| Larix principis-rupprechtii Mayr.is the main alpine afforestation tree species in northern China.Afforestation activities in China are mainly applied in spring and autumn,when there is less precipitation in northern China.The limited supply of soil moisture in the afforestation land causes afforestation failure.Therefore,Summer planting has become an alternative choice.However,seedlings are rapid growing and vulnerable to planting stress in this period of summer planting,which will seriously affect the field performance of the top slightly dominant tree species.Therefore,it is vital that how to improve the top slightly lignified degree of summer afforestation seedlings.Many foreign studies show that short-day treatment can effectively solve this problem.At the same time,it can also improve the degree of lignification and the quality of seedlings by reducing the irrigation parameters of the tree species that are not sensitive to light.Both short-day treatment and drought hardening can improve the field performance in summer.However,the current researches focus on the single aspect of short-day treatment or drought hardening.The effects of combined short-day treatment and drought hardening on buds formation,dry mass accumulation and distribution,mineral nutrition storage and non-structural carbohydrate distribution and the field performance are still unknown.Whether the combination of the two methods can produce synergistic effect is worth studying.The establishment of photoperiod and drought hardening treatment is of great significance to improve the quality of seedlings and field performance.The results are as follows: short-day treatment significantly increased bud formation of seedlings,promoted the degree of dormancy and lignification of seedlings.Bud formation of short-day treatments was average 66.11%,which was 2.5 times higher than that of natural day length treatments.Drought hardening treatments restricted the growth of diameter,but there is no effect on the height of seedlings,and accordingly increased the ratio of height to diameter;Drought hardening treatments inhibited the growth of shoot,Strong treatment decreased 33.3% compared with normal drought hardening treatment,and increased the proportion of root biomass(strong drought hardening treatment 28.0% VS normal drought hardening treatment 26.0%),compared with the normal drought hardening treatment,the distribution of starch in roots was increased(strong drought hardening treatment 37.6% VS normal drought hardening treatment 26.5%),the concentration of soluble sugar was increased(strong drought hardening treatment 40.4mg/g VS normal drought hardening treatment 37.3mg/g),the concentration of starch was decreased(strong drought hardening treatment 19.1mg/g VS normal drought hardening treatment 28.7mg/g),and the conversion of starch to soluble sugar was promoted.SD treatment can significantly increase the N concentration of the shoot(ND = 1.48% vs SD = 1.52%),the N concentration of the plant(ND = 1.43% vs SD = 1.44%),the P concentration of the shoot(ND = 0.39% vs SD = 0.41%)and the K concentration of the plant(root: ND = 1.77% vs SD = 1.84%;shoot: ND = 1.87% vs SD = 1.95%;plant: ND = 1.84% vs SD = 1.92%).It was found that the survival of L.principis-rupprechtii Mayr.seedlings in summer planting was affected by short-day treatment(ND = 81.3% vs SD = 92.1%).In conclusion,short-day treatment can promote the terminal bud formation of L.principis-rupprechtii Mayr.,promote the hardening of the seedlings,improve the resistance of the seedlings,and improve the survival of the outplanted seedlings.Drought hardening treatments improved the nutrient status of seedlings,promoted the conversion of starch and soluble sugar in aboveground tissues and the distribution of starch in the roots,and kept the seedlings of L.principis-rupprechtii Mayr.growing well in summer afforestation.At the same time,owing to the experimental seedlings are 0.5a seedlings,the monitor duration of the outplanting field performance was limited,and the growth of the stem volume growth and growth increment after summer afforestation is lower than that under natural photoperiod conditions,but the effect of short-day treatment on the growth of L.principis-rupprechtii Mayr.can be verified in the subsequent monitoring,which is more feasible after 3-5 years of outplanting and receive a reliable conclusion. |
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