ObjectiveSorbus pohuashanensis is one of the important Chinese native tree species with high ornamental value ranging from 500 to 2 000 m altitude. In this study, the field trial for heat resistance of different clones was evaluated comprehensively, which provided scientific basis for early selecting fine varieties adapting to high plains in Beijing.

Method2-year-old grafted seedlings of 14 clones from 5 provenances were used as materials. In the field trial, which performed in Yanqing County of Beijing with 500 m altitude, the height and stem growth of seedlings, content of malondialdehyde (MDA), soluble protein, soluble sugar, chlorophyll in the leaves, activity of superoxide dismutase (SOD) and peroxidase (POD) in the leaves were measured; and the heat resistance of 14 clones was evaluated comprehensively by membership function analysis based on principal component analysis.

ResultThe value of each single index showed significant difference among 4 months and was significantly different among different clones. The growth performance of Wuling1 (WL1),Wuling2 (WL2), Shihui1 (SH1) and Shihui2 (SH2) was significantly better than other clones. The growth performance of Taibai1 (TB1) and Taibai2 (TB2) was the worst; the MDA contents of TB1 and TB2 increased most significantly from May to June, showing poor heat resistance. However, the MDA contents of Fengning2 (FN2) and WL2 decreased, showing stronger heat resistance than other clones. The activity of two protective enzymes of WL2, Fengning1 (FN1) and FN2 was higher than other clones. The chlorophyll content of FN1 and FN2 was minimally impacted by high temperature; the content of osmotic regulator of Songshan1 (SS1), Songshan2 (SS2), Songshan3 (SS3) and Songshan4 (SS4) was higher than other clones. Correlation analysis showed significantly positive correlation between every two groups of chlorophyll content (P < 0.01); chlorophyll and ground diameter growth (P < 0.05) were significantly negatively correlated. Significantly positive correlation was found between seedling height and ground diameter of seedlings; after principal component analysis, 10 single indexes were transformed into 4 new independent comprehensive indexes;

ConclusionAfter the comprehensive evaluation of membership function, the sequence of field heat resistance of each clone seedling from strong to weak is: WL2, WL1, FN1, SH2, SH1, FN2, SS2, Huangshan shuiyu2 (HS2), SS4, SS3, SS1, Huangshan shuiyu1 (HS1), TB2, TB1.