BUSCADOR RECOLECTA

Research Highlights: Tree decline can alter soil carbon cycling, given the close relationship between primary production and the activity of roots and soil microbes. Background and Objectives: We studied how tree decline associated to old age and accelerated by land-use change and increased drought in the last decades, affects soil properties and soil respiration (Rs). Materials and Methods: We measured Rs over two years around centennial European beech (Fagus sylvatica L.) trees representing a gradient of decline in a sub-Mediterranean forest stand, where the number of centennial beech trees has decreased by 54% in the last century. Four replicate plots were established around trees (i) with no apparent crown dieback, (ii) less than 40% crown dieback, (iii) more than 50% crown dieback, and (iv) dead. Results: Temporal variations in Rs were controlled by soil temperature (Ts) and soil water content (SWC). The increase in Rs with Ts depended on SWC. The temperature-normalized Rs exhibited a parabolic relationship with SWC, suggesting a reduced root and microbial respiration associated to drought and waterlogging. The response of Rs to SWC did not vary among tree-decline classes. However, the sensitivity of Rs to Ts was higher around vigorous trees than around those with early symptoms of decline. Spatial variations in Rs were governed by soil carbon to nitrogen ratio, which had a negative effect on Rs, and SWC during summer, when drier plots had lower Rs than wetter plots. These variations were independent of the tree vigor. The basal area of recruits, which was three times (although non-significantly) higher under declining and dead trees than under vigorous trees, had a positive effect on Rs. However, the mean Rs did not change among tree-decline classes. These results indicate that Rs and related soil physico-chemical variables are resilient to the decline and death of dominant centennial trees. Conclusions: The development of advanced regeneration as overstory beech trees decline and die contribute to the Rs homeostasis along forest succession.

Global change-driven forest succession may modify key soil processes with potentially important impacts over carbon (C) and nutrient cycling. We studied how changes in litter throughout the replacement of Pinus sylvestris by Quercus pyrenaica influence the structure and functioning of soil microbial communities and the capacity of soils to sequester C and retain nitrogen (N). We designed a microcosm experiment to simulate the chronological sequence from pine to oak forest conversion in Central Spain, using mixtures of senescent litter (oak leaves, pine needles and an equal mixture of needles:leaves) and soils (from pure oak, mixed and pure pine stands). We investigated changing patterns of soil C and N contents, microbial community structure (PLFA) and greenhouse gas fluxes (CO2, CH4, N2O) across the chronosequence. The succession from pine to oak forest was associated with substantial changes in microbial community structure and functioning. Soil-C sink capacity was reduced, although soil-N availability was enhanced. We further show how effects of secondary succession on the C cycle were mismatched with N dynamics in response to two chronologically decoupled facts. First, there was an acceleration in soil organic matter (SOM) turnover after microbial –especially bacterial– growth ceased to be so intensely inhibited by needle litter (ecotone soils), resulting in lower fungal to bacterial ratios; and second, N mineralization was stimulated once pine-derived SOM was no longer present in soils (pure oak forest soils), resulting in further acceleration of SOM turnover, suppression of CH4 consumption and an increase in gram-negative bacteria. Our findings suggest that different sensitivities of key mechanisms (SOM decomposition, N mineralization, CH4 consumption) to factors associated with succession (e.g. recalcitrance of pine SOM and allelopathic effects over bacteria) could have significant impacts on soil microbial ecology, C and nutrient cycling.

Vegetables, once harvested and stored on supermarket shelves, continue to perform
biochemical adjustments due to their modular nature and their ability to retain physiological
autonomy. They can live after being harvested. In particular, the content of some essential
nutraceuticals, such as carotenoids, can be altered in response to environmental or internal stimuli.
Therefore, in the present study, we wondered whether endogenous rhythms continue to operate
in commercial vegetables and if so, whether vegetable nutritional quality could be altered by such
cycles. Our experimental model consisted of rocket leaves entrained under light/darkness cycles
of 12/12 h over 3 days, and then we examined free-run oscillations for 2 days under continuous
light or continuous darkness, which led to chlorophyll and carotenoid oscillations in both constant
conditions. Given the importance of preserving food quality, the existence of such internal rhythms
during continuous conditions may open new research perspective in nutrition science. However,
while chromatographic techniques employed to determine pigment composition are accurate, they
are also time-consuming and expensive. Here we propose for the first time an alternative method to
estimate pigment content and the nutritional quality by the use of non-destructive and in situ optical
techniques. These results are promising for nutritional quality assessments., This work was funded by the following research grants: UPV/EHU-GV IT-1018-16 (from the Basque Government) and CTM2014-53902-C2-2-P, CGL2017-84723-P (IBERYCA) and PGC2018-093824-B-C44 (from the Spanish Ministry of Economy and Competitiveness, MINECO, and the ERDF). RE received a IJCI-2014-21452 Juan de la Cierva incorporation contract. This research was also supported by the Basque Government through the BERC 2018-2021 program, and by the Spanish Ministry of Science, Innovation and Universities through the BC3 María de Maeztu excellence accreditation (MDM-2017-0714).

The metabolic activity of water-limited ecosystems is strongly linked to the timing and magnitude of precipitation pulses that can trigger disproportionately high (i.e., hot-moments) ecosystem CO2 fluxes. We analyzed over 2-years of continuous measurements of soil CO2 efflux (Fs) under vegetation (Fsveg) and at bare soil (Fsbare) in a water-limited grassland. The continuous wavelet transform was used to: (a) describe the temporal variability of Fs; (b) test the performance of empirical models ranging in complexity; and (c) identify hot-moments of Fs. We used partial wavelet coherence (PWC) analysis to test the temporal correlation between Fs with temperature and soil moisture. The PWC analysis provided evidence that soil moisture overshadows the influence of soil temperature for Fs in this water limited ecosystem. Precipitation pulses triggered hot-moments that increased Fsveg (up to 9000%) and Fsbare (up to 17,000%) with respect to pre-pulse rates. Highly parameterized empirical models (using support vector machine (SVM) or an 8-day moving window) are good approaches for representing the daily temporal variability of Fs, but SVM is a promising approach to represent high temporal variability of Fs (i.e., hourly estimates). Our results have implications for the representation of hot-moments of ecosystem CO2 fluxes in these globally distributed ecosystems., This work was supported in part by the Spanish Ministry of Economy and Competitiveness projects SOILPROF (CGL2011-15276-E), GEISpain (CGL2014-52838-C2-1-R), CARBORAD (CGL2011-27493), VERONICA (CGL2013-42271-P), IBERYCA (CGL2017-84723-P), Junta de Andalucía project GLOCHARID, including European Union ERDF funds; and by the European Commission project DIESEL (PEOPLE-2013-IOF-625988). RV acknowledges support from the University of Delaware, Universidad de Almería, Universidad de Granada, and Estación Experimental de Zonas Áridas (EEZA-CSIC) to visit the study site, and support from NSF (Award #1652594) while writing this manuscript., Peer reviewed

The extent to which the increasingly frequent episodes of drought-induced tree decline and mortality could alter key soil biogeochemical cycles is unclear. Understanding this connection between tree decline and mortality and soils is important because forested ecosystems serve as important long-term sinks for carbon (C) and essential nutrients (e.g., nitrogen and phosphorus). In order to fill in this knowledge gap, we conducted a study on 13 sites distributed across the Spanish Iberian Peninsula where the dominant tree species was the Mediterranean evergreen Holm oak (Quercus ilex L. subsp. ballota [Desf.] Samp), a species that has shown important drought-induced crown defoliation and mortality rates in recent decades. Our study covered different climatic, soil, land-use type (forests, dehesas, and open woodlands), and crown defoliation (healthy, affected, and dead Holm oaks) gradients that characterize this species distribution within the Spanish Iberian Peninsula. Specifically, the soil C and nutrient content (nitrogen, N; phosphorus, P; magnesium, Mg), several functional parameters (heterotrophic respiration (R); N mineralization (i.e., N ammonification, R; and N nitrification, R)), and relative abundances of key microbial soil functional groups (nitrifiers and ectomycorrhizal fungi (ECM)) were studied. Our results showed that aside from the potential effects associated with the climatic gradient, Holm oak decline and mortality resulted in soil stoichiometric imbalances triggered by net losses of essential oligonutrients (e.g., Mg) and the accumulation of very mobile forms of nitrogen (NO - N) and available phosphorus (Av P). Changes in the abundance of key microbial soil functional groups (nitrifiers and ECM) co-occurred with observed nitrate and available P accumulation. Therefore, we conclude that the potential vulnerability of soil C and nutrient stocks to ongoing changes in climate may strongly depend on tree vulnerability to climate change, its effect on soil-plant relationships, and how this may impact the ecology and functioning of key soil functional groups and key metabolic pathways., This research was supported by the VERONICA (CGL2013-42271-P) and IBERYCA (CGL2017-84723-P) projects, both funded by the Spanish Government. D. García-Angulo was financed through a FPI fellowship (BES-2014-067971) from the Spanish Ministry of Science, Innovation and Universities, and O. Flores through a FPU fellowship (FPU14/05408) from the Spanish Ministry of Education, Culture and Sport. This research was also supported by the Basque Government through the BERC 2018–2021 program, and by the Spanish Ministry of Science, Innovation and Universities through the BC3 María de Maeztu excellence accreditation (MDM-2017-0714). This work was also financed by the NATIvE (PN-III-P1-1.1-PD-2016-0583) project through UEFISCDI (Romanian Ministry of Education and Research).

New knowledge on soil structure highlights its importance for hydrology and soil organic matter (SOM) stabilization, which however remains neglected in many wide used models. We present here a new model, KEYLINK, in which soil structure is integrated with the existing concepts on SOM pools, and elements from food web models, that is, those from direct trophic interactions among soil organisms. KEYLINK is, therefore, an attempt to integrate soil functional diversity and food webs in predictions of soil carbon (C) and soil water balances. We present a selection of equations that can be used for most models as well as basic parameter intervals, for example, key pools, functional groups’ biomasses and growth rates. Parameter distributions can be determined with Bayesian calibration, and here an example is presented for food web growth rate parameters for a pine forest in Belgium. We show how these added equations can improve the functioning of the model in describing known phenomena. For this, five test cases are given as simulation examples: changing the input litter quality (recalcitrance and carbon to nitrogen ratio), excluding predators, increasing pH and changing initial soil porosity. These results overall show how KEYLINK is able to simulate the known effects of these parameters and can simulate the linked effects of biopore formation, hydrology and aggregation on soil functioning. Furthermore, the results show an important trophic cascade effect of predation on the complete C cycle with repercussions on the soil structure as ecosystem engineers are predated, and on SOM turnover when predation on fungivore and bacterivore populations are reduced. In summary, KEYLINK shows how soil functional diversity and trophic organization and their role in C and water cycling in soils should be considered in order to improve our predictions on C sequestration and C emissions from soils., This article is based upon work from COST Actions FP1305 (BioLink) and ES1406 (KEYSOM), supported by COST (European Cooperation in Science and Technology), and their Short Term Scientific Mission (STSM) programs. Omar Flores’ work was funded by FPU PhD grant program of the Spanish Ministry of Science, Innovation and Universities. Jorge Curiel Yuste received funding from the Spanish Ministry of Economy and Competitiveness (MINECO) under projects IBERYCA (CGL2017-84723-P) and the BC3 María de Maeztu excellence accreditation (MDM-2017-0714). Jorge Curiel Yuste also received funding from the Basque Government through the BERC 2018-2021 program., We also acknowledge institutional support from the Unit of Information Resources for Research at the Unit of Information Resources for Research at the "Consejo Superior de Investigaciones Científicas" (CSIC) for the article-processing charges contribution., Peer reviewed

11 Pág., The current increase of severe droughts associated with climate change is one of the main causes of the observed dieback in Mediterranean holm-oak (Quercus Ilex subs ballota) forests. Effects of forest dieback in soils are greatly variable and depend on a number of local factors, but generally include increased soil organic C due to increased litter inputs, alterations in soil nutrient contents, changes in the nitrogen cycle, and detrimental effects on soil microbial communities and their functioning. There is little evidence, however, of the effects of forest dieback on soil faunal diversity. In this study, we assessed the effects of holm-oak dieback and induced nutrient shifts on soil microfaunal communities and their relationships with soil properties and functioning. We studied 13 Holm oak forest sites affected by tree dieback in the Iberian Peninsula and assessed the relationship between soil properties, microbial functions, and nematode diversity under healthy, defoliated, and dead trees at each site. We found that nematode abundances were variable and significantly patchy across sites. Bacterivore and herbivore nematodes were the most abundant nematode trophic groups. Nematode abundance increased with increasing levels of soil C only if soil P was available, indicating that nematode abundances might be P-limited in these semi-arid systems. Bacterivore nematodes were especially affected by tree death, since tree dieback switched the relationship between bacterivore abundance and soil nutrient contents. Opportunistic bacterivores, able to exploit ephemeral bacterial resources blooming after soil organic enrichment, seemed more resilient to tree death than generalist ones, while fungivores did not clearly respond to forest dieback. We found complex and unexpected effects of tree dieback on soil microfaunal communities, which should receive further attention., This research was supported by the VERONICA (CGL2013-42271-P), IBERYCA (CGL2017-84723-P), and ATLANTIC (PID2020-113244GB-C21) projects funded by the Spanish Government. This research was also supported by the Basque Government through the BERC 2022–2025 program, and by the Spanish Ministry of Science and Innovation through the BC3 María de Maeztu excellence accreditation (MDM-2017-0714)., Peer reviewed

Indole-3-acetaldoxime (IAOx) is a particularly relevant molecule as an intermediate in the pathway for tryptophan-dependent auxin biosynthesis. The role of IAOx in growth-signalling and root phenotype is poorly studied in cruciferous plants and mostly unknown in non-cruciferous plants. We synthesized IAOx and applied it to M. truncatula plants grown axenically with NO3-, NH4+ or urea as the sole nitrogen source. During 14 days of growth, we demonstrated that IAOx induced an increase in the number of lateral roots, especially under NH4+ nutrition, while elongation of the main root was inhibited. This phenotype is similar to the phenotype known as “superroot” previously described in SUR1- and SUR2-defective Arabidopsis mutants. The effect of IAOx, IAA or the combination of both on the root phenotype was different and dependent on the type of N-nutrition. Our results also showed the endogenous importance of IAOx in a legume plant in relation to IAA metabolism, and suggested IAOx long-distance transport depending on the nitrogen source provided. Finally, our results point out to CYP71A as the major responsible enzymes for IAA synthesis from IAOx., This work was supported by the grants AGL2017-86293-P, CGL2017-84723-P (IBERYCA) and AGL2014-52396-P, from the Spanish Ministry of Economy and Competitiveness (MINECO) and the Ministry of Science Innovation and Universities (MICINN) and by the Basque Government (IT932-16). JB and PL-G are holders of PhD fellowships from the Public University of Navarre. ACh received a Juan de la Cierva initiation grant FJCI-2016-27905 and RE received a Juan de la Cierva incorporation grant IJCI-2014-21452. This research was also supported by the Basque Government through the BERC 2018-2021 program, and by the Spanish Ministry of Science, Innovation and Universities through the BC3 María de Maeztu excellence accreditation (MDM-2017-0714).

Climate change and pathogen outbreaks are the two major causes of decline in Mediterranean holm oak trees (Quercus ilex L. subsp. ballota (Desf.) Samp.). Crown-level changes in response to these stressful conditions have been widely documented but the responses of the root systems remain unexplored. The effects of environmental stress over roots and its potential role during the declining process need to be evaluated. We aimed to study how key morphological and architectural root parameters and nonstructural carbohydrates of roots are affected along a holm oak health gradient (i.e. within healthy, susceptible and declining trees). Holm oaks with different health statuses had different soil resource-uptake strategies. While healthy and susceptible trees showed a conservative resource-uptake strategy independently of soil nutrient availability, declining trees optimized soil resource acquisition by increasing the phenotypic plasticity of their fine root system. This increase in fine root phenotypic plasticity in declining holm oaks represents an energy-consuming strategy promoted to cope with the stress and at the expense of foliage maintenance. Our study describes a potential feedback loop resulting from strong unprecedented belowground stress that ultimately may lead to poor adaptation and tree death in the Spanish dehesa., This research was mainly funded by the Spanish Government through the IBERYCA project (CGL2017-84723-P), its associated FPI scholarship BES-2014-067971 (ME-V) and SMARTSOIL (PID2020-113244GB-C21). It was further supported by the BC3 María de Maeztu excellence accreditation (MDM-2017-0714; the Spanish Government) and by the BERC 2018–2021 and the UPV/EHU-GV IT-1018-16 programme (Basque Government). Additionally, this research was further supported through the ‘Juan de la Cierva programme’ (MV; IJCI-2017-34640; the Spanish Government) and one project funded by the Romanian Ministry of Research, Innovation and Digitization through UEFISCDI (A-MH; REASONING, PN-III-P1-1.1-TE-2019-1099).