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Although studies have investigated the influence of the emotionality of primes on the cross-modal affective priming effect, it is unclear whether this effect is due to the contribution of the arousal or the valence of primes. We explored how the valence and arousal of primes influenced the cross-modal affective priming effect. In Experiment 1 we manipulated the valence of primes (positive and negative) that were matched by arousal. In Experiments 2 and 3 we manipulated the arousal of primes under the conditions of positive and negative valence, respectively. Affective words were used as auditory primes and affective faces were used as visual targets in a priming task. The results suggest that the valence of primes modulated the cross-modal affective priming effect but that the arousal of primes did not influence the priming effect. Only when the priming stimuli were positive did the cross-modal affective priming effect occur, but negative primes did not produce a priming effect. In addition, for positive but not negative primes, the arousal of primes facilitated the processing of subsequent targets. Our findings have great significance for understanding the interaction of different modal affective information.

This study examined the influence of semantic and phonological priming on L2 speech planning, as well as the difference between native and non-native speakers of English in terms of lemma activation. Two potential explanations for the contrast between the performance of L2 speakers and native controls were considered. The first of which was that L2 speakers’ phonological forms are activated before selection of syntactic frame occurred, whereas the reverse is true for native speakers. The second explanation posits that the organisation of the speech production procedure is fundamentally similar in native and L2 speakers, and the disparity in performance arises from difference in the levels of activation of stored items. The results of the present experiment suggest that lemma selection is indeed what drives syntactic frame selection. However, lemmas in L2 speakers can be primed through a chain of connections demonstrated as: L2 phonological form L1 phonological form L1 lemma.

We synthesized 20 years of research to explain the interrelated processes that determine soil and plant responses to biochar. The properties of biochar and its effects within agricultural ecosystems largely depend on feedstock and pyrolysis conditions. We describe three stages of reactions of biochar in soil: dissolution (1–3 weeks); reactive surface development (1–6 months); and aging (beyond 6 months). As biochar ages, it is incorporated into soil aggregates, protecting the biochar carbon and promoting the stabilization of rhizodeposits and microbial products. Biochar carbon persists in soil for hundreds to thousands of years. By increasing pH, porosity, and water availability, biochars can create favorable conditions for root development and microbial functions. Biochars can catalyze biotic and abiotic reactions, particularly in the rhizosphere, that increase nutrient supply and uptake by plants, reduce phytotoxins, stimulate plant development, and increase resilience to disease and environmental stressors. Meta‐analyses found that, on average, biochars increase P availability by a factor of 4.6; decrease plant tissue concentration of heavy metals by 17%–39%; build soil organic carbon through negative priming by 3.8% (range −21% to +20%); and reduce non‐CO2 greenhouse gas emissions from soil by 12%–50%. Meta‐analyses show average crop yield increases of 10%–42% with biochar addition, with greatest increases in low‐nutrient P‐sorbing acidic soils (common in the tropics), and in sandy soils in drylands due to increase in nutrient retention and water holding capacity. Studies report a wide range of plant responses to biochars due to the diversity of biochars and contexts in which biochars have been applied. Crop yields increase strongly if site‐specific soil constraints and nutrient and water limitations are mitigated by appropriate biochar formulations. Biochars can be tailored to address site constraints through feedstock selection, by modifying pyrolysis conditions, through pre‐ or post‐production treatments, or co‐application with organic or mineral fertilizers. We demonstrate how, when used wisely, biochar mitigates climate change and supports food security and the circular economy. Plant responses to biochar are driven by interrelated biotic and abiotic processes. Biochar properties depend on the feedstock, pyrolysis conditions, and formulation, explaining the variation in responses to biochars. Through its persistence, negative priming effect, and capacity to build soil organic carbon and reduce N2O and CH4 emissions from soil, biochar contributes to climate change mitigation. By improving physical, chemical, and biological soil properties, particularly in the rhizosphere, biochars can stimulate plant growth and increase resilience to disease and environmental stressors. Biochars increase crop yields on average by 10%–42%, with greatest response in acidic tropical soils and sandy dryland soils.

• Understanding how plant species influence soil nutrient cycling is a major theme in terrestrial ecosystem ecology. However, the prevailing paradigm has mostly focused on litter decomposition, while rhizosphere effects on soil organic matter (SOM) decomposition have attracted little attention. • Using a dual 13C/15N labeling approach in a ‘common garden’ glasshouse experiment, we investigated how the economic strategies of 12 grassland plant species (graminoids, forbs and legumes) drive soil nitrogen (N) cycling via rhizosphere processes, and how this in turn affects plant N acquisition and growth. • Acquisitive species with higher photosynthesis, carbon rhizodeposition and N uptake than conservative species induced a stronger acceleration of soil N cycling through rhizosphere priming of SOM decomposition. This allowed them to take up larger amounts of N and allocate it above ground to promote photosynthesis, thereby sustaining their faster growth. The N₂-fixation ability of legumes enhanced rhizosphere priming by promoting photosynthesis and rhizodeposition. • Our study demonstrates that the economic strategies of plant species regulate a plant–soil carbon–nitrogen feedback operating through the rhizosphere. These findings provide novel mechanistic insights into how plant species with contrasting economic strategies sustain their nutrition and growth through regulating the cycling of nutrients by soil microbes in their rhizosphere.

From recent developments on how roots affect soil organic carbon (SOC) an apparent paradox has emerged where roots drive SOC stabilization causing SOC accrual, but also SOC destabilization causing SOC loss. We synthesize current results and propose the new Rhizo-Engine framework consisting of two linked components: microbial turnover and the soil physicochemical matrix. The Rhizo-Engine is driven by rhizodeposition, root turnover, and plant uptake of nutrients and water, thereby accelerating SOC turnover through both stabilization and destabilization mechanisms. This Rhizo-Engine framework emphasizes the need for a more holistic approach to study root-driven SOC dynamics. This framework would provide better understanding of plant root effects on soil carbon sequestration and the sensitivity of SOC stocks to climate and land-use changes.

Root exudation is an important process determining plant interactions with the soil environment. Many studies have linked this process to soil nutrient mobilization. Yet, it remains unresolved how exudation is controlled and how exactly and under what circumstances plants benefit from exudation. The majority of root exudates including primary metabolites (sugars, amino acids, and organic acids) are believed to be passively lost from the root and used by rhizosphere-dwelling microbes. In this review, we synthetize recent advances in ecology and plant biology to explain and propose mechanisms by which root exudation of primary metabolites is controlled, and what role their exudation plays in plant nutrient acquisition strategies. Specifically, we propose a novel conceptual framework for root exudates. This framework is built upon two main concepts: (1) root exudation of primary metabolites is driven by diffusion, with plants and microbes both modulating concentration gradients and therefore diffusion rates to soil depending on their nutritional status; (2) exuded metabolite concentrations can be sensed at the root tip and signals are translated to modify root architecture. The flux of primary metabolites through root exudation is mostly located at the root tip, where the lack of cell differentiation favors diffusion of metabolites to the soil. We show examples of how the root tip senses concentration changes of exuded metabolites and translates that into signals to modify root growth. Plants can modify the concentration of metabolites either by controlling source/sink processes or by expressing and regulating efflux carriers, therefore challenging the idea of root exudation as a purely unregulated passive process. Through root exudate flux, plants can locally enhance concentrations of many common metabolites, which can serve as sensors and integrators of the plant nutritional status and of the nutrient availability in the surrounding environment. Plant-associated micro-organisms also constitute a strong sink for plant carbon, thereby increasing concentration gradients of metabolites and affecting root exudation. Understanding the mechanisms of and the effects that environmental stimuli have on the magnitude and type of root exudation will ultimately improve our knowledge of processes determining soil CO emissions, ecosystem functioning, and how to improve the sustainability of agricultural production.

The stability and decomposition of biochar are fundamental to understand its persistence in soil, its contribution to carbon (C) sequestration, and thus its role in the global C cycle. Our current knowledge about the degradability of biochar, however, is limited. Using 128 observations of biochar‐derived CO2 from 24 studies with stable (13C) and radioactive (14C) carbon isotopes, we meta‐analyzed the biochar decomposition in soil and estimated its mean residence time (MRT). The decomposed amount of biochar increased logarithmically with experimental duration, and the decomposition rate decreased with time. The biochar decomposition rate varied significantly with experimental duration, feedstock, pyrolysis temperature, and soil clay content. The MRTs of labile and recalcitrant biochar C pools were estimated to be about 108 days and 556 years with pool sizes of 3% and 97%, respectively. These results show that only a small part of biochar is bioavailable and that the remaining 97% contribute directly to long‐term C sequestration in soil. The second database (116 observations from 21 studies) was used to evaluate the priming effects after biochar addition. Biochar slightly retarded the mineralization of soil organic matter (SOM; overall mean: −3.8%, 95% CI = −8.1–0.8%) compared to the soil without biochar addition. Significant negative priming was common for studies with a duration shorter than half a year (−8.6%), crop‐derived biochar (−20.3%), fast pyrolysis (−18.9%), the lowest pyrolysis temperature (−18.5%), and small application amounts (−11.9%). In contrast, biochar addition to sandy soils strongly stimulated SOM mineralization by 20.8%. This indicates that biochar stimulates microbial activities especially in soils with low fertility. Furthermore, abiotic and biotic processes, as well as the characteristics of biochar and soils, affecting biochar decomposition are discussed. We conclude that biochar can persist in soils on a centennial scale and that it has a positive effect on SOM dynamics and thus on C sequestration.

The microbial priming effect—the decomposition of soil organic carbon (SOC) induced by plant inputs—has long been considered an important driver of SOC dynamics, yet we have limited understanding about the direction, intensity, and drivers of priming across ecosystem types and biomes. This gap hinders our ability to predict how shifts in litter inputs under global change can affect climate feedbacks. Here, we synthesized 18,919 observations of CO₂ effluxes in 802 soils across the globe to test the relative effects (i.e., log response ratio [RR]) of litter additions on native SOC decomposition and identified the dominant environmental drivers in natural ecosystems and agricultural lands. Globally, litter additions enhanced native SOC decomposition (RR = 0.35, 95% CI: 0.32–0.38), with greater priming effects occurring with decreasing latitude and more in agricultural soils (RR = 0.43) than in uncultivated soils (RR = 0.28). In natural ecosystems, soil pH and microbial community composition (e.g., bacteria: fungi ratio) were the best predictors of priming, with greater effects occurring in acidic, bacteria-dominated sandy soils. In contrast, the substrate properties of plant litter and soils were the most important drivers of priming in agricultural systems since soils with high C:N ratios and those receiving large inputs of low-quality litter had the highest priming effects. Collectively, our results suggest that, though different factors may control priming effects, the ubiquitous nature of priming means that alterations of litter quality and quantity owing to global changes will likely have consequences for global C cycling and climate forcing.

I. II. III. IV. V. References SUMMARY: Although hypothesized for many years, the involvement of ectomycorrhizal fungi in decomposition of soil organic matter remains controversial and has not yet been fully acknowledged as an important factor in the regulation of soil carbon (C) storage. Here, we review recent findings, which support the view that some ectomycorrhizal fungi have the capacity to oxidize organic matter, either by ‘brown‐rot’ Fenton chemistry or using ‘white‐rot’ peroxidases. We propose that ectomycorrhizal fungi benefit from organic matter decomposition primarily through increased nitrogen mobilization rather than through release of metabolic C and question the view that ectomycorrhizal fungi may act as facultative saprotrophs. Finally, we discuss how mycorrhizal decomposition may influence organic matter storage in soils and mediate responses of ecosystem C sequestration to environmental changes.

Soil samples from an Alfisols with long-term (> 12 years) contrasting tillage intensities (i.e., no-till versus plow-till) were first divided into three distinct dry aggregate-size classes (i.e., mega-, macro-, and microaggregates) and then incubated with 13C-labeled wheat residue at three input levels of balanced nutrients supply under controlled laboratory conditions. Across all the treatments, from 55.1 to 83.4% of total straw-C was mineralized within the incubation period. The microaggregates significantly increased the straw-C mineralization rate by 3.6 and 3.1 mg C g−1 straw-C day−1 compared to the mega- and macroaggregates respectively, mainly due to the higher microbial biomass. The high input of balanced nutrients enhanced the straw-C mineralization. Moreover, the microbial C-use efficiency (CUE) of straw residue in the microaggregates was 25.1% and 7.3% higher than that in the mega- and macroaggregates, respectively. Legacy effect of the long-term no-till increased microbial CUE, mainly by reducing the C-nutrient stoichiometric imbalance. In contrast, straw addition to the microaggregates resulted in the lowest positive priming effect (PE) of SOC compared to that added to the mega- and macroaggregates. Both the nutrient input and no-till treatments positively contributed to the decrease in positive PE. The negative correlation between the microbial CUE of the straw residue and the positive PE was reported for the first time, and the inputs of straw residue and high-level nutrients to the microaggregates from the no-till treatment increased CUE but decreased positive PE.