More tolerant than expected: Taking into account the ability of Cladonia portentosa to cope with increased nitrogen availability in environmental policy

Abstract

The lichen Cladonia portentosa is generally considered to be sensitive to increased environmental nitrogen (N) deposition. However, the presence of this lichen in impacted environments suggests that it can cope with prolonged exposure to high N availability. To test the tolerance of this species to N, photosynthetic parameters, carbon and N concentrations and isotopic signature, chitin concentration, surface pH and extracellular enzymatic activity were measured in samples exposed for 11 years to different N doses and forms at the Whim bog N manipulation experimental site (United Kingdom). The results showed that C. portentosa is tolerant to long-term exposure to wet N deposition, maintaining its functionality with almost unaltered physiological parameters. The comparison of the proteome of short-and long-term exposed samples showed similar changes in protein expression suggesting that mechanisms to cope with N are not dependent on the exposure time even after more than a decade. Since empirical N Critical Loads are based on the response of sensitive components of the ecosystem, like C. portentosa, its capacity to cope with short-and long-term exposure to N needs to be recognized and taken into account when setting them, likewise, the significance of the form of N. Capsule: Updated knowledge on tolerance of sensitive species to nitrogen must be taken into account to establish environmental policy.

Resilience of Epiphytic Lichens to Combined Effects of Increasing Nitrogen and Solar Radiation

“…Our data during 20 days of N addition, pre solar radiation, support this view, with reduced vitality in N sensitive species. Other researchers have found a fertilizing effect of moderate N supply shown by increased thalli N, chlorophyll concentration, and rates of photosynthesis [ 21 , 40 ]. It is well documented that N performs as a nutrient below the toxicity threshold, especially in oligotrophic environments [ 41 , 42 , 43 ].…”

“…Such alterations can have a strong effect on lichens, which are amongst the most sensitive organisms to environmental changes [ 15 ], providing meaningful ecological systems to model and foresee the response of other less sensitive organisms of the ecosystem [ 16 , 17 ]. These poikilohydric organisms are especially sensitive to climate [ 15 , 18 ] and air pollution [ 19 , 20 , 21 ] because their physiology is tightly linked to their water status, and they lack mechanisms to control their water and nutrient contents [ 22 ]. For this reason, they have been considered as valuable ecological indicators of environmental factors such as temperature and N deposition [ 15 , 21 , 23 ].…”

“…These poikilohydric organisms are especially sensitive to climate [ 15 , 18 ] and air pollution [ 19 , 20 , 21 ] because their physiology is tightly linked to their water status, and they lack mechanisms to control their water and nutrient contents [ 22 ]. For this reason, they have been considered as valuable ecological indicators of environmental factors such as temperature and N deposition [ 15 , 21 , 23 ].…”

“…To attribute a species to a given functional group, researchers assess the data available in the literature (e.g., LIAS [ 25 ]; Nimis and Martellos [ 26 ]; United States Forest Service [ 27 ]), and this knowledge has frequently been used to support environmental policies [ 28 ]. Therefore, the scientific community has considered of pivotal relevance to keep knowledge about species used in monitoring surveys as detailed and updated as possible [ 21 ]. This has been the case for lichens used to identify N pollution status: Oligotrophic species are highly sensitive to N pollution, whereas nitrophytic species tolerate such conditions [ 16 ].…”

Wanted: virtual or live! How lichens are becoming part of mass internet culture

“…Abas 2021;Nimis et al 2002;Sutton et al 2020). When extensive or rapid environmental changes occur, some species are unable to adapt (Munzi et al 2020), yet lichens respond to climate changes and environmental stress with shifts in community composition (Nimis et al 2002;van Herk 2001), physiological impairment (Paoli et al 2015;Yemets et al 2015) and finally, with their disappearance (Isocrono et al 2007;Munzi et al 2007).…”