Nick A. Cutler

Eukaryotic Microorganisms and Stone Biodeterioration

Eukaryotic microorganisms (especially green algae and fungi) can have a significant impact on the structure and appearance of stone cultural heritage. This paper reviews current knowledge on the role of eukaryotes in the biodeterioration of stone. Considerable uncertainty remains over community-level interactions and the response of lithobiontic communities to environmental change. Three inter-linked approaches to future research are proposed: (1) long-term ecological field studies; (2) diversity studies based on new molecular techniques and (3) laboratory-based simulation studies. The overall goal of these research efforts should be the formulation of robust models of stone deterioration that integrate biotic and abiotic factors and can be used to aid prediction and management of eukaryotic growths on stone cultural heritage.

Vegetation structure influences the retention of airfall tephra in a sub-Arctic landscape:

Vegetation cover mediates a number of important geomorphological processes. However, the effect of different vegetation types on the retention of fine aeolian sediment is poorly understood. We investigated this phenomenon, using the retention of fine, pyroclastic material (tephra) from the 2011 eruption of the Grímsvötn volcano, Iceland, as a case study. We set out to quantify structural variation in different vegetation types and to relate structural metrics to the thickness of recently deposited volcanic ash layers in the sedimentary section. We utilised a combination of vegetation and soil surveys, along with photogrammetric analysis of vegetation structure. We found that indices of plant community composition were a poor proxy for vegetation structure and were largely unrelated to tephra thickness. However, structural metrics, derived from photogrammetric analysis, were clearly related to variations in tephra layer thickness at a landscape scale and tephra layers under shrub patches were significantly thicker than those outside the shrub canopy. We therefore concluded that: a) vegetation cover was a critical factor in the retention of fine aeolian sediment for deposit depths up to few centimetres; b) structural variation in vegetation cover played a major role in determining the configuration of tephra deposits in the sedimentary section. These findings have implications for the analysis of ancient volcanic eruptions and archaeological/palaeoenvironmental reconstructions based on the interpretation of tephra deposits. Furthermore, they present the possibility that the detailed form of tephra layers may be used as a proxy for palaeo vegetation structure.

Non-destructive sampling of rock-dwelling microbial communities using sterile adhesive tape.

Building stone provides a habitat for an array of microorganisms, many of which have been demonstrated to have a deleterious effect on the appearance and/or structural integrity of stone masonry. It is essential to understand the composition and structure of stone-dwelling (lithobiontic) microbial communities if successful stone conservation strategies are to be applied, particularly in the face of global environmental change. Ideally, the techniques used to sample such assemblages should be non-destructive due to the sensitive conservation status of many stone buildings. This paper quantitatively assesses the performance of sterile adhesive tape as a non-destructive sampling technique and compares the results of tape sampling with an alternative, destructive, sampling method. We used DNA fingerprinting (TRFLP) to characterise the algal, fungal and bacterial communities living on a stone slab. Our results demonstrate that tape sampling may be used to collect viable quantities of microbial DNA from environmental samples. This technique is ideally suited to the sampling of microbial biofilms, particularly when these communities are dominated by green algae. It provides a good approximation of total community diversity (i.e. the aggregate diversity of epilithic and endolithic communities). Tape sampling is straightforward, rapid and cost effective. When combined with molecular analytical techniques, this sampling method has the potential to make a major contribution to efforts to understand the structure of lithobiontic microbial communities and our ability to predict the response of such communities to future environmental change.

Nutrient limitation during long-term ecosystem development inferred from a mat-forming moss

Abstract Extant models of long-term ecosystem nutrient status, largely formulated using data from mid- and low-latitude settings dominated by vascular vegetation, predict nitrogen (N) limitation in the early stages of primary succession and phosphorus (P) limitation in the latter stages. The aims of this study were a) to examine the use of mosses to establish ecosystem nutrient status; b) to test an existing model of nutrient limitation during long-term primary succession and c) to assess the connection between nutrient dynamics and the emergence of spatially structured vegetation in a high-latitude, moss-dominated community. Spatiotemporal changes in nutrient availability were inferred using tissue nutrient concentrations in a moss sampled from a long (850-year) chronosequence of lava flows in Iceland. This is the first use of bryophyte nutrient concentrations, even though they should be a good indicator of nutrient status in high-latitude habitats. Samples of the moss, Racomitrium lanuginosum, from different topographic positions were collected from seven lava flows of different ages (26–848 years) and analyzed to establish concentrations of N, P and major mineral nutrients. Concentrations of N were low on all sites and evidence of progressive N accumulation is lacking; increasing concentrations of phosphorus indicated increasing N limitation with terrain age. This pattern contrasts with other studies of long-term nutrient limitation, where N limitation reduces and P limitation increases with increasing terrain age. Concentrations of mineral nutrients did not vary significantly with terrain age. Nutrient concentrations were only weakly related to spatial patterning in the vegetation. It is likely that element concentrations were strongly influenced by inputs of allochthonous sediment. These findings suggest that mat-forming, pleurocarpous mosses may be used to infer long-term changes in N & P limitation during primary succession and that existing models of nutrient limitation may not be robust over century – millennial timescales in low productivity, high-latitude habitats.

Impact of small-scale vegetation structure on tephra layer preservation

The factors that influence tephra layer taphonomy are poorly understood, but vegetation cover is likely to play a role in the preservation of terrestrial tephra deposits. The impact of vegetation on tephra layer preservation is important because: 1) the morphology of tephra layers could record key characteristics of past land surfaces and 2) vegetation-driven variability in tephra thickness could affect attempts to infer eruption and dispersion parameters. We investigated small- (metre-) scale interactions between vegetation and a thin (<10 cm), recent tephra layer. We conducted surveys of vegetation structure and tephra thickness at two locations which received a similar tephra deposit, but had contrasting vegetation cover (moss vs shrub). The tephra layer was thicker and less variable under shrub cover. Vegetation structure and layer thickness were correlated on the moss site but not under shrub cover, where the canopy reduced the influence of understory vegetation on layer morphology. Our results show that vegetation structure can influence tephra layer thickness on both small and medium (site) scales. These findings suggest that some tephra layers may carry a signal of past vegetation cover. They also have implications for the sampling effort required to reliably estimate the parameters of initial deposits.