Response of Carbon-Fixing Bacteria to Patchy Degradation of the Alpine Meadow in the Source Zone of the Yellow River, West China.

This study aims to enlighten our understanding of the distribution of soil carbon-fixing bacteria (cbbL-harboring bacteria) and their community diversity in differently degraded patches at three altitudes. MiSeq high-throughput sequencing technology was used to analyze the soil carbon-fixing bacteria community diversity of degraded patches and healthy meadow at three altitudes. Redundancy analysis (RDA) and structural equation model (SEM) were used to analyze the correlation and influence path between environmental factors and carbon-fixing bacteria. The results showed that degradation reduced the relative abundance of Proteobacteria from 99.67% to 95.57%. Sulfurifustis, Cupriavidus, and Alkalispirillum were the dominant genera at the three altitudes. Hydrogenophaga and Ectothiorhodospira changed significantly with altitude. RDA results confirmed that available phosphorus (AP) was strongly and positively correlated with Proteobacteria. AP and total nitrogen (TN) were strongly and positively correlated with Hydrogenophaga. Grass coverage and sedge aboveground biomass were strongly and positively correlated with Sulfurifustis and Ectothiorhodospira, respectively. Elevation adversely affected the relative abundance of dominant carbon-fixing bacteria and diversity index by reducing the coverage of grass and soil volumetric moisture content (SVMC) indirectly, and also had a direct positive impact on the Chao1 index (path coefficient = 0.800). Therefore, increasing the content of nitrogen, phosphorus and SVMC and vegetation coverage, especially sedge and grass, will be conducive to the recovery of the diversity of soil carbon-fixing bacteria and improve the soil autotrophic microbial carbon sequestration potential in degraded meadows, especially in high-altitude areas.

The degradation of residual pesticides and the quality of white clover silage are related to the types and initial concentrations of pesticides.

In order to understand the degradation of different residual pesticides of white clover silage and their influence on silage quality, three commonly used orchard pesticides with different concentrations were added to the white clover and fermented for 90 days. The results showed that the degradation rate of cypermethrin and its toxic degradation product 3-phenoxybenzoic acid (3-PBA) was the highest after silage, at different concentrations, both were 100%. The degradation rate of Tebuconazole and chloropyridine was 72.47-80.27% and 47.76-64.82%, of which 3,5,6-trichloro-2-pyridinol (TCP) content, poisonous toxic degradation product, increased 0.0525-0.253 mg·kg-1. The residues of beta-cypermethrin and tebuconazole had reached safety standards after silage. As compared with the control, the contents of lactic acid, acetic acid, and propionic acid increased in the treated samples. The higher concentrations of three pesticides all significantly reduced the lactic acid content of silage (p<0.05). Pesticides had different effects on the nutritional components of white clover silage. Conclusively, silage is a potential way to expand the utilization of covering plants in orchards.

Can white clover facilitate apple orchard residue composting?

Aiming to assess the efficiency of white clove (WC) as an alternative nitrogen source for composting and to facilitate the utilization of orchard waste, WC as compared with chicken manure (CM) was aerobically composted with apple tree leaves (ATL) in initial C/N ratios of 25(R25), 30(R30) and 35(R35). The results show that WC facilitated the rapid and harmless treatment of ATL with the compost temperature above 55°C for more than 3 days. After composting, for all final products, organic matter content was 69.9%-72.9%, electrical conductivity (EC) 1.48-2.31 ms cm-1, germination index (GI) more than 80% and C/N ratios less than 20. Among all treatments, the product from R30 was most nutrient-rich. Compared with CM, WC facilitated the harmless treatment of ATL and required less time for high quality compost production. It is concluded that WC is an excellent replacement for animal manure as a nitrogen source in field composting of orchard waste in areas with limited transportation. WC and ATL can produce high quality organic fertilizer and initial C/N ratio of 30 is recommended.

Positive effects of dietary supplementation of three probiotics on milk yield, milk composition and intestinal flora in Sannan dairy goats varied in kind of probiotics.

In this study, we investigated the effects of Saccharomyces cerevisiae (SC), Bacillus subtilis (BS) and Enterococcus faecalis (EF), singly and in combination, on the dry matter intake (DMI), milk production and composition, and faecal microflora of Saanen dairy goats. Fifty goats were randomly divided into five groups: (a) basal diet (control); (b) basal diet + SC; (c) basal diet + BS; (d) basal diet + EF; and (e) basal diet + mixed probiotics. Each treated animal received 5 g/d of probiotics for a total administration of 5 × 1,011 CFU/goat per day. The inclusion of B. subtilis and E. faecalis in the diet of lactating Saanen goats increased DMI (p < .05). Enhanced milk yield was observed with BS and EF. Milk fat percentage was significantly increased by feeding mixed probiotics compared with the control (p < .05); supplying SC, BS and mixed probiotics enhanced the protein percentage (p < .05). The milk lactose percentage in the SC and BS groups was higher than in the control (p < .05). The amount of milk total solids was higher after feeding EF or mixed probiotics than in the control group (p < .05). Non-fat solids showed no notable differences among groups (p > .05). There was no significant influence on gut bacterial abundance and diversity from adding these three probiotics, singly or in combination. Bacteroidales, Escherichia-Shigella and Christensenellaceae abundances were decreased by supplying these probiotics but Succinivibrionaceae increased. In conclusion, there were positive influences of probiotic feed supplementation on intake, milk performance and intestinal microecology.

Obstacles in the quantification of the cyclic electron flux around Photosystem I in leaves of C3 plants.

Sixty years ago Arnon and co-workers discovered photophosphorylation driven by a cyclic electron flux (CEF) around Photosystem I. Since then understanding the physiological roles and the regulation of CEF has progressed, mainly via genetic approaches. One basic problem remains, however: quantifying CEF in the absence of a net product. Quantification of CEF under physiological conditions is a crucial prerequisite for investigating the physiological roles of CEF. Here we summarize current progress in methods of CEF quantification in leaves and, in some cases, in isolated thylakoids, of C3 plants. Evidently, all present methods have their own shortcomings. We conclude that to quantify CEF in vivo, the best way currently is to measure the electron flux through PS I (ETR1) and that through PS II and PS I in series (ETR2) for the whole leaf tissue under identical conditions. The difference between ETR1 and ETR2 is an upper estimate of CEF, mainly consisting, in C3 plants, of a major PGR5-PGRL1-dependent CEF component and a minor chloroplast NDH-dependent component, where PGR5 stands for Proton Gradient Regulation 5 protein, PGRL1 for PGR5-like photosynthesis phenotype 1, and NDH for Chloroplast NADH dehydrogenase-like complex. These two CEF components can be separated by the use of antimycin A to inhibit the former (major) component. Membrane inlet mass spectrometry utilizing stable oxygen isotopes provides a reliable estimation of ETR2, whilst ETR1 can be estimated from a method based on the photochemical yield of PS I, Y(I). However, some issues for the recommended method remain unresolved.

Partially dissecting the steady-state electron fluxes in Photosystem I in wild-type and pgr5 and ndh mutants of Arabidopsis.

Cyclic electron flux (CEF) around Photosystem I (PS I) is difficult to quantify. We obtained the linear electron flux (LEFO2) through both photosystems and the total electron flux through PS I (ETR1) in Arabidopsis in CO2-enriched air. ΔFlux = ETR1 - LEFO2 is an upper estimate of CEF, which consists of two components, an antimycin A-sensitive, PGR5 (proton gradient regulation 5 protein)-dependent component and an insensitive component facilitated by a chloroplastic nicotinamide adenine dinucleotide dehydrogenase-like complex (NDH). Using wild type as well as pgr5 and ndh mutants, we observed that (1) 40% of the absorbed light was partitioned to PS I; (2) at high irradiance a substantial antimycin A-sensitive CEF occurred in the wild type and the ndh mutant; (3) at low irradiance a sizable antimycin A-sensitive CEF occurred in the wild type but not in the ndh mutant, suggesting an enhancing effect of NDH in low light; and (4) in the pgr5 mutant, and the wild type and ndh mutant treated with antimycin A, a residual ΔFlux existed at high irradiance, attributable to charge recombination and/or pseudo-cyclic electron flow. Therefore, in low-light-acclimated plants exposed to high light, ΔFlux has contributions from various paths of electron flow through PS I.

Estimation of the steady-state cyclic electron flux around PSI in spinach leaf discs in white light, CO2-enriched air and other varied conditions.

Cyclic electron flux (CEF) around PSI is essential for efficient photosynthesis and aids photoprotection, especially in stressful conditions, but the difficulty in quantifying CEF is non-trivial. The total electron flux through PSI (ETR1) and the linear electron flux (LEFO2) through both photosystems in spinach leaf discs were estimated from the photochemical yield of PSI and the gross oxygen evolution rate, respectively, in CO2-enriched air. ΔFlux=ETR1 - LEFO2 is an upper estimate of CEF. Infiltration of leaf discs with 150µM antimycin A did not affect LEFO2, but decreased ΔFlux 10-fold. ΔFlux was practically negligible below 350µmolphotonsm-2s-1, but increased linearly above it. The following results were obtained at 980µmolphotonsm-2s-1. ΔFlux increased 3-fold as the temperature increased from 5°C to 40°C. It did not decline at high temperature, even when LEFO2 decreased. ΔFlux increased by 80% as the relative water content of leaf discs decreased from 100 to 40%, when LEFO2 decreased 2-fold. The method of using ΔFlux as a non-intrusive upper estimate of steady-state CEF in leaf tissue appears reasonable when photorespiration is suppressed.

The time course of photoinactivation of photosystem II in leaves revisited.

Since photosystem II (PS II) performs the demanding function of water oxidation using light energy, it is susceptible to photoinactivation during photosynthesis. The time course of photoinactivation of PS II yields useful information about the process. Depending on how PS II function is assayed, however, the time course seems to differ. Here, we revisit this problem by using two additional assays: (1) the quantum yield of oxygen evolution in limiting, continuous light and (2) the flash-induced cumulative delivery of PS II electrons to the oxidized primary donor (P700(+)) in PS I measured as a 'P700 kinetics area'. The P700 kinetics area is based on the fact that the two photosystems function in series: when P700 is completely photo-oxidized by a flash added to continuous far-red light, electrons delivered from PS II to PS I by the flash tend to re-reduce P700(+) transiently to an extent depending on the PS II functionality, while the far-red light photo-oxidizes P700 back to the steady-state concentration. The quantum yield of oxygen evolution in limiting, continuous light indeed decreased in a way that deviated from a single-negative exponential. However, measurement of the quantum yield of oxygen in limiting light may be complicated by changes in mitochondrial respiration between darkness and limiting light. Similarly, an assay based on chlorophyll fluorescence may be complicated by the varying depth in leaf tissue from which the signal is detected after progressive photoinactivation of PS II. On the other hand, the P700 kinetics area appears to be a reasonable assay, which is a measure of functional PS II in the whole leaf tissue and independent of changes in mitochondrial respiration. The P700 kinetics area decreased in a single-negative exponential fashion during progressive photoinactivation of PS II in a number of plant species, at least at functional PS II contents ≥6 % of the initial value, in agreement with the conclusion of Sarvikas et al. (Photosynth Res 103:7-17, 2010). That is, the single-negative-exponential time course does not provide evidence for photoprotection of functional PS II complexes by photoinactivated, connected neighbours.

Operation of dual mechanisms that both lead to photoinactivation of Photosystem II in leaves by visible light.

Photosystem II (PS II) is photoinactivated during photosynthesis, requiring repair to maintain full function during the day. What is the mechanism(s) of the initial events that lead to photoinactivation of PS II? Two hypotheses have been put forward. The 'excess-energy hypothesis' states that excess energy absorbed by chlorophyll (Chl), neither utilized in photosynthesis nor dissipated harmlessly in non-photochemical quenching, leads to PS II photoinactivation; the 'Mn hypothesis' (also termed the two-step hypothesis) states that light absorption by the Mn cluster in PS II is the primary effect that leads to dissociation of Mn, followed by damage to the reaction centre by light absorption by Chl. Observations from various studies support one or the other hypothesis, but each hypothesis alone cannot explain all the observations. We propose that both mechanisms operate in the leaf, with the relative contribution from each mechanism depending on growth conditions or plant species. Indeed, in a single system, namely, the interior of a leaf, we could observe one or the other mechanism at work, depending on the location within the tissue. There is no reason to expect the two mechanisms to be mutually exclusive.