RESUMEN
Deadwood decomposition is a complex and dynamic process with large implications for biogeochemical cycling of carbon (C) and nitrogen (N) in forest soil and litter. Moreover, it affects functional and structural diversity of fungal and bacterial communities in these components. Mesocosms with deadwood blocks at progressive decay classes were set in a black pine forest and incubated for 28 months in the field with the aim to assess the impact of deadwood decomposition on i) CO2, CH4 and N2O fluxes; ii) C and N pools and allocation among deadwood, litter and soil; iii) the fungal and bacterial structural diversity and activity. CO2, CH4 and N2O fluxes from deadwood were monitored throughout the field incubation; deadwood biomass loss and decay rate for each decay class were calculated. The stock of C and N, enzyme activities, fungal and bacterial communities in deadwood, litter fractions (fresh, fragmented and humified) and soil at two depths were measured. Emissions of CO2 and CH4 increased over the deadwood decomposition advancement and the decay reached the maximum rates in the last decomposition classes. N2O fluxes were low and showed either production (prevalent in the first year) or consumption. Independent of the decay class, 20% of C stored in deadwood was lost as CO2 in the atmosphere, whereas 32% was transferred to the fragmented and humified litter fractions in the last decay class. A corresponding increase of cellulose and hemicellulose degrading enzymes was found in deadwood, also favored by substrates accessibility through fragmentation and successional changes in fungal and bacterial communities. Deadwood, litter fractions and soil components were clearly distinguished in terms of chemical and microbiological properties and activities. Fragmented and humified litter fractions were the only components responsive to the advanced stage of deadwood decomposition, being directly affected by the physical redistribution of fragmented organic matter.
Asunto(s)
Pinus , Suelo , Biomasa , Ecosistema , Bosques , Microbiología del SueloRESUMEN
This multidisciplinary research work evaluated the effects of soil erosion on grape yield and quality and on different soil functions, namely water and nutrient supply, carbon sequestration, organic matter recycling, and soil biodiversity, with the aim to understand the causes of soil malfunctioning and work out a proper strategy of soil remediation. Degraded areas in nineteen organically farmed European and Turkish vineyards resulted in producing significantly lower amounts of grapes and excessive concentrations of sugar. Plants suffered from decreased water nutrition, due to shallower rooting depth, compaction, and reduced available water capacity, lower chemical fertility, as total nitrogen and cation exchange capacity, and higher concentration of carbonates. Carbon storage and organic matter recycling were also depressed. The general trend of soil enzyme activity mainly followed organic matter stock. Specific enzymatic activities suggested that in degraded soils, alongside a general slowdown in organic matter cycling, there was a greater reduction in decomposition capacity of the most recalcitrant forms. The abundance of Acari Oribatida and Collembola resulted the most sensitive indicator of soil degradation among the considered microarthropods. No clear difference in overall microbial richness and evenness were observed. All indices were relatively high and indicative of rich occurrence of many and rare microbial species. Dice cluster analyses indicated slight qualitative differences in Eubacterial and fungal community compositions in rhizosphere soil and roots in degraded soils. This multidisciplinary study indicates that the loss of soil fertility caused by excessive earth movement before planting, or accelerated erosion, mainly affects water nutrition and chemical fertility. Biological soil fertility is also reduced, in particular the ability of biota to decompose organic matter, while biodiversity is less affected, probably because of the organic management. Therefore, the restoration of the eroded soils requires site-specific and intensive treatments, including accurately chosen organic matrices for fertilization, privileging the most easily decomposable. Restoring soil fertility in depth, however, remain an open question, which needs further investigation.
Asunto(s)
Biodiversidad , Ecosistema , Microbiología del Suelo , Carbono , Granjas , Nitrógeno , SueloRESUMEN
Acacia dealbata Link (Fabaceae) is one of the most invasive species in the Mediterranean ecosystems of Europe, Africa and America, where it has been proved to exert strong effects on soil and plant communities. In Italy A. dealbata has been largely used for ornamental and forestry purpose and is nowadays spreading in several areas. The present study was addressed to evaluate the impacts on soil chemical properties, soil microbial communities and understory plant communities and to assess the relationships among these compartments after the invasion of A. dealbata in a typical Mediterranean shrubland. Towards these aims, a soil and vegetation sampling was performed in Elba Island where A. dealbata is invading the sclerophyllous native vegetation. Three levels of invasion status were differentiated according to the gradient from invaded, to transitional and non-invaded vegetation. Quantitative and qualitative alterations of soil chemical properties and microbial communities (i.e. bacterial and fungal communities) and above-ground understory plant communities were found. In particular, the invaded soils had lower pH values than both the non-invaded and transitional ones. High differences were detected for both the total N and the inorganic fraction (NH4(+) and NO3(-)) contents, which showed the ranking: invaded>transitional>non-invaded soils. TOC and C/N ratio showed respectively higher and lower values in invaded than in non-invaded soils. Total plant covers, species richness and diversity in both the non-invaded and transitional subplots were higher than those in the invaded ones. The contribution of the nitrophilous species was significantly different among the three invasion statuses, with a strong increase going from native to transitional and invaded subplots. All these data confirm that A. dealbata modifies several compartments of the invaded ecosystems, from soil chemical properties to soil and plant microbial communities determining strong changes in the local ecosystem processes.