Nitrogen addition stimulated soil respiration more so than carbon addition in alpine meadows

The soil carbon (C) and nitrogen (N) availability are important in the regulation of soil C cycling under climate change. Fertilizers alter soil C and N availability, which can affect C balance. However, the impact of fertilizers on C balance in grassland restoration has been equivocal and warrants more research. We determined the direct and indirect effects of the addition of three levels of C (sucrose) (0, 60, and 120 kg C ha-1 yr-1), three levels of N (urea) (0, 50, and 100 kg N ha-1 yr-1), and a combination of C plus N at each of the levels on soil respiration (Rs) dynamics and C balance in an alpine meadow in northern Tibet (4700 m above sea level). This study was undertaken during the middle of the growing season in 2011-2012. The addition of C and/or N stimulated CO2 emission, which was 2-fold greater in 2011 (102-144 g C m-2) than in 2012 (43-54 g C m-2). The rate of Rs increased with the addition of N, but was not affected with the addition of C plus N. Microbial biomass C, dissolved organic C and inorganic N were the main drivers of Rs. We concluded that N addition stimulated Rs to a greater extent than C addition in the short term. The application of fertilizer in the restoration of degraded grassland should be re-considered.

A hierarchical dataset of vegetative and reproductive growth in apple tree organs under conventional and non-limited carbon resources

A monitoring of apple fruit, shoot and trunk growth was performed on 15 trees, equally split according to three treatments, which determined heavily contrasting carbon assimilate availability: unmanipulated trees (FRU), thinned trees (THI) and defruited trees (DEF). Several variables describe the vegetative growth on FRU and DEF trees (shoot length, base diameter, number of fruits on shoot, and height, diameter, pruning intensity and number of fruits of the branch carrying the shoot; trunk circumference), as well as the fruit growth on FRU and THI trees (3 fruit diameters). Additional measurements from ancillary shoots (apical diameter, number of leaves, leaf dry weight, stem dry weight, fresh mass, volume) and fruits (3 diameters, dry weight) from trees undergoing the same treatments, provide a more complete (destructive) characterization of organs growth, thanks to several measurements performed across the growing season. Organs are provided with categorical variables indicating the treatment, tree, canopy height, orientation (for both shoots and fruit), as well as branch and shoot identifiers, so that hierarchical modeling of the dataset can be performed. The dataset is completed with dates and day of the year of the measurements and the accumulated growing degree days from full bloom. Data can be used to calculate apple tree absolute and relative growth rates, maximum potential growth rates, as well as shoot growth responses to thinning and pruning. The dataset can also be used to calibrate allometric relationships, estimate structural apple tree growth parameters and their variability.

The regulators of soil organic carbon mineralization upon lime and/or phosphate addition vary with depth

Knowledge of the key factors regulating soil organic carbon (OC) mineralization in response to fertilizers and lime application is essential to understanding the effects of agricultural land management on soil OC preservation. Microbial community composition and OC availability to microorganisms have been proposed as the two most imperative factors controlling soil OC mineralization, although their relative importance is still under debate. Here we performed a laboratory incubation in combination with high-throughput sequencing and structural equation modeling to examine the mechanisms underlying the responses of OC mineralization in the topsoil and the subsoil of a volcanic soil (an Andosol) to the additions of lime and/or phosphate. Results showed that lime and/or phosphate additions induced distinct shifts in the microbial community composition and functional profiles in the topsoil and the subsoil. We found that OC mineralization relied on microbial community composition and functionality in the topsoil but was strongly related to the quality and quantity of the water-extractable OC (indicative of the OC availability) in the subsoil. These data suggest that the key regulator controlling the response of OC mineralization to lime and/or P additions shifts from microbial community composition to OC availability as soil depth increases in the Andosol. Our findings highlight the central role of mechanisms controlling soil OC mineralization in regulating the responses of mineralization to intensive agricultural management practices.

Impacts of elevated CO2 on plant resistance to nutrient deficiency and toxic ions via root exudates: A review

Elevated atmospheric CO₂ (eCO₂) concentration can increase root exudation into soils, which improves plant tolerance to abiotic stresses. This review used a meta-analysis to assess effect sizes of eCO₂ on both efflux rates and total amounts of some specific root exudates, and dissected whether eCO₂ enhances plant's resistance to nutrient deficiency and ion toxicity via root exudates. Elevated CO₂ did not affect efflux rates of total dissolved organic carbon, a measure of combined root exudates per unit of root biomass or length, but increased the efflux amount of root systems per plant by 31% which is likely attributed to increased root biomass (29%). Elevated CO₂ increased efflux rates of soluble-sugars, carboxylates, and citrate by 47%, 111%, and 16%, respectively, but did not affect those of amino acids and malate. The increased carbon allocation to roots, increased plant requirements of mineral nutrients, and heightened detoxification responses to toxic ions under eCO₂ collectively contribute to the increased efflux rates despite lacking molecular evidence. The increased efflux rates of root exudates under eCO₂ were closely associated with improved nutrient uptake whilst less studies have validated the associations between root exudates and resistance to toxic ions of plants when grown under eCO₂. Future studies are required to reveal how climate change (eCO₂) affect the efflux of specific root exudates, particularly organic anions, the corresponding nutrient uptake and toxic ion resistance from plant molecular biology and soil microbial ecology perspectives.

A novel fed-batch strategy enhances lipid and astaxanthin productivity without compromising biomass of Chromochloris zofingiensis

To improve lipid and astaxanthin productivity without compromising biomass during the whole cultivation period, carbon-dependent kinetics involving nitrogen stress was applied under excess light to elevate intracellular carbon availability and metabolic activity of Chromochloris zofingiensis. Results suggested that fed-batch strategy proposed could increase lipid and astaxanthin productivity to 457.1 and 2.0 mg L^-1 d^-1, respectively. Biomass productivity at 1084.3 mg L^-1 d^-1 was comparable with that under suitable condition. Then ¹³C tracer-based metabolic flux analysis (¹³C-MFA) demonstrated that central carbon metabolism provided ATP, NADPH and carbon availability for lipid biosynthesis during the strategy. In combination with targeted metabolite analysis, ¹³C-MFA revealed that the strategy improved precursor content for lipid biosynthesis and elevated path rate to synthesize C16:0 and C18:0. The enhanced lipid content potentially accounted for the high biomass productivity. Therefore, comprehensively understanding relationships between carbon availability and carbon conversion could precisely design strategy for productivity improvements during cultivation.

Boost carbon availability and value in algal cell for economic deployment of biomass

This study elucidated storage carbon metabolism in a dynamic manner through kinetic model, metabolomics and stable metabolic flux analysis. Results revealed nutrient uptake rate, carbon availability and synthetic path rate accounted for the integration of process-compatible products. The uptake rate could be enhanced by promoting carbohydrate accumulation, inducing high performance of tricarboxylic acid cycle and anaplerotic routes. Values of specific rate for lipid from kinetic model and synthetic path rate from metabolic flux analysis revealed that conversion of carbon sinks occupied a key position in increasing productivities of lipid and astaxanthin to 302.34 and 1.83 mg g^-1 d^-1, respectively. Additionally, economic estimation was applied to link cultivation factors with market scenario and demonstrated that regulating such carbon metabolism raised 30% increase of biomass value. This study therefore provided a new orientation to boost carbon efficiency that helped to engineer carbon flux from carbon source to targeted products precisely and rapidly.