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Purposes: The aim of this paper was to characterize elements dynamics, including resorption before leaf shedding and accumulation/release during decomposition, of two functionally different tree species, the N-fixing, broadleaf, deciduous black locust (Robinia pseudoacacia L.), and the Mediterranean black pine (Pinus nigra Arn.), planted on recent unconsolidated volcanic deposits. Methods: In two paired, 40 years old stands, we investigated the stoichiometry of thirteen elements in green leaves, newly shed leaf litter, stable litter residue and soil. Results: Black locust leaves were richer in N, P, K, Mg and Mn; black pine needles were richer in Na, Fe, Zn, Cr, and Pb. Resorption efficiency was Pb > Zn > Fe ~ N ~ Mn ~ Mg > Cd ~ K > P in black locust, and Pb ~ Cu > Zn ~ Na > Mn > K ~ Cr in black pine. Compared to black pine, black locust newly shed litter was richer in K, Na, Mn, Cu, and Ni. During decomposition, black locust leaf litter released N, K, Mg, Na, Mn, Zn, Cu and Cd, and accumulated Fe, Ni, Cr and Pb, whilst black pine needles released N, Zn and Cd, and accumulated all the other elements. Compared to black locust black pine had a stable needle litter residue richer in all elements but N, whilst the mineral soil was poorer in all elements but Pb. Conclusions: The two functionally different tree species have distinct element dynamics from leaf to far decomposed litter. Element sequestration in the stable residue of black pine litter, likely prevents their release in the mineral soil that is thus poorer in nutrients and minor elements compared to the soil of black locust. [ABSTRACT FROM AUTHOR]

Aims: In Mediterranean ecosystems fire and drought are two natural disturbances that affect plant traits and generate a highly heterogeneous landscape. The objective of this research was to analyze leaf chemistry, one important driver of carbon and nutrients cycles, and decomposition of Phillyrea angustifolia L. in a landscape affected by recurrent fire disturbance. Methods: We investigated leaf litter collected in a low-maquis at sites burned by a wildfire 10 years before the current study, at sites burned by an experimental fire 1 year before and at sites located at the edge low-maquis/gaps. Results: The three litters differed in chemical composition, mass loss and dynamics of lignin/AUR (Acid-Unhydrolizable-Residue), nitrogen and manganese. During the early decomposition phase lignin/AUR increased in litters from sites burned 1 year before and from sites located at the edge low-maquis/gaps and decreased in litter from sites burned 10 years before. Nitrogen and manganese were immobilized in litter during the early and the middle phase of decomposition. 13 C NMR spectroscopy revealed that all the litters were rich in Alkyl-C, the fraction including waxes and cutin that are effective barriers to water loss from the leaves. Litter from sites burned 1 year before had the highest hydrophobicity and aromaticity indexes and the highest alkyl ratio, and decomposed at the lowest rate. Conclusions: Differences of leaf chemical composition within the same plant species across an uneven landscape affect decomposition. The traditional approach and 13 C NMR spectroscopy complementarily explain decomposition pattern and give a comprehensive view of the individual drivers of litter decomposition. [ABSTRACT FROM AUTHOR]

Background and aims: Invasion by N-fixing species may alter biogeochemical processes. We hypothesized that the grade of invasion by the N-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.). Methods: A 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. Results: Compared 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. Conclusion: Black 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]