Effects Of Leaf Litter Extract Liquid Of Pinus Sylvestris Var.mongolica On Soil Phenols And Seedlings Growth

Pinus sylvestris var.mongolica plantation plays a favourable role in windbreak,sand-fixation and water conservation in semi-arid areas of northern China.In recent years,with the maturity of P.sylvestris var.mongolica plantation,there have been problems of growth decline and difficulty in regeneration.The previous investigation found that seeds of P.sylvestris var.mongolica could germinate smoothly,but there were few regenerated seedlings over 3 years old in the plantation,which may be due to some factors limiting the survival of P.sylvestris var.mongolica seedlings.Allelopathic autotoxicity is widespread in nature.Leaf litter decomposition of parent trees may release allelochemicals into soil to inhibit seedling growth and cause soil acidification.Phenols are one of the main types of allelochemicals.In order to explore whether the litter of P.sylvestris var.mongolica has allelopathic effects on its seedlings and the effects of litter of P.sylvestris var.mongolica on soil phenols and soil acidity,in this experiment,2-year-old P.sylvestris var.Mongolica seedlings and their culture matrix soil were used as research objects,and indoor culture experiments were carried out by pot method.4concentration gradients of 12,6,3,and 1.5 g·L^-1were set for leaf litter extract liquid treatment and 4 coverage gradients of 4.30,2.15,1.08,and 0.54 kg·m^-2were set for leaf litter covering treatment and blank control treatment（CK）,respectively.The effects of different treatment gradients and treatment time on soil phenols and soil acidity were analyzed.The effects of leaf litter and its extract liquid on seedling growth and physiological indexes,soil phenols content and soil acidity,as well as the correlation among the three,were investigated,in order to provide theoretical basis for the sustainable management of P.sylvestris var.mongolica plantation and improve the survival rate of P.sylvestris var.mongolica seedlings.The results showed that:（1）In the range of experimental concentration,the extract liquid of leaf litter of P.sylvestris var.mongolica could promote the growth and physiology of seedlings with low concentration and inhibit with high concentration.3 g·L^-1had the best promoting effect on the growth indexes of seedlings,6 g·L^-1had the best promoting effect on the physiological indexes of seedlings,and 12 g·L^-1had the most serious inhibiting effect on the growth and physiological indexes of seedlings.When the litter cover amount was 2.15 kg·m^-2,the comprehensive promotion effect was the best,and when the litter cover amount was 0.54 kg·m^-2,the comprehensive inhibition effect was the strongest.（2）5 phenolic substances,including caffeic acid,syringic acid,vanillin,cinnamic acid and taxifolin,were commonly found in this experiment soil.Before and after the experiment,the variation range of total phenolic content in soil treated with extract liquid was small,ranging from-9.58%to 167.03%.The total phenolic content in soil of litter treatment increased greatly,it increased to 5.20-11.79 times of that before the experiment.The caffeic acid content was the highest in both extract liquid treatment and leaf litter treatment.On the 90 d,the average content of phenols in extract liquid treatments was as follows:caffeic acid>vanillin>taxifolin>syringic acid>cinnamic acid;the average content of phenols in litter treatments was as follows:caffeic acid>syringic acid>cinnamic acid>vanillin>taxifolin.（3）The soil acidity increased after the experiment,and the exchangeable acidity increased significantly during 60-90 d,the hydrolytic acidity increased gradually.The total exchangeable base of soil decreased,the cation exchange capacity（CEC）increased,and the base saturation percentage（BSP）decreased.（4）In the extract liquid treatment,caffeic acid and cinnamic acid contribute to soil acidity and soil CEC.The growth and physiological indexes of P.sylvestris var.mongolica seedlings were significantly affected by the contents of total phenols,caffeic acid,syringic acid,vanillin and cinnamic acid in soil.With the increase of soil phenols and soil acidity,the content of chlorophyll and malondialdehyde（MDA）increased,while the content of soluble protein and root activity were inhibited.But in the leaf litter treatment,the contents of soluble protein and MDA in P.sylvestris var.mongolica seedlings were significantly affected by cinnamic acid.The total phenolic content and caffeic acid content contribute to soil acidity and CEC,made the soil BSP decreased.The reduction of soil exchangeable base increased MDA content in leaves and CAT activity in roots.In conclusion,6 g·L^-1leaf litter extract liquid treatment and 2.15 kg·m^-2leaf litter cover treatment had the best effect on promoting the seedlings of P.sylvestris var.mongolica.Soil caffeic acid and cinnamic acid are the main phenolic substances affecting the growth physiology of P.sylvestris var.mongolica seedlings.The caffeic acid released into soil by the litter of P.sylvestris var.mongolica had the greatest influence on the soil total phenolic content and soil acidity.The increase of soil caffeic acid content made the soil acidity enhanced,the CEC increased and the BSP decreased.