3.3 | Phylogenetic diversity and structure
The TR and PD were higher at both ends of the ranges. The lowest TR and PD values were observed in Minfeng County, and the values in the eastern area were higher than those in the western area (Table 2).
In the present study, only one SES-PD value was greater than 0, and all other SES-PD values were less than 0. The maximum and minimum SES-PDs were 3.56 and -5.69, respectively (Table 2). The negative SES-PD values indicated that 27 of the 28 county-level communities were young flora, while the positive SES-PD value for the Banma County indicated that the flora there were relatively ancient. No significant differences were observed in the SES-PDs between Jiuzhi County and Shache County, whereas significant differences were detected among the other SES-PD values (P < 0.05) (Table 2).
Phylogenetic structure can be revealed by the NRI and NTI. These indexes indicated that the different counties had different phylogenetic structures (Figures 3, 4). Negative NRIs in 11 county-level communities indicated phylogenetic dispersion. These counties were located mainly in the western and middle parts of the Kunlun Mountains. Conversely, positive NRIs in the 17 other county-level communities indicated phylogenetic clustering. These counties were distributed mainly in the eastern and middle parts of the Kunlun Mountains. Significant differences were detected between four negative NRIs (P < 0.05) and three positive NRIs (P < 0.05), while the NRIs of the remaining 21 counties were not significant (Figure 3). In addition, the NTIs of 27 county-level communities were positive, of which 24 NTIs were statistically significant (P < 0.05). Only the community in Banma County had a negative NTI that was also significantly different (P < 0.05) (Figure 4). However, inconsistent trends were observed between the NRIs and NTIs in 10 counties, most of which bordered the Qaidam and Tarim Basins (Figures 3, 4).
Overall, both the NRI and NTI values were negative in the Banma County. The other 27 counties had positive NTI values, 17 of which also had positive NRI values. Ten counties had negative NRI values and were adjacent to the Qaidam and Tarim Basins (Figures 3, 4).