Shuangshuang Li

Submerged vegetation removal promotes shift of dominant phytoplankton functional groups in a eutrophic lake

Historical data indicate that the dominance of submerged plants in Dianchi Lake in the 1960s was characterized by low algal density with dominance of non-toxic group J (Scenedesmus, Pediastrum, etc.). The removal of submerged plants, which began in the 1970s, resulted in the expansion of bloom-forming Microcystis (group M). Laboratory experiments suggested that Microcystis aeruginosa was inclined to grow and develop at elevated temperatures. The growth of Scenedesmus obliquus was slower than that of co-cultivated M. aeruginosa in the absence of Ceratophyllum demersum, especially at higher temperatures. The existence of submerged plant C. demersum could inhibit the growth of the harmful algae M. aeruginosa and this inhibitory effect by C. demersum was enhanced with an increase in temperature. Instead, with C. demersum, the growth of S. obliquus was not inhibited, but the co-cultivated M. aeruginosa was eliminated in a short time. Combined with the historical data and laboratory experiments, it was indicated that the submerged plants might play important roles in the dominance of the non-toxic group J in the historical succession. Consequently, the introduction of the submerged plant such as C. demersum might alter the dominant phytoplankton functional groups from M to J and benefit the restoration of the eutrophic lake.

Erratum to: Microbial Succession and Nitrogen Cycling in Cultured Biofilms as Affected by the Inorganic Nitrogen Availability.

Biofilms play important roles in nutrients and energy cycling in aquatic ecosystems. We hypothesized that as eutrophication could change phytoplankton community and decrease phytoplankton diversity, ambient inorganic nitrogen level will affect the microbial community and diversity of biofilms and the roles of biofilms in nutrient cycling. Biofilms were cultured using a flow incubator either with replete inorganic nitrogen (N-rep) or without exogenous inorganic nitrogen supply (N-def). The results showed that the biomass and nitrogen and phosphorous accumulation of biofilms were limited by N deficiency; however, as expected, the N-def biofilms had significantly higher microbial diversity than that of N-rep biofilms. The microbial community of biofilms shifted in composition and abundance in response to ambient inorganic nitrogen level. For example, as compared between the N-def and the N-rep biofilms, the former consisted of more diazotrophs, while the latter consisted of more denitrifying bacteria. As a result of the shift of the functional microbial community, the N concentration of N-rep medium kept decreasing, while that of N-def medium showed an increasing trend in the late stage. This indicates that biofilms can serve as the source or the sink of nitrogen in aquatic ecosystems, and it depends on the inorganic nitrogen availability.

Influence of phosphorus availability on the community structure and physiology of cultured biofilms

Biofilms have important effects on nutrient cycling in aquatic ecosystems. However, publications about the community structure and functions under laboratory conditions are rare. This study focused on the developmental and physiological properties of cultured biofilms under various phosphorus concentrations performed in a closely controlled continuous flow incubator. The results showed that the biomass (Chl a) and photosynthesis of algae were inhibited under P-limitation conditions, while the phosphatase activity and P assimilation rate were promoted. The algal community structure of biofilms was more likely related to the colonization stage than with the phosphorus availability. Cyanobacteria were more competitive than other algae in biofilms, particularly when cultured under low P levels. A dominance shift occurred from non-filamentous algae in the early stage to filamentous algae in the mid and late stages under P concentrations of 0.01, 0.1 and 0.6 mg/L. However, the total N content, dry weight biomass and bacterial community structure of biofilms were unaffected by phosphorus availability. This may be attributed to the low respiration rate, high accumulation of extracellular polymeric substances and high alkaline phosphatase activity in biofilms when phosphorus availability was low. The bacterial community structure differed over time, while there was little difference between the four treatments, which indicated that it was mainly affected by the colonization stage of the biofilms rather than the phosphorus availability. Altogether, these results suggested that the development of biofilms was influenced by the phosphorus availability and/or the colonization stage and hence determined the role that biofilms play in the overlying water.

Differential responses of different phenotypes of Microcystis (Cyanophyceae) to UV-B radiation

Abstract: Microcystis can be single celled or colonial under certain conditions, thereby possessing phenotypic plasticity. Differential physiological and biochemical responses of colonial Microcystis aeruginosa FACHB 939 and its single-celled strain to ultraviolet type B radiation (UV-B) exposure were investigated. Results suggested that UV-B exposure exerted a lower inhibitory effect on the growth of colonial Microcystis, and that the single-celled strain had higher ability to recover after exposure to UV-B. Carotenoids/chlorophyll a (Chl a) ratios were increased, whereas phycobilisome/Chl a ratios were decreased by UV-B exposure. The photosynthetic activities of both phenotypes were inhibited, but colonial Microcystis showed higher tolerance and recovery ability to UV-B exposure. The sheath and shading effect, as well as changes of pigments of colonial Microcystis, were believed to play roles in resisting UV-B exposure. UV-B radiation can increase the sinking rate of the single-celled Microcystis and cause colonial Microcystis to shift from a floating to a sinking state. The observed reduction of colony size and increase in total carbohydrate content induced by UV-B radiation presumably caused the decrease in buoyancy in Microcystis. However, the increase in sinking rate is also an important way for Microcystis to avoid damage inflicted by UV-B radiation.

Nitrogen-cycling microbial community functional potential and enzyme activities in cultured biofilms with response to inorganic nitrogen availability

Biofilms mediate crucial biochemical processes in aquatic ecosystems. It was hypothesized that eutrophication may promote the growth of biofilms, resulting in larger numbers of functional genes. However, the metabolic activity and the roles of biofilms in N cycling will be affected by ambient inorganic nitrogen availability, not by the abundance of functional genes. Biofilms were cultured either with replete inorganic nitrogen (N-rep) or without exogenous inorganic nitrogen supply (N-def) in a flow incubator, and the N-cycling gene abundances (nifH, N2 fixation; amoA, ammonia oxidation, archaea and bacteria; nirS and nirK, denitrification) and enzyme activities (nitrogenase and nitrate reductase) were analyzed. The results showed that, comparing the N-def and N-rep biofilms, the former contained lower nifH gene abundance, but higher nitrogenase activity (NA), while the latter contained higher nifH gene abundance, but lower NA. Different patterns of NA diel variations corresponded to the dynamic microbial community composition and different stages of biofilm colonization. Ammonia oxidizing bacteria (AOB), detected only in N-def biofilms, were responsible for nitrification in biofilms. N-rep biofilms contained high nirS and nirK gene abundance and high denitrification enzyme activity, but N-def biofilms contained significantly lower denitrification gene abundance and activity. In general, the strong N2 fixation in N-def biofilms and strong denitrification in N-rep biofilms assured the balance of aquatic ecosystems. The results suggested that evaluation of the functional processes of N cycling should not only focus on genetic potential, but also on the physiological activity of biofilms.

The influence of desiccation on the recovery process of nitrogenase activity in restored biological soil crusts

Biological soil crusts (BSCs), a layered structure formed by associations of soil organisms and topsoil, dominate arid and semiarid areas and serve important ecological functions in these areas (Eldridge and Greene, 1994). Nitrogen fixation by BSCs is the main source of N in arid and semi-arid ecosystems. Desiccation is the most notable factor that influences BSCs, which recover physiological activity only after moistening. By influencing the amount of carbohydrates, energy pools, nitrogen compounds, and nitrogenase enzyme, desiccation affects nitrogen fixation of BSCs (Belnap, 2003). Desiccation patterns are common and diverse due to the episodic and reduced precipitation leading to varied and complex effects of desiccation on nitrogen fixation, which require a deeper understanding. In addition, responses of nitrogen fixation to desiccation vary among different crust types and compositions (Jeffries et al., 1992). Therefore, it is essential to study the response of nitrogen fixation in BSCs with different successional stages to drought regimes. In this study, we aimed to investigate the effect of prior desiccation duration on the recovery process of the nitrogenase activity (NA) in BSCswith different successional stages. As nitrogen fixation requires ATP and electrons provided by photosynthates, the effect of prior desiccation duration on the

Microbial Succession and Nitrogen Cycling in Cultured Biofilms as Affected by the Inorganic Nitrogen Availability (vol 73, pg 1, 2017)

Biofilms play important roles in nutrients and energy cycling in aquatic ecosystems. We hypothesized that as eutrophication could change phytoplankton community and decrease phytoplankton diversity, ambient inorganic nitrogen level will affect the microbial community and diversity of biofilms and the roles of biofilms in nutrient cycling. Biofilms were cultured using a flow incubator either with replete inorganic nitrogen (N-rep) or without exogenous inorganic nitrogen supply (N-def). The results showed that the biomass and nitrogen and phosphorous accumulation of biofilms were limited by N deficiency; however, as expected, the N-def biofilms had significantly higher microbial diversity than that of N-rep biofilms. The microbial community of biofilms shifted in composition and abundance in response to ambient inorganic nitrogen level. For example, as compared between the N-def and the N-rep biofilms, the former consisted of more diazotrophs, while the latter consisted of more denitrifying bacteria. As a result of the shift of the functional microbial community, the N concentration of N-rep medium kept decreasing, while that of N-def medium showed an increasing trend in the late stage. This indicates that biofilms can serve as the source or the sink of nitrogen in aquatic ecosystems, and it depends on the inorganic nitrogen availability.

Application of sodium alginate in induced biological soil crusts: enhancing the sand stabilization in the early stage

Induced biological soil crust (IBSC) technology has proved to be an effective means for speeding up the recovery of biological soil crusts (BSC) in arid and semi-arid regions. This study aims at improving the IBSC technology by using sodium alginate (SA) due to its sand-stabilizing ability in the early development stage of IBSCs. Results showed that SA can easily form a thin film on the surface of soil and can significantly enhance the compressive strength of the topsoil. More importantly, no negative effects of SA on the development and physiological activity of IBSCs were observed, and SA could facilitate the colonization and growth of cyanobacteria on sand. Moreover, the application of SA was much cheaper than the straw checkerboard barriers which are widely used in desertification control. This study suggests that SA can promote and accelerate the formation of BSCs; thus, it can be applied in IBSC technology to enhance the sand-stabilizing property of BSCs in the early stage.