Soil microarthropods affect soil ecosystems in a manner that may contribute to balancing the goals of building soil health and controlling weeds in organic agricultural systems. While soil microarthropod feeding behavior can affect plant growth, their impacts on plant communities in agricultural systems are largely unknown. A greenhouse experiment was conducted to investigate the impacts of microarthropods on weed communities. A model weed seed bank was used in each mesocosm, which included yellow foxtail (Setaria pumila (Poir.) Roem&Schult.), giant foxtail (Setaria faberi Herrm.), Powell amaranth (Amaranthus powellii S. Watson), water-hemp (Amaranthus tuberculatus (Moq.) Sauer), common lambsquarters (Chenopodium album L.), and velvetleaf (Abutilon theophrasti Medik.). The study included three treatments: Collembola (Isotomiella minor, Schaffer 1896) abundance (none, low, high), soil microbial community (sterilized/non-sterilized), and fertilizer (presence/ absence of compost). A lab experiment examining individual weed species interactions with I. minor was conducted to elucidate the mechanisms driving the greenhouse experiment findings. Twenty seeds of each weed species were placed on moistened germination paper in containers with varying I. minor abundance levels (none, low, high, very high). Seed germination was recorded after five and seven days. In the greenhouse, the presence of I. minor increased total weed emergence during the first two weeks, but this effect diminished after three weeks. Increasing I. minor abundances generally decreased weed biomass, though this effect was greater in the non-sterilized soil. In the non-sterilized soil, I. minor presence decreased total aboveground weed biomass production by up to 23 %. The Amaranthus species, Powell amaranth and waterhemp, drove this effect with a 55 % and 32 % reduction in biomass, respectively. In tandem, the Amaranthus species had reduced abundances in the presence of I. minor. I. minor increased yellow foxtail germination in the lab, while not affecting the other weed species. This suggests that their effects on the Amaranthus weeds in the greenhouse were likely not caused by direct effects on germination, but instead through nutrient cycling or root herbivory. The proposed mechanism underlying these interactions is that I. minor can initially stimulate germination by feeding on seed coats, but when the seed coats are minimal can damage the seedling. Our findings indicate I. minor could impact weed growth in a manner that affects management decisions and outcomes.

The use of mixed forests and non-native tree species have the potential to mitigate climate change impacts and enhance biodiversity. However, little is known about how forest composition and environmental factors affect each step of natural regeneration in mixed forests, especially in mixtures with non-native trees. Here we investigated how forest composition affected European beech seed survival (through seed tracking), seed sprouting (via field germination experiments), and seedling survival (monthly seedling monitoring) in pure beech forests and in admixtures with Norway spruce and the introduced Douglas-fir in a mast and non-mast year of beech. We also assessed how biotic and abiotic factors (small mammal abundance, ungulate access, seed production, seed burial, canopy cover, distance to nearest adult tree, seedling aggregation, understory density, browsing damage, and soil properties) affected these regeneration dynamics. Seed survival was negatively affected by the presence of conifers and mouse abundance. Seed germination was influenced by whether seeds were buried or not. Seedling survival increased in Douglas-fir admixtures, and in forests with higher soil quality. Browsing damage and ungulate access diminished seedling survival. Seed production had the greatest influence on absolute number of seedlings. Forest composition and environmental factors had distinct impacts on regeneration of beech depending on its ontogenetic stage. Here, we provide evidence supporting the notion that Douglas-fir is not impairing the regeneration of native trees in mixed forests. In fact, mixtures with Douglas-fir benefited the survival of beech seedlings, likely due to better soil properties and less damage from herbivores on these stands.

Invasive plants often express above-ground traits, such as higher growth than native plants, which promote their success. This may reflect low levels of invertebrate herbivory and/or high rates of arbuscular mycorrhizal fungi (AMF) association. However, the root traits that contribute to invasive success are less well known. Moreover, the combined roles of above-ground herbivory, AMF, and root traits in the invasion process are poorly understood. We conducted field surveys at 17 sites along a latitudinal gradient in China (22.77 degrees N to 42.48 degrees N) to investigate the relationships among above-ground herbivory, AMF colonization, and root traits for five pairs of closely related invasive and native Asteraceae plant species. We experimentally manipulated above-ground insect feeding for two of these pairs of plant species in a middle latitude (34.79 degrees N) common garden. We measured above-ground invertebrate abundance, leaf damage, AMF colonization, root morphological traits associated with nutrient uptake, and root soluble sugar concentrations. In the field survey, invasive plants had lower leaf damage and Hemiptera abundances plus higher AMF colonization, thinner roots with more surface area and higher concentrations of root soluble sugars than native plants. Leaf damage decreased with increasing latitude for native plants. In the common garden, invasive plants had lower leaf damage and Hemiptera abundances plus higher AMF and greater surface area of fine roots than native plants. Leaf damage and Hemiptera reduced AMF colonization via a phenotypic effect of reduced fine root soluble sugars. Synthesis: Our results indicate that low above-ground invertebrate herbivory on invasive plants contributes to their success directly by increasing their growth and indirectly via root soluble sugars that increase their AMF colonization. Invasive plants appear to benefit from greater root volume and surface area, but this did not vary with latitude or above-ground invertebrate herbivory. These results highlight the importance of considering above- and below-ground processes simultaneously to understand how they interact to determine plant invasion success.

The acclimation capacity of Betula pendula and Betula pubescens was studied over 4 years in common gardens in central Italy (43 degrees N) and southern (61 degrees N) and northern Finland (67 degrees N), representing drastically different photoperiod and climate in temperate, boreal and subarctic vegetation zones. Two study sites that differed in soil fertility were established at each location, giving a total of six common gardens. The birch material was micropropagated from naturally regenerated stands of B. pendula and B. pubescens from Susa Valley and Rochemolle Valley in northern Italy, Punkaharju in southern Finland and Kittil & auml; in northern Finland. The plants were measured for height growth, stem diameter, leaf chlorophyll content, leaf herbivory and pathogen damage. The effects of soil fertility on the common garden results were also analyzed. The results showed high acclimation capacity of B. pendula and B. pubescens after a long-range transfer from southern to northern Europe, despite the major shift in climate and photoperiod. First-year growth on average was best in boreal southern Finland for all origins. Betula pendula grew more than B. pubescens in Italy and southern Finland, while B. pubescens grew more in northern Finland and better tolerated the northward transfer. The height growth of origins showed a clear latitude gradient from slowly growing northern to fast growing southern origins in the nursery and laboratory, but not in the field. Soil fertility explained a significant part of variation among locations not only for growth variables, but also for leaf chlorophyll content and leaf herbivory and pathogen damage. Leaf herbivore and pathogen damage was greatest in southern Finland. Our results demonstrate good survival of birch from northern Italy in Finnish conditions and support the possibility of long-range south-to-north transfer of Betula species to provide resistant planting material in boreal forests for the rapidly changing climate.

Insect foliar herbivory is ubiquitous in terrestrial ecosystems, yet its impacts on soil nitrogen cycling processes remain not yet well known. To examine the impacts of insect foliar herbivory on soil N2O emission flux and available nitrogen (N), we conducted a pot experiment to measure soil available N content and soil N2O emission flux among three treatments (i.e., leaf herbivory, artificial defoliation, and control,) in two broad-leaved trees (Cinnamomum camphora and Liquidambar formosana) and two conifer trees (Pinus massonianna and Cryptomeria fortunei). Our results showed that insect foliar herbivory significantly increased soil inorganic N (i.e., NH4+-N and NO3--N), dissolved organic nitrogen (DON) and microbial biomass nitrogen (MBN) contents, and urease activity compared to control treatment. However, there were no differences in soil available N contents and urease activity between artificial defoliation and control treatments, implying that insect foliar herbivory had greater impacts on soil available N contents compared to physical damage of leaves. Moreover, soil N2O emission fluxes were increased by insect foliar herbivory in Cinnamomum camphora and Pinus massonianna, but not for the other two tree species, indicating various effect of insect foliar herbivory on soil N2O emission among tree species. Furthermore, our results showed the positive correlations between soil N2O emission flux and soil NO3--N, DON, MBN, and acid protease activity, and soil inorganic N, pH, and MBN mainly explained soil N2O emission. Our results implied that insect foliar herbivory can speed up soil nitrogen availability in subtropical forests, but the impacts on soil N2O emission are related to tree species.

To limit damage from insect herbivores, plants rely on a blend of defensive mechanisms that includes partnerships with beneficial microbes, particularly those inhabiting roots. While ample evidence exists for microbially mediated resistance responses that directly target insects through changing phytotoxin and volatile profiles, we know surprisingly little about the microbial underpinnings of plant tolerance. Tolerance defenses counteract insect damage via shifts in plant physiology that reallocate resources to fuel compensatory growth, improve photosynthetic efficiency, and reduce oxidative stress. Despite being a powerful mitigator of insect damage, tolerance remains an understudied realm of plant defenses. Here, we propose a novel conceptual framework that can be broadly applied across study systems to characterize microbial impacts on expression of tolerance defenses. We conducted a systematic review of studies quantifying the impact of rhizosphere microbial inoculants on plant tolerance to herbivory based on several measures-biomass, oxidative stress mitigation, or photosynthesis. We identified 40 studies, most of which focused on chewing herbivores (n = 31) and plant growth parameters (e.g., biomass). Next, we performed a meta-analysis investigating the impact of microbial inoculants on plant tolerance to herbivory, which was measured via differences in plant biomass, and compared across key microbe, insect, and plant traits. Thirty-five papers comprising 113 observations were included in this meta-analysis, with effect sizes (Hedges' d) ranging from -4.67 (susceptible) to 18.38 (overcompensation). Overall, microbial inoculants significantly reduce the cost of herbivory via plant growth promotion, with overcompensation and compensation comprising 25% of observations of microbial-mediated tolerance. The grand mean effect size 0.99 [0.49; 1.49] indicates that the addition of a microbial inoculant increased plant biomass by similar to 1 SD under herbivore stress, thus improving tolerance. This effect was influenced most by microbial attributes, including functional guild and total soil community diversity. Overall, results highlight the need for additional investigation of microbially mediated plant tolerance, particularly in sap-feeding insects and across a more comprehensive range of tolerance mechanisms. Such attention would round out our current understanding of anti-herbivore plant defenses, offer insight into the underlying mechanisms that promote resilience to insect stress, and inform the application of microbial biotechnology to support sustainable agricultural practices.

Studies have reported the important role of soil properties in regulating insect herbivory under controlled conditions or at relatively large scales. However, whether fine-scale variation of soil properties affects insect herbivory under natural conditions in forests is still unclear. We selected a ca. 300 ha Quercus variabilis forest area where the leaf damage was mainly caused by Lampronadata cristata (Lepidoptera: Notodontidae) and set 200 10 x 10 m plots within the area. We examined insect herbivory (percent leaf area damaged) on Q. variabilis and correlated it to soil properties and tree characteristics. Insect herbivory decreased with soil sand percentage and bulk density and increased with DBH and tree height. Effects of soil sand percentage and bulk density on insect herbivory were partly mediated by DBH and tree height. Our results indicated that soil physical properties may have significant effects on insect herbivory by directly influencing insect herbivores that need to complete their life cycle in the soil, or by indirectly affecting insect herbivores through influencing DBH and tree height which reflects the total leaf biomass available to the insect herbivore. This study may help to understand the complex relationship between soil and plant-insect interactions in forest ecosystems.

As primary producers, plants play a central role in mediating interactions across trophic levels. Although plants are the primary food source for herbivorous insects, they can protect themselves from herbivore damage. Many plants produce toxic compounds that directly reduce herbivore feeding, but plants also protect themselves indirectly by attracting natural enemies of the attacking herbivore through volatile signaling. These so-called tritrophic interactions have historically been documented aboveground in aerial plant parts but are also known to occur belowground in root systems. In addition to herbivores, plants directly interact with other organisms, which can influence the outcomes of tri-trophic interactions. Arbuscular mycorrhizal fungi (AMF) are symbiotic soil microbes that colonize the roots of plants and facilitate nutrient uptake. These microbes can alter plant chemistry and subsequent resistance to herbivores. Few studies, however, have shown how AMF affect tri-trophic interactions above- or belowground. This study examines how AMF colonization affects the emission of root volatiles when plants are under attack by western corn rootworm, a problematic pest of corn, and subsequent attraction of entomopathogenic nematodes, a natural enemy of western corn rootworm. Mycorrhizal fungi increased rootworm survival but decreased larval weight. Differences were detected across root volatile profiles, but there was not a clear link between volatile signaling and nematode behavior. Nematodes were more attracted to non-mycorrhizal plants without rootworms and AMF alone in soil, suggesting that AMF may interfere with cues that are used in combination with volatiles which nematodes use to locate prey.

Silicon (Si) is essential to the nutritional status of many monocot and dicot plant species, and it aids them in resisting abiotic and biotic challenges in various ways. This article explained the progress in exploring silicon-mediated resistance to sugarcane insect pests, its role in increasing juice quality attributes and cane production, the silicon status of soil and uptake by sugarcane plant, and the mechanisms involved. The aim is to determine the influence of different sources of Si application on the availability of silicon in soil, silicon uptake by plants, silicon effect in minimizing biotic stresses such as defence against sugarcane insect pest herbivory along with its effect on sugarcane yield in terms of juice and other component traits. There are two basic modes of action: enhanced physical or mechanical barriers and biochemical or molecular mechanisms that activate plant defence responses via bitrophic (plant-herbivore) interactions and tritrophic (plant-herbivore-natural enemy) interactions. By integrating the data reported in this research, a comprehensive understanding of the relationship between various sources of silicon treatments, increased sugarcane plant resistance and decreased sugarcane insect pest damage might be attained.

Phytoliths, the microscopic silica structures formed within plant tissues, are an emerging component of many sustainable plant protection attempts. They offer defense in multiple directions, physically strengthening plant tissues and biochemically engaging with the surroundings, and can diminish reliance on chemical pesticides and fertilizers. Physically, phytoliths enhance plant tissue rigidity and toughness, rendering them indigestible and less nutritious to herbivores and pathogens, thereby reducing feeding damage and disease incidence. Biochemically, phytoliths influence plant-microbe and plant-herbivore interactions by decreasing leaf palatability to herbivores, altering rhizosphere microbial communities including silica-specializing, plant-growth-promoting rhizobacteria, and diminishing pathogen proliferation. These effects enhance plant health by reducing pathogen spread and improving overall resilience. Furthermore, phytoliths accomplish crucial biogenic environmental roles such as facilitating biogeochemical silica and participating in essential nutrient cycles that uphold soil pH, fertility, and agricultural sustainability. Their enduring presence in soil enhances its structure, augments water retention, and improves nutrient availability, thereby fostering optimal conditions for plant growth. Additionally, phytoliths play a pivotal role in carbon sequestration and can immobilize heavy metals, mitigating soil contamination and advocating safer agricultural practices. This dual function in bolstering direct plant defense and indirectly enhancing soil health through carbon sequestration underscores the significant potential of phytoliths in sustainable agriculture. In our comprehensive exploration, we delve deeply into the imperative of integrating phytoliths into sustainable agricultural practices to cultivate innovative, eco-friendly, and resilient farming systems. Harnessing the complete potential of phytoliths can lead to advanced strategies for sustainable plant protection, aligning with global initiatives aimed at promoting environmental sustainability and agricultural resilience.