Magnitude Of Priming Research Articles

Vegetative stage and soil horizon respectively determine direction and magnitude of rhizosphere priming effects in contrasting tree line soils

Abstract Tree lines in high latitudes and high altitudes are considered sentinels of global change. This manifests in accelerated encroachment of trees and shrubs and enhanced plant productivity, with currently unknown implications for the carbon balance of these biomes. Given the large soil organic carbon stocks in many tree line soils, we here wondered whether introducing highly productive plants would accelerate carbon cycling through rhizosphere priming effects and if certain soils would be more vulnerable to carbon loss from positive priming than others. To test this, organic and mineral soils were sampled above and below tree lines in the Swedish sub‐arctic and the Peruvian Andes. A greenhouse experiment was then performed to quantify plant‐induced changes in soil mineralisation rates (rhizosphere priming effect) and new C formation using natural abundance labelling and the C4‐species Cynodon dactylon. Several environmental, plant, soil and microbial parameter were monitored during the experiment to complement the observations on soil C cycling. Priming was predominantly positive at the beginning of the experiment, then systematically decreased in all soils during the plant growth season to be mostly negative at the end of the experiment at plant senescence. Independent of direction of priming, the magnitude of priming was always greater in organic than in corresponding mineral soils, which was best explained by the higher C contents of these soils. Integrated over the entire study period, the overall impact of priming (positive and negative) on the soil C balance was mostly negligible. Though net soil C loss was observed in organic soils from the sub‐arctic tundra in Sweden. Most notably, positive and negative priming effects were not mutually exclusive, rather omnipresent across ecosystems, depending on sampling time. The direction of priming seems to be fluctuating with plant productivity, rhizosphere carbon inputs and nutrient uptake. This highlights the need for integrative long‐term studies if we aim to understand priming effects at ecosystem scale and greenhouse and laboratory studies must be validated in situ to enable reliable ecological upscaling. Read the free Plain Language Summary for this article on the Journal blog.

Masked cognate translation priming with Arabic-English bilinguals: Further support for the morphological account

The aim of this study is to test the two accounts that have been posited as how cognates are represented in the bilingual mind: the mophological account and the phonological account. More specifically, this study exploits the uique feature of pluralization in Arabic (i.e., concatenative vs. non-concatenative process of pluralization) to invetigate how cognates are represented in the bilingual mind of different-script bilinguals (Arabic-English bilinguals) using the masked priming technique. Two types of cognates were used: cognates that are pluralized concatenatively and cognates that pluralized non-concatenatively in Arabic. In concatenative pluralization, the phonology of the singualr form is intact such as هرمون /hormōn/ (hormone in English), which is pluralized as هرمونات/hormōnat/ (hormones in English). On the other hand, in non-concatenative pluralization, the phonology of the singular form is broken when a word is plualized non-concatenatively as in ترم /tirm/ (term in English) and أترام atrām/ (terms in English). The results show a comparable priming effect for both types of pluralizations indicating that cognates in Arabic-English bilinguals may have a shared morphological representation since the magnitude of priming was not affected by the type of pluralization. This similar priming effect for concatenative and non-concatenative pluralization indicates that cognates may share a special kind of morphological representation as suggested by the morphological account. Author: Alhassan Alzahrani 0000-0003-4547-6582 aajzahrani@bu.edu.sa

Individual differences in structural priming in bilingual and monolingual children: the influence of perspective-taking

Abstract When speaking or writing, people tend to re-use the syntactic structures they recently encountered (structural priming). Individuals differ in the extent to which they are primed (primeability). Previous research has suggested that perspective-taking, that is, the ability to imagine the feelings, thoughts and perceptions of others, predicts the magnitude of priming in adults. The present study investigates if this also holds for monolingual and bilingual children. We primed the possessive structure in monolingual Dutch children and bilingual children with varying L2s. There was individual variation in children’s primeability in both groups. For both monolinguals and bilinguals, we found that the better children were at perspective-taking, the more likely they were to be primed. Dutch language proficiency also influenced children’s primeability: higher language proficiency resulted in more priming in both groups. The findings suggest that structural priming serves a social function which is mediated by perspective-taking abilities.

Controls and significance of priming effects in lake sediments

AbstractWarming and eutrophication influence carbon (C) processing in sediments, with implications for the global greenhouse‐gas budget. Temperature effects on sedimentary C loss are well understood, but the mechanism of change in turnover through priming with labile organic matter (OM) is not. Evaluating changes in the magnitude of priming as a function of warming, eutrophication, and OM stoichiometry, we incubated sediments with 13C‐labeled fresh organic matter (FOM, algal/cyanobacterial) and simulated future climate scenarios (+4°C and +8°C). We investigated FOM‐induced production of CH4 and microbial community changes. C loss was primed by up to 17% in dominantly allochthonous sediments (ranging from 5% to 17%), compared to up to 6% in autochthonous sediments (−9% to 6%), suggesting that refractory OM is more susceptible to priming. The magnitude of priming was dependent on sediment OM stoichiometry (C/N ratio), the ratio of fresh labile OM to microbial biomass (FOM/MB), and temperature. Priming was strongest at 4°C when FOM/MB was below 50%. Addition of FOM was associated with activation and growth of bacterial decomposers, including for example, Firmicutes, Bacteroidetes, or Fibrobacteres, known for their potential to degrade insoluble and complex structural biopolymers. Using sedimentary C/N > 15 as a threshold, we show that in up to 35% of global lakes, sedimentation is dominated by allochthonous rather than autochthonous material. We then provide first‐order estimates showing that, upon increase in phytoplankton biomass in these lakes, priming‐enabled degradation of recalcitrant OM will release up to 2.1 Tg C annually, which would otherwise be buried for geological times.

62 Repetition priming of novel geometric shapes is associated with cortical arousal in young adults but spatial attention in older adults

Objective:Repetition priming is a form of implicit memory in which prior exposure to a stimulus facilitates the subsequent processing of that stimulus. While explicit memory has consistently been shown to decline with age, the effect of age on implicit memory remains unresolved. Most studies examining age-related effects on priming have utilized words or pictures of real objects with pre-existing representations that may differentially involve implicit and explicit memory processes across age groups. Repetition priming may also be influenced by attentional processes during encoding that are differentially affected by age. In a previous study using word-stem completion, we found that individual differences in cortical arousal, but not spatial attention, influenced the magnitude and temporal dynamics of conceptual priming in healthy older adults. The objective of this study is to investigate whether cortical arousal and spatial attention play differential roles in the magnitude and temporal dynamics of repetition priming in young and older adults using novel shapes that do not have pre-existing representations within memory.Participants and Methods:Healthy young (n=25, M age=19.4) and older adults (n=54, M age=70.0) completed a perceptual repetition priming task that was followed by a recognition memory test and an alerting/spatial orienting task from which behavioral measures of cortical arousal and spatial attention were derived. Older adults also completed a battery of neuropsychological tests. In the perceptual priming task, participants made a speeded judgment on whether novel nonverbal shapes had “closed” or “open” perimeters. Each shape was presented twice: half following the first presentation (immediate repetition) and half after three intervening items (delayed repetition). Participants were then shown closed and open versions of each shape and asked to identify which version was presented in the previous task. In the alerting/orienting task, participants made a speeded response to the location of a visual target; on a subset of trials, either nonspatial alerting or spatial orienting cues were presented 300ms prior to the target.Results:Response times were slower and judgment accuracy greater in older adults (ps<0.05). However, the groups showed comparable levels of immediate and delayed repetition priming along with chance levels of recognition memory accuracy. Cortical arousal was reduced (p<0.001) and costs associated with spatial attention were larger (p<0.01) in the older adults. Despite comparable priming, cortical arousal and spatial attention were differentially related to priming across groups. In the young group, lower cortical arousal was associated with greater delayed priming (r=-.47, p=0.017) and slower decay rate (r=.44, p=0.03). In the older group, higher cost of spatial orienting was associated with greater immediate priming (r=.40, p=0.003) and faster decay rate (r=.29, p=0.03). Better category fluency performance was also associated with greater immediate priming (r=.32, p=0.035) and faster decay rate (r=.34, p=0.025) in older adults.Conclusions:These findings suggest that different attentional systems support repetition priming across age groups. Priming is modulated by the efficiency of cortical arousal in young adults, but by the costs of spatial attention in older adults with reduced cortical arousal, consistent with a shift from bottom-up to top-down attentional processes and broader attentional scope with age.

The influence of semantic predictability on transposition effects in Chinese and English

Abstract Semantic predictability is one of the important factors that influence word processing and recognition. Based on the SPaM paradigm (Self-paced reading + Masked priming), the present study explores the influence of semantic predictability on TL effects in Chinese and English. The findings show that in both languages, internal and final transpositions produce priming effect in low-predictability preceding and following contexts as well as in high-predictability following contexts. From the perspective of priming magnitude, internal transposition produces greater priming effect than final transposition in English, while in Chinese, final transposition produces greater priming effect than internal transposition. In high-predictability preceding contexts, internal and final transpositions reveal significant priming effect and initial transposition produces close-to-significant-level priming effect in English, while in Chinese, no significant priming effect is observed in initial, internal or final transpositions.

Syntactic representation of missing-verb anomalous utterances in Mandarin: Evidence from structural priming.

Theories of how people interpret utterances with verb-related anomalies are chiefly based on English, but relatively little is known about the syntactic representation of missing-verb anomalous utterances in Mandarin, which has strikingly different typological features. In the current study, two experiments in structural priming paradigm were carried out to investigate whether native Mandarin speakers reconstructed a full syntactic form of missing-verb anomalous utterances. Our study shows that the magnitude of priming following a missing-verb anomalous sentence is equivalent to that following an error-free sentence, indicating that native Mandarin speakers reconstruct a full syntactic representation of missing-verb anomalous utterances. The results thus provide robust evidence for the syntactic reconstruction account.

Microbial properties control soil priming and exogenous carbon incorporation along an elevation gradient

Fresh carbon (C) input can modify soil C cycling through priming and exogenous C incorporation. Identifying the patterns and drivers of these two processes is essential for understanding C cycling in terrestrial ecosystems. We conducted a laboratory analysis based on 51 soils collected along an elevation gradient to evaluate the magnitude of priming and exogenous C incorporation. The priming effect showed a hump-shaped pattern along the elevation, and the proportion of exogenous C incorporation decreased with elevation. Deep soils had significantly higher priming and exogenous C incorporation than surface soils. The variance in priming effect was negatively controlled by soil initial metabolic quotient (qCO2), possibly because of the different microbial energy requirements and consequently, selective utilization of energy-rich or energy-poor substrates. Exogenous C incorporation was negatively correlated with soil qCO2 and the relative abundance of copiotrophic microorganisms, and positively correlated with soil C saturation deficit. The magnitude of exogenous C incorporation was greater than that of priming, resulting in a net C balance averaging 48.8% of the added exogenous C. Our findings highlight the critical roles of the various microbial properties in regulating soil C cycling under exogenous C input. Considering the above-mentioned factors could improve the performance of C models under changing environments.

Cumulative Genetic Score of DRD2 Polymorphisms Is Associated with Impulsivity and Masked Semantic Priming

Individual differences in the magnitude of semantic priming effects are associated with executive functions (EF). Striatal dopamine has been shown to be associated with EF as well as impulsivity and could therefore be associated with differences in the magnitude of semantic priming. We investigated n = 155 individuals in an unmasked as well as in a masked semantic priming paradigm. We additionally assessed self-reported impulsivity and a cumulative genetic score (CGS) comprising six polymorphisms that have been found to be functionally relevant for the expression of the DRD2 gene. We found a significantly negative association between the DRD2 CGS and reaction time priming in the masked semantic priming paradigm. In addition, the DRD2 CGS was positively associated with self-reported impulsivity. Our findings complement previous research by showing a role of the DRD2 gene for masked semantic priming. Therefore, the investigation of genes within the dopamine system might improve our understanding of the genetic basis of impulsivity and semantic processing. Thus, the DRD2 CGS is of interest for clinical as well as experimental psychological research.

Unconscious priming shares a common resource pool with the manipulation subsystem.

BackgroundWorking memory can be subdivided into two relatively independent subordinate systems, the maintenance subsystem and the manipulation subsystem. Although the two subsystems are quite heterogeneous, research thus far has not adequately distinguished the resource pools of the two subsystems. Additionally, previous research on the relationship between working memory and unconscious priming is paradoxical. Different subsystems leading to different effects on unconscious priming might be the reason for the paradoxical research. Therefore, the current article aimed to distinguish the resource pools among two working-memory subsystems and to investigate the relationship between the two subsystems and unconscious priming.MethodsTo address these issues, a maintenance dual-task and a manipulation dual-task program were developed. Each participant had to separately perform the two dual tasks in a balanced order. In each dual task, participants first completed a masked priming task accompanied by working-memory load. As a control, participants completed a prime identification test to confirm that the processing of the masked prime was at the unconscious level. The maintenance dual task comprised sandwich masking trials accompanied by Sternberg trials, while the manipulation dual task comprised sandwich masking trials accompanied by N-back trials.ResultsThe results of the prime identification test indicated that the participants could not consciously perceive the masked prime of both dual tasks. The results of the working-memory task of both dual tasks indicated that the load manipulation was successful for both dual tasks. Most importantly, the results of the masking task of both dual tasks showed that an increase in working-memory load decreased the magnitude of unconscious priming in the manipulation dual task, whereas an increase in working-memory load did not decrease unconscious priming in the maintenance dual task. These observations demonstrate that the manipulation subsystem, rather than the maintenance subsystem, interferes with unconscious priming. Together with previous research, we propose a two-pool attention resource model to explain the modulation of working memory on unconscious priming by dissociating the executive resource pool of the manipulation system from the retention resource pool of the maintenance system. Thus, the current work confirms and extends the extant literature about the dependence of unconscious processing on attention resources by suggesting that unconscious priming shares a common resource pool with the manipulation subsystem.

Distinct deficits of repetition priming following lateral versus anteromedial frontal cortex damage

Object repetition commonly leads to long-lasting improvements in identification speed and accuracy, a behavioral facilitation referred to as “repetition priming”. Neuroimaging and non-invasive electromagnetic stimulation studies have most often implicated the involvement of left lateral frontal cortex in repetition priming, although convergent evidence from neuropsychological studies is lacking. In the current study, we examine the impact of surgical resection for the treatment of epilepsy on the magnitude of repetition priming at relatively short-term (30–60 min delay) and long-term (3 months) delays in 41 patients with varying seizure foci and resection locations. Overall, patients exhibited significant repetition priming at both short-term and long-term delays. However, patients with frontal resections (largely anterior and medial frontal) differed significantly from those with right anterior temporal resections in showing fully intact short-term priming but absent long-term priming. In a comparison set of 10 recovered aphasic patients, patients with left lateral frontal damage exhibited impaired short-term priming relative to other frontal damage locations, suggesting the differential involvement of lateral and anteromedial frontal regions in mediating repetition priming at short-lag and long-lag timescales, respectively.

What happens to our representation of identity as familiar faces age? Evidence from priming and identity aftereffects.

Matching identity in images of unfamiliar faces is error prone, but we can easily recognize highly variable images of familiar faces – even images taken decades apart. Recent theoretical development based on computational modelling can account for how we recognize extremely variable instances of the same identity. We provide complementary behavioural data by examining older adults’ representation of older celebrities who were also famous when young. In Experiment 1, participants completed a long‐lag repetition priming task in which primes and test stimuli were the same age or different ages. In Experiment 2, participants completed an identity after effects task in which the adapting stimulus was an older or young photograph of one celebrity and the test stimulus was a morph between the adapting identity and a different celebrity; the adapting stimulus was the same age as the test stimulus on some trials (e.g., both old) or a different age (e.g., adapter young, test stimulus old). The magnitude of priming and identity after effects were not influenced by whether the prime and adapting stimulus were the same age or different age as the test face. Collectively, our findings suggest that humans have one common mental representation for a familiar face (e.g., Paul McCartney) that incorporates visual changes across decades, rather than multiple age‐specific representations. These findings make novel predictions for state‐of‐the‐art algorithms (e.g., Deep Convolutional Neural Networks).

Rats spontaneously perceive global motion direction of drifting plaids

Computing global motion direction of extended visual objects is a hallmark of primate high-level vision. Although neurons selective for global motion have also been found in mouse visual cortex, it remains unknown whether rodents can combine multiple motion signals into global, integrated percepts. To address this question, we trained two groups of rats to discriminate either gratings (G group) or plaids (i.e., superpositions of gratings with different orientations; P group) drifting horizontally along opposite directions. After the animals learned the task, we applied a visual priming paradigm, where presentation of the target stimulus was preceded by the brief presentation of either a grating or a plaid. The extent to which rat responses to the targets were biased by such prime stimuli provided a measure of the spontaneous, perceived similarity between primes and targets. We found that gratings and plaids, when used as primes, were equally effective at biasing the perception of plaid direction for the rats of the P group. Conversely, for the G group, only the gratings acted as effective prime stimuli, while the plaids failed to alter the perception of grating direction. To interpret these observations, we simulated a decision neuron reading out the representations of gratings and plaids, as conveyed by populations of either component or pattern cells (i.e., local or global motion detectors). We concluded that the findings for the P group are highly consistent with the existence of a population of pattern cells, playing a functional role similar to that demonstrated in primates. We also explored different scenarios that could explain the failure of the plaid stimuli to elicit a sizable priming magnitude for the G group. These simulations yielded testable predictions about the properties of motion representations in rodent visual cortex at the single-cell and circuitry level, thus paving the way to future neurophysiology experiments.

The magnitude and direction of priming were driven by soil moisture and temperature in a temperate forest soil of China

Increased temperature and extreme precipitation due to global climate change play a critical role in the soil carbon cycle. The priming effect describes the changes in soil organic carbon (SOC) mineralization after fresh organic matter (FOM) inputs and is a major component of the soil carbon cycle. However, further research is needed to improve understanding of the interactive influence of warming and soil moisture changes on soil carbon priming. In this study, we conducted a 57-day incubation experiment to investigate the interactive effects of soil moisture and temperature on priming on forest soils from a temperate region of China. 13C labeled Glucose was added to simulate the priming effect induced by rhizosphere exudates at three soil moisture levels (20 %, 55 %, and 90 % of field capacity (FC)) and three temperature levels (5, 15, and 25 °C). Soil priming increased significantly with the increase of moisture; the cumulative priming effects were positive at 55 % and 90 % FC, but were negative at 20 % FC. Warming significantly stimulated the magnitude of priming at all moisture levels, with the greatest negative priming under 20 %FC×25 °C (−165.9 mg C kg−1) and the greatest positive priming under 90 %FC×25 °C (588.0 mg C kg−1). Furthermore, priming considerably influenced the soil carbon balance, which resulted in maximum carbon storage under 20 %FC×25 °C (279.4 mg C kg−1) and the greatest carbon loss under 90 %FC×25 °C (−493.9 mg C kg−1). Furthermore, temperature sensitivity (Q10) of SOC mineralization was highly dependent on FOM inputs. In unprimed soils, Q10 was negatively and significantly related to moisture; however, no significant correlation was observed between Q10 and moisture after glucose addition because of the priming. The findings of this study contribute to the better understanding of the temperate forest soil carbon cycle under global climate change by highlighting the interactive effects of soil moisture and temperature on the priming effect.

Structural priming is supported by different components of nondeclarative memory: Evidence from priming across the lifespan.

Structural priming is the tendency to repeat syntactic structure across sentences and can be divided into short-term (prime to immediately following target) and long-term (across an experimental session) components. This study investigates how nondeclarative memory could support both the transient, short-term and the persistent, long-term structural priming effects commonly seen in the literature. We propose that these characteristics are supported by different subcomponents of nondeclarative memory: Perceptual and conceptual nondeclarative memory respectively. Previous studies have suggested that these subcomponents age differently, with only conceptual memory showing age-related decline. By investigating how different components of structural priming vary across the life span, we aim to elucidate how nondeclarative memory supports 2 seemingly different components of structural priming. In 167 participants ranging between 20 and 85 years old, we find no change in short-term priming magnitude and performance on perceptual tasks, whereas both long-term priming and conceptual memory vary with age. We suggest therefore that the 2 seemingly different components of structural priming are supported by different components of nondeclarative memory. These findings have important implications for theoretical accounts of structural priming. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Enhanced inter-regional coupling of neural responses and repetition suppression provide separate contributions to long-term behavioral priming

Stimulus identification commonly improves with repetition over long delays (“repetition priming”), whereas neural activity commonly decreases (“repetition suppression”). Multiple models have been proposed to explain this brain-behavior relationship, predicting alterations in functional and/or effective connectivity (Synchrony and Predictive Coding models), in the latency of neural responses (Facilitation model), and in the relative similarity of neural representations (Sharpening model). Here, we test these predictions with fMRI during overt and covert naming of repeated and novel objects. While we find partial support for predictions of the Facilitation and Sharpening models in the left fusiform gyrus and left frontal cortex, the data were most consistent with the Synchrony model, with increased coupling between right temporoparietal and anterior cingulate cortex for repeated objects that correlated with priming magnitude across participants. Increased coupling and repetition suppression varied independently, each explaining unique variance in priming and requiring modifications of all current models.

The Influence of the BDNF Val66Met Polymorphism on Mechanisms of Semantic Priming: Analyses with Drift-Diffusion Models of Masked and Unmasked Priming.

Automatic and strategic processes in semantic priming can be investigated with masked and unmasked priming tasks. Unmasked priming is thought to enable strategic processes due to the conscious processing of primes, while masked priming exclusively depends on automatic processes due to the invisibility of the prime. Besides task properties, interindividual differences may alter priming effects. In a recent study, masked and unmasked priming based on mean response time (RT) and error rate (ER) differed as a function of the BDNF Val66Met polymorphism (Sanwald et al., 2020). The BDNF Val66Met polymorphism is related to the integrity of several cognitive executive functions and might thus influence the magnitude of priming. In the present study, we reanalyzed this data with drift-diffusion models. Drift-diffusion models conjointly analyze single trial RT and ER data and serve as a framework to elucidate cognitive processes underlying priming. Masked and unmasked priming effects were observed for the drift rates ν, presumably reflecting semantic preactivation. Priming effects on nondecision time t0 were especially pronounced in unmasked priming, suggesting additional conscious processes to be involved in the t0 modulation. Priming effects on the decision thresholds a may reflect a speed-accuracy tradeoff. Considering the BDNF Val66Met polymorphism, we found lowered drift rates and decision thresholds for Met allele carriers, possibly reflecting a superficial processing style in Met allele carriers. The present study shows that differences in cognitive tasks between genetic groups can be elucidated using drift-diffusion modeling.

Finding the man amongst many: A developmental perspective on mechanisms of morphological decomposition

Skilled reading is characterized by rapid recognition of morphologically complex words. Evidence suggests that adult readers segment complex words into their constituent morphemes during visual word recognition, and that this extends to items that have only a surface morphological structure (e.g., corner), a process termed ‘morpho-orthographic segmentation’. It is not yet known how and when this mechanism is established over the course of reading development, although data from English-speaking children suggest that it may be a relatively late-acquired milestone. The purpose of this study was to examine for the first time the mechanisms driving morphological processing across late childhood and adolescence. A cross-sectional sample of 204 children and adolescents from South-East England, ranging in age from 9 to 18 years (M age = 13.74 years, SD = 2.68; 110 female), completed a visual masked prime lexical decision task using three sets of prime-target pairs: morphological (e.g., teacher – TEACH), pseudomorphological (sharing an apparent morphological relationship in the absence of a semantic relationship, e.g., corner – CORN), and form (sharing an orthographic relationship only, e.g., window – WIND). Linear mixed effects models revealed both morphological and pseudomorphological priming in the absence of form priming, with priming magnitude increasing in line with age, and stronger evidence of morpho-orthographic segmentation emerging in line with word reading efficiency. Our findings reveal advances in the reading system during adolescence which may reflect accumulated exposure to regularities in the writing system, facilitating rapid access to meaning from print.

Sources and priming of nitrous oxide production across a range of moisture contents in a soil with high organic matter.

Adding nitrogen fertilizers to agricultural soils contributes to increasing concentrations of nitrous oxide (N2 O) in the atmosphere. However, the impacts of N addition on soil organic matter (SOM) turnover, SOM availability, and the ensuing SOM-derived N2 O emissions remain elusive. Within this context, the net change in direction and rate of SOM-derived N2 O production triggered by added N is termed the N2 O priming effect. This incubation study examined the sources and priming of N2 O production as a function of urea addition and multiple moisture contents in a soil with high SOM (55g organic C kg-1 ). We assessed four water-filled pore space (WFPS) conditions: 28, 40, 52, and 64%. Relative to controls receiving no N, urea addition increased N2 O production by 2.6 times (P<.001). Cumulative N2 O production correlated well with nitrification rates (r=.75; P=.03). We used 15 N-labeled urea to trace the added urea into N2 O. Of the N added via urea, the recovery as N2 O-N shifted from 0.02 to 0.17% when WFPS increased from 28 to 64% (P<.05). We also partitioned the N2 O production into urea vs. SOM sources. More N2 O was sourced from SOM than urea, with 59 ± 2% N2 O originating from SOM. The magnitude of SOM-derived N2 O under urea was larger than that of the control, revealing that positive N2 O priming was triggered by urea addition. Upon subtracting the controls, the primed N2 O was a consistent 19 ± 2% of the total N2 O produced by urea-amended soils. Nevertheless, the priming magnitude rose sharply with increasing moisture by more than one order of magnitude from 4 to 48μg N2 O-N kg-1 soil and in exponential mode (R2 =.98). Soil moisture, SOM, and nitrification interacted to drive the sources and priming of N2 O.

Labile carbon addition alters soil organic carbon mineralization but not its temperature sensitivity in a freshwater marsh of Northeast China

Inland freshwater marshes are notable contributors to soil organic carbon (SOC) pool across the globe. Input of labile C can greatly affect the direction and intensity of priming effects (PE) on SOC decomposition, which will likely be altered under climate warming. However, the effects of temperature on priming of wetland SOC mineralization and its temperature sensitivity (Q10) under varied C inputs remain unclear. We conducted a laboratory incubation experiment with 13C-glucose addition to investigate the effects of labile C on priming and Q10 values of the freshwater wetland SOC decomposition at 10 and 20 °C in Northeast China. Results showed that temperature and glucose additions had significant effects on CO2 efflux rates, but interactive effects were not observed. The positive priming that increased with increasing C added at both temperatures was detected, while the magnitude of priming at 10 °C was higher than that at 20 °C. There were no significant differences in Q10 values under low and high glucose additions, both of which were obviously lower than that of no glucose addition treatment. Total microbial biomass (total PLFAs) at 20 °C was significantly decreased compared to that at 10 °C, while the opposite trend was observed for CO2 efflux at the end of incubation. High glucose addition induced higher PLFAs than other treatments at both temperatures, but the composition of microbial community was not significantly altered by temperature under labile additions. We conclude that substrate availability and temperature change may have great impacts on wetland soil C turnover through priming effects. We highlight that more attention should be paid on the relationship between labile substrates and temperature sensitivity of decomposition under climate warming.