Hagai Shemesh

Tel-Hai Academic College, Jā‘ūna, Northern District, Israel

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Publications (10)9.98 Total impact

  • Stav Livne-Luzon · Hagai Shemesh · Osnat Gilor · Ofer Ovadia
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    ABSTRACT: Aims Release of carbon from plant roots initiates a chain of reactions involving the soil microbial community and microbial predators, eventually leading to nutrient enrichment, a process known as the ‘microbial loop’. However, root exudation has also been shown to stimulate nutrient immobilization, thereby reducing plant growth. Both mechanisms depend on carbon exudation, but generate two opposite soil nutrient dynamics. We suggest here that this difference might arise from temporal variation in soil carbon inputs.
    No preview · Article · Nov 2015 · Journal of Plant Ecology
  • Hagai Shemesh · Efrat Dener
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    ABSTRACT: Background/Question/Methods Plants are known to discriminate between soil patches with different resource levels and tend to allocate more roots to rich patches. We tested the hypothesis that in addition to their ability to discriminate in response to mean differences in resource availability, plants can also discriminate in response differences in habitat variance. Split-root Pisum sativum plants were grown in two separated pots. While one of the root-systems was subjected to a constant nutrient supply (constant fertilizer concentrations throughout the season) the other experienced temporal variability in nutrient availability (randomly changing fertilizer concentrations). Overall, mean nutrient availability was equal for both root systems. Since theoretical models of risk sensitivity predict an energy-status dependent response, the experiment was replicated 3 times, with plants of low, medium and high energy-status. Results/Conclusions Root allocation was dependent on the plants energy-status. Plants of low energy-status developed significantly more roots in the variable pot (25% more biomass). In contrast, plants of high energy-status developed significantly more roots in the constant pot (58% more biomass). These results are in agreement with the energy budget rule and suggest that in addition to their ability to notice mean differences plants are also able to perceive within season environmental variability. This ability might enable plants to manage their risks while foraging in variable environments.
    No preview · Conference Paper · Aug 2014
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    ABSTRACT: Background/Question/Methods Root carbon (C) exudation initiates a chain of reactions involving soil microbial community and microbial predators, leading to nutrient enrichment (i.e. 'microbial loop'). However, C exudation was also shown to stimulate nutrient immobilization, thereby reducing plant growth. Both mechanisms depend on C exudation, but generate two opposite soil nutrient dynamics. We suggest that this apparent contradiction between 'microbial loop' and 'immobilization' hypotheses can be reconciled when considering temporal C dynamics. We address two possible modes of C exudation: (1) Continuous; (2) Pulsed. Each C dynamic should influence the soil microbial community differently, resulting in opposing nutrient availabilities. We carried out two experiments: the first manipulated the initiation time of temporal C dynamics and the second manipulated both temporal C dynamics and soil nutrient availability. In both experiments, a fast-growing wheat plant was planted together with a slow-growing sage plant in the same pot, but the focus was on the performance of the wheat plant. We hypothesized that wheat plants should perform better under C pulses (leading to nutrient enrichment) than under continuous C supply (leading to nutrient limitation). However, this pattern should be stronger when C dynamic begins early during the growing season of the wheat plants. Results/Conclusions Temporal C dynamics restricted the performance of both plant species. Moreover, this pattern was stronger when C supply began early during the wheat growing season. Contrasting only the pulsed and continuous C supply regimes, exemplified that wheat plants performed better under C pulses. Under rich soil conditions, the addition of both C and nitrogen (N) had the most prominent effect on soil characteristics, bacterial abundance and plant performance. Specifically, when N was added, continuous C supply led to a higher abundance of soil bacteria, while causing wheat plants to exhibit a growth pattern typical to nutrient stress conditions. When taking into consideration all measured variables and looking for differences emerging from temporal C dynamics, it appears that C pulses differed both from the control and from the continuous C supply. This separation based on temporal C dynamics supports our assertion that C pulses lead to below-ground chain reactions in the microbial community cascading up to affect plant performance. Deciphering the complex temporal dynamics and interactions which control the availability of growth-limiting nutrients to plants is expected to generate a broader picture of the ecological links between above- and below-ground interactions, which are currently at the cutting edge of soil science.
    No preview · Conference Paper · Aug 2014
  • H Shemesh · A Novoplansky
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    ABSTRACT: It has been suggested that architectural plasticity in shoot size and number allows plants to manage environmental risks. Simpler structures require shorter development times and fewer resources, which secure minimal fitness even under risky and unfavourable conditions. Here we tested the hypothesis that the magnitude of such architectural plasticity depends on the species' developmental strategy. Specifically, species with late reproduction were expected to express the highest levels of architectural plasticity in response to environmental cues predicting high probability of abrupt deterioration in growth conditions. This hypothesis was tested by comparing Mediterranean and semi-arid populations of three species, which differed in growth strategy: Trifolium purpureum, a determinate and late flowerer, and Emex spinosa and Hippocrepis unisiliquosa that flower indeterminately throughout the season. All plants were exposed to varying levels of water availability and competition, but only T. purpureum displayed plastic architectural responsiveness to the experimental manipulations. In contrast, the early and extended step-by-step flowering of both E. spinosa and H. unisiliquosa reflected a relatively deterministic bet-hedging reproductive schedule, whereby minimum fitness is secured even under adverse conditions. These two opposing strategies gave contrasting results, with E. spinosa and H. unisiliquosa displaying reduced efficiency under favourable conditions under which T. purpureum had the highest reproductive efficiency. The evolutionary interplay between deterministic risk-averse and plastic risk-prone growth strategies might reflect contrasts in the probability and severity of environmental risks, and the costs of missed opportunities.
    No preview · Article · Dec 2012 · Plant Biology
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    ABSTRACT: Size variability in plants may be underlain by overlooked components of architectural plasticity. In annual plants, organ sizes are expected to depend on the availability and reliability of resources and developmental time. Given sufficient resources and developmental time, plants are expected to develop a greater number of large branches, which would maximize fitness in the long run. However, under restrictive growth conditions and environmental reliability, developing large branches might be risky and smaller branches are expected to foster higher final fitness. Growth and architecture of Trifolium purpureum (Papilionaceae) plants from both Mediterranean (MED) and semi-arid (SAR) origins were studied, when plants were subjected to variable water availability, photoperiod cues and germination timing. Although no clear architectural plasticity could be found in response to water availability, plants subjected to photoperiod cuing typical to late spring developed fewer basal branches. Furthermore, plants that germinated late were significantly smaller, with fewer basal branches, compared with plants which grew for the same time, starting at the beginning of the growing season. The results demonstrate an intricate interplay between size and architectural plasticities, whereby size modifications are readily induced by environmental factors related to prevalent resource availability but architectural plasticity is only elicited following the perception of reliable anticipatory cues.
    Preview · Article · Apr 2012 · Plant signaling & behavior
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    Hagai Shemesh · Ofer Ovadia · Ariel Novoplansky
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    ABSTRACT: Naturally growing plants are able to plastically respond to myriad environmental challenges and opportunities. When confronted with multiple stresses, plants are expected to be able to prioritize their responses according to immediacy and predicted acuteness of these stresses. Here, we studied the interactive effects of competition and nutrient deprivation on growth responses of damaged Trifolium purpureum plants to salivary cues of a mammalian grazer. Salivary cues elicited marked growth responses in damaged but otherwise well-nourished and competition-free T. purpureum plants; however, this positive effect was annulled under Stipa capensis competition and was reversed under nutrient deficiency. The results suggest that the magnitude and direction of the effects of salivary cues on plant growth depend on an intricate prioritization of plant responses to prevailing and expected challenges and that T. purpureum plants perceive competition as a more acute stress than grazing. While herbivore saliva enables plants to reliably differentiate between herbivory and physical damage, the limited correlation between prevailing and future herbivory might reduce the informative value of salivary cues, rendering their effects weaker than those of prevalent competition and nutrient deficiency, whose continued detrimental effects are usually highly predictive. The results stress the importance of further studying the interactive effects of the acuteness and reliability of prevailing and anticipated stresses, and the informational content and adaptive value of environmental cues under various environmental circumstances.
    Full-text · Article · Jan 2012 · Plant Ecology
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    Hagai Shemesh · Ran Rosen · Gil Eshel · Ariel Novoplansky · Ofer Ovadia
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    ABSTRACT: Plants are able to discriminately allocate greater biomass to organs that grow under higher resource levels. Recent evidence demonstrates that split-root plants also discriminately allocate more resources to roots that grow under dynamically improving nutrient levels, even when their other roots grow in richer patches. Here, we further tested whether, besides their responsiveness to the direction of resource gradients, plants are also sensitive to the steepness of environmental trajectories. Split-root Pisum sativum plants were grown so that one of their roots developed under constantly-high nutrient levels and the other root was subjected to dynamically improving nutrient levels of variable steepness. As expected, plants usually allocated a greater proportion of their biomass to roots that developed under constantly high resource availability; however, when given a choice, they allocated greater biomass to roots that initially experienced relatively low but steeply improving nutrient availabilities than to roots that developed under continuously-high nutrient availability. Such discrimination was not observed when the roots in the poor patch experienced only gentler improvements in nutrient availability. The results are compatible with the notion that responsiveness to the direction and steepness of environmental gradients could assist annual plants to increase their performance by anticipating resource availabilities foreseeable before the end of their growing season. The results exemplify the ability of plants to integrate and utilize environmental information and execute adaptive behaviours which, until recently, were attributed only to animals with central nervous systems.
    Full-text · Article · Sep 2011 · Plant signaling & behavior
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    Hagai Shemesh · Ofer Ovadia · Ariel Novoplansky
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    ABSTRACT: Plants are known to be highly responsive to environmental heterogeneity and normally allocate more biomass to organs which grow in richer patches. However, recent evidence demonstrates that plants can discriminately allocate more resources to roots that develop in patches with increasing nutrient levels, even when their other roots develop in richer patches. Responsiveness to the direction and steepness of spatial and temporal trajectories of environmental variables might enable plants to increase their performance by improving their readiness to anticipated resource availabilities in their immediate proximity. Exploring the ecological implications and mechanisms of trajectory- sensitivity in plants is expected to shed new light on the ways plants learn their environment and anticipate its future challenges and opportunities.
    Full-text · Article · Nov 2010 · Plant signaling & behavior
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    ABSTRACT: Plants have been recognized to be capable of allocating more roots to rich patches in the soil. We tested the hypothesis that in addition to their sensitivity to absolute differences in nutrient availability, plants are also responsive to temporal changes in nutrient availability. Different roots of the same Pisum sativum plants were subjected to variable homogeneous and heterogeneous temporally - dynamic and static nutrient regimes. When given a choice, plants not only developed greater root biomasses in richer patches; they discriminately allocated more resources to roots that developed in patches with increasing nutrient levels, even when their other roots developed in richer patches. These results suggest that plants are able to perceive and respond to dynamic environmental changes. This ability might enable plants to increase their performance by responding to both current and anticipated resource availabilities in their immediate proximity.
    Full-text · Article · May 2010 · PLoS ONE
  • Hagai Shemesh · Adi Arbiv · Ofer Ovadia · Ariel Novoplansky
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    ABSTRACT: Background/Question/Methods The rate at which environmental factors change often varies overtime. Phenotypic plasticity is one solution organisms have adopted to cope with such variability. Since developmental plasticity takes time, mechanisms that assist plants to estimate future growth conditions should be selected for. Absolute values of environmental factors are good predictors for future conditions only when the rate of change is constant among growing seasons. But if this is not the case, sensitivity to gradients is expected. We tested whether plants can preempt future growth conditions by responding to both absolute values and the dynamics of resource availability. Pea plants were grown in a split-root choice experiment where different roots of the same plant experienced both constant and dynamic (increasing or decreasing) resource levels. Results/Conclusions Plants invested significantly more in roots growing in improving habitats rather than deteriorating ones. This was true regardless of absolute resource levels, implying that they developed according to future rather than prevailing conditions.
    No preview · Conference Paper · Aug 2009