Document Type : Research Paper

Authors

• Khadijeh Bahalkeh ¹
• Mehdi Abedi ²
• Sara Palacio ³
• Arantzazu Luzuriaga ⁴
• Adrian Escudero ⁴

¹ PhD student, Department of Range Management, Faculty of Natural Resources and Marine Sciences, Tarbiat Modares University, Noor, Mazandaran Province, Iran

² Associate Professor, Department of Range Management, Faculty of Natural Resources and Marine Sciences, Tarbiat Modares University, Noor, Iran

³ Instituto Pirenaico de Ecología (IPE-CSIC), Jaca, Huesca, Spain

⁴ Área de Biodiversidad y Conservación. Universidad Rey Juan Carlos, Tulipán s/n, 28933 Móstoles, Madrid, Spain

Abstract

Abstract
Background and objective
Gypsum habitats create a stressful environment for plant and the establishment of plants is affected by ionomic toxicity. Shrub plants as nurse plants can safeguard their understory species in the harsh conditions of this habitat. These plants are more important in extreme environmental conditions because they use particular processes to modify the microhabitat conditions and assist the development of subordinate species. This study attempted to explore the biotic effect of Artemisia diffusa shrubs on its subordinate species in an altitude gradient in the gypsum habitat of Semnan province.
Methodology
For this purpose, four habitats with gypsum content above 40% were chosen based on their altitude gradient. These habitats include Talkheh, Sorkheh Down, Rameh and Sorkheh Up with altitudes 1302, 1358, 1431 and 1544 meters above sea level, respectively. In each habitat, 20 twin plots were established under a canopy of A. diffusa and their nearby open spaces and then, their percentage of cover was measured within the plots. The sampling unit is the shrub, which is considered as a patch. To investigate the response of the plants, they were divided into four functional groups: annual grasses, annual forbs, perennial forbs and shrubs. To analyze the soil parameters in each habitat, ten soil samples were collected as pairs under canopy of A. diffusa and their nearby open spaces and physicochemical properties including pH, EC, gypsum content, CaCO₃, sand, silt, clay, phosphorus, organic carbon, nitrogen and sulfur were examined. The difference between treatments was examined using the generalized linear mixed model, and means were compared using Tukey's HSD test. Soil properties were examined using multivariate PCA analysis. All computations were performed with R program. The relative interaction index was developed to measure biotic interactions between plants.
Results
Based on the obtained results, 22 plant species from 16 families were recognized. The findings revealed that the altitude and location of the species under the patch and their nearby open spaces have a major impact on various ecosystems. In Talkheh (7.7±1.9), Sorkheh down (13.2±2.36), and Sorkheh up (12.75±5.3), the percentage of total cover of species under patch is greater than their nearby open spaces. Additionally, in Talkheh, the percentage of annual forbs (5.3±1.2) and at Sorkheh down annual grasses (8.3±2.3) and annual forbs (5±1.06) under patch, also in Sorkheh up shrubs (7.5±3.5) and annual grasses (3.15±0.84) were more abundant under patch than in their nearby open spaces. Also the results showed that the biotic interaction of A.diffusa facilitates all species in all environments, however the intensity decreased with increasing altitude (F=2.95; P<0.05).
The study found that annual forbs facilitation declines with increasing altitude (F=10.01; P < 0.001), while shrub species only experience facilitation at high altitude (F = 5; P < 0.006). The model's results demonstrated that altitude, position, and their interactions had a considerable effect on soil properties. In the Talkhe habitat, the amount of sulfur (4.57±1.21), phosphorus (2.1±0.3), clay (17.12±2.24), silt (31.78±1.61), and carbon (4.17±0.78) was much higher under the patch than in their nearby open spaces and the amount of sand (71.8±3.22) and gypsum content (56.93±3.47) was lower than the nearby open spaces. In general, lower altitudes had less gypsum and higher acidity, while the opposite was true in the upper environment.
Conclusion
In general, Artemisia diffusa plants in Semnan province's gypsum ecosystem have enabling effects that decrease as altitude increases. Because as altitude and gypsum levels rise, environmental conditions grow more severe, increasing competition among plants for limited resources. Given that gypsum ecosystems feature unique and endemic species, it is critical to understand the types of interactions so that, if necessary, appropriate nurse species can be employed to restore these places.

Keywords

• Altitude
• Facilitation
• Semnan
• Competition
• Functional group