| Alpine timberline has become the key areas of research in climate change adaptation and mitigation as its special structure, function and high sensitivity to the climate change, the timberline response to global warming and human activities on global change is a hot research. Climate change and human interference are two important factors affect biodiversity. The research combined two factors, studied of natural timberline and forest-grassland ecotone by grazing of ZheGu Mountain in western Sichuan with the field investigation and laboratory analysis as well as molecular biology methods, analyzed the distribution patterns of above-and belowground biodiversity include plant diversity, soil fauna and soil microbial diversity simultaneously under different driving mechanisms, interaction between plant diversity and soil organism diversity as well as biodiversity related to the environmental factors. The results were important for the understanding of the relationship between above-and belowground diversity and ecological processes in alpine forest-grassland ecotone, which provide the important scientific basis for the research of timberline and management of forest-grassland ecotone.The major findings are as follows:(1) 221 species of plants were recorded belonging to 48 families,124 genera, which 42 species of woody plants and 179 species of herbs in timberline ecotone and forest-grassland ecotone. From the distribution of plant families, the majority species were northern temperate plant type and the world wide distribution type. Gramineae, Compositae, Ranunculaceae, Rosaceae, Scrophulariaceae, Polygonaceae, Saxifragaceae, Gentianaceae, Apiaceae, Caprifoliaceae were the dominant species of ten families in alpine timberline ecotone and forest-grassland ecotone, and most of the families belong to the ingredients of polar-alpine.Richness and diversity of woody plants were lower than herbaceous plants in ecotone. Plant abundance decreased with grazing intensity decreasing in forest-grassland ecotone.The number of species with elevation rasing show partial front patterns in timberline ecotone. The species richness in shrub reached its peak in ecotone. HAS had 88 species while VAS had 79 spcecies. Abundance of woody plants of two ecotone were tested with bell-shaped curve, which maximum species were in VAT and HAS. Plant diversity in herb layer increased with the elevation and then decreased in timberline ecotone, reached its peak in the shrub, showed a partial distribution pattern front, while the herb diversity index H'with a similar trend of D as U-distribution, herbal diversity of meadow and conifer forest were lower than timberline and treeline. Herb richness with increasing disturbance intensity soared and reaches its peak in the meadow in forest-grassland ecotone, but the herb diversity and evenness were showed single peak distribution.Since the two ecotone have similar landscape interlaced with the distribution of the transition from alpine meadow to the coniferous forest, the families of woody and herbaceous species plants were in consistent with the trend in two ecotone. Woody dominant species were from the Rosaceae, Ericaceae, Salicaceae, Caprifoliaceae transition to the Pinaceae, Betulaceae, Ribes, etc., but lack of hardwood species such as Betula albo-sinensis, Betula utilis in timberline ecotone. Herb dominant species were from Gentianaceae, Gramineae transition to Scrophulariaceae, Onagraceae, Ranunculaceae, and finally then ferns, Araliaceae, sedge, etc.. Two ecotone also had similar species composition although the formation mechanism were different, plant communities had high degree of similarity between adjacent vegetation in the same ecotone and similar vegetation in the different ecotone. Plant species composition in alpine meadow were most different with other communities. From the view ofβdiversity, the most obvious transitions of woody plants were from VPCF to VTi and from HAT to HBF. The most obvious transition of herbaceous plant were from VTr to VAS and from HAS to HAT. The maximum species of four functional group were deciduous woody plants, basal forbs, semi-basal forbs, erect leafy forbs in two ecotone. Basal forbs, semi-basal forbs and erect leafy forbs and bunch grass species were first increased and then decreased as elevation rising.Plant functional group diversity reached its peak in timberline and reached bottom in the treeline, evenness of plant functional groups were highest in the coniferous forest.Species of broadleaf weeds and bunch grasses increase with grassing intensity increased, the diversity and evenness of PFTs increased with disturbance intensity decreased.(2) Macro soil fauna was with minimum number and most species; while micro soil fauna was maximum number and least groups in three size categories, which 103 groups were same in two ecotones. Nematoda is the only dominant group, accounting for more than 80% of individual density, Enchytraeidae, Eutardigrada, Harpacticoida, Isotomidae were the common groups, and the remaining 126 were the rare groups.The distribution of Acarina and Collembola were different in seasons and ecotones. The characteristics of A/C values were consistent with cold zone climates from the overall trends. A/C values first increased and then decreased in timberline ecotone with rasing altitude, while in forest-grassland ecotone A/C value increased gradually with decreasing disturbance intensity. That show the mite can be habitat indicator species to predict the environment and climate change, and fall was the most active season for mite. Soil fauna density and the number of individuals had obvious surface accumulation, moss layer was the ideal living place for soil faunas. fauna groups in soil layers showed a single peak in two ecotones. Soil fauna diversity index H' and evenness index E showed gradual reduction with altitude rising in timberline ecotone, dominance index D showed the opposite trend; soil fauna diversity index H' and evenness index E showed a slight decrease and then gradually upward trend with the disturbance gradient reducing. DG index can better reflect the structure and diversity of soil faunas under high density and abundant groups.Wilson-Shmida diversity index showed that soil fauna alternatives were higher in alpine meadow with the rest of communities. The group composition of soil faunas were quite different between different vegetations while in similar between the same or similar types of vegetation ecosystems. Earthworm biomass occupies the main position in macro-fauna biomass, followed by Malaysia in two ecotones. Average biomass of soil macrofauna in timberline ecotone was higher than forest-grassland ecotone.Soil macrofauna biomass significantly different in seasons and was negatively correlated with elevation in timberline ecotone. And soil fauna community structure has changed significantly with reduced grassing intensity. the soil fauna density, group, biomass was the lowest in the meadow subject to serious interference, the largest groups were in HAT with moderate disturbance, soil macrofauna biomass was highest in HBF and soil fauna density was highest in almost undisturbed HPCF. Can see thereby, soil fauna density, group, biomass and community structure had obvious relationship with grazing interference.Soil bacterial count was dominated of soil microorganisms, followed by actinomycetes count and fungi count was at least, account for less than 0.1% of the total number in two ecotones. The quantity of soil microorganism was significantly different in vegetation types. Culturable soil microorganism count were highest in VAT and HAT. Soil microbial biomass were highest in VAS and VAT, while lowest in VPCF, the spatial distribution showing a single peak trend, soil microorganism count and soil microbial biomass were highest in the fall, soil microbial biomass reached peak in summer and autumn of forest-grassland ecotone, while SMBC and SMBN were highest in the meadow, SMBC were highest in fall but seasonal trends of SMBN were not obvious. Soil microbial diversity and microbial biomass as well as culturable soil microorganism count interaction has the positive effect. Bacterial diversity, SMBC, SMBN, soil bacteria, fungi, actinomycetes count were tested positive correlation with fungal diversity. SMBC and SMBN were in positive correlation of two ecotones and the correlation was highly significant in forest-grassland ecotone. Also soil microbial biomass was positively correlated with culturable soil microorganism count.According to DGGE patterns reflected the diversity of soil bacteria higer than fungal diversity, fungal diversity were more amplitude than bacteria. Diversity of soil bacterial share some common characteristics in two ecotones, meadow soil bacterial diversity had significant seasonal variation while coniferous forests were more stable niche, while the percentage changes in soil bacteria were minimum, indicating bacteria sensitive to external factors. Seasonal changes of soil bacteria diversity showed spring> autumn> summer. Similarity analysis showed that the fungal species similarity was generally lower than soil bacteria similarity. Soil bacteria and fungi between adjacent plots had higher degree of similarity, while with greater difference in different vegetation samples.There were four main groups of bacteria in timberline ecotone and forest-grassland ecotone:α,βandγgroups of Proteobacteria, Bacteroidetes, Acidobacteria, Verrucomicrobia, of which Proteobacteria were predominant of bacteria diversity. Most similar sequences in the genetic relationships were similar with cold-adapted strains isolated from habitats of subalpine forests and meadow soil, meadow soil in Qinghai-Tibet Plateau, the East Qilian Mountains alpine meadows and glaciers in the Himalayas series soil.Ecosystems above and below ground was an inter-connected and inter-dependent whole. There was a close connection and dynamic interaction between soil organisms and plants aboveground. Soil fauna groups were negatively correlated with herbaceous plants richness. Soil meso- and micro-fauna was the important regulator of feeding microbial community structure and biomass. There was a mutual relationship between growth and decline between microbial and soil fauna. Such as negatively related between soil bacteria diversity and soil meso and micro-fauna groups in timberline ecotone while negatively related between soil bacteria diversity and soil macro, meso and microfauna groups in forest-grassland ecotone. There was positively correlated between soil fungal diversity and macrofauna groups, which indicate soil macro-fauna improve fungi diversity by improving the structure of soil. The relevance of soil fauna and microorganisms with plant diversity aboveground was more obvious in timberline ecotone, such as significant positive correlation of fungi and woody richness, significantly negatively correlated between soil microfauna and herb richness. As the formation mechanism of two ecotones were different, the relationship of plant diversity and soil biodiversity became more complex in forest-grassland ecotone as a result of grazing,leading to the relationship more complex between plant diversity and soil fauna and microorganisms that difficult to explain with single correlation, there may be the result of many factors.Average temperature of growing season in 10cm soil layer was 6.40℃in timberline, which close to the average soil temperature of global timberline. DCCA can better express the species composition of plant communities and ecological gradient of environment interaction. Herb richness and woody diversity had significant correlation with environmental factors in timberline ecotone, the elevation, soil pH value, SOC, TN, TP, AN, AK, herbaceous biomass, moss and litter reserves significantly affect the richness and diversity of herbaceous plants; SOC, TN, TP,AN, herbaceous biomass, moss and litter storage significantly affected the diversity of woody plants. Richness of woody plants or dominance and evenness of herbaceous plants were not significant associated with environmental factors. Relationship between plant diversity and environmental factors was less obviously than that of timberline ecotone. Only soil pH, herbaceous biomass, moss and litter reserves significantly affect the richness of herbaceous plants, the remaining factors were not significant correlation with herb species diversity and woody plants diversity.CCA analysis of plant functional groups and environmental factors showed that altitude, soil type, pH, ground cover reserves and soil nutrient were the main environmental factors affect the distribution of plant functional group differentiation in timberline ecotone; while soil type, grazing, herbage biomass and ground cover reserves were the main environmental factors affect the distribution of plant functional group differentiation in forest-grassland ecotone. Bunchgrass and erect leafy forbs suited to survive in the meadow and shrub while ferns was suitable for survive in the environment of damp and thick ground cover.CCA analysis showed that soil fauna of same dominant groups chose to live in similar suitable environment. Soil microfauna and mesofauna as well as macrofauna such as Carabidae, Lithobiomorpha, Linyphiidae, Theridiosomatidae mainly concentrated in thick and damp environmental conditions of coniferous forest and timberline. soil macrofauna such as Lumbricomorpha, Formicidae, Penthimiinae, Scarabaeidate, Tentherdinidate perfered to live in alpine meadow and scrubs of timberline ecotone. Soil microfauna and mesofauna as well as macrofauna such as Polydesmida, Carabidae, Lithobiomorpha, Geophilomorpha, Tipulidate, Linyphiidae, Theridiosomatidae mainly concentrated in thick and damp environmental conditions of coniferous forest and broadleaf forest. soil macrofauna such as Lumbricomorpha, Formicidae, Penthimiinae, Scarabaeidate, Staphilinidae, Cecidomyiidae perfered to live in alpine meadow and scrubs with grazing interference of forest-grassland ecotone.CCA analysis of species composition of soil bacteria and fungi with environmental factors in spring, summer and autumn showed that soil temperature had the most important effects on composition and distribution of soil bacteria, which influence significantly in spring and summer; secondly, soil TP and AN affected significantly in spring, soil moisture affected significantly in fall, soil TK affected significantly in summer. Soil pH had the most important effects on composition and distribution of soil fungi, which influence significantly in spring, summer and autumn; SMBC and the elevation were in secondly that affect significantly in the summer and fall, soil temperature influenced more in the spring and soil moisture influenced apparently in the summer.Correlation analysis indicated that soil pH, organic matter, total N and available K were main factors influence soil microbial community, soil temperature had much influence on bacterial diversity and culturable fungi count, connection between soil moisture and soil microorganisms was weak. Compared to timberline ecotone, there were little key soil factors effect soil microorganisms in forest-grassland ecotone, only the soil organic carbon and nitrogen affected significantly. On the whole, degree of interference in forest-grassland ecotone was greater compared to the natural state of the timberline ecotone, thereby interference affected the structure and function of soil fauna and microbial communities by changing environmental conditions and plant species composition and diversity within community, which lead to more complex relationship between ecological factors and plant diversity as well as soil fauna diversity and soil microbial diversity.
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