Density Functional Theory Study on the Mechanism of Biochar Gasification in CO2 Environment

This work presents a comprehensive analysis on the CO2 gasification of miscanthus derived biochar by using combined experimental and computational methods. The empirical formula and the 2D molecular model of the biochar were proposed based on the results from elemental analysis, Fourier infrared spectroscopy, and solid-state 13C NMR spectroscopy. The density functional theory (DFT) method was used to study the conversion of biochar to gaseous products under the CO2 condition at the B3LYP/6-31G(d,p) level. The reactants, intermediates, transition states, and products during the CO2 gasification process were analyzed, and the activation energy (ΔE) of each reaction step and thermodynamic parameters (Gibbs free energy, ΔG, and enthalpy, ΔH) were obtained. By comparison of the kinetic and thermodynamic parameters of different reaction paths, it was found that the proposed path 1 and path 5 could occur spontaneously with the changes in Gibbs free energy (ΔG) being -182.6 and -170.6 kJ/mol, respectively. The order of the reaction path was path 1 < path 5 < path 3 < path 4 < path 2, in terms of the degree of difficulty. It was also found that, for the benzene ring having a ring-opening reaction, when the substituents were located in the 2 and 3 carbon atoms or the 2, 3, and 5 carbon atoms, the C-C bond between the 1 and 6 carbon atoms was more prone to homolytic reaction than that between the 1 and 2 carbon atoms

Cassava genome from a wild ancestor to cultivated varieties

Cassava is a major tropical food crop in the Euphorbiaceae family that has high carbohydrate production potential and adaptability to diverse environments. Here we present the draft genome sequences of a wild ancestor and a domesticated variety of cassava and comparative analyses with a partial inbred line. We identify 1,584 and 1,678 gene models specific to the wild and domesticated varieties, respectively, and discover high heterozygosity and millions of single-nucleotide variations. Our analyses reveal that genes involved in photosynthesis, starch accumulation and abiotic stresses have been positively selected, whereas those involved in cell wall biosynthesis and secondary metabolism, including cyanogenic glucoside formation, have been negatively selected in the cultivated varieties, reflecting the result of natural selection and domestication. Differences in microRNA genes and retrotransposon regulation could partly explain an increased carbon flux towards starch accumulation and reduced cyanogenic glucoside accumulation in domesticated cassava. These results may contribute to genetic improvement of cassava through better understanding of its biology

Effects of nitrogen addition and drought on the relationship between nitrogen- and water-use efficiency in a temperate grassland

Abstract Background Nitrogen- and water-use efficiency (NUE and WUE) reflect the capacity of plants to take up and utilize resources in the environments. Although N deposition and drought are known to affect plant growth and persistence, it remains elusive how plants adjust NUE, WUE and their relationship to adapt to the concurrent N deposition and drought under the context of global change. We conducted a field experiment in a temperate grassland in Inner Mongolia, in which N addition (10 g m– 2 yr−1), drought (reduced 66% precipitation during growing season) and their combination were manipulated, and we explored the responses of both instantaneous (NUEINST and WUEINST) and long-term (NUELT and WUELT) WUE and NUE for six common plant species (Leymus chinensis, Stipa baicalensis, Thermopsis lanceolata, Potentilla bifurca, Thalictrum squarrosum, Klasea centauroide). Results Across all the six species, NUEINST decreased and WUEINST increased with both N addition and drought; NUELT decreased with both N addition and drought, while WUELT decreased with N addition and increased with drought. A significant interactive effect between N addition and drought was detected, in that, drought weakened the negative effect of N addition on WUELT and NUELT, and N addition weakened the negative effect of drought on NUELT, but enhanced the positive effect of drought on WUELT. As a consequence, drought caused a trade-off between NUE and WUE, and N addition brought forth positive correlation between NUE and WUE. Meanwhile, the relationship between NUE and WUE varied among the species of different functional groups. Conclusions Our study demonstrated that NUE, WUE and their relationship play an important role in determining their responses and adaptability to changes in soil nitrogen and water availability induced by N deposition and drought. Our results shed light on the antagonistic, synergetic and neutral effects between nitrogen deposition and drought on resource use efficiency, and further clarified the different adaptability among species of different functional groups, which will conduce to a comprehensive understanding on the role of NUE and WUE in plant persistence and coexistence in grassland ecosystems

Use of Multi-Carbon Sources by Zooplankton in an Oligotrophic Lake in the Tibetan Plateau

We applied natural abundance stable isotope C-13 and radiocarbon C-14 analyses to investigate trophic linkages between zooplankton and their potential food sources (phytoplankton, submersed plants, and allochthonous organic carbon) in Lake Nam Co, one of the largest oligosaline and oligotrophic lakes in the Tibetan Plateau, in south-west China. The C-13 and C-14 levels of the calanoid copepod Arctodiaptomus altissimus pectinatus indicate that it uses different carbon sources. Thus, based on a two-isotope mixing model, our results suggested that recently synthesized but C-14-depleted primary producers (phytoplankton and submersed plants) were the most important sources of carbon, together contributing 92.2% of the zooplankton biomass. Allochthonous organic carbon and dissolved organic carbon constituted 4.7% and 3.1% of the carbon in the diet of zooplankton, respectively. Our findings from Lake Nam Co suggest that the carbon in the food webs of lakes located in a glaciated environment originates from various sources of different ages

Phytoplankton response to winter warming modified by large-bodied zooplankton: an experimental microcosm study

While several field investigations have demonstrated significant effects of cool season (winter or spring) warming on phytoplankton development, the role played by large-bodied zooplankton grazers for the responses of phytoplankton to winter warming is ambiguous. We conducted an outdoor experiment to compare the effect of winter warming (heating by 3°C) in combination with presence and absence of Daphnia grazing (D. similis) on phytoplankton standing crops and community structure under eutrophic conditions. When Daphnia were absent, warming was associated with significant increases in phytoplankton biomass and cyanobacterial dominance. In contrast, when Daphnia were present, warming effects on phytoplankton dynamics were offset by warming-enhanced grazing, resulting in no significant change in biomass or taxonomic dominance. These results emphasize that large-bodied zooplankton like Daphnia spp. may play an important role in modulating the interactions between climate warming and phytoplankton dynamics in nutrient rich lake ecosystems

Effects of different tillage and straw return on soil organic carbon in a rice-wheat rotation system.

Soil management practices, such as tillage method or straw return, could alter soil organic carbon (C) contents. However, the effects of tillage method or straw return on soil organic C (SOC) have showed inconsistent results in different soil/climate/cropping systems. The Yangtze River Delta of China is the main production region of rice and wheat, and rice-wheat rotation is the most important cropping system in this region. However, few studies in this region have been conducted to assess the effects of different tillage methods combined with straw return on soil labile C fractions in the rice-wheat rotation system. In this study, a field experiment was used to evaluate the effects of different tillage methods, straw return and their interaction on soil total organic C (TOC) and labile organic C fractions at three soil depths (0-7, 7-14 and 14-21 cm) for a rice-wheat rotation in Yangzhong of the Yangtze River Delta of China. Soil TOC, easily oxidizable C (EOC), dissolved organic C (DOC) and microbial biomass C (MBC) contents were measured in this study. Soil TOC and labile organic C fractions contents were significantly affected by straw returns, and were higher under straw return treatments than non-straw return at three depths. At 0-7 cm depth, soil MBC was significantly higher under plowing tillage than rotary tillage, but EOC was just opposite. Rotary tillage had significantly higher soil TOC than plowing tillage at 7-14 cm depth. However, at 14-21 cm depth, TOC, DOC and MBC were significantly higher under plowing tillage than rotary tillage except for EOC. Consequently, under short-term condition, rice and wheat straw both return in rice-wheat rotation system could increase SOC content and improve soil quality in the Yangtze River Delta

Fish-mediated plankton responses to increased temperature in subtropical aquatic mesocosm ecosystems: Implications for lake management

Although it is well established that climate warming can reinforce eutrophication in shallow lakes by altering top-down and bottom-up processes in the food web and biogeochemical cycling, recent studies in temperate zones have also shown that adverse effects of rising temperature are diminished in fishless systems. Whereas the removal of zooplanktivorous fish may be useful in attempts to mitigate eutrophication in temperate shallow lakes, it is uncertain whether similar mitigation might be achieved in warmer climates. We compared the responses of zooplankton and phytoplankton communities to climate warming in the presence and absence of fish (Aristichthys nobilis) in a 4-month mesocosm experiment at subtropical temperatures. We hypothesized that 1) fish and phytoplankton would benefit from warming, while zooplankton would suffer in fish-present mesocosms and 2) warming would favor zooplankton growth but reduce phytoplankton biomass in fish-absent mesocosms. Our results showed significant interacting effects of warming and fish presence on both phytoplankton and zooplankton. In mesocosms with fish, biomasses of fish and phytoplankton increased in heated treatments, while biomasses of Daphnia and total zooplankton declined. Warming reduced the proportion of large Daphnia in total zooplankton biomass, and reduced the zooplankton to phytoplankton biomass ratio, but increased the ratio of chlorophyll a to total phosphorus, indicating a relaxation of zooplankton grazing pressure on phytoplankton. Meanwhile, warming resulted in a 3-fold increase in TP concentrations in the mesocosms with fish present. The results suggest that climate warming has the potential to boost eutrophication in shallow lakes via both top-down (loss of herbivores) and bottom-up (elevated nutrient) effects. However, in the mesocosms without fish, there was no decline in large Daphnia or in total zooplankton biomass, supporting the conclusion that fish predation is the major driver of low large Daphnia abundance in warm lakes. In the fishless mesocosms, phytoplankton biomass and nutrient levels were not affected by temperature. Our study suggests that removing fish to mitigate warming effects on eutrophication may be potentially beneficial in subtropical lakes, though the rapid recruitment of fish in such lakes may present a challenge to success in the long-term. (C) 2018 Elsevier Ltd. All rights reserved

Species-specific responses of submergedmacrophytes to the presence of a small omnivorous bitterling Acheilognathus macropterus

Recovery of submerged macrophytes has been considered a key factor in the restoration of shallow eutrophic lakes. However, in some subtropical restored lakes, small omnivorous fish dominate the fish assemblages and feed in part on submerged macrophytes. Knowledge of the effects of small omnivores on the growth of submerged macrophytes is scarce and their responses are potentially species-specific, i.e. the growth of some species may be hampered by fish grazing while growth of others may be promoted by the nutrients becoming available by fish excretion. We conducted mesocosm experiments to examine the effects of the small omnivorous bitterling Acheilognathus macropterus, a common species in restored subtropical lakes in China, on nutrient concentrations and the growth of four species of submerged macrophytes (Hydrilla verticillata, Vallisneria denseserrulata, Ceratophyllum demersum and Myriophyllum spicatum). We found that the bitterling significantly increased nutrient concentrations via excretion and thereby enhanced the net growth of the less grazed nuisance macrophyte M. spicatum. In contrast, the net growth of C. demersum was reduced by the bitterling, most likely due to grazing as indicated by gut content analyses. Dominance by bitterling may, therefore, pose a threat to the long-term success of lake restoration by provoking a shift in the submerged macrophyte community towards nuisance species through selective grazing. Nutrient excretion may potentially also stimulate the growth of phytoplankton and periphyton, hampering the growth of submerged macrophyte. (C) 2020 Elsevier B.V. All rights reserved

Effects of Exposed Artificial Substrate on the Competition between Phytoplankton and Benthic Algae: Implications for Shallow Lake Restoration

Phytoplankton and benthic algae coexist in shallow lakes and the outcome of the competition between these two photoautotrophs can markedly influence water clarity. It is well established that exposed artificial substrate in eutrophic waters can remove nutrients and fine particles from the water column via the attached periphyton canopy. However, the effects of the introduction of artificial substrate on the competition between planktonic and benthic primary producers remain to be elucidated. We conducted a short-term outdoor mesocosm experiment to test the hypothesis that the nutrient and light changes induced by exposed artificial substrate (polythene nets) would benefit the benthic algae. Artificial substrate significantly reduced total nitrogen and phosphorus concentrations and water clarity improved, the latter due to the substrate-induced reduction of both organic and inorganic suspended solids. Consequently, as judged from changes in chlorophyll a (Chl-a) concentrations in water and sediment, respectively, exposed artificial substrate significantly reduced the phytoplankton biomass, while benthic algae biomass increased. Our results thus indicate that exposed artificial substrate may be used as a tool to re-establish benthic primary production in eutrophic shallow lakes after an external nutrient loading reduction, paving the way for a benthic- or a macrophyte-dominated system. Longer term and larger scale experiments are, however, needed before any firm conclusions can be drawn on this

A small omnivore fish (

Transplantation of submerged macrophytes has been widely used to improve water quality in restoring shallow lakes in China. However, in some lakes, small omnivorous fish predominated the fish assemblages and fed mainly on submerged macrophytes. Despite significant research examining grazing selectivity in herbivorous fishes, macrophyte feeding preferences of small omnivorous fishes are poorly understood. We conducted a mesocosm experiment to examine the effects of a prolific small omnivorous bitterling fish Acheilognathus macropterus on the relative growth rate (RGR) and biomass of submerged macrophytes (Ceratophyllum demersum, Myriophyllum spicatum, Vallisneria denseserrulata, and Hydrilla verticillata). Our results showed that the presence of A. macropterus significantly increased nutrient concentrations (e.g. total nitrogen and total phosphorus). The RGR of C. demersum in the bitterling-present treatment was significantly lower than the controls, in the presence of other macrophyte species. Further, total biomass of the four species of macrophytes in the fish-present mesocosms was markedly lower than in the fish-absent treatment, suggesting considerable consumption of macrophytes by bitterling. Moreover, the percent biomass of V. denserrulata and H. verticillata were significantly enhanced by the presence of bitterling. Our findings suggest that A. macropterus may increase nutrient concentrations through excretion and reduce the biomass and RGR of certain submerged macrophytes which may shift macrophyte community structure via selective grazing