Physiological and Biochemical Mechanism of Prevention for Cucumber Downy Mildew by High Temperature Treatment Allelopathy mechanism of flowers of Parthenium hysterophorus L. on wheat Soil NH4+/NO3- nitrogen characteristics in primary forests and the adaptability of some coniferous species Allelopathy of Trifolium repens L. on Abutilon theophrasti Medic. and Echinochloa crusgalli L. Effect of Arbuscular Mycorrhizal Fungi on Growth and Physiology of Elaeagnus angustifolia Seedlings Subjected to Salinity Stress