Effects of water stress and application of manure on growth indices and accumulation of dry matter of Thymus vulgaris and Thymus daenensis

Environmental stress is one of the main factors limiting the growth and production of crops in the world. In general, water is one of the most effective factors on a Total Dry Matter (TDM) and water stress on plants can reduce the Crop Growth Rate(CGR), Relative Growth Rate(RGR), Leaf Area Index(LAI) and Total Dry Matter(TDM). One of the most accurate ways to study the responses of plants to environmental condition is evaluation of growth indices. Sanchez-Rodrigo et al (2010) reported that in water stress condition that reduced moisture for plants, manure might help plants to maintain their moisture content, provide water for plant and is effective in reducing the negative effects of water stress. Due to the water stress influences on plant growth, measurement of TDM of medicinal herbs like thyme is of vital importance to evaluate the effect of water stress on plans. The quality of medicinal plants is largely determined by the relevant natural compounds (secondary metabolites) and the quantity and quality of these compounds are determined by environmental factors such as water availability. In general, water reduction in plant tissues reduces the growth of different parts of the plant like the roots and aerial organs of the plant. In this regard, Sharafzadeh and Zare (2011) reported that drought stress reduces dry weight and height of Thymus vulgaris. Given that the large parts of Iran’s lands are situated in the arid and semi-arid regions. Therefore evaluating the effect of drought stress on qualitative and quantitative changes in medicinal plant species of thyme is important.This study aimed at examining the effects of water stress and manure on some the growth indices and TDM of Thymus daenensis and Thymus vulgaris

In order to evaluate the effect of water stress and manure on some of the growth indices and accumulation of total dry matter of Thymus daenensis and Thymus vulgaris an experiment was conducted as factorial based on a randomized complete block design (RCBD) with three replications in the Agriculture research field of the University of Birjand, located at latitude 53º: 32N, longitude 13:55ºE and altitude 1480 m above sea level in 2015. Experimental factors were including water stress (100%, 67% and 33% of field capacity), two species of thyme (Thymus vulgaris L. and Thymus daenensis celak) and manure at two levels (30tons.ha-1 and No manure).

The results showed that water stress reduced traits such as LAI, CGR, NAR, SLA, LWR and TDM and only non-significant effect on RGR. In all traits the highest and lowest amount obtained from 100% FC (normal condition) and 33% FC (The highest level of water stress) respectively. The higher LAI, CGR, RGR, NAR, and SLA in the normal condition (100% FC) might be due to better availability to water and food and the result of efforts to expand the plant canopy. TDM decreased 26.56 percent with increasing stress from 100 to 33% field capacity. Manure treatment had a positive impact on growth indices and the highest the and lowest amount of growth indices and TDM obtained from of 30ton.ha-1 manure. So the application of manure to the soil in water shortage conditions is recommended to achieve the highest TDM.

In the current study, the highest TDM obtained from 30 ton ha-1 manure that having a significant difference with the situation where no manure. The TDM and growth indices increased after the soil physical properties were modified and nutrient available for thyme in the manure treatment. In between the two species, Thymus daenensis showed the highest growth indices (With the exception of LWR) compared to the Thymus vulgaris. Therefore, we can say that Thymus daenensis can introduce superior species when exposed to water stress.