[Noise exposure-induced stress response and its measurement methods].

Noise, as an unavoidable stress (pressure) source in the modern life, affects animals in many ways, both behaviorally and physiologically. Behavioral changes may be driven by changes in hormone secretion in animals. When animals face with noise stress, the neuroendocrine systems, mainly the hypothalamic-pituitary-adrenal (HPA) axis, are activated, which promotes the secretion and release of stress hormones, and then leads to a series of behavioral changes. The behavioral changes can be easily observed, but the changes in physiological indicators such as hormone levels need to be accurately measured. Currently, many studies have measured the variations of stress hormone levels in animals under different noise conditions. Taking glucocorticoid as an example, this paper summarizes the different measurement methods of stress hormones, especially the non-invasive measurement methods, and compares the advantages and shortcomings of them. It provides a variety of measurement choices for the study of related issues, and also helps us to further understand the sources of animal stress, in order to provide a better habitat for animals.

Nitrogen fertilization modulates beneficial rhizosphere interactions through signaling effect of nitric oxide.

Chemical nitrogen (N) fertilization is customary for increasing N inputs in agroecosystems. The nutritional effects of N fertilization on plants and soil microbes have been well studied. However, the signaling effects of N fertilization on rhizosphere plant-microbe interactions and the following feedback to plant performance remain unknown. Here, we investigated the effect of different N fertilizations on the behavior of the plant growth-promoting rhizobacteria (PGPR) Bacillus velezensis SQR9 in the cucumber (Cucumis sativus L.) rhizosphere. Moderate N fertilization promoted higher rhizosphere colonization of strain SQR9 than insufficient or excessive N input. Nitric oxide (NO) produced through the denitrification process under N fertilization was identified as the signaling molecule that dominates the root colonization of PGPR, and this effect could be neutralized by the NO-specific scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxy-3-oxide. Gene expression analysis demonstrated that NO regulated the biofilm formation of strain SQR9 by affecting the synthesis of extracellular matrix γ-polyglutamic acid, consequently impacting its root colonization. Finally, we demonstrated that moderate N fertilization-modulated enhanced PGPR root colonization can significantly promote plant growth and nitrogen use efficiency. This study provides insights into our understanding of the beneficial rhizosphere plant-microbe interactions under N fertilization and suggests that rational fertilization is critical to promote beneficial rhizosphere interactions for sustainable agricultural production.

The role of rice cultivation in changes in atmospheric methane concentration and the Global Methane Pledge.

Resumption of the increase in atmospheric methane (CH4 ) concentrations since 2007 is of global concern and may partly have resulted from emissions from rice cultivation. Estimates of CH4 emissions from rice fields and abatement potential are essential to assess the contribution of improved rice management in achieving the targets of the Global Methane Pledge agreed upon by over 100 countries at COP26. However, the contribution of CH4 emissions from rice fields to the resumed CH4 growth and the global abatement potential remains unclear. In this study, we estimated the global CH4 emissions from rice fields to be 27 ± 6 Tg CH4 year-1 in the recent decade (2008-2017) based on the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. The trend of CH4 emissions from rice cultivation showed an increase followed by no significant change and then, a stabilization over 1990-2020. Consequently, the contribution of CH4 emissions from rice fields to the renewed increase in atmospheric CH4 concentrations since 2007 was minor. We summarized the existing low-cost measures and showed that improved water and straw management could reduce one-third of global CH4 emissions from rice fields. Straw returned as biochar could reduce CH4 emissions by 12 Tg CH4 year-1 , equivalent to 10% of the total reduction of all anthropogenic emissions. We conclude that other sectors than rice cultivation must have contributed to the renewed increase in atmospheric CH4 concentrations, and that optimizing multiple mitigation measures in rice fields could contribute significantly to the abatement goal outlined in the Global Methane Pledge.

Enhanced CO2 uptake is marginally offset by altered fluxes of non-CO2 greenhouse gases in global forests and grasslands under N deposition.

Despite the increasing impact of atmospheric nitrogen (N) deposition on terrestrial greenhouse gas (GHG) budget, through driving both the net atmospheric CO2 exchange and the emission or uptake of non-CO2 GHGs (CH4 and N2 O), few studies have assessed the climatic impact of forests and grasslands under N deposition globally based on different bottom-up approaches. Here, we quantify the effects of N deposition on biomass C increment, soil organic C (SOC), CH4 and N2 O fluxes and, ultimately, the net ecosystem GHG balance of forests and grasslands using a global comprehensive dataset. We showed that N addition significantly increased plant C uptake (net primary production) in forests and grasslands, to a larger extent for the aboveground C (aboveground net primary production), whereas it only caused a small or insignificant enhancement of SOC pool in both upland systems. Nitrogen addition had no significant effect on soil heterotrophic respiration (RH ) in both forests and grasslands, while a significant N-induced increase in soil CO2 fluxes (RS , soil respiration) was observed in grasslands. Nitrogen addition significantly stimulated soil N2 O fluxes in forests (76%), to a larger extent in grasslands (87%), but showed a consistent trend to decrease soil uptake of CH4 , suggesting a declined sink capacity of forests and grasslands for atmospheric CH4 under N enrichment. Overall, the net GHG balance estimated by the net ecosystem production-based method (forest, 1.28 Pg CO2 -eq year-1 vs. grassland, 0.58 Pg CO2 -eq year-1 ) was greater than those estimated using the SOC-based method (forest, 0.32 Pg CO2 -eq year-1 vs. grassland, 0.18 Pg CO2 -eq year-1 ) caused by N addition. Our findings revealed that the enhanced soil C sequestration by N addition in global forests and grasslands could be only marginally offset (1.5%-4.8%) by the combined effects of its stimulation of N2 O emissions together with the reduced soil uptake of CH4 .

Uncovering the prevalence and drivers of antibiotic resistance genes in soils across different land-use types.

The emergence and spread of antibiotic resistance genes (ARGs) in soil due to animal excreta and organic waste is a major threat to human health and ecosystems, and global efforts are required to tackle the issue. However, there is limited knowledge of the variation in ARG prevalence and diversity resulting from different land-use patterns and underlying driving factors in soils. This study aimed to comprehensively characterize the profile of ARGs and mobile genetic elements and their drivers in soil samples collected from 11 provinces across China, representing three different land-use types, using high-throughput quantitative polymerase chain reaction and 16S rRNA amplicon sequencing. Our results showed that agricultural soil had the highest abundance and diversity of ARGs, followed by tea plantation and forest land. A total of 124 unique ARGs were detected in all samples, with shared subtypes among different land-use patterns indicating a common origin or high transmission frequency. Moreover, significant differences in ARG distribution were observed among different geographical regions, with the greatest enrichment of ARGs found in southern China. Biotic and abiotic factors, including soil properties, climatic factors, and bacterial diversity, were identified as the primary drivers associated with ARG abundance, explaining 71.8% of total ARG variation. The findings of our study demonstrate that different land-use patterns are associated with variations in ARG abundance in soil, with agricultural practices posing the greatest risk to human health and ecosystems regarding ARGs. Our identification of biotic and abiotic drivers of ARG abundance provides valuable insights into strategies for mitigating the spread of these genes. This study emphasizes the need for coordinated and integrated approaches to address the global antimicrobial resistance crisis.

Data-driven estimates of fertilizer-induced soil NH3 , NO and N2 O emissions from croplands in China and their climate change impacts.

Gaseous reactive nitrogen (Nr) emissions from agricultural soils to the atmosphere constitute an integral part of global N cycle, directly or indirectly causing climate change impacts. The extensive use of N fertilizer in crop production will compromise our efforts to reduce agricultural Nr emissions in China. A national inventory of fertilizer N-induced gaseous Nr emissions from croplands in China remains to be developed to reveal its role in shaping climate change. Here we present a data-driven estimate of fertilizer N-induced soil Nr emissions based on regional and crop-specific emission factors (EFs) compiled from 379 manipulative studies. In China, agricultural soil Nr emissions from the use of synthetic N fertilizer and manure in 2018 are estimated to be 3.81 and 0.73 Tg N yr-1 , with a combined contribution of 23%, 20% and 15% to the global agricultural emission total of ammonia (NH3 ), nitrous oxide (N2 O) and nitric oxide (NO), respectively. Over the past three decades, NH3 volatilization from croplands has experienced a shift from a rapid increase to a decline trend, whereas N2 O and NO emissions always maintain a strong growth momentum due to a robust and continuous rise of EFs. Regionally, croplands in Central south (1.51 Tg N yr-1 ) and East (0.99 Tg N yr-1 ) of China exhibit as hotspots of soil Nr emissions. In terms of crop-specific emissions, rice, maize and vegetable show as three leading Nr emitters, together accounting for 61% of synthetic N fertilizer-induced Nr emissions from croplands. The global warming effect derived from cropland N2 O emissions in China was found to dominate over the local cooling effects of NH3 and NO emissions. Our established regional and crop-specific EFs for gaseous Nr forms provide a new benchmark for constraining the IPCC Tier 1 default EF values. The spatio-temporal insight into soil Nr emission data from N fertilizer application in our estimate is expected to advance our efforts towards more accurate global or regional cropland Nr emission inventories and effective mitigation strategies.

Global methane and nitrous oxide emissions from inland waters and estuaries.

Inland waters (rivers, reservoirs, lakes, ponds, streams) and estuaries are significant emitters of methane (CH4 ) and nitrous oxide (N2 O) to the atmosphere, while global estimates of these emissions have been hampered due to the lack of a worldwide comprehensive data set of CH4 and N2 O flux components. Here, we synthesize 2997 in-situ flux or concentration measurements of CH4 and N2 O from 277 peer-reviewed publications to estimate global CH4 and N2 O emissions from inland waters and estuaries. Inland waters including rivers, reservoirs, lakes, and streams together release 95.18 Tg CH4  year-1 (ebullition plus diffusion) and 1.48 Tg N2 O year-1 (diffusion) to the atmosphere, yielding an overall CO2 -equivalent emission total of 3.06 Pg CO2  year-1 . The estimate of CH4 and N2 O emissions represents roughly 60% of CO2 emissions (5.13 Pg CO2  year-1 ) from these four inland aquatic systems, among which lakes act as the largest emitter for both CH4 and N2 O. Ebullition showed as a dominant flux component of CH4 , contributing up to 62%-84% of total CH4 fluxes across all inland waters. Chamber-derived CH4 emission rates are significantly greater than those determined by diffusion model-based methods for commonly capturing of both diffusive and ebullitive fluxes. Water dissolved oxygen (DO) showed as a dominant factor among all variables to influence both CH4 (diffusive and ebullitive) and N2 O fluxes from inland waters. Our study reveals a major oversight in regional and global CH4 budgets from inland waters, caused by neglecting the dominant role of ebullition pathways in those emissions. The estimated indirect N2 O EF5 values suggest that a downward refinement is required in current IPCC default EF5 values for inland waters and estuaries. Our findings further indicate that a comprehensive understanding of the magnitude and patterns of CH4 and N2 O emissions from inland waters and estuaries is essential in defining the way of how these aquatic systems will shape our climate.

Changes in microbial community composition drive the response of ecosystem multifunctionality to elevated ozone.

Increasing tropospheric ozone poses a potential threat to both above- and belowground components of the terrestrial biosphere. Microorganisms are the main drivers of soil ecological processes, however, the link between soil microbial communities and ecological functions under elevated ozone remains poorly understood. In this study, we assessed the responses of three crop seedlings (i.e., soybean, maize, and wheat) growth and soil microbial communities to elevated ozone (40 ppb O3 above ambient air) in a pot experiment in the solardomes. Results showed that elevated ozone adversely affected ecosystem multifunctionality by reducing crop biomass, inhibiting soil extracellular enzyme activities, and altering nutrient availability. Elevated ozone increased bacterial and fungal co-occurrence network complexity, negatively correlated with ecosystem multifunctionality. Changes in the relative abundance of some specific bacteria and fungi were associated with multiple ecosystem functioning. In addition, elevated ozone significantly affected fungal community composition but not bacterial community composition and microbial alpha-diversity. Crop type played a key role in determining bacterial alpha-diversity and microbial community composition. In conclusion, our findings suggest that short-term elevated ozone could lead to a decrease in ecosystem multifunctionality associated with changes in the complexity of microbial networks in soils.

Global soil-derived ammonia emissions from agricultural nitrogen fertilizer application: A refinement based on regional and crop-specific emission factors.

Ammonia (NH3 ) emissions from fertilized soils to the atmosphere and the subsequent deposition to land surface exert adverse effects on biogeochemical nitrogen (N) cycling. The region- and crop-specific emission factors (EFs) of N fertilizer for NH3 are poorly developed and therefore the global estimate of soil NH3 emissions from agricultural N fertilizer application is constrained. Here we quantified the region- and crop-specific NH3 EFs of N fertilizer by compiling data from 324 worldwide manipulative studies and focused to map the global soil NH3 emissions from agricultural N fertilizer application. Globally, the NH3 EFs averaged 12.56% and 14.12% for synthetic N fertilizer and manure, respectively. Regionally, south-eastern Asia had the highest NH3 EFs of synthetic N fertilizer (19.48%) and Europe had the lowest (6%), which might have been associated with the regional discrepancy in the form and rate of N fertilizer use and management practices in agricultural production. Global agricultural NH3 emissions from the use of synthetic N fertilizer and manure in 2014 were estimated to be 12.32 and 3.79 Tg N/year, respectively. China (4.20 Tg N/year) followed by India (2.37 Tg N/year) and America (1.05 Tg N/year) together contributed to over 60% of the total global agricultural NH3 emissions from the use of synthetic N fertilizer. For crop-specific emissions, the NH3 EFs averaged 11.13%-13.95% for the three main staple crops (i.e., maize, wheat, and rice), together accounting for 72% of synthetic N fertilizer-induced NH3 emissions from croplands in the world and 70% in China. The region- and crop-specific NH3 EFs of N fertilizer established in this study offer references to update the default EF in the IPCC Tier 1 guideline. This work also provides an insight into the spatial variation of soil-derived NH3 emissions from the use of synthetic N fertilizer in agriculture at the global and regional scales.

Plasma membrane-localized protein BcHIPP16 promotes the uptake of copper and cadmium in planta.

Cadmium (Cd) is one of the toxic heavy metals in soil, which not only suppresses crop production but also threatens human health. In this study, we aim to clarify the biological function of Cd-related gene BcHIPP16, so as to provide potential genetic solutions to decrease the Cd levels of pak choi. Tissue expression analysis showed that BcHIPP16 expressed in almost all the plant bodies. The transcriptional level of BcHIPP16 in roots was higher than that in shoots, which was significantly induced by copper (Cu) deficiency and Cd exposure conditions. Subcellular localization revealed that BcHIPP16 localized in plasma membrane. Expressing BcHIPP16 in yeast cells improved the sensitivity to Cu and Cd and improved their accumulation in yeast. Furthermore, the Cu and Cd content of Arabidopsis seedlings were increased and complemented, respectively when expressing BcHIPP16 in wild type (WT) and hip16 mutants. Non-invasive Micro-test Technology (NMT) was used to measure the real-time Cd2+ influx from the root surface of BcHIPP16 transgenic Arabidopsis lines, and the result demonstrated that BcHIPP16 promoted Cd2+ influx into Arabidopsis root cells. Taken together, our study showed that BcHIPP16 contributed to absorbing nutrient metal Cu and heavy metal Cd in planta.

Enhanced vacuole compartmentalization of cadmium in root cells contributes to glutathione-induced reduction of cadmium translocation from roots to shoots in pakchoi (Brassica chinensis L.).

Our previous studies showed that exogenous glutathione (GSH) decreased cadmium (Cd) concentration in shoots and alleviated the growth inhibition in pakchoi (Brassica chinensis L.) under Cd stress. Nevertheless, it is largely unknown how GSH decreases Cd accumulation in edible parts of pakchoi. This experiment mainly explored the mechanisms of GSH-induced reduction of Cd accumulation in shoot of pakchoi. The results showed that compared with sole Cd treatment, Cd + GSH treatment remarkably increased the expression of BcIRT1 and BcIRT2, and further enhanced the concentrations of Cd and Fe in root. By contrast, GSH application declined the concentration of Cd in the xylem sap. However, these results were not caused by xylem loading process because the expression of BcHMA2 and BcHMA4 had not significant difference between sole Cd treatment and Cd + GSH treatment. In addition, exogenous GSH significantly enhanced the expression of BcPCS1 and promoted the synthesis of PC2, PC3 and PC4 under Cd stress. At the same time, exogenous GSH also significantly improved the expression of BcABCC1 and BcABCC2 in the roots of seedling under Cd stress, suggesting that more PCs-Cd complexes may be sequestrated into vacuoles by ABCC1 and ABCC2 transporters. The results showed that exogenous GSH could up-regulate the expression of BcIRT1/2 to increase the Cd accumulation in root, and the improvement of PCs contents and the expression of BcABCC1/2 enhanced the compartmentalization of Cd in root vacuole of pakchoi under Cd stress. To sum up, exogenous GSH reduce the concentration of free Cd2+ in the cytoplast of root cells and then dropped the loading of Cd into the xylem, which eventually given rise to the reduction of Cd accumulation in edible portion of pakchoi.

Analysis of the long-term effectiveness of biochar immobilization remediation on heavy metal contaminated soil and the potential environmental factors weakening the remediation effect: A review.

Currently, the research and application of biochar in the remediation of heavy metal contaminated soil has become a hotspot, especially regarding the remediation of agricultural land. Biochar has been proved to be effective in reducing the content of available heavy metals in the soil as well as the heavy metals in plants. However, the long-term effectiveness of biochar immobilization has not been widely studied. In this review, retrospective search was carried out on the published literature results concerning remediation effects of biochar on different areas of heavy metal contaminated soil in the recent years, its application in field remediation (several years), and some potential abiotic and biotic factors that may weaken the immobilization effects of biochar. This results indicate that: (1) biochar is widely used in the remediation of heavy metal contaminated soil in different areas and has excellent immobilization effect. (2) Most of the research demonstrate that the immobilization effect of biochar is effective for 2-3 years or according to few results even for 5 years. However, there have been various reports claiming that the immobilization effect of biochar decreases with time. (3) Abiotic factors such as acid rain, flooded environment, changes in soil condition (pH, redox and dissolved organic matter) and changes in biochar (Cl- and alkali leaching) can significantly weaken the immobilization effect of biochar. (4) Biotic factors such as plant roots, earthworms and soil microorganisms can also significantly reduce the immobilization effect of biochar. Therefore, field experiments having longer time span with biochar need to be further carried out, and the developmental research of modified biochar with a more stable immobilization effect also needs further attention.

Increased soil release of greenhouse gases shrinks terrestrial carbon uptake enhancement under warming.

Warming can accelerate the decomposition of soil organic matter and stimulate the release of soil greenhouse gases (GHGs), but to what extent soil release of methane (CH4 ) and nitrous oxide (N2 O) may contribute to soil C loss for driving climate change under warming remains unresolved. By synthesizing 1,845 measurements from 164 peer-reviewed publications, we show that around 1.5°C (1.16-2.01°C) of experimental warming significantly stimulates soil respiration by 12.9%, N2 O emissions by 35.2%, CH4 emissions by 23.4% from rice paddies, and by 37.5% from natural wetlands. Rising temperature increases CH4 uptake of upland soils by 13.8%. Warming-enhanced emission of soil CH4 and N2 O corresponds to an overall source strength of 1.19, 1.84, and 3.12 Pg CO2 -equivalent/year under 1°C, 1.5°C, and 2°C warming scenarios, respectively, interacting with soil C loss of 1.60 Pg CO2 /year in terms of contribution to climate change. The warming-induced rise in soil CH4 and N2 O emissions (1.84 Pg CO2 -equivalent/year) could reduce mitigation potential of terrestrial net ecosystem production by 8.3% (NEP, 22.25 Pg CO2 /year) under warming. Soil respiration and CH4 release are intensified following the mean warming threshold of 1.5°C scenario, as compared to soil CH4 uptake and N2 O release with a reduced and less positive response, respectively. Soil C loss increases to a larger extent under soil warming than under canopy air warming. Warming-raised emission of soil GHG increases with the intensity of temperature rise but decreases with the extension of experimental duration. This synthesis takes the lead to quantify the ecosystem C and N cycling in response to warming and advances our capacity to predict terrestrial feedback to climate change under projected warming scenarios.

Novel ultrastructural findings on cardiac mitochondria of huddling Brandt's voles in mild cold environment.

Reduced ambient temperature has a damaging effect on mammalian myocardium. Huddling as a cooperative behavior has evolved in social mammals as a strategy to maximize adaptation to environmental cooling. Here, we studied the effects of huddling behavior on mitochondrial morphology, number, and function in the myocardia of Brandt's voles (Lasiopodomys brandtii) under cool environmental temperatures (15 °C). Results showed (1) mitochondrial swelling and cristae disruption in the cool huddling group (CH) and cool separated group (CS). Compared to the control group (CON, 22 °C), damaged mitochondria in the cool huddling and separated groups reached >90%; however, total number of mitochondria in the CH group was similar to that in the CON group. (2) ATP synthase activity was lowest in the CS group, whereas citrate synthetase activity was maintained among the three treatment groups. (3) Bax/bcl2 protein expression in the CH and CS groups was higher than that in the CON group, whereas DNA fragmentation, nuclear number, and caspase3 activity showed no significant differences among the three groups. (4) The protein expression levels of dynamin-related protein1 and mitochondrial fission factor were highest in the CH group. (5) Both protein expression of PINK1 and phosphorylation ratio of Parkin showed the pattern CS > CH > CON. (6) Total number of mitochondria was higher in males than in females. In general, the increased mitochondrial fission level observed in huddling voles partially counteracted the decrease in myocardial mitochondria caused by the increase in autophagy.

High Methane Emissions Largely Attributed to Ebullitive Fluxes from a Subtropical River Draining a Rice Paddy Watershed in China.

Rivers are of increasing concern as sources of atmospheric methane (CH4), while estimates of global CH4 emissions from rivers are poorly constrained due to a lack of representative measurements in tropical and subtropical latitudes. Measurements of complete CH4 flux components from subtropical rivers draining agricultural watersheds are particularly important since these rivers are subject to large organic and nutrient loads. Two-year measurements of CH4 fluxes were taken to assess the magnitude of CH4 emissions from the Lixiahe River (a tributary of the Grand Canal) draining a subtropical rice paddy watershed in China. Over the two-year period, annual CH4 emissions averaged 29.52 mmol m-2 d-1, amounting to 10.78 mol m-2 yr-1, making the river a strong source of atmospheric CH4. The CH4 emissions from rivers during the rice-growing season (June-October) accounted for approximately 70% of the annual total, with flux rates at 1-2 orders of magnitude greater than those for rice paddies in this area. Ebullition contributed to 44-56% of the overall CH4 emissions from the rivers and dominated the emission pathways during the summer months. Our data highlight that rivers draining agricultural watersheds may constitute a larger component of anthropogenic CH4 emissions than is currently documented in China.

The zinc-regulated protein (ZIP) family genes and glutathione s-transferase (GST) family genes play roles in Cd resistance and accumulation of pak choi (Brassica campestris ssp. chinensis).

The molecular mechanisms of the differences among the Cd tolerance and accumulation of different pak choi cultivars are essential to further breed Cd-safe genotypes pak choi. In our research, via morphological comparison, qRT-PCR and yeast function complementary approaches, we explored the differences of Cd tolerance and capacity for Cd uptake in nine various pak choi varieties. Results showed that higher expressions of BcZIPs involved in Cd uptake in 'Kang Re605' may lead to its higher capacity for Cd accumulation. The lowest expressions of transporter gene in 'Wu Yueman' were consistent with its fewest ability to uptake Cd. Beyond that, the difference of resistance was very great among varieties. Meanwhile, the expressions of the BcGSTUs were differentially induced by Cd exposure in different pak choi varieties, and 'Kang Re605' performed the highest BcGSTUs expression overall. To verify the role of GSTUs played in Cd resistance of pak choi, four BcGSTUs, BcGSTU4, BcGSTU11, BcGSTU12 and BcGSTU22 in a high-Cd accumulation and tolerance variety 'Kang Re605' were cloned, quantitated and transferred to Cd-sensitive yeast mutant strain. And finally found that BcGSTU11 increased the Cd tolerance of yeast, which may associate with a high Cd resistance of 'Kang Re605'. Simultaneously, less BcGSTUs abundance in 'Shang Haiqing' may result in its weak tolerance to Cd. These findings will help us to comprehend the roles of BcZIPs and BcGSTUs in Cd absorption and detoxification as well as promote our understanding of the Cd-resistant and Cd-accumulated mechanisms in pak choi.

Increased antioxidative capacity and decreased cadmium uptake contribute to hemin-induced alleviation of cadmium toxicity in Chinese cabbage seedlings.

Hemin (ferroprotoporphyrin IX), a compound derivative of heme, has been shown to exert numerous beneficial physiological functions in the resistance of plant to various abiotic stresses. This work investigated the effects of hemin on ameliorating Cd toxicity in Chinese cabbage (Brassica chinensis L.). Our results showed that leaf chlorosis, growth inhibition, root morphology and photosynthetic activity were significantly improved by the addition of hemin in Cd-stressed plants. Meanwhile, Cd-induced oxidative damage was also alleviated by hemin, which was supported by the decreased level of malondialdehyde (MDA) in roots of the seedlings treated with hemin. In the same time, the activities of antioxidative enzymes, including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), as well as the concentrations of ascorbic acid (AsA) and glutathione (GSH) were elevated by hemin, which contributed to the scavenging of Cd-elicited H2O2 and O2•－ within the roots of Chinese cabbage seedlings. Furthermore, compared with Cd stressed plants, Cd concentrations in both shoots and roots were markedly decreased by exogenous hemin. Hence, it can be speculated that hemin-mediated tolerance to Cd stress may be associated with the inhibition of Cd uptake in Chinese cabbage. This hypothesis was supported by the down-regulated expressions of transporter genes, including BcIRT1, BcIRT2, BcNramp1 and BcZIP2 caused by hemin addition in Chinese cabbage seedlings under Cd treatment. Taken together, these results suggested that hemin alleviated Cd toxicity probably through increasing antioxidative capacities and inhibiting Cd uptake of Chinese cabbage.

Climatic role of terrestrial ecosystem under elevated CO2 : a bottom-up greenhouse gases budget.

The net balance of greenhouse gas (GHG) exchanges between terrestrial ecosystems and the atmosphere under elevated atmospheric carbon dioxide (CO2 ) remains poorly understood. Here, we synthesise 1655 measurements from 169 published studies to assess GHGs budget of terrestrial ecosystems under elevated CO2 . We show that elevated CO2 significantly stimulates plant C pool (NPP) by 20%, soil CO2 fluxes by 24%, and methane (CH4 ) fluxes by 34% from rice paddies and by 12% from natural wetlands, while it slightly decreases CH4 uptake of upland soils by 3.8%. Elevated CO2 causes insignificant increases in soil nitrous oxide (N2 O) fluxes (4.6%), soil organic C (4.3%) and N (3.6%) pools. The elevated CO2 -induced increase in GHG emissions may decline with CO2 enrichment levels. An elevated CO2 -induced rise in soil CH4 and N2 O emissions (2.76 Pg CO2 -equivalent year-1 ) could negate soil C enrichment (2.42 Pg CO2 year-1 ) or reduce mitigation potential of terrestrial net ecosystem production by as much as 69% (NEP, 3.99 Pg CO2 year-1 ) under elevated CO2 . Our analysis highlights that the capacity of terrestrial ecosystems to act as a sink to slow climate warming under elevated CO2 might have been largely offset by its induced increases in soil GHGs source strength.

Diel and seasonal nitrous oxide fluxes determined by floating chamber and gas transfer equation methods in agricultural irrigation watersheds in southeast China.

Agricultural nitrate leaching and runoff incurs high nitrogen loads in agricultural irrigation watersheds, constituting one of important sources of atmospheric nitrous oxide (N2O). Two independent sampling campaigns of N2O flux measurement over diel cycles and N2O flux measurements once a week over annual cycles were carried out in an agricultural irrigation watershed in southeast China using floating chamber (chamber-based) and gas transfer equation (model-based) methods. The diel and seasonal patterns of N2O fluxes did not differ between the two measurement methods. The diel variation in N2O fluxes was characterized by the pattern that N2O fluxes were greater during nighttime than daytime periods with a single flux peak at midnight. The diel variation in N2O fluxes was closely associated with water environment and chemistry. The time interval of 9:00-11:00 a.m. was identified to be the sampling time best representing daily N2O flux measurements in agricultural irrigation watersheds. Seasonal N2O fluxes showed large variation, with some flux peaks corresponding to agricultural irrigation and drainage episodes and heavy rainfall during the crop-growing period of May to November. On average, N2O fluxes calculated by model-based methods were 27% lower than those determined by the chamber-based techniques over diel or annual cycles. Overall, more measurement campaigns are highly needed to assess regional agricultural N2O budget with low uncertainties.

A meta-analysis of fertilizer-induced soil NO and combined NO+N2 O emissions.

Soils are among the important sources of atmospheric nitric oxide (NO) and nitrous oxide (N2 O), acting as a critical role in atmospheric chemistry. Updated data derived from 114 peer-reviewed publications with 520 field measurements were synthesized using meta-analysis procedure to examine the N fertilizer-induced soil NO and the combined NO+N2 O emissions across global soils. Besides factors identified in earlier reviews, additional factors responsible for NO fluxes were fertilizer type, soil C/N ratio, crop residue incorporation, tillage, atmospheric carbon dioxide concentration, drought and biomass burning. When averaged across all measurements, soil NO-N fluxes were estimated to be 4.06 kg ha-1  yr-1 , with the greatest (9.75 kg ha-1  yr-1 ) in vegetable croplands and the lowest (0.11 kg ha-1  yr-1 ) in rice paddies. Soil NO emissions were more enhanced by synthetic N fertilizer (+38%), relative to organic (+20%) or mixed N (+18%) sources. Compared with synthetic N fertilizer alone, synthetic N fertilizer combined with nitrification inhibitors substantially reduced soil NO emissions by 81%. The global mean direct emission factors of N fertilizer for NO (EFNO ) and combined NO+N2 O (EFc ) were estimated to be 1.16% and 2.58%, with 95% confidence intervals of 0.71-1.61% and 1.81-3.35%, respectively. Forests had the greatest EFNO (2.39%). Within the croplands, the EFNO (1.71%) and EFc (4.13%) were the greatest in vegetable cropping fields. Among different chemical N fertilizer varieties, ammonium nitrate had the greatest EFNO (2.93%) and EFc (5.97%). Some options such as organic instead of synthetic N fertilizer, decreasing N fertilizer input rate, nitrification inhibitor and low irrigation frequency could be adopted to mitigate soil NO emissions. More field measurements over multiyears are highly needed to minimize the estimate uncertainties and mitigate soil NO emissions, particularly in forests and vegetable croplands.