C / N ratio, stable isotope (δ&amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C, δ&amp;lt;sup&amp;gt;15&amp;lt;/sup&amp;gt;N), and &amp;lt;i&amp;gt;n&amp;lt;/i&amp;gt;-alkane patterns of bryophytes along hydrological gradients of low-centred polygon of the Siberian Arctic