| The Shibing Karst World Natural Heritage Site embodies the unique biological and ecological evolution characteristics of subtropical dolomite karst forests in terms of biodiversity.In the ancient and primitive mountain forest ecological environment of the Heritage Site,with the increase of altitude gradient,the combination characteristics of water and thermal environmental factors from the river valley to the mountaintop rapidly change.A clear vertical vegetation band spectrum has been developed,providing an ideal natural laboratory for studying the distribution pattern of biodiversity and the mechanism of species coexistence.Soil mites are one of the arthropod groups with the highest abundance and species diversity.They occupy multiple trophic levels in the food web and play a vital role in maintaining the versatility and stability of the underground forest ecosystem.Yet,the spatiotemporal distribution pattern and diversity characteristics of the soil mite community under Heritage Site’s vertical vegetation band spectrum still need to be clarified,which hinders the understanding of crucial underground ecological processes in subtropical dolomite forest ecosystems.Based on this,we selected four typical forest types as research samples based on the vertical vegetation band spectrum of the heritage site,namely,riverbank shrub(RBS),deciduous broad-leaved forest(DBF),evergreen broad-leaved forest(EBF),coniferous broad-leaved mixed forest(CBF).In July(summer)and September(autumn)of 2021,we collected soil samples of the vertical profile soil layers(humus layer,0-50 mm soil layer,and 50-100 mm soil layer)of the above forest types,baked and separated soil animal samples indoors through the Berles Tullgren device.We carried out the sorting,morphological identification,and classification of mites.At the same time,we detected nine soil environmental factors.Data analysis methods such as ANOVA,similarity analysis,cluster analysis,and RDA analysis were used to clarify the characteristics of mite community composition and distribution in the Heritage Site,identify the spatial and temporal distribution patterns of mite community composition and diversity along the vertical band spectrum of mountain vegetation and its change patterns,explore the ecological indicators of mites on the forest vegetation environment and reveal the critical soil environmental factors affecting mite community composition.The study enriches the research results on the biodiversity of the Heritage Site.It enhances its biodiversity value and eco-strategic position on the World Heritage List while providing vital biological information and a scientific basis for future ecological conservation,environmental monitoring,and sustainable development of the Site.The main findings are as follows:(1)During the research period,18421 mites were captured,belonging to 151 genera,72 families,and 3 orders.The abundance of Oribatida and species richness accounted for absolute advantage,followed by predatory gamasid mites.21 genera with relative abundance greater than 1%,such as Perscheloribates,Scheloribates,and Nothrus,are the main dominant genera in the forest environment of Heritage Site.In addition,Scheoribates,Perscheloribates,Nothrus,Trichogalumna,and Parholaspulus have a 100% occurrence rate in various places and are widely distributed in various forest microhabitats.(2)Most of the soil mite community composition and diversity parameters along the vertical banding spectrum of vegetation under the elevation gradient of the Heritage Site showed an increasing trend,i.e.,the lowest mean values of each community parameter were found in the RBS habitat and the highest in the CBF habitat.The results of the Kruskal-Wallis non-parametric test or one-way ANOVA showed that the number of families,genera,and Simpson’s diversity index of soil mites in the RBS forest type were significantly different from those in the EBF and CBF forest types,respectively(p < 0.05),while Shannon’s diversity index,richness index,and evenness index of soil mites in the RBS forest type were significantly different from those in the other three forest types,respectively(p < 0.05).(3)The Morisita Horn similarity index analysis of soil mite communities among different forest types showed that RBS had a moderate similarity level with the other three forest types,while DBF,DBF,and CBF had a very similar level;The Jacard similarity index analysis shows that there is a moderate level of similarity between the two different forest types.NMDS analysis further showed extremely significant differences(p<0.01)in soil mite communities under different forest types during the two sampling periods.(4)The composition and diversity of soil mite communities along the vertical profile layer of soil under various forest types in the Heritage Site showed a decreasing trend,indicating surface aggregation of soil mite community distribution.The variance test results of soil mite community composition showed no significant difference in the number of soil mite individuals between different forest types in the same soil layer(p>0.05).There was a significant difference in the number of soil mite genera in humus and upper soil between RBS and CBF forest types(p<0.05).The variance test results of various parameters of soil mite community diversity showed that there were significant differences among forest types in the soil humus layer(p<0.05),and there were no significant differences between forest types in the upper and lower soil layers(p>0.05).(5)The abundance of mites and species richness in the forest ecosystem of the Heritage Site in autumn were greater than those in summer,and the seasonal variation of mites(22 genera)with relative abundance greater than 1% is relatively small,that was,the common genera of the two seasons were 16 genera,and only 6 genera had seasonal dynamic changes in the abundance of mites.Only six mite genera showed seasonal dynamic changes in abundance.Most of the mite community composition and diversity parameters did not show significant seasonal variation within the same stand type.However,there was a complex variation of mite communities between stand types in the same season.A three-way ANOVA further showed that seasonal and stand-type interactions had a significant effect on mite community parameters(p < 0.05),while other interactions did not show significant effects.(6)MI index analysis showed that the predatory gamasid mites in the forest ecosystem of the Heritage Site were mainly K-selective.There were seasonal changes in the K and r groups of predatory gamasid mites from summer to autumn;both were K-selective.MGP analysis showed that the Gymnonota group(G group)had the highest number of families and genera,and the lowest number of individuals,while the Poronota group(P group)was different;In terms of the percentage of genera,the community type of the forest type mite was all O-type,while in terms of percentage of individual numbers,it was mainly P-type.(7)Kruskal-Wallis non-parametric tests showed significant differences(p < 0.01)between groups of soil chemical environmental factors and ecological stoichiometric ratios under different forest types in the Heritage Site.Correlation analysis showed that soil organic carbon,porosity,carbon stoichiometry ratio,and N: K were significantly and positively correlated with most mite community parameters,while total potassium and bulk weight were different,and the number of individual mites was significantly and negatively correlated with p H and total phosphorus.The Mental test further revealed that soil chemistry factors and ecological stoichiometry ratios were the main factors influencing the dominant family of mites,while the RDA analysis further revealed that soil organic matter and C: K were the main factors influencing the dominant genus of mites.Based on the above results,our research concluded that the soil mite biology of the Shibing Dolomite Karst World Heritage Site was abundant,and the dominant taxa were good indicators of the unique forest ecology of the Site,with the Gamasina and Oribatida ecological taxa indicating a healthy forest soil environment with little disturbance from human activities.At the same time,our research revealed that soil mite communities showed an increasing horizontal distribution pattern under mountain elevation gradients and a decreasing vertical distribution pattern under soil vertical profile gradients,that seasonal changes had a significant effect on soil mite communities,and that the interaction between season and forest type was significant.In addition,our research had shown that soil chemistry factors and ecological stoichiometric ratios were essential environmental factors governing the composition and diversity of the soil mite community.In the future,people should pay particular attention and emphasize strengthening the conservation research of forest soil organisms in karst Heritage Sites. |
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