Despite recent progress in understanding mechanisms of tree species coexistence in tropical forests, a simple explanation for the even more extensive diversity of insects feeding on these plants has been missing. We compared folivorous insects from temperate and tropical trees to test the hypothesis that herbivore species coexistence in more diverse communities could reflect narrow host specificity relative to less diverse communities. Temperate and tropical tree species of comparable phylogenetic distribution supported similar numbers of folivorous insect species, 29.0 ± 2.2 and 23.5 ± 1.8 per 100 square meters of foliage, respectively. Host specificity did not differ significantly between community samples, indicating that food resources are not more finely partitioned among folivorous insects in tropical than in temperate forests. These findings suggest that the latitudinal gradient in insect species richness could be a direct function of plant diversity, which increased sevenfold from our temperate to tropical study sites.

There So Many Species of Herbivorous Insects in Tropical Rainforests

A new genus and species of Hydromedusae is described from the waters off North Queensland. It is placed in the Dipleurosomatidae because of its irregularly branched radial canals, gonads on the radial canals separated from the stomach, hollow marginal tentacles and lack of cirri or cordyli. It differs from all other medusae in its two rows of small, simple, wart-like gonadal papillae. It differs from the other dipleurosomatids in its unique combination of other characters, namely, 5-6 radial canals leaving the stomach, branching dichotomously an irregular number of times; about half as many tentacles as canal branches reaching ring canal, not in correspondence with canal branches; with about 8 globular or heart-shaped stalked clubs between successive tentacles; and lacking ocelli. This report represents the first record of the Dipleurosomatidae in Australian waters. Cnidaria, Hydrozoa, Leptomedusae, Dipleurosomatidae, Hydromedusae.

Memoirs of the Queensland museum.

Silicon crosstalk with reactive oxygen species, phytohormones and other signaling molecules.

Silicon-mediated plant defense against pathogens and insect pests

Plants’ ability to take up silicon from the soil, accumulate it within their tissues and then reincorporate it into the soil through litter creates an intricate network of feedback mechanisms in ecosystems Here, we provide a concise review of silicon’s roles in soil chemistry and physics and in plant physiology and ecology, focusing on the processes that form these feedback mechanisms Through this review and analysis, we demonstrate how this feedback network drives ecosystem processes and affects ecosystem functioning Consequently, we show that Si uptake and accumulation by plants is involved in several ecosystem services like soil appropriation, biomass supply, and carbon sequestration Considering the demand for food of an increasing global population and the challenges of climate change, a detailed understanding of the underlying processes of these ecosystem services is of prime importance Silicon and its role in ecosystem functioning and services thus should be the main focus of future research

https://www.mdpi.com/2223-7747/10/4/652/pdf

Silicon in the Soil-Plant Continuum: Intricate Feedback Mechanisms within Ecosystems.

The role of plant silicon (Si) in the alleviation of abiotic and biotic stress is now widely recognised and researched. Amongst the biotic stresses, Si is known to increase resistance to herbivores through biomechanical and chemical mechanisms, although the latter are indirect and remain poorly characterised. Chemical defences are principally regulated by several anti-herbivore phytohormones. The jasmonic acid (JA) signalling pathway is particularly important and has been linked to Si supplementation, albeit with some contradictory findings. In this Perspectives article, we summarise existing knowledge of how Si affects JA in the context of herbivory and present a conceptual model for the interactions between Si and JA signalling in wounded plants. Further, we use novel information from the model grass Brachypodium distachyon to underpin aspects of this model. We show that Si suppresses reduces JA concentrations in plants subjected to chemical induction (methyl jasmonate; MeJA) and herbivory (Helicoverpa armigera) by 34% and 32%, respectively. Moreover, +Si plants had 13% more leaf macro-hairs than –Si plants. From this study and previous work, our model proposes that Si acts as a physical stimulus in the plant which causes a small, transient increase in JA. When +Si plants are subsequently attacked by herbivores they potentially show a faster induction of JA due to this priming. +Si plants that have already invested in biomechanical defences (e.g. trichomesmacro-hairs), however, have less utility for JA-induced defences and show lower levels of JA-induction overall.

/pdf/the-role-of-silicon-in-antiherbivore-phytohormonal-44qp6vqp7m.pdf

The Role of Silicon in Antiherbivore Phytohormonal Signalling

Silicon (Si) has been widely reported to improve plant resistance to water stress via various mechanisms including cuticular Si deposition to reduce leaf transpiration. However, there is limited understanding of the effects of Si on stomatal physiology, including the underlying mechanisms and implications for resistance to water stress. We grew tall fescue (Festuca arundinacea Schreb. cv. Fortuna) hydroponically, with or without Si, and treated half of the plants with 20% polyethylene glycol to impose physiological drought (osmotic stress). Scanning electron microscopy in conjunction with X-ray mapping found that Si was deposited on stomatal guard cells and as a sub-cuticular layer in Si-treated plants. Plants grown in Si had a 28% reduction in stomatal conductance and a 23% reduction in cuticular conductance. When abscisic acid was applied exogenously to epidermal leaf peels to promote stomatal closure, Si plants had 19% lower stomatal aperture compared to control plants (i.e. increased stomatal sensitivity) and an increased efflux of guard cell K+ ions. However, the changes in stomatal physiology with Si were not substantial enough to improve water stress resistance, as shown by a lack of significant effect of Si on water potential, growth, photosynthesis and water-use efficiency. Our findings suggest a novel underlying mechanism for reduced stomatal conductance with Si application; specifically, that Si deposition on stomatal guard cells promotes greater stomatal sensitivity as mediated by guard cell K+ efflux.

Silicon deposition on guard cells increases stomatal sensitivity as mediated by K+ efflux and consequently reduces stomatal conductance

Elevated atmospheric CO2 suppresses jasmonate and silicon-based defences without affecting herbivores

Grasses accumulate large amounts of silicon (Si) which is deposited in trichomes, specialised silica cells and cell walls. This may increase leaf toughness and reduce cell rupture, palatability and digestion. Few studies have measured leaf mechanical traits in response to Si, thus the effect of Si on herbivores can be difficult to disentangle from Si-induced changes in leaf surface morphology. We assessed the effects of Si on Brachypodium distachyon mechanical traits (specific leaf area (SLA), thickness, leaf dry matter content (LDMC), relative electrolyte leakage (REL)) and leaf surface morphology (macrohairs, prickle, silica and epidermal cells) and determined the effects of Si on the growth of two generalist insect herbivores (Helicoverpa armigera and Acheta domesticus). Si had no effect on leaf mechanical traits; however, Si changed leaf surface morphology: silica and prickle cells were on average 127% and 36% larger in Si supplemented plants, respectively. Prickle cell density was significantly reduced by Si, while macrohair density remained unchanged. Caterpillars were more negatively affected by Si compared to crickets, possibly due to the latter having a thicker and thus more protective gut lining. Our data show that Si acts as a direct defence against leaf-chewing insects by changing the morphology of specialised defence structures without altering leaf mechanical traits.

/pdf/silicon-alters-leaf-surface-morphology-and-suppresses-insect-2qlx2h03px.pdf

Silicon Alters Leaf Surface Morphology and Suppresses Insect Herbivory in a Model Grass Species.

The role of silicon (Si) in alleviating the effects of biotic and abiotic stresses, including defence against insect herbivores, in plants is widely reported. Si defence against insect herbivores is overwhelmingly studied in grasses (especially the cereals), many of which are hyper-accumulators of Si. Despite being neglected, legumes such as soybean (Glycine max) have the capacity to control Si accumulation and benefit from increased Si supply. We tested how Si supplementation via potassium, sodium or calcium silicate affected a soybean pest, the native budworm Helicoverpa punctigera Wallengren (Lepidoptera: Noctuidae). Herbivory reduced leaf biomass similarly in Si-supplemented (+Si) and non-supplemented (-Si) plants (c. 29 and 23%, respectively) relative to herbivore-free plants. Both Si supplementation and herbivory increased leaf Si concentrations. In relative terms, herbivores induced Si uptake by c. 19% in both +Si and -Si plants. All Si treatments reduced H. punctigera relative growth rates (RGR) to a similar extent for potassium (-41%), sodium (-49%) and calcium (-48%) silicate. Moreover, there was a strong negative correlation between Si accumulation in leaves and herbivore RGR. To our knowledge, this is only the second report of Si-based herbivore defence in soybean; the rapid increase in leaf Si following herbivory being indicative of an induced defence. Taken together with the other benefits of Si supplementation of legumes, Si could prove an effective herbivore defence in legumes as well as grasses.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/FFB179918975B0C17E238850F0B6C1BB/S0007485319000798a.pdf/div-class-title-silicon-is-an-inducible-and-effective-herbivore-defence-against-span-class-italic-helicoverpa-punctigera-span-lepidoptera-noctuidae-in-soybean-div.pdf

Casey R. Hall

Papers

The Role of Silicon in Antiherbivore Phytohormonal Signalling

Silicon deposition on guard cells increases stomatal sensitivity as mediated by K+ efflux and consequently reduces stomatal conductance

Elevated atmospheric CO2 suppresses jasmonate and silicon-based defences without affecting herbivores

Silicon Alters Leaf Surface Morphology and Suppresses Insect Herbivory in a Model Grass Species.

Silicon is an inducible and effective herbivore defence against Helicoverpa punctigera (Lepidoptera: Noctuidae) in soybean.