Determinants of ¹⁵N Natural Abundance in Leaves of Co-Occurring Plant Species and Types within an Alpine Lichen Heath in the Northern Caucasus

Abstract

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Are Alpine Gentianaceae Plants Mixotrophic?

“…The δ 15 N values for the Gentianaceae and reference plants were positively correlated (r = 0.57, p < 0.001), which may be explained by the general dependence of δ 15 N values in plants on the variation in the δ 15 N values of soil nitrogen. The mean δ 15 N value for reference plants (-3.89‰) was close to δ 15 N values for other Caucasian AM alpine plants (-3.59‰) reported by Makarov et al (2014). The δ 15 N values for Gentianaceae plants in our study (mean -1.50‰) were significantly higher and similar to alpine legumes (-1.50‰) and non-mycorrhizal sedges (-0.95‰) (Makarov et al, 2014).…”

“…The mean δ 15 N value for reference plants (-3.89‰) was close to δ 15 N values for other Caucasian AM alpine plants (-3.59‰) reported by Makarov et al (2014). The δ 15 N values for Gentianaceae plants in our study (mean -1.50‰) were significantly higher and similar to alpine legumes (-1.50‰) and non-mycorrhizal sedges (-0.95‰) (Makarov et al, 2014). Legumes have a different source of nitrogen (nitrogen fixation) from other AM plants, and sedges may use nitrogen from the soil organic matter (Körner, 2003;Pörtl et al, 2007).…”

“…There are several possible explanations for this result. Products of nitrogen fixation are enriched in 15 N relative to labile soil N as we see for legumes (Bowman et al, 1996;Nadelhoffer et al, 1996;Makarov et al, 2014), but an enhanced nitrogen fixation near Gentiana roots has never been shown. Alternatively, reference green plants may have used certain forms of soil nitrogen depleted in 15 N compared to N sources used by Gentianas.…”

Do afroalpine plants differ from other alpine plants by their leaf functional traits?

“…On the contrary, δ 15 N values differed considerably in tropi cal and temperate mountains. In our case median δ 15 N value was considerably higher (mean -1.0 ‰), than, for example, that in the European Alps (-2.3 ‰, Körner et al 2016) or δ 15 N for non-fixing alpine forbs in the Cau ca sus (-2.2 ‰, Makarov et al 2014). Soil and plant 15 N-enrichment in tropics are significantly higher than in temperate regions (Mar ti nelli et al 1999) due to more open and intensive ni tro gen cycle.…”

Using long-term records to investigate watershed nitrogen supply and demand dynamics at the Fernow Experimental Forest, West Virginia, USA

“…However, these findings may apply primarily to low-N cycling ecosystems. Furthermore, there is considerable overlap in δ 15 N values between ECM and AM species across the globe , and the signature is not always lower in ECM species, even in northern alpine climates (Makarov et al 2014). In temperate forests, ECM tree species can also have higher tissue δ 15 N values than AM species (Pardo et al 2013).…”