The effects of water stress and defoliation on some of quantitative traits of Zataria multiflora, Ziziphora clinopodioides, Thymus vulgaris and Teucrium polium

In order to investigate the effect of water stress and defoliation on Zataria multiflora, Ziziphora clinopodioides, Thymus vulgaris and Teucrium polium, an experiment was conducted under greenhouse conditions. Treatments were combination of four water stress levels (-0.3, -5, -10, -15 bar) and three defoliation levels (0, 25, 50 percent of foliage removal) arranged in a completely randomized desing with 4 replications. For imposing drought levels, percentage of soil moisture was determined in different water potentials by pressure plate method, and pots were weighted daily and the amount of water lost was added to each pot. Criteria such as SPAD readings, stomatal resistance, canopy temperature, leaf/stem ratio, specific leaf weight, percentage of dry leaves and root/shoot ratio were measured. Water stress increased SPAD readings in Ziziphora clinopodioides, specific leaf weight in Thymus vulgaris and Ziziphora clinopodioides, canopy temperature in Thymus vulgaris and Teucrium polium and percentage of dry leafs in Zataria multiflora and Teucrium polium significantly. Defoliation reduced SPAD readings in Zataria multiflora, Ziziphora clinopodioides and Teucrium polium, specific leaf weight in Zataria multiflora, Thymus vulgaris and Ziziphora clinopodioides and leaf/stem ratio in Zataria multiflora significantly. A negative correlation was observed between leaf/stem ratio and different levels of water stress for all species. With increasing defoliation levels, root/shoot ratio was reduced in Zataria multiflora and Thymus vulgaris and increased in Teucrium polium and Ziziphora clinopodioides. Also, root/shoot ratio showed a positive correlation with different levels of water stress. Generally, Ziziphora clinopodioides was most resistant species and Teucrium polium most sensitive species to stress