| As the oldest vascular plants on Earth,lycophytes and ferns were the main building blocks of terrestrial plant communities during the Paleozoic and Mesozoic periods,and are also important components of the herbaceous and interforest layers of present-day forest communities.As lycophytes and ferns play an important ecological role in carbon sequestration and oxygen release,air purification,accumulation of organic matter,improvement of soil physical and chemical properties and promotion of nutrient cycling in forest ecosystems,and their edible,medicinal and ornamental values also have a direct or indirect impact on human production and life,however,with global environmental changes and the impact of human activities,many lycophytes and ferns are facing the danger of endangerment or extinction,so scientific management and reasonable conservation have become a top priority.In this study,lycophytes and ferns were studied in the subtropical mixed evergreen deciduous broad-leaved forests of the Xingdoushan National Nature Reserve in Southwest Hubei,and the resource status and zonal characteristics of lycophytes and ferns in the region are not yet known;the distribution pattern of species and functional diversity and their relationship with environmental factors are not clear;the distribution of C,N,and P ecological stoichiometry characteristics and their relationship with soil supply are not clear,etc.The data required for analysis were first obtained through field surveys,sample collection,trait determination and biochemical experiments,and then analyzed using linear regression(LR),redundancy analysis(RDA),Pearson correlation analysis,RLQ analysis,fourth angle analysis,one-way ANOVA and structural equation modeling(SEM),and finally the data were tabulated and plotted using WPS,Office 2019,Origin Pro 2018 and R 4.1.1.The main results and conclusions are as follows: There are 15 families,26 genera and 73 species of lycophytes and ferns in Xingdoushan National Nature Reserve;the dominant families are Lepidopteridae,Fernidae and Fenneraceae,etc;the dominant genera are Lepidopteridae,Fernidae and Fenneraceae,etc;there are primitive,evolving and more evolved families of lycophytes and ferns distributed in the area,with primitive families accounting for 20% of the total number of families.It indicates that the species of stone pines and ferns in the reserve are richer and of older origin.(2)The families and genera of lycophytes and ferns in Xingdoushan National Nature Reserve are mainly of world distribution,pantropical distribution and Old World tropical distribution;among them,40% of the total number of families with pantropical distribution and 19.23% of the total number of genera with pantropical distribution;the families with Old World tropical distribution account for6.67% of the total number of families and the genera with Old World tropical distribution account for 11.54% of the total number of genera.The overall tropical nature of stone pine and fern flora types in the reserve indicates that the area may have been a paleotropical plant distribution area.(3)The top 3 species in the ecological niche width index of lycophytes and ferns in Xingdoushan National Nature Reserve are Polystichum braunii,Osmunda japonica and Arachniodes tripinnata,respectively;A total of 2628 pairs of overlapping ecotone relationships were formed in the region,of which 91.36% of species pairs had an ecotone overlap index less than 0.50,while only 1.71% of species pairs had an ecotone overlap index of 1.00.It shows that the ecological niches of stone pine and fern species in the reserve are clearly differentiated,the coexistence between species is good,and the community structure is stable,indicating that the conservation of stone pine and fern species should focus on the conservation of their communities.(4)The top 3 species importance values of lycophytes and ferns in Xingdoushan National Nature Reserve are Polystichum braunii,Diplopterygium glaucum and Dryopteris sublacera,respectively;all four ?-diversity indices in the region show peaks at 1250-1300 m and 1400-1450 m above sea level;the Margalef richness index tends to decrease with elevation,and the Pielou evenness index tends to increase and then decrease with elevation;the differences in ?-diversity indices among communities are mainly influenced by species replacement processes;the results of redundancy analysis showed that the distribution of stone pine and fern species was influenced by factors such as altitude,air temperature and humidity,soil physical and chemical properties and forest depression.The distribution pattern of species diversity of stone pines and ferns in the reserve is the result of their interaction with environmental factors,with elevation being the most influential factor,followed by monthly mean air humidity and forest depression.This is consistent with the fact that stone pines and ferns require moisture and light for growth and development,indicating that the conservation of stone pines and ferns should be based on the conservation of their habitats.(5)The coefficients of variation and PPI indices of lycophytes and ferns in Xingdoushan National Nature Reserve were small for all traits except LA and LV,which had larger coefficients of variation and PPI indices;the leaf functional trait SLA tends to decrease and then increase with elevation,and SLW tends to increase and then decrease with elevation in the area;both FRic and FEve indices of leaf functional diversity showed a decreasing and then increasing trend with increasing altitude;correlation analysis between leaf functional traits showed a significant negative correlation between SLW and LNC(P < 0.05);the results of RLQ and fourth angle analysis showed that leaf functional traits SLA and LV were mainly influenced by p H,LA and LWC were mainly influenced by SMC,LNC,LPC and LT were mainly influenced by MAST,MAAH and MAAT,and LOCC,SLW and LDMC were mainly influenced by FD,STP and SOC.It shows that stone pines and ferns grow well in the protected area,and they show strong plasticity of leaf functional traits to adapt to environmental changes,while altitude,monthly mean air humidity,monthly mean air temperature,and soil organic carbon content all affect their survival.It indicates that habitat should be a prerequisite in the conservation and restoration process of stone pines and ferns,and at the same time,reasonable relocation protection can be carried out for their different habitat adaptation strategies to improve conservation and restoration efficiency.(6)The arithmetic mean values of C content of lycophytes and ferns leaves in Xingdoushan National Nature Reserve were(371.07 ± 45.37)mg·g-1,N and P contents were(15.63 ± 3.46)mg·g-1 and(0.38 ± 0.07)mg·g-1,respectively;the arithmetic means of leaf C:N and C:P were(24.74 ± 5.74)and(1006.89 ± 205.33),respectively,and the arithmetic mean of N:P was(42.61 ± 12.68);the results of the correlation analysis of C,N and P elements in different organs showed that the P content of both leaves and stems were highly significantly positively correlated with the P content of roots(P < 0.01),and there was a highly significant positive correlation between C:N and C:P of stems and roots(P < 0.01);structural equation model validation results showed a weak positive correlation between nutrients in the sample soil and nutrients in the inter-root soil,and a strong positive correlation between nutrients in the inter-root soil and nutrients in lycophytes and ferns.It shows that the stone pine species and ferns in the reserve have good ability to transform,absorb and utilize C elements,but their growth is limited by P elements,and the elements required for their growth are mainly supplied by the inter-root soil. |
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