Breeding low-Pi tolerant and Pi-high-efficiency forest tree varieties is one of the effective ways to solve the low phosphorus utilization rate of forest trees and the lack of available phosphorus in forest soil. The evaluation system of low phosphorus tolerance of different families of Choerospondias axillaris was established to evaluate different phosphorus efficiency types and screen low-Pi tolerant and Pi-high-efficiency germplasms, and thus providing a reference for the P efficient cultivar breeding.

A pot experiment with low-Pi (0.2 mg·kg^-1) or normal-Pi (16.0 mg·kg^-1) supply was conducted, 28 families of Choerospondias axillaris were collected for the tested materials. The characterization values of seedling height, ground diameter, tissue phosphorus content, root system and other traits of each Choerospondias axillaris family were measured. The index of low phosphorus stress tolerance was calculated for each index. The low phosphorus tolerance index was analyzed by factor analysis, and the comprehensive evaluation value (D) and the comprehensive value of phosphorus efficiency were calculated by integrated affiliation function. Cluster analysis was conducted on the low phosphorus tolerance ability of the tested Choerospondias axillaris families, and the low phosphorus tolerance ability and phosphorus efficiency types were comprehensively evaluated. The regression equation was established to screen the discriminant index of low phosphorus tolerance family, and the evaluation system of low phosphorus tolerance ability was constructed.

Different families of Choerospondias axillaris showed significant growth differences under low phosphorus stress. The indexes of aboveground weight, root surface area, root tissue phosphorus content, seedling height, ground diameter and total root length were determined as the screening indexes for the evaluation system of low phosphorus tolerance of Choerospondias axillaris at seedling stage. The 28 families were categorized into three groups: low-Pi tolerance tolerance type, intermediate type and low-Pi tolerance intolerance type, and there were 6 families with low-Pi tolerance tolerance, 18 with intermediate type and 4 with low-Pi tolerance intolerance type. Additionally, based on the scatterplot of comprehensive P efficiency values, it was found that there were 5 families with P-high-efficiency under both low-Pi and normal-Pi; 7 families with high-efficiency under low-Pi but low-efficiency under normal-Pi; 7 families with low-efficiency under both low-Pi and normal-Pi; 9 families with low-efficiency under low-Pi but high-efficiency under normal-Pi.

The evaluation system of low phosphorus tolerance of different Choerospondias axillaris families was preliminarily established, and two families (LF001, L56) with low phosphorus tolerance&high-efficiency under both low-Pi and normal-Pi were screened out.

This article was designed to study the effect of different mixed ratios on the growth and soil nutrients of oak mixed plantations and explore the best mixing mode of oak.

Five types of oak mixed plantations were selected in Batangzhen Forest Farm of Ningxiang County in Hunan Province: Pure oak (L10), Oak-Liquidambar formosana mixed (L3F7), Oak- Liquidambar formosana mixed (L7F3), Oak- Cunninghamia lanceolata mixed (L5S5) and Oak- Cunninghamia lanceolata mixed (L7S3), and the oak pure plantation of Eucalyptus was used as the control (CK). Growth factors and soil nutrient indexes were determined and analyzed after 12 years.

1) There were extremely significant differences in the DBH and individual volume of oak in the 5 stands. The average DBH of the other 3 mixed models was higher than that of the L10 mode except for the L5S5 mode, and the order of average individual volume was L7F3 > L3F7 > L7S3 > L10 > L5S5. The diameter distribution range of the L10 mode was 1-2 grades wider than that of the other 4 mixed plantation modes, but the average individual volume was smaller than that of other modes. The order of the volume of each mode was L7S3 > L10 > L7F3 > L5S5 > L3F7. 2) Compared with the L10 mode, the soil nutrient content of forest land had changed, especially the organic matter was significantly improved after mixing with Liquidambar formosana or Cunninghamia lanceolata. With the increase of soil depth, the total phosphorus and total potassium content did not change significantly, while the total nitrogen, organic matter, alkaline nitrogen, available phosphorus and available potassium decreased gradually, and the pH value increased gradually. In addition to the significant difference of available phosphorus between each soil layer, the changes of other available nutrients in the 20-40 cm soil layer were significantly greater than that in the 40-60 cm soil layer. It showed that the changes in soil nutrient content slowed down below the 40 cm soil layer. 3) On the whole, the stand growth was significantly correlated with the 5 factors of pH, total nitrogen, total potassium, available phosphorus and organic matter, and the correlation with soil available potassium was not significant. The comprehensive scores of soil nutrient quality in all modes were ranked as follows: L7F3 > L3F7 > L7S3 > L5S5 > L10.

The mixed plantations of Oak+Liquidambar formosana or Cunninghamia lanceolata were better than that of Oak pure plantation. The research results can provide a theoretical basis for the practical production of mixed afforestation of oak.