Bioethanol production from the hydrolysate of Palmaria palmata using sulfuric acid and fermentation with brewer’s yeast

Seaweeds, particularly species of red macroalgae, are promising resources for bioethanol production because of their exceptionally high carbohydrate content. Of 20 seaweeds evaluated, Palmaria palmata (Rhodymenia palmata) contained the highest carbohydrate content (469.8 mg g^?1 seaweed) with a carrageenan content of 354 mg g^?1 seaweed. Such a high carrageenan content makes the high-volume production of bioethanol feasible. Acid hydrolysis of P. palmata in 0.4 M H₂SO₄ at 125 °C for 25 min released 27 mg of glucose, 218.4 mg of reducing sugars, and 127.6 mg of galactose per gram of seaweed. Ethanol fermentation of these hydrolysis products using an inoculum concentration of 1.5 mg mL^?1 at 30 °C and 72 h in a shaking incubator at 130 rpm yielded 17.3 mg of ethanol per gram of seaweed.     

Comparison of agarophytes (Gelidium, Gracilaria, and Gracilariopsis) as potential resources for bioethanol production

This study explores the possibility of producing ethanol using the acid hydrolysate of three abundant agar-containing red seaweeds (agarophytes): Gelidium amansii, Gracilaria tenuistipitata, and Gracilariopsis chorda. The main component in the seaweed samples was agar, which ranged from 20 to 51 % (g g^?1 dry weight). After optimizing acid hydrolysis, 100 g of seaweed was hydrolyzed at 130 °C for 15 min with 0.2 M H₂SO₄. Then, 120 mL of a 1:2 mixture of the hydrolysate broth and basal medium was fermented in a 200-mL bottle at 30 °C for 96 h. Of the three seaweeds, G. amansii had the best ethanol yield, producing 0.23 g g^?1 of galactose or 45 % of the theoretical yield. This yield increased to 60 % after detoxification of the hydrolysate with activated carbon.     

Integrated effects of organic,inorganic and biological amendments on methane emission,soil quality and rice productivity in irrigated paddy ecosystem of Bangladesh: field study of two consecutive rice growing seasons

Aims

Effects of different soil amendments were investigated on methane (CH₄) emission, soil quality parameters and rice productivity in irrigated paddy field of Bangladesh.

Methods

The experiment was laid out in a randomized complete block design with five treatments and three replications. The experimental treatments were urea (220 kg ha^?1) + rice straw compost (2 t ha^?1) as a control, urea (170 kg ha^?1) + rice straw compost (2 t ha^?1) + silicate fertilizer, urea (170 kg ha^?1) + sesbania biomass (2 t ha^?1 ) + silicate fertilizer, urea (170 kg ha^?1) + azolla biomass (2 t ha^?1) + cyanobacterial mixture 15 kg ha^?1 silicate fertilizer, urea (170 kg ha^?1) + cattle manure compost (2 t ha^?1) + silicate fertilizer.

Results

The average of two growing seasons CH₄ flux 132 kg ha^?1 was recorded from the conventional urea (220 kg ha^?1) with rice straw compost incorporated field plot followed by 126.7 (4 % reduction), 130.7 (1.5 % reduction), 116 (12 % reduction) and 126 (5 % reduction) kg CH₄ flux ha^?1 respectively, with rice straw compost, sesbania biomass, azolla anabaena and cattle manure compost in combination urea and silicate fertilizer applied plots. Rice grain yield was increased by 15 % and 10 % over the control (4.95 Mg ha^?1) with silicate plus composted cattle manure and silicate plus azolla anabaena, respectively. Soil quality parameters such as soil organic carbon, total nitrogen, microbial biomass carbon, soil redox status and cations exchange capacity were improved with the added organic materials and azolla biofertilizer amendments with silicate slag and optimum urea application (170 kg ha^?1) in paddy field.

Conclusion

Integrated application of silicate fertilizer, well composted organic manures and azolla biofertilizer could be an effective strategy to minimize the use of conventional urea fertilizer, reducing CH₄ emissions, improving soil quality parameters and increasing rice productivity in subtropical countries like Bangladesh.     

Probiotic Effect of <Emphasis Type="Italic">Bacillus licheniformis fb11</Emphasis> on the Digestive Efficiency and Growth Performance in Juvenile <Emphasis Type="Italic">Chitala chitala</Emphasis> (Hamilton, 1822)

Five isocaloric (430 kcal 100 g^?1), isonitrogenous (40% CP) experimental diets were formulated with different concentrations of Bacillus licheniformis fb11 probionts (isolated from the gut of Chitala chitala) viz. Control (without probionts), 5 × 10⁴ CFU g^?1 (D₁), 5 × 10⁵ CFU g^?1 (D₂), 5 × 10⁶ CFU g^?1 (D₃), 5 × 10⁷ CFU g^?1 (D₄), 5 × 10⁸ CFU g^?1 (D₅) to evaluate its efficiency in C. chitala juvenile. The best growth performance, feed utilisation, specific α-amylase, total protease and lipase activity were observed with the diet D₃ (P < 0.05). The lowest Presumptive Pseudomonas Count, Motile Aeromonad Count, Total Coliform Count was observed for D₃ (P < 0.05) on 90th day of trial. Two uppermost values were achieved in case of crude protein for D₃ and D₂ (P > 0.05). The highest lipid content (12.12 ± 0.4 g 100 g^?1) was found for D₅ (P < 0.05). The highest gross energy (18.75 ± 0.21 MJ 100 g^?1) of carcass was recorded for D₃. Thus B. licheniformis fb11 at the concentration 5 × 10⁶ CFU g^?1 as probiotic supplement promoted growth, digestion in C. chitala juvenile significantly by modulating intestinal microflora.     

N2O and CH4 Emissions,and NO3 − Leaching on a Crop-Yield Basis from a Subtropical Rain-fed Wheat–Maize Rotation in Response to Different Types of Nitrogen Fertilizer

Guaranteeing high crop yields while reducing environmental impacts of nitrogen fertilizer use due to associated losses of N₂O emissions and nitrate (NO₃ ^?) leaching is a key challenge in the context of sustainable intensification of crop production. However, few field data sets are available that explore the effect of different forms of N management on yields as well as on N losses in the form of N₂O or NO₃ ^?. Here we report on a large-scale field lysimeter (8 × 4 m²) experiment, which was designed to determine soil CH₄ and N₂O emissions, NO₃ ^? leaching losses and crop yields from a subtropical rain-fed wheat–maize rotation in the Sichuan Basin, one of the most intensively used agricultural regions in China. One control and three different fertilizer treatments with the same total rate of N application (280 kg N ha^?1 y^?1) were included: NF: control (no fertilizer); NPK: synthetic N fertilizer; OMNPK: synthetic N fertilizer plus pig manure; RSDNPK: synthetic N fertilizer plus crop residues. As compared to the standard NPK treatment, annual NO₃ ^? leaching losses for OMNPK and RSDNPK treatments were decreased by 36 and 22%, respectively (P < 0.05). Similarly, crop yield-scaled NO₃ ^? leaching for NPK treatment was higher than those for either OMNPK or RSDNPK treatments (P < 0.05). Direct N₂O emissions for RSDNPK treatment were decreased as compared with NPK and OMNPK treatments (P < 0.05). Furthermore, the yield-scaled GWP (global warming potential) was lower for the treatments where either pig manure or crop residues were incorporated as compared to the standard NPK treatment (P < 0.05). Our study indicates that it is possible to reduce the negative environmental impact of NO₃ ^? leaching and N₂O emissions without compromising crop productivity. Yield-scaled NO₃ ^? leaching, similar to the yield-scaled GWP, represents another valuable-integrated metric to address the dual goals of reducing nitrogen pollution and maintaining crop grain yield for a given agricultural system.     

Interactive effects of soil salinity and boron on growth,mineral composition and CO<Subscript>2</Subscript> assimilation of pistachio seedlings

Pistachio is a tree of the arid and semi-arid regions where salinity and boron (B) toxicity can be major environmental stresses. In this study, individual and combined effects of different concentrations of NaCl (0, 800, 1600, 2400 and 3200 mg kg^?1 soil) and B (0, 2.5, 5.0, 10.0 and 20.0 mg kg^?1 soil) were studied on growth, gas-exchange and mineral composition of pistachio seedlings for a duration of 120 days. Excess amounts of salinity (> 1600 mg NaCl kg^?1 soil) and B (20.0 mg kg^?1 soil) significantly reduced the plant growth and CO₂ assimilation, which was associated with accumulation of Na, Cl and B in leaves. There was also a decline in cell membrane stability index (MSI). Reduced stomatal conductance (g _s) was the primary cause of inhibition of photosynthesis rate (P _N) under mild to moderate salinity. However, under severe salt stress and B toxicity, non-stomatal effects contributed to the inhibition of CO₂ assimilation in addition to the decline in g _s value. Application of 5.0–10.0 mg B kg^?1 soil significantly improved the plant growth and P _N and also recovered the MSI as countermeasures against salt stress. These observations were related to the role of B in cell membrane structure and functioning which reduced the concentration of toxic ions in the leaves. However, cell membrane damages and chlorophyll loss in plants affected by salt were observed to be exacerbated when excess amounts of B were present. In conclusion, the results revealed that optimizing the B nutrition can improve the performance of pistachio seedlings under salt stress, and NaCl also showed a mitigating effect on B toxicity if its concentration in the soil is kept under the plant salt tolerance threshold.     

Plant growth regulator and nitrogen fertilizer effects on soil organic carbon sequestration in creeping bentgrass fairway turf

The objective of this study was to determine the effects of plant growth regulator (PGR) (no PGR, trinexapac-ethyl, and paclobutrazol) and N fertilizer (zero N, an average of 37 kg N ha^?1 month^?1, 6 and 12 kg N ha^?1 week^?1) on soil organic C (SOC) and soil N in creeping bentgrass (Agrostis stolonifera L.) fairway turf. After 4 years of field experiments soil samples were obtained from soil depths of 0–2.5, 2.5–5, 5–7.5, 7.5–10, 10–15, 15–20, and 20–30 cm. Soil bulk density, SOC, total N, NO ₃ ^? –N, and NH ₄ ⁺ –N concentrations were determined. Paclobutrazol and trinexapac-ethyl application increased SOC. The 37 kg N ha^?1 month^?1 application increased SOC at the 0–2.5 cm depth with both PGRs. When paclobutrazol was used, N fertilizer always increased SOC; however, the greatest increase was observed with the 12 kg N ha^?1 week^?1 application when compared to other rates, inversely related to the NH ₄ ⁺ –N concentration. Nitrogen application increased soil total N and NO ₃ ^? –N in the upper three depths. The application of PGRs and N fertilizer to creeping bentgrass fairway turf is an effective strategy for promoting C sequestration.     

Swainsonine,a novel fungal metabolite: optimization of fermentative production and bioreactor operations using evolutionary programming

The optimization of bioreactor operations towards swainsonine production was performed using an artificial neural network coupled evolutionary program (EP)-based optimization algorithm fitted with experimental one-factor-at-a-time (OFAT) results. The effects of varying agitation (300–500 rpm) and aeration (0.5–2.0 vvm) rates for different incubation hours (72–108 h) were evaluated in bench top bioreactor. Prominent scale-up parameters, gassed power per unit volume (P _g/V _L, W/m³) and volumetric oxygen mass transfer coefficient (K _L a, s^?1) were correlated with optimized conditions. A maximum of 6.59 ± 0.10 μg/mL of swainsonine production was observed at 400 rpm-1.5 vvm at 84 h in OFAT experiments with corresponding P _g/V_L and K _L a values of 91.66 W/m³ and 341.48 × 10^?4 s^?1, respectively. The EP optimization algorithm predicted a maximum of 10.08 μg/mL of swainsonine at 325.47 rpm, 1.99 vvm and 80.75 h against the experimental production of 7.93 ± 0.52 μg/mL at constant K _L a (349.25 × 10^?4 s^?1) and significantly reduced P _g/V _L (33.33 W/m³) drawn by the impellers.     

Root distribution in relation to soil nitrogen availability in field-grown tomatoes

Tomato root growth and distribution were related to inorganic nitrogen (N) availability and turnover to determine 1) if roots were located in soil zones where N supply was highest, and 2) whether roots effectively depleted soil N so that losses of inorganic N were minimized. Tomatoes were direct-seeded in an unfertilized field in Central California. A trench profile/monolith sampling method was used. Concentrations of nitrate (NO₃ ^-) exceeded those of ammonium (NH₄ ⁺) several fold, and differences were greater at the soil surface (0–15 cm) than at lower depths (45–60 cm or 90–120 cm). Ammonium and NO₃ ^- levels peaked in April before planting, as did mineralizable N and nitrification potential. Soon afterwards, NO₃ ^- concentrations decreased, especially in the lower part of the profile, most likely as a result of leaching after application of irrigation water. Nitrogen pool sizes and rates of microbial processes declined gradually through the summer.Tomato plants utilized only a small percentage of the inorganic N available in the large volume of soil explored by their deep root systems; maximum daily uptake was approximately 3% of the soil pool. Root distribution, except for the zone around the taproot, was uniformly sparse (ca. 0.15 mg dry wt g^-1 soil or 0.5 cm g^-1 soil) throughout the soil profile regardless of depth, distance from the plant stem, or distance from the irrigation furrow. It bore no relation to N availability. Poor root development, especially in the N-rich top layer of soil, could explain low fertilizer N use by tomatoes.     

Short-term effects of crop rotation,residue management,and soil water on carbon mineralization in a tropical cropping system

The purpose of this study was to investigate the short-term effects of maize (Zea mays)-fallow rotation, residue management, and soil water on carbon mineralization in a tropical cropping system in Ghana. After 15 months of the trial, maize–legume rotation treatments had significantly (P?C ₀ (μg CO₂–C g^?1) than maize–elephant grass (Pennisetum purpureum) rotations. The C ₀ for maize–grass rotation treatments was significantly related to the biomass input (r?=?0.95; P?=?0.05), but that for the maize–legume rotation was not. The soil carbon mineralization rate constant, k (per day), was also significantly related to the rotation treatments (P?k values for maize–grass and maize–legume rotation treatments were 0.025 and 0.036 day^?1 respectively. The initial carbon mineralization rate, m ₀ (μg CO₂–C g^?1 day ^?1), was significantly (P?θ. The m ₀ ranged from 3.88 to 18.67 and from 2.30 to 15.35 μg CO₂–C g^?1 day^?1 for maize–legume and maize–grass rotation treatments, respectively, when the soil water varied from 28% to 95% field capacity (FC). A simple soil water content (θ)-based factor, f _w, formulated as: \(f_{\text{w}} = \left[ {\frac{{\theta - \theta _{\text{d}} }}{{\theta _{{\text{FC}}} - \theta _{\text{d}} }}} \right]\), where θ _d and θ _FC were the air-dry and field capacity soil water content, respectively, adequately described the variation of the m ₀ with respect to soil water (R ²?=?0.91; RMSE?=?1.6). Such a simple relationship could be useful for SOC modeling under variable soil water conditions.     

Measurement of net ecosystem exchange,productivity and respiration in three spruce forests in Sweden shows unexpectedly large soil carbon losses

Measurement of net ecosystem exchange was made using the eddy covariance method above three forests along a north-south climatic gradient in Sweden: Flakaliden in the north, Knottåsen in central and Asa in south Sweden. Data were obtained for 2 years at Flakaliden and Knottåsen and for one year at Asa. The net fluxes (N_ep) were separated into their main components, total ecosystem respiration (R_t) and gross primary productivity (P_g). The maximum half-hourly net uptake during the heart of the growing season was highest in the southernmost site with ?0.787 mg CO₂ m^?2 s^?1 followed by Knottåsen with ?0.631 mg CO₂ m^?2 s^?1 and Flakaliden with ?0.429 mg CO₂ m^?2 s^?1. The maximum respiration rates during the summer were highest in Knottåsen with 0.245 mg CO₂ m^?2 s^?1 while it was similar at the two other sites with 0.183 mg CO₂ m^?2 s^?1. The annual N_ep ranged between uptake of ?304 g C m^?2 year^?1 (Asa) and emission of 84 g C m^?2 year^?1 (Knottåsen). The annual R_t and P_g ranged between 793 to 1253 g C m^?2 year^?1 and ?875 to ?1317 g C m^?2 year^?1, respectively. Biomass increment measurements in the footprint area of the towers in combination with the measured net ecosystem productivity were used to estimate the changes in soil carbon and it was found that the soils were losing on average 96–125 g C m^?2 year^?1. The most plausible explanation for these losses was that the studied years were much warmer than normal causing larger respiratory losses. The comparison of net primary productivity and P_g showed that ca 60% of P_g was utilized for autotrophic respiration.     

Influence of organic and inorganic sources of nutrients on the functional diversity of microbial communities in the vegetable cropping system of the Indo-Gangetic plains

The aim of the present study was to assess the effects of different organic and inorganic fertilizers on the functional diversity of soil microbial community under a vegetable production system. The Biolog^® Eco-plate technique and indices, such as average well-colour development (AWCD), McIntosh and Shannon diversity were employed to study the diversity of soil microorganisms. The AWCD, i.e. overall utilization of carbon sources, suggested that different organic treatments had a significant impact on the metabolic activity of soil microorganisms. After 120 h, the highest AWCD values were observed in poultry manure (2.5 t·ha^?1) + vermicompost (3.5 t·ha^?1) (0.63) and farm yard manure (FYM) (10 t·ha^?1) + vermicompost (3.5 t·ha^?1) (0.61). After 72 h, the highest value of the McIntosh diversity index was recorded in poultry manure (2.5 t·ha^?1) + vermicompost (3.5 t·ha^?1) (3.87), followed by poultry manure (2.5 t·ha^?1) + vermicompost (3.5 t·ha^?1) + biofertilizers (Azotobacter 500 g·ha^?1 applied as seed treatment) (3.12). In the case of the Shannon diversity index, the highest values were noticed in organic treatments; however, there was no significant differences between organic and inorganic treatments. Biplot analysis showed a clear differentiation of organic treatments from the inorganic control. The amino acids, phenolics and polymer utilizing microorganisms were dominant in organic treatments. Inorganic control recorded the lowest values of the microbial diversity indices. Through this study, we have identified the best combination of organic nutrients, i.e. poultry manure (2.5 t·ha^?1) + vermicompost (3.5 t·ha^?1) for the stimulation of metabolically active soil microbial communities.     

Soil mineralizable nitrogen and soil nitrogen supply under two-year potato rotations

Two-year potato rotations were evaluated for their effects on soil mineralizable N and soil N supply. Pre-plant soil samples (0–15 cm) collected from the potato year after seven rotation cycles were used to estimate soil mineralizable N using a 24 week aerobic incubation. Potentially mineralizable N (N ₀ ) ranged from 102 to 149 kg N ha^?1, and was greater after pea/white clover and oats/Italian ryegrass than after oats by an average of 35 and 22%, respectively. Labile, intermediate and stable mineralizable N pools were increased after pea/white clover compared with oats, whereas only the stable mineralizable N pool was increased after oats/Italian ryegrass. Potato plant N uptake with no fertilizer applied was greater in potato-pea/white clover compared with the three other rotations (126 vs. average of 67 kg N ha^?1). Choice of rotation crop in potato production influences both the quantity and quality of soil mineralizable N.     

Long-term field fertilization alters the diversity of autotrophic bacteria based on the ribulose-1,5-biphosphate carboxylase/oxygenase (RubisCO) large-subunit genes in paddy soil

Carbon dioxide (CO₂) assimilation by autotrophic bacteria is an important process in the soil carbon cycle with major environmental implications. The long-term impact of fertilizer on CO₂ assimilation in the bacterial community of paddy soils remains poorly understood. To narrow this knowledge gap, the composition and abundance of CO₂-assimilating bacteria were investigated using terminal restriction fragment length polymorphism and quantitative PCR of the cbbL gene [that encodes ribulose-1,5-biphosphate carboxylase/oxygenase (RubisCO)] in paddy soils. Soils from three stations in subtropical China were used. Each station is part of a long-term fertilization experiment with three treatments: no fertilizer (CK), chemical fertilizers (NPK), and NPK combined with rice straw (NPKM). At all of the stations, the cbbL-containing bacterial communities were dominated by facultative autotrophic bacteria such as Rhodopseudomonas palustris, Bradyrhizobium japonicum, and Ralstonia eutropha. The community composition in the fertilized soil (NPK and NPKM) was distinct from that in unfertilized soil (CK). The bacterial cbbL abundance (3–8?×?10⁸ copies g soil^?1) and RubisCO activity (0.40–1.76 nmol CO₂ g soil^?1 min^?1) in paddy soils were significantly positively correlated, and both increased with the addition of fertilizer. Among the measured soil parameters, soil organic carbon and pH were the most significant factors influencing the community composition, abundance, and activity of the cbbL-containing bacteria. These results suggest that long-term fertilization has a strong impact on the activity and community of cbbL-containing bacterial populations in paddy soils, especially when straw is combined with chemical fertilizers.     

Temporal and spectral characterization of the photosynthetic reaction center from Heliobacterium modesticaldum

A time-resolved spectroscopic study of the isolated photosynthetic reaction center (RC) from Heliobacterium modesticaldum reveals that thermal equilibration of light excitation among the antenna pigments followed by trapping of excitation and the formation of the charge-separated state P₈₀₀ ⁺A₀ ^– occurs within ~25 ps. This time scale is similar to that reported for plant and cyanobacterial photosystem I (PS I) complexes. Subsequent electron transfer from the primary electron acceptor A₀ occurs with a lifetime of ~600 ps, suggesting that the RC of H. modesticaldum is functionally similar to that of Heliobacillus mobilis and Heliobacterium chlorum. The (A₀ ^– ? A₀) and (P₈₀₀ ⁺ ? P₈₀₀) absorption difference spectra imply that an 8¹-OH-Chl a _F molecule serves as the primary electron acceptor and occupies the position analogous to ec3 (A₀) in PS I, while a monomeric BChl g pigment occupies the position analogous to ec2 (accessory Chl). The presence of an intense photobleaching band at 790 nm in the (A₀ ^– ? A₀) spectrum suggests that the excitonic coupling between the monomeric accessory BChl g and the 8¹-OH-Chl a _F in the heliobacterial RC is significantly stronger than the excitonic coupling between the equivalent pigments in PS I.     

Fourteen Annually Repeated Droughts Suppressed Autotrophic Soil Respiration and Resulted in an Ecosystem Change

Predictions of future climate over the next 100 years show that the frequency of long periods of droughts in summer will increase in the Netherlands. This study investigated the effect of 14 annually repeated droughts on soil respiration at a Dutch heathland. Field measurements of total soil respiration (R_S) and microbial respiration (R_H) were modeled to determine annual C losses and to derive root respiration (R_A) C losses. The application of repeated droughts resulted in suppression of the total soil C loss from 392 to 332 g C m^?2 year^?1 in 2010–2011 and from 427 to 358 g C m^?2 year^?1 in 2011–2012. The R_H was the greatest contributor to heathland soil C loss (74–76%) and this was suppressed when directly exposed to drought conditions, although not significantly reduced on an annual basis. Annual R_A was suppressed by 42% (2010–2011) and 45% (2011–2012) under repeated drought, indicating there was a greater effect of the repeated annual drought in roots than in microbes. Field observations of photosynthesis (P_G) showed paradoxical results, with significantly greater ecosystem P_G on the drought treatment than the control treatment. Inclusion of plant activity (P_G) as a variable did not improve the fit of the models used in this study. However, other changes in plant composition and structure, such as increasing moss cover on the drought treatment, were noted to have occurred during the 14 years of annually repeated drought and these long term trends may help explain the effects of climate change (drought) on soil processes.     

Soil CO2 efflux and soil carbon balance of a tropical rubber plantation

Natural rubber is a valuable source of income in many tropical countries and rubber trees are increasingly planted in tropical areas, where they contribute to land-use changes that impact the global carbon cycle. However, little is known about the carbon balance of these plantations. We studied the soil carbon balance of a 15-year-old rubber plantation in Thailand and we specifically explored the seasonal dynamic of soil CO₂ efflux (F _S) in relation to seasonal changes in soil water content (W _S) and soil temperature (T _S), assessed the partitioning of F _S between autotrophic (R _A) and heterotrophic (R _H) sources in a root trenching experiment and estimated the contribution of aboveground and belowground carbon inputs to the soil carbon budget. A multiplicative model combining both T _S and W _S explained 58 % of the seasonal variation of F _S. Annual soil CO₂ efflux averaged 1.88 kg C m^?2 year^?1 between May 2009 and April 2011 and R _A and R _H accounted for respectively 63 and 37 % of F _S, after corrections of F _S measured on trenched plots for root decomposition and for difference in soil water content. The 4-year average annual aboveground litterfall was 0.53 kg C m^?2 year^?1 while a conservative estimate of belowground carbon input into the soil was much lower (0.17 kg C m^?2 year^?1). Our results highlighted that belowground processes (root and rhizomicrobial respiration and the heterotrophic respiration related to belowground carbon input into the soil) have a larger contribution to soil CO₂ efflux (72 %) than aboveground litter decomposition.     

Selection of phosphate-solubilizing diazotrophic Herbaspirillum and Burkholderia strains and their effect on rice crop yield and nutrient uptake

Background and Aims

Plant growth-promoting bacteria, mainly diazotrophs and phosphate solubilizers, can reduce the use of chemical fertilizers for rice crops. Here, diazotrophic bacteria isolated from rice were screened for their ability to solubilize inorganic P (P_i) in vitro and in association with rice plants cultivated in pots.

Methods

Forty-nine isolates were tested for the ability to solubilize P_i on NBRIP and GL agar plate media and seven selected strains were further evaluated in NBRIP liquid medium. Three of these strains were inoculated in rice plants grown in soil pots containing ¹⁵N-labeled fertilizer and two sources of P: tricalcium phosphate (TCP) or simple superphosphate (SSP). The dry matter, yield, N, P, and the ¹⁵N content accumulated in plant tissues were measured at 135 days after planting.

Results

Seven strains belonging to the genera Herbaspirillum and Burkholderia formed a halo of solubilized P_i on agar plates. The Burkholderia strains showed peak soluble P (around 200 mg P L^?1) on the fifth day when grown in NBRIP liquid medium for 14 days. Inoculation of Herbaspirillum strains (H18, ZA15) and a Burkholderia vietaminensis strain (AR114) increased rice grain yield from 33 to 47 % with TCP and 18 to 44 % with TSS, respectively. The bacterial inoculation led to enhanced N-use efficiency of the ¹⁵N-labeled fertilizer.

Conclusion

These results suggest that the selection and use of P-solubilizing diazotrophic bacteria are a good strategy to promote P solubilization and/or N use efficiency in rice plants.     

Ozone pollution influences soil carbon and nitrogen sequestration and aggregate composition in paddy soils

Background and aims

Much attention has focused on the effects of tropospheric ozone (O₃) on terrestrial ecosystems and plant growth. Since O₃ pollution is currently an issue in China and many parts of the world, understanding the effects of elevated O₃ on soil carbon (C) and nitrogen (N) sequestration is essential for efforts to predict C and N cycles in terrestrial ecosystems under predicted increases in O₃. Thus the main objective of this study was to determine whether an increases in atmospheric O₃ concentration influenced soil organic C (SOC) and N sequestration.

Methods

A free-air O₃ enrichment (O₃-FACE) experiment was started in 2007 and used continuous O₃ exposure from March to November each year during crop growth stage in a rice (Oryza sativa L.)—wheat (Triticum aestivum L.) rotation field in the Jiangsu Province, China. We investigated differences in SOC and N and soil aggregate composition in both elevated and ambient O₃ conditions.

Results

Elevated atmospheric O₃ (18–80 nmol mol^?1 or 50 % above the ambient) decreased the SOC and N concentration in the 0–20 cm soil layer after 5 years. Elevated O₃ significantly decreased the SOC concentration by 17 % and 5.6 % in the 0–3 cm and the 10–20 cm layers, respectively. Elevated O₃ significantly decreased the N concentration by 8.2–27.8 % in three layers at the 20 cm depth. In addition, elevated O₃ influenced the formation and transformation of soil aggregates and the distribution of SOC and N in the aggregates across soil layer classes. Elevated O₃ significantly decreased the macro-sized aggregate fraction (16.8 %) and associated C and N (0.5 g kg^?1 and 0.32 g kg^?1, respectively), and significantly increased the silt+ clay-sized aggregate fraction (61 %) and associated C (1.7 g kg^?1) in the 0–3 cm layer. Elevated O₃ significantly decreased the macro-sized aggregate fraction (9.6 %) and associated C and N (1.4 g kg^?1 and 0.35 g kg^?1, respectively), and significantly increased the silt+ clay-sized aggregate fraction (41.8 %) and decreased the corresponding associated N (0.14 g kg^?1) in the 3–10 cm layer. Elevated O₃ did not significantly effect the formation and transformation of aggregates in the 10–20 cm layer, yet it did significantly increase the C concentration in the macro-sized fraction (1 g kg^?1) and decrease the N concentration in the macro- and micro-sized fractions (0.24 g kg^?1 and 0.16 g kg^?1, respectively).

Conclusion

Long-term exposure to elevated atmospheric O₃ negatively affected the physical structure of the soil and impaired soil C and N sequestration.     

Soil CO2 efflux in response to the addition of water and fertilizer in temperate semiarid grassland in northern China

Background and aims

Knowledge about the effects of water and fertilizer on soil CO₂ efflux (SCE) and Q ₁₀ is essential for understanding carbon (C) cycles and for evaluating future global C balance. A two-year field experiment was conducted to determine the effects of water, fertilizer, and temperature on SCE in semiarid grassland in northern China.

Methods

SCE, as well as environmental factors was measured in two grasslands, one with bunge needlegrass (BNE, Stipa bungeana) and one with purple alfalfa (ALF, Medicago sativa), with four treatments: CK (unwatered and unfertilized); W (50 mm water addition yr^?1); F (50 kg phosphorus (P) fertilizer ha^?1 yr^?1 for ALF, 100 kg nitrogen (N)?+?50 kg P fertilizer ha^?1 yr^?1 for BNE); and W + F.

Results

During the 11-month experimental period from July 2010 to October 2011, the addition of water consistently stimulated mean SCE in BNE and ALF, and the positive effects were relatively stronger during dry seasons. P fertilization consistently enhanced SCE in ALF, and the positive effect was strongly dependent on the availability of soil water. The effects of N plus P fertilization on SCE in BNE varied seasonally from significant increases to small reductions to no response. Water addition increased the Q ₁₀ of SCE in ALF by 11 % but had no effect in BNE. Fertilization, however, reduced the Q ₁₀ of SCE by 21 % and 13 % for BNE and ALF, respectively. Models that rely only on Q ₁₀ underestimated the emissions of soil CO₂ by 8–15 % at the study site, which was mediated by species and treatment.

Conclusions

Responses of SCE and its temperature sensitivity to water and fertilizer may vary with species and depend on the period of measurement. Models of SCE need to incorporate the availability of ecosystemic water and nutrients, as well as species, and incorporate different environmental factors when determining the impact of water, nutrients, and species on SCE.