The effects of long-term fertilization on the accumulation of organic carbon in the deep soil profile of an oasis farmland

Background and aims

Deeper soils represent a poorly understood, but potentially important, sink for carbon sequestration. The objective of this study was to determine the effects of long-term fertilization on soil organic carbon (SOC), its labile fractions and aggregate-associated carbon throughout a 0–3 m soil profile.

Methods

The investigation was conducted in a field experiment started in 1990 in an oasis farmland cropped with winter wheat. The following treatments were compared with the desert from which the oasis was created: CK (no fertilizer), NPK, N2P2K, NPKR, and N2P2R2 (“2” for double fertilizer and “R” for straw residue)

Results

SOC contents increased by 14–56 % in the topsoil (0–0.2 m), but decreased by 15–22 % in the subsoil (0.2–0.6 m) under all fertilizer treatments. In the deep layer (0.6–3 m) there were significant differences between the treatments: SOC decreased by 5–9 % in treatments without straw, but increased by 4–9 % in treatments with straw. Labile fractions (particulate organic carbon and light fraction organic carbon) also showed similar trends. Both the fertilizer and CK treatments led to an increase in the amount of macro-aggregates (>0.25 mm), especially small macro-aggregates (0.25–2 mm), throughout the soil profile. SOC content was highest in the macro-aggregates, intermediate in the silt + clay fraction (<0.053 mm), and lowest in the micro-aggregates (0.25–0.053 mm). However, 44–87 % of total SOC was stored in the silt + clay fraction, especially in the deep layer (at least 80 %).

Conclusions

After 20 years of fertilizer applications, difference in SOC mainly occurred in the deep layer, and preservation of SOC in the silt + clay fraction appeared to be a prerequisite for soil-carbon sequestration. Applying inorganic fertilizer alone decreased SOC content in the silt + clay fraction in the deep layer, while the combined applications with straw resulted in higher SOC content in the silt + clay fraction in that layer, which turned out to be the main mechanism for increasing SOC content. Our study indicated that applying straw with inorganic fertilizer is the best practice for carbon sequestration, which occurred mainly in the deep soil layer.     

Summer rain pulses may stimulate a CO2 release rather than absorption in desert halophyte communities

Background and aims

The response of plants and soil to rain pulses determines seasonal variations in the exchange of materials and energy at the ecosystem scale in arid and semi-arid regions. We assessed how the ecosystem carbon exchange (NEE) of desert halophyte communities of different plant functional-types responds to summer precipitation pulses in Tamarix and Haloxylon communities.

Methods

Plant water status, photosynthetic gas exchange, soil respiration and net ecosystem carbon exchange were measured to test the hypothesis that high physiological sensitivity may induce a greater changes in NEE resulting from the summer precipitation pulses in Haloxylon community.

Results

Plant water status and photosynthetic assimilation did not differ before and after summer precipitation pulses in either community. In contrast, soil respiration and NEE responded strongly to summer precipitation events in both communities. At the ecosystem level, precipitation pulses induced a pulse of CO₂ release, rather than absorption. The NEE response to summer precipitation was less in the deep-rooted Tamarix community, compared to the shallow-rooted Haloxylon community, which was even converted into a carbon source after summer precipitation inputs. As a result, the effect of summer precipitation inputs on soil respiration was more important than the plant (carbon assimilation) response in determining the ecosystem response to episodic precipitation pulses.     

A core functional region of the RFP1 promoter from Chinese wild grapevine is activated by powdery mildew pathogen and heat stress

RING-finger proteins (RFP) function as ubiquitin ligases and play key roles in plant responses to biotic and abiotic stresses. However, little information is available on the regulation of RFP expression. Here, we isolate and characterize the RFP promoter sequence from the disease-resistant Chinese wild grape Vitis pseudoreticulata accession Baihe-35-1. Promoter-GUS fusion assays revealed that defense signaling molecules, powdery mildew infection, and heat stress induce VpRFP1 promoter activity. By contrast, the RFP1 promoter isolated from Vitis vinifera was only slightly induced by pathogen infection and heat treatment. By promoter deletion analysis, we found that the ?148 bp region of the VpRFP1 promoter was the core functional promoter region. We also found that, in Arabidopsis, VpRFP1 expressed under its own promoter activated defense-related gene expression and improved disease resistance, but the same construct using the VvRFP1 promoter slightly improve disease resistance. Our results demonstrated that the ?148 bp region of the VpRFP1 promoter plays a key role in response to pathogen and heat stress, and suggested that expression differences between VpRFP1 and VvRFP1 may be key for the differing disease resistance phenotypes of the two Vitis genotypes.     

Sodium Taurocholate Cotransporting Polypeptide Mediates Woolly Monkey Hepatitis B Virus Infection of Tupaia Hepatocytes

Primary Tupaia hepatocytes (PTHs) are susceptible to woolly monkey hepatitis B virus (WMHBV) infection, but the identity of the cellular receptor(s) mediating WMHBV infection of PTHs remains unclear. Recently, sodium taurocholate cotransporting polypeptide (NTCP) was identified as a functional receptor for human hepatitis B virus (HBV) infection of primary human and Tupaia hepatocytes. In this study, a synthetic pre-S1 peptide from WMHBV was found to bind specifically to cells expressing Tupaia NTCP (tsNTCP) and it efficiently blocked WMHBV entry into PTHs; silencing of tsNTCP in PTHs significantly inhibited WMHBV infection. Ectopic expression of tsNTCP rendered HepG2 cells susceptible to WMHBV infection. These data demonstrate that tsNTCP is a functional receptor for WMHBV infection of PTHs. The result also indicates that NTCP''s orthologs likely act as a common cellular receptor for all known primate hepadnaviruses.     

Infection Status of Hydatid Cysts in Humans and Sheep in Uzbekistan

Uzbekistan is endemic of cystic echinococcosis (CE). In order to estimate endemicity of CE, we collected data from emergency surgery due to CE in 2002-2010 and also investigated the prevalence of hydatid cysts in the liver and lungs of sheep at an abattoir in Uzbekistan from July 2009 to June 2010. In 14 emergency hospitals, 8,014 patients received surgical removal or drainage of CE during 2002-2010, and 2,966 patients were found in 2010. A total of 22,959 sheep were grossly examined of their liver and lungs, and 479 (2.1%) and 340 (1.5%) of them were positive for the cyst in the liver and lungs, respectively. Echinococcus granulosus is actively transmitted both to humans and sheep, and CE is a zoonotic disease of public health priority in Uzbekistan.     

Correlations and comparisons of quantitative trait loci with family per se and testcross performance for grain yield and related traits in maize

Simultaneous improvement in grain yield and related traits in maize hybrids and their parents (inbred lines) requires a better knowledge of genotypic correlations between family per se performance (FP) and testcross performance (TP). Thus, to understand the genetic basis of yield-related traits in both inbred lines and their testcrosses, two F _2:3 populations (including 230 and 235 families, respectively) were evaluated for both FP and TP of eight yield-related traits in three diverse environments. Genotypic correlations between FP and TP, $ \hat{r}_{\text{g}} $ (FP, TP), were low (0–0.16) for grain yield per plant (GYPP) and kernel number per plant (KNPP) in the two populations, but relatively higher (0.32–0.69) for the other six traits with additive effects as the primary gene action. Similar results were demonstrated by the genotypic correlations between observed and predicted TP values based on quantitative trait loci positions and effects for FP, $ \hat{r}_{\text{g}} $ (M _FP, Y _TP). A total of 88 and 35 QTL were detected with FP and TP, respectively, across all eight traits in the two populations. However, the genotypic variances explained by the QTL detected in the cross-validation analysis were much lower than those in the whole data set for all traits. Several common QTL between FP and TP that accounted for large phenotypic variances were clustered in four genomic regions (bin 1.10, 4.05–4.06, 9.02, and 10.04), which are promising candidate loci for further map-based cloning and improvement in grain yield in maize. Compared with publicly available QTL data, these QTL were also detected in a wide range of genetic backgrounds and environments in maize. These results imply that effective selection based on FP to improve TP could be achieved for traits with prevailing additive effects.     

Heterotrophic nitrification and aerobic denitrification by a novel Halomonas campisalis

A novel halophilic strain that could carry out heterotrophic nitrification and aerobic denitrification was isolated and named as Halomonas campisalis ha3. It removed inorganic nitrogen compounds (e.g. NO₃ ^?, NO₂ ^? and NH₄ ⁺) simultaneously, and grew well in the medium containing up to 20 % (w/v) NaCl. PCR revealed four genes in the genome of ha3 related to aerobic denitrification: napA, nirS, norB and nosZ. The optimal conditions for aerobic denitrification were pH 9.0, at 37 °C, with 4 % (w/v) NaCl and sodium succinate as carbon source. The nitrogen removal rate was 87.5 mg NO₃ ^?–N l^?1 h^?1. Therefore, this strain is a potential aerobic denitrifier for the treatment of saline wastewater.     

Towards a hybrid anaerobic digester-microbial fuel cell integrated energy recovery system: An overview of the development of an electrogenic biofilm

An electrogenic biofilm was developed on a macroporous chitosan-carbon nanotube (CHIT-CNT) electrode under constant poised potential (?0.25 V versus Ag/AgCl reference electrode) and flow through conditions utilizing the effluent of an anaerobic digester as both the inoculant and substrate for the electrogenic biofilm. After 125 days of inoculation the bioelectrode demonstrated an open circuit potential of ?0.62 V and a current density of 9.43 μA cm^?3 (at ?0.25 V). Scanning electron microscopy images indicate thorough surface coverage of the biofilm with a high density of bacterial nanowires physically connecting bacteria to bacteria and bacteria to carbon nanotube (electrode surface) suggesting the nanowires are electrically conductive. DGGE was used to identify the major bacterial and archaeal populations.