•BSCs is superior to the vascular vegetation in degraded meadow patches, especially restoring LOC, TN and SOM in soil.•Altitude and soil depth significantly reduced the content of LOC in soil.•BSCs ...promote the restoration of soil LOC by increasing soil TN content.
Biological soil crusts (BSCs) play an important ecological role in the biogeochemical cycles, but there is limited knowledge about their effects on the composition of soil labile organic carbon (LOC) in the soil of patchy alpine meadow. In patchy alpine meadow with different altitudes, the different LOC compartments, vegetation, soil properties and C-hydrolase activity of active patches (with plateau pika), inactive patches (without plateau pika), restored patches, BSCs patches, and healthy alpine meadow were analyzed to assess the effects of BSCs on LOC. The key influence pathway of eco-environmental factors of LOC was determined by the structural equation model (SEM). The results showed that the BSCs at the altitude of 3570 m increased dissolved organic carbon (DOC), easily oxidized organic carbon (EOC) and microbial carbon (MBC) by 293%, 73% and 36%, respectively, compared with active patches in the 0–2 cm layer, which was significantly higher than those of inactive patches and recovered patches. There was no significant difference among DOC, EOC and MBC in different patches at the altitude of 4224 m. The MBC content of active patches decreased, but other patches and healthy alpine meadow showed a Λ- shaped change with altitude. The contents of soil total nitrogen and organic matter of BSCs patches were generally higher than those of active and inactive patches at three different altitudes. Structural equation model results showed that at the altitude of 3570 m, total nitrogen had a strong positive correlation with DOC, with a path coefficient of 0.677. There was a direct negative relationship between soil organic matter and DOC (path coefficient = −0.278) at the altitude of 4013 m. At the altitude of 4224 m, there was no direct correlation among soil nutrient, C-hydrolase activity, and soil LOC. Therefore, BSCs mainly promote the accumulation and recovery of LOC by increasing the soil total nitrogen content in different patches at different altitudes, which are beneficial to the restorations of LOC, total nitrogen and soil organic matter. Hence, they should be considered as key factors in the processes of restoring patchy alpine meadows.
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.
Phosphorus is critical for the regulation of numerous metabolic processes in plants, and so understanding the mechanisms by which plants acquire phosphorus is important. Phosphate solubilizing ...bacteria (PSB) are thought to promote the uptake of phosphorus by plants. The effects of PSB YJILJH and YJ101 strains on the growth of white clover (
Trifolium repens
L.) were investigated through the production of the plant hormone IAA and the change of available phosphorus content in the soil. Two strains of YJILJH and YJ101 were selected from the rhizosphere soil of white clover among rows of apple orchards. Combined with 16S rDNA and next-generation sequencing (NGS), the strains were identified as
Staphylococcus hominis
and
Staphylococcus epidermidis
, respectively. The two strains had strong phosphate solubilizing ability, and had solubilization index (SI) values of 4.39 and 3.95, respectively. The dissolved amounts of soy lecithin were 351.2 and 387.3 mg/L in liquid medium, respectively. The amount of Ca
3
(PO
4
)
2
dissolved reached 506.3 and 789.8 mg/L, respectively. The pot experiment showed that the biomass of white clover after adding the two strains increased by 21.17% and 36.49%, the total phosphorus (TP) content increased by 28.87% and 30.41%, and the soil available phosphorus (AP) content increased by 86.63% and 47.16%, respectively. This study also found that both strains can produce IAA content reaching 55.95 and 54.33 pmol / L in 72 h. In regard to relative gene expression,
trpD
and
trpA
genes were expressed in the different treatments, while
ipdC
was only expressed in Luria-Bertani broth (LB broth) and NBRIP media (+ soy lecithin). It is speculated that the pathway of IAA synthesis by both strains may be related to the tryptophan side chain pathway and the indole-3-pyruvate pathway. The IAA produced by the two bacteria strains is an important reason to promote the growth of white clover and participate in the process of reducing the environmental pH of the growth medium.
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%.
,
, and
were the dominant genera at the three altitudes.
and
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
. Grass coverage and sedge aboveground biomass were strongly and positively correlated with
and
, 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 alpine meadows on the Qinghai–Tibet Plateau is a major issue affecting both the ecology and the economy. Microorganisms play an important role in soil nutrient cycling and the ...regulation of ecosystem function. This study aimed to investigate the species composition and diversity of microbial communities and understand the response of microbial communities to changes in physicochemical properties resulting from meadow degradation. In this study, the soil bacterial and fungal communities’ composition and diversity of alpine meadows of degradation gradient were sequenced by high-throughput sequencing. During the process of grassland degradation, there were 59 bacterial taxa and 29 fungal taxa showing significant differences. The relative abundance of meadow pathogenic fungi significantly increased (p < 0.05). PICRUSt2 analysis showed a decrease in synthesis-related functional gene abundance and an increase in metabolism-related functional gene abundance. FUNGuild analysis showed that symbiotic and saprophytic nutrient fungi decreased significantly (p < 0.05). The soil nutrient cycling was mainly influenced by the beta diversity of microbial communities. Grassland degradation affects soil structure, thereby affecting the diversity of soil microbial composition and functional soil nutrient content. This work reveals the response of microbial communities to the degradation of alpine meadows and their impact on nutrient cycling, providing theoretical support for the protection and sustainable development of alpine meadows.
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.
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.
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.
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.
Wind erosion happens frequently in winter and spring, when vegetation is bare and the surface soil is prone to erosion. Therefore, the erosion resistance provided by litter is important. To ...investigate the soil erosion-reducing efficiency of different types of litter, litter-covered sites of Populus simonii (LPS), Caragana korshinskii (LCK) and Bothriochloa ischaemum (LBI) were studied, respectively, and bare sandy land (BSL) was taken as a control. Results showed that litter cover increased the aerodynamic roughness by 44.9%–107.1% and the friction velocity by 11.5%–52.0%. Under the conditions of fixed coverage, changing wind speed and conditions of fixed wind speed, changing coverage, the average soil erosion-reducing efficiency both showed the highest in LBI, followed by LCK and LPS. According to the trend analysis, the critical coverage of litter of Populus simonii (PS), Caragana korshinskii (CK) and Bothriochloa ischaemum (BI) to reduce the soil erosion were 8.7%, 8.2% and 9.1%, respectively. We concluded that the soil erosion-reducing efficiency varied due to the shape of litter, and the difference was significant at high wind speed (10 m s−1 and 12 m s−1). Besides, not all litter cover was effective in reducing erosion, and the critical coverage was a crucial factor that cannot be ignored.
•When the coverage of litter was fixed and the wind speed was adjusted, the erosion reduction efficiencies were 49.1% ~ 96.6%.•When the wind speed was fixed and the coverage of litter was changed, the wind erosion reduction efficiencies were –10.2% ~ 80.6%.•According to the trend, the critical coverage of litter to reduce soil erosion were 8.2% ~ 9.1%.•The erosion reduction effect caused by the difference in the shape of litter was particularly obvious at high wind speeds.•The wind erosion reduction efficiency showed that litter-covered sites of BI > CK > PS.
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