Inter- and intra-tree variability of carbon and oxygen stable isotope ratios of modern pollen from nine European tree species

Abstract

Stable carbon and oxygen isotope ratios of raw pollen sampled from nine abundant tree species growing in natural habitats of central and northern Europe were investigated to understand the intra-and inter-specific variability of pollen-isotope values. All species yielded specific δ 13 C pollen and δ 18 O pollen values and patterns, which can be ascribed to their physiology and habitat preferences. Broad-leaved trees flowering early in the year before leaf proliferation (Alnus glutinosa and Corylus avellana) exhibited on average 2.6‰ lower δ 13 C pollen and 3.1‰ lower δ 18 O pollen values than broad-leaved and coniferous trees flowering during mid and late spring (Acer pseudoplatanus, Betula pendula, Carpinus betulus, Fagus sylvatica, Picea abies, Pinus sylvestris and Quercus robur). Mean species-specific δ 13 C pollen values did not change markedly over time, whereas δ 18 O pollen values of two consecutive years were often statistically distinct. An intra-annual analysis of B. pendula and P. sylvestris pollen revealed increasing δ 18 O pollen values during the final weeks of pollen development. However, the δ 13 C pollen values remained consistent throughout the pollen-maturation process. Detailed intra-individual analysis yielded circumferential and height-dependent variations within carbon and oxygen pollen-isotopes and the sampling position on a tree accounted for differences of up to 3.5‰ for δ 13 C pollen and 2.1‰ for δ 18 O pollen. A comparison of isotope ranges from different geographic settings revealed gradients between maritime and continental as well as between high and low altitudinal study sites. The results of stepwise regression analysis demonstrated, that carbon and oxygen pollen-isotopes also reflect local non-climate environmental conditions. A detailed understanding of isotope patterns and ranges in modern pollen is necessary to enhance the accuracy of palaeoclimate investigations on δ 13 C and δ 18 O of fossil pollen. Furthermore, pollen-isotope values are species-specific and the analysis of species growing during different phenophases may be valuable for palaeoweather reconstructions of different seasons.

Carbon isotope values of hazelnut shells: a new proxy for canopy density

“…The mean 3.1‰ intra-tree range in nutshell δ 13 C values (Figure 4) is relatively large and is actually the same as the mean intra-tree range of Corylus avellana pollen δ 13 C values determined in another study (3.1‰, n = 4; Müller et al, 2020). This suggests that the carbon used to synthesize the lignin and structural carbohydrates (cellulose, hemicellulose) that make up the majority of nutshell (Licursi et al, 2017) is either (i) sourced from different (groups of) leaves that experience different conditions, which influence their stomatal conductance and photosynthetic activity and therefore the level of discrimination against 13 C; or (ii) different nuts are formed at slightly different times when conditions that affect 13 C-discrimination differ.…”

Quantifying the impact of chemicals on stable carbon and oxygen isotope values of raw pollen

“…Nevertheless, A. glutinosa and C. avellana show differing patterns for δ 18 O pollen and δ 13 C pollen after chemical treatment (Figs 1 and 2). This might be related to their plantspecific time of pollination from January to March, which is why these species have generally low baseline values of raw pollen isotopes (Müller et al, 2020).…”

“…Moore et al, 1991;Stanley and Linskens, 2012) and therefore also carbon and oxygen isotope values of raw pollen have species-specific patterns and ranges (e.g. Amundson et al, 1997;Jahren, 2004;Loader and Hemming, 2004;King et al, 2012;Nelson, 2012;Schwarz, 2016;Müller et al, 2020). Chemicals applied on raw pollen change the composition of the pollen wall coating substancedependently, but the degree of contamination of the sporopollenin layer is unknown.…”

Effects of Sitka spruce masting on phenology and demography of siskins Spinus spinus

“…more on Sitka spruce seeds and less on invertebrates), and at a lower trophic level in years with larger Sitka spruce cone crops. The carbon isotope ratio varies considerably among plant species 20 , and we therefore also expected to detect a difference in carbon isotope ratios between siskins and other small passerines, reflecting a strong dependence of siskins on Sitka spruce seed to feed their nestlings. However, in contrast to the nitrogen isotope ratio, we were unable to predict exactly how the carbon isotope ratio would differ among bird species at the study site, given that it is influenced by the specific ecology of producers in ecosystems 21 , 22 , with a relatively small effect of trophic level 19 , 23 .…”