Amalia Virzo De Santo

Effects of urban heavy metal pollution on organic matter decomposition in quercus ilex L. woods

Decomposition of oak (Quercus ilex) leaves containing different concentrations of Fe, Zn, Cu, Cr, Ni and Pb was measured in laboratory microcosms. The leaves were collected from a polluted site inside the city of Naples and from a control site away from the city. Soil was sampled from the upper A horizon (0–5 cm) at both sites and analyzed for respiration, microbial biomass and abundance of fungal mycelia. The soils from the two sites differed significantly in heavy metals concentrations. The accumulated mass loss reached an asymptotic value after four months both for the control and polluted litters. However, control and polluted litters significantly differed in accumulated mass loss, that was respectively 40 % and 29 % of the initial weight, after 10 months. Moreover decomposition rates appeared to be strongly influenced by metal contamination in the early stages, while in later stages, they did not differ significantly. Litter respiration appeared to be inhibited by metal contamination and showed pattern and rates consistent with those found for litter decomposition. Fungal mycelia were significantly less abundant both in litter and soil from the polluted site than from the control site. Metabolic activity (both as soil respiration and degree of mineralization) was lower in the polluted soil. Soil respiration and amount of soil mycelia correlated negatively with soil Pb, Zn and Cr concentration.

Factors regulating early-stage decomposition of needle litters in five different coniferous forests

The decomposition dynamics of needle litter of Stone pine (Pinus pinea), Corsican pine (Pinus laricio), Scots pine (Pinus sylvestris) and Silver fir (Abies alba) were investigated in a comparative study including five coniferous forest sites. Initial chemical composition, mass-loss rates, and the water-holding capacities of the litters were determined in the early stages of decomposition. Water-holding capacity differed among the fresh litters but increased in linear proportion to litter mass both over each species and over all species combined in a linear regression (r = 0.708; n = 45; P < 0.001). At the early decomposition stages the daily mass-loss rate of Scots pine needles in two dry sites was positively related to (1) the measured litter water content at sampling (r = 0.727; n = 16; P < 0.0025), (2) mean daily precipitation in the period of measurement (r =0.909; n = 16; P < 0.0001). These models could explain water as a rate-limiting factor to the extent of 49 and 81% respectively. A significant linear relationship was also found between decay rate during a moist period and accumulated mass loss (r = 0.771; n = 8; P < 0.05) which has been suggested to be due to the increase of litter water-holding capacity with increasing accumulated mass loss. Three types of decay curve are described and the pattern of decomposition at dry sites has been found to be influenced by moisture variations more than by litter quality.

Decomposition of litter and soil organic matter—can we distinguish a mechanism for soil organic matter buildup?

This synthesis paper presents a model for estimating the buildup of soil organic matter in various types of coniferous forests. The knowledge used was obtained from a well‐studied forest with good Iitterfall data, decomposition information and validation measurements of the soil organic matter layer. By constructing a simple model for litterfall, and the information on maximum decomposition levels for litter, we could estimate the annual increase in soil organic matter and extend this to encompass stand age. The validation measurement and the estimated amount of soil organic matter differed by about 8 or 26% over a 120‐yr period, depending on the litterfall model. The estimated increased storage of soil organic matter as a consequence of climate change was found to be drastic. We thus found that the soil organic matter layer would grow about four times as fast as a result of the needle component only. This estimate was based on a comparison between latitudes with a difference of 17°.

Changes in chemical composition of Pinus sylvestris needle litter during decomposition along a European coniferous forest climatic transect.

The objective of this investigation was to assess the changes in chemical composition (lignin, cellulose, hemicelluloses, non-structural compounds, N, and ash) of decomposing litter. Standard Pinus sylvestris needle litter, originating from southern Sweden, was incubated in litterbags at 15 sites selected from the Netherlands to south Spain. The changes in chemical composition of this litter were determined using near infrared reflectance spectroscopy. The hypothesis was that standard (chemically uniform) litter decomposing under a range of climates would show different dynamics of accumulation and loss of C-fractions, N, and ash, relative to mass loss. It was shown that, for a given mass-loss value (10, 20, 30, 40, or 50%), the proportion of lignin, cellulose, hemicelluloses, non-structural compounds, N, and ash in the decomposing pine needles differed between sites. Lignin concentration in the litter residue at 50% mass loss ranged from approximately 26 to 43%, cellulose from 19 to 27%, hemicelluloses from 7 to 11%, non-structural compounds from 19 to 25%, N from 0.7 to 1.3%, and ash content from 1.4 to 10.1%. Lignin concentrations showed the highest range of variation. Lignin concentrations during decomposition were positively related to moisture factors as significant correlations were found with actual evapotranspiration and were improved in multiple regressions by the mean annual precipitation or the water surplus. Cellulose was degraded further at sites with high precipitation whereas hemicellulose degradation was related to temperature. This leads to the conclusion that the remaining organic matter produced by standard litter decomposition within the studied climatic range of variations tended to be more recalcitrant under wet and warm climatic conditions than under cold or dry climate.

Organic matter, nutrient content and biological activity in burned and unburned soils of a Mediterranean maquis area of southern Italy

Experimental fires were performed during the summer-drought period in a Mediterranean maquis in the Castel Volturno Nature Reserve in south-western Italy. The two different fuel loads applied (4 kg m−2 and 2 kg m−2) resulted in complete and partial combustion of the vegetation, respectively. Soil organic matter content (SOM), total and available element concentrations (K, Mg, Na, Mn, Fe, Cu, Pb, Cd), microbial carbon, respiration, metabolic quotient (qCO2), and the coefficient of endogenous mineralization (CEM) were measured at intervals in the dry and wet seasons over a period of about 3 years, in burned and adjacent unburned soils. Soil samples (0–5 cm depth) were collected under the cover of Phillyrea angustifolia L., a dominant species in the study area. Both fires induced long-lasting increases in SOM. As indicated by the increase in CEM, part of the accumulated SOM was mineralized in the first 3 months after fire whereas part of the accumulated SOM was instead stable. Both fires increased the total and available fractions of nutrients and trace elements. During the first 3 months after fire, microbial biomass and qCO2 were higher in the burned soils, which were richer in nutrients, but were characterized by harsher environmental conditions compared to unburned soils.

Functional diversity of the microbial community in Mediterranean maquis soils as affected by fires

Fire is a disturbance in the Mediterranean region associated with frequent drought periods, and can affect the soil microbial community, which plays a fundamental role in nutrient cycling. In the present study the effect of low- and high-severity experimental fires on the soil microbial community was evaluated in an Italian Mediterranean maquis. Burned and unburned soils were compared for functional diversity, specific activities, microbial biomass, fungal mycelia and fungal fraction of microbial carbon, during the first year after fire. In the first week after fire, changes in the functional diversity were observed in burned soils, differing also between low- and high-severity fires. Respiration responses to specific organic compounds were generally lower in burned soils during the whole study period, with a percentage of changed responses from 2 to 70%. The general reduction in burned soils of the fungal fraction of microbial carbon (19–61%) and active mycelia (16–55%), together with the increase in microbial biomass carbon (29–42%) during the first 3 months after fire, suggest a larger and longer effect of fire on fungi than on bacteria. The results indicate a rapid recovery of functional diversity in soil after burning despite the persistent reduction of microbial community activity and the change in its structure.

Non-additive effects of litter mixtures on decomposition of leaf litters in a Mediterranean maquis

Many studies across a range of ecosystems have shown that decomposition in mixed litter is not predictable from single-species results due to synergistic or antagonistic interactions. Some studies also reveal that species composition and relative abundance may be more important than just richness in driving non-additive effects. Most studies on litter decomposition in Mediterranean maquis, an high-diversity shrubby ecosystem, have dealt exclusively with single species. In this study we investigated, at the individual-litter level, as well as at the litter-mixture level, the effect of litter mixing on decomposition of 3-species litter assemblages with different relative abundance of the component litters; we set up two types of litter assemblages that reflected the heterogeneity of bush cover in the inner maquis and at the edge maquis/gaps, as related to the leaf traits, i.e. sclerophylly vs mesophylly. We measured mass loss, decay of lignin, cellulose and ADSS (acid detergent soluble substances) and fungal mycelium ingrowth. The results show that over a 403-day incubation period, the decomposition of individual litters in mixtures deviated from that of monospecific litters and had different directions. In litter mixtures of the sclerophylls Phillyrea angustifolia and Pistacea lentiscus with the mesophyll Cistus, decomposition was lower than expected (antagonistic effect); in the mixtures of litters with similar physical structure (Ph. angustifolia and P. lentiscus with Quercus ilex) decomposition was faster than expected (synergistic effect). When considering the different decomposition phases, both negative and positive effects occurred in Quercus mixtures depending on the phase of decomposition. In both types of 3-species litter assemblages the greatest effect occurred in uneven mixtures rather than in even mixtures. Our results show that species composition drives the direction whilst the decomposability and the relative abundance drive the magnitude of non-additive effects of litter mixing on decomposition.

Lignin decomposition in decaying leaves of Fagus sylvatica L. and needles of Abies alba Mill

Abstract Lignin decomposition in litter of beech leaves and fir needles as related to litter N concentration and litter mass loss was studied for 7 y in two forests at Mount Taburno (41°05′N., 12°07′E.; Campania Apennines). Both types of litter showed a pattern of decomposition characterized by two stages with significantly decreasing decomposition rates. Litter N concentration did not appear to influence the rate of litter decomposition in either the early or the late stage of the process. On the contrary mass loss rates of litter were influenced by lignin concentrations at the beginning of the late stage: the lower the lignin concentration the higher was mass loss rate. Both in beech and fir litter lignin degradation started immediately during incubation. Lignin degradation throughout the study was less in fir needles than in beech leaves with lignin losses of 60–67% and 73–87% of initial amount, respectively. Both in beech and fir litter, lignin loss rate was negatively correlated to the initial N concentration. Lignin loss rate of both beech and fir litter was correlated to litter mass loss rate during the early as well as during the late phase of decomposition. Different dynamics of lignin decomposition between the two species were observed with a higher lignin decomposition rate in the early stage than in the late stage in beech litter, and rates of lignin decomposition increasing from early to late phase in fir litter.

Fungal mycelium and decomposition of needle litter in three contrasting coniferous forests

The fungal mycelium ingrowth and the rates of mass loss and respiration of needle litter of Pinus pinea, Pinus laricio, Pinus sylvestris, and Abies alba were investigated, in three coniferous forests, over a 3-year period by means of a composite set of incubations. In the early stages, the fungal flora of the decomposing needles was dominated by dematiaceous hyphomycetes and coelomycetes. Basidiomycetes reached a peak after 6 months on pine needles, but were absent from the N-rich needles of A. alba. Soil fungi (Penicillium, Trichoderma, Absidia, Mucor sp. pl.) became most frequent in later stages. At the end of the study period, the total mycelium amount showed the lowest values in all pine needles incubated in the P. laricio forest and the highest ones in P. pinea needles incubated in the P. pinea forest. In all data sets, as in data for boreal forests examined for comparison, the concentration of litter fungal mycelium versus litter mass loss followed a common exponential model. However, in later stages, the amount of litter fungal mycelium was very close to that of the humus at the incubation site, thus supporting the hypothesis of a logistic growth pattern. Respiration rates of decomposing litters varied with season and decreased with litter age to values close to those of the humus at the incubation site. Respiration of water-saturated litter was negatively correlated with the total mycelium concentration, and this was consistent with the observation that in far-decomposed litter only a minor fraction of the total mycelium is alive.

Impact of the invasive tree black locust on soil properties of Mediterranean stone pine-holm oak forests

Background and aimsInvasion by N2-fixing species may alter biogeochemical processes. We hypothesized that the grade of invasion by the N2-fixer black locust (Robinia pseudoacacia L.) could be related to the distribution and pools of carbon (C) and nitrogen (N) along the profile of two Mediterranean mixed forests of stone pine (Pinus pinea L.) and holm oak (Quercus ilex L.).MethodsA low-invaded (LIN) and a high-invaded (HIN) mixed forest were studied. We assessed: N concentration in green and in senescent leaves; C and N pools along the soil profile; seasonal changes of soluble C and N fractions, and microbial activity.ResultsCompared to coexisting holm oak and stone pine, black locust had higher N content in green and in senescent leaves. In the mineral soil: N stocks were similar in LIN and HIN; water soluble C and microbial activity, were lower in HIN compared to LIN; water soluble N showed seasonal changes consistent with tree growth activity in both HIN and LIN. In the organic layer of HIN, C and N stocks were about twofold larger than expected on the basis of stand density.ConclusionBlack locust increased C and N stocks in the upper organic layers that are more vulnerable to disturbance. However, it did not increase N stocks in the mineral soil.