Proteomic response of Phaeocystis globosa to nitrogen limitation

Phaeocystis globosa is an important unicellular eukaryotic alga that can also form colonies.P.globosa can cause massive harmful algal blooms and plays an important role in the global carbon or sulfur cycling.Thus far,the ecophysiology of P.globosa has been investigated by numerous studies.However,the proteomic response of P.globosa to nitrogen depletion remains largely unknown.We compared four protein preparation methods of P.globosa for two-dimensional electrophoresis(2-DE)(Urea/Triton X-100 with trichloroacetic acid(TCA)/acetone precipitation;TCA/acetone precipitation;Radio Immuno Precipitation Assay(RIPA)with TCA/acetone precipitation;and Tris buffer).Results show that the combination of RIPA with TCA/acetone precipitation had a clear gel background and showed the best protein spot separation effect,based on which the proteomic response to nitrogen depletion was studied using 2-DE.In addition,we identified six differentially expressed proteins whose relative abundance increased or decreased more than 1.5-fold(P<0.05).Most proteins could not be identified,which might be attributed to the lack of genomic sequences of P.globosa.Under nitrogen limitation,replication protein-like,RNA ligase,and sn-glycerol-3-phosphate dehydrogenase were reduced,which may decrease the DNA replication level and ATP production in P.globosa cells.The increase of endonucleaseⅢand transcriptional regulator enzyme may affect the metabolic and antioxidant function of P.globosa cells and induce cell apoptosis.These findings provide a basis for further proteomic study of P.globosa and the optimization of protein preparation methods of marine microalgae.

Effects of phosphorus and nitrogen limitation on PHA production in activated sludge

The effects of phosphorus and nitrogen limitation on polyhydroxyalkanoate （PHA） production and accumulation by activated sludge biomass with acetate as a carbon source were investigated. Pre-selected influent carbon-phosphorus （C：P, W/W） of 100, 160, 250, 500 and 750, and carbon-nitrogen （C：N, W/W） of 20, 60, 100, 125 and 180 were applied in the phosphorus limitation experiments and the nitrogen limitation experiments, respectively. The maximum PHA accumulation up to 59% of the cell dry weight with a PHA productivity of 1.61 mg PHA/mg COD consumed was observed at the C：N 125 in the nitrogen limitation experiment. This value was much higher than that obtained in previous studies with a normal substrate feeding. The study showed that activated sludge biomass would produce more polyhydroxybutyrate than polyhydroxyvalerate under the stress of nutrient limitation, especially under phosphorus limitation conditions. The experimental result also indicated that both phosphorus and nitrogen limitation may cause sludge bulking.

How do nitrogen-limited alpine coniferous forests acquire nitrogen?A rhizosphere perspective

Background:Alpine coniferous forest ecosystems dominated by ectomycorrhizal(ECM)tree species are generally characterized by low soil nitrogen(N)availability but stabilized plant productivity.Thus,elucidating potential mechanisms by which plants maintain efficient N acquisition is crucial for formulating optimized management practices in these ecosystems.Methods:We summarize empirical studies conducted at a long-term field monitoring station in the alpine coniferous forests on the eastern Tibetan Plateau,China.We propose a root-soil interaction-based framework encompassing key components including soil N supply,microbial N transformation,and root N uptake in the rhizosphere.Results:We highlight that,(i)a considerable size of soil dissolved organic N pool mitigates plant dependence on inorganic N supply;(ii)ectomycorrhizal roots regulate soil N transformations through both rhizosphere and hyphosphere effects,providing a driving force for scavenging soil N;(iii)a complementary pattern of plant uptake of different soil N forms via root-and mycorrhizal mycelium-pathways enables efficient N acquisitions in response to changing soil N availability.Conclusions:Multiple rhizosphere processes abovementioned collaboratively contribute to efficient plant N acquisition in alpine coniferous forests.Finally,we identify several research outlooks and directions to improve the understanding and prediction of ecosystem functions in alpine coniferous forests under on-going global changes.

Effects of soil nitrate:ammonium ratio on plant carbon:nitrogen ratio and growth rate of Artemisia sphaerocephala seedlings

Can soil nitrate： ammonium ratios influence plant carbon： nitrogen ratios of the early succession plant？ Can plant carbon： nitrogen ratios limit the plant growth in early succession？ To address these two questions, we performed a two-factor （soil nitrate： ammonium ratio and plant density） randomized block design and a uniform-precision rotatable central composite design pot experiments to examine the relationships between soil nitrate： ammonium ratios, the carbon： nitrogen ratios and growth rate of Artemisia sphaerocephala seedlings. Under adequate nutrient status, both soil nitrate： ammonium ratios and plant density influenced the carbon： nitrogen ratios and growth rate of A. sphaerocephala seedlings. Under the lower soil nitrate： ammonium ratios, with the increase of soil nitrate： ammonium ratios, the growth rates of plant height and shoot biomass of A. sphaerocephala seedlings decreased significantly; with the increase of plant carbon： nitrogen ratios, the growth rates of shoot biomass of A. sphaerocephala seedlings decreased significantly. Soil nitrate： ammonium ratios affected the carbon： nitrogen ratios of A. sphaerocephala seedlings by plant nitrogen but not by plant carbon. Thus, soil nitrate： ammonium ratios influenced the carbon： nitrogen ratios of A. sphaerocephala seedlings, and hence influenced its growth rates. Our results suggest that under adequate nutrient environment, soil nitrate： ammonium ratios can be a limiting factor for the growth of the early succession plant.

Dynamic carbon-nitrogen coupling under global change

Carbon-nitrogen coupling is a fundamental principle in ecosystem ecology.However,how the coupling responds to global change has not yet been examined.Through a comprehensive and systematic literature review,we assessed how the dynamics of carbon processes change with increasing nitrogen input and how nitrogen processes change with increasing carbon input under global change.Our review shows that nitrogen input to the ecosystem mostly stimulates plant primary productivity but inconsistently decreases microbial activities or increases soil carbon sequestration,with nitrogen leaching and nitrogenous gas emission rapidly increasing.Nitrogen fixation increases and nitrogen leaching decreases to improve soil nitrogen availability and support plant growth and ecosystem carbon sequestration under elevated CO_(2)and temperature or along ecosystem succession.We conclude that soil nitrogen cycle processes continually adjust to change in response to either overload under nitrogen addition or deficiency under CO_(2)enrichment and ecosystem succession to couple with carbon cycling.Indeed,processes of both carbon and nitrogen cycles continually adjust under global change,leading to dynamic coupling in carbon and nitrogen cycles.The dynamic coupling framework reconciles previous debates on the“uncoupling”or“decoupling”of ecosystem carbon and nitrogen cycles under global change.Ecosystem models failing to simulate these dynamic adjustments cannot simulate carbonnitrogen coupling nor predict ecosystem carbon sequestration well.

Comparing the temperature sensitivity of organic matter decomposition in oxic and oxygen-deprived soils

No consistent variation was found in soil respiration Q10 under various O2 conditions.Substrate C quality had a strong effect on Q10 in oxic soils.N limitation had a large impact on Q10 in soils under O2 limitation.Current studies on the temperature sensitivity(Q10)of soil organic matter(SOM)decomposition mainly focus on aerobic conditions.However,varia-tions and determinants of Q10 in oxygen(O2)-deprived soils remain unclear.Here we incubated three grassland soils under oxic,suboxic,and anoxic conditions subjected to varying temperatures to compare variations in Q10 in relation to changing substrates.No consistent variation was found in Q10 under various O2 conditions.Further analysis of edaphic properties demon-strated that substrate carbon quality showed a strong influence on Q10 in oxic soils,whereas nitrogen limitation played a more important role in suboxic and anoxic soils.These results suggest that substrate carbon quality and nitrogen limitation may play roles of varying importance in determining the temperature sensitivity of SOM decomposition under various O2 conditions.

Controlling cyanobacterial blooms by managing nutrient ratio and limitation in a large hypereutrophic lake: Lake Taihu, China

Excessive nitrogen（N） and phosphorus（P） loading of aquatic ecosystems is a leading cause of eutrophication and harmful algal blooms worldwide, and reducing nutrient levels in water has been a primary management objective. To provide a rational protection strategy and predict future trends of eutrophication in eutrophic lakes, we need to understand the relationships between nutrient ratios and nutrient limitations. We conducted a set of outdoor bioassays at the shore of Lake Taihu. It showed that N only additions induced phytoplankton growth but adding only P did not. Combined N plus P additions promoted higher phytoplankton biomass than N only additions, which suggested that both N and P were deficient for maximum phytoplankton growth in this lake（TN：TP = 18.9）. When nutrients are present at less than 7.75–13.95 mg/L TN and 0.41–0.74 mg/L TP, the deficiency of either N or P or both limits the growth of phytoplankton. N limitation then takes place when the TN：TP ratio is less than 21.5–24.7（TDN：TDP was 34.2–44.3）, and P limitation occurs above this. Therefore, according to this ratio, controlling N when N limitation exists and controlling P when P deficiency is present will prevent algal blooms effectively in the short term. But for the long term, a persistent dual nutrient（N and P） management strategy is necessary.