Current Projects:
Disentangling
seasonal
vegetation
effects
on
ecosystem
evapotranspiration and water use efficiency of a Mediterranean
savannah-type oak forest (WATERFLUX, DFG)
Water represents one of the key factors driving ecosystem
productivity due to the tight coupling between ecosystem water
and carbon fluxes. A functional understanding of
evapotranspiration and photosynthesis is required to
understand the development of water and carbon fluxes,
particularly in water-limited ecosystems where global climate
change is expected to intensify drought and alter precipitation
patterns. The aim of this project is a detailed mechanistic
evaluation of the water balance and water use efficiency of a
typical Mediterranean savannah-type oak woodland. The
project will focus on seasonal dynamics of over- and
understorey vegetation of this two-component system and on
the vegetation feedbacks on water and carbon fluxes. The
study will combine (1) ecosystem and understorey
measurements of net CO2 and H2O fluxes with (2) an
experimental approach (trenching plot design) to disentangle
major vegetation effects on water and carbon processes, and
(3) a modelling approach to integrate the information gained
from the different scales. Partitioning of net water fluxes into
their individual components will be achieved by the use of
stable isotopes. This project will deliver a process-based
understanding of ecosystem water cycling and water use
efficiency with a particular focus on the contribution of the
understorey, which will be evaluated under consideration of
future climate trends. Such improved understanding will help to
develop appropriate management strategies and is needed for
a risk assessment of climate change impact on Mediterranean
ecosystems.
PhD-Student Maren Dubbert, in collaboration with Stephan Unger, Matthias Cuntz, Cristina
Máguas, Joao Santos Pereira
Changing ground water levels: the impact on an invasive species and
native plant communities in a Mediterranean dune ecosystem
(TransDune, DFG)
The introduction of non-native
species and
its spread are
recognized to be one of the major
threats to biodiversity and ecosystem
functioning. Climate change is
expected to enhance ecosystem
invasibility through changes in
resource availability (e.g. water) and
the risks of desertification in
Mediterranean areas, however scientific studies are rare. This
project will evaluate specific traits of a characteristic invader
towards competition for limited resources and the consequent
alteration of community functioning under decreasing ground
water availability. We selected a protected Mediterranean
costal dune system of high ecological value, where largescale extraction of ground water provides excellent
experimental conditions to study changes in the competitive
balances among invasive and native species. We will analyse
the effects i) at the seedling level to evaluate changes in plant
establishment; ii) at the plant level to gain major insights on
the spatial and temporal partitioning of water sources and
regulating mechanisms of selected species and iii) at the
community level to evaluate changes in water flow,
competition and facilitation (e.g. hydraulic lift), community
functioning, and changes in invasibility of the system. The aim
is the identification of key processes controlling the
competitive balances between invasive neophytes and native
species and invasibility of semi-arid systems to contribute to a
risk assessment under global change scenarios.
PhD-student Katie Rascher, Tine Hellmann in collaboration with Cristina Máguas
Ecological relevance of carbon isotope fractionation during dark respiration
(ECORES, DFG)
Stable isotopes provide a powerful diagnostic tool to analyze
carbon pools and fluxes, which along with the isotopic composition
of ecosystem respiration (δ13CR) are now measured in ecosystems
world-wide. Recently, a mechanistic understanding on isotopic
fractionation during dark respiration has been achieved on the
physiological scale, while much less is known on its impact at
larger scales, under natural conditions or in different functional
groups. This project aims to close the gap between recent
advances on mechanisms of fractionation during dark respiration
and its ecological significance by combining metabolic, whole-plant
and ecosystem approaches. Our innovative and low-cost technique
enables a high-time resolved assessment of dark respired δ13CO2
(δ13Cres) (Werner et al 2007). Starting with a wide species survey of
diurnal courses of δ13Cres, this study will focus on the analysis of
these short-term variations in selected functional groups
considering leaf, shoot and root diurnal dynamics of metabolite
pools and partitioning. Possible involvement in larger temporal and
spatial scales will be assessed by evaluating their respective
contribution first at the “whole-plant” and second at the ecosystem scale using a component mass
balance approach in a natural Mediterranean ecosystem. Understanding the dynamics of δ 13CR has
significant implications for the evaluation of ecosystem response to global change.
PhD-Student Frederick Wegener, in collaboration with Pierrick Priault, Cristina Máguas, Joao S.
Pereira, Jaleh Ghashghaie, Kolby Jardine
Further Project Cooperation:
Invasive Species Evaluation, ConTrol & Education (EU-Marie-Currie
IRSES)
coordinated by Tillmann Buttschardt (University of Münster), with Tine Hellmann (University
Bielefeld), Cristina Máguas (University of Lisbon), Joao Meiro (University Federal de Viçosa, Brazil)
DeInvader project EUFAR hyperspectral LIDAR-flight
André Große-Stoltenberg, T. Buttschardt, (University Münster)
Shrub invasion in Mediterranean Cork oak woodlands (MEDshrub, DAAD)
with Maria Caldeira, Instituto Superior de Agronomia, Lisbon
Foraging strategies of sea lion populations in Galapagos
Jana Jeglinski, Fritz F. Trillmich (University Bielefeld), National Geographic
Mechanisms of isotope fractionation during respiration
Marco Lehmann, Roland Werner and Nina Buchmann (ETH Zürich) Rolf Siegwolf (Paul
Scherer Institut, Schweiz), Arthur Gessler (ZALF Berlin)
Former Projects
Partitioning of N-sources in different successional stages in a nutrient poor
sandy grassland by15N-labelling-experiments
Open sandy grasslands are characteristic nutrient poor habitats
with extreme microclimatic conditions. Because of land use
change and atmospheric nutrient input these ecosystems
become more and more endangered. In order to better
understand the mechanisms of succession, competition and coexistence in these ecosystems, we are presently investigating
the influence of different nitrogen sources on N-partitioning
between species by 15NO3- and 15NH4+ labelling under natural
conditions. Particularly, causes for the disappearance of early
successional species during succession are investigated. In
these nutrient poor systems niche differentiation in respect to
differential N-source utilization (e.g. NO3- ; NH4+) may play a
major role. We tested the hypothesis of changes in N-source
utilization from the most available nitrogen source (NO 3-) to less
available NH4+ with ongoing succession occurs to coexist with
other species in later successional stages with higher
competition. Particularly, we compared two typical pioneer
species with different strategies - Rumex acetosella and
Corynephorus canescens. The latter is a pioneer species
characteristic for open sand areas, e.g. after disturbance,
whereas the former shows a longer presence in succession.
Therefore we hypothesised that C. canescens has a lower benefit from increased nitrogen availability
than R. acetosella.
PhD-student: Vanessa M. Stahl, co-orientated by: Wolfram Beyschlag, Tom Steinlein
Partitioning seasonal changes in carbon fluxes of a Mediterranean
woodland into photosynthetic and respiratory components by stable
isotope analysis (ISOFLUX, DFG)
A functional understanding of carbon fixation by terrestrial
ecosystems and atmosphere/biosphere gas exchange is particularly
important regarding global climate change. However, a mechanistic
understanding of changes in photosynthetic carbon fixation and
respiratory CO2 release is difficult to achieve from the analysis of net
ecosystem exchange rates (NEE). Naturally abundant stable isotopes
provide a unique way to partition these opposing fluxes. We will
analyse the seasonal changes in the photosynthetic and respiratory
carbon fluxes in a Mediterranean evergreen woodland (at the
Euroflux site in Portugal). This well characterized system provides
unique conditions for a functional analysis of the temporal dynamics
and environmental parameters, since the natural changes in climate
conditions result in large seasonal variations in net ecosystem fluxes.
The temporal dynamics of ecosystem and soil respiration (Keelingplot approach) will be assessed, as well as the contribution of heteroand autotrophic respiration. Furthermore, the contribution of different
functional plant groups (grass-, shrub, and tree-layer) to the net
fluxes will be analysed. Model approaches will be used, first, to
estimate ecosystem fluxes from isotope gradient measurements
(isofluxes) and analyse fractionation processes at the ecosystem
level; and second, to evaluate the contribution of different functional
groups to ecosystem productivity and seasonal changes carbon
source/sink strength. By identifying critical factors for ecosystem
functioning, a risk assessment of climate changes effects for this
semi-arid ecosystem can be developed.
PhD-Student Stephan Unger, in collaboration with Cristina Máguas, Joao S. Pereira