Hagai Shemesh

Ben-Gurion University of the Negev, Beersheba, Southern District, Israel

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Publications (6)7.58 Total impact

  • 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.
    Plant Biology 12/2012; · 2.32 Impact Factor
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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.
    Plant signaling & behavior 04/2012; 7(4):492-501.
  • 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.
    Plant Ecology 01/2012; 213(1). · 1.53 Impact Factor
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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.
    Plant signaling & behavior 09/2011; 6(9):1356-60.
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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.
    Plant signaling & behavior 11/2010; 5(11):1501-3.
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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.
    PLoS ONE 01/2010; 5(5):e10824. · 3.73 Impact Factor

Publication Stats

18 Citations
7.58 Total Impact Points

Institutions

  • 2010–2012
    • Ben-Gurion University of the Negev
      • • Jacob Blaustein Institutes for Desert Research
      • • Department of Life Sciences
      Beersheba, Southern District, Israel