Cation ratios inCladonia portentosaas indices of precipitation acidity in the British Isles

Abstract

SUMMARYThe relationship between rainfall chemistry and the concentrations of potassium, calcium and magnesium in the apices (top 5 mm) of the cushion-forming lichen Cladonia portentosa (Dufour) Coem. was investigated. Lichen samples, together with underlying topsoil, were collected from heathlands m close proximity to rain gauges in the UK Acid Deposition Monitoring Network, located in rural areas of the British Isles, which provide wet deposition data based on weekly bulk samples. The ratios K'^:Mg^^ and extracellular Mg^*:intracellular Mg^"^ in the lichen apices were strongly correlated with H"^ concentration in precipitation. It is suggested that shifts in these ratios occur owing to enhanced displacement of extracellular Mg"' by elevated H" concentration in acid rain. By contrast, there was no indication of any relationship between total acid deposition and lichen chemistry. The concentration of Mg^"" in the lichen was weakly correlated with that in soil, whereas lichen Ca^' content was not correlated with either precipitation or soil chetnistry. It is concluded that these ratios describing changes in lichen Mg^"^ content provide good biomarkers for wet-deposited acidity.

Relationships between atmospheric nitrogen inputs and the vertical nitrogen and phosphorus concentration gradients in the lichen Cladonia portentosa

“…This is perhaps unexpected because the effect on [N] lichen of high N input resulting from high rainfall would be moderated if lichen growth was concomitantly greater at wetter sites as is suggested by data presented in Ka$ renlampi (1971), Armstrong (1993 and Crittenden et al (1994). The relationship between N deposition and [N] lichen in C. portentosa is the converse of that reported previously between rainfall chemistry and regional variation in cation ratios in the apices of the same species : mean H + concentration in precipitation rather than total acid load was found to be the best correlate with the ratios Crittenden, 1996) and therefore the response of [N] lichen to [N] ppt may not be linear at the event level. In her studies on the effects of acid rain on mat-forming lichens, Kyto$ viita (1993) observed that when [NO $ − ] ppt was artificially raised (together with [H + ] ppt ) total NO $ − capture by Cladonia stellaris and Stereocaulon paschale increased but capture efficiency decreased (i.e.…”

“…It is not surprising, therefore, that in C. portentosa there is regional covariation between [N] base and ([K + ]\[Mg# + ]) lichen (Fig. 9), a parameter shown in a previous study to be an indicator of acid level (Hyva$ rinen & Crittenden, 1996). Lichens indicating a clean atmospheric regime were found in remote western and northern areas of the British Isles (sites 1, 21, 27, 32), and the most chemically modified material in terms of the perceived response of this species to both N load and [H + ] ppt occurred in the east and north-east of England (sites 16, 17).…”

“…the proportion of total NO $ − deposition that was retained by lichen thalli decreased). Furthermore, although in unpolluted oligotrophic environments lichens can scav-enge NO $ − and NH % + simultaneously and efficiently from intercepted precipitation (Crittenden, 1989(Crittenden, , 1996, it is possible that high values of [NH % + ] ppt inhibit NO $ − capture at N-polluted sites. This proposal is consistent with results of laboratory studies demonstrating that lichens absorb NH % + preferentially when both NO $ − and NH % + are supplied at relatively high concentrations (Smith, 1960 ;Lang, Reiners & Heier, 1976 ;Greenfield, 1992), a phenomenon that is well documented in both fungi and algae (e.g.…”

“…Third, lichen mats are efficient scavengers of inorganic N and P in precipitation (Crittenden, 1983(Crittenden, , 1989Hyva$ rinen & Crittenden, 1998) such that mats several cm deep become very strong sinks for ions such as NO $ − , NH % + and PO % $−. The limited experimental data on the uptake of these ions by lichens suggest that they are actively absorbed (Smith, 1960 ;Farrar, 1976 ;Tapper, 1983 ;Crittenden, 1996) ; this is consistent with the abundant evidence for active uptake of inorganic N and P in free-living fungi (Jennings, 1995) and microalgae (Darley, 1982 ;Hellebust & Ahmad, 1989). Capture of NH % + by lichens might initially involve cation exchange (Brown, Standell & Miller, 1995).…”

Atmospheric background trace elements deposition in Tierra del Fuego region (Patagonia, Argentina), using transplanted Usnea barbata lichens

“…In particular, the K + /Mg ++ ratio and the Mg ++ (extracellular)/Mg ++ (intracellular) in lichens is highly correlated to H + concentrations in precipitation. High concentrations of H + that are found in acid rain cause increases in extracellular Mg ++ (Hyvarinen and Crittenden 1996). In general, the .…”