Effects Of Biochar Size And Proportion On Physiology Of Lithocarpus Polystachys Rehd. And Calcareous Soil Physicochemical Properties

Biochar is formed by the biomass in hypoxia under the condition of high temperature pyrolysis of solid matter,due to its strong adsorption ability,large specific surface area,developed pore structure,high pH value and high stability,it can improve soil physical and chemical properties,reduce nutrient loss,improve soil fertility and promote the growth of plants when applied to the soil.Calcareous soil in karst areas is rich in calcium and alkaline,heavy in texture,poor in pellet structure,poor in fertility and so on,which brings great obstacles to agricultural production in karst mountain areas.Lithocarpus Polystachys Rehd.is a fast growing tree with high economic value,strong growth capacity and adaptability.Planting this tree in karst areas can effectively reduce soil loss and improve economic benefits.Therefore,this study took Lithocarpus Polystachys Rehd.seedlings as the object of culture,and yellow calcareous soil in karst areas as the medium of culture,the effects of biochar particle size?0.25⁰.5mm,0.5¹mm,1²mm and mixture?and proportion?1%,2%,5%?on the growth,physiological characteristics of Lithocarpus Polystachys Rehd.seedlings and physical and chemical properties of calcareous soil were studied by pot experiment,and the optimal application particle size and carbon-soil ratio of biochar to promote the growth of Lithocarpus Polystachys Rehd.seedlings were discussed,so as to provide theoretical basis and practical guidance for biochar application in calcareous soil improvement in karst region.The results show that:?1?The application of biochar promoted the growth of plant height,ground diameter and leaf parameters of Lithocarpus Polystachys Rehd.seedlings.With the increase of biochar concentration,the growth trend was first increased and then decreased.At low concentration?1%or 2%?,each index reached the maximum.The application of biochar significantly increased the Chlorophyll content,Net photosynthetic rate,soluble sugar and soluble protein content in leaves of Lithocarpus Polystachys Rehd.seedlings,and both increased first and then decreased with the increase of biochar ratio.At the same time,the content of Malondialdehyde decreased first and then increased with the increase of biochar ratio.Generally speaking,the 2%ratio is the best addition ratio of biochar,of which 0.25⁰.5mm size biochar treatment has better effect on increasing chlorophyll content,but mixed size biochar treatment has greater promotion effect on soluble protein and can relieve leaf damage to a greater extent.Biochar treatment had no significant effect on Transpiration rate,Intercellular CO₂ concentration,Stomatal conductance,Water use efficiency and soluble sugar.The application of biochar also increased the contents of P,K,Ca,Mg and decreased the content of N in seedling leaves.The difference of biochar particle size showed that the larger the biochar particle size,the better the absorption of K,Ca and Mg by seedlings,and the smaller the particle size,the better the absorption of P.There was a certain correlation between physiological indexes of Lithocarpus Polystachys Rehd.seedlings under different biochar treatments.Principal component analysis was carried out on 18 selected indexes.The results showed that 2%biochar with 1²mm particle size was the best for the growth and development of Lithocarpus Polystachys Rehd.seedlings,which was the best applied particle size and proportion,followed by 1%biochar with mixed particle size.?2?The application of biochar improved the natural water content of yellow calcareous soil,increased the total porosity and reduced the soil bulk density,and the changes of the three were proportional to the proportion of biochar.The particle size of biochar had a significant effect on soil bulk density and total porosity,and the bulk density and total porosity of 1²mm particle size treatment had the largest changes,varying by-24.5%and 27.78%respectively.The application of biochar increased the pH value of yellow calcareous soil from 0.01 to 0.54,and increased the contents of soil organic matter,total nitrogen,total phosphorus,available phosphorus,total potassium and available potassium.In the same proportion,biochar with 0.25⁰.5mm particle size had the greatest increase.However,biochar treatment reduced the content of alkali-hydrolyzable nitrogen in soil.?3?The application of biochar improved the activities of catalase,invertase and neutral phosphatase in yellow calcareous soil.The particle size and proportion of biochar had significant effects.The catalase and invertase treated with 1²mm and mixed particle size increased with the increase of biochar addition.The activities of catalase and invertase treated with 0.25⁰.5mm and0.5¹mm particle size increased at first and then decreased with the increase of biochar addition,with the highest activity at 2%proportion.The urease activity increased with the increase of biochar ratio.The application of biochar reduced the activity of soil neutral phosphatase,and the 5%ratio of 0.25⁰.5mm biochar treatment showed the greatest reduction in phosphatase activity.The comparison results of soil enzyme index?SEI?under different biochar treatments showed that the SEI increased with the increase of biochar proportion,and the smaller the particle size and the higher the proportion,the better the effect of improving SEI.In addition,there were strong correlations between soil enzyme activities and between soil enzymes and soil chemical properties,indicating that it is reliable to use soil enzyme activities as an index to evaluate soil fertility.In summary,biochar could improve the physicochemical properties of calcareous soil and promote the growth and physiological indexes of Lithocarpus Polystachys Rehd.Therefore,the application of biochar and the planting of Lithocarpus Polystachys Rehd.played an important role in soil improvement and vegetation restoration of karst rocky desertification.The results showed that the best effect was obtained by using 2%biochar with the size of 1²mm at the seedling stage of polypanicle.