The influence of solar activity on plant growth has been studied for over 100 years,
however, this phenomenon is still poorly understood on a daily scale. The data from
extensive monitoring of the growth of peat moss Sphagnum riparium, which we are
conducting in the mires of Karelia (Russia), may shed light on this issue. During the
6 years of observation, 161,190 shoots were measured, and 1075 growth rates were
obtained. Considering together the growth rates with the sunspot number and
involving data on seasonal temperature, we found previously unknown effects of
daily-scale solar activity on plant growth. It was found that the sunspot number
weakly but significantly inhibits the growth of Sphagnum. The extreme sunspot number
in the 4 days before the growth rate values have a stronger influence. The
involvement of temperature data showed that inhibition in growth is observed only
in the temperature range from 6.7
C to 15.3
C and disappears beyond these limits.
In addition, the data obtained showed that the influence of sunspot number on the
growth of Sphagnum is progressively increasing along the gradient from the minimum
to the maximum of the 11-year solar cycle. The study provides one of the first results
on the effect of solar activity on plant growth on a daily scale. The results expand our
knowledge of the biological effects of solar activity. Indirectly, they can also be useful
to better our understanding of the ozone layer's involvement in this process.