Effects of drought-induced forest die-off on litter decomposition

Aims: drought-induced forest die-off and subsequent species replacement may modify environmental conditions and eventually affect litter decomposition. We aimed to disentangle the effects of tree species and die-off state on litter decomposition in a mixed forest where Pinus sylvestris populations experiencing severe drought-induced die-off are being replaced by Quercus ilex. - Methods: litter bags with leaves and fine roots from both species were placed under canopies representing three habitats of the die-off and replacement process (healthy and dead P. sylvestris and healthy Q. ilex). Mass was assessed over 3 years. - Results: species-specific chemistry of litter (C:N ratio) had a direct effect on mass loss, but also indirect effects, attributed to the decomposer microbial community associated with a given habitat-species. In their respective original habitats, oak leaves decomposed 44 % faster than pine needles, whereas oak roots decomposed 46 % slower than pine roots. - Conclusions: forest die-off and species replacement affected litter decomposition. This effect can have great implications in forest functioning, particularly if drought-induced die-off worsens in the next decades, according with the trend observed in the studied system

Land-use practices (coppices and dehesas) and management intensity modulate responses of Holm oak growth to drought

Last decades increase in reported events of drought-induced tree mortality evidences how climate-change is transforming forest ecosystems all over the world. The parallel increase in human pressure over the land is also causing major changes in forest functioning but it remains unclear how these two driving forces interact between them. We combined tree-ring data with aboveground cover, leaf area index (LAI), soil variables, and the standardized precipitation evapotranspiration index (SPEI) as water availability indicator to disentangle the existence of linkages between contrasting Holm oak (Quercus ilex L. subsp. ballota [Desf.] Samp) land-use practices and its drought-induced decline and mortality. We selected ten sites covering different soil and climatic gradients, land-use practices (i.e., declining dehesas, DH; declining coppices, FRd; and healthy coppices, FRh), and tree vigour classes (i.e., living, affected, and dead trees) in Spain. DH sites presented lower tree coverage, soil water holding capacity and soil pH than coppice (FR) sites. Dead Holm oaks from DH sites were younger than living ones, whereas dead trees from FRd sites were smaller and showed lower growth rates than living ones. We also found that conservation of traditional land-use practices in FR sites, resulting in less understorey cover but more soil erosion (less nutrients and microbial biomass and more bare soil), may positively affect the growth plasticity and sensitivity to drought of Holm oak trees by alleviating inter-specific competition, but in detriment of vegetation cover and soil health. Further studies should evaluate whether what holds true for FRh sites regarding the maintenance of traditional land-use practices might also apply for healthy DH. In the face of drier and hotter scenarios, our results add robust evidences on how the modulation of the intensity of the traditional uses could be a useful tool to optimize ecosystem services in Mediterranean systems highly vulnerable to climate change. © 2020This research was funded by the Spanish Government projects VERONICA (CGL2013-527 42271-P) and IBERYCA (CGL2017-84723-P). Additionally, it 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). Ana-Maria Hereş was financially supported by the projects NATIvE (PN-III-P1-1.1-PD-2016-0583) and REASONING (PN-III-P1-1.1-TE-2019-1099), both funded by the Romanian Ministry of National Education and by the Romanian Ministry of Research and Innovation through UEFISCDI ( link ). A. Gazol acknowledges funding by project RTI2018-096884-B-C31 (Spanish Ministry of Science). We thank Daniel García Angulo, Miguel Fernandez, David López Quiroga, Bárbara Carvalho, Matheus Lopes Souza, and Mario Díaz for their priceless support during the field campaigns and the laboratory work

Hot-Moments of Soil CO2 Efflux in a Water-Limited Grassland

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

Strong resilience of soil respiration components to drought-induced die-off resulting in forest secondary succession

How forests cope with drought-induced perturbations and how the dependence of soil respiration on environmental and biological drivers is affected in a warming and drying context are becoming key questions. The aims of this study were to determine whether drought-induced die-off and forest succession were reflected in soil respiration and its components and to determine the influence of climate on the soil respiration components. We used the mesh exclusion method to study seasonal variations in soil respiration (R S) and its components: heterotrophic (R H) and autotrophic (R A) [further split into fine root (R R) and mycorrhizal respiration (R M)] in a mixed Mediterranean forest where Scots pine (Pinus sylvestris L.) is undergoing a drought-induced die-off and is being replaced by holm oak (Quercus ilex L.). Drought-induced pine die-off was not reflected in R S nor in its components, which denotes a high functional resilience of the plant and soil system to pine die-off. However, the succession from Scots pine to holm oak resulted in a reduction of R H and thus in an important decrease of total respiration (R S was 36 % lower in holm oaks than in non-defoliated pines). Furthermore, R S and all its components were strongly regulated by soil water content-and-temperature interaction. Since Scots pine die-off and Quercus species colonization seems to be widely occurring at the driest limit of the Scots pine distribution, the functional resilience of the soil system over die-off and the decrease of R S from Scots pine to holm oak could have direct consequences for the C balance of these ecosystems

Tree species effects on soil microbial community composition and greenhouse gases emissions in a Mediterranean ecotone forest

Resumen de una presentación realizada en: I Simposio sobre Interacciones Planta-Suelo (ICA-CSIC, Madrid, 25-26 Febrero 2016)Over recent decades in the Iberian Peninsula, altitudinal shifts from Pinus sylvestris L. to Quercus pyrenaica Willd species has been observed as a consequence of Global Change, meaning changes in temperature, precipitation, land use and forestry. The forest conversion from pine to oak can alter the litter quality and quantity provided to the soil and thereby the soil microbial community composition and functioning. Since soil microbiota plays an important role in organic matter decomposition, and this in turn is key in biogeochemical cycles and forest ecosystems productivity, the rate in which forests produce and consume greenhouse gases can be also affected by changes in forest composition. In other words, changes in litter decomposition will ultimately affect downstream carbon and nitrogen dynamics although this impact is uncertain. In order to predict changes in carbon and nitrogen stocks in Global Change scenarios, it is necessary to deepen the impact of vegetation changes on soil microbial communities, litter decomposition dynamics (priming effect) and the underlying interactions between these factors. To test this, we conducted a full-factorial transplant microcosms experiment mixing both fresh soils and litter from Pyrenean oak, Scots pine and mixed stands collected inside their transitional area in Central Spain. The microcosms consisted in soil cylinders inside Kilner jars used as chambers inside an incubator. In this experiment, we investigated how and to what extent the addition of litter with different quality (needles, oak leaves and mixed needlesleaves) to soil inoculums with contrasting soil microbiota impact on soil (i) CO2, NO, N2O and CH4 efflux rates, (ii) total organic carbon and nitrogen and (iii) dissolved organic carbon and nitrogen. Furthermore, we assessed if these responses were controlled by changes in the microbial community structure using the PLFA analyses prior and after the incubation period of 54 days.Peer reviewe

The ecosystem carbon sink implications of mountain forest expansion into abandoned grazing land: The role of subsoil and climatic factors

Woody encroachment is a widespread phenomenon resulting from the abandonment of mountain agricultural and pastoral practices during the last century. As a result, forests have expanded, increasing biomass and necromass carbon (C) pools. However, the impact on soil organic carbon (SOC) is less clear. The main aim of this study was to investigate the effect of woody encroachment on SOC stocks and ecosystem C pools in six chronosequences located along the Italian peninsula, three in the Alps and three in the Apennines. Five stages along the chronosequences were identified in each site. Considering the topsoil (0 30 cm), subsoil (30 cm-bedrock) and whole soil profile, the temporal trend in SOC stocks was similar in all sites, with an initial increment and subsequent decrement in the intermediate phase. However, the final phase of the woody encroachment differed significantly between the Alps (mainly conifers) and the Apennines (broadleaf forests) sites, with a much more pronounced increment in the latter case. Compared to the previous pastures, after mature forest (>62 years old) establishment, SOC stocks increased by: 2.1(mean) ± 18.1(sd) and 50.1 ± 25.2 Mg C·ha -1 in the topsoil, 7.3 ± 17.4 and 93.2 ± 29.7 Mg C·ha -1 in the subsoil, and 9.4 ± 24.4 and 143.3 ± 51.0 Mg C·ha -1 in the whole soil profile in Alps and Apennines, respectively. Changes in SOC stocks increased with mean annual air temperature and average minimum winter temperature, and were negatively correlated with the sum of summer precipitation. At the same time, all other C pools (biomass and necromass) increased by 179.1 ± 51.3 and 304.2 ± 67.6 Mg C·ha -1 in the Alps and the Apennines sites, respectively. This study highlights the importance of considering both the subsoil, since deep soil layers contributed 38% to the observed variations in carbon stocks after land use change, and the possible repercussions for the carbon balance of large areas where forests are expanding, especially under pressing global warming scenarios. © 2019 Elsevier B.V.The project of this work is part of the research activities of the PhD in science, technology and biotechnology for sustainability. The first author received a fully founded scholarship partially by the University of Tuscia (Viterbo - Italy) and partially by the University of Molise . Tommaso Chiti participated in the project by conducting his work with the funding obtained through the LIFE MediNet project (grant number LIFE15 PRE IT/732295 ). Jorge Curiel Yuste was financed in part by the Basque Government through the BERC 2018-2021 (grant code) program and by Spanish Ministry of Economy and Competitiveness (MINECO) through BC3 María de Maeztu excellence accreditation MDM-2017-0714. I.C (grant code)

Climate-induced die-off affects plant-soil-microbe ecological relationship and functioning

Altres ajuts rebuts per dur a terme aquest projecte: ICTS-Reserva Biológica de Doñana (projects 38/2007, 27/2009, and 11/2013) i Goverment of Madrid (REMEDINAL 2; CM S2009 AMB 1783)This study reports the relationship between the diversity and functioning of fungal and bacterial soil communities with vegetation in Mediterranean woodland that experienced severe die-off after a drought episode. Terminal restriction fragment length polymorfism (TRFLP) was used to describe microbial community structure and diversity five years after the episode in different habitats (Juniperus woodland, shrubland, grassland), when the vegetation had not yet recovered. Vegetation diversity was positively related to TRF bacterial richness under unaffected canopies and was higher in diverse grassland. Fungal TRF richness correlated with vegetation type, being greater in Juniperus woodland. Microbial respiration increased in grassland, whereas microbial biomass, estimated from soil substrate-induced respiration (SIR), decreased with bacterial diversity. Die-off increased bacterial richness and changed bacterial composition, particularly in Juniperus woodland, where herbaceous species increased, while fungal diversity was reduced in Juniperus woodland. Die-off increased microbial respiration rates. The impact on vegetation from extreme weather episodes spread to microbial communities by modifying vegetation composition and litter quantity and quality, particularly as a result of the increase in herbaceous species. Our results suggest that climate-induced die-off triggers significant cascade effects on soil microbial communities, which may in turn further influence ecosystem C dynamics

Spatial variability of soil respiration (R<inf>s</inf>) and its controls are subjected to strong seasonality in an even-aged European beech (Fagus sylvatica L.) stand

Uncertainties arising from the so-far poorly explained spatial variability of soil respiration (Rs) remain large. This is partly due to the limited understanding about how spatially variable Rs actually is, but also on how environmental controls determine Rs's spatial variability and how these controls vary in time (e.g., seasonally). Our study was designed to look more deeply into the complexity of Rs's spatial variability in a European beech even-aged stand, covering both phenologically and climatically contrasting periods (spring, summer, autumn and winter). Although we studied a relatively homogeneous stand, we found a large spatial variability of Rs (coefficients of variation &gt; 30%) characterized by strong seasonality. This large spatial variability of Rs suggests that even in relatively homogeneous stands there is a large potential source of error when estimating Rs. This was also reflected by the sampling effort needed to obtain seasonally robust estimates of Rs, which may actually require a number of samples above that used in Rs studies. We further postulate that the effect of seasonality on the spatial variability and environmental controls of Rs was determined by the seasonal shifts of its microclimatic controls: during winter, low temperatures constrain plant and soil metabolic activities and hence reduce Rs variability (temperature-controlled processes), whereas during summer, water demand by vegetation and changes in water availability due to the microtopography of the terrain (i.e., slope) increase Rs variability (water-controlled processes). This study provides novel information on the spatiotemporal variability of Rs and looks more deeply into the seasonality of its environmental controls and the architecture of their causal-effect relationships controlling Rs's spatial variability. Our study further shows that improving current estimates of Rs at local and regional levels might be necessary in order to reduce uncertainties and improve CO2 estimates at larger spatial scales. Highlights: The spatial variability of soil respiration (Rs) and its environmental controls vary seasonally. Seasonal shifts from temperature- to water-controlled processes determine Rs's spatial variability. Besides microclimate, slope and grass cover explain the spatiotemporal variability of Rs. An intense sampling effort is needed to obtain robust Rs estimates even in homogeneous forests. © 2021 British Society of Soil Science.This research was supported by the Forest GHG Management (PN‐II‐ID‐PCE‐2011‐3‐0781), TREEMORIS (PN‐II‐RU‐TE‐2014‐4‐0791), BIOCARB (PN‐III‐P1‐1.1‐TE‐2016‐1508), NATIvE (PN‐III‐P1‐1.1‐PD‐2016‐0583) and REASONING (PN‐III‐P1‐1.1‐TE‐2019‐1099) projects, all financed by the Romanian Ministry of Education and Research through UEFISCDI ( link ). This research was also supported by the IBERYCA (CGL2017‐84723‐P) project and by the BC3 María de Maeztu excellence accreditation 2018‐2022 (Ref. MDM‐2017‐0714), both financed by the Spanish Ministry of Science, Innovation and Universities. The Basque Government also supported this research through the BERC 2018‐2021 programme

Below-ground functional resilience along drought-induced forest die-off and species replacement

Resumen de una presentación realizada en: I Simposio sobre Interacciones Planta-Suelo (ICA-CSIC, Madrid, 25-26 Febrero 2016)Understanding how ecosystems functioning may respond to increments of temperature and climatic variability is crucial in the global change context. We studied the plant-and-soil interaction in a mixed Mediterranean forest where several drought events since 1990’s have resulted in Scots pine defoliation and mortality, with a subsequent replacement by Holm oak (HO). The study focused on how this die-off and species replacement affected soil respiration (SR) and its heterotrophic and autotrophic components. It dealt with SR dependency on abiotic and biotic controls (i.e. soil temperature and moisture, photosynthetic activity, forest structure, litter inputs on soil, fine roots biomass) at different temporal and spatial scales. The study also determined rates of litter decomposition (both leaves and fine roots) along the die-off process. Soil temperature and moisture strongly regulated temporal variability of SR (from daily to seasonal), including both autotrophic and heterotrophic components. Plant activity exerted strong control over temporal variability of SR, with higher influence on living pines at daily time scales but stronger effect on HO at seasonal scale. SR and its components remained apparently unaffected by drought-induced Scots pine die-off denoting a high functional resilience of the studied plant-and-soil system. This functional resilience of SR was the result of colonization by HO of the gaps created by the dead of pines. Additionally, litter decomposition rates, specific root respiration, plant activity and soil bacterial communities compared between living pines, dead pines and HO also supported the role of HO rhizosphere colonization on below-ground functioning resilience.Peer reviewe

Efectos de varios factores ambientales sobre las tasas de descomposición en encinares mediterráneos

Resumen de una presentación realizada en: I Simposio sobre Interacciones Planta-Suelo (ICA-CSIC, Madrid, 25-26 Febrero 2016)[ES] Los encinares son ecosistemas de gran valor que están sufriendo un proceso de decaimiento, lo que puede afectar a su capacidad para almacenar carbono. Se plantea este proyecto de tesis para estudiar el efecto del decaimiento de encinares sobre las tasas de descomposición de la hojarasca, las raíces y las herbáceas, y los factores medioambientales que la controlan. Los factores que se pretende estudiar son: la calidad de la materia en descomposición, el clima, la fotodegradación, y el efecto de diferentes conjuntos de fauna del suelo. El efecto de dichos factores sobre la descomposición se analizará a través de 4 experimentos con bolsas de descomposición. Experimento 1: Efecto del clima, de la fotodegradación y de la calidad de la hojarasca sobre las tasas de descomposición. Se ha diseñado un experimento factorial para el seguimiento de las tasas de descomposición de herbáceas y de hojas y raíces de encinas, situando bolsas en 8 encinares afectados distribuidos por el territorio peninsular español. Experimento 2: Efecto de la microfauna, la mesofauna y la macrofauna del suelo sobre los procesos de descomposición de hojarasca. Se estudiará mediante tratamientos de exclusión de fauna del suelo. Experimento 3: Efecto interactivo de la temperatura, precipitación y radiación solar sobre la descomposición de hojarasca. Se utilizarán mesocosmos para someter bolsas de hojarasca de herbáceas a dos niveles para cada uno de esos tres factores, con todas las interacciones entre ellos. Experimento 4: Contribución de diferentes procesos abióticos (fotodegradación y degradación térmica), bióticos (descomposición microbiana) así como su interacción en la descomposición de la materia orgánica. Se realizará con herbáceas bajo condiciones controladas de laboratorio. Estos experimentos permitirán describir de una manera mecanicista un proceso tan relevante para las interacciones planta-suelo como es la descomposición así como los factores medioambientales que la controlan.Peer reviewe