Saline-alkali land reclamation boosts topsoil carbon storage by preferentially accumulating plant-derived carbon.

Saline-alkali land is an important cultivated land reserve resource for tackling global climate change and ensuring food security, partly because it can store large amounts of carbon (C). However, it is unclear how saline-alkali land reclamation (converting saline-alkali land into cultivated land) affects soil C storage. We collected 189 adjacent pairs of salt-affected and cultivated soil samples (0-30 cm deep) from the Songnen Plain, eastern coastal area, Hetao Plain, and northwestern arid area in China. Various soil properties, the soil inorganic C (SIC), organic C (SOC), particulate organic C (POC), and mineral-associated organic C (MAOC) densities, and plant- and microbial-derived C accumulation were determined. Saline-alkali land reclamation inconsistently affected the SIC density but significantly (P < 0.001) increased the SOC density. The SOC, POC, and MAOC densities were predicted well by the integrative soil amelioration index. Saline-alkali land reclamation significantly increased plant-derived C accumulation and the plant-derived C to microbial-derived C ratios in all saline-alkali areas, and less microbial transformation of plant-derived C (i.e., less lignin degradation or oxidation) occurred in cultivated soils than salt-affected soils. The results indicated that saline-alkali land reclamation leads to plant-derived C becoming the dominant contributor of SOC storage. POC storage and MAOC storage were strongly linked to plant- and microbial-derived C accumulation, respectively, caused by saline-alkali land reclamation. Our findings suggest that saline-alkali land reclamation increases C storage in topsoil by preferentially promoting plant-derived C accumulation.

Long-term conservation tillage enhances microbial carbon use efficiency by altering multitrophic interactions in soil.

Microbial carbon (C) use efficiency (CUE) plays a key role in soil C storage. The predation of protists on bacteria and fungi has potential impacts on the global C cycle. However, under conservation tillage conditions, the effects of multitrophic interactions on soil microbial CUE are still unclear. Here, we investigate the multitrophic network (especially the keystone ecological cluster) and its regulation of soil microbial CUE and soil organic C (SOC) under different long-term (15-year) tillage practices. We found that conservation tillage (CT) significantly enhanced microbial CUE, turnover, and SOC (P < 0.05) compared to traditional tillage (control, CK). At the same time, tillage practice and soil depth had significant effects on the structure of fungal and protistan communities. Furthermore, the soil biodiversity of the keystone cluster was positively correlated with the microbial physiological traits (CUE, microbial growth rate (MGR), microbial respiration rate (Rs), microbial turnover) and SOC (P < 0.05). Protistan richness played the strongest role in directly shaping the keystone cluster. Compared with CK, CT generally enhanced the correlation between microbial communities and microbial physiological characteristics and SOC. Overall, our results illustrate that the top-down control (the organisms at higher trophic levels affect the organisms at lower trophic levels) of protists in the soil micro-food web plays an important role in improving microbial CUE under conservation tillage. Our findings provide a theoretical basis for promoting the application of protists in targeted microbial engineering and contribute to the promotion of conservation agriculture and the improvement of soil C sequestration potential.

Bacteria-Virus Interactions Are More Crucial in Soil Organic Carbon Storage than Iron Protection in Biochar-Amended Paddy Soils.

Iron oxides supposedly provide physicochemical protection for soil organic carbon (SOC) under anoxic conditions. Likewise, biochar can modulate the composition of soil microbial communities. However, how Fe oxides and microbial communities influence the fate of SOC with biochar amendment remains unresolved, especially the effect of the bacteria-virus interaction on SOC dynamics. Here, we performed a four-month pot experiment using rice seedlings with a biochar amendment under waterlogged conditions. Then, soil aggregate sizes were examined to explore the factors influencing the SOC patterns and the underlying mechanisms. We found that biochar altered soil enzyme activities, especially in macroaggregates. Fe oxides and necromass exhibited significant negative relationships with SOC. Bacterial communities were notably associated with viral communities. Here, the keystone ecological cluster (module 1) and keystone taxa in the bacteria-virus network showed significant negative correlations with SOC. However, Fe oxides exhibited substantial positive relationships with module 1. In contrast to the prevailing view, the SOC increase was not primarily driven by Fe oxides but strongly influenced by bacteria-virus interactions and keystone taxa. These findings indicate that biochar governs microbial-mediated SOC accumulation in paddy soil and ascertains the role of viruses in regulating the bacterial community, thus predicting SOC stock.

Jacalin-related lectin 45 (OsJRL45) isolated from 'sea rice 86' enhances rice salt tolerance at the seedling and reproductive stages.

BACKGROUND: Rice (Oryza sativa L.) is one of the most widely cultivated grain crops in the world that meets the caloric needs of more than half the world's population. Salt stress seriously affects rice production and threatens food security. Therefore, mining salt tolerance genes in salt-tolerant germplasm and elucidating their molecular mechanisms in rice are necessary for the breeding of salt tolerant cultivars. RESULTS: In this study, a salt stress-responsive jacalin-related lectin (JRL) family gene, OsJRL45, was identified in the salt-tolerant rice variety 'sea rice 86' (SR86). OsJRL45 showed high expression level in leaves, and the corresponding protein mainly localized to the endoplasmic reticulum. The knockout mutant and overexpression lines of OsJRL45 revealed that OsJRL45 positively regulates the salt tolerance of rice plants at all growth stages. Compared with the wild type (WT), the OsJRL45 overexpression lines showed greater salt tolerance at the reproductive stage, and significantly higher seed setting rate and 1,000-grain weight. Moreover, OsJRL45 expression significantly improved the salt-resistant ability and yield of a salt-sensitive indica cultivar, L6-23. Furthermore, OsJRL45 enhanced the antioxidant capacity of rice plants and facilitated the maintenance of Na+-K+ homeostasis under salt stress conditions. Five proteins associated with OsJRL45 were screened by transcriptome and interaction network analysis, of which one, the transmembrane transporter Os10g0210500 affects the salt tolerance of rice by regulating ion transport-, salt stress-, and hormone-responsive proteins. CONCLUSIONS: The OsJRL45 gene isolated from SR86 positively regulated the salt tolerance of rice plants at all growth stages, and significantly increased the yield of salt-sensitive rice cultivar under NaCl treatment. OsJRL45 increased the activity of antioxidant enzyme of rice and regulated Na+/K+ dynamic equilibrium under salinity conditions. Our data suggest that OsJRL45 may improve the salt tolerance of rice by mediating the expression of ion transport-, salt stress response-, and hormone response-related genes.

Tradeoffs of microbial life history strategies drive the turnover of microbial-derived organic carbon in coastal saline soils.

Stable soil organic carbon (SOC) formation in coastal saline soils is important to improve arable land quality and mitigate greenhouse gas emissions. However, how microbial life-history strategies and metabolic traits regulate SOC turnover in coastal saline soils remains unknown. Here, we investigated the effects of microbial life history strategy tradeoffs on microbial carbon use efficiency (CUE) and microbial-derived SOC formation using metagenomic sequencing technology in different salinity soils. The results showed that high-salinity is detrimental to microbial CUE and microbial-derived SOC formation. Moreover, the regulation of nutrients stoichiometry could not mitigate adverse effects of salt stress on microbial CUE, which indicated that microbial-derived SOC formation is independent of stoichiometry in high-salinity soil. Low-salinity soil is dominated by a high growth yield (Y) strategy, such as higher microbial biomass carbon and metabolic traits which are related to amino acid metabolism, carbohydrate metabolism, and cell processes. However, high-salinity soil is dominated by stress tolerance (S) (e.g., higher metabolic functions of homologous recombination, base excision repair, biofilm formation, extracellular polysaccharide biosynthesis, and osmolytes production) and resource acquisition (A) strategies (e.g., higher alkaline phosphatase activity, transporters, and flagellar assembly). These trade-offs of strategies implied that resource reallocation took place. The high-salinity soil microbes diverted investments away from growth yield to microbial survival and resource capture, thereby decreasing biomass turnover efficiency and impeding microbial-derived SOC formation. Moreover, altering the stoichiometry in low-salinity soil caused more investment in the A-strategy, such as the production of more ß-glucosidase and ß-N-acetyl-glucosaminidase, and increasing bacterial chemotaxis, which thereby reduced microbial-derived SOC formation. Our research reveals that shift the microbial community from S- and A- strategies to the Y-strategy is important to increase the microbial CUE, and thus enhance SOC turnover in coastal saline soils.

Can Stringent Government Initiatives Lead to Global Economic Recovery Rapidly during the COVID-19 Epidemic?

This paper investigates the effectiveness of government measures implemented against COVID-19 and the factors influencing a country's economic growth from a global perspective. With the help of the data of the Government Response Stringency Index (GRSI), Google mobility, and confirmed COVID-19 daily cases, we conducted a panel model for 105 countries and regions from 11 March 2020 to 31 June 2021 to explore the effects of response policies in different countries against the pandemic. First, the results showed that staying in residential places had the strongest correlation with confirmed cases. Second, in countries with higher government stringency, stay-at-home policies carried out in the early spread of the pandemic had the most effective the impact. In addition, the results have also been strictly robustly analyzed by applying the propensity score matching (PSM) method. Third, after reconstructing a panel data of 47 OECD countries, we further concluded that governments should take stricter restrictive measures in response to COVID-19. Even though it may also cause a shock to the market in the short term, this may not be sustainable. As long as the policy response is justified, it will moderate the negative effect on the economy over time, and finally have a positive effect.

Organic amendments with high proportion of heterocyclic compounds promote soil microbiome shift and microbial use efficiency of straw-C.

Soil microbial use efficiency of straw carbon (C), which is the proportion of straw-C microbes assimilate into new biosynthetic material relative to C lost out of the system as CO2, is critical in increasing soil organic C (SOC) content, and hence maintaining soil fertility and productivity. However, the effect of chemical structures of the organic amendments (OAs) on the microbial use efficiency of straw-C remains unclear. The effect of the chemical structure of the OAs on microbial use efficiency of straw-C was elucidated by a combination of 13C-straw labeling with high-throughput sequencing and pyrolysis-GC/MS. We found a strong positive correlation between the microbial use efficiency of straw-C and the proportion of heterocyclic compounds (Hete_C). The microbial use efficiency of straw-C was highest in soil supplemented with Hete_C-dominant OAs, which significantly shifted microbial community structure toward fungal dominance. Specifically, fungal-to-bacterial ratio, fungal richness, and the relative abundance of Ascomycota were higher in soil with a higher proportion of Hete_C-dominant OAs. Together, our study suggests that OAs with high proportion of Hete_C promote the microbial use efficiency of straw-C by increasing the dominance of fungi in the soil microbial community in agroecosystems.

The addition of discrimination inhibitors stimulations discrimination potential and N2O emissions were linked to predation among microorganisms in long term nitrogen application and straw returning systems.

Introduction: Ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) have been proven to be key microorganisms driving the ammonia oxidation process. However, under different fertilization practices, there is a lack of research on the impact of interaction between predators and AOA or AOB on nitrogen cycling at the multi-trophic level. Methods: In this study, a network-oriented microscopic culture experiment was established based on four different long-term fertilization practices soils. We used the nitrification inhibitors 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxide-3-oxyl (PTIO) and 3, 4-Dimethylpyrazole phosphate (DMPP) inhibited AOA and AOB, respectively, to explore the impact of interaction between protists and AOA or AOB on nitrogen transformation. Results: The results showed that long-term nitrogen application promoted the potential nitrification rate (PNR) and nitrous oxide (N2O) emission, and significantly increased the gene abundance of AOB, but had no obvious effect on AOA gene abundance. DMPP significantly reduced N2O emission and PNR, while PTIO had no obvious effect on them. Accordingly, in the multi-trophic microbial network, Cercozoa and Proteobacteria were identified as keystone taxa of protists and AOB, respectively, and were significantly positively correlated with N2O, PNR and nitrate nitrogen. However, Nitrososphaerota archaeon as the keystone species of AOA, had an obvious negative linkage to these indicators. The structural equation model (SEM) showed that AOA and AOB may be competitors to each other. Protists may promote AOB diversity through direct trophic interaction with AOA. Conclusion: The interaction pattern between protists and ammonia-oxidizing microorganisms significantly affects potential nitrification rate and N2O emission, which has important implications for soil nitrogen cycle.

Effects of Biochar and Manure Co-Application on Aggregate Stability and Pore Size Distribution of Vertisols.

BACKGROUND: The combination of biochar and organic manure has substantial local impacts on soil properties, greenhouse gas emissions, and crop yield. However, the research on soil health or quality is still in its early stages. Four pot experiments were carried out: C (30 g biochar (kg soil)-1), M (10 g manure (kg soil)-1), CM (15 g biochar (kg soil)-1 + 5 g manure (kg soil)-1), and the control (without any amendments). RESULTS: When compared to C and M treatments, the MWD of CM was reduced by 5.5% and increased by 4.9%, respectively, and the micropore volume (5-30 m) was increased by 17.6% and 89.6%. The structural equation model shows that soil structural parameters and physical properties regulate the distribution of micropores (5-30 µm) in amended soil. CONCLUSION: Our studies discovered that biochar mixed with poultry manure had antagonistic and synergistic effects on soil aggregate stability and micropore volume in vertisol, respectively, and thus enhanced crop yield by 71.1%, which might be used as a technological model for farmers in China's Huang-Huai-Hai region to improve low- and medium-yielding soil and maintain soil health.

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Large-scale mining has greatly damaged vegetation and caused ecological degradation in the semi-arid area in China. It is urgent to restore the vegetation to solve the deteriorating ecological and environmental problems in mining area. How to reclaim soils for effectively storing and utilizing precipitation is the primary issue for vegetation restoration in the area. In this study, we proposed to take the mixture of attapulgite clay and local sandy soils as covering materials to improve the weak water conservation function of soils in mining areas, and studied the effects of the addition of attapulgite clay on soil infiltration, drainage and water storage sampled from the Shenmu mining area. The results showed that, with increasing application rates of attapulgite clay, the cumulated infiltration volumes decreased by 4.8%-37.4%, the infiltration rates dropped by 6.4%-46.3%, the wetting front advance rates decreased by 9.8%-116.9%, the saturated hydraulic conductivities decreased by 14.3%-59.5%, the drained water volumes reduced by 0.3%-4.3% for 24 hours and by 0.3%-2.5% for 72 hours, and the maximum soil water storages increased by 1.6%-22.4%. The maximum effect of attapulgite clay peaked at the application rate of 150 t·hm-2. Considering the economic cost, the optimum application rate should be 30-150 t·hm-2. The results syste-matically revealed the mechanism of reclaiming mining soils with attapulgite clay to restore the function of water conservation, and demonstrated that attapulgite clay is an effective material for soil reclamation in the semi-arid mining area, which can provide references for soil reclamation and ecological restoration in the semi-arid mining area.

Effect of compost and inorganic fertilizer on organic carbon and activities of carbon cycle enzymes in aggregates of an intensively cultivated Vertisol.

BACKGROUND AND AIMS: This paper was primarily devoted to understand the interactions of soil aggregates, organic carbon (C) and carbon cycle enzymes in aggregates under different fertilization managements, aiming to identify the effects of organic and inorganic fertilizer amendments on soil organic C accumulation and the activities of carbon cycle enzymes within aggregates in Vertisol. METHODS: A Vertisol soil following 4-year compost and inorganic fertilizer amendments, i.e. no fertilizer (CK), mineral fertilizer (FR) and 60% compost N plus 40% fertilizer N (FRM), was collected to identify the dynamics of organic C, enzymes activities and their associations with macroaggregation using aggregate fractionation techniques. RESULTS: The organic C content in all FR and FRM treatments was 8.24-41.15% higher than that in CK. An increased amounts of carbon cycle enzymes in aggregates or 0-20 cm bulk soil were also observed in FRM plots. Compared to FR, FRM significantly strengthened the structural stability of macroaggregates and the intimate connection between enzyme activities and macroaggregates. CONCLUSIONS: As a recommended measure, supplementation with organic manure such as compost strengthened the process of mutual promotion between carbon cycle enzymes and macroaggregates, and the synergistic effect would be highly beneficial to soil organic C sequestration.

Elevated CO2 improved soil nitrogen mineralization capacity of rice paddy.

Elevated CO2 would increase rice yields and may lead to nitrogen limitation and potentially influence the sustainability of agricultural production. Blindly increasing the amount of chemical fertilizer will damage the environment and is very unwise. Therefore, clarifying the response of soil nitrogen mineralization capacity to elevated CO2 is critical for both sustainable agriculture production and environmental protection. Here, we relied on Free-Air CO2 Enrichment (FACE) platform and used a waterlogged incubation method to investigate the effects of elevated CO2 on soil nitrogen mineralization capacity under different fertilization levels when planted different rice cultivars (strong and weak-CO2 response rice). According to the first-order kinetic equation fitting, compared with Ambient, elevated CO2 increased soil potential mineralized nitrogen (Np) by 16.18%. Path analysis indicated that fertilization status, rice cultivar, soil organic carbon and soil C: N ratio might affect Np. There was a significant positive correlation between soil nitrogen mineralization rate and Np. Under different fertilization conditions and rice cultivars, the improvement degree of soil nitrogen mineralization capacity (Np and soil nitrogen mineralization rate) by elevated CO2 was different. These findings suggest that more parameters and influencing factors should be taken into account when studying soil nitrogen cycle models under the condition of global change.

Succession of organics metabolic function of bacterial community in response to addition of earthworm casts and zeolite in maize straw composting.

Succession and metabolism functions of bacterial communities were determined in maize straw composting with earthworm casts and zeolite addition by using high-throughput sequencing, Biolog and PICRUSt. Results showed that earthworm casts and zeolite addition increased the temperature, decreased NH4+ contents and affected bacterial community structure. The relative abundances of Firmicutes and Betaproteobacteria increased with earthworm casts and zeolite addition in the late stage. The abundances of genes related to carbohydrate metabolism, amino acid metabolism, and energy metabolism were increased by these two additives in the early stage, but decreased in the late stage. Network analysis demonstrated that members of Bacillaceae were identified as the keystone taxa. Temperature showed negative relationship with Georgenia, while NH4+ exhibited positive associations with Georgenia, Devosia, Ruania and Mycobacterium. These results indicated that earthworm casts and zeolite addition benefitted the keystone species and enhanced the metabolism capacity of bacterial community, thereby improved the quality of compost.

Potential Root Foraging Strategy of Wheat (Triticum aestivum L.) for Potassium Heterogeneity.

Potassium (K) distribution is horizontally heterogeneous under the conservation agriculture approach of no-till with strip fertilization. The root foraging strategy of wheat for K heterogeneity is poorly understood. In this study, WinRHIZO, microarray, Non-invasive Micro-test Technology (NMT) and a split-root system were performed to investigate root morphology, gene expression profiling and fluxes of K+ and O2 under K heterogeneity and homogeneity conditions. The split-root system was performed as follows: C. LK (both compartments had low K), C. NK (both compartments had normal K), Sp. LK (one compartment had low K) and Sp. NK (the other compartment had normal K). The ratio of total root length and root tips in Sp. NK was significantly higher than that in C. NK, while no significant differences were found between Sp. LK and C. LK. Differential expression genes in C. LK vs. C. NK had opposite responses in Sp. LK vs. C. LK and similar responses in Sp. NK vs. C. NK. Low-K responsive genes, such as peroxidases, mitochondrion, transcription factor activity, calcium ion binding, glutathione transferase and cellular respiration genes were found to be up-regulated in Sp. NK. However, methyltransferase activity, protein amino acid phosphorylation, potassium ion transport, and protein kinase activity genes were found to be down-regulated in Sp. LK. The up-regulated gene with function in respiration tended to increase K+ uptake through improving O2 influx on the root surface in Sp. NK, while the down-regulated genes with functions of K+ and O2 transport tended to reduce K+ uptake on the root surface in Sp. LK. To summarize, wheat roots tended to perform active-foraging strategies in Sp. NK and dormant-foraging strategies in Sp. LK through the following patterns: (1) root development in Sp. NK but not in Sp. LK; (2) low-K responsive genes, such as peroxidases, mitochondrion, transcription factor activity, calcium ion binding and respiration, were up-regulated in Sp. NK but not in Sp. LK; and (3) root K+ and O2 influxes increased in Sp. NK but not in Sp. LK. Our findings may better explain the optimal root foraging strategy for wheat grown with heterogeneous K distribution in the root zone.

Nitrate accumulation and leaching potential reduced by coupled water and nitrogen management in the Huang-Huai-Hai Plain.

Irrigation and nitrogen (N) fertilization in excess of crop requirements are responsible for substantial nitrate accumulation in the soil profile and contamination of groundwater by nitrate leaching during intensive agricultural production. In this on-farm field trial, we compared 16 different water and N treatments on nitrate accumulation and its distribution in the soil profile (0-180cm), nitrate leaching potential, and groundwater nitrate concentration within a summer-maize (Zea mays L.) and winter-wheat (Triticum aestivum L.) rotation system in the Huang-Huai-Hai Plain over five cropping cycles (2006-2010). The results indicated that nitrate remaining in the soil profile after crop harvest and nitrate concentration of soil solutions at two depths (80cm and 180cm) declined with increasing irrigation amounts and increased greatly with increasing N application rates, especially for seasonal N application rates higher than 190kgNha-1. During the experimental period, continuous torrential rainfall was the main cause for nitrate leaching beyond the root zone (180cm), which could pose potential risks for contamination of groundwater. Nitrate concentration of groundwater varied from 0.2 to 2.9mgL-1, which was lower than the limit of 10mgL-1 as the maximum safe level for drinking water. In view of the balance between grain production and environmental consequences, seasonal N application rates of 190kgNha-1 and 150kgNha-1 were recommended for winter wheat and summer maize, respectively. Irrigation to the field capacity of 0-40cm and 0-60cm soil depth could be appropriate for maize and wheat, respectively. Therefore, taking grain yields, mineral N accumulation in the soil profile, nitrate leaching potential, and groundwater quality into account, coupled water and N management could provide an opportunity to promote grain production while reducing negative environmental impacts in this region.

Improving "color rendering" of LED lighting for the growth of lettuce.

Light plays a vital role on the growth and development of plant. On the base of white light with high color rendering to the benefit of human survival and life, we proposed to improve "color rendering" of LED lighting for accelerating the growth of lettuce. Seven spectral LED lights were adopted to irradiate the lettuces under 150 µmol·m-2·s-1 for a 16 hd-1 photoperiod. The leaf area and number profiles, plant biomass, and photosynthetic rate under the as-prepared LED light treatments were investigated. We let the absorption spectrum of fresh leaf be the emission spectrum of ideal light and then evaluate the "color rendering" of as-prepared LED lights by the Pearson product-moment correlation coefficient and CIE chromaticity coordinates. Under the irradiation of red-yellow-blue light with high correlation coefficient of 0.587, the dry weights and leaf growth rate are 2-3 times as high as the sharp red-blue light. The optimized LED light for lettuce growth can be presumed to be limited to the angle (about 75°) between the vectors passed through the ideal light in the CIE chromaticity coordinates. These findings open up a new idea to assess and find the optimized LED light for plant growth.

Effects of changes in straw chemical properties and alkaline soils on bacterial communities engaged in straw decomposition at different temperatures.

Differences in the composition of a bacterial community engaged in decomposing wheat straw in a fluvo-aquic soil at 15 °C, 25 °C, and 35 °C were identified using barcode pyrosequencing. Functional carbon groups in the decomposing wheat straw were evaluated by (13)C-NMR (nuclear magnetic resonance). Actinobacteria and Firmicutes were more abundant, whereas Alphaproteobacteria and Bacteroidetes were less abundant, at higher temperatures during the later stages of decomposition. Differences in the chemical properties of straw accounted for 19.3% of the variation in the community composition, whereas soil properties accounted for more (24.0%) and temperature, for less (7.4%). Carbon content of the soil microbial biomass and nitrogen content of straw were significantly correlated with the abundance of Alphaproteobacteria, Actinobacteria, and Bacteroidetes. The chemical properties of straw, especially the NCH/OCH3, alkyl O-C-O, and O-alkyl functional groups, exercised a significant effect on the composition of the bacterial community at different temperatures during decomposition-results that extend our understanding of bacterial communities associated with the decomposition of straw in agro-ecosystems and of the effects of temperature and chemical properties of the decomposing straw and soil on such communities.

Mass loss and chemical structures of wheat and maize straws in response to ultraviolet-B radiation and soil contact.

The role of photodegradation, an abiotic process, has been largely overlooked during straw decomposition in mesic ecosystems. We investigated the mass loss and chemical structures of straw decomposition in response to elevated UV-B radiation with or without soil contact over a 12-month litterbag experiment. Wheat and maize straw samples with and without soil contact were exposed to three radiation levels: a no-sunlight control, ambient solar UV-B, and artificially elevated UV-B radiation. A block control with soil contact was not included. Compared with the no-sunlight control, UV-B radiation increased the mass loss by 14-19% and the ambient radiation by 9-16% for wheat and maize straws without soil contact after 12 months. Elevated UV-B exposure decreased the decomposition rates of both wheat and maize straws when in contact with soil. Light exposure resulted in decreased O-alkyl carbons and increased alkyl carbons for both the wheat and maize straws compared with no-sunlight control. The difference in soil contact may influence the contribution of photodegradation to the overall straw decomposition process. These results indicate that we must take into account the effects of photodegradation when explaining the mechanisms of straw decomposition in mesic ecosystems.

Comparative analysis of potassium deficiency-responsive transcriptomes in low potassium susceptible and tolerant wheat (Triticum aestivum L.).

Potassium (K(+)) deficiency as a common abiotic stress can inhibit the growth of plants and thus reduce the agricultural yields. Nevertheless, scarcely any development has been promoted in wheat transcriptional changes under K(+) deficiency. Here we investigated root transcriptional changes in two wheat genotypes, namely, low-K(+) tolerant "Tongzhou916" and low-K(+) susceptible "Shiluan02-1". There were totally 2713 and 2485 probe sets displayed expression changes more than 1.5-fold in Tongzhou916 and Shiluan02-1, respectively. Low-K(+) responsive genes mainly belonged to the categories as follows: metabolic process, cation binding, transferase activity, ion transporters and so forth. We made a comparison of gene expression differences between the two wheat genotypes. There were 1321 and 1177 up-regulated genes in Tongzhou916 and Shiluan02-1, respectively. This result indicated that more genes took part in acclimating to low-K(+) stress in Tongzhou916. In addition, there were more genes associated with jasmonic acid, defense response and potassium transporter up-regulated in Tongzhou916. Moreover, totally 19 genes encoding vacuolar H(+)-pyrophosphatase, ethylene-related, auxin response, anatomical structure development and nutrient reservoir were uniquely up-regulated in Tongzhou916. For their important role in root architecture, K(+) uptake and nutrient storage, unique genes above may make a great contribution to the strong low-K(+) tolerance in Tongzhou916.

The influence of long-term fertilization on cadmium (Cd) accumulation in soil and its uptake by crops.

Continuous application of organic and inorganic fertilizers can affect soil and food quality with respect to heavy metal concentrations. The risk of cadmium (Cd) contamination in a long-term (over 20 years) experimental field in North China with an annual crop rotation of winter wheat and summer maize was investigated. The long-term experiment had a complete randomized block design with seven fertilizer treatments and four replications. The seven fertilizer treatments were (1) organic compost (OM), (2) half organic compost plus half chemical fertilizer (OM + NPK), (3) NPK fertilizer (NPK), (4-6) chemical fertilizers without one of the major nutrients (NP, PK, and NK), and (7) an unamended control (CK). Soil samples from 0 to 20 cm were collected in 1989, 1999, and 2009 to characterize Cd and other soil properties. During the past 20 years, various extents of Cd accumulation were observed in the soil, and the accumulation was mainly affected by atmospheric dry and wet deposition and fertilization. In 2009, the average Cd concentration in the soil was 148 ± 15 µg kg(-1) and decreased in the order of NPK ≈ OM + NKP ≈ PK > NP ≈ NK > OM ≈ CK. Sequential extraction of Cd showed that the acid-soluble fraction (F1, 32 ± 7 %) and the residual fraction (F4, 31 ± 5 %) were the dominant fractions of Cd in the soil, followed by the reducible fraction (F2, 22 ± 5 %) and oxidizable fraction (F3, 15 ± 6 %). The acid-soluble Cd fraction in the soil and Cd accumulation in the crops increased with soil plant available K. Fraction F3 was increased by soil organic C (SOC) and crop yields, but SOC reduced the uptake of soil Cd by crops. The long-term P fertilization resulted in more Cd buildup in the soil than other treatments, but the uptake of Cd by crops was inhibited by the precipitation of Cd with phosphate in the soil. Although soil Cd was slightly increased over the 20 years of intensive crop production, both soil and grain/kernel Cd concentrations were still below the national standards for environmental and food safety.