Effects of Planting Date and Biofertilizer on Seedling Growth of Thymus daenensis Celak and T. vulgaris L. Cultivated in Borujerd, Iran

Sajad Shams Beyranvand ¹ ( Department of Range and Watershed Management, Ferdowsi University of Mashhad, Iran )
Mohammad Farzam ² ( Department of Range and Watershed Management, Ferdowsi University of Mashhad, Iran )
Ali Ariapour ³ ( Department of Rangeland, Faculty of Agriculture and Natural Resources, Borujerd Branch, Islamic Azad University, Borujerd, Iran )
Jafar Nabati ⁴ ( Legume Department, Research Centre for Plant Sciences, Ferdowsi University of Mashhad )

تاريخ الإرسال : 19 الأحد , ربيع الثاني, 1444 تاريخ التأكيد : 29 الخميس , صفر, 1445

الکلمات المفتاحية: Seedling establishment, Mycorrhiza, Rangeland restorations, Free living bacteria,

ملخص المقالة :

Seedling establishment is a crucial stage in the restoration of degraded rangelands. The effects of sowing dates and bio-fertilizers on the growth and establishment of Thymus daenensis Celak (native) and Thymus vulgaris L. (introduced) were studied over two growth seasons at Islamic Azad University, Borujerd branch, Lorestan, Iran. The treatments consisted of four bio-fertilizers treatments i.e., mycorrhiza fungi, nitrogen-fixing free-living bacteria (NFB), phosphate solubilizing bacteria (PSB), and a control group, two species of Thymus sp. and two transplantation dates (November 2017 and March 2018) were also included. PSB and NFB (50 mm/lit of dissolved water) as well as mycorrhiza were applied twice: once during seed sowing in pots and again after transplanting the seedlings in the field. The results demonstrated that T. vulgaris exhibited superior performance (ranging from 31.8% to 51%) in various plant traits such as height, canopy cover, leaf area, dry leaf weight, dry shoot weight, aerial dry weight, root dry weight, shoot-to-root ratio, and root volume compared to T. daenensis. The transplantation date did not significantly affect seedling survival rate and shoot growth. However, seedlings transplanted in November had a higher root-to-shoot ratio (0.94), root dry weight (3.48 mm), root volume (3.56 m3), main root length, and mycorrhiza colonization (11.4%). In exceptionally wet year in in 2018, T. vulgaris performed better than T. daenensis. However, we anticipate T. daenensis to outperform T. vulgaris during normal and dry years, particularly with the application of PSB biofertilizer in its root medium. We recommend simultaneous comparisons of plant growth and thymol concentration under various cultivation and/or biofertilizer treatments on Thymus species in future studies.

نص كامل:



Effects of planting date and biofertilizer on seedling growth of Thymus daenensis Celak and T. vulgaris L. cultivated in Brujerd, Iran

 

Sajad Shams BeyranvandA, Mohammad FarzamB*, Jafar AnabatC, Ali AriapourD

 

AMSc Graduated, Department of Range and Watershed Management, Ferdowsi University of Mashhad, Iran.

B Professor, Department Range and Watershed Management, Ferdowsi University of Mashhad, Iran. *Corresponding Author: [e-mail]

C Assistant Professor, Legume Department, Research Centre for Plant Sciences, Ferdowsi University of Mashhad, Iran.

D Associated Professor, Department of Range Managment, Boroujerd Branch, Islamic Azad University, Borujerd , Iran

 

Abstract:

Seedling establishment is a critical stage in restoring degraded rangelands. We studied the effects of sowing dates and bio-fertilizers on the growth and establishment of Thymus daenensis Celak (native) and Thymus vulgaris L. (introduced) species over two years at Islamic Azad University, Borujerd branch, Lorestan, Iran. The treatments included 4 bio-fertilizer treatments namely Mycorrhiza fungi, nitrogen-fixing free-living bacteria (NFB), phosphate solubilizing bacteria (PSB), and a control group, two Thymus species and two transplantation dates (November 2017 or March 2018). PSB and NFB (50 mm/lit of dissolved water) as well as Mycorrhiza were applied twice: once during seed sowing in pots and again after transplanting the seedlings in the field. Our results showed that T. vulgaris exhibited superior performance (ranging from 31.8% to 51%) in various plant traits such as height, canopy cover, leaf area, dry leaf weight, dry shoot weight, aerial dry weight, root dry weight, shoot-to-root ratio, and root volume compared to T. daenensis. The transplantation date did not significantly affect seedling survival rate and shoot growth; however, seedlings transplanted in November had a higher root-to-shoot ratio (0.94), root dry weight (3.48 mm), root volume (3.56 m3), main root length, and mycorrhiza colonization (11.4%). In exceptionally wet years, T. vulgaris performed better than the native T. daenensis. However, we expect T. daenensis to outperform T. vulgaris during normal and dry years, especially with the application of PSB biofertilizer in its root medium. Future studies, we suggest simultaneous comparisons of plant growth and thymol concentration under various cultivation and/or biofertilizer treatments on Thymus species.

 

 

 

Key words: Rangeland restorations, Mycorrhiza, Free living bacteria, Seedling establishment.

 

 

Introduction

Arid land restoration using medicinal plants offers dual benefits of soil conservation and income generation. Consequently, such projects receive a warm reception from landowners and local communities. The primary and critical stage in the restoration of degraded rangelands is the establishment of primary seedlings, which often fails due to harsh microclimate conditions (Pessarakli, 1994; Moradshahi et al., 2004; Sangtarash et al., 2009; Omidi et al., 2009). Although direct seeding is the main method of plant establishment, it is characterized by slow and steady seedling growth and establishment under field conditions. In natural rangelands, new seedlings must contend with drought, nutrient deficiencies, and competition from neighboring plants, all of which can hinder plant establishment, growth, and fitness (Evans et al., 2003; Habibi Savadkoohi et al., 2008). Particularly for medicinal plants in their natural habitats, seedling establishment and time to harvest can take 2-3 years, resulting in increased management costs and reduced income for stakeholders. Therefore, the transfer of seedlings to the field should aim to minimize environmental stress while expediting the establishment process (Dharmalingam and Basu, 1993; Hosseinzade et al., 2008). In the harsh climate conditions of arid zones, cultivating seedlings in pots is considered a method to alleviate environmental stresses on young seedlings during the establishment period under field conditions (Jankju, 2016). Thus, this research focuses on testing methods that can enhance seedling growth and survival for pot-cultivated plants under natural field conditions.

Many rangelands worldwide have suffered from destruction caused by improper utilizations, overgrazing, and ploughing (Wanga et al., 2014; Tarhouni et al., 2017). The resulting soil erosion depletes soil nutrients and creates harsh microclimate conditions. Consequently, treatments that enhance soil fertility and improve soil moisture can promote seedling establishment under natural field conditions (Nassiri Mahallati et al., 2001). In recent decades, the use of biofertilizers has been introduced as a means to increase soil fertility and create favorable physical and chemical soil conditions (Yousefi et al., 2011), ultimately leading to improved seedling establishment and growth (Hamidi., 2006). Biofertilizers, including beneficial bacteria and fungi, enhance the chemical and biological properties of the soil. Therefore, managing microbial communities and their coexistence can play a crucial role in restoring damaged ecosystems (Renanta et al., 2010).

Soil microorganisms play important roles in the cycling and absorption of nutrients, as well as vegetation recovery (Smith et al., 2010). The application of Mycorrhiza fungi, specifically Glomus mosseae, has been shown to increase the plant height and yield of Origanum sp. (Kaosaad et al., 2006) and Thymus vulgaris (Dolatabadi et al., 2012). Previous research has demonstrated a greater impact of fungi on soil particle sustainability compared to bacteria and actinomycetes, which have relatively lower effects (Martin et al., 2012; FoKom et al., 2013).

 

In terms of nutrient absorption and access, Mycorrhiza fungi can provide a wide area for transferring nutrients, especially phosphorus, to the plant through numerous internal hyphae splittings (Baum et al., 2015; Habibzade et al., 2015; Rahimzadeh and Pirzad, 2017). The increased growth and efficiency of water consumption lead to changes in the chemical mixture of root secretions via element absorption (Azul et al., 2010). Mycorrhiza may also enhance sustainability in ecosystem performance, as well as plant species yield and growth (Klironomus, 2003; Sambandan, 2014).

In previous research (Hector et al., 2004), the application of Azospirillum bacteria increased seed germination, root growth, and the dry and wet weight of Eragrostis sp., Bouteloua sp., and Raphanus sativus L. Several other studies have also indicated that inoculation with Azospirillum bacteria can increase plant biomass, nutrient absorption, nitrogen content in tissues, plant length, leaf size, and root length (Bashan et al., 2004), ultimately leading to improvements in forage production, root growth, and plant biomass (Hector et al., 2004), as well as higher seed germination. Additionally, these bacteria may increase the solubility of materials and nutrients, help plants defend against pathogens, pests, and environmental stresses, and enhance plant growth intensity (Glick et al., 1998; Chen, 2006; Nagananda et al., 2010).

Numerous studies have been conducted on the effects of Mycorrhiza and bacterial bio-fertilizer on increasing soil fertility and plant growth. However, the current literature mostly focuses on crops and fruits (Ozturk et al., 2003; Gholami et al., 2009). Few studies have been undertaken in natural rangelands, despite 90% of roots showing symbiosis with Mycorrhiza under natural field conditions (Brandreth, 2002). Moreover, while the individual impacts of Mycorrhiza and bacterial fertilizers have frequently been studied, few studies have compared them simultaneously (Renanta et al., 2010).

The development of medicinal plants in ploughed rangelands and abandoned low-yield rainfed lands is important for soil and water conservation, as well as the well-being of the local inhabitants. Therefore, we compared the growth and survival of T. daenensis, an endemic species in the Zagros Mountains (Shahnazi et al., 2007), with garden thyme (Thymus vulgaris L.), a non-native but common Thymus species that has been increasingly found in agricultural and natural lands in recent years. The research aimed to investigate the efficacy of bio-fertilizers such as azotobacteria, phosphobacteria, and Mycorrhizae fungi in improving the yield and production of the Thymus species. Additionally, we were interested in determining the optimal transplantation times for these species under field conditions. The research sought to answer the following questions: 1) Can the single or combined application of Mycorrhiza, azotobacter, and phosphobacter increase plant growth and establishment of Thymus species compared to the control? and 2) Which planting date for seedling transplantation (autumn or late winter) may significantly enhance the growth and establishment of Thymus species under field conditions?

 

Materials and Methods

Study area

This study was conducted in the rangelands of Borujerd, Iran. The study area is located at 33°55' N latitude and 48°41' E longitude, at an elevation of 1629 meters above sea level. The biome is a semi-arid steppe, with a mean annual precipitation of 460.8 mm. The average, absolute minimum, and absolute maximum temperatures are 14.6°C, 41.4°C, and -22°C, respectively. The study area covered approximately two hectares and resembled a north-facing slope with an inclination rate of 30-40 percent.

Seed cultivation and seedling transplant

Seeds of T. densensis and T. vulgaris were sown in plastic pots (30 cm depth and 15 cm wide) in 15th of March 2018, in a glasshouse with no control on air humidity, temperature and light. Seedlings were transferred to the ambient conditions in early May and grown till the transplantation times. Half of the seedlings (240) were transplanted in mid-autumn (4th of November 2018) and the remaining pots were transplanted at 15th of March 2019. Seedlings were planted in the hand-made pits (50 cm wide and 30 cm depth), in 40 cm within and 100 cm distance between the rows. Seedlings were planted in 10 cm distance within each pit. 

Growth Media

Soil for the pot growth was provided from the natural rangeland site, where the experiment had been planned to be conducted. Soil parameters were analysed, and the results indicated a loamy-sand soil and low fertility in terms of nitrogen (0.06 mg.kg-1), and organic carbon (0.6%). It contained a reasonable amount of phosphorus (13.4 mg.kg-1) and high potassium (293 mg.kg-1) levels, which led to relatively high pH (7.8). EC was 0.4 dS.m-1 and soil depth varied from 10-30 cm.

Study design

The experiment was designed as a completely randomized block, and treatments were applied as split plot with three replications. Biofertilizers were considered as the main plot, plant species as sub plot and cultivation times as the sub-sub plot. Main treatments were seedling cultivation planting date (November 2018 or March 2019(, four biofertilizers and two Thymus species (T. daenensis and T. vulgaris(. Biofertilizer treatments included application of NFB, PSB, Mycorrhiza and control (no biofertilizer). PSB contained Pseudomonas sp and Bacillus sp. NFB contained Bacillus sp., Azotobacter sp. and Azospirillum sp. All the bacteria strains had been taken from the natural fields of Iran and processed by Khosheparvaran Biotechnology Company Mashhad, Iran. For both the phosphate soluble bacteria and free-living nitrogen fixing bacteria, we used 50 ml of biofertilizers and dissolved it within 2 litres of water. For Mycorrhiza treatment, we used 10 g of soil contained Glomus mosseae in each pot. All (NFB) and (PSB) and Mycorrhiza treatments were applied twice on Thymus seedlings; once at the time of seed cultivation within pots and at the second time was at seedling transplanttaion into the field. 

Growth measurements

Seedling growth and survival rate were measured at 12th of May 2019 for all seedlings transplanted in the autumn or spring. At this planting date, numbers of alive seedlings were measured together with plant height and canopy cover. Furthermore, three replicates of each treatment (total of 80 plant samples (were harvested and following traits were measured in the laboratory, stem dry weight, leaf dry weight, root dry weight, shoot dry weight, leaf area, total root length, average root diameter, root volume, root area, main root length and Mycorrhiza colonization percentage.

To measure canopy cover, three individual plants were randomly selected and their photos were taken from the 1m above. Canopy cover was calculated by image processing software, JMicro Vision V1.27. Leaf area was measured by Leaf Area Meter (Delta-T England). Root volume was measured based on Archimedes law, i.e., water volume increased by floating roots. Root area, diameter and length were measured by Delta-scan scanner (CB50EJ) and software. Finally, for measuring dry weights, plant samples were put at 70 °C for 48 h oven.

Colonization percentage was measured using Malibari et al. (1988) method. In which, Mycorrhiza contamination percentage was estimated for each piece of root separately and then the total contamination percentage was estimated. Vesicle’s surface and hypha length were estimated by JMicro Vision. 27 image processing software.

Data analysis

Data were analysed as Two-Way ANOVA and means were compared using Duncan’s test at 5% probability level.

Results

The effects of biofertilizer, planting date, species types, and their interaction were compared to assess their impact on the survival rate, morphological growth (Table 1), and root traits (Table 2) of Thymus species. None of the main factors, namely transplanting date, biofertilizer, and planting date, had a significant effect on the survival rate and stem dry weight of Thymus species. However, the main effect of biofertilizer was found to be significant (p < 0.05) for plant height, root dry weight, root volume, and root-to-shoot ratio. Similarly, the main effect of species was significant (p < 0.05) for canopy cover, plant height, leaf dry weight, shoot dry weight, and root diameter. Furthermore, the main effect of planting date was significant (p < 0.05) for canopy cover, shoot dry weight, root dry weight, root volume, root-to-shoot ratio, root area, root diameter, and root colonization with mycorrhiza.

The interaction effects between biofertilizer and species were found to be significant (p < 0.05) for root diameter. Similarly, the interaction effects between biofertilizer and planting date were significant (p < 0.05) for leaf area and plant height. Additionally, the interaction effects between species and planting date were significant (p < 0.05) for plant height. Lastly, the interaction effects among biofertilizer, species, and planting date were significant (p < 0.05) for plant height and root diameter (Table 1 and Table 2).

 

 

Table 1. Effects of biofertilizers, planting date (time), species types (Species), and their interaction effects on survival rate and growth traits of Thymus species 

SOV	DF	Survival rate	Canopy Cover	Leaf area	Plant height	Leaf dry weight	Stem dry weight	Shoot dry weight
Block	2	1654ns	2025ns	2754ns	99.6ns	0.235ns	0.058ns	1.48ns
Biofertilizer (F)	3	5.1na	151ns	1034ns	18.06**	0.046ns	0.010ns	0.079ns
Error1	6	46.8ns	133ns	838ns	8.32ns	0.118ns	0.266ns	0.550
Species (S)	1	112ns	2386**	25.7ns	66.1**	0.573*	0.321ns	1.11*
F×S	3	68.1ns	243nsn	281ns	15.8**	0.043ns	0.402ns	0.69ns
Error2	8	37.5ns	146ns	453ns	9.95ns	0.128ns	0.070ns	0.098ns
Planting date (D)	2	1852ns	2297*	1296ns	1021ns	0.152ns	1.314ns	2.27*
F × D	6	5.57ns	250ns	2085**	33.9**	0.149ns	0.408ns	0.504ns
S×D	2	154ns	420ns	1293ns	6.42**	0.076ns	0.207ns	0.708ns
F×S×D	6	48.6ns	512ns	510ns	25.1**	0.141ns	0.311ns	0.675ns
Error3	32	224ns	299ns	798ns	8.59ns	0.153ns	0.192ns	0.334ns
(CV%)		7.31	17.6	34.9	15.71	17.5	25.1	12.6

*, ** and ns indicate a significant difference in P> 0.05 and P> 0.01, and non-significant differences, respectively

 

 

 

 

 

Table 2. Effects of biofertilizers, planting date (time), species types (Species), and their interaction effects on root traits of Thymus species

SOV	DF	Root  dry weight	Root Volume	Root to shoot ratio	Root  area	Root diameter	Root colonization with Mycorrhiza
Block	2	0.019ns	1.40ns	0.236ns	118ns	0.101ns	7.18ns
Biofertilizer (F)	3	2.57**	0.502**	0.329**	86.7ns	0.055ns	12.3ns
Error1	6	0.329ns	0.377ns	0.056ns	83.5ns	0.116ns	8.85ns
Species (S)	1	0.258ns	1.69ns	0.021ns	91.8ns	0.015*	0.546ns
F×S	3	0.216ns	0.730ns	0.032ns	139ns	0.052**	8.11ns
Error2	8	0.158ns	0.206ns	0.095ns	90.4ns	0.022ns	3.57ns
Planting date (D)	2	8.63**	5.56*	1.10**	4025**	1.16*	113*
F × D	6	1.36ns	0.762ns	0.218ns	93.7ns	0.026ns	2.19ns
S×D	2	0.197ns	0.344ns	0.056ns	42.9ns	0.024ns	1.90ns
F×S×D	6	0.410ns	0.294ns	0.090ns	176ns	0.059**	2.94ns
Error3	32	0.390ns	0.494ns	0.067ns	122ns	0.064ns	4.32ns
(CV%)		2.34	16.7	21.1	40.7ns	18.45	21.4

*, **and ns indicate a significant difference in P> 0.05 and P> 0.01, and no significant differences, respectively

 

Canopy cover;

T. vulgaris exhibited an 18% larger canopy cover compared to T. daenensis (Fig. 1A). Additionally, for both species, seedling plantation in March resulted in a 12.5% higher canopy cover compared to November (Fig. 1B).

 

Fig. 1. Effect of species (a) and planting date (b) on the canopy of Thymus species

        

Leaf area

Both Thymus species displayed the most significant response to NFB treatments, with a greater effect observed in November compared to March (Fig. 2). Specifically, the application of NFB treatment on Thymus seedlings in November resulted in a 77% increase in leaf area compared to those growing under PSB, Mycorrhiza, and control treatments.

 

 

 

 

Fig. 2. Effect of planting dates and biofertilizer interaction effect of on leaf area index of Thymus species.

Abbreviations; NFB: Nitrogen-fixing free bacteria, PSB: Phosphorus-soluble bacteria

Plant height and root diameters

By the end of the study, T. vulgaris seedlings exhibited a 51% greater canopy height compared to T. daenensis seedlings. The application of phosphate-dissolving bacteria did not yield significant differences in the two planting dates of November and March for both Thymus species. While the use of Mycorrhiza fungus had no significant effect on T. daenensis across the two planting dates, it resulted in a 27.2% increase in plant height for T. vulgaris when comparing the March date with November (Table 3).

Root diameters;

For seedlings transplanted in March, NFB treatments resulted in a 26% higher root diameter for T. daenensis compared to T. vulgaris. The utilization of Mycorrhiza fungi in both November and March planting dates did not yield a significant difference between the Thymus species. However, for seedlings transplanted in November, T. daenensis exhibited a 66.6% thicker root diameter compared to T. vulgaris. Overall, the thickest root diameters were observed in T. daenensis planted in November under the control treatment, measuring 1.08 mm. On the other hand, the thinnest root diameter of 0.50 mm was recorded for T. vulgaris planted in March with NFB treatment (Table 3).

 

Table3. Effects of biofertilizer treatments, plant species and times of cultivation on canopy height and root diameter of Thymus species

Treatments	Species	Planting date	Plant height (cm)	Root diameter (mm)
NFB	T. daenensis	November	21.0 b	0.90abs
		March	20.8b	0.63cd
	T. vulgaris	November	31.8 a	0.93ab
		March	23.1ab	0.50d
PSB	T. daenensis	November	19.2b	1.00a
		March	22.1b	0.52d
	T. vulgaris	November	20.6b	1.01a
		March	20.2b	0.59d
Mycorrhiza	T. daenensis	November	22.7ab	0.92ab
		March	21.7b	0.53d
	T. vulgaris	November	20.0b	0.94a
		March	27.6ab	0.53d
Control	T. daenensis	November	18.2b	1.08a
		March	21.2b	0.61d
	T. vulgaris	November	18.9b	0.65bcd
		March	24.9ab	0.54d

Similar letters indicate no significant differences at the 5% probability level.

Abbreviations NFB: Nitrogen fixing free - bacteria, PSB: Phosphorus-soluble bacteria

Root Dry weight        

Plants transplanted in November exhibited a 32% higher root weight compared to those planted in March. Thymus seedlings that were inoculated with Mycorrhiza fungi demonstrated 49% and 22.2% greater root dry weight than those inoculated with bacteria and phosphate fertilizers, respectively. However, these differences were not statistically significant when compared to the control treatment (Table 4).

 

Root colonization with Mycorrhiza fungi

The thymus seedlings planted in November had a root colonization that was 50% higher compared to those planted in March (Fig. 3). 

 

 

Fig. 3. Effects of date of seedling planting on Mycorrhiza colonization percentage

 

The root surface increased by 65% and the root dry weight increased by 14.4% when the seedlings were transplanted in March compared to November. Additionally, the stem dry weight showed an increase of 25.8%. In terms of Thymus vulgaris, it produced 15.9% more leaf dry weight and 14.4% more shoot dry weight compared to T. densensis (Table 4).

 

The application of nitrogen-fixing free bacteria (NFB) resulted in a reduction in root dry mass compared to shoot dry mass. The shoot-to-root ratio was 44.7% higher for seedlings transplanted in March than in November (Table 4). Furthermore, the mycorrhiza fungus increased the root volume (RV) of Thymus species, resulting in a 32.3% and 19.9% higher RV compared to the NFB and PSB treatments, respectively. Additionally, we observed that seedling transplantation in November rather than March led to a 23.6% higher RV for Thymus species (Table 4). 

 

Table 4. The effect of biofertilizer treatments, species types and planting date on root morphological traits of Thymus species

Treatments	Root area (mm2)	Leaf dry Weight (g)	Stem dry Weight (g)	Shoot dry Weight (g)	Root dry  weight (g)	Root to Shoot ratio	Root volume  (cm3)
NFB	32.5a	1.89a	1.43a	3.32a	2.36b	1.42a	2.69b
PSB	30.6a	1.76a	1.41a	3.17a	2.88ab	1.14ab	2.97ab
Mycorrhiza	24.9a	1.80a	1.46a	3.26a	3.52a	0.98b	3.56a
Control	26.8a	1.88a	1.47a	3.35a	3.48a	1.06b	3.64a
Species
T. daenensis	30.5a	1.70b	1.36a	3.06b	2.95a	1.11a	3.03a
T. vulgaris	26.9a	1.97a	1.52a	3.50a	3.17a	1.19a	3.40a
Planting date
November	21.7a	1.78a	1.28b	3.06b	3.48a	0.94b	3.56a
March	35.8a	1.88a	1.61a	3.50a	2.63b	1.36a	2.88b

Similar letters are not significantly different from each other at the 5% probability level.

 

 

Discussion

Planting dates

We transplanted seedlings of two Thymus species on November 2018 and March 2019, when they had been grown in pots for about 8 and 12 months respectively. The date of planting in March was coincident with the early days of spring, when there were favourite conditions for the early transplanted seedlings in terms of temperature, precipitation and soil moisture storage. The mild environmental conditions in early days of plant establishment can stimulate the vegetative and reproductive growth stages and herby increase their growth performances (Hosseinzade et al., 2008; Dharmalingam and Basu 1993). Furthermore, the newly established would plants gain more opportunities for benefiting from the early season sporadic rainfall in the arid ecosystems (Jankju and Griffiths, 2006). We did not find clear effects of transplanting date on aboveground biomass during the first growing season; i.e. higher canopy diameters for the seedlings that had been transplanted in March was compensated by higher leaf area by those of November. However, for all root growth parameters, plant cultivation in November was more beneficial for both T. daenensis and T. vulgaris species. Thymus seedlings that had been transplanted in November displayed thicker root diameters, greater root weight and root volume, and higher biomass allocation to roots than shoots (higher root: shoot ratio). Furthermore, planting Thymus seedlings in November provided more opportunity for Mycorrhiza inoculation as compared those of planted in March.

A proper time for plant transplantation into the field, provides a set of environmental factors that are suitable for seedlings establishment and survival (Hoffman and Kluge-Severin, 2010; Khajepour, 2001). In this experiment also, the Thymus species favoured mild temperature, high light and soil moisture in the early days of spring, which could increase their canopy growth. Therefore, the reason for the larger canopy size of the Thymus vulgaris as compared with T. danaensis might be due to its higher capability for using the environmental resources. Since the study site is located in a semiarid area, higher plant investment on root traits would be more beneficial for its long-term survival (Salmani Biary et al., 2010). The ability of a plant to avoid drought is measured by the mechanism of change and distribution of the root system in deep soils that increases water absorption efficiency (Songseri et al., 2008). Plant genotypes with larger root volume occupy more soil and hence absorb more water that eventually leading to higher drought resistance (Adda et al., 2005; Wang et al., 2009).

Earlier seedling plantation provide more opurtunities for making adaptation to the field conditions. This was found as higher Mycorrhiza colonization for Thymus seedlings that were transplanted in November, as compared those cultivated in March. Mycorrhiza symbiosis may help plants for higher uptake of nitrogen, phosphate, potassium, iron and other nutrients (Wu et al., 2005). They may also be effective in improving the physical, chemical and biological soil conditions (Cardoso and Kuyper, 2006). Accordingly, we expect higher drought tolerance for seedling cultivated in November than March.

Biofertilizer treatments

We applied two free-living bacteria fertilizers (NFB and PSB) and a Mycorrhiza inoculation treatment on Thymus species and compared them with control plants. Generally, the biofertilizers increased total biomass of Thymus species. However, their effects on the above versus belowground organs varied depending on the type of biofertilizers. Currently, it has been proven that these micro-organisms increase nutrients in the rhizosphere environment also increase the absorption of nutrients, furthermore they help to control plant pathogens and increase plant resistance to environmental stresses through several mechanisms (Jehan and Nassiri Mahallati, 2012, Chen, 2006; Glick et al., 1998; Nagananda et al., 2010); Therefore, for the species studied in this research, the positive interaction between Mycorrhizal symbiosis and higher growth of seedlings in that were planted in November can ultimately improve plant growth and subsequently increase the establishment of Thymus species in autumn than winter. 

T. daenensis vs. T. vulagris performances

We compared performances of a native and a non-native Thymus species. Thymus vulgaris, which is an introduced plant species from southern Europe, showed higher performances in terms of total biomass. The higher biomass of T. vulgaris was mainly due to its higher shoot growth, whereas both species were similar in terms of root growth parameters. On the other hand, we found higher responses of the native species to PSB treatments, i.e. the phosphorous treatment significantly increased root growth for T. daenensis as compared to its effect on T. vulgaris. Higher biomass allocation to above-grounds usually increases plant sensitivity to periodical droughts (Hoffmann and Kluge, 2010), and this may be the case for T. vulgaris in the study area. Therefore, during the wet years and under the irrigating conditions, cultivation of T. vulgaris will perform higher biomass and hence provides higher incomes for the farmers. In contrary, under the drought years and under natural field conditions we may expect higher survival and persistence of the native Thymus species.

 

Conclusion

Although there are numerous studies on the effects of biofertilizer on plant growth, but most studies have been in the cropland and under irrigation. In this research, we found that both Thymus species can be grown in pots and be successfully transplanted and established within the natural vegetation of rangelands. Seedling transplantation reduces competition and planting date to plant harvesting, hereby increases chances of establishment and incomes. For the rainfed agriculture, seed sowing is usually advised to be in November, when it promotes root higher plant allocation to root media that are so critical for plant growth and establishment in the arid areas and within the natural vegetation. Under the exceptionally wet years of the study, the introduced Thymus species (T. vulgaris) performed better than the native species (T. daenensis). However, we expect that T. daenensis will outperform T. vulgaris during the normal and dry years, especially if we apply PSB fertilizer in its root media. A higher concentration of thymol in plant tissues may offer advantages for plants with lower aboveground biomass. Therefore, future studies should consider conducting simultaneous comparisons of plant growth and thymol concentration under various cultivation and/or biofertilizer treatments on Thymus species.

Acknowledgement

Financial support for this research was provided by Ferdowsi University of Mashhad, Iran as grant number 47340.

 

 

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اثر تاریخ کاشت و کودهای زیستی بر رشد نهالهای آویشن دنایی Thymus daenensis و آویشن باغی Thymus vulgaris در شرایط آب و هوایی بروجرد

 

سجاد شمس بیرانوند1، محمد فرزام 2، جعفر نیاتی3، علی آریاپور4

1-دانش آموختع کارشناسی ارشد، گروه مرتع و آبخیزداری، دانشگاه فردوسی مشهد، ایران

2- استاد، گروه مرتع و آبخیزداری، دانشگاه فردوسی مشهد، ایران

3- استادیار، گروه بقولات، پژوهشکده علوم گیاهی، دانشگاه فردوسی مشهد، ایران

4- دانشیار گروه مرتعداری، دانشگاه آزاد اسلامی، واحد بروجرد، ایران 

 

 

چکیده

استقرار گیاهچه بحرانی ترین مرحله در فرآیند احیاء عرصه‌های مرتعی تخریب یافته محسوب می‌شود.  در این پژوهش اثر زمان‌های کاشت و  ۳ نوع کود زیستی بر استقرار نشاء و رشد دو گونه گیاه آویشن دنایی ((Thymus daenensis Celak و آویشن باغی (Thymus vulgaris L). در دو فصل رویش در مراتع دانشگاه آزاد اسلامی واحد بروجرد در استان لرستان، ایران انجام شد. تیمارهای مورد مطالعه شامل چهار سطح کودهای زیستی (قارچ مایکوریزا، باکتری‌های آزادزی تثبیت ‌کننده نیتروژن و باکتری‌های حل‌کننده فسفات و شاهد)، دو گونه آویشن و دو تاریخ کاشت در عرصه (آبان و اسفند۱397) بود. میزان مصرف تیمار فسفوپاورباکتر و نیتروباکتر هر کدام به میزان 50 میلی لیتر در دو لیتر آب محلول و برای هر گونه آویشن دنایی و آویشن باغی بعد از قرار دادن گیاهچه ها داخل چاله استفاده شد. اما استفاده از تیمار قارچ میکوریزا در زمان انتقال و کاشت برای هریک از چاله‌ها در عرصه و هر کدام از تاریخ‌های کاشت به میزان 10 گرم در نظر گرفته شد. مایع تلقیح حاوی کودهای میکوریزایی و باکتریایی یکبار در گلخانه هنگام کاشت بذز در سینی های نشاء و بار دوم در طبیعت در زمان انتقال نهال ها به داخل چاله های کاشت اضافه شد. گونه آویشن باغی در اکثر صفات از جمله ارتفاع گیاه، تاج پوشش، سطح برگ، وزن خشک برگ، وزن خشک ساقه، وزن خشک اندام هوایی، وزن خشک ریشه، نسبت وزن اندام هوایی به ریشه و حجم ریشه به میزان 8/31 تا 51 درصد نسبت به آویشن دنایی افزایش عملکرد داشت. تاریخ کاشت تاثیر معنی‌داری بر درصد بقای گیاهان یا رشد اندام‌های هوایی نداشت اما گیاهان کاشته شده در آبان ماه باعث افزایش وزن خشک ریشه(48/3) ، حجم ریشه(56/3) و نسبت وزن اندام هوایی به ریشه(94/0)، و همچنین (4/11) درصد کلونیزاسیون بیشتری نسبت به گیاهان کشت شده در اسفند ماه داشت. در سال بسیار پرباران و استثنایی ۱۳۹۹ که این پژوهش انجام شد، گیاه آویشن باغی نسبت به گونه بومی آویشن دنایی عملکرد بهتری داشت، اما ما انتظار داریم که در سالهای معمولی یا در خشکسالی ها، بویژه اگر کود زیستی فسفر دار نیز درمحیط ریشه افزوده گردد، گونه آویشن بومی رشد بهتر داشته باشد. برای مطالعات آینده، بررسی همزمان تغییرات تیمول و رشد اندام هوایی دو گونه آویشن در تاریخ های مختلف کاشت و تحت تیمارهای مختلف کودی پیشنهاد می گردد.

 

کلمات کلیدی: احیای مرتع، میکوریزا، باکتری های آزادزی، استقرار نهال

 

 

 

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