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Understanding the ecological consequences of biodiversity is a fundamental challenge. Research on a key component of biodiversity, genetic diversity, has traditionally focused on its importance in evolutionary processes, but classical studies in evolutionary biology, agronomy and conservation biology indicate that genetic diversity might also have important ecological effects. Our review of the literature reveals significant effects of genetic diversity on ecological processes such as primary productivity, population recovery from disturbance, interspecific competition, community structure, and fluxes of energy and nutrients. Thus, genetic diversity can have important ecological consequences at the population, community and ecosystem levels, and in some cases the effects are comparable in magnitude to the effects of species diversity. However, it is not clear how widely these results apply in nature, as studies to date have been biased towards manipulations of plant clonal diversity, and little is known about the relative importance of genetic diversity vs. other factors that influence ecological processes of interest. Future studies should focus not only on documenting the presence of genetic diversity effects but also on identifying underlying mechanisms and predicting when such effects are likely to occur in nature.

/pdf/ecological-consequences-of-genetic-diversity-19pxvjx8hv.pdf

Ecological consequences of genetic diversity.

Summary 1 Root competition is defined as a reduction in the availability of a soil resource to roots that is caused by other roots. Resource availability to competitors can be affected through resource depletion (scramble competition) and by mechanisms that inhibit access of other roots to resources (contest competition, such as allelopathy). 2 It has been proposed that soil heterogeneity can cause size-asymmetric root competition. Support for this hypothesis is limited and contradictory, possibly because resource uptake is affected more by the amount and spatial distribution of resource-acquiring organs, relative to the spatial distribution of resources, than by root system size per se . 3 Root competition intensity between individual plants generally decreases as resource availability (but not necessarily habitat productivity) increases, but the importance of root competition relative to other factors that structure communities may increase with resource availability. 4 Soil organisms play important, and often species-specific, roles in root interactions. 5 The findings that some roots can detect other roots, or inert objects, before they are contacted and can distinguish between self and non-self roots create experimental challenges for those attempting to untangle the effects of self/non-self root recognition, self-inhibition and root segregation or proliferation in response to competition. Recent studies suggesting that root competition may represent a ‘tragedy-of-the-commons’ may have failed to account for this complexity. 6 Theories about potential effects of root competition on plant diversity (and vice versa) appear to be ahead of the experimental evidence, with only one study documenting different effects of root competition on plant diversity under different levels of resource availability. 7 Roots can interact with their biotic and abiotic environments using a large variety of often species-specific mechanisms, far beyond the traditional view that plants interact mainly through resource depletion. Research on root interactions between exotic invasives and native species holds great promise for a better understanding of the way in which root competition may affect community structure and plant diversity, and may create new insights into coevolution of plants, their competitors and the soil community.

https://besjournals.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1365-2745.2006.01124.x

Root competition: beyond resource depletion

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

Kin recognition is important in animal social systems. However, though plants often compete with kin, there has been as yet no direct evidence that plants recognize kin in competitive interactions. Here we show in the annual plant Cakile edentula, allocation to roots increased when groups of strangers shared a common pot, but not when groups of siblings shared a pot. Our results demonstrate that plants can discriminate kin in competitive interactions and indicate that the root interactions may provide the cue for kin recognition. Because greater root allocation is argued to increase below-ground competitive ability, the results are consistent with kin selection.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsbl.2007.0232

Kin recognition in an annual plant.

Recent evidence suggests that self/non-self discrimination exists among roots; its mechanisms, however, are still unclear. We compared the growth of Buchloe dactyloides cuttings that were grown in the presence of neighbors that belonged to the same physiological individual, were separated from each other for variable periods, or originated from adjacent or remote tillers on the same clone. The results demonstrate that B. dactyloides plants are able to differentiate between self and non-self neighbors and develop fewer and shorter roots in the presence of other roots of the same individual. Furthermore, once cuttings that originate from the very same node are separated, they become progressively alienated from each other and eventually relate to each other as genetically alien plants. The results suggest that the observed self/non-self discrimination is mediated by physiological coordination among roots that developed on the same plant rather than allogenetic recognition. The observed physiological coordination is based on an as yet unknown mechanism and has important ecological implications, because it allows the avoidance of competition with self and the allocation of greater resources to alternative functions.

http://www.bgu.ac.il/desert_ecology/Novoplansky/novoplansky4.pdf

Physiologically mediated self/non-self discrimination in roots

Plants can plastically respond to light competition in three strategies, comprising vertical growth, which promotes competitive dominance; shade tolerance, which maximises performance under shade; or lateral growth, which offers avoidance of competition. Here, we test the hypothesis that plants can 'choose' between these responses, according to their abilities to competitively overcome their neighbours. We study this hypothesis in the clonal plant Potentilla reptans using an experimental setup that simulates both the height and density of neighbours, thus presenting plants with different light-competition scenarios. Potentilla reptans ramets exhibit the highest vertical growth under simulated short-dense neighbours, highest specific leaf area (leaf area/dry mass) under tall-dense neighbours, and tend to increase total stolon length under tall-sparse neighbours. These responses suggest shifts between 'confrontational' vertical growth, shade tolerance and lateral-avoidance, respectively, and provide evidence that plants adopt one of several alternative plastic responses in a way that optimally corresponds to prevailing light-competition scenarios.

/pdf/decision-making-in-plants-under-competition-3kd2pa7qbs.pdf

Decision-making in plants under competition

Summary
The success of invasive plants has often been attributed to their rapid evolution at the introduced range. In particular, release from native enemies has been suggested to select for an evolutionary shift in resource allocation patterns from herbivore defence to increased size. Such evolutionary processes can take place not only between the native and invasive ranges but also within the invasive range over time, but this premise has been very seldom studied.
In this study, we examined the potential for post-invasion evolution in two traits hypothesized to facilitate plant invasion success, that is herbivore resistance and allelopathic ability. We studied these traits in the invasive plant Impatiens glandulifera by comparing plants from its native populations and from populations across its invasion chronosequence.
Results of common-garden experiment and chemical analyses revealed that plants from native populations or older populations within the invasive range show greater resistance to the generalist herbivore, Deilephila elpenor, coupled with greater production of the secondary defence compound 2-methoxy-1,4-naphthoquinone glycoside. In contrast, no differences were found between populations in their allelopathic effect on the germination of the co-occurring neighbour, Urtica doica. Finally, results from a field survey suggested that older populations within the invasive range incur greater attack rates from local herbivores compared to more recently established populations.
Synthesis. Our findings support the idea that the selection pressure of enemy release at the introduced range might attenuate over time, leading to the evolutionary recovery of enemy resistance. This study emphasizes the importance of incorporating the effect of time since introduction when examining evolutionary or ecological processes of plant invasions.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/1365-2745.12660

Evolution of plant defences along an invasion chronosequence: defence is lost due to enemy release – but not forever

Plant invasiveness was commonly attributed to the invader’s competitive superiority over the native community, but a general pattern supporting this prediction is still lacking. This is particularly enhanced by the fact that competitive dominance and its role in plant invasiveness require the use of scarcely-practiced experimental elements. Here, we used a comprehensive experimental approach to evaluate the competitive superiority of the highly invasive annual Impatiens glandulifera. We used two competition-setting treatments, which independently examine competitive effect versus response of both native and invasive genotypes. As a neighbour species we used Urtica dioica, a vigorous perennial co-occurring with I. glandulifera at both its native and introduced ranges. By examining both components of competitive ability we were able to show that although invasive genotypes exert a weaker competitive pressure compared to their native conspecifics, they are still competitively superior to U. dioica. Our results also suggest that the high competitive ability of I. glandulifera could be attributed it to allelopathic effects on co-occurring native species. We suggest that an appropriate experimental setup, which examines competitive effect and response independently, can provide a more factual evaluation of the competitive ability of invasive plants. Furthermore, the use of a dominant species as a target plant rather than a random species or one with poor competitive ability, renders our results more general, implying that I. glandulifera might exert greater competitive effect on the less robust co-occurring species. We conclude that our approach is highly useful and advocate its application in future tests of invasion success.

Michal Gruntman

Papers

Physiologically mediated self/non-self discrimination in roots

Decision-making in plants under competition

Evolution of plant defences along an invasion chronosequence: defence is lost due to enemy release – but not forever

Competitive dominance of the invasive plant Impatiens glandulifera: using competitive effect and response with a vigorous neighbour

Ontogenetic contingency of tolerance mechanisms in response to apical damage