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The information about the impacts of thinning on the availability of micro-nutrients, as well as macro-nutrients other than N, P and K, is still scarce. We assessed the changes in the concentrations of 12 elements (Al, B, Ca, Cu, Fe, K, Mg, Mn, N, Na, P and Zn) with needle age (current year or 1-year-old) and three early thinning treatments in two of the most widely distributed pines in SW Europe: P. pinaster and P. radiata. Four treatments were setup in triplicate: control (C), light thinning (LT), heavy thinning (HT) and selection thinning of dominant trees (ST), with 0%, 10%, 20% and 20% of total basal area removed, respectively. Needle δ15N varied little with needle age and most thinning treatments in both species, but ST triggered an increase of N in P. pinaster needles. Needle Ca and Na increased with age, but were unaffected by treatment. Foliar K, Zn and Cu decreased with age in both species and increased with ST only in P. pinaster. Jointly considering all treatments, there was no needle age effect on Mn concentration, neither in P. radiata nor in P. pinaster, but in the latter species Mn levels increased with age in the selection thinning plots. There were significant thinning effects on Mn levels in both P. pinaster (ST>C) and P. radiata (HT > LT, ST). Foliar Fe and Al concentration increased with age in both pines; the former increased with ST only in P. pinaster while the latter was affected by thinning only in current year needles and without a clear tendency. Neither age nor treatment effects on needle Mg and B were found, while for P needle age had a significant effect only in P. pinaster.

In NW of the Iberian Peninsula, the incidence of anthropogenic fires is very high and, due to the climatologic and topographical conditions, burnt soils are prone to high erosion risks. In recent years several environmental management techniques (BAER: burnt area emergency response) have been applied after some wildfires, but there are still few field studies about their effects on soils (the foundations of terrestrial ecosystems) and most of them are short-term. Aiming to fill this gap of knowledge, sixteen properties useful as soil quality indices (pH, WHC, total N, δ 15 N, NH 4 + -N, NO 3 - -N, and NH 4 Ac-DTPA extractable Na, K, Ca, Mg, P, Al, Fe, Mn, Cu and Zn) were studied four years after BAER application in a severely burnt area in the 0-2 and 2-5 cm depth layers of unburnt soil (US), burnt soil untreated (BS), and burnt soil treated with two BAERs techniques: rye seeding (BSS) and straw mulching (BSM). The effects of fire on soil WHC, total N, Mg, Na, P, Zn, NO 3 - -N, Cu and K were mitigated in both BSS and BSM, but especially in the latter. The highest values for Ca and Mn were recorded in BSM. The BAER treatments affect NO 3 - -N, Cu and K only in the top layer, but no clear effects were found for soil pH, δ 15 N, NH 4 + -N, Al and Fe. Soil samples were quite similarly grouped by the hierarchical cluster and the principal component analyses (PCA): a) 0-2 cm layers of US plots; b) 0-2 cm layers of BSM plots; c) 2-5 cm layers of US plots; d) most of top layers of BS and BSS plots; and e) most of the 2-5 cm layers of BS, BSM and BSS plots. The distribution of soil samples in the PCA showed that straw mulching and, to a lesser extent, rye seeding reduced the distance between burnt and unburnt topsoil along Factor 1, but not along Factor 2 (explaining 56% and 29% of the variance, respectively). Consequently, these BAER treatments mitigated, but not wiped out, the effects of fire on soil quality after four years., Competing Interests: Declaration of competing interest None., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The Umia-Grove Intertidal Complex is located within the Ria of Arousa (NW Iberian Peninsula). Out of its significance for wintering shorebirds it has been included in the Ramsar List of Wetlands of International Importance as well as in international protection networks such as the European Natura 2000 and Important Bird and Biodiversity Areas-BirdLife International. In a sediment analysis conducted in the year 1999, the wetland was found to have been contaminated by potentially toxic trace metals, to wit: Cr, Cu, Ni, and Pb. Sediment samples retrieved in 2014 to make an updated assessment of the condition of the ecosystem showed evidence of the presence of selected trace elements, namely, Cd, Co, Cr, Cu, Ni, Pb, and Zn, within or slightly above the background ranges of local, regional, and general references. In the 15-year time frame between the two samplings there has been noticeable change in the relationship between nature and society as a consequence of the entry into force of a number of regulations aimed at avoiding the emission of contaminants; among others, the ban of Pb in gasoline, the deployment of wastewater treatment plants according to the European Water Framework Directive, and the limitation of the use of Cu pesticides. With the ensuing drop of human pressure, the self-purifying capacity of the ecosystem has effectively contributed to the wetland's recovery. Nevertheless, the application of a normalized enrichment factor to the more recent set of samples suggests the presence of relict low contamination by Cd, Cu, and Ni in localized areas. The compared analysis of the wetland condition in the two years is a sign of the success of the policies and regulations for environmental protection, but further work and more effectiveness are necessary in order to preserve threatened ecosystems of such importance as the Umia-Grove wetland., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The effects of alien plants on whole nutrient cycles have been scarcely studied, despite the increasing evidence on their impact on nutrient pools and fluxes. Carpobrotus edulis, a dangerous invasive plant in coastal areas worldwide, is considered an ecosystems engineer which, by changing many soil properties, benefits its own invasion and hampers the restoration of the invaded habitats. To study, for the first time, the 'true' impact of C. edulis on the soil N cycle, we used a paired 15 N labelling experiment and a Ntrace compartment model to estimate the gross N fluxes in the 0-5cm and 5-10cm soil layers of non-invaded and C. edulis invaded areas of two temperate-humid coastal rocky locations. Carpobrotus edulis invasion generally increased NH 4 + immobilization (I NH4 , 1.19-4.48×), presumably due to a lower N availability for the microbiota. The invasion also decreased autotrophic nitrification (O NH4, 0.20-0.79×), either by a direct effect over soil microbiota or by the acidification triggered by C. edulis. Unexpectedly, the dissimilatory nitrate reduction (D NRA ) was the exclusive NO 3 - consuming process modelled on most of the studied soils, although the incubation was aerobic. Apparently, the high organic C content of these soils induced a higher O 2 consumption and the formation of anaerobic microsites where the D NRA could have taken place. The lower NO 3 - availability of invaded soils could explain their lower D NRA rates (0.04-0.70×) compared to native soils. Both D NRA and O NH4 were more affected in the 0-5cm layer, but the invasion also significantly affected N rates in the 5-10cm layer. Overall, net nitrification and mineralization generally decreased in the invaded soils. This study shows that the invasion of C. edulis alters soil gross and net N fluxes in a 0-10cm depth through its effects on soil properties and microbiota., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The study addresses a knowledge-gap in the long-term ecological consequences of fire and fire-fighting chemicals. Ten years after a prescribed fire and the application of three fire-fighting chemicals, their effects on the soil-plant system were evaluated. Five treatments were established: unburnt soils (US) and burnt soils treated with water alone (BS), foaming agent (BS+Fo), Firesorb (BS+Fi) and ammonium polyphosphate (BS+Ap). Soils (0-2 cm depth) and foliar material of shrubs (Erica umbellata, Pterospartum tridentatum and Ulex micranthus) and trees (Pinus pinaster) were analysed for total N, δ(15)N, and soil-available and plant total macronutrients and trace elements. Soil pH, NH₄(+)-N and NO₃(-)-N; pine basal diameter and height; and shrub cover and height were also measured. Compared with US plots, burnt soils had less nitrates and more Mo. Although differences were not always significant, BS+Ap had the highest levels of soil available P, Na and Al. Plants from BS+Ap plots had higher values of δ(15)N (P. pinaster and E. umbellata), P (all species), Na (P. tridentatum and U. micranthus) and Mg (E. umbellata and P. tridentatum) than other treatments; while K in plants from BS+Ap plots was the highest among treatments for P. pinaster and the lowest for the shrubs. Pines in US plots were higher and wider than in burnt treatments, except for BS+Ap, where the tallest and widest trees were found, although half of them were either dead (the second highest mortality after BS+Fi) or had a distorted trunk. BS+Ap was the treatment with strongest effects on plants, showing E. umbellata the lowest coverage and height, P. tridentatum the highest coverage, U. micranthus one of the lowest coverages and being the only treatment where Genista triacanthos was absent. Consequently, it is concluded that both fire and ammonium polyphosphate application had significant effects on the soil-plant system after 10 years., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In NW Spain, a European region with very high fire incidence and erosion risks, the effects on soils of a medium-to-high severity wildfire and two emergency stabilization techniques were studied. In burned plots (control, BS; seeded with cereal, BSS; straw mulched, BSM) and adjacent unburned plots (US), the topsoil (0-2 cm) pH and thirteen NH4Ac-DTPA extractable elements were evaluated at t = 0, 4, 8 and 12 months after the fire. Compared to US, fire increased by 0.3-0.5 units the soil pH which decrease slowly over time, but remaining significantly higher at t = 12 (BS, BSM, BSS>US). Ammonium nitrogen (N) levels were higher (p<0.05) in burned plots than in US, difference decreasing progressively from 48-fold (t = 0) to 25-fold (t = 12). Although no significant effect of fire was immediately observed, the extractable sodium (Na) and potassium (K) were higher (p<0.05) in burned plots than in US at t = 4 and t = 8, probably due to cation leaching from the overlying ash. Fire did not modify the extractable magnesium (Mg), but at t = 0 the extractable calcium (Ca) and phosphorous (P) were transiently and significantly higher in burned plots than in US. Extractable aluminum (Al), iron (Fe), copper (Cu), cobalt (Co) and zinc (Zn) were lower and manganese (Mn) was higher in burned plots than in US. Neither seeding nor mulching significantly modified the topsoil concentrations of the elements considered. The PCA revealed that BS, BSM and BSS became more similar to US over the study period due to a rapid decrease in extractable Ca and Mg and a slow decrease in extractable Mn and NH4(+)-N. At t = 12, the most notable differences between burned plots and US were in the concentrations of extractable Al and Zn. Data suggest that at least another 4-8 months will be required for full recovery of the burned plots to unburned conditions., (Copyright © 2014 Elsevier B.V. All rights reserved.)

A pot experiment was used to assess N uptake by pine seedlings during 2 years on a burnt soil to which was added (15)N-labelled ryegrass, obtained from a (15)N-enriched sample of this soil after a fire. The nitrogen concentration in needles, stems and roots of seedlings decreased significantly from the first to the second growing period (from 2.55, 1.30 and 2.19% to 1.19, 0.47 and 1.00%, respectively), with needles accounting for 53-58% of the pine-N. At the end of the experiment, 98.87 +/- 1.12% of the added ryegrass-(15)N was recovered: two-thirds in the soil organic N pool and one-third in the pine seedlings. Therefore, the post-fire pulse of inorganic-N, which was successfully kept in the burnt soil-plant system through its uptake by the pioneer species, is available for trees in the medium term. Pine seedlings assimilated 16.4% and 16.9% of the added ryegrass-(15)N in the first and second year, respectively. This result contrasts with the usual yearly decrease of added N uptake by plants; a possible explanation is the transient increase of available N in burnt soils that would have modified the mineralization pattern of the (15)N-labelled phytomass. The pine-N derived from the ryegrass-N decreased from 4.05% in the first year to 2.53% in the second one, with 3.10% being the 2-year weighed average. In addition to the direct contribution of ryegrass to pine-N nutrition reflected by these figures, the rapid post-fire establishment of a herbaceous cover on the burnt soil also provides important indirect benefits for tree nutrition by reducing organic- and inorganic-N losses., (Copyright (c) 2008 John Wiley & Sons, Ltd.)

The impact of three fire fighting chemicals (FFC) on 11 chemical soil properties and on soil recovery (0-2 cm depth) was evaluated 1, 30, 90 and 365 days after a prescribed fire. Five treatments were considered: unburnt soil (US) and burnt soil with 2 l m(-2) of water alone (BS) or mixed with the foaming agent Auxquímica RFC-88 at 1% (BS+Fo), Firesorb at 1.5% (BS+Fi) and FR Cross ammonium polyphosphate at 20% (BS+Ap). At t=1 day, soil pH increases in the order US

Soil CO2 effluxes from recently added 13C-labeled phytomass versus endogenous soil organic matter (SOM) were studied in an acid soil from Atlantic pine forests (NW Spain). After several cultures to incorporate fresh 13C-enriched Lolium perenne to a Humic Cambisol with predominance of humus--Al over humus--Fe complexes, potential soil C mineralization was determined by laboratory aerobic incubation (84 days). Isotopic 13C analyses of SOM fractions were assessed to know in which organic compartments the 13C was preferentially incorporated. Although in the 13C-labeled soil the C mineralization coefficient totalized less than 3% of soil C, the 13C mineralization coefficient exceeded 14%, indicating a greater lability of the newly incorporated organic matter. Organic compounds coming from added phytomass showed a higher lability and contributed considerably to the total soil CO2 effluxes (52% of total soil CO2 evolved during the first decomposition stages and 27% at the end), even though added-C comprised less than 4% of total soil C. Good determination coefficients, when values of CO2--C released were fitted to a first-order double exponential kinetic model, support the existence of two C pools of different lability. Kinetic parameters obtained with this model indicated that phytomass addition augmented the biodegradability of the labile pool (instantaneous mineralization rate k increased from 0.07 d(-1) to 0.12 d(-1)) but diminished that of the recalcitrant pool (instantaneous mineralization rate h decreased from 2.7 x 10(-4) d(-1) to 1.6 x 10(-4) d(-1)). Consequently, the differentiation between both SOM pools increased, showing the importance of SOM quality on CO2 emissions from this kind of soil to the atmosphere.

Pine forest plantations of Pinus pinaster Ait. and P. sylvestris L. located in Galicia, NW Spain, were selected to study the 13C/12C-isotopic fingerprint in wood core samples in order to find possible relationships between the delta(13)C at natural abundance levels and the quality of the standing tree mass. For each pine species, 24 forests growing on acidic soils were studied: half developed over granite and half over schists. Two dominant trees from each plot, corresponding to all possible combinations of forest stands with high or low site index and with adults or young trees, were drilled at the basal part of trunks using a Pressler drill to obtain tree ring samples. The C-isotopic compositions of the litter and the soil organic matter from different soil depths were also determined and statistically significant correlations between these values and the 13C content of the wood were observed. Despite internal variations due to the influence of site index, tree age and parent material, the isotopic fingerprint of P. pinaster wood (mean value delta13C=-26.2+/-0.8 per thousand) significantly differed (P<0.001) from that of P. sylvestris (mean value delta13C=-24.6+/-0.7 per thousand). Relationships between the quality of the stand and the C-isotopic composition of the wood were observed, high quality stands having trees more 13C-depleted than low quality ones. A high correlation between wood delta13C and site index values for P. pinaster stands (r=-0.667, P<0.001) was found, this correlation being even clearer when only P. pinaster growing over schists (r=-0.833, P<0.001) are considered. Again, the correlation between the site index and the wood delta13C of young P. pinaster trees is higher when plots over granite or schists are separately considered. A similar fact occurs for adult P. sylvestris trees from schists stands, high quality specimens being 13C-depleted compared with low quality ones. On the other hand, 13C natural abundance of wood from P. sylvestris trees seems to be also strongly influenced by the underlying parent material, young trees from granite stands having a statistically higher 13C-isotopic composition (P<0.05) than young trees from schists stands., (Copyright (c) 2005 John Wiley & Sons, Ltd.)

Soil organic matter (SOM) transformations caused by heating were analyzed using the stable carbon isotope (13)C as a tracer to follow C mineralization dynamics and C transfers between different organic compartments. A (13)C-labelled soil, obtained by incorporation of (13)C-enriched Lolium perenne phytomass into a pine forest soil, was heated for 10 min at 385 degrees C to reproduce conditions typical of a forest fire and changes in total C content, potential C mineralization activity and C distribution between the different soil organic fractions were determined. Changes caused by heating on the potential soil C mineralization, determined by laboratory aerobic incubation, reveal alterations to the SOM biodegradability; some stabilized SOM showed an increase in biodegradability, whereas less stabilized SOM became more resistant to microorganisms. Chemical fractionations of SOM allowed us to monitor changes in its composition. As a consequence of heating, the less polymerized humic fractions were the most strongly affected, with the total disappearance of fulvic acids. A significant increase in the quantity and degree of polymerization of the humic acids at the expense of other more (13)C-enriched substances was also found. Finally, a large decrease in humin was observed, its solubilizable part disappearing completely, probably as a consequence of the incorporation of the byproducts into the free organic matter fraction., (Copyright 2004 John Wiley & Sons, Ltd.)