Effects of NaCl and CaCl2 Salinization on Morpho-Anatomical and Physiological Traits of Potted Callistemon citrinus Plants

The aim of this work was to assess the possible coordination mechanisms between leaf functional anatomical traits and physiological acclimation of potted Callistemon citrinus plants when subjected to two saline iso-osmotic solutions using NaCl or CaCl2. Digital image analysis was applied to quantify anatomical parameters with a specific focus on the occurrence of signs of structural damage as well as on alterations, such as the occurrence of shrunk tissues and accumulation of phenolic compounds. Morpho-anatomical analyses were accompanied by measurements of leaf gas exchange and chlorophyll fluorescence emission. Results showed that C. citrinus plants, when irrigated with the CaCl2 solution, induced a leaf morpho-anatomical structure which did not allow the maintenance of high photosynthetic performance under such conditions, compared to both controls and plants treated with the iso-osmotic solution of NaCl. Data collected seem to suggest a close relationship between anatomical traits and eco-physiological strategies in maintaining the photosynthetic efficiency under saline stress conditions and highlight the fundamental role of leaf anatomy in imposing the limits of plant physiology.

Rapid specialization of counter defenses enables two-spotted spider mite to adapt to novel plant hosts

Genetic adaptation, occurring over a long evolutionary time, enables host-specialized herbivores to develop novel resistance traits and to efficiently counteract the defenses of a narrow range of host plants. In contrast, physiological acclimation, leading to the suppression and/or detoxification of host defenses, is hypothesized to enable broad generalists to shift between plant hosts. However, the host adaptation mechanisms used by generalists composed of host-adapted populations are not known. Two-spotted spider mite (TSSM; Tetranychus urticae) is an extreme generalist herbivore whose individual populations perform well only on a subset of potential hosts. We combined experimental evolution, Arabidopsis thaliana genetics, mite reverse genetics, and pharmacological approaches to examine mite host adaptation upon the shift of a bean (Phaseolus vulgaris)-adapted population to Arabidopsis. We showed that cytochrome P450 monooxygenases are required for mite adaptation to Arabidopsis. We identified activities of two tiers of P450s: general xenobiotic-responsive P450s that have a limited contribution to mite adaptation to Arabidopsis and adaptation-associated P450s that efficiently counteract Arabidopsis defenses. In approximately 25 generations of mite selection on Arabidopsis plants, mites evolved highly efficient detoxification-based adaptation, characteristic of specialist herbivores. This demonstrates that specialization to plant resistance traits can occur within the ecological timescale, enabling the TSSM to shift to novel plant hosts.

Roles of photosynthetic, respiratory, stomatal and phenological acclimation in controlling carbon and water fluxes of mature Norway spruce in a changing climate

<p>Boreal regions are undergoing rapid climate change but our understanding of the long-term consequences for forest processes is hampered by limited knowledge of how trees acclimate to rising atmospheric CO<sub>2</sub> concentrations and temperature. This study used the detailed canopy flux model MAESTRA to simulate the effects of elevated CO<sub>2</sub> (eCO<sub>2</sub>) and warming on net photosynthesis (<em>A</em><sub>n</sub>) and transpiration (<em>E</em>) of mature boreal Norway spruce, investigating how these effects are influenced by the observed acclimation of photosynthetic capacity, respiration, stomatal behavior, and phenology. Without any type of acclimation, eCO<sub>2</sub> increased shoot and crown <em>A</em><sub>n</sub> during the non-frost growing season by 23-44%, while warming only had a minor effect (±2%). Photosynthetic downregulation greatly decreased the positive effect under eCO<sub>2</sub>. Under warming, both stomatal and phenological acclimation had substantial effects on <em>A</em><sub>n</sub> but in opposite directions. Transpiration at shoot and crown level was greatly decreased (23-50%) by eCO<sub>2</sub> and increased by warming (27-42%) in the absence of acclimation. However, both these effects were largely cancelled by stomatal acclimation. Effects of eCO<sub>2</sub> on <em>A</em><sub>n</sub> were generally smaller at entire crown compared to shoot level, as a result of photosynthetic stimulation being smaller in shaded canopy positions. In addition, upregulation of respiration in eCO<sub>2</sub> had a considerably larger negative effect on <em>A</em><sub>n</sub> at crown compared to shoot level. Overall, tree physiological acclimation generally acted to dampen non-acclimated responses. We conclude that photosynthetic and respiratory acclimation greatly reduce the positive effect of eCO<sub>2</sub> on tree CO<sub>2</sub> assimilation, while stomatal and phenological acclimation are crucial for annual water consumption under warming. These results highlight the critical need to account for acclimation in models.</p><p> </p>

Nutrient ratios in marine particulate organic matter are predicted by the population structure of well-adapted phytoplankton

A common assumption of a constant nitrogen-to-phosphorus ratio (N:P) of 16:1 in marine particulate organic matter (POM) appears to be invalidated by observations of major spatial variations in N:P. Two main explanations have been proposed. The first attributes the N:P variability to changes in the community composition of well-adapted phytoplankton. The second proposes that variability arises from physiological acclimation involving intracellular adjustments of nutrient allocation under nutrient deficiency. Using a model of phytoplankton physiology, observational datasets, and a review of laboratory culture results, we assess the mechanistic basis of N:P variability. We find that the taxonomic composition of well-adapted phytoplankton best explains observed variations in POM N:P. Furthermore, we show that acclimation to nutrient deficiency may be safely neglected when considering the effects of ecology on POM N:P. These findings provide insight into the controls on global variability in POM composition and average phytoplankton physiological performance in the oceans.

The generalist herbivore Tetranychus urticae (Koch) adapts to novel plant hosts through rapid evolution of metabolic resistance

Genetic adaptation, occurring over long evolutionary time, enables host-specialized herbivores to develop novel resistance traits and to counteract the defenses of a narrow range of host plants. In contrast, physiological acclimation, leading to the suppression and/or detoxification of host defenses is hypothesized to enable generalists to shift between plant hosts. Here, we examined the long-term response of an extreme generalist, the two-spotted spider mite, Tetranychus urticae Koch (TSSM), to the shift to the non-preferred and novel host plant Arabidopsis thaliana. We identified the key requirement of two tiers of cytochrome P450 monooxygenases for TSSM adaptation to Arabidopsis: general xenobiotic-responsive P450s that have a limited contribution to mite adaptation to Arabidopsis and adaptation-associated P450s that efficiently counteract Arabidopsis defenses, illustrating that in about 25 generations of TSSM selection on Arabidopsis plants mites evolved metabolic resistances characteristic of both generalist and specialist herbivores.