Introduction. Ecologically Meaningful Germination Studies. Types of Seed Dormancy. Germination Ecology of Seeds with Nondeep Physiological Dormancy. Germination Ecology of Seeds with Morphophysiological Dormancy. Germination Ecology of Seeds with Physical Dormancy. Germination Ecology of Seeds in the Persistent Seed Bank. Causes of Within-Species Variations in Seed Dormancy and Germination Characteristics. A Geographical Perspective on Germination Ecology: Tropical and Subtropical Zones. A Geographical Perspective on Germination Ecology: Temperate and Arctic Zones. Germination Ecology of Plants with Specialized Life Cycles and/or Habitats. Biogeographical and Evolutionary Aspects of Seed Dormancy. Subject Index.

A Definitive Book on Seed Ecology@@@Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination

Summary 1 Once neglected, the role of facilitative interactions in plant communities has received considerable attention in the last two decades, and is now widely recognized It is timely to consider the progress made by research in this field 2 We review the development of plant facilitation research, focusing on the history of the field, the relationship between plant‐plant interactions and environmental severity gradients, and attempts to integrate facilitation into mainstream ecological theory We then consider future directions for facilitation research 3 With respect to our fundamental understanding of plant facilitation, clarification of the relationship between interactions and environmental gradients is central for further progress, and necessitates the design and implementation of experiments that move beyond the clear limitations of previous studies 4 There is substantial scope for exploring indirect facilitative effects in plant communities, including their impacts on diversity and evolution, and future studies should connect the degree of non-transitivity in plant competitive networks to community diversity and facilitative promotion of species coexistence, and explore how the role of indirect facilitation varies with environmental severity 5 Certain ecological modelling approaches (eg individual-based modelling), although thus far largely neglected, provide highly useful tools for exploring these fundamental processes 6 Evolutionary responses might result from facilitative interactions, and consideration of facilitation might lead to re-assessment of the evolution of plant growth forms

/pdf/facilitation-in-plant-communities-the-past-the-present-and-572accn7oh.pdf

Facilitation in plant communities: the past, the present, and the future

Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives.

/pdf/try-plant-trait-database-enhanced-coverage-and-open-access-25uv128bwj.pdf

TRY plant trait database : Enhanced coverage and open access

https://doi.org/10.1016/j.physrep.2020.05.004

Networks beyond pairwise interactions: Structure and dynamics

The tremendous diversity of species in ecological communities has motivated a century of research into the mechanisms that maintain biodiversity However, much of this work examines the coexistence of just pairs of competitors This approach ignores those mechanisms of coexistence that emerge only in diverse competitive networks Despite the potential for these mechanisms to create conditions under which the loss of one competitor triggers the loss of others, we lack the knowledge needed to judge their importance for coexistence in nature Progress requires borrowing insight from the study of multitrophic interaction networks, and coupling empirical data to models of competition

Beyond pairwise mechanisms of species coexistence in complex communities

Seed Ecology and Assembly Rules in Plant Communities

Question: Aluminium (Al) toxicity is one of the most important factors restricting plant establishment on acidic soils, but its ecological significance for the occurrence of species along natural pH gradients is still under investigation. Are species occurring on acidic sandy soils less susceptible to Al toxic effects on germination and seedling root growth rate than species from calcareous sandy soils? How strong is the explanatory power of species’ Al susceptibility for their occurrence along a pH gradient, as represented by their Ellenberg indicator value (EIV) for soil reaction (R)? Can Al tolerance of species be used as an independent trait to support Ellenberg’s empiricallyderived reaction indicator values? Location: Dry sandy grasslands in Southern Germany, with soil reactions ranging from acidic to calcareous. Methods: We tested early seedling responses to different Al concentrations in 15 species from dry sandy grasslands. A filter paper-based system was used to germinate seeds under Al concentrations of up to 10 mM. Germination, absolute root growth and the length of the root hair zone were recorded 7 and 14 d after first germination. Al concentrations that reduced root growth by 50 or 95% (ED50 and ED95, respectively) were correlated to Ellenberg indicator values (EIV) for soil reaction. Results: EIV explained 66% of the variance in species’ Al sensitivity. Tolerated Al concentrations resemble those concentrations the individual species are exposed to in their natural habitats. Conclusions: Among all soil factors varying with soil pH, Alis one of the strongest restrictions to species’ occurrence in acidic soils. Al acts as an environmental filter by allowing only Al-tolerant seedlings to grow roots and establish. Al sensitivity is a measurable objective trait that could form a crucial physiological component in defining R indicator values.

Aluminium toxic effects on seedling root survival affect plant composition along soil reaction gradients – a case study in dry sandy grasslands

Root-root interactions are much more sophisticated than previously thought, yet the mechanisms of belowground neighbor perception remain largely obscure. Genome-wide transcriptome analyses allow detailed insight into plant reactions to environmental cues. A root interaction trial was set up to explore both morphological and whole genome transcriptional responses in roots of Arabidopsis thaliana in the presence or absence of an inferior competitor, Hieracium pilosella. Neighbor perception was indicated by Arabidopsis roots predominantly growing away from the neighbor (segregation), while solitary plants placed more roots towards the middle of the pot. Total biomass remained unaffected. Database comparisons in transcriptome analysis revealed considerable similarity between Arabidopsis root reactions to neighbors and reactions to pathogens. Detailed analyses of the functional category ‘biotic stress’ using MapMan tools found the sub-category ‘pathogenesis-related proteins’ highly significantly induced. A comparison to a study on intraspecific competition brought forward a core of genes consistently involved in reactions to neighbor roots. We conclude that beyond resource depletion roots perceive neighboring roots or their associated microorganisms by a relatively uniform mechanism that involves the strong induction of pathogenesis-related proteins. In an ecological context the findings reveal that belowground neighbor detection may occur independently of resource depletion, allowing for a time advantage for the root to prepare for potential interactions.

/pdf/belowground-neighbor-perception-in-arabidopsis-thaliana-ohzk7auz5s.pdf

Belowground neighbor perception in Arabidopsis thaliana studied by transcriptome analysis: roots of Hieracium pilosella cause biotic stress

Strong hints exist that belowground competition is generally size-symmetric. While this has frequently been shown by use of integrative indicators like growth or biomass, resource-focussed approaches are still lacking, especially those investigating the competitive effect. Here, we present a correlation between neighbour plants’ root sizes and their competitive effect on their target plants’ nitrate uptake. This was derived from a controlled field experiment where intra- and interspecific combinations of five different herbaceous species from nutrient poor sand ecosystems were examined in an additive design. Short-term pulses of 15N-labelled nitrate were applied between competing pairs of plant individuals. The sizes of neighbour root systems had high explanatory power for the competitive effect on target plants’ nitrate uptake. Equally important, a curve fitting approach revealed that the competitive effect based on 15N-uptake matched predictions of a size-symmetric interaction. With 66% of the variation in competitive effect on nitrate uptake explained by root system size, the degree to which root size results in a belowground overlap of zones of influence is crucial. Within this overlap, further attributes like architecture or uptake capacity may be important. Our data represent experimental support for a size symmetric competitive effect for a specific belowground resource. Since this is not consistent with an overproportional size advantage when mobile soil resources are limiting, it suggests that the survival of small individuals or species should be facilitated by the symmetric nature of belowground competitive effects.

15N-nitrate-labelling demonstrates a size symmetric competitive effect on belowground resource uptake

Questions

Dominance and occurrence of plant species change distinctly along soil reaction gradients; this has been attributed to different chemicals that can be either toxic or nutritional factors, varying with soil pH. The availability of different chemical forms of nitrogen (N) is one such factor, but the extent to which this can explain species distribution is yet unclear. We asked (1) is it possible to correlate the extent of species' physiological preference for ammonium vs nitrate to species occurrence along the soil reaction gradient; (2) how strong is the explanatory power of species occurrence along the soil reaction gradient for this preference, i.e. how much variation in species preference is explained by Ellenberg indicator values (EIV) for soil reaction; and (3) does inter-specific competition result in any shifts of this preference?



Location

Dry sandy grasslands in Southern Germany, with soil reactions ranging from acidic to calcareous.



Methods

We carried out a common garden experiment and a greenhouse experiment with species from Central European sandy grasslands. In addition, we re-analysed previously published data. Availability of ammonium and nitrate was manipulated in the presence and absence of interspecific competition, while other factors including soil pH were kept constant. Growth responses were used to calculate species preferences concerning chemical N forms.



Results

Species habitat niches for soil reaction, represented by their EIV, were found to strongly correlate with species preferences for certain N forms, with acidophilous species preferring ammonium and calciphilous species preferring nitrate. This was the case in all experiments and treatments without species interaction, but surprisingly not for species mixture treatments that might have involved additional soil biota with impact on N cycling.



Conclusions

High importance must be attributed to species' physiological preferences for certain N forms, because these impact on species occurrence along soil reaction gradients. Considering the known importance of other restrictions, e.g. aluminium toxicity or iron nutrition, it is likely that these factors, together with N form preference, act in concert. Our finding that species interaction impacts on such interrelations in an unexpected manner poses a future challenge to devise multi-factorial experiments on species occurrence along soil reaction gradients.

The response of grassland species to nitrate versus ammonium coincides with their pH optima

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