Xiuli Xin

Carbon Mineralization and Microbial Attributes in Straw-Amended Soils as Affected by Moisture Levels

An 80-d incubation experiment was conducted to investigate straw decomposition, the priming effect and microbial characteristics in a non-fertilized soil (soil 1) and a long-term organic manure-fertilized soil (soil 2) with and without 13C-labeled maize straw amendment under different moisture levels. The soil 2 showed a markedly higher priming effect, microbial biomass C (Cmic), and β-glucosidase activity, and more abundant populations of bacteria and fungi than the soil 1. Also, soil CO2 emission, Cmic, β-glucosidase activity, and bacterial and fungal population sizes were substantially enhanced by straw amendment. In the presence of straw, the amount of straw mineralization and assimilation by microbes in the soil at 55% of water holding capacity (WHC) were significantly higher by 31% and 17%, respectively, compared to those at 25% of WHC. In contrast, β-glucosidase activity and fungal population size were both enhanced as the moisture content decreased. Cmic decreased as straw availability decreased, which was mainly attributed to the reduction of straw-derived Cmic. Amended soils, except the amended soil 2 at 25% of WHC, had a more abundant fungal population as straw availability decreased, indicating that fungal decomposability of added straw was independent of straw availability. Non-metric multidimensional scaling analysis based on fungal denatured gradient gel electrophoresis band patterns showed that shifts in the fungal community structure occurred as water and straw availability varied. The results indirectly suggest that soil fungi are able to adjust their degradation activity to water and straw availability by regulating their community structure.

Influence of Long-Term Fertilization on Selenium Accumulation in Soil and Uptake by Crops

Continuous applications of organic and inorganic fertilizers can affect soil and food quality with respect to selenium (Se) concentrations. A long-term (over 20 years) experimental field study, started in 1989, was conducted to investigate the changes in soil Se fractions and its uptake by crops, as affected by different fertilizer practices, in the North China Plain with an annual crop rotation of winter wheat and summer maize. The long-term experiment was arranged in a complete randomized block design consisting of 4 replications with 7 fertilizer treatments: 1) organic compost (OC), 2) half organic compost plus half N-P-K chemical fertilizers (OC + NPK), 3) N-P-K fertilizers (NPK), 4) N-P fertilizers (NP), 5) P-K fertilizers (PK), 6) N-K fertilizers (NK), and 7) an un-amended control. Soil samples from the surface (20 cm) were collected in 1989, 1994, 1999, 2004 and 2009 to characterize Se and other soil properties. In 2009, the average soil Se concentrations in the treatments (149 ± 8 pg kg−1) were higher than those in the soil samples collected in 1989 at the beginning of the experiment (112 ± 4 pg kg−1), and decreased in the order of OC > OC + NPK > NPK ≈ NP > PK ≈ NK > control. Sequential extraction showed the oxidizable fraction (50.06% ± 3.94%) was the dominant form of Se in the soil, followed by the residual fraction (24.12% ± 2.89%), exchangeable fraction (15.09% ± 4.34%) and Fe-Mn oxides fraction (10.73% ± 4.04%). With an increase of soil K, the exchangeable Se concentrations in the soil increased. The Se concentrations in the soil tillage layer (0–20 cm) were mainly related to soil organic carbon (SOC), although different contributions came from atmospheric deposition, irrigation and fertilizers. With the accumulation of SOC, the uptakes of soil Se by two crops were inhibited. For the OC and OC + NPK treatments, Se concentrations in wheat grains were lower than the critical standard of Se in stable food (100 µg kg−1). Additionally, Se concentrations in grains were also decreased by the deficiencies of major soil nutrients, especially P.

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.

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 13C-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.

Changes in soil organic carbon and aggregate stability after conversion to conservation tillage for seven years in the Huang-Huai-Hai Plain of China

Abstract Soil aggregate stability and organic carbon (OC) are regarded as effective indicators of soil structure and quality. A long-term field experiment was established in 2006 to examine the influence of tillage systems on soil aggregation and OC in a sandy loam soil in the Huang-Huai-Hai Plain of China. The study involved eight treatments: plowing every year with (TS) and without residue (T), plowing every 2 years with (2TS) and without residue (2T), plowing every 4 years with (4TS) and without residue (4T), and no plowing with (NTS) and without residue (NT). In 2013, soil samples were collected at depths of 0–5, 5–10 and 10–20 cm, and separated into three aggregate-size classes: macroaggregates (>250 μm), microaggregates (53–250 μm) and the silt+clay fraction ( microaggregates>silt+clay fraction. In the 0–5 cm soil layer, concentrations of macroaggregate-associated OC in 2TS, 4TS and NTS were 14, 56 and 83% higher than for T, whereas T had the greatest concentration of OC associated with the silt+clay fraction in the 10–20 cm layer. Soil OC concentrations under 4TS and NTS were significantly higher (P

Elymus dahuricus H+-PPase EdVP1 enhances potassium uptake and utilization of wheat through the development of root system

We investigated the differences of K acquisition and utilization, morphological and physiological characteristics of roots and grain yield between Elymus dahuricus H+-PPase (EdVP1) transgenic wheat and wild type wheat under low K stress. The results showed that, the grain yield and K economic utilization index (KUI-E) in wild type wheat were only 61.14% and 50.20% of those in EdVP1 transgenic wheat. EdVP1 increased the free IAA accumulations in roots, which may play a key role in the development of root system. The total root length, total root surface area, root tips and total root volume in transgenic wheat were 2.26, 2.23, 2.34 and 2.00 times as high as those in wild type wheat, respectively. Excretion H+ and cation exchange capacity (CEC) of roots, which were enhanced in transgenic wheat, were positively correlated with K content.The exudate of organic acid intransgenic wheat was 2.22 times as high as that in wild type wheat, leading to the strong K activation of transgenic wheat. Therefore, we assume that well-developed rootsystem containing prosperous root morphology, high excretion H+ and CEC of roots and strong excretion ability of organic acids improved K acquisition and utilization efficiency in EdVP1 transgenic wheat.

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.

Soil Characteristics Overwhelm Cultivar Effects on the Structure and Assembly of Root-Associated Microbiomes of Modern Maize

Abstract Modern breeding primarily targets crop yield traits and is likely to influence root-associated microbiomes, which play significant roles in plant growth and health. The relative importance of soil and cultivar factors in shaping root-associated microbiomes of modern maize (Zea mays L.) remains uncertain. We conducted a pot experiment in a controlled environment using three soils (Mollisol, Inceptisol, and Ultisol) and four contrasting cultivars, Denghai 605, Nonghua 816, Qiaoyu 8, and Zhengdan 958, which are widely planted in China. We used 16S rRNA gene amplicon sequencing to characterize the bacterial communities in the bulk soil, rhizosphere, and endosphere. Our results showed that the four cultivars had different shoot biomass and root exudate total organic carbon and organic acid contents. The microbiomes in the bulk soil, rhizosphere, and endosphere were different. We observed apparent community divergence between soils rather than cultivars, within which edaphic factors substantially contributed to microbiome variation. Moreover, permutational multivariate analysis of variance corroborated significant contributions of soil type but not cultivar on the root-associated microbiome structure. Differential abundance analysis confirmed that each soil presented a distinct root microbiome, while network analysis indicated different co-occurrence patterns of the root microbiome among the three soils. The core root microbiome members are implicated in plant growth promotion and nutrient acquisition in the roots. In conclusion, root-associated microbiomes of modern maize are much more controlled by soil characteristics than by cultivar root exudation. Our study is anticipated to help improve breeding strategies through integrative interactions of soils, cultivars, and their associated microbiomes.

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.

Chemical nature of soil organic carbon under different long-term fertilization regimes is coupled with changes in the bacterial community composition in a Calcaric Fluvisol

Fertilization is an important factor influencing the chemical structure of soil organic carbon (SOC) and soil microbial communities; however, whether any connection exists between the two under different fertilization regimes remains unclear. Soils from a 27-year field experiment were used to explore potential associations between SOC functional groups and specific bacterial taxa, using quantitative multiple cross-polarization magic-angle spinning 13C nuclear magnetic resonance and 16S rRNA gene sequencing. Treatments included balanced fertilization with organic materials (OM) and with nitrogen (N), phosphorus (P), and potassium (K) mineral fertilizers (NPK); unbalanced fertilization without one of the major elements (NP, PK, or NK); and an unamended control. These treatments were divided into four distinct groups, namely OM, NPK, NP plus PK, and NK plus control, according to their bacterial community composition and SOC chemical structure. Soil total P, available P, and SOC contents were the major determinants of bacterial community composition after long-term fertilization. Compared to NPK, the OM treatment generated a higher aromatic C–O and OCH3 and lower alkyl C and OCH abundance, which were associated with the enhanced abundance of members of the Acidobacteria subgroups 6 and 5, Cytophagaceae, Chitinophagaceae, and Bacillus sp.; NP plus PK treatments resulted in a higher OCH and lower aromatic C–C abundance, which showed a close association with the enrichment of unclassified Chloracidobacteria, Syntrophobacteraceae, and Anaerolineae and depletion of Bacillales; and NK plus control treatments resulted in a higher abundance of aromatic C–C, which was associated with the enhanced abundance of Bacillales. Our results indicate that different fertilization regimes changed the SOC chemical structure and bacterial community composition in different patterns. The results also suggest that fertilization-induced variations in SOC chemical structure were strongly associated with shifts in specific microbial taxa which, in turn, may be affected by changes in soil properties.