Solute fluxes via bulk precipitation, throughfall & stemflow in a humid tropical lowland rainforest, Costa Rica

Tropische Regenwälder könnten eine große Rolle in der globalen Kohlenstoffbilanz spielen, da sie als eine der größten terrestrischen C-Senken angesehen werden. Anhand vieler Studien wird deshalb versucht den Beitrag und die Verteilung von Nährstoffflüssen in Ökosystemen zu quantifizieren. Wüsste man erst einmal über momentane Umsatzraten bescheid, könnte man vorhersehen wie sich Veränderungen der Nährstoffzusammensetzung in Zukunft auf ein Ökosystem auswirken. Derzeit besteht die Möglichkeit dass sich der Status der tropischen Regenwälder als C-Senken aufgrund von anthropogenen Eingriffen (Abholzung von Regenwäldern, Landwirtschaft und vermehrter Düngereintrag) insofern umkehren könnte, als dass sie letztendlich zu C-Quellen werden könnten. Im Zuge dieser Diplomarbeit in einem tropischen Tieflandregenwald in Costa Rica wurde in mehreren Arbeitsgruppen versucht die Dynamik und Stoffflüsse des außerordentlich diversen Ökosystems zu quantifizieren. Die Datenerhebung umfasste zahlreiche Aufnahmen: Angefangen von der Ausweisung der vorgesehenen Untersuchungsflächen, Messung des pflanzlichen Biomasse-Zuwachs mittels Dendrometerbändern, Besammlung von Laubstreu und Charakterisierung des C/N-Verhältnisses, über die Bestimmung der Flussmengen von Kronentrauf, Stammabfluss und des Bodenwassergehalts, bis hin zu Untersuchungen der Nährstoff-turnover Prozesse anhand von pool-dilution Experimenten mittels stabiler Isotope. Es wurden insbesondere die Stoffflüsse und Quellen der häufigsten Nährstoffe, in Form von DOC, DON und der An- und Kationen Cl-, NO3-, SO42-, PO43- und Na+, K+, NH4+, Mg2+ und Ca2+ untersucht und deren Herkunft und Verteilung in einem tropischen Waldökosystem beschrieben. Dazu wurden Proben von Laubstreu, Regenwasser, Kronentrauf, Stammabfluss und Bodenwasser zur Beantwortung der Fragestellungen betreffend der Dekomposition, nutrient use efficiency (NUE) und turnover Prozesse des Ökosystems Regenwald entnommen und in konservierter Form zur Analyse an das Department überstellt. Die darauf folgende Laborarbeit bezog sich vor allem auf die Quantifizierung des gesammelten Probenmaterials durch Analyse von Bodenextrakten, Blattmaterial, Groblitter und Wasserproben. Für die Bestimmung und Auswertung der Stoffflüsse der Hydrologie wurden Analysen mittels HPLC-Ionenchromatographie, Massenspektrometrie, Photometrie und TOC/TN Analysen verwendet. Die Studie ergab im Wesentlichen, dass der Eintrag von Nährstoffen durch Freilandniederschlag, Kronentrauf und Stammabfluss im Zeitraum von einem Jahr extremen Schwankungen unterliegt, welche auf mehrere Faktoren zurückzuführen waren. Hauptsächlich bestimmten die Faktoren: Saisonalität, Topographie, Geologie, Sukzession etc. die Nährstoffverfügbarkeit auf den unterschiedlichen Standorten. Es konnten auch gemeinsame Quellen betreffend der Herkunft von Nährstoffen ausgewiesen werden. So wurden Na, Cl, Mg und SO4 etwa hauptsächlich durch Verdunstungsprozesse an der Meeresoberfläche eingebracht während Stoffflüsse von NO3 und PO4 der besseren Versorgung von Nährstoffen auf unterschiedlich situierten Standorten zugewiesen werden konnten. Obwohl Unterschiede im Diversitäts- und Blattflächenindex zwischen verschiedenen Sukzessionsstadien nachgewiesen werden konnten, war es nicht möglich die Zusammensetzung der Baumarten der einzelnen Standorte mit den Nährstoffflüssen zu korrelieren. Dies mag daran liegen das der ausgesprochene Artenreichtum von über 200 Baumarten in der Region des Esquinas Nationalparks, die unterliegenden Differenzierungen betreffend der Zusammensetzung und Verteilung von Nährstoffen in diesem tropischen Ökosystem überschattet. Tropische Regenwälder gehören zu den diversesten Ökosystemen der Erde und daher wird es weiterhin eine Herausforderung bleiben darin Stoffflüsse zu messen, zu quantifizieren und zu beschreiben. Diese Studie bietet einen weiteren Einblick in die Funktionen und Mechanismen von Nährstoffflüssen, welche in Zukunft hinsichtlich der Kohlenstoff-Bilanz, besonders in Zeiten globaler Erwärmung, von erhöhter Bedeutung sein könnten.Tropical rainforests are considered to play major roles as sinks in the planet’s carbon budget; therefore numerous studies try to quantify the input, cycling and dispersal of nutrients. By calculating present states and turnover rates we will be able to foresee the impact of shifts in nutrient fluxes in future scenarios (e.g. global warming caused by the alteration of pristine landscapes) which may invert the current status insofar as tropical regions might soon act as carbon source instead. In this study measurements of Bulk Precipitation, throughfall and stemflow were used to investigate nutrient fluxes in three forest sites in different stages of succession. Collectors for throughfall (n=45), stemflow (n=36), soil water content (n=9) and litter percolate (n=6) were put into three forest sites of 0.12 hectares each, and sampled on event basis up to intervals of two weeks over a period of 2 years. Nutrients (H+, Na+, HH4+, K+, Mg2+, Ca2+, Cl-, NO32-, CO32-, SO42-, PO43-, DOC and DON) were determined by HPLC (Dionex) and tested statistically to investigate significant differences between sites by one-way and two-way ANOVA, after log normalization of data, and Tuckey-HSD post-hoc test. Here, we constitute an innovative approach for the quantification of nutrient inputs via net throughfall fluxes (NTF) deriving from BP and DD, based on the multiple regression model (Lovett & Lindberg 1984) which announced that the role of canopy exchange is of major importance in terms of tropical nutrient cycling, whereas the influence of dry deposition was weak since largely independent of rainfall. We moreover investigated the major controls on NTF such as soil fertility, topography, canopy structure and species assemblage. The use of a Sun Scan probe (estimating canopy closure) did reveal significant differences between forest sites, but spearman-rank correlation of NTF and canopy closure showed no significant coherency. Investigating species inventory, Fisher’s alpha diversity index, ANOSIM and SIMPER analysis indicated differences in species composition between pristine and secondary forests. However, relating resemblance matrices showed no significant influence of species assemblages on nutrient composition of forest sites. The clustering of nutrients revealed by PCA gave insight on origin and sources of associated solutes in NTF

A high-­resolution monitoring network investigating stem growth of tropical forest trees.

Ref. B51D-0453

Amazon forest responses to projected climate change, elevated CO2 and biodiversity loss

Rapid changes in the Earth's climate caused by the burning of fossil fuels and deforestation pose a severe threat to forests of the Amazon basin. Warmer temperatures and drier conditions are predicted to cause widespread forest die back, with associated threats to regional economies, social welfare, and natural capital through changes in agricultural output and hydropower supply. Nonetheless, the implications will be global as the Amazon forest provides substantial services to humankind by regulating the climate through the cycling of carbon, water, and energy; and harbouring a large part of the world's biodiversity. I will address some of the overarching questions of how climate change will affect the Amazon forest, the biodiversity it harbours, and the ecosystem services it provides to humanity

Optimal balancing of xylem efficiency and safety explains plant vulnerability to drought

In vast areas of the world, forests and vegetation are water limited and plant survival depends on the ability to avoid catastrophic hydraulic failure. Therefore, it is remarkable that plants take hydraulic risks by operating at water potentials (psi) that induce partial failure of the water conduits (xylem). Here we present an eco-evolutionary optimality principle for xylem conduit design that explains this phenomenon based on the hypothesis that conductive efficiency and safety are optimally co-adapted to the environment. The model explains the relationship between the tolerance to negative water potential (psi(50)) and the environmentally dependent minimum psi (psi(min)) across a large number of species, and along the xylem pathway within individuals of two species studied. The wider hydraulic safety margin in gymnosperms compared to angiosperms can be explained as an adaptation to a higher susceptibility to accumulation of embolism. The model provides a novel optimality-based perspective on the relationship between xylem safety and efficiency

Modeling wildfire dynamics using FLAM coupled with deep learning methods

We improve the accuracy of modeling burned areas using the FLAM model by identifying the hidden relationships between human and natural impacts on wildfire suppression efficiency using the deep learning-based methods. The wildfire climate impacts and adaptation model (FLAM) is able to capture impacts of climate, population, and fuel availability on burned areas. FLAM uses a process-based fire parameterization algorithm with a daily time step. The model uses daily temperature, precipitation, relative humidity and wind speed to assess climate impacts on ignition probability and fire spread. The key features implemented in FLAM include fuel moisture computation based on the Fine Fuel Moisture Code (FFMC) of the Canadian Forest Fire Weather Index (FWI), and a procedure to calibrate spatial fire suppression efficiency. The coupled FLAM and deep learning approach consists in the following steps. First, using FLAM we calibrate the suppression efficiency map by comparing model output with observed burned area (satellite data). Secondly, we use deep learning methods to identify and assess the drivers behind the calibrated map. The features used in the analysis include several socio-economic factors, including accessibility, GPP, land use maps, as well as burned areas and other parameters modeled by FLAM. Our approach allows classifying those features by their importance and find correlations between them. Finally, we implement the output of deep learning network to estimate the spatial suppression efficiency within FLAM (instead of calibrating it), and validate the approach using observed burned area. The proposed approach is implemented using the Google Earth Engine platform that provides flexibility in terms of input data sets and visualization tools. We will present the case study for Indonesia at 0.083 arc degree spatial resolution. It is planned to consider climate change impacts in more detail. Modeling burned areas and suppression efficiency can help the implementation of fire prevention policies for decision maker and provide important information for building adequate and cost-efficient fire response infrastructure

Partitioning of plant functional trait variation into phenotypic plasticity and neutral components reveals functional differences among neotropical tree species

Background: Tropical plant communities exhibit extraordinary species richness and functional diversity in highly heterogeneous environments. Albeit the fact that such environmental filtering shapes local species composition and associated plant functional traits, it remains elusive to what extend tropical vegetation might be able to acclimate to environmental changes via phenotypic plasticity, which could be a critical determinant affecting the resistance and resilience of tropical vegetation to projected climate change. Methods: Based on a dataset compiled from 345 individuals and comprising 34 tropical tree species we here investigated the role of phenotypic plasticity versus non-plastic variation among key plant functional traits, i.e. wood density, maximum height, leaf thickness, leaf area, specific leaf area, leaf dry mass, nitrogen and phosphorus content. We hypothesized that trait variation due to plasticity is driven by environmental variability independently of spatial effects due to geographic distance between forest stands, whereas non-plastic variation increases with geographic distance due to adaption of the plant community to the local environment. Based on these hypotheses we partitioned total observed trait variation into phenotypic plasticity and neutral components and quantified respective amount of variation related to environmental filtering and neutral community assembly. Results: We found that trait variation was strongly related to spatial factors, thus often masking phenotypic plasticity in response to environmental cues. However, respective environmental factors differed among plant functional traits, such that leaf traits varied in association with light regime and soil nutrient content, whereas wood traits were related to topography and soil water content. Our results further suggest that phenotypic plasticity increased with the range size of congeneric tree species, indicating less plasticity within range restricted endemics compared to their widespread congeners. Conclusions: Differences in phenotypic trait plasticity affect stress tolerance and range size of tropical tree species, therefore endemic species could be especially prone to projected climate change

Topographical heterogeneity governs species distribution and regeneration potential by mediating soil attributes in Western Himalayan forests

The present study is an attempt to understand variation in species composition and diversity and soil properties along topographic gradients in Western Himalayan reserve forests (400-3000m asl). To analyze changes in floristic composition, diversity, and regeneration status, we measured woody vegetation in forest plots at different altitudinal levels and contrasting aspects (North and south). Trees (diameter at breast height (DBH) > 10cm) and saplings (3-10cm DBH) were sampled in 10m×10m plots, shrubs were sampled in 5m×5m plots and seedlings (0-3cm DBH) were sampled in 1m×1m plots. To study variation in soil properties, samples were collected from each forest stand in five replicates from layers of 0-10cm, 10-20cm, and 20-30cm in soil depths. Canonical Correspondence Analysis (CCA) was applied to identify important factors that govern species distribution. Variance partitioning was conducted to quantify the relative contribution of elevation, slope aspect, vegetation attributes, and soil properties on regeneration potential of tree species. We found that environmental filtering shapes local species composition and associated edaphic factors in the region. Species richness and diversity were found to decrease with elevation. Soil properties (Organic Carbon, pH, and texture) and associated vegetation parameters did not vary significantly between the aspects. CCA confirmed that species composition was positively related to moisture content and available phosphorous at higher elevations, while reduced weathering rates and bulk density at lower elevations might have caused relatively lower nutrient turnover rates. Our study concludes that topographical variation and increased sum of soil nutrients are highly favorable for growth and development of plant species

Optimal balancing of xylem efficiency and safety explains plant vulnerability to drought

In vast areas of the world, the growth of forests and vegetation is water-limited and plant survival depends on the ability to avoid catastrophic hydraulic failure. Therefore, it is remarkable that plants take high hydraulic risks by operating at water potentials (ψ) that induce partial failure of the water conduits (xylem). Here we present an eco-evolutionary optimality principle for xylem conduit design that explains this phenomenon. Based on the hypothesis that conductive efficiency and safety are optimally co-adapted to the environment, we derive a simple relationship between the intrinsic tolerance to negative water potential (ψ50) and the environmentally dependent minimum xylem, ψmin. This relationship is constrained by a physiological tradeoff between xylem conductivity and safety, which is relatively strong at the level of individual conduits although it may be weak at the whole sapwood level. The model explains observed variation in ψ50 both across a large number of species, and along the xylem path in two species. The larger hydraulic safety margin in gymnosperms compared to angiosperms is explained as an adaptation to the gymnosperms' lower capacity to recover from conductivity loss. The constant xylem safety factor provides a powerful principle for simplifying and improving plant and vegetation models