Response of perennial woody plants to seed treatment by electromagnetic field and low-temperature plasma

Abstract

Radiofrequency (5.28 MHz) electromagnetic radiation and low-temperature plasma were applied asshort-term (2–15 min) seed treatments to two perennial woody plant species, including Smirnov’srhododendron (Rhododendron smirnowii Trautv.) and black mulberry (Morus nigra L.). Potentialeffects were evaluated using germination indices and morphometry. The results suggest thattreatment with electromagnetic field stimulated germination of freshly harvested R. smirnowii seeds(increased germination percentage up to 70%), but reduced germination of fresh M. nigra seeds (by24%). Treatment with low-temperature plasma negatively affected germination for R. smirnowii,and positively for M. nigra. The treatment-induced changes in germination depended on seeddormancy state. Longer-term observations revealed that the effects persisted for more than a year; however, even negative effects on germination came out as positive effects on plant morphometrictraits over time. Treatments characterized as distressful based on changes in germination andseedling length increased growth of R. smirnowii after 13 months. Specific changes included stemand root branching, as well as increased leaf count and surface area. These findings imply thatlonger-term patterns of response to seed stressors may be complex, and therefore, commonly usedstressor-effects estimates, such as germination rate or seedling morphology, may be insufficient forqualifying stress response.