Phosphorus Limitation Research Articles

Orthophosphate fluxes in scattered trees from fragmented Andean landscapes highlight a biogeochemical role of foliar traits in pioneer species

AbstractHighly diverse neotropical ecosystems exhibit a natural limitation of phosphorus in the soil, sufficient to limit productivity and structure. This is more pronounced in Andean ecosystems, with high forest fragmentation and forest loss rates aggravating the effect. Previous studies have highlighted the importance of precipitation and its interaction with the canopy on nutrient inputs into forests. However, few studies have quantified the potential effects of structural and morphological tree diversity on the dynamics of phosphorous inputs on these ecosystems. In this study, we determined the association between 12 morphological plant functional traits and the movement of water‐driven orthophosphate from the canopy into the soil in 20 individuals of five tree species, on single individuals scattered across a human‐disturbed montane landscape in the Colombian Andes: Croton magdalenensis, Andesanthus lepidotus, Vismia baccifera and Quercus humboldtii and a commonly planted exotic species Eucalyptus globulus. We quantified PO4‐P concentrations in precipitation, throughfall and stemflow in all trees for 14 isolated rainfall events. In general, our results show a general enrichment of PO4‐P concentration in the net precipitation after passing through tree canopies. One particular species, C. magdalenensis, an ecological pioneer, had notably higher values of PO4‐P concentration. This condition relates, potentially, to a particularly higher epiphyte load, high leaf area and high trichome density. This condition potentially facilitates biogeochemical exchange and improves ecological functions associated with early stages of forest recovery (where pioneer species dominate forest composition). Our results are particularly relevant given that the highest contributions of PO4‐P to the soil occur in native species, which become key structures in the recovery of fragmented Andean ecosystems.

Monsoon-induced response of algal chlorophyll to trophic state, light availability, and morphometry in 293 temperate reservoirs

Eutrophication management is one of the greatest environmental challenges for lacustrine systems worldwide. The empirically predicted models between algal chlorophyll (CHL-a) and total phosphorus (TP) provide a basis for managing eutrophication in lakes and reservoirs, but other environmental factors influencing the empirical relations must be considered. Here, we tested the impacts of morphological and chemical variables, as well as the effect of the Asian monsoon, on the functional response of CHL-a to TP using two-year data of 293 agricultural reservoirs. This study was based on the approaches of empirical models (linear and sigmoidal), CHL-a:TP ratio, and trophic state index deviation (TSID). Algal CHL-a exhibited a strong log-linear relation with TP on the basis of 2-year average data (R2 = 0.69, p < 0.001), whereas it had a more sigmoidal relation in terms of monsoon-seasonal averages (R2 = 0.52, p < 0.001). The linear segment of the CHL-a–TP relation aligned with the gradient of TP (10 mg/L < TP < 100 mg/L) from mesotrophic to eutrophic conditions. The transfer efficiency of TP to CHL-a based on the 2-year mean CHL-a:TP was high (0.6 <) across all assessed agricultural systems. CHL-a:TP showed insignificant correlations with reservoir morphological variations, but it decreased (<0.5) in eutrophic and hypereutrophic systems during the monsoon season (July–August). Because TP and total suspended solids (TSS) have become increasingly abundant, light conditions become insufficient for algal growth during and after the monsoon season. Light-limited conditions become more prevalent in hypereutrophic systems with shallow depth and high dynamic sediment ratio (DSR) because of the intense rainfall inputs and wind-induced sediment resuspension of the post-monsoon season. TSID reflected the degree of phosphorus limitation and the reduction in underwater light corresponding to changes in reservoir water chemistry (ionic content, TSS, and TN:TP ratio), trophic state gradient, and morphological metrics (mainly mean depth and DSR). Our findings suggest that monsoon-induced changes in water chemistry and light attenuation, which are also associated with anthropogenic pollutant runoffs and reservoir morphology, are critical factors that influence the functional response of algal CHL-a to TP in temperate reservoirs. Modeling and assessing eutrophication should therefore take into account monsoon seasonality along with individual morphological features further.

Sulfolipid substitution ratios of Microcystis aeruginosa and planktonic communities as an indicator of phosphorus limitation in Lake Erie

AbstractPhosphorus (P) availability frequently limits primary production in lakes, influences the physiology of phytoplankton, shapes community structure, and can stimulate or constrain the formation of cyanobacterial blooms. Given the importance of P, numerous methods are available to assess P stress in phytoplankton communities. Marine phytoplankton are known to substitute sulfolipids for phospholipids in response to P limitation. We asked whether sulfolipid substitution might serve as an additional indicator of P stress in freshwater phytoplankton communities. The question was addressed using cultures of Microcystis aeruginosa, Lake Erie microcosms, and surveys of lipid profiles in Lake Erie during a Microcystis spp. bloom. Peak area response ratios of the intact polar lipids sulfoquinovosyldiacylglycerol (SQDG) to phosphatidylglycerol (PG) were used as the metric of lipid substitution. In cultures of M. aeruginosa NIES‐843, the SQDG : PG ratio increased from ~ 0.9 to ~ 3.3 with decreasing P concentration. In P‐limited communities, the SQDG : PG ratio increased from ~ 6 to ~ 11 after 48 h in microcosm controls, while P amendments reduced the ratio to ~ 3. In Lake Erie surveys, the SQDG : PG ratio ranged from ~ 0.4 to ~ 7.4 and was negatively correlated (Pearson r = −0.62) with total dissolved P. The SQDG : PG ratio was not correlated with concentrations of chlorophyll a, soluble reactive P, or N : P molar ratios. These results demonstrated that M. aeruginosa and Microcystis‐dominated communities remodel lipid profiles in response to P scarcity, providing a potential short‐term, time‐integrated biomarker of nutrient history and P stress in fresh waters.

Potato root-associated microbiomes adapt to combined water and nutrient limitation and have a plant genotype-specific role for plant stress mitigation

BackgroundDue to climate change and reduced use of fertilizers combined stress scenarios are becoming increasingly frequent in crop production. In a field experiment we tested the effect of combined water and phosphorus limitation on the growth performance and plant traits of eight tetraploid and two diploid potato varieties as well as on root-associated microbiome diversity and functional potential. Microbiome and metagenome analysis targeted the diversity and potential functions of prokaryotes, fungi, plasmids, and bacteriophages and was linked to plant traits like tuber yield or timing of canopy closure.ResultsThe different potato genotypes responded differently to the combined stress and hosted distinct microbiota in the rhizosphere and the root endosphere. Proximity to the root, stress and potato genotype had significant effects on bacteria, whereas fungi were only mildly affected. To address the involvement of microbial functions, we investigated well and poorly performing potato genotypes (Stirling and Desirée, respectively) under stress conditions and executed a metagenome analysis of rhizosphere microbiomes subjected to stress and no stress conditions. Functions like ROS detoxification, aromatic amino acid and terpene metabolism were enriched and in synchrony with the metabolism of stressed plants. In Desirée, Pseudonocardiales had the genetic potential to take up assimilates produced in the fast-growing canopy and to reduce plant stress-sensing by degrading ethylene, but overall yield losses were high. In Stirling, Xanthomonadales had the genetic potential to reduce oxidative stress and to produce biofilms, potentially around roots. Biofilm formation could be involved in drought resilience and nutrient accessibility of Stirling and explain the recorded low yield losses. In the rhizosphere exposed to combined stress, the relative abundance of plasmids was reduced, and the diversity of phages was enriched. Moreover, mobile elements like plasmids and phages were affected by combined stresses in a genotype-specific manner.ConclusionOur study gives new insights into the interconnectedness of root-associated microbiota and plant stress responses in the field. Functional genes in the metagenome, phylogenetic composition and mobile elements play a role in potato stress adaption. In a poor and a well performing potato genotype grown under stress conditions, distinct functional genes pinpoint to a distinct stress sensing, water availability and compounds in the rhizospheres.

Effects of Phosphorus Limitation on the Bioavailability of DOM Released by Marine Heterotrophic Prokaryotes.

Heterotrophic prokaryotes (HP) contribute largely to dissolved organic matter (DOM) processing in the ocean, but they also release diverse organic substances. The bioavailability of DOM released by HP under varying environmental conditions has not been fully elucidated. In this study, we investigated the bioavailability of DOM released by a single bacterial strain (Sphingopyxis alaskensis) and 2 natural HP communities grown under P-replete and P-limited conditions. The released DOM (HP-DOM) was used as a substrate for natural HP communities at a coastal site in the Northwestern Mediterranean Sea. We followed changes in HP growth, enzymatic activity, diversity, and community composition together with the consumption of HP-DOM fluorescence (FDOM). HP-DOM produced under P-replete and P-limited conditions promoted significant growth in all incubations. No clear differences in HP-DOM lability released under P-repletion and P-limitation were evidenced based on the HP growth, and P-limitation was not demonstrated to decrease HP-DOM lability. However, HP-DOM supported the growth of diverse HP communities, and P-driven differences in HP-DOM quality were selected for different indicator taxa in the degrading communities. The humic-like fluorescence, commonly considered recalcitrant, was consumed during the incubations when this peak was initially dominating the FDOM pool, and this consumption coincided with higher alkaline phosphatase activity. Taken together, our findings emphasize that HP-DOM lability is dependent on both DOM quality, which is shaped by P availability, and the composition of the consumer community.

Mixed planting improves soil aggregate stability and aggregate-associated C-N-P accumulation in subtropical China

Research on the variations in soil aggregate stability and ecological stoichiometry at aggregate scales by stand type is of great significance in investigating the distribution, limitation, balance, and cycling of organic carbon, nitrogen, and phosphorus (C-N-P). However, the effect of pure and mixed Chinese fir plantations on soil aggregate stability, organic carbon (OC), total nitrogen (TN), and total phosphorus (TP) stoichiometry characteristics at aggregate scales is still unclear. In this research, we explored the variations in soil aggregate mean weight diameter (MWD) and geometric mean diameter (GMD); soil OC, TN, and TP contents and stocks and the C:N:P ratios as affected by different stand types (mixed stands of Chinese fir and Mytilaria laosensis, mixed stands of Chinese fir and Michelia macclurei, and pure stand of Chinese fir); and aggregate size (&amp;lt;0.25, 0.25–1, 1–2, and &amp;gt;2 mm) at 0–20 and 20–40 cm depths in subtropical China. The soil OC and TN contents, as well as C:N:P ratios declined as aggregate size increased, whereas the C-N-P stocks showed the opposite tendencies, which were more distributed in &amp;gt;2 mm aggregates. Mixed stands of Chinese fir and M. laosensis with Chinese fir and M. macclurei displayed significantly higher soil aggregate stability, aggregate-associated TP content, OC and TN contents and stocks, and C:N and C:P ratios than did pure stands of Chinese fir. Soil aggregate stability was significantly positively correlated with the C-N-P contents and stocks as well as the C:N and C:P ratios, especially the C:N ratio and TN content. Overall, this work offers further information for scientific management and sustainable development of Chinese fir plantations, soil OC and nutrient cycling with ecological stoichiometry in the global terrestrial ecosystem.

Phosphorus limitation reduces microbial nitrogen use efficiency by increasing extracellular enzyme investments

Microbial nitrogen use efficiency (NUE), which reflects the proportion of nitrogen (N) taken up to be allocated to microbial biomass and growth, is central to our understanding of soil N cycling. However, the factors influencing microbial NUE remain unclear. Here, we explored the effects of climate factors, soil properties, and microbial variables on microbial NUE based on a survey of soils from 11 locations along a forest transect in eastern China. We found microbial NUE decreased with the ratio of acid phosphatase (AP) activity versus microbial growth rate. This suggested that increased microbial phosphorus acquisition decreased microbial NUE due to increasing investment in AP. However, microbial NUE increased with soil organic carbon content, because soil organic carbon is the source of material and energy for microbial growth and metabolism. Soil pH and mean annual temperature indirectly affected microbial NUE through their effects on the ratio of AP activity relative to microbial growth rate and soil organic carbon content, respectively. Our results improve our understanding and prediction of microbial NUE on a large spatial scale and emphasize the importance of phosphorus in affecting microbial metabolic efficiency.

Foliar nutrient resorption stoichiometry and microbial phosphatase catalytic efficiency together alleviate the relative phosphorus limitation in forest ecosystems.

Understanding how plants adapt to spatially heterogeneous phosphorus (P) supply is important to elucidate the effect of environmental changes on ecosystem productivity. Plant P supply is concurrently controlled by plant internal conservation and external acquisition. However, it is unclear how climate, soil, and microbes influence the contributions and interactions of the internal and external pathways for plant P supply. Here, we measured P and nitrogen (N) resorption efficiency, litter and soil acid phosphatase (AP) catalytic parameters (Vmax(s) and Km ), and soil physicochemical properties at four sites spanning from cold temperate to tropical forests. We found that the relative P limitation to plants was generally higher in tropical forests than temperate forests, but varied greatly among species and within sites. In P-impoverished habitats, plants resorbed more P than N during litterfall to maintain their N:P stoichiometric balance. In addition, once ecosystems shifted from N-limited to P-limited, litter- and soil-specific AP catalytic efficiency (Vmax(s) /Km ) increased rapidly, thereby enhancing organic P mineralization. Our findings suggested that ecosystems develop a coupled aboveground-belowground strategy to maintain P supply and N:P stoichiometric balance under P-limitation. We also highlighted that N cycle moderates P cycles and together shape plant P acquisition in forest ecosystems.

Phosphorus Limitation on Carbon Sequestration in China under RCP8.5

Phosphorus Limitation on Carbon Sequestration in China under RCP8.5

Nitrogen removal in improved subsurface wastewater infiltration system: Mechanism, microbial indicators and the limitation of phosphorus

To enhance the nitrogen removal capacity, scrap iron filings and Si–Al porous clay mineral material (PCMW) was used to improve a subsurface wastewater infiltration system (SWIS). The results showed TN and NH4+-N removal efficiencies of improved SWIS were 20.72% and 5.49% higher than those of the control SWIS, respectively. Based on the response of the removal performance, microbial community and function analysis of 16s rRNA amplicon sequencing results, the amending soil matrix substantially enriched the nitrogen removal bacteria (Rhizobiales_Incertae_Sedis and Gemmatimonadaceae), and significantly improved the activities of key enzymes (Hao, NasAB, NarGHI, NirK, NorBC, NirA and NirBD), particularly at co-occurrence zone of nitrification and denitrification (70–130 cm depth). The amending soil matrix not only extended the growth space of microbes, but also provided additional electrons and carbon sources for denitrifying bacteria by regulating the structure and function of the microbial community. In addition, amending soil matrix could enhance phosphate metabolism genes and phosphate solubilizing microbes in the denitrification zone by increasing the phosphorus source, thus strengthening nitrogen metabolism. Nitrospiraceae, Rhizobiales_Incertae_Sedis and Gemmatimonadaceae related to nitrogen removal and Bacillaceae with phosphate-solubilizing ability could be used as microbial indicators of nitrogen removal in SWISs. The reciprocal action of environmental on microbial characteristics exhibited microbial functional were related to DO, Fe2+, TOC, TP, TN, NH4+-N and NO3−-N. Those could be used as physicochemical and biological indicators for application and monitoring of SWIS. In conclusion, this study provided a low-cost and efficient enhancement approach for the application of SWIS in decentralized domestic sewage treatment, and furnished theoretical support for subsequent applications.

High light stress under phosphorus limitation in summer may accelerate diatom shift from Skeletonema to Chaetoceros in an oligotrophic coastal area of Japan

In the Seto Inland Sea, the largest semi-enclosed sea in Japan, the most dominant diatom in the past, Skeletonema spp., has been replaced by another diatom Chaetoceros spp. since the 1980s, and this shift is often explained as the result of oligotrophication. Based on previous observations of a shift from Skeletonema spp. to Chaetoceros spp. under prolonged sunny conditions, the recent increase in solar insolation over the last 30 years might have also accelerated the replacement of Skeletonema by Chaetoceros, especially during the summer when nutrient levels are relatively low and solar insolation is high. In our experiments, culture strains of Skeletonema costatum and Chaetoceros lorenzianus under severely nitrogen-limited conditions exhibited less non-photochemical quenching (NPQ) under prolonged exposure (1 h) to high light (800 µmol-photons m-2 s-1) and a decrease in photochemical quenching (qP) which was especially notable in S. costatum. Conversely, marked increases in NPQ were observed under severely phosphorus-limited conditions, even under short time exposure (30 s) to high light, even though the increase in NPQ could not relieve the decrease in qP, which was more apparent in S. costatum. These trends in NPQ and qP were attributed to the limited nutrients because replenishment of the nutrients led to a decrease in NPQ and an increase in qP. Interestingly, this recovery was faster in C. lorenzianus than S. costatum. The results showed that phosphorus depletion caused severe photoinhibition especially in S. costatum, irrespective of active NPQ induction. Further, given the severe phosphorus-limited conditions in the Seto Inland Sea for an extended period, we conducted competition experiments using continuous coculture of both species to simulate the typical summer environment where severe phosphorus limitation and high light occur. The results showed that the shift from S. costatum to C. lorenzianus was accelerated by continuous exposure to high light, which could explain the recent shift in the dominant species in the summer in the study area.

Daphnia magna as biological harvesters for green microalgae grown on recirculated aquaculture system effluents

The sustainability of recycling aquaculture systems (RAS) is challenged by nutrient discharges, which cause water eutrophication. Efficient treatments for RAS effluents are needed to mitigate its environmental impacts. Microalgae assimilate nutrients and dissolved carbon into microbial biomass with value as feed or food ingredient. However, they are difficult to harvest efficiently. Daphnia magna is an efficient filter feeder that grazes on microalgae at high rates and serves as valuable fish feed. Combining nutrient removal by microalgae and biomass harvesting by D. magna could be a cost-effective solution for wastewater valorization. Nutrient removal from unsterilized aquaculture wastewater was evaluated using the microalgae species Chlorella vulgaris, Scenedesmus dimorphus, and Haematococcus pluvialis. The first two algae were subsequently harvested using D. magna as a grazer, while H. pluvialis failed to grow stably. All phosphorus was removed, while only 50–70 % nitrogen was recovered, indicating phosphorus limitation. Shortening the hydraulic retention time (HRT) or phosphorus dosing resulted in increased nitrogen removal. C. vulgaris cultivation was unstable at 3 days HRT or when supplied with extra phosphorus at 5 days HRT. D. magna grew on produced algae accumulating protein at 20–30 % of dry weight, with an amino acid profile favorable for use as high value fish feed. Thus, this study demonstrates the application of a two steps multitrophic process to assimilate residual nutrients into live feeds suitable for fish.

Topography modulates effects of nitrogen deposition on soil nitrogen transformations by impacting soil properties in a subtropical forest

Soil nitrogen (N) transformations play key roles in ecosystem productivity and other functions of terrestrial ecosystems via regulating soil N availability. Although the effects of elevated atmospheric N deposition on soil N transformations have been intensively investigated, it remains unclear whether the effects are mediated by topography, which impacts multiple soil abiotic and biotic properties. Here, we conducted an N addition experiment consisting of three treatments: control (0 kg N ha−1 yr−1), moderate N addition (50 kg N ha−1 yr−1), and high N addition (100 kg N ha−1 yr−1) in the valley and on the slope, respectively, of a subtropical karst forest. Under the control, protein depolymerization, amino acid uptake, nitrification and dissimilatory nitrate reduction to ammonium (DNRA) rates were significantly higher on the slope than in the valley attributed to the higher soil dissolved organic carbon, total dissolved N and pH on the slope. Nitrogen addition significantly increased the rates of protein depolymerization, amino acid uptake, mineralization, nitrification and DNRA through alleviating microbial carbon limitation in the valley, but decreased the rates of depolymerization, amino acid uptake, mineralization and DRNA by enhancing microbial carbon and phosphorus limitations on the slope. The increase in soil N transformations, microbial N use efficiency (NUE) and microbial biomass N but lowered microbial N turnover time resulted in a 94 % increase of total microbial necromass N in the valley under N addition. However, increase in NUE and microbial biomass N led to a 33 % decrease of necromass N due to enhanced microbial necromass destabilization on the slope under N addition. Our results suggest that the responses of soil N transformations to N addition may be mediated by topography, and hence highlight the importance of incorporating topography into Earth system models to better predict soil N dynamics in forest in the context of elevated atmospheric N deposition.

Fluctuation of growth and photosynthetic characteristics in Prorocentrum shikokuense under phosphorus limitation: Evidence from field and laboratory

Exploring the complex interaction between algal growth and their photo-physiology is of significant interest as it can further the understanding of harmful algal blooms. To this end, we investigate variations in cell abundance and chlorophyll fluorescence parameters during the algal bloom formation of Prorocentrum shikokuense in the field and batch culture via the pulse amplitude modulated fluorometry. Furthermore, based on the interaction between algal growth and its photo-physiology status, we develop a novel algal growth model incorporating cell growth delay. The model parameters are estimated by fitting the experimental data of P. shikokuense and validated by the experimental data of Symbiodinium sp. The experimental results show that the growth status and photosynthetic parameters of algal cells fluctuate in both field and laboratory experiments and that the photosynthetic parameters have a faster response than growth parameters. According to the experimental and mathematical results, the time delay between the slow growth of algae and the rapid change of photosynthetic parameters may be a physiological mechanism leading to the fluctuations in algal growth. These results are significant for studying the relationship between phytoplankton growth dynamics and photosynthetic parameters and will help resource managers to predict and deepen the understanding of harmful algal blooms.

Interactions between Phosphorus Enrichment and Nitrification Accelerate Relative Nitrogen Deficiency during Cyanobacterial Blooms in a Large Shallow Eutrophic Lake.

Regime shifts between nitrogen (N) and phosphorus (P) limitation, which trigger cyanobacterial succession, occur in shallow eutrophic lakes seasonally. However, the underlying mechanism is not yet fully illustrated. We provide a novel insight to address this from interactions between sediment P and nitrification through monthly field investigations including 204 samples and microcosm experiments in Lake Chaohu. Total N to P mass ratios (TN/TP) varied significantly across seasons especially during algal bloom in summer, with the average value being 26.1 in June and descending to 7.8 in September gradually, triggering dominant cyanobacterial succession from Microcystis to Dolichospermum. The regulation effect of sediment N/P on water column TN/TP was stronger in summer than in other seasons. Iron-bound P and alkaline phosphatase activity in sediment, rather than ammonium, contributed to the higher part of nitrification. Furthermore, our microcosm experiments confirmed that soluble active P and enzymatic hydrolysis of organic P, accumulating during algal bloom, fueled nitrifiers and nitrification in sediments. These processes promoted lake N removal and led to relative N deficiency in turn. Our results highlight that N and P cycles do not exist independently but rather interact with each other during lake eutrophication, supporting the dual N and P reduction program to mitigate eutrophication in shallow eutrophic lakes.

Alleviation of cold stress in wheat with psychrotrophic phosphorus solubilizing Acinetobacter rhizosphaerae EU-KL44.

Low-temperature stress can seriously impair plant physiology. Chilling injury leads to a complex array of cellular dysfunctions, and symptoms include chlorosis, sterility, loss of vigor, wilting, and even death of the plants. Furthermore, phosphorus limitations additionally halt the growth of plants. Low-temperature adaptive plant growth-promoting microbes through various direct and indirect mechanisms help in the survival of plants under stress conditions. The present investigation deals with isolation of P-solubilizing psychrotrophic bacteria from diverse cultivars of wheat grown in the Keylong region of Himachal Pradesh. A total of 33 P-solubilizing bacterial isolates were obtained. P-solubilizers were screened for different plant growth-promoting (PGP) attributes of K and Zn solubilization, production of IAA, siderophores, and different hydrolytic enzymes. Among 33 P-solubilizers, 8 efficient strains exhibiting multiple PGP attributes were used as bioinoculants for wheat under low-temperature stress in different in vitro and in vivo experiments. The psychrotrophic bacterial isolates positively influenced the growth and physiological parameters as well as nutrient uptake and yield of wheat and efficiently alleviated low-temperature stress. The potential of low-temperature stress adaptive and PGP microbes can be utilized in agricultural sector for amelioration of low-temperature stress and plant growth promotion. The present study deals with the isolation of psychrotrophic P-solubilizers with multiple PGP attributes and their role in alleviation of cold stress in wheat.

Straw return, rather than warming, alleviates microbial phosphorus limitation in a cultivated Mollisol

The release of carbon (C), nitrogen (N), and phosphorus (P) from soil organic matter by extracellular enzymes is essential for biogeochemical cycles and is sensitive to field management practices and climate change. However, the way in which straw return and warming shift microbial C and nutrient (N and P) limitation is not fully understood. We conducted a field experiment with straw return and warming treatments in a cultivated Mollisol on the Songnen Plain, China, and assessed their effects on extracellular enzyme activities (EEAs) for nutrient cycling and the status of microbial nutrient limitation. The length and angle of vectors defined by ratios of EEAs (C: N vs C: P) were used to indicate relative microbial investments in C-acquiring enzymes (length), and N- or P-acquiring enzymes (angle). We found that microbial biomass C and 16S gene abundances increased by 104.7 % and 18.7 % in response to straw return, but they decreased by 46.0 % and 25.5 % in response to warming, respectively. Vector analysis highlighted that microbial metabolism was co-limited by C (vector length ranging from 2.99 to 3.23) and P (vector angle ranging from 78.88 to 82.49°) in Mollisols, and straw return significantly alleviated microbial P limitation, while warming did not affect microbial nutrient limitation. Moreover, structural equation modeling further indicated that microbial C limitation was significantly associated with soil nutrient content, and microbial biomass was the main determinant of microbial N or P requirements. Overall, our study provides specific and useful insights into the responses of microbial nutrient limitation to straw return and warming, and improves the understanding of nutrient cycling in temperate cropland ecosystems.

The phosphorus limitation in the post-fire forest soils increases soil CO2 emission via declining cellular carbon use efficiency and increasing extracellular phosphatase

Wildfires cause severe disruptions to forest soils and modify the carbon (C) cycle in the post-fire soils. Yet, the contribution of abiotic and biotic drivers to CO2 emission in the post-fire forest soils is not well understood. This study investigated soil CO2 emission from the burned and corresponding unburned forest soils across a large latitudinal gradient of mean average precipitation (from 422 to 1640 mm) and temperature (from 0.20 to 25.8 °C). We compared the soil chemical properties (e.g., dissolved organic carbon, nutrients) and microbial properties (biomass, metabolic quotient (qCO2), and community diversity and composition) in the burned and unburned soils. Microbial metabolism was also addressed through extracellular enzyme activity and intracellular C use efficiency (CUE) using the stoichiometric modeling approach. Here, we showed that the wildfires: i) increased phosphorous (P) pressure to soil microbes (indicated by increased qCO2), ii) decreased microbial biomass, community diversity and abundance of some microbial groups (e.g., Phylum Actinobacteria), and iii) resulted in larger basal respiration due to lower cellular CUE and higher extracellular alkaline phosphatase (AP) ratio to other enzymes like β-glucosidase, Cellobiohydrolase and N-Acetyl-glucosaminidase. The latter indicated the wildfires-induced P:N imbalance (P-limitation) caused significant C loss via microbial exploitation of P from soil organic matter. The study highlights the ecological significance of intracellular and extracellular metabolisms in soil respiration and consequent C sequestration in post-fire forest soils.

What controls the future phytoplankton change over the Yellow and East China Seas under global warming?

The Yellow and East China Seas (YECS) are productive continental shelves where essential nutrients for phytoplankton growth are mainly supplied by the intrusion of the Kuroshio Current, riverine inputs, and atmospheric deposition. Surface temperatures in YECS are increasing due to global warming, and are projected to increase further. In this study, future changes in YECS biogeochemical processes were evaluated using Coupled Model Intercomparison Project Phase 6 (CMIP6) Earth System Models. We found a great diversity in predictions of future changes in chlorophyll-a over the YECS region. This diversity was determined to be closely related to the extent of phosphorus (P) limitation for phytoplankton growth. Models simulating positive chlorophyll changes tend to simulate increased Dissolved Inorganic Phosphate (DIP) supplies under future global warming. Our study also demonstrated that the intrusion of the Kuroshio Current into the YECS plays a critical role in future changes in DIP and chlorophyll-a by transporting relatively DIP-rich subsurface water from the Kuroshio Current into the marginal sea.

Correction to: Extracellular enzyme ratios reveal locality and horizon-specific carbon, nitrogen, and phosphorus limitations in Arctic permafrost soils

Correction to: Extracellular enzyme ratios reveal locality and horizon-specific carbon, nitrogen, and phosphorus limitations in Arctic permafrost soils