Stable carbon and oxygen isotope variability of modern pollen from nine abundant European tree species.
Authors: Müller Carolina , Hethke Manja , Riedel Frank , Helle Gerhard 
Published: March 2020

&lt;p&gt;A detailed understanding of the carbon and oxygen isotope ratios of modern pollen is crucial for the interpretation of fossil &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C&lt;em&gt;&lt;sub&gt;pollen&lt;/sub&gt;&lt;/em&gt; and &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;&lt;em&gt;pollen&lt;/em&gt; &lt;/sub&gt;values. To broaden our knowledge of pollen-isotope ratios we investigated the isotope ranges of nine abundant tree species from central and northern Europe (vegetation periods 2015 and 2016).&lt;/p&gt;&lt;p&gt;In general, the isotope values of modern pollen are highly species-specific and yield site-specific patterns. Trees of different locations revealed distinct &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C&lt;em&gt;&lt;sub&gt;pollen&lt;/sub&gt;&lt;/em&gt; and &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;em&gt;&lt;sub&gt;pollen&lt;/sub&gt;&lt;/em&gt; patterns for maritime and continental growing conditions and for high and low altitudes. Furthermore, pollen-isotope ratios reflect the time of blossoming. &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C&lt;em&gt;&lt;sub&gt;pollen&lt;/sub&gt;&lt;/em&gt; values of broad-leaved species flowering before leaf proliferation (Janurary to March; &lt;em&gt;Alnus glutinosa&lt;/em&gt; and &lt;em&gt;Corylus avellana&lt;/em&gt;) are on average 2.6&amp;#8240; lower in comparison to broad-leaved and coniferous trees flowering during late spring and early summer (April to June; &lt;em&gt;Acer pseudoplatanus&lt;/em&gt;, &lt;em&gt;Betula pendula&lt;/em&gt;, &lt;em&gt;Carpinus betulus&lt;/em&gt;, &lt;em&gt;Fagus sylvatica&lt;/em&gt;, &lt;em&gt;Picea abies&lt;/em&gt;, &lt;em&gt;Pinus sylvestris&lt;/em&gt; and &lt;em&gt;Quercus robur&lt;/em&gt;). &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;em&gt;&lt;sub&gt;pollen&lt;/sub&gt;&lt;/em&gt; values yielded similar results, which are on average 3.1&amp;#8240; lower for species flowering early in the year. An intra-annual analysis of Betula pendula and Pinus sylvestris pollen revealed increased &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;em&gt;&lt;sub&gt;pollen&lt;/sub&gt;&lt;/em&gt; values during the last stages of pollen-maturation, whereas &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C&lt;em&gt;&lt;sub&gt;pollen &lt;/sub&gt;&lt;/em&gt;values of both species remain consistent during late pollen development. Additionally, pollen-isotope values vary markedly within individual trees. Circumferential and height-dependent variations within single trees can be as high as 3.5&amp;#8240; for &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C&lt;em&gt;&lt;sub&gt;pollen&lt;/sub&gt;&lt;/em&gt; and 2.1&amp;#8240; for &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;em&gt;&lt;sub&gt;pollen&lt;/sub&gt;&lt;/em&gt;.&lt;/p&gt;&lt;p&gt;Our results suggest that local environmental conditions are generally reflected in the carbon and oxygen pollen-isotopes, but some species seem to reflect the conditions more closely than others. The data indicate that it may even be feasible to reconstruct intra-annual climate conditions by analysing isotopes of species whose pollen develop during different seasons throughout the year.&lt;/p&gt;