Empirical assessment of state-and-transition models with a long-term vegetation record from the Sonoran Desert

Resilience-based frameworks, including state-and-transition models (STM), are being increasingly called upon to inform policy and guide ecosystem management, particularly in rangelands. Yet, multiple challenges impede their effective implementation: (1) paucity of empirical tests of resilience concepts, such as alternative states and thresholds, and (2) heavy reliance on expert models, which are seldom tested against empirical data. We developed an analytical protocol to identify unique plant communities and their transitions, and applied it to a long-term vegetation record from the Sonoran Desert (1953-2009). We assessed whether empirical trends were consistent with resilience concepts, and evaluated how they may inform the construction and interpretation of expert STMs. Seven statistically distinct plant communities were identified based on the cover of 22 plant species in 68 permanent transects. We recorded 253 instances of community transitions, associated with changes in species composition between successive samplings. Expectedly, transitions were more frequent among proximate communities with similar species pools than among distant communities. But unexpectedly, communities and transitions were not strongly constrained by soil type and topography. Only 18 transitions featured disproportionately large compositional turnover (species dissimilarity ranged between 0.54 and 0.68), and these were closely associated with communities that were dominated by the common shrub (burroweed, Haplopappus tenuisecta); indicating that only some, and not all, communities may be prone to large compositional change. Temporal dynamics in individual transects illustrated four general trajectories: stability, nondirectional drift, reversibility, and directional shifts that were not reversed even after 2-3 decades. The frequency of transitions and the accompanying species dissimilarity were both positively correlated with fluctuation in precipitation, indicating that climatic drivers require more attention in STMs. Many features of the expert models, including the number of communities and participant species, were consistent with empirical trends, but expert models underrepresented recent increases in cacti while overemphasizing the introduced Lehmann's lovegrass (Eragrostis lehmanniana). Quantification of communities and transitions within long-term vegetation records presents several quantitative metrics such as transition frequency, magnitude of accompanying compositional change, presence of unidirectional trajectories, and lack of reversibility within various timescales, which can clarify resilience concepts and inform the construction and interpretation of STMs.     

Protective effect of exogenous nitric oxide and salicylic acid on the photosynthetic apparatus of tomato seedling leaves under NaCl stress北大核心CSCD

Using the tomato variety 'Qin Feng Bao Guan' as experimental material, and by the hydroponics nutrient solution method, we investigated the effects of single and compound applications of nitric oxide (NO) donor sodium nitroprusside (SNP) and salicylic acid (SA) on the gas exchange and chlorophyll fluorescence parameters, RuBisCO activation, CO2 response curve, photosynthetic pigment content, and xanthophyll cycle in seedling leaves under an NaCl stress of 100 mmol/L. The main findings were as follows: (1) Single or combined applications of SNP and SA could increase the net photosynthetic rate (Pn), stomatal conductance (Gs), PS II maximal photochemistry efficiency (Fv/Fm), antenna conversion efficiency (Fv'/Fm'), practical photochemical efficiency (φPS?), photochemical fluorescence quenching coefficient (qP), and chlorophyll fluorescence decay rate (Rfd) of tomato seedling leaves at different rates, and significantly reduce the intercellular CO2 concentration (Ci), original fluorescence (Fo), and PS II non-photochemical fluorescence quenching coefficient (NPQ), after NaCl stress treatment. The strongest effect was observed after applying a combination of SNP and SA. (2) Under NaCl stress, the decrease of CO2 carboxylation efficiency (CE), RuBP maximum regeneration rate (Jmax), RuBisCO and its activation enzyme activity, and the maximum carboxylation rate (Vc max) in tomato seedling leaves could be effectively relieved by SNP, SA, or SNP + SA applications; however, SNP + SA treatment had the strongest effect. (3) Single or combined applications of SNP and SA could effectively inhibit the decrease of the contents of photosynthetic pigments (chlorophyll a, chlorophyll b, and carotenoids), the ratio of chlorophyll a and chlorophyll b, xanthophyll cycle pool size (V + A + Z), and the increase of the de-epoxidation extent of the xanthophyll cycle (A + Z)/(V + A + Z). The combined application of SNP and SA had the most prominent effect. In conclusion, the heat dissipation of the antenna, which is dependent on the xanthophyll cycle, is not the physiological mechanism for the protection of the photosynthetic apparatus by exogenous NO, SA alone, or compound treatment in tomato seedling leaves under NaCl stress. It is the main reason for the increase of photosynthetic function and enhanced salt tolerance of leaves tomato seedlings that the protection of PS II and its primary electron acceptor quinone (QA) downstream electron transfer patency, and the improvement of CO2 assimilation activity by application of exogenous NO, SA alone, or a combination of the two; synergistic effects were observed after using a combination of SNP and SA. © 2018 Science Press. All rights reserved.     

Growth release and growth inhibition of Pinus tabulaeformis forest in the Loess Plateau of western Shanxi Province,China北大核心CSCD

There has been increased focus on the impacts of climate change on vegetation growth, and human activities that interfere with the vegetation. Discussing the effects of climate change and thinning activity on forest growth is essential to expand plantation areas. In this study, the dendroecological method was used to analyze the radial growth of Pinus tabulaeformis to reveal the impacts of climate change and human activities on forest stand growth. These samples were derived from three different density areas of P. tabulaeformis forest at the Linfen City of Shanxi Province (the east of Loess Plateau). The correlation analysis between tree ring width index and climatic factors indicated that the growth of P. tabulaeformis was negatively related to precipitation in January and the monthly maximum temperature in December of the previous year, whereas positively correlated with precipitation in July and the monthly maximum temperature in October in that year. The phenomena of growth release and inhibition could be attributed to the impacts of climate change and thinning during 1978-2003. However, growth inhibition was closely related to unsuitable climatic conditions. Plot 1 showed a moderate growth inhibition period when the growth variation was less than -50%, and growth release was caused by thinning. The growth variation was greater than 47% in the period of growth release. Moreover, a slight growth release occurred due to tending in plot 2, and the rate of growth change exceeded 39%. A slight growth suppression induced by uncomfortable climatic condition caused growth variation less than -32% and a moderate growth release by the interaction of cutting and comfortable counterpart made variation rate larger than 75% in plot 3. The release effects of thinning can last for about 5 years. In summary, inappropriate climatic conditions can inhibit the growth of trees, and thinning can promote tree growth by about 5 years. The results can provide a reference for local forest management. © 2018 Science Press. All rights reserved.     

Chemical composition of the mycelium of Daldinia eschscholtzii北大核心CSCD

To investigate the chemical composition of the fungus Daldinia eschscholtzii, the compounds were separated by silica gel, Sephadex LH-20, and preparative chromatography. Their structures were identified by spectral methods. The MTT method was applied to measure the cytotoxicity of representative components. Eleven compounds were isolated and identified as 3β-hydroxyl-6,22-dien-5α,8α-peroxynitrite (1); ergosterol-9(11)-dehydroperoxide (2); mangiferonic acid (3); ergosta-4,6,8 (14),22-tetraen-3-one (4); (+)-syringaresinol (5); 3,5,3',5'-tetramethoxy-4,4,-diphenol (6); 5-methoxycoumarin (7); 5-hydroxy-2-methyl-4H-chromen-4-one (8); (2R,4R)-3,4-dihydro-5-methoxy-2-methyl-2H-1-benzopyran-4-ol (9); 2,3-dihydro-5-methoxy-2-methylchromen-4-one (10); and 7β-caruilignan C (11), respectively. Compound 4 showed inhibitory activity against H1299, H460, HGC-27, A5491, and MNK-45, with the IC50 value of 25.2 ± 2.9, 32.3 ± 4.2, 29.2 ± 1.2, 33.9 ± 3.7, and 18.0 ± 7.0 μmol/L, respectively. © 2018 Science Press. All rights reserved.     

Inhibitory kinetics of β-N-acetyl-D-glucosaminidase from Nile tilapia (Oreochromis niloticus) by cadmium北大核心CSCD

Cadmium (Cd2+) pollution in an aquatic environment can negatively affect certain reproductive parameters of aquatic animals. β-N-acetyl-D-glucosaminidase (NAGase) is considered to play an important role in the fertilization process. The aim of the present study was to investigate the effect of Cd2+ on the activity of NAGase purified f rom the testis of Nile tilapia, toward contributing new knowledge on the breadth of negative effects of Cd2+ for Nile tilapia production. The kinetic method of substrate reaction was used for this assessment, and an inhibitory model was established to study the kinetics of NAGase under inhibition by Cd2+. The results showed that Cd2+ could reversibly inhibit the enzymatic activity of NAGase, and the half-maximal inhibitory concentration was estimated to be 40.95 mmol/L. Cd2+ was found to be a competitive inhibitor of NAGase, and the inhibitory constant was determined to be 17.13 mmol/L. The microscopic rate constants of inactivation were also determined. Together, these findings demonstrate that Cd2+ is a reversible inhibitor that can competitively inhibit NAGase. These results may provide a theoretical foundation for further studies on the reproduction of tilapia. © 2018 Science Press. All rights reserved.     

Microorganisms and physico-chemical properties of soils with different slope-protecting vegetation in Daguang Highway北大核心CSCD

In order to investigate the effect of different slope-protecting vegetation on soil restoration in the highways, we collected soils at depths of 0-10 cm, 10-20 cm, and 20-30 cm from areas planted with Amorpha fruticosa, Periploca sepium, and Paederia scandens for 6-7 years in the Daming road section of the Daguang Highway, in October 2016. The physico-chemical properties and microbial community of the soils were then analyzed. The soil microbial community was analyzed by terminal restriction fragment length polymorphism (T-RFLP). The correlation between the microbial community and the physico-chemical properties of the soils was determined by redundancy analysis (RDA). The results showed that (1) the physico-chemical properties were the best for soils with Paederia scandens; the nutrient content, water holding capacity, and porosity of the soils with the three types of slope-protecting vegetation were better in the 0-10 cm layer than in the other layers; (2) the contents of soil aggregates (diameter > 5 mm) were the highest in the 0-10 cm and 10-20 cm layers for the soil with Paederia scandens; (3) the dominant bacteria in the 0-10 cm layer and dominant fungi in the 0-10 cm, 10-20 cm, and 20-30 cm layers were higher in the soils with Pe. sepium and Pa. scandens than in the soil with A. fruticosa; and (4) results of RDA showed that the physical properties of the soils were the main factors that influenced the soil microbial community. The physical properties of the soils were sensitive to the change of soil quality. Soil quality can be improved by appropriate management measures, such as burying litter, which can subsequently improve the ecological environment of soils in sloping regions. © 2018 Science Press. All rights reserved.     

An ecotoxicological view on neurotoxicity assessment

The numbers of potential neurotoxicants in the environment are raising and pose a great risk for humans and the environment. Currently neurotoxicity assessment is mostly performed to predict and prevent harm to human populations. Despite all the efforts invested in the last years in developing novel in vitro or in silico test systems, in vivo tests with rodents are still the only accepted test for neurotoxicity risk assessment in Europe. Despite an increasing number of reports of species showing altered behaviour, neurotoxicity assessment for species in the environment is not required and therefore mostly not performed. Considering the increasing numbers of environmental contaminants with potential neurotoxic potential, eco-neurotoxicity should be also considered in risk assessment. In order to do so novel test systems are needed that can cope with species differences within ecosystems. In the field, online-biomonitoring systems using behavioural information could be used to detect neurotoxic effects and effect-directed analyses could be applied to identify the neurotoxicants causing the effect. Additionally, toxic pressure calculations in combination with mixture modelling could use environmental chemical monitoring data to predict adverse effects and prioritize pollutants for laboratory testing. Cheminformatics based on computational toxicological data from in vitro and in vivo studies could help to identify potential neurotoxicants. An array of in vitro assays covering different modes of action could be applied to screen compounds for neurotoxicity. The selection of in vitro assays could be guided by AOPs relevant for eco-neurotoxicity. In order to be able to perform risk assessment for eco-neurotoxicity, methods need to focus on the most sensitive species in an ecosystem. A test battery using species from different trophic levels might be the best approach. To implement eco-neurotoxicity assessment into European risk assessment, cheminformatics and in vitro screening tests could be used as first approach to identify eco-neurotoxic pollutants. In a second step, a small species test battery could be applied to assess the risks of ecosystems.     

The oligopeptides production by the feather-degrading bacterium Bacillus methylotrophicus H0北大核心CSCD

Due to the high nutritive value of oligopeptides and the waste of feather resources, this study aimed at screening efficient strains of bacteria able to rapidly degrade feathers and produce large quantities of value-added oligopeptides. In order to assess the potential yield of oligopeptides, the promising strain H0 was selected from 16 feather-degrading microorganisms. To identify the strain, we analyzed the morphological and physiological characteristics of different strains, and carried out a gene sequence analysis of their 16S rRNAs. A single factor experiment was used to promote feather degradation and oligopeptide production, and the characteristics of the oligopeptides produced were also analyzed by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). The strain was identified as Bacillus methylotrophicus. The optimal initial pH and temperature for oligopeptide production were 11 and 40 °C, respectively. After 72 h of fermentation under these optimal conditions, the feathers were almost completely degraded, with a 38.19% of oligopeptides (accounting for 67.53% of the total soluble peptides) and a 11.11% of free amino acids produced. LC-MS/MS analysis indicated that the oligopeptides were mainly short peptides containing 5-10 amino acids, with a molecular mass (Mr) of less than 1 300. Moreover, the peptides were abundant in branched-chain amino acids, that might be responsible for the antioxidant property of the feather hydrolysate. Our results demonstrate the great capability of B. methylotrophicus H0 in feather degradation and oligopeptide production. This research provides a high-quality microorganism resource, and the scientific basis for the development of feather-derived oligopeptide products. © 2018 Science Press. All rights reserved.