Extreme isotopic depletion of nitrogen in New Zealand lithophytes and epiphytes; the result of diffusive uptake of atmospheric ammonia?

Abstract

Several lichens and the terrestrial alga Trentepohlia were found to have extremely depleted 15N signatures at two sites near the Rotorua geothermal area, New Zealand. Values, typically -20 per thousand, with several extreme cases of -24 per thousand, are more isotopically depleted than any previously quoted delta15N signature for vegetation growing in natural environments. For Trentepohlia, distance from a geothermal source did not affect isotopic signature. A 100-km transect showed that the phenomenon is widespread and the discrimination is not related to substrate N, or to elevation. Rainfall NHx and atmospheric gaseous NH3 (NH3(g)) were shown to be isotopically depleted in the range -1 per thousand to -8 per thousand and could not, of themselves, be responsible for the plant values obtained. A simulation of Trentepohlia thallus was created using an acidified fiberglass mat and was allowed to absorb NH3(g) from the atmosphere. Mats exposed at the geothermal sites and on farm-land showed a significant further depletion of 15N to -17 per thousand. We hypothesize that the extreme isotopic depletion is due to dual fractionation: firstly by the volatilization of NH3(g) from aqueous sources into the atmosphere; secondly by the diffusive assimilation of that NH3(g) into vegetation. We further hypothesize that lithophytes, epiphytes, and higher plants, growing on strongly N-limited substrates, will show this phenomenon more or less, depending on the proportion of diffusively assimilated NH3(g) utilized as a N source. Many of the isotopically depleted delta15N signatures in vegetation, previously reported in the literature, especially epiphytes, may be due to this form of uptake depending on the concentration of atmospheric NH3(g), and the degree of reliance on that form of N.

Reservoirs and Radiocarbon:14C Dating Problems in Mývatnssveit, Northern Iceland

“…The low values for these δ 15 Ν measurements may reflect lower values for Icelandic plants than in other regions. Low δ 15 Ν values in terrestrial plants have been observed in various locations as a result of interactions between specific plant physiological and environmental variables (Erskine et al 1998;McKee et al 2002;Tozer et al 2005). In a study of stable isotopic measurements of Icelandic plants and lichens, including material from sites in the north of Iceland, Wang and Wooller (2006) found a series of low δ 15 Ν values, with an overall range down to -12%c for terrestrial plants.…”

Lichen response to ammonia deposition defines the footprint of a penguin rookery

“…There is a dearth of published data on 15 N natural abundance in atmospheric NH 3 . The three positive d 15 N values reported in Table 4 (?2.4 to ?6.9 %) were for air samples drawn through either H 2 SO 4 or acid impregnated filters, whereas the negative d 15 N value (-10.0 %) recorded by Erskine et al (1998) was for NH 3 collected passively relying on diffusion into inverted jars which could have greatly underestimated [ 15 N-NH 3 ] due to isotopic fractionation during diffusive transfer (Högberg 1997;Tozer et al 2005). The positive d…”

“…By contrast, environmental circumstances relating to N capture in lichens are potentially far less complex: atmospheric deposition is spatially and chemically more homogeneous and N uptake strategies in lichens are probably considerably less variable than in plants. Lichens in remote background locations are often strongly 15 Ndepleted (Tozer et al 2005;Huiskes et al 2006;Fogel et al 2008) rendering a local positive 15 N signal easier to detect. Hence seeking a relationship between lichen chemistry and a point source of NH 3 emissions is likely to be associated with fewer confounding factors than in plant/soil systems.…”

Root fungal associations in some non-orchidaceous vascular lithophytes

“…Nevertheless, lithophytes also colonize rocks that are constantly misted by waterfalls or rocks dripping with water. Lithophytes have certain biological peculiarities, including capturing moisture from rain, dew, melting snow or water trickling down the rocks, and acquire nutrients from rain water, litter, and feeding on insects or their own dead tissues (Alves & Kolbeck 1993;Gold & Bliss 1995;Tozer et al 2005). Th ese features enable lithophytes to occupy and thrive on the rock surfaces.…”

“…One of the harshest habitats is the surfaces and crevices of rock where low moisture, nutrients and high temperatures limit plant's existence. Plants growing on rocks are termed lithophytes and these types of plants occur in diff erent arid (Zwieniecki & Newton 1995;Bashan et al 2002;Lopez et al 2009) and non arid (Tozer et al 2005;Grӧger & Huber 2007;Muthuraja et al 2014) ecosystems. Nevertheless, lithophytes also colonize rocks that are constantly misted by waterfalls or rocks dripping with water.…”