Atmospheric dustfall exhibits consistent sedimentary sorting with height evidenced by grain size characteristics.

The grain size of aeolian deposits is a key property to understanding their sedimentary sorting characteristics, which determine the sedimentary dynamics of an airflow field. Although atmospheric dust sedimentary sorting processes are understood well in the horizontal direction, those in the vertical direction and their influencing factors remain unclear. Herein, modern atmospheric dustfall was collected using dust traps at heights of 1, 2, 4, 6, and 8 m to reveal its sedimentary sorting characteristics. The analysis demonstrated that atmospheric dustfall exhibits a bimodal grain size distribution, and the bimodal grain size distribution curves change within a height of 8 m. However, either peak 1 or peak 2 exhibits consistent grain size characteristics with height; hence, each sub-peak indicates consistent sedimentary sorting within a height of 8 m. The modification of grain size distribution curves with height is mainly driven by different sedimentary fluxes for peak 1 at different heights. Dustfall grain size characteristics are also potentially affected by the settling height, concentration of the atmospheric dust, and dust sedimentary flux. However, the sedimentary sorting of sub-peak components is mainly governed by the near-surface airflow field. Thus, this reveals the process of formation and grain size distribution of aeolian deposits. Overall, atmospheric dustfall with mixed multi-peak components conceals information on the sedimentary environment.

Abrupt climatic shift at ~4000 cal. yr B.P. and late Holocene climatic instability in arid Central Asia: Evidence from Lop Nur saline lake in Xinjiang, China.

Although the trends and driving mechanisms of Holocene climate change in arid Central Asia (ACA) on various timescales have attracted much research interest over the past few decades, a major question remains regarding whether the changes were gradual or abrupt. We reconstructed the pattern of Holocene climate change at Lop Nur saline lake in northwestern China, ACA, using multiple climatic proxies (grain size, TOC, sediment color, and magnetic properties). The results demonstrate that the Holocene climatic pattern in the Lop Nur region during the past 8400 years can be divided into two distinct stages, with the boundary dated to ~4000 cal. yr B.P. During the first stage (8400-4000 cal. yr B.P.), the climate was relatively dry and stable; and during the second stage the climate was more humid with high-amplitude variations. This finding is corroborated by other paleoclimatic records from the surrounding area and it is also consistent with the latest international strata chronology for the Holocene. The abrupt climatic shift at ~4000 cal. yr B.P. and late Holocene climatic instability in ACA are highlighted in this study. The decreasing temperatures in the study region during the middle to late Holocene were modulated by Northern Hemisphere summer insolation, which led to decreasing evaporation and thus to the wetting trend of the middle through late Holocene. The abrupt change at ~4000 cal. yr B.P. was caused mainly by a more negative trend of the North Atlantic Oscillation (NAO) and by an enhanced El Niño - Southern Oscillation (ENSO).

Similar effects as shade tolerance induced by dust accumulation and size penetration of particulates on cotton leaves.

BACKGROUND: Dust accumulation covers the leaf's surface and influences foliar physiological activity. Two independent experiments were carried out to instigate the foliar responses to dust accumulation and the penetration limitation of small dust particles (< 1 µm) on the foliar surface, respectively. In experiment I, three dust accumulation intensities were achieved by a dust spraying treatment. Photosynthesis CO2 exchange and fast chlorophyll fluorescence transient were measured, as well as chlorophyll contents and leaf thickness. In experiment II, the penetration limits of small particulates on the leaf surface were examined by feeding nano-fluorescent microspheres. RESULTS: Dust accumulation alleviated the photoinhibition of Photosystem II and decreased photosynthesis, as represented by net photosynthetic rates (PN) and stomatal conductance to water vapor (gs). Photosynthetic response curves between net photosynthetic rate (PN) and photosynthetically active radiation (PAR) showed that heavy dust accumulation (34.98 ± 2.6 mg cm- 2) increased the light compensation point (LCP) and light saturation point (LSP) and decreased photosynthesis rates under saturating light (PNmax). Leaves became thin due to the lack of a palisade layer while chlorophyll content increased under dust accumulation. Confocal laser scanning microscopy (CLSM) images showed that the larger particles (1 µm) distributed in the regions below the stomata and the smaller ones (0.1 µm) were detected in the wider areas below stomata. CONCLUSIONS: These results suggested that dust accumulation induced similar effects as shade tolerance in cotton leaves but did not trigger more photochemical acclimation to low light. Dust particles (< 1 µm) penetrated leaf surface through stomata.

Transport of airborne Picea schrenkiana pollen on the northern slope of Tianshan Mountains (Xinjiang, China) and its implication for paleoenvironmental reconstruction.

The understanding of airborne pollen transportation is crucial for the reconstruction of the paleoenvironment. Under favorable conditions, a considerable amount of long-distance-transported pollen can be deposited far from its place of origin. In extreme arid regions, in most cases, such situations occur and increase the difficulty to interpret fossil pollen records. In this study, three sets of Cour airborne pollen trap were installed on the northern slope of Tianshan Mountains to collect airborne Picea schrenkiana (spruce) pollen grains from July 2001 to July 2006. The results indicate that Picea pollen disperses extensively and transports widely in the lower atmosphere far away from spruce forest. The airborne Picea pollen dispersal period is mainly concentrated between mid-May and July. In desert area, weekly Picea pollen began to increase and peaked suddenly in concentration. Also, annual pollen indices do not decline even when the distance increased was probably related to the strong wind may pick up the deposited pollen grains from the topsoil into the air stream, leading to an increase of pollen concentration in the air that is irrelevant to the normal and natural course of pollen transport and deposition. This, in turn, may lead to erroneous interpretations of the pollen data in the arid region. This study provided insight into the shift in the Picea pollen season regarding climate change in arid areas. It is recorded that the pollen pollination period starts earlier and the duration became longer. The results also showed that the temperature of May and June was positively correlated with the Picea pollen production. Furthermore, the transport of airborne Picea pollen data is useful for interpreting fossil pollen records from extreme arid regions.

[Changes and analysis of soil quality under different land use types in oasis rim].

The aggravation process of oasisization leads to changes of land use type in oasis rim. In order to discuss the effects of different land use types on soil properties and soil quality, the four land use types located Cele oasis rim in south margin of Tarim Basin, which are the cotton field, orchard, and Caligonum mongolicum Turcz land use type reclaimed by people and nature state land use type covered by Alhagi sparsifolia SHAP, were selected as study object. The relative soil quality index (RI) and the soil quality synthesis index (SQI) were used to analyse the changes of soil quality between four land use types within 0-20 cm, 2040 cm, 40-60 cm soil depth, respectively. Meantime, the fractal theory was used to analyse the particle-size distribution (PSD) property of top soil under different land use types. The results indicated that there was a significant difference in the soil organic matter and total nitrogen in same soil depth between four land use types; the order ranked according to RI was same to the order ranked according to SQI in each soil depth between four land use types. The cotton field and orchard have an obviously positive effect on soil quality of the top soil, however, the soil quality of Alhagi sparsifolia SHAP land use type was gradually increasing along with the increasing soil depth. The soil properties and soil quality of Caligonum mongolicum Turcz land use type were at the lowest level according to the comparison results among all land use types, and the calculation results of PSD fractal dimension also indicated the Caligonum mongolicum Turcz land use type had the worst ability on maintaining soil fine fractions.

Complexation between Hg(II) and biofilm extracellular polymeric substances: an application of fluorescence spectroscopy.

The three-dimensional excitation emission matrix (EEM) fluorescence spectroscopy was employed to investigate the interaction of extracellular polymeric substances (EPS) from natural biofilm with Hg(II). The EEM spectra demonstrated that EPS with molecular weight over 14 kDa had two protein-like fluorescence peaks. The fluorescence intensity at both peaks was strongly dependent on the solution pH in the absence and presence of Hg(II), with the maximal fluorescence intensity at neutral pH. Fluorescence of both protein-like peaks was significantly quenched by Hg(II). The values of conditional stability constants (log K(a)=3.28-4.48) derived from modified Stern-Volmer equation are approximate to those for humic substances and dissolved organic matter (DOM), indicating that fluorescent components in EPS have strong binding capacity for Hg(II). Our findings suggest that EPS from biofilm is a class of important organic ligands for complexation with Hg(II) and may significantly affect the chemical forms, mobility, bioavailability and ecotoxicity of heavy metals in the aquatic environment.

Effects of levofloxacin hydrochloride on photosystem II activity and heterogeneity of Synechocystis sp.

Effects of LH on photosynthesis of Synechocystis sp. were investigated by a variety of in vivo chlorophyll fluorescence. O2 evolution and the photosystem II (PSII) activity were clearly inhibited by LH. Exposure to LH increased the proportion of PSIIbeta and this weakened the connectivity between PSII units and hindered excitation energy-transfer between PSII units. LH decreased the density of the active photosynthetic reaction centers, inhibited electron transport, and increased the dissipated energy flux per reaction center. The inhibitory effect of LH on Q(A)(-) reoxidation process could be divided into several stages. LH first inhibited the electron transfer from Q(A)(-) to Q(B) by weakening the connectivity between Q(A)(-) and Q(B), and PQ binding began taking part in Q(A)(-) reoxidation. At the second stage, the connectivity between Q(A)(-) and PQ pool was broken and inhibition on PQ binding occurred. At this stage, some Q(A)(-) began to be oxidized by S2(Q(A)Q(B))(-). Finally, when the connectivity between Q(A)(-) and Q(B) and PQ was completely broken, all Q(A)(-) was oxidized through charge recombination.

[Assessment of farmland soil quality under different utilization intensity in arid area].

Based on the 2005-2007 experimental data in Cele oasis in the southern margin of Tarim Basin of Xinjiang, the soil quality of four typical types of farmland with different utilization intensity, i.e., farmland with high input, farmland with normal input, newly reclaimed farmland, and farmland in oasis' interior, was analyzed and assessed by using sustainable yield index, soil improvement index, and soil quality synthesis index. Among the farmlands, there were significant differences in the contents of soil organic matter, available nitrogen, and available phosphorus. Newly reclaimed farmland had the lowest level of soil quality, while the farmland in oasis' interior had relatively higher soil quality. This study could help the reasonable exploitation and utilization of farmlands in Cele oasis, and the protection of local farmland eco-environment.

EFFECT OF CHROMIUM(VI) ON PHOTOSYSTEM II ACTIVITY AND HETEROGENEITY OF SYNECHOCYSTIS SP. (CYANOPHYTA): STUDIED WITH IN VIVO CHLOROPHYLL FLUORESCENCE TESTS(1).

The inhibitory effect of Cr(VI) on the PSII of Synechocystis sp. was studied. Cr(VI) reduced O2 evolution and inhibited the water-splitting system in PSII. S-states test and flash induction test showed that Cr(VI) exposure increased the proportion of inactivated PSII (PSIIX ) and PSIIß reaction centers, which increased the fluxes of dissipated energy. JIP test and QA (-) reoxidation test demonstrated that Cr(VI) treatment induces inhibition of electron transport from QA (-) to QB /QB (-) and accumulation of P680 (+) . More QA (-) had to be oxidized through S2 (QA QB )(-) charge recombination and oxidation by PQ9 molecules in PSII under Cr(VI) stress. These changes finally decreased the index of photosynthesis performance.

Toxic effects of amoxicillin on the photosystem II of Synechocystis sp. characterized by a variety of in vivo chlorophyll fluorescence tests.

Amoxicillin is one of the widely used antibiotics of environmental concern. This study shows that amoxicillin has toxic effects on the photosynthesis of Synechocystis sp. Its inhibitory effects on photosystem II (PSII) of Synechocystis sp. were investigated by using a variety of in vivo chlorophyll fluorescence tests. The inhibitory effects of amoxicillin on PSII activity of Synechocystis sp. are concentration-dependent. Amoxicillin exposure leads to slowing down of electron transport on both donor side and acceptor side and causes accumulation of P680(+). Q(A)(-) reoxidation test revealed that amoxicillin hinders electron transfer from Q(A)(-) to Q(B)/Q(B)(-) and more Q(A)(-) is oxidized through S(2)(Q(A)Q(B))(-) charge recombination. Analysis of PSII heterogeneity demonstrated that an exposure to amoxicillin increases the proportion of inactive PSII (PSII(X)) centers and the proportion of PSII centers with small antenna (PSIIbeta). These changes finally result in deterioration of full photosynthesis performance.