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We assessed the phototoxicity of TiO2 nanoparticles on fungal structure and function. The fungal diversity was reduced by long-term exposure. However, the leaf decomposition rate was not inhibited rather than promoted under natural photoperiod.

In this study, exposure experiments were conducted to assess the effects of polystyrene nanoparticles (PS) and amine-modified polystyrene nanoparticles (APS) at environmental concentrations (1, 10, and 100 µg L

The toxic effects of silver nanoparticles (AgNP) to aquatic species and ecosystem processes have been the focus of increasing research in ecology, but their effects under different environmental stressors, such as the ongoing anthropogenic artificial light at night (ALAN) which can cause a series of ecological effects and will potentially interact with other stressors, remain poorly understood. Here, we aimed to assess the combined effects of AgNP and ALAN on the activities and community structure of fungi and bacteria associated to plant litter in a stream. The results showed that ALAN not only led to changes in the average hydrodynamic diameter, ζ-potential and dissolved concentration of AgNP but also inhibited the enzyme activities of leucine-aminopeptidase (LAP), polyphenol oxidase (PPO) and peroxidase (PER) associated with microbes involved in litter decomposition. The negative effect of AgNP on the decomposition of Pterocarya stenoptera leaf litter was alleviated by ALAN owing to the reduction of the Ag+ concentration in the microcosm and of the lignin content of the leaf litter in the A-AgNP treatments, the enhancement of β-glucosidase (β-G) activities and the increase in microbial biomass. The effect of ALAN alone or combined with AgNP or AgNO3 on the taxonomic composition of fungi was much greater than that on bacteria. Linear discriminant analysis effect size (LEfSe) demonstrated that each treatment had its own fungal and bacterial indicator taxa, from the phylum to genus levels, indicating that the microbial communities associated with litter decomposition can change their constituent taxa to cope with different stressors. These results reveal that ALAN can decrease the toxicity of AgNP and highlight the importance of considering ALAN during the assessment of the risk posed by nanoparticles to freshwater biota and ecosystem processes.

To better understand the impact of warming on heavy metals (HM) associated with plant litter decomposition in streams, we investigated the impact of high and low HM (Cu and Zn) levels and different water temperatures (10,15 and 20 o C) on microbial decomposition of TyphaangustifoliaL.litter and the associated extracellular enzyme activities. During a 100-day incubation, changes in litter mass losses, chemical composition (lignin and total carbohydrate), and extracellular enzyme activity were determined. The decomposition rates were accelerated by the low HM levels at 20 o C (0.0051 day–1 at CK vs 0.0061 day–1 at low HM levels). The negative effects of Cu and Zn on Typha litter decomposition were more pronounced at lower temperatures (10 and 15°C). The enhanced enzyme activities of cellulase and β-glucosidase and the higher lignin/litter weight loss and lignin/carbohydrate ratios were found at 20 o C and low HM treatment. The enzyme activities of β-glucosidase and cellulase were positively correlated with litter mass losses at 20 o C and low HM levels. These results suggest that a 5 o C increase in water temperature may attenuate the inhibition of low HM level on litter decomposition.

Artificial light at night (ALAN/A) can not only alter the behavior and communication of biological organisms, it can also interact with other stressors. Despite its widespread use and the numerous potential ecological effects, little is known about the impact of ALAN on plant litter decomposition under cadmium (Cd) pollution in aquatic ecosystems. In an indoor microcosm experiment, we tested single and combined effects of ALAN and Cd on the activities and community structure of fungi associated with plant litter. The results showed that ALAN and/or Cd can change both water and leaf litter characteristics. ALAN exposure not only altered fungal community structure and their correlations, but also increased the activities of alkaline phosphatase, &beta, glucosidase, and cellobiohydrolase. The leaf litter decomposition rate was 71% higher in the A-Cd treatment than that in the N-Cd treatment, indicating that the presence of ALAN weakened the negative impact of Cd on leaf litter decomposition. These results suggested that ALAN exposure mitigated the negative effect of Cd on leaf litter decomposition, contributing to the duel effect of ALAN on leaf litter decomposition. Overall, the results expand our understanding of ALAN on the environment and highlight the contribution of ALAN to Cd toxicity in aquatic ecosystems.

While karst tiankengs have a higher capacity to act as safe havens for biodiversity in changing climates, little is known about their soil microorganisms. To fill this gap, we investigate the distribution and driving factors of the bacterial community in karst tiankeng systems. There is a significant difference in the soil characteristics between the inside and the outside of a karst tiankeng. At the karst tiankeng considered in this study, the bacterial composition, in terms of the operational taxonomic unit (OTU), was found to be significantly different in different soil samples, taken from diverse sampling sites within the collapsed doline or the external area, and showed a high habitat heterogeneity. The dominant phylum abundances vary with the sampling sites and have their own indicator taxa from phylum to genus. Unlike the primary controlling factors of plant diversity, the microclimate (soil moisture and temperature), soil pH, and slope dominated the distribution of the bacterial community in karst tiankeng systems. Our results firstly showed the distribution characteristics of bacterial communities and then revealed the importance of microhabitats in predicting the microbial distribution in karst tiankeng systems.

Artificial light at night (ALAN, also known as light pollution) has been proved to be a contributor to environmental change and a biodiversity threat worldwide, yet little is known about its potential interaction with different metal pollutants, such as arsenic (As), one of the largest threats to aquatic ecosystems. To narrow this gap, an indoor microcosm study was performed using an ALAN simulation device to examine whether ALAN exposure altered the impact of arsenic on plant litter decomposition and its associated fungi. Results revealed that microbial decomposers involved in the conversion of As(III) to As(V), and ALAN exposure enhanced this effect; ALAN or arsenic only exposure altered fungal community composition and the correlations between fungi species, as well as stimulated or inhibited litter decomposition, respectively. The negative effects of arsenic on the decomposition of Pterocarya stenoptera leaf litter was alleviated by ALAN resulting in the enhanced photodegradation of leaf litter lignin and microbiological oxidation of As(III) to As(V), the increased microbial biomass and CBH activity, as well as the enhanced correlations between CBH and litter decomposition rate. Overall, results expand our understanding of ALAN on environment and highlight the contribution of ALAN to the toxicity of arsenic in aquatic ecosystems.

The geomorphologic features called tiankengs were first discovered and named at the end of the twentieth century in karst areas of China. They have enjoyed increasing attention owing to their unusual geologic processes and unique ecological communities. However, the understanding of classification, geomorphic evolution, developmental conditions, geological dating and ecological environments of tiankengs are still extensively disputed by geomorphologists and geologists. This article focuses on combining all main areas of recent research activities from three aspects: development, evolution and transformation of karst tiankengs; biodiversity of karst tiankeng forests; and the impact of human activities on karst tiankeng ecosystems. Finally, we suggest future direction for research on karst tiankeng ecosystems: (1) multidisciplinary systematic study; (2) processes of ecological change and environmental effects under the influence of both natural and human impacts; (3) research on their protection, rational utilization, and sustainable management.

Forage production and quality of five tropical grass accessions (Guimu-1 hybrid elephant grass (PG1), Mulato II (M II), Ubon paspalum (PU), hybrid elephant grass (PH) and Reyan 11 paspalum (PR11)) and two tropical legume accessions (Reyan 5 stylo (SR5) and Ubon stylo (SU)) were evaluated in a field experiment in a subtropical area with hot summers and cold winters in Guangxi, China. Three forage stubble cover managements: no cover (CK), dry mass cover (MC) and plastic cover (PC) were applied at the end of the summer period to evaluate cold tolerance and accession survival over the winter. Photosynthesis measurements were taken from the forages in mid-summer. The results showed that PG1 accession produced significantly higher dry matter yields (67.0 t·ha-1) than the other grass and legume accessions. Legume accessions SU and SR5 produced much less dry matter (6.4 - 7.2 t·ha-1) compared to the grasses. M II, PU and PR11 contained the largest proportion of leaf. PG1 and PH showed good cold tolerance (survival rate >85%) under -1°C conditions without any cover management. PR11 had better cold tolerance than PU. M II exhibited very poor winter survival under no cover and with massive cover, and only survived well under plastic cover. The two stylo accessions died completely under all winter cover management treatments. In the growing season, under a given photosynthesis photon flux density (PPFD) = 1500 μmol m-2 s-1, the net photosynthesis rate Pn of all the seven accessions was above 28 μmol m-2 s-1, of which hybrid elephant grass and M II were above 42 μmol m-2 s-1. Though these 7 tropical accessions yielded high production in the grow season, stylo and M II are sensitive to cold in subtropical region of Guangxi. The result suggests that PG1 and PU are good accessions and can be used as productive perennial pasture, while stylo and M II are simply considered as annual one. Additionally, if paspalum was trained in cool region before being introduced to subtropical region, it may present both productivity and enhancive cold tolerance.

Artificial light at night (ALAN) is an increasing phenomenon worldwide that can cause a series of biological and ecological effects, yet little is known about its potential interaction with other stressors in aquatic ecosystems. Here, we tested whether the impact of lead (Pb) on litter decomposition was altered by ALAN exposure using an indoor microcosm experiment. The results showed that ALAN exposure alone significantly increased leaf litter decomposition, decreased the lignin content of leaf litter, and altered fungal community composition and structure. The decomposition rate was 51% higher in Pb with ALAN exposure treatments than in Pb without ALAN treatments, resulting in increased microbial biomass, &beta, glucosidase (&beta, G) activity, and the enhanced correlation between &beta, G and litter decomposition rate. These results indicate that the negative effect of Pb on leaf litter decomposition in aquatic ecosystems may be alleviated by ALAN. In addition, ALAN exposure also alters the correlation among fungi associated with leaf litter decomposition. In summary, this study expands our understanding of Pb toxicity on litter decomposition in freshwater ecosystems and highlights the importance of considering ALAN when assessing environmental metal pollutions.

Acid rain pollution is changing gradually from sulfuric acid rain (SAR) to mixed acid rain (MAR) and then to nitric acid rain (NAR) with the rapidly growing number of motor vehicles. The influences of changed acid rain types on ecosystem functions, particularly on litter decomposition, remain unclear. Two dominant litter types from a coniferous forest and a broad-leaved forest were incubated in microcosms with original forest soils and treated by five types of acid rain with different SO42− to NO3− ratios (1:0, 5:1, 1:1, 1:5, and 0:1). During a six-month incubation period, litter mass losses, soil microbial biomass, and enzyme activities were investigated. Results showed that various acid treatments inhibited litter decomposition, soil microbial biomass, and most enzyme activities, and the inhibitory effects of NAR were more significant than those of SAR and MAR. The resistance to external acid of microbial communities in broad-leaved forest was higher than that in coniferous forest. NAR and MAR treatments slowed down soil carbon (C), nitrogen (N), and phosphorus (P) mineralization by attenuating the correlations between litter mass losses and the enzymes involved in C, N, and P cycling. Results reveal that the ratio of SO42− to NO3− in acid rain is an important factor which profoundly influences litter decomposition process. In the future, a decreasing ratio of SO42− to NO3− in acid rain will be observed in subtropical forests. Thus, soil C would accumulate as a consequence of future acid precipitation, and this may seriously affect the balance of ecosystem C, N flux.

a b s t r a c t To better understand the effects of Typha angustifolia litter pre-exposure to ambient atmospheric exposure on its subsequent decomposition, we investigated the decomposition of Typha litter during exposure and its subsequent decomposition process, including changes in fungal community structure and extracellu- lar enzyme activity in aquatic environment. Results showed that pre-exposure treatments of Typha litter increased its nitrogen content but reduced its lignin content and carbon-to-nitrogen ratios. The results from the decomposition of pre-exposed litter in aquatic environments showed that the changes in chem- ical characters of Typha litter increased its digestibility, which changed the dominant fungal species, their contributions to leaf litter decomposition, and the relationships of enzyme activities with litter mass loss. The changes also promoted nitrate reductase activities. These results suggest that environmental exposure of Typha litter can increase its digestibility.

A bacterium isolated from Lake Taihu was identified as Pseudomonas sp. A3CT, which performed different effects on Microcystis spp. Growth of Microcystis flos-aquae and Microcystis aeruginosa was assessed in co-culture with A3CT to determine the stimulatory or inhibitory effects on these toxic, bloom-forming Microcystis strains. Results demonstrated that the impacts of A3CT were species specific. A3CT promoted the growth of M. aeruginosa but inhibited growth of M. flos-aquae. To investigate the cause of this phenomenon, the chemical composition of A3CT exudates and the impact of exposure to A3CT exudates on the two Microcystis species were determined. Results suggested that the observed differential growth responses of the two microalgae to A3CT exposure might be related to two components in A3CT exudates NH4 + and cadaverine. Growth stimulation of M. aeruginosa by A3CT was significantly related to NH4 + concentration. Cadaverine possibly acted as a growth inhibitor of M. flos-aquae. The different effects of cadaverine on growth of the two Microcystis strains suggested that A3CT might play a role in intrageneric succession patterns observed during Microcystis blooms in Lake Taihu.

Anthropogenic nitrogen (N) deposition is an expanding problem that affects the functioning and composition of forest ecosystems, particularly the decomposition of forest litters. Legumes play an important role in the nitrogen cycle of forest ecosystems. Two litter types were chosen from Zijin Mountain in China: Robinia pseudoacacia leaves from a leguminous forest (LF) and Liquidambar formosana leaves from a non-leguminous forest (NF). The litter samples were mixed into original forest soils and incubated in microcosms. Then, they were treated by five forms of N addition: NH4 +, NO3 −, urea, glycine, and a mixture of all four. During a 6-month incubation period, litter mass losses, soil microbial biomass, soil pH, and enzyme activities were investigated. Results showed that mixed N and NO3 −-N addition significantly accelerated the litter decomposition rates of LF leaves, while mixed N, glycine-N, and urea-N addition significantly accelerated the litter decomposition rates of NF leaves. Litter decomposition rates and soil enzyme activities under mixed N addition were higher than those under single form of N additions in the two forest types. Nitrogen addition had no significant effects on soil pH and soil microbial biomass. The results indicate that nitrogen addition may alter microbial allocation to extracellular enzyme production without affecting soil microbial biomass, and then affected litter decomposition process. The results further reveal that mixed N is a more important factor in controlling litter decomposition process than single form of N, and may seriously affect soil N cycle and the release of carbon stored belowground.

A simulated wetland experiment was used to investigate the effect of thallium (Tl) accumulation on the growth of Arundo donax L., its photosynthetic characteristics and its antioxidant enzyme activities. Tl accumulated in the order of stems

Studies have shown that microorganisms may be used to eliminate cyanobacteria in aquatic environments. The present study showed that the white-rot fungus Trametes versicolor F21a could degrade Microcystis aeruginosa . After T. versicolor F21a and Microcystis spp. were co-incubated for 60 h, > 96% of Microcystis spp. cells were degraded by T. versicolor F21a. The activities of extracellular enzymes showed that cellulase, β-glucosidase, protease, and laccase were vital to Microcystis spp. degradation in the early stage (0 h to 24 h), while β-glucosidase, protease, laccase, and manganese peroxidase in the late stage (24 h to 60 h). The positive and significant correlation of the degradation rate with these enzyme activities indicated that these enzymes were involved in the degradation rate of Microcystis spp. cells at different phases. It suggested that the extracellular enzymes released by T. versicolor F21a might be vital to Microcystis spp. degradation. The results of this study may be used to develop alternative microbial control agents for cyanobacterial control.

To understand the further impacts of multiple stressors in freshwater, we investigated the effects of heavy metal (HM, Cu and Zn) and nutrient enrichments (nitrogen and phosphorus, NP) on microbial decomposition of Pterocarya stenoptera litter and the associated extracellular enzyme activities and microbial biomass with microcosms. Results showed that the decomposition rates were slower in the polluted stream waters than those in the unpolluted ones, which corresponded to lower microbial biomass and integrated enzyme activities of cellulose and β-glucosidase. The decomposition rates were accelerated at low HM level, which was associated with the stimulated enzyme activities of hydrolytic enzymes or was stimulated by both NP levels in polluted stream waters. In particular, the hydrolase enzyme activities of microbial communities in polluted stream waters were stimulated by low HM level, suggesting that low HM level-stimulated litter decomposition may be due to the increased enzymatic activities. When microbial communities were exposed to HM and NP simultaneously, the inhibitory effect (in unpolluted stream waters) or the stimulated effect (in polluted stream waters) of low HM concentration was enhanced and attenuated, respectively, which suggests that the NP antagonistic effect against HM toxicity on litter decomposition may contribute to the litter-associated extracellular enzyme activities. These results suggest that the co-occurrence of HM and NP may have antagonistic effects on stream ecosystem functioning.