Effects of water stress and manure on stomatal conductance, relative water content, photosynthetic pigments and quantitative and qualitative yield of Thymus vulgaris L. and Thymus daenensis Celak

This research was aimed to evaluate the effects of drought and manure on some physiological characteristics and yield of Thymus vulgaris L. and Thymus daenensis Celak.The study was conducted as factorial based on a randomized complete block design (RCBD) with three replications during crop years of 2015 and 2016 at the agriculture research farm of University of Birjand, Iran. Experimental factors were including: water stress at three levels (100%, 67% and 33% of field capacity), manure at two levels (30 tons.ha-1 and no manure), and two thyme species (Thymus vulgaris L. and Thymus daenensis Celak). Water stress reduced stomatal conductance, relative water content (RWC), Chl a, b and quantitative and qualitative yield; however, carotenoids content was increased under water stress. Although the quantity and quality yield of the study species decreased under water stress condition, manure application at 30 tons per ha led to the increased quantity and quality yield of both species. Thymus daenensis had more relative water content and quantity and quality yield (oil) in both crop years as compared with T. vulgaris. According to the results, T. daenensis can grow successfully in arid and semi-arid regions and could be recommended. There was a significant difference between two crop years; in the 2nd year, the quantity and quality yield (essential oil yield) of both study species increased.