Responses Of Ground Bryophyte Plant Diversity To Site Environme Ntal Factors In A Subtropical Forest

Bryophytes are important components of forest ecosystems which play an important role in maintaining the biodiversity of forest and promoting the cycling of water and nutrients.We surveyed the canopy trees,bryophytes,and soils in a 4-ha permanent forest plot.The leaf area indices(LAI)of the canopy trees were determined using hemispherical photography.We examined the effects of environmental factors on the distribution of bryophytes diversity and the potential underlying mechanisms,and detected the indicative bryophyte species of the specific environmental factors.The main results were as follows:(1)We recorded 40 bryophyte species(including varieties)from 23 families and 34 genera by conducting a survey in a 4-hapermanent forest plot established in Kanghe nature reserve in Dongyuan city,Guangdong province.There were 14 liverwort species from 11 genera of 7 families and 26 moss species from 23 genera of 16 families.The analysis of the species composition of bryophytes in this area showed that the dominant families and species of bryophytes in this area belonged to tropical and subtropical flora.There were a large number of single families in the sample plot,which indicated high habitat specificity of the bryophytes in this area.(2)Based on tree DBH of the overstory trees,all subplots within the 4-ha permanent plot are divided into 4 community types by performing TWINSPAN.The results of Kruskal-Wallis test showed no significant differences among community types in maximum cover class and evenness index of bryophyte,but highly significant differences(P < 0.01)in the total cover class,number of species,Shannon-Wiener diversity index,and Simpson diversity index of bryophytes.The total cover class,maximum cover class,species number,evenness index,Shannon-Wiener diversity index and Simpson diversity index of bryophyte were the highest in community 4.(3)The results of Mantel test showed a significant correlation between bryophyte species composition and species composition of canopy tree(P < 0.01).The leaf area index of the canopy trees was highly significantly and negatively correlated with the maximum cover class of bryophytes,but highly significantly and positively correlated with the evenness index of bryophytes and not significantly correlated with number of species,the Shannon-Wiener index,the Simpson index,and the total cover class of bryophytes(P<0.05).(4)The Spearman’s Rank correlation,a non parametric method,showed no significant correlation between the soil factors and the maximum cover class,and evenness of bryophytes;The total cover class was significantly and positively correlated with the soil total K(P < 0.05);both Shannon-Wiener diversity index and Simpson diversity index were significantly and positively correlated with soil bulk density and the soil total P(P < 0.05);Number of species of bryophytes was significantly and positively correlated with the soil bulk density,the soil total P and total K(P < 0.05),but significantly and negatively correlated with organic matter(P < 0.05).(5)The Kruskal-Wallis test showed no significant differences in bryophyte diversity index along the soil moisture,bulk density,and total nitrogen gradients,respectively;The Shannon-Wiener diversity index,number of species,Simpson diversity index,and the total cover class significantly differed along a soil organic matter gradient(P < 0.05);Bryophytes evenness significantly differed along a soil total P gradient(P < 0.05);Both the total cover class and the maximum cover class significantly differed along a soil total K gradient(P < 0.05).(6)The results of Random Forest showed that community types was the most important driver of the total cover class,number of species,Shannon-Wiener diversity index,and Simpson diversity index of bryophytes,while the soil total P exerted the greatest influence on the bryophyte evenness;The soil pH exerted a great influence on the maximum cover class.The results indicated that the change of soil nutrient content played a major role in the distribution of bryophytes,and the heterogeneity of forest communit y played a leading role in the diversity of bryophytes.(7)Indicator Species Analysis(ISA)showed that the bryophytes were highly associated with environmental factors.Twenty-three bryophyte species were detected as indictors of the community types and soil factors,with the corresponding indicator species for each environmental factor gradient.The results showed that indicator species were indicative of specific environmental conditions.