of Nitraria tangutorun nebkhas at different succession stages

Abstract： Soil water repellency （WR） is an important physical characteristic of soil surface. It is capable of largely influencing the hydrological and geomorphological processes of soil, as well as affecting the ecological processes of plants, such as growth and seed germination, and has thus been a hot topic in recent research around the world. In this paper, the capillary rise method was used to study the soil WR characteristics of Nitraria tangutorun nebkhas. Soil water repellencies at different succession stages of Nitraria tangutorun were investigated, and the relationships between soil WR and soil organic matter, total N, and total P, soil texture, pH, and concentrations of CO32, HCO3-, CI, SO42-, Na~, K~, Ca2~ and Mg2＋ were discussed. Soil WR may be demonstrated at the following nebkhas dune evolvement stages： extremely degraded〉degraded〉stabilized〉well developed〉newly developed〉quick sand. Apart from some soil at the bottom, the WR of other soils （crest and slope of dune） was found to be largest at the topsoil, and decreased as the soil depth increased. The results showed that multiple factors affected soil WR characteristics e.g. WR increased significantly as the contents of soil organic matter and total N increased, but did not change as the total P content increased. Soil texture was a key factor affecting soil WR; soil WR increased significantly as clay content increased, and decreased significantly as sand content increased. Low pH was shown to be more suitable for the occurrence of soil WR. Four cations （Ca2＋, Mg2＋, K＋ and Na＋） and two anions （CI and SO42） enhanced soil WR, while CO32-decreased it. HCO3- did not show any observable effect. Finally, we established a best-fit general linear model （GLM） between soil-air-water contact angle （CA） and influencing factors （CA=5.606 sand＋6.496 （clay and silt）-2.353 pH＋470.089 CQ2＋11.346 Na＋-407.707 Cl--14.245 SO42-＋0.734 total N-519.521 ）. It was concluded that all soils contain subcritical WR （0°〈CA〈90°）. The development and succession of Nitraria tangutorun nebkhas may improve the formation of soil subcritical WR. There exist significant relationships between soils subcritical WR and soil physical or chemical properties.

Impact of vegetation succession on leaf-litter-soil C:N:P stoichiometry and their intrinsic relationship in the Ziwuling Area of China’s Loess Plateau

Long-term natural vegetation succession plays a substantial role in the accumulation and distribution of plant and soil C:N:P stoichiometry.However,how plant and soil C:N:P relationships or ratios change along with successional stages over a century in the severely eroded areas remain unclear.These were measured over a 100-year natural succession in five successional stages from annual grasses to climax forests.The results show that natural succession had significant effects on carbon(C),nitrogen(N)and phosphorous(P)concentrations in leaf-litter-soil and their ratios in severely eroded areas.Nitrogen concentrations and N:P ratios in leaf and litter increased from annual grasses to the shrub stage and then decreased in the late successional forest stages.Leaf P levels decreased from annual grasses to shrub stages and did not significantly change during late successional stages.Litter P concentration decreased in the early successional stages and increased during late successional stages,with no overall significant change.Soil C and N concentrations and C:N,C:P and N:P ratios increased with successional stages.Soil C and N concentrations decreased with the increasing soil depth.Both were significantly different between any successional stages and controls(cropland)in the upper 10 cm and 10–20 cm soil layers.Leaf N:P ratios may be used to indicate nutrient limitations and this study suggests that plant growth during the grass stages was limited by N,during the shrub stage,by P,and during the forest stages,by both of N and P.In addition,there were close correlations between litter and leaf C:N:P ratios,soil and litter C and N levels,and C:P and N:P ratios.These results show that long-term natural vegetation succession is effective in restoring degraded soil properties and improving soil fertility,and provide insights into C:N:P relationships of leaf,litter and soil influenced by vegetation succession stage.

Acanthomorph Biostratigraphic Succession of the Ediacaran Doushantuo Formation in the East Yangtze Gorges,South China

Large acanthomorphic acritarchs have been found in chert of the Ediacaran Doushantuo Formation at several localities in South China, including the East Yangtze Gorges of Hubei Province,Weng＇an area of Guizhou Province, and elsewhere. However, their potential for biostratigraphic subdivision and correlation of Ediacaran successions is limited by facies control, taphonomic biases,and taxonomic problems. In the Yangtze Gorges, the Doushantuo Formation is generally subdivided into four lithologic members. However, in the Weng＇an area, the Doushantuo Formation comprises just a lower and upper part separated by a mid-Doushantuo erosional surface. In the Yangtze Gorges at the Zhangcunping section, the Doushantuo succession is similar to that at Weng＇an. So far, the correlation between the Yangtze Gorges and Weng＇an area, and elsewhere has been an issue of debate. To resolvethe debate, we selected eight sections in the Yangtze Gorges area and systemically sampled chert nodules of the Doushantuo Formation, focusing in particular on the upper Doushantuo Formation. Our data confirm two different assemblages appearing separately in the second and third members, which are separated by a negative δ13C excursion （EN2）. The lower assemblage is characterized by Tianzhushania and a diverse suite of large acanthomorphic acritarchs. The upper assemblage is distinguished from the lower assemblage, by （1） absence of Tianzhushania; （2） occurrence of abundant,100-150 μm, smooth-walled spherical microfossils; （3） occurrence of highly diverse acanthomorphic acritarchs including species extending from the second member and new forms in this member; （4）occurrence of unnamed new forms of protist; and （5） occurrence of the tubular microfossil Sinocyclocylicus guizhouensis. Since the Tianzhushania-dominated assemblage is not present in Australia, it seems that only the upper acanthomorph assemblage is present and thus the lower Doushantuo acanthomorph assemblage is missing in Australia.

Hurricane disturbances, tree diversity, and succession in North Carolina Piedmont forests, USA

Windthrow plays a critical role in maintaining species diversity in temperate forests. Do large-scale strong wind events(i.e., tropical cyclones, including hurricanes,typhoons and severe cyclonic storms) increase tree diversity in severely damaged forest areas? Do hurricanes(tropical cyclones that occurs in the Atlantic Ocean and northeastern Pacific Ocean) lead to altered relative abundance of shade-tolerant and shade-intolerant species? Did historic hurricanes alter the succession trajectory of the damaged forests? We used nearly 70-year tree demographic data to assess the effects of two major hurricanes on woody species diversity in Piedmont forests, North Carolina, USA. Species richness(S) and Shannon–Wiener's diversity index(H') were used to evaluate the changes in tree diversity. The changes in composition were assessed with Nonmetric Multidimensional Scaling. The pre-hurricane successional phase can strongly influence both the damage severity and subsequent responses. Although there is often an immediate drop in diversity following a hurricane, understory tree diversity quickly increases to levels that exceed those prior to the disturbance. This leads to an increase in diversity in stands that were substantially damaged. Hurricanes significantly decrease the dominance of shade-intolerant canopy species while increasing preestablished, more shade-tolerant species. We conclude that large, and infrequent hurricanes help to maintain local tree diversity, but also accelerate the increase in dominance of understory species such as red maple and beech.

Effects of Vegetation Succession on Soil Fertility Within Farming-Plantation Ecotone in Ziwuling Mountains of the Loess Plateau in China

To further understand the relationship between vegetation succession and soil fertility within farming-plantation ecotone in Ziwuling Mountains of the Loess Plateau, nine kinds of widely distributed communities at different succession stages were selected, and the effects of vegetation succession on soil fertility were studied through the methods of comparing two hierarchical clustering （similarity index： B） and other multivariate analysis. The results showed that： （i） the similarity in clustering pattern of nine communities which classified by plant species and soil nutrients respectively showed a trend of B ^-overall plant-soil0-10cn〉B^-overall plant-soil 10-20 cm 〉B^- overall plant-soil 20-40 cm, and for the top soil, it showed a trend of B^- grass-soil 0-10 cm 〉 B^-shrub-soil 0-10 cm 〉 Btree-soil0-10 cm; （ii） soil fertility increased during the succession process from abandoned land to forest community, and the soil fertility of forest community showed an increased order of coniferous forest →mixed forest →broadleaf forest; （iii） during the process of vegetation succession, the variation of topsoil fertility was higher than that of the subsurface soil （coefficient of variation： CV0-10 cm 〉CV 10-20 cm 〉 CV20-40 cm）, and when the succession developed into the stages of shrub and forest communities, the top soil fertility had been improved significantly; and （iv） for the subsurface soil of the communities at the advanced succession stages, the soil fertility also increased to some extent. Our results suggested that the method of comparing two hierarchical clustering reflected the similarity level of different cluster patterns, therefore, it was helpful to study the relationship between vegetation succession and soil fertility. There was a corresponding relationship between the change process of soil fertility from the top soil to subsurface soil and the process of vegetation succession from the early stages to the advanced stage. The differentiations of soil fertility in vertical space and horizontal space were both caused by vegetation succession, which was significant for both the shrub and forest communities. The improved level of forest soil fertility was related to forest vegetation types and the improved fertility level of broad-leaved forest-soil community was higher than that of the coniferous forest soil. In the practice on soil fertility ecological restoration of the loess plateau, it is important to carry out reasonably artificial forestation so as to enhance the restoration and improvement of soil fertility.

Sedimentary Features and Implications for the Precambrian Non-stromatolitic Carbonate Succession:A Case Study of the Mesoproterozoic Gaoyuzhuang Formation at the Qiangou Section in Yanqing County of Beijing

In the long Precambrian period, stromatolitic carbonate successions were very common. However, the non-stromatolitic carbonate succession that is marked by subtidal deposits shows a sharp contrast to the stromatolitic carbonate succession. Both the non-stromatolitic and the stromatolitic carbonate successions are important clues for the further understanding of the evolving carbonate world of the Precambrian. The Mesoproterozoic Gaoyuzhuang Formation at the Qiangou section in northwestern suburb of Beijing is a set of more than 1000 m-thick carbonate strata that can be divided into four members （or subformations）, in which a non-stromatolitic carbonate succession marked by the scarcity of stromatolites makes up the third member of the formation. This non-stromatolitic carbonate succession can further be subdivided into three third-order sequences that are marked by the regular succession of sedimentary facies. In third-order sequences, a lot of subtidal carbonate meter-scale cycles made up of medium-bedded leiolite limestones and thin-bedded marls constitute their transgressive system tracts （TSTs） and the early high-stand system tracts （EHSTs）, a lot of meter- scale cycles made up by thin-bedded limestones and marls constitute their condensed sections （CSs）, and thick-bedded to massive dolomitic limestones or lime dolomites make up the late high-stand system tracts （LHSTs）. The particularly non-stromatolitic carbonate succession making up the third member of the Mesoproterozoic Gaoyuzhuang Formation at the Qiangou section might be the representative of the non-stromatolitic carbonate succession of the Precambrian because of its special lithological features and particular sedimentary structures, and its general sedimentary features are helpful and meaningful for the further understanding of the evolution rules of the sophisticate and evolving carbonate world of the Precambrian. The time scale of the Gaoyuzhuang Formation is deduced as that from 1600 Ma to 1400 Ma; thus, the non-stromatolitic sedimentary succession making up the third member of the Gaoyuzhuang Formation may demonstrate a stromatolite decline event occurring at ca. 1450 Ma of the Proterozoic besides other three events that occurred respectively at ca. 2000 Ma, ca. 1000 Ma and ca. 675 Ma. The forming duration of this non-stromatolitic sedimentary succession of the third member of the Gaoyuzhuang Formation can be generally correlated with a similar sedimentary succession in North America, i.e. a non-stromatolitic sedimentary succession of the Helena Formation of the Belt Supergroup, which suggests that the stromatolite decline occurring at ca. 1450 Ma might be a global event. Therefore, the non-stromatolitic sedimentary succession discussed in the paper provides an important example for further understanding of carbonate sedimentology in the Precambrian.