Source-sink Relationships Research Articles

Tuning of sulfur flows and sulfur seed metabolism in oilseed rape facing sulfate limited conditions.

The response of oilseed rape to sulfur (S) restriction usually consists of increasing the components of S utilization efficiency (absorption, assimilation and remobilization) to provide S to seeds. However, source-sink relationships and S management in developing seeds under sulfate restriction are poorly understood. To address this, impacts of sulfate restrictions applied at "visible bud" or "start of pod filling" stages were studied with two genotypes (Aviso, Capitol) showing similar seed yield but higher seed weight and lower number of seeds per plant for Capitol under non-limited conditions. S flows at the whole plant level (using 34S-sulfate labelling) and S metabolism changes (S-compounds, ATP sulfurylase and adenosine 5'phosphosulfate reductase (APR) activities) were followed during seed development. Seed yield, protein quality and accumulation of S metabolites were affected by sulfate restriction less and later in Aviso than in Capitol. This is related to higher S uptake and stronger remobilization of S from vegetative organs to seeds during early seed development in response to sulfate restriction. A higher seed APR activity was observed for Capitol in response to sulfate limitation, suggesting that APR is not limiting for sulfate assimilation and that seed S metabolism is principally devoted to S-amino acids and protein synthesis.

PROCERA interacts with JACKDAW in gibberellin-enhanced source-sink sucrose partitioning in tomato.

Proper regulation of the source-sink relationship is an effective way to increase crop yield. Gibberellin (GA) is an important regulator of plant growth and development, and physiological evidence has demonstrated that GA can promote source-sink sucrose partitioning. However, the underlying molecular mechanism remains unclear. Here, we used a combination of physiological and molecular approaches to identify the components involved in GA-enhanced source-sink sucrose partitioning in tomato (Solanum lycopersicum). GA treatment increased the sucrose export rate from source leaves and the sucrose level in young leaves (sink organ). GA-mediated enhancement of source-sink sucrose partitioning depended on SlPROCERA (SlPRO), the DELLA protein in tomato. Sucrose transporter 1 (SlSUT1) was involved in phloem sucrose loading. SlJACKDAW (SlJKD) was identified as an interaction partner of SlPRO. SlJKD negatively regulated the sucrose export rate from source leaves and could directly bind to the promoter of SlSUT1 and repress its expression, while SlPRO enhanced the transcription repression function of SlJKD. This study reveals the molecular mechanism by which GA promotes source-sink sucrose partitioning in tomato and provides potential targets for source-sink relationship optimization.

Prohexadione Calcium Improves Rice Yield Under Salt Stress by Regulating Source-Sink Relationships During the Filling Period.

Salt stress is an important factor affecting the growth and development of rice, and prohexadione calcium (Pro-Ca) plays an important role in alleviating rice salt stress and improving rice yield. However, there are few studies on how Pro-Ca improves rice yield under salt stress by regulating the source-sink metabolism. In this study, we used Guanghong 3 (salt-tolerant variety) and Huanghuazhan (salt-sensitive variety) as experimental materials to investigate the dynamic changes in the synthesis and partitioning of nonstructural carbohydrates among source-sink, the dynamic changes in related enzyme activities, the effects of the source-sink metabolism on yield in rice under salt stress and the effect of Pro-Ca during the filling period. The results of this study showed that Pro-Ca improved photosynthetic efficiency by increasing leaf photosynthetic gas exchange parameters and other stomatal factors on the one hand and, on the other hand, promoted sugar catabolism and reduced sugar synthesis by increasing leaf sucrose synthase activity and decreasing sucrose phosphate synthase activity, alleviating the inhibitory effect of high concentrations of sugars in the leaves on photosynthesis. Meanwhile, Pro-Ca promotes the transport of sugars from source (leaves) to sink (seeds), increases the sugar content in the seeds, and promotes starch synthesis in the seeds by increasing starch phosphorylase, which promotes seed filling, thus increasing the number of solid grains on the primary and secondary branches of the panicle in rice, increasing the 1000-grain weight, and ultimately increasing the seed setting rate and yield. These results indicated that Pro-Ca alleviated the inhibitory effect of salt stress on rice leaf photosynthesis through stomatal and non-stomatal factors. Meanwhile, Pro-Ca promotes the transport of rice sugars from source to sink under salt stress, regulates the source-sink relationship during the filling period of rice, promotes starch synthesis, and ultimately improves rice yield.

Same, yet different: towards understanding nutrient use in hemp- and drug-type Cannabis.

Cannabis sativa L., one of the oldest cultivated crops, has a complex domestication history due to its diverse uses for fibre, seed, oil, and drugs, and its wide geographic distribution. This review explores how human selection has shaped the biology of hemp and drug-type Cannabis, focusing on acquisition and utilization of nitrogen and phosphorus, and how resulting changes in source-sink relations shape their contrasting phenology. Hemp has been optimized for rapid, slender growth and nutrient efficiency, whereas drug-type cultivars have been selected for compact growth with large phytocannabinoid-producing female inflorescences. Understanding these nutrient use and ontogenetic differences will enhance our general understanding of resource allocation in plants. Knowledge gained in comparison with other model species, such as tomato, rice, or Arabidopsis can help inform crop improvement and sustainability in the cannabis industry.

Lodging susceptibility index is associated with impaired source-sink relationship and sucrose allocation in oat varieties

Lodging susceptibility index is associated with impaired source-sink relationship and sucrose allocation in oat varieties

Post-flowering Nitrogen Source–Sink Relationship Underlying Mechanisms Explain the Genotypic Variation in Seed N Accumulation of Rapeseed Genotypes

Post-flowering Nitrogen Source–Sink Relationship Underlying Mechanisms Explain the Genotypic Variation in Seed N Accumulation of Rapeseed Genotypes

Sugar Transport and Signaling in Shoot Branching.

The source-sink relationship is critical for proper plant growth and development, particularly for vegetative axillary buds, whose activity shapes the branching pattern and ultimately the plant architecture. Once formed from axillary meristems, axillary buds remain dormant or become active to grow into new branches. This transition is notably driven by the regulation of the bud sink strength, which is reflected in the ability to unload, metabolize and store photoassimilates. Plants have so far developed two main mechanisms for unloading sugars (sucrose) towards sink organs, a symplasmic pathway and an apoplasmic pathway, but so far limited investigations have been reported about the modes of sugar uptake during the transition from the dormant to the active outgrowth state of the bud. The available data indicate that the switch from dormant bud to active outgrowing state, requires sugar and is shortly preceded by an increase in bud metabolic activity and a remobilization of the stem starch reserves in favor of growing buds. This activation of the bud sink strength is accompanied by an up-regulation of the main markers of apoplasmic unloading, such as sugar transporters (sucrose transporters-SUTs; sugar will eventually be exported transporters-SWEETs), sucrose hydrolyzing enzymes (cell wall invertase-CWINV) and sugar metabolic pathways (glycolysis/tricarboxylic cycle-TCA; oxidative pentose phosphate pathway-OPPP). As these results are limited to a few species, they are not sufficient to provide a complete and accurate picture of the mode(s) of sugar unloading toward axillary buds and deserve to be complemented by additional studies in a wide variety of plants using systems integration, combining genetic, molecular and immunolocalization approaches. Altogether, we discuss here how sugar is a systemic regulator of shoot branching, acting both as an energy-rich molecule and a signaling entity in the establishment of the bud sink strength.

Engineering source-sink relations by prime editing confers heat-stress resilience in tomato and rice.

A 2°C climate-warming scenario is expected to further exacerbate average crop losses by 3%-13%, yet few heat-tolerant staple-crop varieties are available toward meeting future food demands. Here, we develop high-efficiency prime-editing tools to precisely knockin a 10-bp heat-shock element (HSE) into promoters of cell-wall-invertase genes (CWINs) in elite rice and tomato cultivars. HSE insertion endows CWINs with heat-responsive upregulation in both controlled and field environments to enhance carbon partitioning to grain and fruits, resulting in per-plot yield increases of 25% in rice cultivar Zhonghua11 and 33% in tomato cultivar Ailsa Craig over heat-stressed controls, without fruit quality penalties. Up to 41% of heat-induced grain losses were rescued in rice. Beyond a prime-editing system for tweaking gene expression by efficiently delivering bespoke changes into crop genomes, we demonstrate broad and robust utility for targeted knockin of cis-regulatory elements to optimize source-sink relations and boost crop climate resilience.

Microbiota dynamics and source tracing during the growing, aging, and decomposing processes of Eucommia ulmoides leaves.

Eucommia ulmoides, an important tree, faces serious threat to its growth from environmental stress, particularly climate change. Using plant microbes to enhance host adaptation to respond climate change challenges has been recognized as a viable and sustainable strategy. However, it is still unclear how the perennial tree microbiota varies across phenological stages and the links between respective changes in aboveground and belowground niches. Here, we sequenced 27 root and 27 leaf samples of E. ulmoides using 16S rRNA and ITS amplicon sequencing techniques. These samples were obtained from the three main phenological stages of leaves, including leaf growing, aging and decomposing stages. Results showed that the diversity, composition, and function of the leaf microbiota of E. ulmoides showed more obvious changes at three phenological time points compared to roots. Regarding alpha diversity, the root microbiota showed no difference across three sampling stages, while the leaf microbiota varied with sampling stages. Regarding beta diversity, the root microbiota clustered from different sampling stages, while the leaf microbiota exhibited distinct separation. Regarding composition and function, the dominant taxa and main functions of the root microbiota were the same in three sampling stages, while the leaf microbiota in the decomposing stage was obviously different from the remaining two stages. Additionally, taxa overlap and source-sink relationship existed between E. ulmoides microbiota. Specifically, the degree of overlap among root microbiota was higher than that of leaf microbiota in three sampling stages. The bidirectional source-sink relationship that existed between the root and leaf niches varied with sampling stage. During the leaf growing and aging stages, the proportion of microbial members migrating from roots to leaves was higher than the proportion of members migrating from leaves to roots. During the leaf decomposing stage, the migration characteristics of the fungal community between the root and leaf niches maintained the same as in the remaining two stages, but the proportion of bacterial members migrating from leaves to roots was significantly higher than that of members migrating from roots to leaves. Our findings provide crucial foundational information for utilizing E. ulmoides microbiota to benefit their host under climate change challenges.

Physiological parameters dictate bearing pattern in different mango cultivars: Study from Sub-tropical India

The bearing habit of mango has long been a subject of interest for pomologists. The difference in bearing pattern among various mango cultivars is attributed to complex physiological interaction. Despite multiple studies on mango bearing, detailed investigations in this area remain limited. This study aims to explore the interrelationship between the bearing patterns and the associated physiological changes in different mango cultivars. The physiological parameters were examined at various growth stages in Baramasi (a perennial bearer), Amrapali (a regular bearer) and Langra and Alphonso (irregular bearer) of mango (Mangifera indica L.). Significant variations were observed in chlorophyll content, internal carbon dioxide concentration, photosynthetic rate and flowering intensity. An increase in internal carbon dioxide concentration led to reduced carbon dioxide uptake, which impacted net photosynthesis production. A direct correlation between flowering intensity and photosynthetic rate was identified, while a nonlinear relationship between photosynthetic rate and total carbohydrate content was also noted. The study suggests that variations in the photosynthetic rate and the subsequent source-sink relationship may contribute to the differences in bearing patterns across mango cultivars. While further studies are needed for more conclusive results, this research can be valuable for pomologists, physiologists and breeders working with mango.

The Timing of Phosphorus Availability to Corn: What Growth Stages Are Most Critical for Maximizing Yield?

Phosphorus (P) is critical for maximizing agricultural production and represents an appreciable input cost. Geologic sources of P that are most easily mined are a finite resource, while P transported from agricultural land to surface waters contributes to water quality degradation. Improved knowledge of P timing needs by corn (maize) can help inform management decisions that increase P use efficiency, which is beneficial to productivity, economics, and environmental quality. The objective of this study was to evaluate P application timing on the growth and yield components of corn. Corn was grown in a sand-culture hydroponics system that eliminated confounding plant–soil interactions and allowed for precise control of nutrient availability and timing. All nutrients were applied via drip irrigation and were therefore 100% bioavailable. Eight P timing treatments were tested using “low” (L) and “sufficient” (S) P concentrations. In each of the three growth phases, solution P application levels were changed or maintained, resulting in eight possible combinations, LLL, LLS, LSL, LSS, SLL, SSL, SLS, and SSS, where the first, second, and third letters indicate P solution application levels from planting to V6, V6 to R1, and R1 to R6, respectively. All other nutrients were applied at sufficient levels. Sacrificial samples were harvested at V6, R1, and R6 and evaluated for various yield parameters. Plants that received sufficient P between V6 and R1 produced a significantly higher grain yield than plants that received low P between V6 and R1 regardless of the level of P supply before V6 or after R1. The grain yield of plants that received sufficient P only between V6 and R1 did not differ significantly from plants that received only sufficient P (SSS), due to (1) a greater ear P concentration at R1; (2) an efficient remobilization of assimilates from the stem and leaf to grains between R1 and R6 (source–sink relationship); (3) a higher kernel/grain weight; and (4) less investment into root biomass.

Keystone taxa drive the synchronous production of methane and refractory dissolved organic matter in inland waters

The production of both methane (CH4) and refractory dissolved organic matter (RDOM) depends on microbial consortia in inland waters, and it is unclear yet the link of these two processes and the underlying microbial regulation mechanisms. Therefore, a large-scale survey was conducted in China's inland waters, with the measurement of CH4 concentrations, DOM chemical composition, microbial community composition, and relative environmental parameters mainly by chromatographic, optical, mass spectrometric, and high-throughput sequencing analyses, to clarify the abovementioned questions. Here, we found a synchronous production of CH4 and RDOM linked by microbial consortia in inland waters. The increasing microbial cooperation driven by the keystone taxa (mainly Fluviicola and Polynucleobacter) could promote the transformation of labile DOM into RDOM and meanwhile benefit methanogenic microbial communities to produce CH4. As such, CH4 and RDOM showed consistent spatial differences, which were mainly influenced by total nitrogen and dissolved oxygen concentrations. This finding deepened the understanding of microbial-driven carbon transformation and will help to more accurately evaluate the carbon source-sink relationship in inland waters.

Internal physiological drivers of leaf development in trees: Understanding the relationship between non‐structural carbohydrates and leaf phenology

Abstract Plant phenology is crucial for understanding plant growth and climate feedback. It affects canopy structure, surface albedo, and carbon and water fluxes. While the influence of environmental factors on phenology is well‐documented, the role of plant intrinsic factors, particularly internal physiological processes and their interaction with external conditions, has received less attention. Non‐structural carbohydrates (NSC), which include sugars and starch essential for growth, metabolism and osmotic regulation, serve as indicators of carbon availability in plants. NSC levels reflect the carbon balance between photosynthesis (source activity) and the demands of growth and respiration (sink activity), making them key physiological traits that potentially influence phenology during critical periods such as spring leaf‐out and autumn leaf senescence. However, the connections between NSC concentrations in various organs and phenological events are poorly understood. This review synthesizes current research on the relationship between leaf phenology and NSC dynamics. We qualitatively delineate seasonal NSC variations in deciduous and evergreen trees and propose testable hypotheses about how NSC may interact with phenological stages such as bud break and leaf senescence. We also discuss how seasonal variations in NSC levels, align with existing conceptual models of carbon allocation. Accurate characterization and simulation of NSC dynamics are crucial and should be incorporated into carbon allocation models. By comparing and reviewing the development of carbon allocation models, we highlight the shortcomings in current methodologies and recommend directions to address these gaps in future research. Understanding the relationship between NSC, source–sink relationships, and leaf phenology poses challenges due to the difficulty of characterizing NSC dynamics with high temporal resolution. We advocate for a multi‐scale approach that combines various methods, which include deepening our mechanistic understanding through manipulative experiments, integrating carbon sink and source data from multiple observational networks with carbon allocation models to better characterize the NSC dynamics, and quantifying the spatial pattern and temporal trends of the NSC‐phenology relationship using remote sensing and modelling. This will enhance our comprehension of how NSC dynamics impact leaf phenology across different scales and environments. Read the free Plain Language Summary for this article on the Journal blog.

Exogenous melatonin improves peanut field productivity and quality at reduced nitrogen application

ContextNitrogen (N) plays integral roles in plant growth and yield. Finding ways to increase plant yield with reduced N usage will promote both agricultural and environmental sustainability. Melatonin acts as a multifunctional regulatory molecule in numerous metabolic processes crucial for plant growth and development as well as response to environmental stresses. The effects of melatonin on the material accumulation and transport, source-sink dynamics, as well as its association with yield and quality formation of peanut (Arachis hypogaea L.) remain unclear, especially at different N levels. ObjectivesWe aim to investigate the response mechanism of melatonin in peanut plants subjected to reduced N application, in order to confirm the hypothesis that melatonin regulates carbon and N accumulation and transport, and coordinates source-sink relationships to increase production and improve quality. MethodsThis study examined the effects of two seed dressing treatments (with or without 0.5 μM MT) and three N fertilizer levels (90, 135, and 180 kg/ha) using a randomized complete block design with split plots and three biological replications over 2021 and 2022. The evaluation focused on photosynthetic physiology, enzyme activities related to carbon and N metabolism, accumulation and transport of dry matter and N, yield, and quality, while exploring the relationships among these variables. ResultsMelatonin-treated plants had more stable carbon and N metabolism than the untreated ones. This stability was linked to improved photosynthesis, sucrose production, and N assimilation, especially at the reduced N levels (90 and 135 kg/ha). Across three N levels and two years of field tests, MT increased peanut dry matter by 23.49 % from 455.63 g/m2 to 562.66 g/m2, enhanced the accumulation and mobilization of dry matter and N to grains by increasing peanut grain mass by 22.41–29.07 % at different N levels. This process appears to subsequently elevate the effective pod rate, leading to an average increase in pod yield, fat and protein content by 12.63 %, 7.95 %, and 10.33 %, respectively, over a two-year period and across three N application levels. ConclusionsPlants subjected to melatonin treatment exhibited a coordinated source-sink relationship, which is manifested in high photosynthetic capacity and a high proportion of assimilates transported to pods, thus promoting effective proportions and pod fullness to improve peanut yield and quality under reduced N application. SignificanceOur research provided insights into the response mechanism of melatonin on peanut carbon and N metabolism across various N treatments, contributing to a deeper understanding of how melatonin enhances crop yield and quality.

On the use of isotopic differences of carbon fractions of biomass in plants to study transport flows and source-sink relations under different light conditions

It is shown that the differences in the isotopic composition of carbon in the water-soluble and water-insoluble fractions of plant leaf biomass, as well as phloem, are evolutionarily determined. They associated with metabolic reactions during assimilation and photorespiration and do not depend on the illumination mode and on the spectral ranges of headlights used in illumination. The above isotopic shifts are the cause of isotopic differences in assimilatory and photorespiratory carbon stocks that feed various metabolic processes. Due to the strict temporal and spatial organization of metabolism, carbon fluxes from the funds retain isotopic differences without complete mixing. The differences in the isotopic composition of carbon of the water-soluble fraction of biomass and carbon of phloem juice from carbon of the water-insoluble fraction are small (1–3%), but they are quite stable and easily fixed. The carbon of the water-soluble fraction is very close in isotopic composition to the carbon of the phloem and is noticeably enriched with the isotope 13C relative to the water-insoluble fraction, which makes it possible to use it as a marker in the study of assimilate transport in plants, especially during budding and fruiting. It is shown that the reason for the enrichment of autotrophic organs and tissues with isotope 12C relative to carbon of heterotrophic parts of the plant is the predominant participation in their formation of an isotopically light assimilation fund, whereas an isotopically heavy photorespiratory fund takes part in the formation of heterotrophic organs. It is shown that the manifestation of the formation of two isotopically different funds is the discovered relationship of the carbon isotope composition of leaves with their age.

Combined transcriptome and physiological analysis reveals exogenous sucrose enhances photosynthesis and source capacity in foxtail millet

Foxtail millet (Setaria italica (L.) P. Beauv.) is an environmentally friendly crop that meets the current requirements of international food security and is widely accepted as a photosynthesis research model. However, whether exogenous sucrose treatment has a positive effect on foxtail millet growth remains unknown. Here, we employed physiological and molecular approaches to identify photosynthesis and source capacity associated with exogenous sucrose during the growth of Jingu 21 seedlings. RNA-seq analysis showed that some differentially expressed genes (DEGs) related to photosynthesis and carotenoid biosynthesis were induced by exogenous sucrose and that most of these genes were up-regulated. An increase in gas exchange parameters, chlorophyll content, and chlorophyll fluorescence of Jingu 21 was noted after exogenous sucrose addition. Furthermore, exogenous sucrose up-regulated genes encoding sucrose and hexose transporters and enhanced starch and sucrose metabolism. More DEGs were up-regulated by sucrose, the nonstructural carbohydrate (NSC) content in the leaves increased and energy metabolism and sucrose loading subsequently improved, ultimately enhancing photosynthesis under normal and dark conditions. Further analysis revealed that WRKYs, ERFs, HY5, RAP2, and ABI5 could be key transcription factors involved in growth regulation. These results indicate that exogenous sucrose affects the normal photosynthetic performance of foxtail millet by increasing NSC transport and loading. They improve our understanding of the molecular mechanisms of the effects of exogenous sucrose on photosynthesis in foxtail millet, providing an effective measure to enhance source–sink relationships and improve yield.

Optimizing daylily (Hemerocallis citrina Baroni) cultivation: integrating physiological modeling and planting patterns for enhanced yield and resource efficiency

IntroductionOptimizing the dynamics of daylily (Hemerocallis citrina Baroni) growth under various planting patterns is critical for enhancing production efficiency. This study presents a comprehensive model to simulate daylily growth and optimize planting patterns to maximize bud yield while minimizing land resource utilization.MethodsThe model incorporates source-sink relationship specific to daylilies into physiological process modeling, considering environmental factors such as micro-light and temperature climate, and CO2 concentration. Spatial factors, including planting pattern, row spacing, plant spacing, and plant density were examined for their impact on light interception, photosynthesis, and resource efficiency. Employing partial least square path modeling (PLS-PM), we analyzed the interrelations and causal relationships between planting configurations and physiological traits of daylily canopy leaves and buds. Through in situ simulations of 36 planting scenarios, we identified an optimal configuration (Scenario ID5) with a density of 83,000 plants·ha−1, row spacing of 0.8 m, and equidistant planting with a plant spacing of 0.15 m.Results and discussionOur research findings indicate that increased Wide+Narrow row spacing can enhance yield to a certain extent. Although planting patterns influence daylily yield, their overall impact is relatively minor, and there is no clear pattern regarding the impact of plant spacing on individual plant yield. This modeling approach provides valuable insights into daylily plant growth dynamics and planting patterns optimization, offering practical guidance for both farmers and policymakers to enhance daylily productivity while minimizing land use.

Evidence for the translocation of fixed N in the N2-fixing lichen Stereocaulon vesuvianum.

The fruticose lichen Stereocaulon vesuvianum is among the most abundant and widespread lichens in upland Britain. It typically produces cephalodia (nodules) that contain the cyanobacterium Stigonema, which can fix atmospheric nitrogen. However, over much of England, Wales, and southern Scotland S. vesuvianum no longer produces cephalodia and does not fix nitrogen, a morphological change linked to elevated atmospheric nitrogen deposition. This provided a unique opportunity to compare the 15N natural abundance signatures in N2-fixing and non-N2-fixing lichen populations, keeping in mind that fixed nitrogen has a 15N content close to that of atmospheric N2 while, in comparison, several components of atmospheric combined N (e.g. nitrate and ammonium in precipitation) tend to be 15N depleted. We found that in N2-fixing samples, there was a steep gradient in 15N relative abundance in the terminal 15 mm of thallus branches (pseudopodetia), changing from 15N depleted tissues at 10-15 mm below the tips to values close to that of atmospheric N2 at the apices while in non-N2-fixing samples thallus branches were uniformly 15N depleted. The 15N gradient in N2-fixing material could not be explained by the presence of cephalodia since these are more abundant towards branch bases. The data provide the first evidence in lichens of translocation of recently fixed N to sink regions of active growth and production of asexual reproductive propagules, bringing lichens into line with N source-sink relationships in N2-fixing plant symbioses.

Development of an integrated framework for dissecting source-oriented ecological and health risks of heavy metals in soils

Heavy metals (HMs) in soils pose significant risks on ecosystem and human health. To design targeted regulatory measures for mitigating and controlling the risk, it is necessary to accurately identify the pollution sources and environmental risks of soil HMs, as well as to reveal the linkages between them. To date, yet systematic investigation aimed at deciphering the links between source apportionment of soil HMs and their associated environmental risks is still lacking. To fill the gap, an integrated framework has been developed in this study and applied for dissecting the source-sink relationship and source-oriented ecological and health risks of soil HMs in Shanxi, a province with rich coal resource, in which long-term coal mining activities in history has resulted in soil HMs pollution and unavoidably posed environmental risks. Two advanced receptor models, multivariate curve resolution alternating least squares based on maximum likelihood principal component analysis (MCR-ALS/MLPCA) and multilinear engine 2 (ME2), have been employed for apportioning the potential sources, and their apportionment results are jointly incorporated into a modified ecological risk index and a probabilistic health risk assessment model for identifying the source-oriented ecological and health risks posed by soil metals. The results show that the soils in study area have been polluted by HMs (i.e., Cd, Cr, Hg and As) to varying degrees. Industrial activities (35%–35.8%), agricultural activities (11.1%–20.5%), atmospheric deposition (10.5%–13%) and mix source (31.5%–42.6%) are apportioned as the main contributors of soil HMs in the area. The source-oriented ecological risk assessment suggests Hg has presented significant ecological risk and largely contributed by the sources from atmospheric deposition and industrial activities. The source-oriented health risk assessment shows the non-carcinogenic hazard level and carcinogenic risk posed by soil HMs in the study area are acceptable. Relatively, industrial activities and mix source have contributed more on the health risks.

Exploring soil nitrogen and sulfur dynamics: implications for greenhouse gas emissions on the Qinghai-Tibet Plateau.

The Qinghai-Tibet Plateau is particularly vulnerable to the effects of climate change and disturbances caused by human activity. To better understand the interactions between soil nitrogen and sulfur cycles and human activities on the plateau, the distribution characteristics of soil nitrogen and sulfur density and their influencing factors for three soil layers in Machin County at depths of 0-20cm, 0-100cm, and 0-180cm are discussed in this paper. The results indicated that at depths of 0-180cm, soil nitrogen density in Machin County varied between 1.36 and 16.85kg/m2, while sulfur density ranged from 0.37 to 4.61kg/m2. The effects of three factors-geological background, land use status, and soil type-on soil nitrogen and sulfur density were all highly significant (p < 0.01). Specifically, natural factors such as soil type and geological background, along with anthropogenic factors including land use practices and grazing intensity, were identified as decisive in causing spatial variations in soil nitrogen and sulfur density. Machin County on the Tibetan Plateau exhibits natural nitrogen and sulfur sinks; However, it is crucial to monitor the emissions of N2O and SO2 into the atmosphere from areas with high external nitrogen and sulfur inputs and low fertility retention capacities, such as bare land. On this basis, changes in the spatial and temporal scales of the nitrogen and sulfur cycles in soils and their source-sink relationships remain the focus of future research.