Congzhi Zhang

Characterization of genetic diversity of Frankia strains in nodules of Alnus nepalensis (D. Don) from the Hengduan Mountains on the basis of PCR-RFLP analysis of the nifD-nifK IGS

Nodule samples from 90A. nepalensis individuals were collected at five sites in the Hengduan Mountains. PCR-RFLP analysis of IGS betweennifD andnifK genes was directly applied to unculturedFrankia strains in the nodules. Sizes of thenifD-nifK IGS amplicons and genetic distance between the RFLP patterns from these samples were noticeably different, indicating significant genetic variation in theFrankia population. There were some nodule samples, which produced more than one PCR fragment, and compound RFLP patterns, indicating thatFrankia strains with different PCR-RFLP patterns coexisted in the same host plant under natural conditions. Among the 29 restriction patterns obtained, 5 patterns were found in more than one population and occurred in the majority of samples, while each of the other 24 patterns were represented by only one or two samples and were endemic to a particular population. From the calculatedGst and UPGMA cluster analysis, genetic diversity ofFrankia strains was inferred to be related to climate and glaciation history in the Hengduan Mountains.

Removal of bacteriophages MS2 and phiX174 from aqueous solutions using a red soil

Adsorption and desorption of viruses onto and from an adsorbent may have a dominant role in evaluating removal efficiency of a material. This study evaluated the effectiveness of a red soil from south part of China to remove two viruses, MS2 and phiX174, by adsorption from dilute aqueous solutions using a set of equilibrium and kinetic batch experiments. The effect of presence/absence of autochthonous microorganisms was also investigated. The results showed that when the autochthonous microorganisms were present, the red soil adsorbed more than 99.95% of MS2 and 98.23% of phiX174, in which most of them were inactivated and/or irreversibly adsorbed. Sterilization led to an increase in MS2 adsorption, while decreased the adsorption of phiX174, indicating that sterilization-induced virus adsorption is virus type dependent. Fewer viruses could be desorbed from the sterilized soil as compared to the nonsterilized soil, probably because sterilization led to an increase in the strength of adsorption force between the soil and viruses. Though the overall virus removal efficiency by the red soil was less than the USPEA required value of 99.99%, we suggest the potential of the red soil as a starting material in removing water heavily polluted with viruses.

Acid and Alkali Buffer Capacity of Typical Fluvor-Aquic Soil in Huang-Huai-Hai Plain

Soil acid and alkali buffer capacity, as a major indicator for evaluating its vulnerability and resistibility to acidification and alkalization, is an important factor affecting the sustainable agriculture, through knowledge on which soil acidification process can be predicted and modified. In this study, titration curve method was adopted to investigate the pH buffer capacity (pHBC) of fluvor-aquic soil, and separate titration curves were established by adding incremental amounts of either standardized hydrochloric acid (HCl) (0.12 mol L−1) or sodium hydroxide (NaOH) (0.10 mol L−1) to soil suspended in deionized water (soil:solution = 1:5). Soil pH was measured after 7 d resuspension and isothermal equilibrium (T = 25°C). Linear regressions were fitted to the linear portion of each titration curve and the slopes of these lines were derived as the soil pHBC. The results showed that significant correlations between the amounts of adding acid or alkali and each pH change were presented, and titration curve method was feasible for measurement of pHBC on typical fluvor-aquic soil in Huang-Huai-Hai Plain, and the coefficients of determination were higher than the similar researches on acid soil (R2 = 0.96). The slope-derived pHBC of acid and alkali were 158.71 and 25.02 mmol kg−1, respectively. According to the classification of soil buffer systems, the soil tested belongs to the calcium carbonate buffer system, carbonates contribute the most to pHBC, and the contribution of soil organic matter relatively less than it.

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.

Temperature and Straw Quality Regulate the Microbial Phospholipid Fatty Acid Composition Associated with Straw Decomposition

Abstract Variations in temperature and moisture play an important role in soil organic matter (SOM) decomposition. However, relationships between changes in microbial community composition induced by increasing temperature and SOM decomposition are still unclear. The present study was conducted to investigate the effects of temperature and moisture levels on soil respiration and microbial communities involved in straw decomposition and elucidate the impact of microbial communities on straw mass loss. A 120-d litterbag experiment was conducted using wheat and maize straw at three levels of soil moisture (40%, 70%, and 90% of water-holding capacity) and temperature (15, 25, and 35 °C). The microbial communities were then assessed by phospholipid fatty acid (PLFA) analysis. With the exception of fungal PLFAs in maize straw at day 120, the PLFAs indicative of Gram-negative bacteria and fungi decreased with increasing temperatures. Temperature and straw C/N ratio significantly affected the microbial PLFA composition at the early stage, while soil microbial biomass carbon (C) had a stronger effect than straw C/N ratio at the later stage. Soil moisture levels exhibited no significant effect on microbial PLFA composition. Total PLFAs significantly influenced straw mass loss at the early stage of decomposition, but not at the later stage. In addition, the ratio of Gram-negative and Gram-positive bacterial PLFAs was negatively correlated with the straw mass loss. These results indicated that shifts in microbial PLFA composition induced by temperature, straw quality, and microbial C sources could lead to changes in straw decomposition.

Mechanisms for the relationships between water-use efficiency and carbon isotope composition and specific leaf area of maize (Zea mays L.) under water stress

Abstract The quick assessment approaches for accurately measuring water-use efficiency (WUE) in maize under water stress are important to water-saving agriculture. We investigated how and whether carbon isotope composition (δ13C) and specific leaf area (SLA) could be used to assess WUE for maize as influenced by water stress. A pot experiment was conducted twice during six typical maize (Zea mays) growth stages of seedling, jointing, booting, tasseling, filling and maturity, respectively. The ratio between the activities of ribulose 1,5-bisphosphate carboxylase (Rubisco) and phosphoenolpyruvate carboxylase decreased bundle sheath leakiness (φ) under water deficiency, caused more 13C to be assimilated, and resulted in increased δ13C in leaves. Water stress increased the fractionation of 13C when assimilates were transported from leaf to stem, indicating that water stress affected leaf expansion and translocation of assimilates from leaf to stem, and resulted in thicker leaves and lower SLA. WUE showed significant positive correlations with leaf δ13C and SLA, implying that leaf δ13C and SLA could effectively reflect the drought adaptation and high WUE under different water conditions.

Habitat correlation of Symbiodinium diversity in two reef-building coral species in an upwelling region, eastern Hainan Island, China

Reef-building corals are fundamental to the most diverse marine ecosystems, and the coral-dinoflagellate (zooxanthellae) associations on fine scale remains largely unknown. Spatial variation in the diversity of symbiotic dinoflagellates of two scleractinian coral species was studied in an upwelling region near Qinlan Harbor in eastern Hainan Island, China. Results showed that stress-tolerant Symbiodinium trenchi in individual colonies of Galaxea fascicularis occurred more frequently in shallow back-reef than in deep fore-reef. The higher symbiont diversity was found in colonies of G. fascicularis in shallow and close to the harbour mouth whereas the coral Pocillipora damicornis always harboured Symbiodinium internal transcribed spacer 2 (ITS2) types C1c or C42a. Furthermore, both corals were found to simultaneously contain Symbiodinium ITS2 types belonging to two distinct phylogenetic clades (C and D). This indicates that the distribution of genetically distinct Symbiodinium may correlate with light regime and possibly temperature in some (but not all) colonies at particular locations, which we interpret as holobiont acclimation to the local environmental conditions. Therefore, we conclude that reef-building corals can adapt to the local environment by harbouring genetically distinct symbionts but depend on their respective symbiont transmission modes.

Stable Isotope Studies of Crop Carbon and Water Relations: A Review

Abstract Crop carbon and water relations research is important in the studies of water saving agriculture, breeding program, and energy and material cycles in soil plant atmosphere continuum (SPAC). The purpose of this paper is to review the current state of knowledge on stable isotopes of carbon, oxygen, and hydrogen in the research of crop carbon and water relations, such as carbon isotope discrimination (Δ13C) during carbon fixation process by photosynthesis, application of Δ13C in crop water use efficiency (WUE) and breeding programs, oxygen isotope enrichment during leaf water transpiration, CO2 fixation by photosynthesis and release by respiration, application of hydrogen isotope composition (δD) and oxygen isotope composition (δ18O) for determination of water source used by a crop, stable isotope coupling Keeling plot for investigating the carbon and water flux in ecosystem, energy and material cycle in SPAC and correlative integrative models on stable isotope. These aspects contain most of the stable isotope researches on crop carbon and water relations which have been widely explored internationally while less referred in China. Based on the reviewed literatures, some needs for future research are suggested.

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.