Tree growth response to drought partially explains regional-scale growth and mortality patterns in Iberian forests

Tree-ring data has been widely used to inform about tree growth responses to drought at the individual scale, but less is known about how tree growth sensitivity to drought scales up driving changes in forest dynamics. Here, we related tree-ring growth chronologies and stand-level forest changes in basal area from two independent data sets to test if tree-ring responses to drought match stand forest dynamics (stand basal area growth, ingrowth, and mortality). We assessed if tree growth and changes in forest basal area covary as a function of spatial scale and tree taxa (gymnosperm or angiosperm). To this end, we compared a tree-ring network with stand data from the Spanish National Forest Inventory. We focused on the cumulative impact of drought on tree growth and demography in the period 1981–2005. Drought years were identified by the Standardized Precipitation Evapotranspiration Index, and their impacts on tree growth by quantifying tree-ring width reductions. We hypothesized that forests with greater drought impacts on tree growth will also show reduced stand basal area growth and ingrowth and enhanced mortality. This is expected to occur in forests dominated by gymnosperms on drought-prone regions. Cumulative growth reductions during dry years were higher in forests dominated by gymnosperms and presented a greater magnitude and spatial autocorrelation than for angiosperms. Cumulative drought-induced tree growth reductions and changes in forest basal area were related, but initial stand density and basal area were the main factors driving changes in basal area. In drought-prone gymnosperm forests, we observed that sites with greater growth reductions had lower stand basal area growth and greater mortality. Consequently, stand basal area, forest growth, and ingrowth in regions with large drought impacts was significantly lower than in regions less impacted by drought. Tree growth sensitivity to drought can be used as a predictor of gymnosperm demographic rates in terms of stand basal area growth and ingrowth at regional scales, but further studies may try to disentangle how initial stand density modulates such relationships. Drought-induced growth reductions and their cumulative impacts have strong potential to be used as early-warning indicators of regional forest vulnerability.This study was financially supported by Xunta de Galicia, Grant/Award Number PGIDIT06PXIB502262PR, GRC GI-1809; INIA, Grant/Award Number RTA2006-00117; CANOPEE, 2014-2020-FEDER funds, Spanish Science Ministry RTI2018-096884-B-C31, RTI2018-096884-B-C33, AGL2017-83828-C2-2R, RTI2018-096884-B-C3,1 and RTI2018-096884-B-C32 projects. Gabriel Sangüesa-Barreda was supported by a “Juan de la Cierva-Formación” grant from MINECO (FJCI 2016-30121). Antonio Gazol and Paloma Ruiz-Benito were supported by a project “2018 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation.” Ana-Maria Hereş was supported by the project PN-III-P1-1.1-TE-2019-1099 financed by the Romanian Ministry of Education and Research through UEFISCDI. Raúl Sánchez-Salguero was supported by VULBOS project (UPO-1263216, FEDER Funds, Andalusia Regional Government, Consejería de Economía, Conocimiento, Empresas y Universidad 2014-2020). Paloma Ruiz-Benito was supported by the Community of Madrid Region under the framework of the multi-year Agreement with the University of Alcalá (Stimulus to Excellence for Permanent University Professors, EPU-INV/2020/010) and the University of Alcalá “Ayudas para la realización de Proyectos para potenciar la Creación y Consolidación de Grupos de Investigación.” Andrea Hevia was supported by PinCaR project (UHU-1266324, FEDER Funds, Andalusia Regional Government, Consejería de Economía, Conocimiento, Empresas y Universidad 2014-2020).Peer reviewe

Large spatial variability of prokaryotic communities and their activity along a subterranean estuary during two different hydrological seasons

ASLO Aquatic Sciences Meeting, Resilience and Recovery in Aquatic Systems, 4-9 June 2023, Palma de Mallorca, SpainSubmarine Groundwater Discharge (SGD) supplies large amounts of solutes to the ocean. In coastal areas, the confluence of fresh and saline groundwater results in subterranean estuaries (STEs), biogeochemically active sites in which biogeochemical transformations mediated by microbes can control SGD-driven nutrient fluxes to the ocean. However, very little is known about microbial communities in STEs and their drivers. Our aim was to explore the spatio-temporal variations in prokaryotic abundance and heterotrophic activity along a STE in a Mediterranean alluvial aquifer. Groundwater was collected from several piezometers (depths 6-22m) along the entire salinity gradient in two different hydrological seasons. Prokaryote abundance and activity (inferred by single-cell activity measurements and radioactive leucine incorporation) were compared with different physicochemical parameters. Results show large spatial variations in prokaryotic abundance and activity following physicochemical gradients, but little seasonal variability. Prokaryote abundance was maximum at the deepest saline layers and lowest in intermediate fresh groundwater. More active cells in saline samples were observed, which coincided with increases in nitrate and ammonium, suggesting microbial transformations of groundwater along STEs. Our results indicate that prokaryotic communities in coastal aquifers are highly heterogeneous in terms of biomass and activity, implying that their role in nutrient transformations will vary throughout STEs and calling for detailed spatial explorations of these key ecosystem

Variability and drivers of total mercury and methylmercury concentrations along a Mediterranean coastal alluvial aquifer in Barcelona (Spain)

1st Joint International Conference ICOBTE & ICHMET - 16 st International Conference of Biogeochemistry of Trace Elements (ICOBTE) - 21st International Conference of Heavy Metals (ICHMET), Clean Environment, Human Health, Our future, 6-10 September 2023, Wuppertal, GermanySubmarine groundwater discharge (SGD) can be defined as the flow of water from coastal aquifers to the sea and might be a potential, yet overlooked, source of trace elements to the ocean. Very little is known about total mercury (Hg) contamination and methylmercury (MeHg) formation in coastal aquifers, despite being enriched in land-derived nutrients and generally oxygen-depleted, conditions that could promote the activity of anaerobic bacteria such as Hg methylators. In this study we explored the spatio-temporal variability and drivers of total Hg (THg) and MeHg concentrations in groundwater samples collected from 19 piezometers located along a coastal alluvial aquifer connected to the Mediterranean Sea in Barcelona (Spain). THg and MeHg were measured at depths ranging from 6 to 22 mbs (meters below surface) and were compared to variations in an array of physicochemical variables, prokaryotic abundance and activity in two different occasions, representing different hydrologic seasons (December 2021 and July 2022). THg concentrations were not significantly different between seasons but varied largely along the aquifer, ranging from 0.68 to 449 pM. The highest THg concentrations were measured in some of the deepest (>14 mbs) saline groundwater samples, indicating a source of contamination and/or physicochemical conditions enabling Hg absorption. Our results hint some source/s of Hg to the coastal aquifer waters, as well as the localized presence and activity of Hg methylating bacteria. Due to the negative impacts of increased MeHg concentrations in marine ecosystems, future studies should clarify which could be the Hg sources to coastal aquifers and the biophysicochemical factors that might promote MeHg formation in coastal groundwatersPeer reviewe