Structural deviations in secondary phloem of young shoots of Spiraea beauverdiana near magma volcanoes

Abstract

We performed a comparative analysis of the internal structure of the secondary phloem of one, two and three-year-old stems of Spiraea beauverdiana growing in extreme conditions of solfataric fields of Golovnin Volcano caldera and Mendeleyev Volcano and in normal conditions. The combination of environmental factors in conditions of solfataric activity, such as high temperatures in the soil and in the near-surface air, as well as saturation with gases toxic to plants, rare elements accumulating in the nearby substrate, and lack of soil moisture, interfere with normal phellogen and cambium activity. Deviations from the normal structure involve changes in the following parameters of the internal structure of a year-old stem of S. beauverdiana. Secondary phloem parameters in the studied habitats are normal, except for the length of the segments of sieve tubes, the height of single-row rays, the length of parenchymal girder; these are shorter in S. beauverdiana stems from volcanos. At two and three years of age in volcanic conditions we see reduction in the width of the secondary phloem (both conductive and non-conductive) and the diameter of the segments of sieve tubes. In samples from Golovnin Volcano we see reduction in tangential diameter, while in the samples from Mendeleyev Volcano it’s the radial diameter. We also see reduction in the height of multiple-row rays. At that age we see changes in the structure of the radial parenchyma; namely, we find no double-row rays in samples from Golovnin Volcano caldera. One of the signs of impact of volcanic activity on the bark structure is development of non-specific anomalies in the internal structure of the S. beauverdiana bark, namely, in the outer bark, or in deeper levels, such as the secondary phloem. That causes sclerification and dilatation of parenchyma, and multiple layers in some tissues.