P1: Spatial above- and belowground complementarity

Above- and belowground complementarity of resource use is considered an important mechanism for increased biomass production in diverse tree communities. Complementary space occupation and spatial niche differentiation in tree crowns and the rhizosphere may contribute to competitive reduction and may facilitate individual tree and community productivity. Plasticity in crown and root architecture, in turn, are mediated by tree-tree interactions at the local neighbourhood level, improving three-dimensional (3D) space filling and enhancing biomass density in diverse neighbourhoods.

In-depth analyses of 3D space filling and above-/belowground biomass density along diversity gradients, however, received little attention. In P1 we will analyse (i) effects of local neighbours on complementarity in crown and root architecture of the TSPs by quantifying the spatio-temporal dynamics of above- and belowground growth and biomass allocation patterns, and (ii) how these processes will translate into enhanced tree growth.

P1G: Spatio-temporal dynamics of canopy space filling

Doctoral Researcher:

Maria Dolores Perles Garcia

Principal Investigators:

Prof. Dr. Goddert von Oheimb, Prof. Dr. Werner Härdtle

Objectives:

  • to analyse crown, branch and leaf traits in relation to tree-tree interactions (TSPs and local neighbourhood)
  • to analyse trait variability related to canopy filling and light interception;
  • to quantify how canopy space use complementarity translates into enhanced tree growth.

P1C: Belowground productivity and complementarity

Doctoral Researcher:

Hanjiao Gu

Principal Investigators:

Assoc. Prof. Dr. Xiaojuan Liu, Dr. Wensheng Bu, Prof. Dr. Keping Ma

Objectives:

  • to analyse species richness effects on fine-root production
  • to analyse effects of species composition on fine-root turnover and distribution
  • to find the connection between below- and aboveground processes

P2: Complementarity through trait variation

Chemical and morphological leaf and root traits of trees have been shown to vary (1) among species, (2) within species and among individuals, and (3) within individuals. So far it is unknown how these three components of trait variation contribute to complementarity effects of ecosystem functions. In the TreeDì design with comparing mono- and heterospecific TSPs, complementarity effects are easily visible in over-yielding.

Increased complementarity can be achieved through increasing trait variance between the two trees of a TSP or by increasing trait variance within the individual TSP trees. In addition, the contribution of the three components of trait variation to complementarity can vary with the abiotic environment, such as differences in soil nutrient supply, and the biotic environment, such as differences in tree species identity and diversity of the local neighborhood.

P2G: Causes and effects of leaf trait variation

Doctoral Researcher:

Andréa Davrinche

Principal Investigators:

Dr. Sylvia Haider, Prof. Dr. Stan Harpole

Objectives:

  • to quantify to which degree leaf traits are adjusted to different light conditions along the interaction plane of two tree species
  • to analyze trait variation as a response to species and functional diversity of the local neighborhood of the TSP andthe dependence of traits and trait variation on soil nutrient availability
  • to relate trait variation and performance of the TSP
  • to quantify different components of trait variation to complementarity effects of ecosystem functions

 

 

P2C: Roots and mycorrhizal traits

Doctoral Researcher:

Gaigai Ding

Principal Investigator:

Assist. Prof. Dr. Zeqing Ma, Dr. Bo Yang

Objectives:

  • to characterize tree species by their root morphological and anatomical root traits
  • to assess the response of root and mycorrhizal traits to resource patches, different tree neighborhoods, and site-scale resource gradients
  • to test whether complementary traits translate into enhanced tree productivity

P3: Tree interaction history and temporal complementarity

Water use
Theory predicts that diverse communities use resources more efficiently than monocultures. Under water shortage resource complementarity of water use may buffer growth decline. Carbon isotopes (d13C) in tree rings are used to infer diversity effects during drought.

Temporal complementarity
Variation in growth phenology – expected to occur in diverse mixtures – is predicted to exploit the resource ‘time’ more efficiently – as first results suggest. Using dendrometers we will test the hypothesis that diverse mixtures have an extended growth period.

Asymmetry
Size dependency of relative growth rates of two interacting individuals can be used to infer competitive asymmetry. Low asymmetry promotes coexistence and complementarity. We hypothesize that asymmetry is minimal in a diverse neighborhood and at intermediate levels of trait dissimilarity.

P3G: Spatio-temporal complementarity

Doctoral Researcher:

Florian Schnabel

Principal Investigators:

Prof. Dr. Christian Wirth, Prof. Jürgen Bauhus

Objectives:

  • Assess how neighborhood diversity affects water use efficiency (~stomatal closure) and growth during an extreme drought year (2016) for tree species with contrasting stomatal control (water savers vs. spenders)
  • Test how competitive asymmetry is controlled by diversity at the level of TSPs and their neighborhood based on biometric measurements

 

 

P3C: Seasonal complementarity of wood growth

Doctoral Researcher:

Tongyan Liu

Principal Investigators:

Assoc. Prof. Dr. Zhiyao Tang

Objectives:

  • Analyze whether diverse forests express complementarity in seasonal growth and whether this translates into higher productivity
  • Analyze whether diversity advances the start of the growing season
  • Relate seasonal growth complementarity to functional diversity of available proxy traits

 

 

P4: Herbivory

Local tree interactions might explain community-level associations of herbivores, their enemies, and tree diversity, but are likely modified by the wider tree neighborhood. The relative importance of potential bottom-up and top-down mechanisms underlying such associational effects, and their scale-dependence, remain unclear. Analyses of functional consumer traits, aided by molecular methods, may facilitate a mechanistic understanding.

P4G: Associational effects of herbivory across spatial scales

Doctoral Researcher:

Perttu Anttonen

Principal Investigator:

PD Dr. Andreas Schuldt

Objectives:

  • Herbivory & community structure of herbivore feeding guilds across space & time
  • Top-down vs. bottom-up control
  • Consequences for tree growth & productivity

 

 

P4C: Associational effects mediated by parasitoids

Doctoral Researcher:

Yi Li

Principal Investigators:

Prof. Dr. Chaodong Zhu, Assis. Prof. Douglas Chesters

Objectives:

  • Moth larvae-predator-parasitoid networks
  • Molecular identification pipelines
  • Phylogenetic framework for trophic communities

 

 

P5: Leaf fungal pathogens

Foliar fungal pathogens negatively affect plant performance, directly or indirectly by changing the outcome of competition. In contrast, it is not known how leaf fungal pathogen infestation affects other ecosystem functions such as leaf litter decomposition. As leaf litter decomposition is dependent on the chemical composition of the leaf tissue and fungi feed on organic compounds in the leaf, fungal infection can be expected to have an effect on leaf decomposition rates. There is also evidence that leaf inhabiting fungi play a direct role in leaf litter decomposition.

Leaf fungal pathogens are mostly highly host-specialized, which also applies to the BEF-China experiment. In the BEF-China experiment, both fungal richness and fungal infestation increase with increasing proportion of conspecifics in the local neighbourhood. Such neighbourhood effects are thought to be mediated by the modification of sun exposure, local microclimate or soil conditions.

P5G: Drivers of leaf fungal pathogen load

Doctoral Researcher:

Mariem Saadani

Principal Investigator:

Prof. Dr. Helge Bruelheide

Objectives:

  • to estimate the leaf area infected by fungal pathogens
  • to identify all fungal species found on the TSP trees, using morphological and molecular approaches
  • to monitor pathogen load and fungal species richness under different crown interaction points of TSPs and to relate these patterns to microclimate
  • to study the effect of pathogen load on tree productivity

 

 

P5C: Effects of leaf pathogens on leaf litter decomposition

Doctoral Researcher:

NA

Principal Investigator:

Prof. Dr. Xiaoyong Cui

Objectives:

  • to study the temporal course of fungal species composition, in parallel with the leaf chemical composition
  • to study leaf decomposition rates and to relate them to species leaf litter composition, pathogen load and local neighbourhood diversity

 

 

P6: Complementarity in root functions

Root exudates play a critical role in tree growth and survival. They mobilize nutrients and govern interactions with soil microorganisms and neighbors. The chemical profiles of root exudates are species-specific but also depend on the biotic and abiotic environment of the tree. Consequently, differences in tree community composition and (functional) diversity may lead to belowground niche differentiation with regards to nitrogen acquisition and allelopathy. In this sub-project, we test the hypothesis that differences in tree diversity and local neighborhood composition leads to complementarity in root chemical traits, which are reflected in exudate metabolome profiles and spatial-temporal nitrogen acquisition strategies.

P6G: Biodiversity effects on tree root exudate metabolomes

Doctoral Researcher:

Gonzalo Alejandro Garcia De Leo

Principal Investigators:

Prof. Dr. Nicole van Dam, Dr. Steffen Neumann, Prof. Dr. Dierk Scheel, Dr. Alexander Weinhold

Objectives:

  • Characterise tree species-specific root exudation metabolomes in plots with different levels of (functional) diversity
  • Analyse if tree species interactions drive changes in root exudation patterns and profiles
  • Assess the degree of complementarity in root exudate metabolomes in local neighbourhoods

P6C: Complementarity in nitrogen uptake by roots

Doctoral Researcher(s):

Sirong Zhang

Min Liu

Principal Investigators:

Prof. Dr. Xingliang Xu, Assoc. Prof. Dr. Naili Zhang

Objectives:

  • Characterise N-acquisition strategies, incl. soil microbes
  • Explore how trees and soil microbes acquire available N via chemical, temporal and spatial niche differentiation
  • Examine if tree species benefit from shared mycorrhizal networks
  • Analyse degree of complementarity N- uptake in local neighbourhoods over different soil depths and seasons

 

 

P7: Rhizosphere and root microbes

Tree species identity, plant successional stage, plant diversity level, and mycorrhizal type affect the soil microbial community composition. Plant genus diversity was also found to be an important predictor of ectomycorrhizal fungal community composition in subtropical forests. Both arbuscular and ectomycorrhizal fungal diversity and identity are known to influence tree species diversity and composition. Plant diversity level influences fungal community composition and the plant beta-diversity predicts the beta-diversity of fungal functional groups including mycorrhizal fungi.

Despite the number of recent advances in the rhizosphere and endosphere microbiome research, there is a limited knowledge on the inter- and intra-kingdom variation in community composition, co-occurrence network patterns, the functional gene profiles, and the drivers of these network patterns and functional gene profiles in the interaction zones of mono- and hetero-specific tree species pairs.

P7G: Rhizosphere microbiome and meta-transcriptome of TSPs

Doctoral Researcher:

Bala Singavarapu

Principal Investigator:

Dr. Tesfaye Wubet

Objectives:

  • Assess how the rhizosphere microbiome composition of mono- and hetero-specific TSPs change within and across diversity levels
  • Study the patterns of rhizosphere metagenome/ metatranscriptome profiles of TSPs across diversity levels
  • Identify the drivers and assess the relationships of the microbial co-occurrence network patterns and the functional gene profiles of mono- and hetero-specific TSPs across diversity levels

 

 

P7C: Mycorrhizal and endophytic fungal communities of TSPs

Doctoral Researcher:

Huiyun Gan

Principal Investigator:

Prof. Dr. Liangdong Guo

Objectives:

  • Analyze how root associated bacterial and fungal community composition of mono- and hetero-specific TSPs change within and across diversity levels and environmental conditions
  • Assess the link between root associated microbial communities with root traits, nitrogen acquisition and exudation profiles

 

 

P8:Functional diversity of soil organisms

The functional dissimilarity of species is hypothesised to determine the positive relationship between biodiversity and ecosystem functioning. However, functional dissimilarity effects might be context-dependent and strongest in complex environments (e.g. high resource complexity), where dissimilar species are able to occupy different niches. Thus, studying  the effects of functional  dissimilarity of interacting  trees in neighbourhoods of different diversity on the functional diversity and biomass of soil organisms may provide a generalisable framework to link biodiversity to ecosystem functions across above-belowground ecosystem compartments.

P8G: Functional diversity of soil microbial and nematode communities

Doctoral Researcher:

Rémy Beugnon

Principal Investigators:

Dr. Simone Cesarz, Prof. Dr. Nico Eisenhauer

Objectives:

  • To analyse if dissimilarity of TSPs increases functional diversity of soil microorganisms and soil nematodes
  • To analyse if more complex environments (diversity of the local neighbourhood) steepen this  slope  due  to  a  higher  diversity  of  organic  inputs  and  microhabitats,  which  is expected  to  increase  the  functional  diversity  of  soil  microorganisms  and  soil  nematodes
  • To analyse if increased functional diversity of soil organisms results in increased biomass of microorganisms and nematodes (consumer biomass)

 

 

P8C: Microbial function potential and its linkage with ecosystem functioning

Doctoral Researcher:

Jianqing Du

Principal Investigators:

Prof. Dr. Yanfen Wang, Assoc. Prof. Dr. Kai Xue

Objectives:

  • To identify the functional diversity of soil microorganisms involved in nitrogen cycling processes
  •  To link microbial functional diversity with corresponding ecosystem functioning by measuring soil extracellular enzyme activities and ecosystem process rates
  •  To determine the response of microbial functional gene diversity and corresponding ecosystem functioning to the functional dissimilarity of the local tree neighbourhood

 

 

P9: Modelling generalised diversity interactions

Individual tree-based modeling approaches rest on the assumption that resource supply and tree performance are spatially explicit processes at a local neighborhood scale. Models built on pairwise interactions suffer from the fact that local neighborhoods beyond the interaction partners are not taken into account.

The focus of TreeDì, on the one hand, on binary interactions between tree species pairs (TSPs), and on the other hand, on the wider neighborhood surrounding the TSPs allows to model interaction coefficients between tree pairs as a function of neighborhood diversity. This neighborhood diversity can also take functional or phylogenetic diversity into account. This project will develop a novel modeling approach addressing the interplay between (i) tree individuals, (ii) the local abiotic environment and (iii) the populations of herbivores, pathogens and rhizosphere species composing the above- and belowground food webs.

P9G: Integrated modeling of tree individuals and animal population dynamics

Doctoral Researcher:

Georg Albert

Principal Investigator:

Prof. Dr. Ulrich Brose

Objectives:

  • To model the dynamics of herbivore, pathogen and rhizosphere populations on landscapes (grids) composed of tree individuals as habitat compartments (grid cells)
  • To establish spatially-explicit models of tree individuals, their tree-tree interactions, and neighborhood effects
  • To predict tree growth in novel models synthesizing population- and individual-level processes for animals and trees, respectively, which will address interaction processes such as enemy dilution and facilitation

 

 

9PC: Modeling forest community dynamics and neighbor TSP competition

Doctoral Researcher:

NA

Principal Investigator:

Prof. Dr. Weiguo Sang

Objectives:

  • To model the change between TSP partners and the whole patch change through time
  • To simulate tree interactions for forest development
  • To use the models to understand the dynamic interactions of trees in mature forests

 

 

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