Sunspot activity influences tree growth: Molecular evidence and ecological implications

Solar activity has a significant influence on Earth's climate and may drive many biological processes. Here, we measured growth in 11 tree species distributed along an ≈600-km latitudinal gradient in South-Central Chile, recording the width of their growth-rings among periods of maximum (highest number of sunspots) and minimum (lowest number of sunspots) solar activity. In one of these species, Quillaja saponaria, we experimentally assessed three ecophysiological traits (CO₂ fixation through photosynthesis [A_max], growth and leaf production) as well as the expression of five genes related to cell wall elongation and expansion following exposure to high and low levels of UV-B radiation, simulating scenarios of maximum and minimum solar activity, respectively. We found lower tree growth during the periods of maximum solar activity, with this trend being more evident at lower latitudes, where UV-B radiation is higher. Exposure of Q. saponaria to higher levels of UV-B affected the ecophysiological parameters, revealing a decrease in A_max, growth and leaf production. In addition, higher levels of UV-B led to repression in four of the five genes studied. Our results may help foresee environmental scenarios for different plant species associated with solar activity.