Unveiling the Intricate Sinking behavior of Large Diatoms: Insights from Time-Frequency Analysis of Palmerina hardmaniana Sinking under Silicate-Depleted Conditions

Abstract

Nutrient limits impact diatom sinking in time domain, but response in time-frequency domain is unclear. Studying the response of large diatoms to nutrients exclusively in the time domain fails to fully capture the complete impact of nutrient limitations on sinking behavior due to the absence of crucial information, including period and frequency. Wavelet analysis provides valuable insights into the period and frequency of signals and unveils their positions in the time. This study investigated the sinking behavior response of the large diatom Palmerina hardmaniana to silicate-depleted conditions in the time-frequency domain using wavelet analysis. The results showed that P. hardmaniana was capable of regulating its sinking speed, and this regulation occurred intermittently in time. The predominant frequency of intermittent regulation fell within the range of 0.13-0.50 Hz (equivalent to a period of 2-8 s) for both control and silicate-depleted conditions. The similarity in the frequency range of regulation between the two groups suggests the involvement of shared physiological mechanisms. P. hardmaniana responded to silicate depletion by intensifying the regulation of 0.13-0.50 Hz, which was reflected in the time domain as a change in the proportion of different instantaneous sinking speeds and consequently lead to a significant increase or decrease in the mean sinking speed (p<0.05). Additionally, the regulation of P. hardmaniana sinking behavior was also influenced by the physiological state of the cells. Short-term silicate stress (30 min) enhanced the oscillation power of sinking regulation, while prolonged silicate stress ([≥] 3 d) led to a decline in oscillation power.