Effects Of Construction And Demolition Waste On The Growth And Physiology Of Container-grown Duranta Repens

A large amount of construction and demolition waste（CDW）is produced with the acceleration of urbanization every year.Larger size of CDW is used in road engineering and the smaller size of CDW is treated as waste,which has caused many environmental problems.Theoretically,CDW can be used as a component of substrate because of its large specific surface area and good water absorption which can increase the aerated porosity of soil.In addition,the main components of CDW,such as red brick,concrete,mortar,contain necessary mineral elements of potassium,calcium,sodium,and magnesium for plants.In the present study,CDW less than 1cm was chosen and was separated into four sizes of 0-3mm,3-6mm,6-8mm and 0-10mm,which were mixed with clay soil（S）and clay loam soil（L）based on the mass ratio of 20%,35%,and 50%.One-year Duranta repens seedlings were planted in the different mixed substrates with three controls of S,L,and CDW.The most suitable sizes and proportions of CDW for plant growth and physiological function were screened and evaluated according to the physicochemical properties of the mixed substrates and the growth and physiology of plants.The main results are as follows:（1）The main plant parameters for evaluating the quality of the mixed substrates are ground diameter,branches,and leaf size based on the principal component analysis.（2）Adding CDW can improve the aeration porosity and air-water ratio of the mixed substrates compared with S and L,which is beneficial to root growth and water retention.（3）The S6 group with 3-6mm size and 50%proportion was the best substrate among CDW and S mixed substrates,decreased substrate density(1.26 g·cm^-3),suitable EC(0.52 ms·cm^-1),increased aeration porosity（11.68%）,better air-water ratio（0.44）,and reduced water loss rate（12.76%）.The plants grew best with the biggest ground diameter（15 mm）,the longest total branches（740 cm）,the largest number of total branches（36）,the biggest leaf area（24.08 cm²）,and the highest root activity（0.54mg/g·h）.（4）The L5 group with 3-6mm size and 35%proportion was the best substrate among CDW and L mixed substrates,suitable p H（6.64）and EC(0.81 ms·cm^-1),increased aeration porosity（10.58%）,lower water loss rate（0.37）,higher contents of available nitrogen(41.07 mg·kg^-1)and available phosphorus(40.33 mg·kg^-1).The plants grew best with the biggest ground diameter（10 mm）,the larger number of total branches（31）,the largest leaf area（24.08 cm²）,and the highest net photosynthetic rate(11.18μmol·CO2m^-2s^-1),stomatal conductivity(0.27 mmol m^-2S^-1),transpiration rate(2.84 mmol m^-2S^-1),contents of total soluble sugar(419.71 mg·g^-1)and leaf nitrogen(40.96mg·g^-1).Therefore,CDW less than 1 cm can not only be a substrate component but also improve the physiochemical properties of sticky soil and plant growth with water and fertilizer management.3-6 mm CDW is the best sizes for both clay soil and clay loam soil with the best physiochemical properties of the substrates and plant growth.We suggest that proportion of3-6mm CDW should range from 35%to 50%when mixed with different types of soil.The reuse of smaller sizes of CDW can decrease urban garbage,environmental pollution,and substrate cost,and protecting soil resources.The rational utilization and development of CDW is ecological and economic significance.