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Flooding threatens the functioning of managed grasslands by decreasing primary productivity and increasing nitrogen losses, notably as the potent greenhouse gas nitrous oxide (N2O). Sowing species with traits that promote flood resilience and mitigate flood-induced N2O emissions within these grasslands could safeguard their productivity while mitigating nitrogen losses. We tested how plant traits and resource acquisition strategies could predict flood resilience and N2O emissions of 12 common grassland species (eight grasses and four legumes) grown in field soil in monocultures in a 14-week greenhouse experiment. We found that grasses were more resistant to flooding while legumes recovered better. Resource-conservative grass species had higher resistance while resource-acquisitive grasses species recovered better. Resilient grass and legume species lowered cumulative N2O emissions. Grasses with lower inherent leaf and root δ13C (and legumes with lower root δ13C) lowered cumulative N2O emissions during and after the flood. Our results highlight the differing responses of grasses with contrasting resource acquisition strategies, and of legumes to flooding. Combining grasses and legumes based on their traits and resource acquisition strategies could increase the flood resilience of managed grasslands, and their capability to mitigate flood-induced N2O emissions. A free Plain Language Summary can be found within the Supporting Information of this article.

Grasses accumulate large amounts of silicon (Si) which acts as a highly effective physical defence against insect herbivory, however recent evidence shows that Si supplementation also modifies plant secondary metabolite concetrations. Changes in plant secondary metabolites concentrations can have cascading effects on higher trophic levels, such as parasitoids, as they are dependent on the host herbivore for growth and development. However, relatively little is known about how Si application affects higher trophic levels. We examined the effects of Si addition on alkaloid content in leaves of Phalaris aquatica (Poaceae) and the effect on interactions between an aphid (Rhopalosiphum padi) and its parasitoid (Aphidius colemani). Si supplementation had no effect on aphid abundance or parasitism rate. Adult aphids, aphid mummies (parasitised aphids) and the emergent parasitoids were, however, significantly smaller on Si+ plants. Parasitoid traits (size and emergence) were correlated with aphid mummy size. Si addition reduced parasitoid emergence rate and size due to reduced host mummy size, in addition, significantly fewer females emerged from mummies on Si+ plants. Aphid infestation significantly altered alkaloids concentrations, reducing gramine by 80% while increasing tryptamine by 91% in Si- plants. Si addition reduced aphid-induced tryptamine concentrations by 64% and increased 5-MeO-tryptamine by over 800% in control and 142% in aphid infested plants. Our results show that while Si addition has modest impacts on the herbivore, it significantly alters secondary metabolites and has stronger effects on the higher trophic level through changes in the quality of the parasitised host.

The uptake and deposition of silicon (Si) as silica phytoliths is common among land plants and is associated with a variety of functions. Among these, herbivore defense has received significant attention, particularly with regard to grasses and grasslands. Grasses are well known for their high silica content, a trait which has important implications ranging from defense to global Si cycling. Here, we test the classic hypothesis that C4 grasses evolved stronger mechanical defenses than C3 grasses through increased phytolith deposition, in response to extensive ungulate herbivory ("C4 -grazer hypothesis"). Despite mixed support, this hypothesis has received broad attention, even outside the realm of plant biology. Because C3 and C4 grasses typically dominate in different climates, with the latter more abundant in hot, dry regions, we also investigated the effects of water availability and temperature on Si deposition. We compiled a large dataset of grasses grown under controlled environmental conditions. Using phylogenetically informed generalized linear mixed models and character evolution models, we evaluated whether photosynthetic pathway or growth condition influenced Si concentration. We found that C4 grasses did not show consistently elevated Si concentrations compared with C3 grasses. High temperature treatments were associated with increased concentration, especially in taxa adapted to warm regions. Although the effect was less pronounced, reduced water treatment also promoted silica deposition, with slightly stronger response in dry habitat species. The evidence presented here rejects the "C4 -grazer hypothesis." Instead, we propose that the tendency for C4 grasses to outcompete C3 species under hot, dry conditions explains previous observations supporting this hypothesis. These findings also suggest a mechanism via which anthropogenic climate change may influence silica deposition in grasses and, by extension, alter the important ecological and geochemical processes it affects.

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.

Plants protect themselves against pest attack utilizing both direct and indirect modes of defense. The direct mode of defense includes morphological, biochemical, and molecular barriers that affect feeding, growth, and survival of herbivores whereas the indirect mode of defense includes release of a blend of volatiles that attract natural enemies of the pests. Both of these strategies adopted by plants are reinforced if the plants are supplied with one of the most abundant metalloids, silicon (Si). Plants absorb Si as silicic acid (Si(OH)4) and accumulate it as phytoliths, which strengthens their physical defense. This deposition of Si in plant tissue is up-regulated upon pest attack. Further, Si deposited in the apoplast, suppresses pest effector molecules. Additionally, Si up-regulates the expression of defense-related genes and proteins and their activity and enhances the accumulation of secondary metabolites, boosting induced molecular and biochemical defenses. Moreover, Si plays a crucial role in phytohormone-mediated direct and indirect defense mechanisms. It is also involved in the reduction of harmful effects of oxidative stress resulting from herbivory by accelerating the scavenging process. Despite increasing evidence of its multiple roles in defense against pests, the practical implications of Si for crop protection have received less attention. Here, we highlight recent developments in Si-mediated improved plant resistance against pests and its significance for future use in crop improvement.

1. Plants have long been exposed to insect herbivore attack. Crucial to the plant's ability to defend itself is its ability to identify specific signals associated with attacking insects. Distinctive chemical cues, such as those associated with chewing insect oral secretions (OS), activate targeted defence responses to chewing insect herbivores. 2. Herbivore‐associated cues can be complicated by the fact that many herbivores form associations with microbes that produce their own specific signals, which may induce alternative defence processes. 3. Here we report that OS of the global pest, the cotton bollworm (Helicoverpa armigera), induce senescence around wounds in Brachypodium distachyon leaves. Crude OS activate greater levels of senescence than OS with reduced microbial abundance or mechanical wounding alone. Nonetheless, plants closed mechanical wounds more rapidly when treated with H. armigera OS regardless of the microbial component. 4. This study concludes that H. armigera OS can activate senescence and wound closure in plant tissues and that microbes within OS have an important role in shaping plant‐herbivore interactions through additional increases in senescence.

Predicting how plants allocate to different anti-herbivore defences in response to elevated carbon dioxide (CO2) concentrations is important for understanding future patterns of crop susceptibility to herbivory. Theories of defence allocation, especially in the context of environmental change, largely overlook the role of silicon (Si), despite it being the major anti-herbivore defence in thePoaceae. We demonstrated that elevated levels of atmospheric CO2(e[CO2]) promoted plant growth by 33% and caused wheat (Triticum aestivum) to switch from Si (–19%) to phenolic (+44%) defences. Despite the lower levels of Si under e[CO2], resistance to the global pestHelicoverpa armigerapersisted; relative growth rates (RGRs) were reduced by at least 33% on Si-supplied plants, irrespective of CO2levels. RGR was negatively correlated with leaf Si concentrations. Mandible wear was c. 30% higher when feeding on Si-supplemented plants compared to those feeding on plants with no Si supply. We conclude that higher carbon availability under e[CO2] reduces silicification and causes wheat to increase concentrations of phenolics. However, Si supply, at all levels, suppressed the growth ofH. armigeraunder both CO2regimes, suggesting that shifts in defence allocation under future climate change may not compromise herbivore resistance in wheat.

Silicon (Si) fertiliser can improve rice (Oryza sativa) tolerance to salinity. The rate of Si uptake and its associated benefits are known to differ between plant genotypes, but, to date, little research has been done on how the benefits, and hence the economic feasibility, of Si fertilisation varies between cultivars. In this study, a range of rice cultivars was grown both hydroponically and in soil, at different levels of Si and NaCl, to determine cultivar variation in the response to Si. There was significant variation in the effect of Si, such that Si alleviated salt-induced growth inhibition in some cultivars, while others were unaffected, or even negatively impacted. Thus, when assessing the benefits of Si supplementation in alleviating salt stress, it is essential to collect cultivar-specific data, including yield, since changes in biomass were not always correlated with those seen for yield. Root Si content was found to be more important than shoot Si in protecting rice against salinity stress, with a root Si level of 0.5–0.9% determined as having maximum stress alleviation by Si. A cost–benefit analysis indicated that Si fertilisation is beneficial in mild stress, high-yield conditions but is not cost-effective in low-yield production systems.

The decision of the UK to leave the EU has far‐reaching, and often shared, implications for agriculture and fisheries. To ensure the future sustainability of the UK’s agricultural and fisheries systems, we argue that it is essential to grasp the opportunity that Brexit is providing to develop integrated policies that improve the management and protection of the natural environments, upon which these industries rely. This article advances a stakeholder informed vision of the future design of UK agriculture and fisheries policies. We assess how currently emerging UK policy will need to be adapted in order to implement this vision. Our starting point is that Brexit provides the opportunity to redesign current unsustainable practices and can, in principle, deliver a sustainable future for agriculture and fisheries. Underpinning policies with an ecosystem approach, explicit inclusion of public goods provision and social welfare equity were found to be key provisions for environmental, agricultural and fishery sustainability. Recognition of the needs of, and innovative practices in, the devolved UK nations is also required as the new policy and regulatory landscape is established. Achieving the proposed vision will necessitate drawing on best practice and creating more coherent and integrated food, environment and rural and coastal economic policies. Our findings demonstrate that “bottom‐up” and co‐production approaches will be key to the development of more environmentally sustainable agriculture and fisheries policies to underpin prosperous livelihoods. However, delivering this vision will involve overcoming significant challenges. The current uncertainty over the nature and timing of the UK’s Brexit agreement hinders forward planning and investment while diverting attention away from further in‐depth consideration of environmental sustainability. In the face of this uncertainty, much of the UK’s new policy on the environment, agriculture and fisheries is therefore ambitious in vision but light on detail. Full commitment to co‐production of policy with devolved nations and stakeholders also appears to be lacking, but will be essential for effective policy development and implementation. A free Plain Language Summary can be found within the Supporting Information of this article.

Plants are subjected to a multitude of stimuli during insect herbivory, resulting in a complex and cumulative defence response. Breaking down the components of herbivory into specific stimuli and identifying the mechanisms of defence associated with them has thus far been challenging. Advances in our understanding of responses to inconspicuous stimuli, such as those induced by microbial symbionts in herbivore secretions and mechanical stimulation caused by insects, have illuminated the intricacies of herbivory. Here, we provide a synthesis of the interacting impacts of herbivory on plants and the consequential complexities associated with uncoupling defence responses. We propose that simulated herbivory should be used to complement true herbivory to decipher the mechanisms of insect herbivore-induced plant defence responses.

Silicon (Si) can adversely affect insect herbivores, particularly in plants that evolved the ability to accumulate large quantities of Si. Very rapid herbivore-induced accumulation of Si has recently been demonstrated, but the level of protection against herbivory this affords plants remains unknown. Brachypodium distachyon, a model Si hyperaccumulating grass, was exposed to the chewing herbivore, Helicoverpa armigera, and grown under three conditions: supplied Si over 34 d (+Si), not supplied Si (-Si), or supplied Si once herbivory began (-Si → +Si). We evaluated the effectiveness of each Si treatment at reducing herbivore performance and measured Si-based defenses and phenolics (another form of defense often reduced by Si). Although Si concentrations remained lower, within 72 h of exposure to Si, -Si → +Si plants were as resistant to herbivory as +Si plants. Both +Si and -Si → +Si treatments reduced herbivore damage and growth, and increased mandible wear compared to -Si. After 6 h, herbivory increased filled Si cell density in -Si → +Si plants, and within 24 h, -Si → +Si plants reached similar filled Si cell densities to +Si plants, although decreased phenolics only occurred in +Si plants. We demonstrate that plants with short-term Si exposure can rapidly accumulate Si-based antiherbivore defenses as effectively as plants with long-term exposure.

Drought stress reduces annual global wheat yields by 20%. Silicon (Si) fertilisation has been proposed to improve plant drought stress tolerance. However, it is currently unknown if and how Si affects different wheat landraces, especially with respect to their innate Si accumulation properties. In this study, significant and consistent differences in Si accumulation between landraces were identified, allowing for the classification of high Si accumulators and low Si accumulators. Landraces from the two accumulation groups were then used to investigate the effect of Si during osmotic and drought stress. Si was found to improve growth marginally in high Si accumulators during osmotic stress. However, no significant effect of Si on growth during drought stress was found. It was further found that osmotic stress decreased Si accumulation for all landraces whereas drought increased it. Overall, these results suggest that the beneficial effect of Si commonly reported in similar studies is not universal and that the application of Si fertiliser as a solution to agricultural drought stress requires detailed understanding of genotype-specific responses to Si.

Grasses accumulate large concentrations of silicon (Si) which alleviates a range of stresses including defence against herbivores. Likewise, grasses symbiotically associate with foliar Epichloë-fungal endophytes which provide herbivore defence, mainly via the production of alkaloids. Some Epichloë-endophytes increase foliar Si concentrations, particularly in tall fescue (Festuca arundinacea) but also in perennial ryegrass (Lolium perenne); it is unknown whether this impacts herbivores. Likewise, while Si is primarily a physical defence against herbivores, it can also affect defensive secondary metabolites; Si supply might therefore also affect alkaloids produced by Epichloë-endophytes, however, this remains untested. We grew tall fescue and perennial ryegrass in a factorial combination with or without Si supplementation, in the absence or presence of a chewing herbivore; Helicoverpa armigera. Grasses were associated with four different Epichloë-endophyte strains (tall fescue: AR584; perennial ryegrass: AR37, AR1, or wild type) or as Epichloë-free controls. Specifically, we assessed how Si supply and Epichloë-endophyte presence impacts plant growth and chemistry, and how their interaction with herbivory affects foliar Si concentrations and alkaloid production. Subsequently, their effects on H. armigera relative growth rates (RGR) were evaluated. In Fescue, the AR584-endophyte increased constitutive (herbivore-free) and induced (herbivore-inoculated) silicon concentrations when Si was supplied. In perennial ryegrass, AR37-endophyte increased constitutive and induced silicon concentration, meanwhile, AR1-endophyte increased constitutive levels only. Si supply and herbivory did not affect alkaloids produced by AR584- or AR1/Wt-endophyte in tall fescue and perennial ryegrass, respectively. However, Si suppressed herbivore-induced production of alkaloids in the AR37-endophyte perennial ryegrass association. Si was a more effective defence in tall fescue than perennial ryegrass, significantly reducing H. armigera RGR. Our results suggest that Si reduced herbivore performance to such an extent in tall fescue that it was operating at maximum effect and endophyte-mediated increases in Si concentration made no further difference. Si had a more modest impact on herbivores in perennial ryegrass, potentially linked to silicon decreasing herbivore feeding and thus, suppressing herbivore-induced alkaloids. We provide novel evidence that increased Si concentrations in some cases interact with endophyte-produced chemical defences, which could ultimately impact plant resistance to herbivores.

Plants associate with bacteria over the course of evolution. For example, leguminous plants (Leguminosae/Fabaceae) have evolved a distinct symbiosis with nitrogen-fixing bacteria (rhizobia) about 60 million years ago. Rhizobia are housed in specialised root structures, the nodules, and provide the host plants with available nitrogen. In exchange, the host plant rewards rhizobia with carbon-based compounds. The legume-rhizobia symbiosis differs from being mutualistic to somewhat parasitic. One of the driving factors of that is soil nutrients, e.g. silicon (Si). Yet, the functional role of Si in legumes is largely overlooked.Previous studies suggest that Si has positive impacts on the legume-rhizobia symbiosis. For example, existing literature demonstrates that Si alleviates a broad range of environmental stresses. Crucially, there is a growing number of studies reporting that Si promotes symbiotic traits, such as increased root nodulation and nitrogen fixation across several leguminous species. To better understand this, a conceptual framework was recently proposed. It is hypothesised that Si uptake and accumulation (silicification) in plant tissues may compensate the high metabolic expenditure of carbon in cell wall formation, accelerate solute transport and gas exchange in the nodules, and protect the plants against stresses.To investigate the impacts of Si enrichment on functional traits in legumes, a glasshouse experiment was conducted with a model legume, barrel medic (Medicago truncatula) associated with a rhizobial (Ensifer meliloti) strain SM1021. Three plant genotypes were either enriched with Si (+Si) or untreated (-Si). Furthermore, a suite of key functional traits broadly grouped as plant growth, physiology, elemental chemistry, nodule activity and nitrogen fixation were quantified using several analytical/chemical techniques. Si enrichment altered several traits depending on plant genotype and symbiosis with rhizobia. For example, nodule activity was generally promoted in +Si relative to -Si plants, but with a more profound impact in one specific genotype (Sephi). This promotion was correlated positively with silicification either in the foliar or nodule depending on plant genotype.To examine a context dependency of Si impacts in legumes, a full-factorial experiment in a glasshouse was undertaken with the same model legume (two genotypes) and two rhizobial strains, i.e. SM1021 and SM1022, which the former strain is less effective than the latter. Each host-rhizobial association was supplemented with and without Si and challenged with the foliar-chewing cotton bollworm (Helicoverpa armigera) for a 5-day larval infestation (+herbivore and -herbivore). At 30-day post infestation, plants were harvested and further analysed for nodule traits and plant chemistry. Silicon enrichment strongly increased nodule numbers in both rhizobial strains but only in -herbivore plants and this impact was wiped out in +herbivore plants. However, foliar Si was induced only in +Si relative to -Si in +herbivore plants and the reverse was true for foliar C that might indicate a trade-off between Si and C following herbivory. In addition, Si enrichment generally promoted total soluble protein. Finally, when foliar amino acids (AAs) were clustered into essential, non-essential and total compounds, Si enrichment consistently promoted AAs only when herbivory was absent and shifted to a lesser extent when herbivory was present.

1) Crop loss due to insect herbivory is one of the largest challenges facing the agricultural industry. As herbivore populations continue to grow in light of global change, securing crop resources is becoming increasingly critical. Silicon (Si) has been shown to effectively mitigate the adverse effects of herbivores such as the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae), in crop species (namely grasses), that have evolved the ability to uptake large amounts of Si through their roots and accumulate it in aboveground tissues. Nevertheless, the effectiveness of Si accumulation as a plant defence against herbivory in the short term, and its consequential effects on alternative defence responses, remain unclear.2) We conducted two discrete experiments to determine the short-term dynamics of Si, chemical defences and resistance to herbivory in the model grass, Brachypodium distachyon: 1) Both Si-supplemented (+Si) and control (-Si) plants were treated with methyl jasmonate (MeJA) as a form of simulated herbivory and we measured the interplay of Si accumulation, the phytohormones jasmonic acid (JA) and salicylic acid (SA), and carbon-based defences over 24 hr. 2) We exposed H. armigera larvae to B. distachyon plants grown under three conditions: +Si, -Si, or treated with Si only once H. armigera feeding began. We measured the effect of short-term plant exposure to Si on H. armigera performance and plant resistance.3) MeJA-induced Si accumulation occurred as early as 6 hr after treatment via increased JA concentrations. Si supplementation decreased SA concentrations, which could have implications on additional downstream defences. We show a trade-off between Si and phenolics in untreated plants, but this relationship was weakened upon MeJA treatment. Although foliar Si concentrations remained lower, within 72 hr of exposure to Si, plants obtained virtually the same level of resistance to H. armigera as plants exposed to Si for over 30 days. H. armigera feeding also accelerated Si deposition after 6 hr of exposure to Si, however, in as little as 24 hr, levels of Si deposition were similar to plants exposed to Si long term.4) In addition to its well-documented role as a long-term defence against herbivores, we demonstrate that, over short-term temporal scales, Si accumulation responds to herbivore signals and impacts on plant defence machinery. Further, we provide novel evidence that plants can rapidly incorporate Si into their tissues to mitigate the adverse effects of herbivory as effectively as plants exposed to Si long term.

Plants deploy an arsenal of chemical and physical defenses against arthropod herbivores, but it may be most cost efficient to produce these only when attacked. Herbivory activates complex signaling pathways involving several phytohormones, including jasmonic acid (JA), which regulate production of defensive compounds. The Poaceae also have the capacity to take up large amounts of silicon (Si), which accumulates in plant tissues. Si accumulation has antiherbivore properties, but it is poorly understood how Si defenses relate to defense hormone signaling. Here we show that Si enrichment causes the model grass Brachypodium distachyon to show lower levels of JA induction when attacked by chewing herbivores. Triggering this hormone even at lower concentrations, however, prompts Si uptake and physical defenses (e.g., leaf hairs), which negatively impact chewing herbivores. Removal of leaf hairs restored performance. Crucially, activation of such Si-based defense is herbivore-specific and occurred only in response to chewing and not fluid-feeding (aphid) herbivores. This aligned with our meta-analysis of 88 studies that showed Si defenses were more effective against chewing herbivores than fluid feeders. Our results suggest integration between herbivore defenses in a model Si-accumulating plant, which potentially allows it to avoid unnecessary activation of other costly defenses.

Agrivoltaic systems concommitently tackle food and energy security challenges on the same area of land, while also improving farmer livelihoods. Designed correctly, they can increase crop yields by reducing water and heat stresses; yield improvements depend on a range of factors including the available photosynthetically active radiation and the shade tolerance of the crop varieties. Several agrivoltaic pilot studies have been developed over the past decade, predominantly in the Global North, but there is an evidence gap in East Africa where the environmental conditions and livelihood challenges faced by agricultural communities mean there are potentially far greater benefits from agrivoltaic technology. In this paper, we discuss how the environmental conditions, electricity supply and access, farming systems, and political scenarios present opportunities and challenges for using agrivoltaic systems to address sustainable development goals in East Africa. We end by summarising what is required to support development of this technology in the region and realise the potential benefits.

As water quality and availability decreases in many parts of the world, salinity is becoming a major challenge that reduces crop yield, even in soilless cultivation systems. Therefore, novel strategies are needed to promote plant salt tolerance in these systems. We hypothesized that the non-essential element silicon (Si) and plant-growth promoting Bacillus spp. can alleviate salt stress of cucumber (Cucumis sativus L.) grown in hydroponics. We tested this hypothesis by growing cucumber seedlings with and without salt stress (75 mM NaCl) and with and without 1.5 mM Si and an inoculum of six rhizosphere Bacillus species in a full-factorial design. Seedlings were grown in a climate room for two weeks in independent deep-water culture containers. The applied salt stress strongly reduced plant biomass, whereas Si application under salt stress resulted in a substantial increase in cucumber shoot and root biomass. This beneficial impact of Si was also observed in increased plant height, leaf area, specific leaf area, root length, specific root length, root surface area and root volume. The Bacillus species increased root dry weight, specific leaf area as well as specific root length. In seedlings grown under salt stress, Si application increased shoot and root Si concentration, whereas Cl− concentration was reduced in the plant shoots. A reduction in Cl− concentration of the shoots was also apparent in the Bacillus treatment. Under non-stress conditions, neither Si nor Bacillus species affected plant growth parameters. However, shoot mineral content was affected as Si application reduced shoot Cl−and Ca2+ concentrations, and inoculation with Bacillus species decreased K concentration. We conclude that Si does promote salt stress alleviation during the early growth stage of cucumber grown in deep water culture and this has implications for soilless crop production. Seed inoculation with Bacillus species showed a beneficial trend for some plant growth characteristics and nutrient status under high salinity, although not as pronounced as for Si.

Silicon accumulation is a key defence against herbivorous pests, but may have wider detrimental impacts if plants become unpalatable for livestock. We argue that some herbivores are better adapted to silicon-rich diets than others; herbivore anatomy and physiology, and the nature of silicon deposition, are crucial to understanding these differences.

Land‐based enhanced rock weathering (ERW) is a biogeochemical carbon dioxide removal (CDR) strategy aiming to accelerate natural geological processes of carbon sequestration through application of crushed silicate rocks, such as basalt, to croplands and forested landscapes. However, the efficacy of the approach when undertaken with basalt, and its potential co‐benefits for agriculture, require experimental and field evaluation. Here we report that amending a UK clay‐loam agricultural soil with a high loading (10 kg/m2) of relatively coarse‐grained crushed basalt significantly increased the yield (21 ± 9.4%, SE ) of the important C4 cereal Sorghum bicolor under controlled environmental conditions, without accumulation of potentially toxic trace elements in the seeds. Yield increases resulted from the basalt treatment after 120 days without P‐ and K‐fertilizer addition. Shoot silicon concentrations also increased significantly (26 ± 5.4%, SE ), with potential benefits for crop resistance to biotic and abiotic stress. Elemental budgets indicate substantial release of base cations important for inorganic carbon removal and their accumulation mainly in the soil exchangeable pools. Geochemical reactive transport modelling, constrained by elemental budgets, indicated CO2 sequestration rates of 2–4 t CO2/ha, 1–5 years after a single application of basaltic rock dust, including via newly formed soil carbonate minerals whose long‐term fate requires assessment through field trials. This represents an approximately fourfold increase in carbon capture compared to control plant–soil systems without basalt. Our results build support for ERW deployment as a CDR technique compatible with spreading basalt powder on acidic loamy soils common across millions of hectares of western European and North American agriculture.

Grazing‐induced changes in plant quality have been suggested to drive the negative delayed density dependence exhibited by many herbivore species, but little field evidence exists to support this hypothesis. We tested a key premise of the hypothesis that reciprocal feedback between vole grazing pressure and the induction of anti‐herbivore silicon defenses in grasses drives observed population cycles in a large‐scale field experiment in northern England. We repeatedly reduced population densities of field voles (Microtus agrestis) on replicated 1‐ha grassland plots at Kielder Forest, northern England, over a period of 1 year. Subsequently, we tested for the impact of past density on vole life history traits in spring, and whether these effects were driven by induced silicon defenses in the voles’ major over‐winter food, the grass Deschampsia caespitosa. After several months of density manipulation, leaf silicon concentrations diverged and averaged 22% lower on sites where vole density had been reduced, but this difference did not persist beyond the period of the density manipulations. There were no significant effects of our density manipulations on vole body mass, spring population growth rate, or mean date for the onset of spring reproduction the following year. These findings show that grazing by field voles does induce increased silicon defenses in grasses at a landscape scale. However, at the vole densities encountered, levels of plant damage appear to be below those needed to induce changes in silicon levels large and persistent enough to affect vole performance, confirming the threshold effects we have previously observed in laboratory‐based studies. Our findings do not support the plant quality hypothesis for observed vole population cycles in northern England, at least over the range of vole densities that now prevail here.

Dryland forests, those characterised as having low precipitation and soil nutrients, account for over a quarter of forests globally. Increasing their productivity often relies on irrigation and fertilisation, but the impacts on the wider habitat are largely unknown. Understory invertebrates, in particular, play key roles in forest systems (e.g. nutrient cycling), but their responses to dryland forest management practices are untested. We investigated the impacts of irrigation, fertilisation and a combination of both on soil chemistry, understory vegetation, tree growth and understory arthropod communities in a Eucalyptus plantation to establish linkages between dryland management and ecosystem responses. Fertilisation increased all soil nutrients (N, NO3N, P and K) with similar effects on the chemical composition of understory grasses. Fertilisation also caused declines in foliar silicon concentrations, an important herbivore defence in grasses. Irrigation increased growth of both understory plants (+90%) and trees (+68%). Irrigation increased the abundance of ground‐dwelling arthropods by over 480% relative to control plots, but depressed higher level taxon arthropod diversity by 15%, declining by a further 7% (−22%) in combined treatment plots. Irrigation also caused a surge in the abundance of Collembola (+1300%) and Isopoda (+323%). Fertilisation drove increases in the abundance of Isopoda (+196%) and Diptera (+63%), whereas fertilisation combined with irrigation increased populations of Thysanoptera (+166%) and Acarina (+328%). Airborne arthropods were less affected, but fertilisation increased the abundance of Apocrita (+95%) and depressed populations of Thysanoptera (−77%). Diptera abundance was positively related to understory vegetation growth, whereas the abundance of other groups (Collembola, Isopoda, Thysanoptera and Acarina) correlated positively with tree growth. We proposed that the large increases in populations of key detritivores, Collembola and Isopoda, were linked to increased leaf litter from enhanced tree growth in irrigated and combined treatment plots. Our findings suggest that dryland management can increase both plant productivity and abundance of arthropods, but cause arthropod diversity at the higher taxon level to decline overall.

Global climate change may increase invasions of exotic plant species by directly promoting the success of invasive/exotic species or by reducing the competitive abilities of native species. Changes in plant chemistry, leading to altered susceptibility to stress, could mediate these effects. Grasses are hyper-accumulators of silicon, which play a crucial function in the alleviation of diverse biotic and abiotic stresses. It is unknown how predicted increases in atmospheric carbon dioxide (CO2 ) and air temperature affect silicon accumulation in grasses, especially in relation to primary and secondary metabolites. We tested how elevated CO2 (eCO2 ) (+240 ppm) and temperature (eT) (+4°C) affected chemical composition (silicon, phenolics, carbon and nitrogen) and plant growth in eight grass species, either native or exotic to Australia. eCO2 increased phenolic concentrations by 11%, but caused silicon accumulation to decline by 12%. Moreover, declines in silicon occurred mainly in native species (-19%), but remained largely unchanged in exotic species. Conversely, eT increased silicon accumulation in native species (+19%) but decreased silicon accumulation in exotic species (-10%). Silicon and phenolic concentrations were negatively correlated with each other, potentially reflecting a defensive trade-off. Moreover, both defences were negatively correlated with plant mass, compatible with a growth-defence trade-off. Grasses responded in a species-specific manner, suggesting that the relative susceptibility of different species may differ under future climates compared to current species rankings of resource quality. For example, the native Microlaena stipoides was less well defended under eCO2 in terms of both phenolics and silicon, and thus could suffer greater vulnerability to herbivores. To our knowledge, this is the first demonstration of the impacts of eCO2 and eT on silicon accumulation in grasses. We speculate that the greater plasticity in silicon uptake shown by Australian native grasses may be partly a consequence of evolving in a low nutrient and seasonally arid environment.

Non-technical summary Until the past half-century, all agriculture and land management was framed by local institutions strong in social capital. But neoliberal forms of development came to undermine existing structures, thus reducing sustainability and equity. The past 20 years, though, have seen the deliberate establishment of more than 8 million new social groups across the world. This restructuring and growth of rural social capital within specific territories is leading to increased productivity of agricultural and land management systems, with particular benefits for those previously excluded. Further growth would occur with more national and regional policy support. Technical summary For agriculture and land management to improve natural capital over whole landscapes, social cooperation has long been required. The political economy of the later twentieth and early twenty-first centuries prioritized unfettered individual action over the collective, and many rural institutions were harmed or destroyed. Since then, a wide range of social movements, networks and federations have emerged to support transitions towards sustainability and equity. Here, we focus on social capital manifested as intentionally formed collaborative groups within specific geographic territories. These groups focus on: (1) integrated pest management; (2) forests; (3) land; (4) water; (5) pastures; (6) support services; (7) innovation platforms; and (8) small-scale systems. We show across 122 initiatives in 55 countries that the number of groups has grown from 0.50 million (in 2000) to 8.54 million (in 2020). The area of land transformed by the 170–255 million group members is 300 Mha, mostly in less-developed countries (98% groups; 94% area). Farmers and land managers working with scientists and extensionists in these groups have improved both environmental outcomes and agricultural productivity. In some cases, changes to national or regional policy supported this growth in groups. Together with other movements, these social groups could now support further transitions towards policies and behaviours for global sustainability. Social media summary Millions of geographically based new social groups are leading to more sustainable agriculture and forestry worldwide.

Above- and below-ground organisms can interact by altering the quality of shared host plants. Arbuscular mycorrhizal fungi (AMF) influence plant nutrient uptake, including nitrogen (N) acquisition. Under low N and phosphorus conditions, AMF delivery of N from organic sources not immediately available to the plant can have large impacts on plant N status, a limiting nutrient in the aphid diet. This study investigated the effect of AMF colonisation upon aphid number and determined the consequences of AMF directly accessing an organic nutrient patch that the plant cannot. We hypothesised that AMF colonisation of plants will increase plant and aphid N status, plant performance and aphid number, but only when the AMF had direct access to the added organic patch. Barley plants hosting the grain aphid Sitobion avenae were colonised by the AMF, Funneliformis mosseae, or no AMF. A two-compartment microcosm was used to separate the plant roots from a 15 N-labelled organic patch in a second compartment. AMF-colonised plants, but without access to the second compartment, were used to examine the effect of AMF colonisation on aphid number. In a separate treatment, and to determine whether AMF access to a plant inaccessible N source modified the effect of AMF colonisation on aphid number, AMF hyphae were permitted access to the second compartment containing an organic patch. As a control for AMF accessing a larger substrate volume, AMF were allowed access to a second compartment without an organic patch. When the AMF accessed the organic patch, more N from the patch was delivered to the plant resulting in a higher grain N concentration although plant growth was depressed. More N from the patch was also delivered to the aphids, but the N status of the aphid remained unchanged. Regardless of the level of access to the organic patch, AMF colonisation did not affect aphid number. Our data show that by accessing N sources not readily available to plants, AMF can indirectly deliver N to above-ground organisms, a finding which has major implications for N-transfer between higher trophic levels. A plain language summary is available for this article.

The objective of this study was to evaluate whether silicon (Si) amendments, known to have a prophylactic role against biotrophic and hemibiotrophic pathogens, could protect soybean against Phytophthora sojae. To fulfill this objective, the initial challenge was to develop a method of inoculation that reproduced the natural infection process while allowing regular Si feeding to the plants. In a first set of experiments, inoculation of P. sojae zoospores directly into hydroponic solutions led to reproducible infections and expected phenotypes when using ‘Williams’ (rps), ‘L75-6141’ (Rps1a), ‘haro15’ (Rps1k), and ‘L77-1863’ (Rps1b) soybean challenged to races 3 and 7 of P. sojae. This approach offers the advantage of testing simultaneously many soybean cultivars against different races of P. sojae in a controlled environment, and the expression of partial and root resistance. In a second set of experiments aimed at testing the effect of Si, our results clearly showed that Si amendments had a significant effect on disease reduction and plant yield. The effect was particularly noticeable when combined with a cultivar displaying a certain level of resistance to the disease. These results demonstrate a useful method of direct inoculation of soybean plants with P. sojae zoospores through a hydroponic system and show that Si amendments can represent an alternative method of control of P. sojae against soybean.

Herbivorous insect pests living in the soil represent a significant challenge to food security given their persistence, the acute damage they cause to plants and the difficulties associated with managing their populations. Ecological research effort into rhizosphere interactions has increased dramatically in the last decade and we are beginning to understand, in particular, the ecology of how plants defend themselves against soil-dwelling pests. In this review, we synthesise information about four key ecological mechanisms occurring in the rhizosphere or surrounding soil that confer plant protection against root herbivores. We focus on root tolerance, root resistance via direct physical and chemical defences, particularly via acquisition of silicon-based plant defences, integration of plant mutualists (microbes and entomopathogenic nematodes, EPNs) and the influence of soil history and feedbacks. Their suitability as management tools, current limitations for their application, and the opportunities for development are evaluated. We identify opportunities for synergy between these aspects of rhizosphere ecology, such as mycorrhizal fungi negatively affecting pests at the root-interface but also increasing plant uptake of silicon, which is also known to reduce herbivory. Finally, we set out research priorities for developing potential novel management strategies.

Climate change is predicted to result in more variable and extreme precipitation regimes, with potentially longer periods between precipitation events. However, the effects of multiple, sequential drought events on ecosystems and potential acclimation, particularly in grasslands, is poorly understood. In this study, we tested if two simulated drought regimes, (i) sustained drought (soil moisture content reduced from 75 to 25 % field capacity over 14 days and maintained for 29 days) and (ii) repeated drought (two cycles of a reduction to 25 % field capacity, reached after 22 days and 15 days, separated by a rewatering event to 75 % field capacity for 5 days), differentially influence fourteen key physiological responses in the model grass species (Brachypodium distachyon). In addition, we aimed to determine whether plants may acclimate differently to sustained and/or repeated drought events. B. distachyon exhibited plasticity in response to drought, exhibiting two distinct drought resistance responses to the two watering regimes. Plants exposed to sustained drought exhibited early reductions in photosynthesis, stomatal conductance and water potential (43 %, 42 % and 37 %, respectively). However, plants showed physiological acclimation and recovery in these parameters after an additional 3–21 days, but had a ∼50 % lower shoot biomass than well-watered plants. These data demonstrate a conservative, albeit plastic, response to soil water deficit. In contrast, plants exposed to repeated drought responded opportunistically whereby greater fluctuations in photosynthesis, stomatal conductance and water potential (reductions of up to 62 %, 71 % and 90 %, respectively) were closely related to drought and rewatering events. Since plants exposed to repeated drought had a greater reduction in water potential and faster reductions in relative photosynthesis in the second drought event compared to the initial drought event, this may indicate a lack of acclimation under this drought regime. Our results provide evidence for differential responses of B. distachyon to drought and rewatering events, which are dependent on the drought regime (sustained or repeated) and must be carefully considered when interpreting experimental data.

The sustainable intensification of agricultural systems offers synergistic opportunities for the co-production of agricultural and natural capital outcomes. Efficiency and substitution are steps towards sustainable intensification, but system redesign is essential to deliver optimum outcomes as ecological and economic conditions change. We show global progress towards sustainable intensification by farms and hectares, using seven sustainable intensification sub-types: integrated pest management, conservation agriculture, integrated crop and biodiversity, pasture and forage, trees, irrigation management and small or patch systems. From 47 sustainable intensification initiatives at scale (each >104 farms or hectares), we estimate 163 million farms (29% of all worldwide) have crossed a redesign threshold, practising forms of sustainable intensification on 453 Mha of agricultural land (9% of worldwide total). Key challenges include investment to integrate more forms of sustainable intensification in farming systems, creating agricultural knowledge economies and establishing policy measures to scale sustainable intensification further. We conclude that sustainable intensification may be approaching a tipping point where it could be transformative.