Heavy Metals Have Adverse Effects On Moss Communities In The Manganese Mines ——A Case Study Of Guizhou And Hunan,Southern China

As the electrolytic manganese metal industry continues to grow,heavy metal pollution from the mining of carbonate-type manganese mines has seriously damaged regional species diversity.Mosses have important ecological functions in the global carbon and nitrogen cycle,soil and water conservation,and ecosystem succession.However,the effects of heavy metals on the functional diversity,and physiological and biochemical activities of moss communities in carbonate manganese mining areas are not yet clear.In this study,moss species composition and functional trait characteristics（life type: turfs,wefts or mats;leaf type: wide or narrow leaves;warty or warts-free leaves;curly or flat leaves）,physiological indicators（superoxide dismutase,peroxide,catalase,and total chlorophyll）,and potential heavy metals（Mn,Cr,Zn,Cu,Pb,and Cd）were investigated at the Huayuan manganese mine,Xiangjiang manganese mine and Nancha manganese mine in southern China.The causal effects between the indicators were assessed using a partial least squares path modeling.The main results were as follows:（1）Heavy metals Mn,Cr,Pb and Cd exerted toxic effects on moss communities.The combined stress of high concentrations of Mn,Cr,Pb and Cd exacerbated the degree of membrane lipid peroxidation in mosses,and excessive ROS substances inhibited the activity of antioxidant enzymes.Heavy metals had an inhibitory effect on the synthesis of total chlorophyll and the antioxidant enzymes（SOD,POD and CAT）were unable to completely eliminate ROS substances.Overall,heavy metal stress had a negative impact on the physiological activity of the moss community,but this conclusion still needs to be validated by laboratory experiments.（2）17 families,31 genera and 73 moss species were found in the Nancha Manganese Mine,Xiangjiang Manganese Mine and Huayuan Manganese Mine.The dominant families were Pottiaceae（30.1%）,Bryaceae（21.9%）,Funariaceae（8.2%）,Brachytheciaceae（8.2%）,Ditrichaceae（5.5%）,Bartramiaceae（4.1%）and Polytrichaceae（4.1%）.Among them,Pottiaceae and Bryaceae were the absolute dominant families,and the dominant genera in the study area were Bryum,Barbula,Brachythecium,Anoectangium,Trichostomum,Ditrichum,Funaria and Physcomitrium.（3）The local species diversity of the moss community tended to decrease as the concentration of topsoil heavy metals increased,and the species richness of the plots with lower levels of heavy metals was higher than that of the plots with higher levels of heavy metals.The spatial variation in species diversity indicated that the structure of the moss community tended to simplify as the concentration of heavy metals in the topsoil increased,with a significant decrease in species richness and greater homogeneity of single species.At the plots with higher levels of heavy metals,the variation in richness between communities was greater and species replacement was more likely to occur,whereas at the plots with lower levels of heavy metals,the variation in richness between communities was smaller and the community structure was relatively more stable.（4）The ecological preferences of different moss species for different topsoil heavy metal plots differed.Twenty-six species favored sample sites with low levels of topsoil heavy metals and disliked sample sites with high levels of topsoil heavy metals.Fifteen species favored sample sites with high levels of topsoil heavy metals and disliked sample sites with low levels of topsoil heavy metals.（5）All species were divided into eight groups based on information on species traits: group1 represented turf-moss species,mostly with narrow,warty,and curly leaves;group 2 represented wefts or mats moss species,mostly with wide,warts-free,and curly or flat leaves;group 3 represented turf-moss species,mostly with wide,warty,and curly leaves;group 4represented turf-moss species,mostly with wide,warts-free,and flat leaves;group 5 represented turf-moss species,mostly with wide,warty,and flat leaves;group 6 represented turf-moss species,mostly with narrow,wartsfree,and flat leaves;group 7 represented turf-moss species,mostly with narrow,warts-free,and curly leaves;and group 8 represented turf-moss species,mostly with narrow,warty,and flat leaves.Topsoil heavy metals impeded vegetation growth by deteriorating soil conditions and subsequently affecting the microenvironment of moss communities.With increasing levels of topsoil heavy metals,the degree of overlap of ecological niches between species in the moss community diminishes,the degree of complementarity of species ecological niches decreases significantly,and the number of functional groups in the community decreases significantly.Turfs and warty leaves exhibit functional traits in response to the microenvironment becoming even drier and more exposed.Additionally,curled leaves and narrow leaves helped to minimize exposure to particulate pollutants.