| The phenomenon of rocky desertification is serious in the karst areas of southern China.At present,forest reconstruction and restoration in rocky desertification areas has become a difficult problem in ecosystem research,and the interaction between plants and soils is a key link to maintain ecosystem stability.To clarify the relationship between plant community composition and soil physicochemical characteristics in rocky desertification areas after afforestation,we selected Camphor-Pinus artificial mixed forest as the research object through field investigation at the National Long-Term Research Base for Comprehensive Management of Rocky Desertification in Wuling Mountains from June 2020 to August 2021.And based on the criteria of rocky desertification grade assessment,we laid out nil-rocky desertification,light rocky desertification,moderate rocky desertification,and heavy rocky desertification respectively.The plant community composition was investigated and the soil physicochemical characteristics were measured.A combination of One-way ANOVA,correlation analysis,and redundancy analysis was used to analyze the characteristics of understory vegetation,soil physical and chemical properties,and the response mechanism to the degree of rocky desertification,to explore the changes of vegetation and soil physical properties in different classes of rocky desertification habitats.The results were as follows.(1)There were 46 common species within the plant communities of the four rocky desertification habitats,such as Cyclosorus,Amphicarpaea edgeworthii.,Serissa japonica,etc.There were only one to two endemic species in each habitat,such as Peristrophe,Ilex chinensis,Symplocos sumuntia,etc.There were 36 species of herbaceous layer plants in 24 families and 35 genera,mainly in the family Gramineae and Asteraceae;47 species of shrub layer plants in 28 families and 43 genera,mainly in the family Rosaceae;13 species of tree layer plants in 13 families and 13 genera,mainly in the family Camphoraceae;newer tree species such as Corylus chinensis and Cornus wilsoniana were mainly distributed in the small diameter range,and large diameter species were still dominated by Camphor and Pinus.The results of species abundance and importance values showed that there were obvious differences in vegetation community composition in different rocky desertification habitats,and there were also significant differences in the adaptive ability of the same species to different degrees of rocky desertification habitats,and Rosaceae plants could be used as an indicator to distinguish the rocky desertification level.(2)In terms of the plant community as a whole,the species diversity indiced of the four types of rocky desertification habitats differed significantly(P<0.05),the Shannon-Wiener index and the Pielou index increased gradually with increasing rocky desertification,and the richness index was the opposite,and the Simpson index was the highest in the moderate rocky desertification habitatst.The herbaceous layer had the highest diversity index in the moderate rocky desertification habitats,and the shrub layer had the highest diversity index in the heavy rocky desertification habitats.The herbaceous layer richness index was significantly lower(P<0.05)than the other three types in the heavy rocky-desert habitats.This further indicated that the rocky exposure rate under heavy rocky desertification habitats had a critical effect on herbaceous species richness and diversity within the plant community,but did not reduce shrub species richness and biodiversity.(3)With the increase of rocky desertification,the soil physical characteristics were not degraded more and more,but showed degradation first and then gradually improved after artificial afforestation.The physical characteristics of soil(soil capacity,maximum water holding capacity,capillary water holding capacity,and field water holding capacity)differed significantly(P<0.05)from one rocky desertification habitats to another;except for soil capacity,other indicators showed a trend of decreasing and then increasing with the increase of rocky desertification.Vertically,in the same rocky desertification habitats,the soil physical indicators such as field water holding capacity,maximum water holding capacity,capillary water holding capacity,capillary porosity,non-capillary porosity,and total porosity tended to decrease with the deepening of the soil layer,except for soil capacity.(4)With the increase of rocky desertification,the soil chemical characteristics in general also showed degradation followed by gradual improvement after artificial afforestation.Except for soil pH value,all nutrient contents showed a trend of increasing,then decreasing,and then increasing with the increase of rocky desertification.Overall,the nutrient content was the highest in the heavy rocky desertification habitats.The nutrient contents of soils at different depths differed significantly,with the highest nutrient contents in the topsoil layer(0-15 cm).(5)Significant correlations(P<0.05)existed between the physical and chemical characteristics of the soils in the four rocky-desert habitats.Except for soil bulk weight,non-capillary porosity,and exchangeable magnesium ions,all significant correlations between physical and chemical characteristics showed positive correlations,and although negative correlations existed,none of the correlations were significant.(6)Based on BioEnv range,five optimal indicators of soil physicochemical characteristics were obtained based on a matrix of species abundance and soil physicochemical characteristics within plant communities in different rocky desertification habitats,namely soil non-capillary porosity,total potassium,hydrolytic nitrogen,effective phosphorus and cation exchange capacity.Further redundancy analysis was done,and the results showed that the four indicators explained 29.82%on the RDA1 axis and 24.63%on the RDA2 axis.Soil cation exchange,total potassium and hydrolysed nitrogen content significantly influenced the species composition and distribution of plant communities in the four rocky desertification habitats(P<0.05).(7)Based on the partial Mantel test,we obtained the optimal indicators of soil physicochemical characteristics to characterize the plant composition and distribution of three community types of trees,shrubs and grasses,respectively,using species abundance and soil physicochemical characteristics as matrices in different rocky desertification habitats.Further redundancy analysis showed that for the species composition and distribution of plant communities in the four rocky-desert habitats,soil exchangeable calcium ions and total potassium content had a significant effect(P<0.05).Soil non-capillary porosity and exchangeable calcium ions significantly affected the distribution of herbaceous layer plants;soil organic carbon and hydrolysed nitrogen content significantly had significant positive driving effects on the distribution of shrub layer plants;and soil total and effective phosphorus significantly affected drove the distribution of tree layer plants.In summary,since the beginning of artificial afforestation in the early 1960s,after years of restoration,the study area has changed from the original Camphor-Pinus mixed forest to a heterogeneous forest with Camphor as the main tree and multiple species mixed,with as many as 87 species of understory irrigation and grasses.There are significant differences in plant community composition in different levels of rocky desertification habitats,and there are also significant differences in the adaptive ability of the same species to different rocky desertification habitats.The physical and chemical characteristics of soils in different levels of rocky desertification habitats still differ significantly,and the physical and chemical characteristics of soils show a trend of degradation followed by gradual improvement as the degree of rocky desertification increased.The RDA analysis shows that the non-capillary porosity,total potassium,total phosphorus,organic carbon content,hydrolyzed nitrogen,effective phosphorus,cation exchange amount,and exchangeable calcium ions have significant driving effects on the species composition and distribution in different rocky desertification habitats after afforestation of rocky desertification lands.Of course,it still takes a long time to restore the study area to a relatively reasonable native forest community structure as a whole.It is suggested that in the later vegetation restoration process,not only the large diameter order of Camphor should be intercut,but also suitable tree species should be selected for ecological restoration according to the different degrees of rocky desertification and its characteristics. |
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