تأثیر همزیستی قارچ Piriformospora indica بر رشد و شاخص‌های فیزیولوژیکی گیاهچه‌های ذرت (Zea mays) در معرض ذرات میکروپلاستیک و تنش کمبود آب

Introduction
The contamination of agricultural soils with microplastic particles is one of the major environmental problems that has recently gained attention. On the other hand, due to climate change, drought stress, as one of the most important factors limiting crop production, is increasing alarmingly. This study was conducted to investigate the biological potential of the fungus Piriformospora indica in mitigating the adverse effects of stress caused by polyvinyl chloride (PVC) microplastic particles and water deficiency in maize crop.

Materials and methods
The experiment was conducted as a factorial arrangement in a completely randomized design with three replicates. The studied factors included the addition of three concentrations of polyvinyl chloride microplastics to the soil (0, 0.1, and 1%), P. indica fungus at two levels (inoculation and non-inoculation), and water deficit stress at three levels of full irrigation (no stress), irrigation at 75 and 50 percent of field capacity (moderate and severe stress, respectively). Germinated maize seeds (cv. ‘Tah’) were inoculated with P. indica and planted in pots containing 3 kg of soil under greenhouse conditions. Water deficit stress was applied 14 days after planting. One month after planting, photosynthetic parameters and relative leaf water content were measured. The plants were then harvested, and the roots of the plants were examined under a microscope to determine the colonization percentage. Additionally, proline content, total chlorophyll content, and plant dry matter were measured.

Research findings
The addition of 1% microplastic to the soil, similar to water deficit stress, significantly reduced relative leaf water content, total chlorophyll content, photosynthetic indices, and shoot dry matter in maize seedlings. Although the percentage of root colonization of maize seedlings by P. indica fungus decreased by 16.9%, 30.9%, and 47.1% under 1% microplastic contamination and water deficit at 75% and 50% of field capacity, respectively, the beneficial effects of the fungus on plant growth and measured parameters was still evident. So that the relative leaf water content, chlorophyll content, net photosynthesis rate, and shoot dry weight of inoculated plants exposed to the highest level of water deficit stress and in the presence of 1% microplastic were (8.2 and 9), (20.5 and 27), (17.9 and 17.8) and (43.5 and 46.8)% higher than plants without the fungus, respectively. In addition, the proline content of the plants also increased significantly in the presence of the fungus.

Conclusion
Overall, the results of this experiment showed that the presence of P. indica fungus was associated with increased growth and improved photosynthetic parameters of maize seedlings exposed to microplastic particles and water deficit stress, and thus, utilizing the potential the fungus could be considered to mitigate the negative impacts of these stresses.