Comparison of Carbon Sequestration of Astragalus gossypinus and Dactylis glomerata Species in Hezarjarib Mountainous Rangelands, Behshahr

Introduction
Nowadays climate changes as one of the major environmental issues have been put forward the most important challenge in sustainable development and poverty elimination. Carbon sequestration is a process in which carbon dioxide absorbs from the atmosphere and accumulates in carbohydrates form in plant tissues, litter, and soil. Rangelands ecosystems have a great potential in carbon sequestration because of including half of the lands on the earth. In addition, their carbon storage is about 10 percent of total biomass carbon storage in terrestrial ecosystems and 30 percent of organic carbon. In a global scale, about 500 billion tons of carbon sequestrate in the rangelands annually. To reduce atmospheric carbon dioxide and greenhouse gas balance, atmospheric carbon should be captured and sequestrated. Carbon as one of the main greenhouse gases element sequesters by photosynthesis in plant biomass. Carbon sequestration by the rangelands plants is the most simple and the cheapest way to decrease this gas. Therefore identifying the species that have high ability to carbon sequestration can help us in the rangelands rehabilitation and reclamation.
 
Materials and methods
The study area was 2598 ha including the exclosures and grazed rangelands in the mountainous region of Behshahr. This region is located on 53°54'01- 53 52' 06" longitudes and 36° 38' 24"- 36° 36' 16" latitude. The maximum and minimum elevations are 1707 meters and 1043 meters above sea level, respectively. The area annual precipitation is 409 mm and the temperature is between -15 °C to 37 °C that its maximum occurs in the May. The climate is semi-arid cold based on Emberger technique.In this study, the effects of exclosure and grazed on the carbon sequestration was studied in two plant species in the Vezvar rangelands of Hezarjarib in Behshahr. Vegetation and soil sampling was done by random-systematic method with two 100 m transects and 40 plots. The plot numbers were obtained based on the plant distribution pattern in the area. The soil sampling was done in two depths  of 0-15 and 15-30 cm with a total 80 soil samples.
 
Organic carbon determined by the Walkley-Black method. The species biomass measurement was done in above-ground and under-ground completely by weight and cutting method.Shooting and rooting organs of the species Astragalus gossypinus F. and Dactylis glomerata L. were separated from each other after transfer to the laboratory. The carbon sequestration coefficient of the plant organs was determined with combustion method.The carbon sequestration coefficient of the different species, organs, and the soils under these species were then analyzed in the Lab. In this study, Comparison of the carbon sequestration in two species was done by t-Test method. This investigation was done by SPSS v.19 and EXCEL software.
 
Results and discussion
The statistical results presented in Table 1 showed that the mean of canopy percent in enclosure area is higher than that of the grazed region.
Table 1. t-Test analysis of canopy percent in the exclosure and grazed area
 





Canopy percent


Study site


Mean


Std. deviation


Df


t




Astragalus gossypinus


exclosure


40.20


6.39


18


5.84**




grazed


21


8.19




Dactylis glomerata


exclosure


6.40


2.17


18


3.60**




grazed


3.30


1.63





**; Significant Level: 1٪
 
The statistical results showed that the conversion coefficients of the plant biomass to the organic carbon in leaves, stems, and roots in non- grazed areas were more than that of the grazed areas. This increase in Astragalus gossypinus root (8.12%) and Dactylis glomerata stem (3.75%) had the most value (Table 2). Figure 1 show a significant difference between carbon sequestrations of various organs in both area .
 
Table 2. Ratio of biomass conversion to organic carbon in the exclosure and grazed area (٪)





Species


Study site


Leaf


Stem


Root




Astragalus gossypinus


exclosure


5.45


5.34


8.12




grazed


4.40


2.72


6.92




Dactylis glomerata


exclosure


2.71


3.75


2.36




grazed


2.51


2.55


1.74





 
 
             (a)                                                                                                (b)
Figure 1. The mean carbon sequestration comparisons of Astragalus gossypinus (a) and Dactylis glomerata (b) in the exclosure and grazed area
 
Table 3 presents the results of total carbon sequestration in two studied sites.  The total carbon sequestration by soil and vegetation in the non-grazed and grazed area showed no significant difference.
 
Table 3. Total carbon sequestration of the soil and vegetation in the exclosure and grazed area





Species


Study site


Mean


Std. deviation


Df


t




Astragalus gossypinus


exclosure


10364464.11


403085.93


18


0.325^ns




grazed


9560630.7


343875.48




Dactylis glomerata


exclosure


9959806.82


457485.10


18


0.919^ns




grazed


8235804.23


378128.49





Ns: Non-Significant
 
Conclusion
The results show that the vegetation percent of Astragalus gossypinus and Dactylis glomerata in the exclosure areas was more than the grazed areas. The carbon sequestration of the species Astragalus gossypinus and Dactylis glomerata in exclosure site was more than the grazed site. These results confirm that grazing has a negative impact on carbon storage regardless of their vegetative form. Also, the data showed that the most conversion coefficients of Astragalus gossypinus and Dactylis glomerata is belong to the root and the stem, respectively. The high conversion coefficients of the root organs can say us the woody organs have high conversion coefficient to herbage organs due to high cellulose and lignin and low water. Comparison of the carbon sequestration potential in two studied sites showed no significant difference. This shows that the grazing has impalpable effect on the root biomass as a source of carbon input to the soil. Also the different organs have a difference in the carbon storage depending on the species type. So, the leaves in woody plant have a greater ability to carbon storage than grass plant form and the stem have more carbon than the other organs in the grass form. This showed that woody tissues have more ability for the carbon sequestration. The study of stored soil carbon also indicated that the soil has more carbon stored than plant species. This can be due to the other components that exist in the rangeland ecosystems such as animals, litter, and so on.