Renato Gerdol

Atmospheric nitrogen deposition promotes carbon loss from peat bogs

Peat bogs have historically represented exceptional carbon (C) sinks because of their extremely low decomposition rates and consequent accumulation of plant remnants as peat. Among the factors favoring that peat accumulation, a major role is played by the chemical quality of plant litter itself, which is poor in nutrients and characterized by polyphenols with a strong inhibitory effect on microbial breakdown. Because bogs receive their nutrient supply solely from atmospheric deposition, the global increase of atmospheric nitrogen (N) inputs as a consequence of human activities could potentially alter the litter chemistry with important, but still unknown, effects on their C balance. Here we present data showing the decomposition rates of recently formed litter peat samples collected in nine European countries under a natural gradient of atmospheric N deposition from ≈0.2 to 2 g·m−2·yr−1. We found that enhanced decomposition rates for material accumulated under higher atmospheric N supplies resulted in higher carbon dioxide (CO2) emissions and dissolved organic carbon release. The increased N availability favored microbial decomposition (i) by removing N constraints on microbial metabolism and (ii) through a chemical amelioration of litter peat quality with a positive feedback on microbial enzymatic activity. Although some uncertainty remains about whether decay-resistant Sphagnum will continue to dominate litter peat, our data indicate that, even without such changes, increased N deposition poses a serious risk to our valuable peatland C sinks.

Fungi isolated from Antarctic mosses

Abstract. Microfungi were isolated from different moss species in Victoria Land. Twenty-eight taxa belonging to 18 genera were identified. New records for continental Antarctica were: Arthrobotrys superba, Conidiobolus sp., Penicillium minioluteum, Verticillium psalliotae and V. lamellicola. The most frequently isolated fungal species were: Cladosporium cladosporioides, Cryptococcus albidus, Cryptococcus laurentii, Geomyces pannorum var. pannorum, G. pannorum var. vinaceus, Mortierella antarctica, Cadophora malorum, Phoma herbarum and V. lecanii. Bryum pseudotriquetrum was the moss richest in fungal species. Within the Antarctic environment, moss is one of the microhabitats richest in microfungi, particularly in psychrophilic indigenous species.

Use of moss (Tortula muralis Hedw.) for monitoring organic and inorganic air pollution in urban and rural sites in Northern Italy

Abstract Concentrations of polycyclic aromatic hydrocarbons (PAHs) and trace metals, as well as stable nitrogen (N) isotope composition, were determined in moss tissues from an urban area and from rural sites in northern Italy. The total PAH contents were higher in the urban area. The percentage fraction of low molecular weight volatile PAHs on total PAHs was greater in rural sites. The mean concentration ratio (urban:rural) was, overall, much lower for trace metals than for PAHs. Among metals, only Pb levels were highest in the city center, and were, in turn, associated with a more positive δ15N signature in moss tissue. This indicates that exposure to slow-moving traffic in the city center resulted both in higher Pb deposition and a greater contribution of NOx, compared with NHx, in atmospheric N pollution. Most metals (namely Cd, Cr, Fe, Ni, V and Zn) were moderately enriched in moss tissues from the urban area, especially in the sectors downwind from the main emission sources. In contrast, Co and Cu contents in the urban area did not differ from those in rural sites. We concluded that organic (PAH) and inorganic (metal) pollution showed varying patterns which reflected differences as regards both emission sources and atmospheric transport pathways. Atmospheric deposition of PAHs peaked in close vicinity to urban emission sources. Conversely, the atmospheric deposition of metals, except Pb, was more diffuse over the territory.

Monitoring of heavy metal deposition in Northern Italy by moss analysis

A survey of heavy metal deposition in the mountainous territories of Northern Italy was carried out in 1995-96. Moss samples (mainly Hylocomium splendens) were collected in a dense network of sites (about 3.2 sites/1000 km(2)) and the data of metal concentrations in moss tissues were statistically correlated with environmental and climatic factors, as well as with bulk deposition of elements and elemental concentrations in the soil. Three main geographic patterns of metal concentration in mosses could be defined: (1) Fe, Ni, and Cr, all derived both by soil particulates and anthropogenic emissions connected with ferrous metal manufacturing, were mostly concentrated in Northwestern Italy; (2) Cu and Zn, as typical multi-source elements, showed rather high concentrations with little ranges of variation over the whole area and small peaks reflecting local source points; (3) Cd and Pb reflected long-distance transport and showed highest concentrations in the regions with highest precipitation, especially in the Eastern Alps.

Are nutrient availability and acidity-alkalinity gradients related in Sphagnum-dominated peatlands?

Abstract Gradients in acidity-alkalinity and nutrient availability were studied in 2 Sphagnum-dominated peatlands on the southeastern Italian Alps. Decreasing concentrations of most mineral elements (Ca2+, Mg2+, Mn2+, Al3+ and Si4+) in pore water indicated a progressively lower influx of mineral-soil water from the slightly minerotrophic conditions in the peatland margins to ombrogenous conditions in the central part of the peatlands. This was paralleled by decreasing concentrations of ash, bulk density, Ca, Fe and, partly, Mn in the peat. The nutrient gradient, as defined by pore water concentrations of N and P, was largely independent of the acidity-alkalinity gradient: NO3− and PO43− had similar concentrations throughout the gradient, whereas NH4+ concentrations increased with increasing pore-water pH. In contrast, the peat nutrient gradient coincided with the acidity-alkalinity gradient, with total concentrations of N and P decreasing from the margin to the centre. Bryophytes and vascular plants had different responses along the acidity-alkalinity gradient and the nutrient gradient. Bryophyte distribution reflected the acidity-alkalinity gradient both in pore water and in peat. Vascular plant distribution was mainly influenced by variations in nutrient availability. Nomenclature: Pignatti (1982) for vascular plants; Frahm & Frey (1987) for bryophytes.

Climatic modifiers of the response to nitrogen deposition in peat-forming Sphagnum mosses: a meta-analysis

Peatlands in the northern hemisphere have accumulated more atmospheric carbon (C) during the Holocene than any other terrestrial ecosystem, making peatlands long-term C sinks of global importance. Projected increases in nitrogen (N) deposition and temperature make future accumulation rates uncertain. Here, we assessed the impact of N deposition on peatland C sequestration potential by investigating the effects of experimental N addition on Sphagnum moss. We employed meta-regressions to the results of 107 field experiments, accounting for sampling dependence in the data. We found that high N loading (comprising N application rate, experiment duration, background N deposition) depressed Sphagnum production relative to untreated controls. The interactive effects of presence of competitive vascular plants and high tissue N concentrations indicated intensified biotic interactions and altered nutrient stochiometry as mechanisms underlying the detrimental N effects. Importantly, a higher summer temperature (mean for July) and increased annual precipitation intensified the negative effects of N. The temperature effect was comparable to an experimental application of almost 4 g N m(-2)  yr(-1) for each 1°C increase. Our results indicate that current rates of N deposition in a warmer environment will strongly inhibit C sequestration by Sphagnum-dominated vegetation.

The Growth Dynamics of Sphagnum Based on Field Measurements in a Temperate Bog and on Laboratory Cultures

1 Linear elongation and dry-matter production of three Sphagnum species (S. capillifolium, S. magellanicum and S. fallax) were measured during three consecutive growing seasons at a nutrient-poor mire in the southern Alps of Italy. The growth data were subjected to path analysis, in which climatic parameters, distance to water table and photoperiod were employed as independent variables in the regressions. 2 Individuals of all three species were also cultured in the laboratory under different combinations of photoperiod x photon flux density x night temperature. The resulting growth data were compared by two-way ANOVA. 3 Long-day photoperiod promoted growth of all species. Induction of dormancy required both short-day photoperiod and low night temperature. 4 Mean temperature had a positive effect on growth of both S. capillifolium and S. magellanicum. Growth of S. fallax, a species which is more prone to desiccation in dry periods, was more affected by water-table depth. 5 The periodic pattern of dry-matter accumulation in Sphagnum is controlled partly by an as yet unknown internal rhythm based on photoperiod, and partly by external factors related to climate. However, the response of Sphagnum to environment differs between species and is reflected in the competitive equilibria between species that are adapted to different microhabitats. Hollow species are usually more productive than hummock species in wet periods but this ratio often reverses in dry periods.

Element concentrations in the forest moss Hylocomium splendens: variation associated with altitude, net primary production and soil chemistry

Net primary production (NPP) of the forest moss Hylocomium splendens increased significantly along an elevational gradient in the southern Alps of Italy. Extracellularly bound metals (Al, Ca, Co, Cr, Fe, Ni, Mo, Ni, Pb) showed declining concentrations in moss tissue with increasing altitude, presumably because the amount of exchange sites on the cell wall increases less than total biomass. Concentrations of intracellular elements did not vary (Cd, Cu, Mg, Na, Zn), or even increased (K) with altitude. The observed patterns were always independent of precipitation amount and soil concentrations of exchangeable elements. A higher soil nutrient status only enhanced K uptake by the moss. We concluded that variations in moss NPP, associated with elevational gradients, may significantly affect estimates of atmospheric deposition based on moss analysis in mountainous regions.

Multiple gradients in mire vegetation: a comparison of a Swedish and an Italian bog

The major environmental gradients underlying plant species distribution were outlined in two climatically and bio-geographically contrasting mires: a Swedish bog in the boreo-nemoral zone, and an Italian bog in the south-eastern Alps. Data on mire morphology, surface hydrology, floristic composition, peat chemistry and pore-water chemistry were collected along transects from the mire margin (i.e., the outer portion of the mire in contact with the surrounding mineral soil) towards the mire expanse (i.e., the inner portion of the mire). The delimitation and the extent of the minerotrophic mire margin were related to the steepness of the lateral mire slope which, in turns, controls the direction of surface water flow. The mineral soil water limit was mirrored in geochemical variables such as pH, alkalinity, Ca2+, Mg2+, Al3+, Mn2+, and SiO2 concentrations in pore-water, as well as Ca, Al, Fe, N and P contents in surface peat. Depending on regional requirements of plant species, different species were useful as fen limit indicators at the two sites. The main environmental factors affecting distribution of habitat types and plant species in the two mires were the acidity-alkalinity gradient, and the gradient in depth to the water table. The mire margin – mire expanse gradient corresponds to a complex gradient mainly reflected in a differentiation of vegetation structure in relation to the aeration of the peat substrate.

Reed (Phragmites australis) decline in a brackish wetland in Italy

A comparative field study was carried out at two sites (a healthy site and a declining site) in a brackish wetland in northern Italy, with the objective to investigate the symptoms and the possible causes leading to reed (Phragmites australis) decline in this area. The declining reed plants presented many of the symptoms (clumping habit, smaller size, weaker culms, abnormal rhizome and root anatomy, low starch levels in rhizomes) comprised within the so-called reed die-back syndrome, frequently observed in central European wetlands but never recorded previously in (Sub)Mediterranean regions. Soil nutrient levels did not differ much between the two sites, with nitrate concentrations in the soil being even higher at the healthy site (1.54 microg g(-1); die-back site 0.76 microg g(-1)). Hence, eutrophication did not seem to represent a major cause in determining reed decline in this area. High sulphate concentrations in saltwater associated with low soil redox potentials (-215 mV) due to waterlogging resulted in high soil sulphide concentrations. Concentrations of organic acids, especially acetic acid, did not differ remarkably between sites. High sulphide levels presumably accounted for abnormal anatomical formations (callus blocking aerenchyma channels), lower rates of net CO2 exchange and reduced reserve storage, observed at the die-back site. This was associated with a lower mechanical resistance of reed culms which accelerated reed mortality in the die-back areas. We concluded that high sulpihde levels in permanently waterlogged soils may result in die-back of reed stands in Mediterranean wetlands.