Study On The Effect Of Barren Resistance And Drought Tolerance Of Short-day Treated Pinus Tabulaeformis Container Seedlings

Short day(SD)treatment was widely used in afforestation in summer.Foreign study has shown that short-day treatment improves adaptability to the environment and significantly enhances summer outplanting performance in high latitude.The effect of short-day on seedling growth was explained from two aspects:shoot lignification and root water uptake.Short photoperiod could induce formation of terminal bud,slowdown the growth of height.More carbohydrates are allocated to roots to promote root development.After short-day treatment,the growth of shoot became slow and the transpiration rate was decreased.Therefore,seedlings after short-day could obtain more water from soil and then improved the drought resistance.Water absorption and leaf water consumption should be considered when mentioned drought resistance.Moreover,the ability to absorb nutrients from the soil was improved owing to developed root system.Research on nutrient absorption after short-day treatment is lacking.In order to explore the impact on the summer afforestation of Pinus tabulaeformis seedlings under short-day,three experiment were set:(1)Pinus tabulaeformis seedlings were fertilized over 12 weeks at accumulated supplementary fertilizers of 80 mg N,26 mg P,33 mg K.After fertilization,seedlings were exposed to two photoperiod treatment:normal day length(ND)and short-day(SD)for 3 weeks.(2)After photoperiod treatment(PT),seedlings were followed by 6-week fertility test with a same dose of 13 mg P and 16.5 mg K as well as with three rates of o,12,and 24 mg N to simulate low fertility(LF),middle fertility(MF)and high fertility(HF).(3)Seedlings after PT were treated under three moisture stress:(1)well watering(WW),irrigating every 4 days;(2)moderate drought(MD),irrigating every 8 days;(3)high drought(HD),no watering.Seedlings were sampled for dry mass,mineral nutrient and other related indicators at the end of growing season.The results are as follows:(1)The results showed that short day treatment decreased the biomass of shoot,did not change theroot biomass,and increased root/shoot.Short-day treatment affected the nutrient status of Pinus tabulaeformis seedlings and decreased root P content and tissue K content but increased N and P concentration in needles.(2)SD treatment could modify seedling subsequently affect nutrient uptake from soil.At the end of growing season,seedlings under SD treatment increased the root length by 26.1%,increased root surface area and volume by 32.2%and 35.7%,raised the total root length and total root surface area and optimized root structure.Short day treatment was beneficial to the absorption of N,P and K.SD treatment was favorable to P concentration in needles and stems,N in stems.And short-day treated seedlings uptake more P in stems and roots,K in stems.At the same time,more soil fertility consistently enhanced N content in any tissues and generally absorbed more P and K despite seedlings being supplied the same amount of P and K.Short-day treatment curtailed shoot growth,induced terminal bud set,and hastened spring bud break(by only one day)for this mid-latitude seed source(41°N).(3)Seedlings exposed to SD treatment were significantly decreased in terms of needle biomass,stem biomass and new roots,no significant difference in root biomass.SD leaf water potential was significantly higher than that of normal day length in middle drought.The short-day treatment can improve the water use efficiency when Pinus tabulaeformis seedlings were well watered.Moisture stress test showed that,on the 32th day,with the increase of the degree of water stress,transpiration and stomatal conductance decreased,and the instantaneous photosynthetic rate increased,but the photoperiod treatment had no effect on the above indexes.From the end of PT to the end of the growing season,shoot/root increased significantly from 24.0%to 62.3%.When well watered,seedlings under short-day treatment had higher ?13C,meaning higher water use efficiency.In conditions of moderate drought stress,leaf water potential of SD treated seedlings was larger than that of ND.Under high drought stress,SD treatment lost effect on seedling to resist drought.In conclusion,SD treatment promoted bud formation and improve seedlings resistance to mechanical damage ability;inhibited the growth of shoot,improved root/shoot,increased the photosynthetic rate per unit needle area;improved the seedling root absorption area,promoted afforestation seedlings absorb more water and nutrients,enhanced the seedling drought resistance and barren resistance ability.