A plant-microbe interaction framework explaining nutrient effects on primary production

Nitrogen addition promotes soil carbon accumulation globally

Soil is the largest carbon (C) reservoir in terrestrial ecosystems and plays a crucial role in regulating the global C cycle and climate change. Increasing nitrogen (N) deposition has been widely considered as a critical factor affecting soil organic carbon (SOC) storage, but its effect on SOC components with different stability remains unclear. Here, we analyzed extensive empirical data from 304 sites worldwide to investigate how SOC and its components respond to N addition. Our analysis showed that N addition led to a significant increase in bulk SOC (6.7%), with greater increases in croplands (10.6%) and forests (6.0%) compared to grasslands (2.1%). Regarding SOC components, N addition promoted the accumulation of plant-derived C (9.7%-28.5%) over microbial-derived C (0.2%), as well as labile (5.7%) over recalcitrant components (-1.2%), resulting in a shift towards increased accumulation of plant-derived labile C. Consistently, N addition led to a greater increase in particulate organic C (11.9%) than mineral-associated organic C (3.6%), suggesting that N addition promotes C accumulation across all pools, with more increase in unstable than stable pools. The responses of SOC and its components were best predicted by the N addition rate and net primary productivity. Overall, our findings suggest that N enrichment could promote the accumulation of plant-derived and non-mineral associated C and a subsequent decrease in the overall stability of soil C pool, which underscores the importance of considering the effects of N enrichment on SOC components for a better understanding of C dynamics in soils.

Early allelopathic input and later nutrient addition mediated by litter decomposition of invasive Solidago canadensis affect native plant and facilitate its invasion

Litter decomposition is essential for nutrient and chemical cycling in terrestrial ecosystems. Previous research on in situ litter decomposition has often underestimated its impact on soil nutrient dynamics and allelopathy. To address this gap, we conducted a comprehensive study involving both field and greenhouse experiments to examine the decomposition and allelopathic effects of the invasive Solidago canadensis L. in comparison with the native Phalaris arundinacea L. In the field, a 6-month litter bag experiment using leaf litter from S. canadensis and P. arundinacea was conducted across three community types: invasive, native, and mixed. Seed germination tests were also performed to investigate the allelopathic effects of decomposing litter. In the greenhouse, a pot experiment with lettuce as a bioindicator was performed to examine the allelochemical inputs from litter decomposition over various time intervals (0, 30, 60, 120, and 180 days). Subsequently, a soil-plant feedback experiment was carried out to further evaluate the effects of decomposing litter on soil biochemistry and plant dynamics. The findings of this study revealed that S. canadensis litter decomposed more rapidly and exhibited greater nitrogen (N) remaining mass compared with P. arundinacea in both single and mixed communities. After 180 days, the values for litter mass remaining for S. canadensis and P. arundinacea were 36% and 43%, respectively, when grown separately and were 32% and 44%, respectively, in mixed communities. At the invasive site, the soil ammonia and nitrate for S. canadensis increased gradually, reaching 0.89 and 14.93 mg/kg by day 120, compared with the native site with P. arundinacea. The soil organic carbon for S. canadensis at the invasive site also increased from 10.6 mg/kg on day 0 to 15.82 mg/kg on day 120, showing a higher increase than that at the native site with P. arundinacea. During the initial decomposition stages, all litters released almost all of their allelochemicals. However, at the later stages, litters continued to input nutrients into the soil, but had no significant impact on the soil carbon (C) and N cycling. Notably, litter-mediated plant-soil feedback facilitated the invasion of S. canadensis. In conclusion, this study highlights the significance of litter decomposition as a driver of transforming soil biochemistry, influencing the success of invasive S. canadensis.

Effects of Increasing the Nitrogen-Phosphorus Ratio on the Structure and Function of the Soil Microbial Community in the Yellow River Delta

Nitrogen (N) deposition from human activities leads to an imbalance in the N and phosphorus (P) ratios of natural ecosystems, which has a series of negative impacts on ecosystems. In this study, we used 16s rRNA sequencing technology to investigate the effect of the N-P supply ratio on the bulk soil (BS) and rhizosphere soil (RS) bacterial community of halophytes in coastal wetlands through manipulated field experiments. The response of soil bacterial communities to changing N and P ratios was influenced by plants. The N:P ratio increased the α-diversity of the RS bacterial community and changed the structure of the BS bacterial community. P addition may increase the threshold, causing decreased α-diversity of the bacterial community. The co-occurrence network of the RS community is more complex, but it is more fragile than that of BS. The co-occurrence network in BS has more modules and fewer network hubs. The increased N:P ratio can increase chemoheterotrophy and denitrification processes in the RS bacterial community, while the N:P ratio can decrease the N-fixing processes and increase the nitration processes. The response of the BS and the RS bacterial community to the N:P ratio differed, as influenced by soil organic carbon (SOC) content in terms of diversity, community composition, mutualistic networks, and functional composition. This study demonstrates that the effect of the N:P ratio on soil bacterial community is different for plant roots and emphasizes the role of plant roots in shaping soil bacterial community during environmental change.

The Effects of Plant-Microbe-Environment Interactions on Mineral Weathering Patterns in a Granular Basalt

The importance of biota to soil formation and landscape development is widely recognized. As biotic complexity increases during early succession via colonization by soil microbes followed by vascular plants, effects of biota on mineral weathering and soil formation become more complex. Knowledge of the interactions among groups of organisms and environmental conditions will enable us to better understand landscape evolution. Here, we used experimental columns of unweathered granular basalt to investigate how early successional soil microbes, vascular plants (alfalfa; Medicago sativa), and soil moisture interact to affect both plant performance and mineral weathering. We found that the presence of soil microbes reduced plant growth rates, total biomass, and survival, which suggests that plants and microbes were competing for nutrients in this environment. However, we also found considerable genotype-specific variation in plant-microbial interactions, which underscores the importance of within-species genetic variation on biotic interactions. We also found that the presence of vascular plants reduced variability in pH and electrical conductivity, suggesting that plants may homogenize weathering reactions across the soil column. We also show that there is heterogeneity in the abiotic conditions in which microbes, plants, or their combination have the strongest effect on weathering, and that many of these relationships are sensitive to soil moisture. Our findings highlight the importance of interdependent effects of environmental and biotic factors on weathering during initial landscape formation.

Unveiling Pervasive Soil Microbial P Limitation in Terrestrial Ecosystems Worldwide

Soil microorganisms are crucial in terrestrial ecosystems, influencing carbon (C) sequestration, yet their metabolic activities are often constrained by nitrogen (N) and phosphorus (P) availability. Despite this, a global understanding of microbial nutrient limitation remains elusive. We synthesised 1245 observations from 225 articles to elucidate patterns and factors of microbial nutrient limitation. Contrary to convention, soil microbial P limitation is widespread (83.78% of observations), with N limitation mainly in temperate zones and pronounced P limitation in tropical and cold zones. Soil microbial P limitation correlates positively with mean annual precipitation and clay content, while N limitation correlates negatively with soil pH. Importantly, microbial nutrient limitation directly affects C cycling, as microbial C limitation increases with decreasing N or P limitation. This underscores the significance of microbial nutrient limitation in terrestrial C cycling and the need to incorporate it into Earth system models for accurate predictions under changing conditions.

Rice-fish coculture without phosphorus addition improves paddy soil nitrogen availability by shaping ammonia-oxidizing archaea and bacteria in subtropical regions of South China

Rice-fish coculture (RFC), as a traditional agricultural strategy in China, can optimally utilize the scarce resource, especially in subtropical regions where phosphorus (P) deficiency limits agricultural production. However, ammonia-oxidizing archaea (AOA) and bacteria (AOB) are involved in the ammonia oxidation, but it remains uncertain whether their community compositions are related to the RFC combined with and without P addition that improves soil nitrogen (N) use efficiency. Here, a microcosm experiment was conducted to assess the impacts of RFC combined with and without inorganic P (0 and 50 mg P kg-1 as KH2PO4) addition on AOA and AOB community diversities, enzyme activities and N availability. The results showed that RFC significantly increased available N content without P addition compared with P addition. Moreover, RFC significantly increased urease activity and AOA shannon diversity, and reduced NAG activity and AOB shannon diversity without P addition, respectively. Higher diversity of AOA compared with that of AOB causes greater competition for resources and energy within their habitats, thereby resulting in lower network complexity. Our findings indicated that the abundances of AOA and AOB are influenced through the introduction of fish and/or P availability, of which AOB is linked to N availability. Overall, RFC could improve paddy soil N availability without P addition in subtropical region, which provides a scientific reference for promoting the practices that reduce N fertilizer application in RFC.

Enriched rhizospheric functional microbiome may enhance adaptability of Artemisia lavandulaefolia and Betula luminifera in antimony mining areas

Dominant native plants are crucial for vegetation reconstruction and ecological restoration of mining areas, though their adaptation mechanisms in stressful environments are unclear. This study focuses on the interactions between dominant indigenous species in antimony (Sb) mining area, Artemisia lavandulaefolia and Betula luminifera, and the microbes in their rhizosphere. The rhizosphere microbial diversity and potential functions of both plants were analyzed through the utilization of 16S, ITS sequencing, and metabarcoding analysis. The results revealed that soil environmental factors, rather than plant species, had a more significant impact on the composition of the rhizosphere microbial community. Soil pH and moisture significantly affected microbial biomarkers and keystone species. Actinobacteria, Proteobacteria and Acidobacteriota, exhibited high resistance to Sb and As, and played a crucial role in the cycling of carbon, nitrogen (N), phosphorus (P), and sulfur (S). The genes participating in N, P, and S cycling exhibited metabolic coupling with those genes associated with Sb and As resistance, which might have enhanced the rhizosphere microbes' capacity to endure environmental stressors. The enrichment of these rhizosphere functional microbes is the combined result of dispersal limitations and deterministic assembly processes. Notably, the genes related to quorum sensing, the type III secretion system, and chemotaxis systems were significantly enriched in the rhizosphere of plants, especially in B. luminifera, in the mining area. The phylogenetic tree derived from the evolutionary relationships among rhizosphere microbial and chloroplast whole-genome resequencing results, infers both species especially B. luminifera, may have undergone co-evolution with rhizosphere microorganisms in mining areas. These findings offer valuable insights into the dominant native rhizosphere microorganisms that facilitate plant adaptation to environmental stress in mining areas, thereby shedding light on potential strategies for ecological restoration in such environments.

Metagenomic insights into inhibition of soil microbial carbon metabolism by phosphorus limitation during vegetation succession

There is growing awareness of the need for regenerative practices in the fight against biodiversity loss and climate change. Yet, we lack a mechanistic understanding of how microbial community composition and functioning are likely to change alongside transition from high-density tillage to large-scale vegetation restoration. Here, we investigated the functional dynamics of microbial communities following a complete vegetation successional chronosequence in a subtropical zone, Southwestern China, using shotgun metagenomics approaches. The contents of total soil phosphorus (P), available P, litter P, and microbial biomass P decreased significantly during vegetation succession, indicating that P is the most critical limiting nutrient. The abundance of genes related to P-uptake and transport, inorganic P-solubilization, organic P-mineralization, and P-starvation response regulation significantly increased with successional time, indicating an increased microbial "mining" for P under P limitation. Multi-analysis demonstrated microbial P limitation strongly inhibits carbon (C) catabolism potential, resulting in a significant decrease in carbohydrate-active enzyme family gene abundances. Nevertheless, over successional time, microorganisms increased investment in genes involved in degradation-resistant compounds (lignin and its aromatic compounds) to acquire P resources in the litter. Our study provides functional gene-level insights into how P limitation during vegetation succession in subtropical regions inhibits soil microbial C metabolic processes, thereby advancing our understanding of belowground C cycling and microbial metabolic feedback during forest restoration.

Addressing the C/N imbalance in the treatment of irrigated agricultural water by using a hybrid constructed wetland at field-scale

To mitigate excess of nitrate-N (NO3--N) derived from agricultural activity, constructed wetlands (CWs) are created to simulate natural removal mechanisms. Irrigated agricultural drainage water is commonly characterized by an organic carbon/nitrogen (C/N) imbalance, thus, C limitation constrains heterotrophic denitrification, the main biotic process implicated in NO3--N removal in wetlands. We studied a pilot plant with three series (169 m2) of hybrid CWs over the first two years of functioning to examine: i) the effect of adding different C-rich substrates (natural soil vs. biochar) to gravel on NO3--N removal in a subsurface flow (Phase I), ii) the role of a second phase with a horizontal surface flow (Phase II) as a source of dissolved organic C (DOC), and its effect in a consecutive horizontal subsurface flow (Phase III) on NO3--N removal, and iii) the contribution of each phase to global NO3--N removal. Our results showed that the addition of a C-rich substrate to gravel had a positive effect on NO3--N removal in Phase I, with mean efficiencies of 40% and 17% for soil and biochar addition, respectively, compared to only gravel (0.75%). In Phase II, the algae growth turned into a DOC concentration increase, but it did not enhance NO3--N removal in Phase III. In series with C-rich substrate addition, the largest contribution to NO3--N removal was found in Phase I. However, in series with only gravel, Phase II was the most effective on NO3--N removal. Contribution of Phase III to NO3--N removal was almost negligible.

Nutrient and Microbiome-Mediated Plant-Soil Feedback in Domesticated and Wild Andropogoneae: Implications for Agroecosystems

Plants influence the abiotic and biotic environment of the rhizosphere, affecting plant performance through plant-soil feedback (PSF). We compared the strength of nutrient and microbe-mediated PSF and its implications for plant performance in domesticated and wild grasses with a fully crossed greenhouse PSF experiment using four inbred maize genotypes (Zea mays ssp. mays b58, B73-wt, B73-rth3, and HP301), teosinte (Z. mays ssp. parviglumis), and two wild prairie grasses (Andropogon gerardii and Tripsacum dactyloides) to condition soils for three feedback species (maize B73-wt, teosinte, Andropogon gerardii). We found evidence of negative PSF based on growth, phenotypic traits, and foliar nutrient concentrations for maize B73-wt, which grew slower in maize-conditioned soil than prairie grass-conditioned soil. In contrast, teosinte and A. gerardii showed few consistent feedback responses. Both rhizobiome and nutrient-mediated mechanisms were implicated in PSF. Based on 16S rRNA gene amplicon sequencing, the rhizosphere bacterial community composition differed significantly after conditioning by prairie grass and maize plants, and the final soil nutrients were significantly influenced by conditioning, more so than by the feedback plants. These results suggest PSF-mediated soil domestication in agricultural settings can develop quickly and reduce crop productivity mediated by PSF involving changes to both the soil rhizobiomes and nutrient availability.

Plant-microbe interactions ameliorate phosphate-mediated responses in the rhizosphere: a review

Phosphorus (P) is one of the essential minerals for many biochemical and physiological responses in all biota, especially in plants. P deficiency negatively affects plant performance such as root growth and metabolism and plant yield. Mutualistic interactions with the rhizosphere microbiome can assist plants in accessing the available P in soil and its uptake. Here, we provide a comprehensive overview of plant-microbe interactions that facilitate P uptake by the plant. We focus on the role of soil biodiversity in improved P uptake by the plant, especially under drought conditions. P-dependent responses are regulated by phosphate starvation response (PSR). PSR not only modulates the plant responses to P deficiency in abiotic stresses but also activates valuable soil microbes which provide accessible P. The drought-tolerant P-solubilizing bacteria are appropriate for P mobilization, which would be an eco-friendly manner to promote plant growth and tolerance, especially in extreme environments. This review summarizes plant-microbe interactions that improve P uptake by the plant and brings important insights into the ways to improve P cycling in arid and semi-arid ecosystems.

Ecosystem-dependent responses of soil carbon storage to phosphorus enrichment

Phosphorus deposition can stimulate both plant carbon inputs and microbial carbon outputs. However, how P enrichment affects soil organic carbon (SOC) storage and the underlying mechanisms remain unclear. We conducted a meta-analysis of 642 SOC observations from 213 field P addition experiments world-wide and explored the regulations of plant inputs, microbial outputs, plant characteristics, and environmental and experimental factors on SOC responses. We found that, globally, P addition stimulated SOC by 4.0% (95% CI: 2.0-6.0%), but the stimulation only occurred in forest and cropland rather than in grassland. Across sites, the response of SOC correlated with that of plant aboveground rather than belowground biomass, suggesting that the change in plant inputs from aboveground was more important than that from belowground in regulating SOC changes due to P addition. Among multiple factors, plant N fixation status and mean annual temperature were the best predictors for SOC responses to P addition, with SOC stimulation being higher in ecosystems dominated by symbiotic nitrogen fixers and ecosystems in high-temperature regions like tropical forests. Our findings highlight the differential and ecosystem-dependent responses of SOC to P enrichment and can contribute to accurate predictions of soil carbon dynamics in a P-enriched world.

C:N:P stoichiometry of plant-soil-microbe in the secondary succession of zokor-made mounds on Qinghai-Tibet Plateau

The knowledge of ecological stoichiometry and stoichiometric homeostasis could contribute to exploring the balance of chemical elements in ecological recovery. However, it is largely unknown how the carbon (C), nitrogen (N), phosphorus (P), and stoichiometric characteristics in the plant-soil-microbe continuum system respond to the spontaneous secondary succession of degraded alpine grasslands. Therefore, we investigated the spontaneous secondary successional recovery of grasslands disturbed by zokor (Myospalax fontanierii) on the Qinghai-Tibetan Plateau, China, via a strategy of substituting space for time. Based on plant richness, biomass, and coverage, plant importance value was employed to assess the recovery degree of zokor-made mounds (ZMMs, large and bare patch areas constructed by zokors). Multiple statistical methods, including stoichiometric homeostatic model, network, and redundancy analysis, were conducted to decipher the stoichiometric patterns. The results indicated that plant C, C:N, and C:P increased with the recovery of ZMMs, contrary to the decrease of plant N and P. In addition, soil C, N, C:N, C:P, and N:P increased with the recovery degree, and the soil became relatively more N rich by increasing organic N under the revegetation of legumes. Meanwhile, soil microbial biomass C, N, and P increased with the recovery of ZMMs, but microbial biomass C:N:P ratios were highly constrained. Soil accessible inorganic nitrogen played an important role in driving plant and microbial nutrient and stoichiometry. Our results demonstrated that the different responses of C, N, and P contents in plant-soil-microbe lead to shifts in C:N:P stoichiometric ratio. Nevertheless, plants and soil microbes exhibited strong stoichiometric homeostasis. Collectively, our study provides new insight into biogeochemical responses to the successional recovery of degraded alpine grassland on the Qinghai-Tibetan Plateau from a stoichiometric perspective.

How arbuscular mycorrhizal fungi drives herbaceous plants' C: N: P stoichiometry? A meta-analysis

Plant element stoichiometry is fundamental for preserving growth-related terrestrial ecosystem structures and functions. However, effects of arbuscular mycorrhizal fungi (AMF) on herbaceous plant element stoichiometry (carbon (C), nitrogen (N), and phosphorus (P)) remain unclear. In this study, we aimed at evaluating the potential effects of AMF on herbaceous plant C, N and P concentration and their C:N:P stoichiometry worldwide through a quantitative meta-analysis. We observed that AMF reduced C:P and N:P ratios in the shoot of plants by 35.83 % and 54.23 %, respectively, and in plant root organs by 36.24 % and 46.35 %, respectively. Conversely, C:N ratios increased in roots by 6.61 %. The negative effect of AMF on N:P and C:P ratios in plant shoots and root organs is mainly attributed to the plant benefits in P and N concentrations. AMF impact on plant C:N:P stoichiometry depends on fungal and plant functional group identities and soil nutrient availability. Our results suggest that plant functional group identity affects plant nutrient concentration, which, in turn, controls herbaceous plant C:N:P stoichiometry. Overall, we emphasize the importance of abiotic and biotic environmental factors in changing AMF effects on plant element stoichiometry. Therefore, clarifying the relationship between AMF and herbaceous plant C:N:P stoichiometry will improve our understanding of herbaceous plant stoichiometric variations in terrestrial ecosystems.

From guest to host: parasite Cistanche deserticola shapes and dominates bacterial and fungal community structure and network complexity

BACKGROUND

Rhizosphere and plant microbiota are assumed to play an essential role in deciding the well-being of hosts, but effects of parasites on their host microbiota have been rarely studied. Also, the characteristics of the rhizosphere and root microbiota of parasites and hosts under parasitism is relatively unknown. In this study, we used Cistanche deserticola and Haloxylon ammodendron from cultivated populations as our model parasites and host plants, respectively. We collected samples from BULK soil (BULK), rhizosphere soil of H. ammodendron not parasitized (NCD) and parasitized (RHA) to study how the parasite influenced the rhizosphere microbiota of the host. We also collected samples from the rhizosphere soil and roots of C. deserticola (RCD and ECD) and Haloxylon ammodendron (RHA and EHA) to explore the difference between the microbiota of the parasite and its host under parasitism.

RESULTS

The parasite reduced the compositional and co-occurrence network complexities of bacterial and fungal microbiota of RHA. Additionally, the parasite increased the proportion of stochastic processes mainly belonging to dispersal limitation in the bacterial microbiota of RHA. Based on the PCoA ordinations and permutational multivariate analysis of variance, the dissimilarity between microbiota of C. deserticola and H. ammodendron were rarely evident (bacteria, R² = 0.29971; fungi, R² = 0.15631). Interestingly, four hub nodes of H. ammodendron in endosphere fungal microbiota were identified, while one hub node of C. deserticola in endosphere fungal microbiota was identified. It indicated that H. ammodendron played a predominant role in the co-occurrence network of endosphere fungal microbiota. Source model of plant microbiome suggested the potential source percentage from the parasite to the host (bacteria: 52.1%; fungi: 16.7%) was lower than host-to-parasite (bacteria: 76.5%; fungi: 34.3%), illustrating that microbial communication was bidirectional, mainly from the host to the parasite.

CONCLUSIONS

Collectively, our results suggested that the parasite C. deserticola shaped the diversity, composition, co-occurrence network, and community assembly mechanisms of the rhizosphere microbiota of H. ammodendron. Additionally, the microbiota of C. deserticola and H. ammodendron were highly similar and shared. Our findings on parasite and host microbiota provided a novel line of evidence supporting the influence of parasites on the microbiota of their hosts.

Warmer winters result in reshaping of the European beech forest soil microbiome (bacteria, archaea and fungi)-With potential implications for ecosystem functioning

In temperate regions, climate warming alters temperature and precipitation regimes. During winter, a decline in insulating snow cover changes the soil environment, where especially frost exposure can have severe implications for soil microorganisms and subsequently for soil nutrient dynamics. Here, we investigated winter climate change responses in European beech forests soil microbiome. Nine study sites with each three treatments (snow exclusion, insolation, and ambient) were investigated. Long-term adaptation to average climate was explored by comparing across sites. Triplicated treatment plots were used to evaluate short-term (one single winter) responses. Community profiles of bacteria, archaea and fungi were created using amplicon sequencing. Correlations between the microbiome, vegetation and soil physicochemical properties were found. We identify core members of the forest-microbiome and link them to key processes, for example, mycorrhizal symbiont and specialized beech wood degraders (fungi) and nitrogen cycling (bacteria, archaea). For bacteria, the shift of the microbiome composition due to short-term soil temperature manipulations in winter was similar to the community differences observed between long-term relatively cold to warm conditions. The results suggest a strong link between the changes in the microbiomes and changes in environmental processes, for example, nitrogen dynamics, driven by variations in winter climate.

Coordinated pattern of multiple element variability in Aegiceras corniculatum propagule in shrimp aquaculture effluent habitats

Human activities and environment changes have changed river estuary ecosystems, which impacts element changes in coastal sediments and mangroves. Mangrove propagule chemical traits showed a systematic shift along environmental gradients. But knowledge about how the pattern of multi-element variability is coordinated in propagule remains limited, and the conservation of macro and trace elements in propagules is also unknown. In this study, the concentrations, variability and coordinated pattern variation of 13 elements in Aegiceras corniculatum propagule across shrimp aquaculture effluent habitats, as well as the relationship between propagule element and environment factors were explored. We used CV to quantify the variability of each element, and then explore the pattern of multi-element variability. The results showed that: (1) in the habitats affected by shrimp aquaculture, the elements content shows: C > K > Cl > N > Na > P > S > Mg > Ca > Fe > Mn > Zn > Cu, and the coefficient variation shows: Mn > Cu > Fe > Zn > S > N > P > Cl > Na > K > Mg > Ca > C, which means that the element concentration are negatively correlated with the element variability and the variability of macro-elements was more conservative than micro-elements in these habitats; (2) pH, OM, C:P, and SiO₃^2- were the four important environmental factors explaining the A. corniculatum propagule variation. In conclusion, effluent from shrimp aquaculture does affect the coordinated pattern of multiple element variability in A. corniculatum propagules. These results provide a strong evidence for assessing the impact of shrimp aquaculture effluent discharges on mangrove and provide an important theoretical basis for mangrove conservation and restoration.

Potential Roles of Soil Microorganisms in Regulating the Effect of Soil Nutrient Heterogeneity on Plant Performance

The spatially heterogeneous distribution of soil nutrients is ubiquitous in terrestrial ecosystems and has been shown to promote the performance of plant communities, influence species coexistence, and alter ecosystem nutrient dynamics. Plants interact with diverse soil microbial communities that lead to an interdependent relationship (e.g., symbioses), driving plant community productivity, belowground biodiversity, and soil functioning. However, the potential role of the soil microbial communities in regulating the effect of soil nutrient heterogeneity on plant growth has been little studied. Here, we highlight the ecological importance of soil nutrient heterogeneity and microorganisms and discuss plant nutrient acquisition mechanisms in heterogeneous soil. We also examine the evolutionary advantages of nutrient acquisition via the soil microorganisms in a heterogeneous environment. Lastly, we highlight a three-way interaction among the plants, soil nutrient heterogeneity, and soil microorganisms and propose areas for future research priorities. By clarifying the role of soil microorganisms in shaping the effect of soil nutrient heterogeneity on plant performance, the present study enhances the current understanding of ecosystem nutrient dynamics in the context of patchily distributed soil nutrients.

The coordination of green-brown food webs and their disruption by anthropogenic nutrient inputs

Aim

Our goal was to quantify nitrogen flows and stocks in green-brown food webs in different ecosystems, how they differ across ecosystems and how they respond to nutrient enrichment.

Location

Global.

Time period

Contemporary.

Major taxa studied

Plants, phytoplankton, macroalgae, invertebrates, vertebrates and zooplankton.

Methods

Data from >500 studies were combined to estimate nitrogen stocks and fluxes in green-brown food webs in forests, grasslands, brackish environments, seagrass meadows, lakes and oceans. We compared the stocks, fluxes and metabolic rates of different functional groups within each food web. We also used these estimates to build a dynamical model to test the response of the ecosystems to nutrient enrichment.

Results

We found surprising symmetries between the green and brown channels across ecosystems, in their stocks, fluxes and consumption coefficients and mortality rates. We also found that nitrogen enrichment, either organic or inorganic, can disrupt this balance between the green and brown channels.

Main conclusions

Linking green and brown food webs reveals a previously hidden symmetry between herbivory and detritivory, which appears to be a widespread property of natural ecosystems but can be disrupted by anthropogenic nitrogen additions.

Carbon-Phosphorus Coupling Governs Microbial Effects on Nutrient Acquisition Strategies by Four Crops

Plants adjust root morphological and/or exudation traits in response to phosphorus (P) mobilization mediated by microorganisms. We hypothesized that straw application coupled with P fertilization would influence microbial P and then root nutrient-acquisition strategies related to crop growth. Root morphological (length and average diameter) and exudation traits (acid phosphatase and carboxylates) of Brassica chinensis, Solanum lycopersicum, Lactuca sativa, and Vigna unguiculata in response to microbial P dynamics were characterized in no-P and P-fertilized soil with/without straw addition. Straw addition increased the growth of fungi and bacteria, stimulating microbial P immobilization at day 24. The high microbial abundance was associated with four tested crops having short roots in straw-amended compared with no-straw soil at day 24. In straw-amended soil, B. chinensis and S. lycopersicum shifted toward root P-acquisition strategies based on fast elongation and strong carboxylate exudation from days 24 to 40. Such effective root P-acquisition strategies together with microbial P release increased shoot P content in S. lycopersicum in straw-amended compared with those without straw at day 40. Conversely, L. sativa and V. unguiculata produced short roots in response to the stable (or even increased) microbial P after straw addition till day 40. In straw-amended soil, high P application stimulated root elongation and carboxylate exudation in L. sativa and V. unguiculata, whereas carboxylate exudation by S. lycopersicum was decreased compared with the straw-amended but non-fertilized treatment at day 40. In summary, root P-acquisition strategies in response to microbial P differed among the tested crop species. Phosphorus fertilization needs to be highlighted when returning straw to enhance P-use efficiency in vegetable cropping systems.

Mycorrhizal fungi alleviate acidification-induced phosphorus limitation: Evidence from a decade-long field experiment of simulated acid deposition in a tropical forest in south China

South China has been experiencing very high rate of acid deposition and severe soil acidification in recent decades, which has been proposed to exacerbate the regional ecosystem phosphorus (P) limitation. We conducted a 10-year field experiment of simulated acid deposition to examine how acidification impacts seasonal changes of different soil P fractions in a tropical forest with highly acidic soils in south China. As expected, acid addition significantly increased occluded P pool but reduced the other more labile P pools in the dry season. In the wet season, however, acid addition did not change microbial P, soluble P and labile organic P pools. Acid addition significantly increased exchangeable Al³⁺ and Fe³⁺ and the activation of Fe oxides in both seasons. Different from the decline of microbial abundance in the dry season, acid addition increased ectomycorrhizal fungi and its ratio to arbuscular mycorrhiza fungi in the wet season, which significantly stimulated phosphomonoesterase activities and likely promoted the dissolution of occluded P. Our results suggest that, even in already highly acidic soils, the acidification-induced P limitation could be alleviated by stimulating ectomycorrhizal fungi and phosphomonoesterase activities. The differential responses and microbial controls of seasonal soil P transformation revealed here should be implemented into ecosystem biogeochemical model for predicting plant productivity under future acid deposition scenarios.

Effects of nitrogen and phosphorus enrichment on soil N2O emission from natural ecosystems: A global meta-analysis

Nitrogen (N) and phosphorous (P) enrichment play an important role in regulating soil N₂O emission, but their interactive effect remains elusive (i.e. whether the effect of P or N enrichment on soil N₂O emission varies between ambient and elevated soil N or P conditions). Here, we conducted a Bayesian meta-analysis across the global natural ecosystems to determine this effect. Our results showed that P enrichment significantly decreased soil N₂O emission by 13.9% at ambient soil N condition. This N₂O mitigation is likely due to the decreased soil NO₃^--N content (-17.6%) derived by the enhanced plant uptake when the P limitation was alleviated by P enrichment. However, this P-induced N₂O (and NO₃^--N) mitigation was not found at elevated soil N condition. Additionally, N enrichment significantly increased soil N₂O emission by 101.4%, which was associated with the increased soil NH₄⁺-N (+41.0%) and NO₃^--N (+82.3%). However, the effect of N enrichment on soil N₂O emission did not differ between ambient and elevated soil P subgroups, indicating that the P-derived N₂O mitigation could be masked by N enrichment. Further analysis showed that manipulated N rate, soil texture, soil dissolved organic nitrogen, soil total nitrogen, soil organic carbon, soil pH, aboveground plant biomass, belowground plant biomass, and plant biomass nitrogen were the main factors affecting soil N₂O emission under N enrichment. Taken together, our study provides evidence that P enrichment has the potential to reduce soil N₂O emission from natural ecosystems, but this mitigation effect could be masked by N enrichment.

Soil Microbe-Mediated N:P Stoichiometric Effects on Solidago canadensis Performance Depend on Nutrient Levels

Both soil microbes and soil N:P ratios can affect plant growth, but it is unclear whether they can interact to alter plant growth and whether such an interactive effect depends on nutrient levels. Here, we tested the hypothesis that soil microbes can ameliorate the negative effects of nutrient imbalance caused by low or high N:P ratios on plant growth and that such an ameliorative effect of soil microbes depends on nutrient supply levels. We grew individuals of six populations of the clonal plant Solidago canadensis at three N:P ratios (low (1.7), intermediate (15), and high (135)), under two nutrient levels (low versus high) and in the presence versus absence of soil microbes. The presence of soil microbes significantly increased biomass of S. canadensis at all three N:P ratios and under both nutrient levels. Under the low-nutrient level, biomass, height, and leaf number of S. canadensis did not differ significantly among the three N:P ratio treatments in the absence of soil microbes, but they were higher at the high than at the low and the intermediate N:P ratio in the presence of soil microbes. Under the high-nutrient level, by contrast, biomass, height, and leaf number of S. canadensis were significantly higher at the low than at the high and the intermediate N:P ratio in the absence of soil microbes, but increased with increasing the N:P ratio in the presence of soil microbes. In the presence of soil microbes, number of ramets (asexual individuals) and the accumulation of N and P in plants were significantly higher at the high than at the low and the intermediate N:P ratio under both nutrient levels, whereas in the absence of soil microbes, they did not differ significantly among the three N:P ratio regardless of the nutrient levels. Our results provide empirical evidence that soil microbes can alter effects of N:P ratios on plant performance and that such an effect depends on nutrient availability. Soil microbes may, therefore, play a role in modulating ecosystem functions such as productivity and carbon and nutrient cycling via modulating nutrient imbalance caused by low and high N:P ratios.

Exploratory Growth in Streptomyces venezuelae Involves a Unique Transcriptional Program, Enhanced Oxidative Stress Response, and Profound Acceleration in Response to Glycerol

Exploration is a recently discovered mode of growth and behavior exhibited by some Streptomyces species that is distinct from their classical sporulating life cycle. While much has been uncovered regarding initiating environmental conditions and phenotypic outcomes of exploratory growth, how this process is coordinated at a genetic level remains unclear. We used RNA sequencing to survey global changes in the transcriptional profile of exploring cultures over time in the model organism Streptomyces venezuelae. Transcriptomic analyses revealed widespread changes in gene expression impacting diverse cellular functions. Investigations into differentially expressed regulatory elements revealed specific groups of regulatory factors to be impacted, including the expression of several extracytoplasmic function (ECF) sigma factors, second messenger signaling pathways, and members of the whiB-like (wbl) family of transcription factors. Dramatic changes were observed among primary metabolic pathways, especially among respiration-associated genes and the oxidative stress response; enzyme assays confirmed that exploring cultures exhibit an enhanced oxidative stress response compared with classically growing cultures. Changes in the expression of the glycerol catabolic genes in S. venezuelae led to the discovery that glycerol supplementation of the growth medium promotes a dramatic acceleration of exploration. This effect appears to be unique to glycerol as an alternative carbon source, and this response is broadly conserved across other exploration-competent species. IMPORTANCE Exploration represents an alternative growth strategy for Streptomyces bacteria and is initiated in response to other microbes or specific environmental conditions. Here, we show that entry into exploration involves comprehensive transcriptional reprogramming, with an emphasis on changes in primary metabolism and regulatory/signaling functions. Intriguingly, a number of transcription factor classes were downregulated upon entry into exploration. In contrast, respiration-associated genes were strongly induced, and this was accompanied by an enhanced oxidative stress response. Notably, our transcriptional analyses suggested that glycerol may play a role in exploration, and we found that glycerol supplementation dramatically enhanced the exploration response in many streptomycetes. This work sheds new light on the regulatory and metabolic cues that influence a fascinating new microbial behavior.

Differentiate Responses of Soil Microbial Community and Enzyme Activities to Nitrogen and Phosphorus Addition Rates in an Alpine Meadow

Nitrogen (N) and phosphorus (P) are the dominant limiting nutrients in alpine meadows, but it is relatively unclear how they affect the soil microbial community and whether their effects are rate dependent. Here, N and P addition rates (0, 10, 20, and 30 g m^-2 year^-1) were evaluated in an alpine meadow and variables related to plants and soils were measured to determine the processes affecting soil microbial community and enzyme activities. Our results showed that soil microbial biomass, including bacteria, fungi, gramme-negative bacteria, and actinomycetes, decreased along with N addition rates, but they first decreased at low P addition rates (10 g m^-2 year^-1) and then significantly increased at high P addition rates (30 g m^-2 year^-1). Both the N and P addition stimulated soil invertase activity, while urease and phosphatase activities were inhibited at low N addition rate and then increased at high N addition rate. P addition generally inhibited peroxidase and urease activities, but increased phosphatase activity. N addition decreased soil pH and, thus, inhibited soil microbial microorganisms, while P addition effects were unimodal with addition rates, achieved through altering sedge, and available P in the soil. In conclusion, our studies indicated that soil microbial communities and enzyme activities are sensitive to short-term N and P addition and are also significantly influenced by their addition rates.

Multiple resource limitation of dryland soil microbial carbon cycling on the Colorado Plateau

Understanding interactions among biogeochemical cycles is increasingly important as anthropogenic alterations of global climate and of carbon (C), nitrogen (N), and phosphorus (P) cycles interactively affect the Earth system. Ecosystem processes in the dryland biome, which makes up over 40% of Earth's terrestrial surface, are often distinctively sensitive to small changes in resource availability, likely because levels of many resources are low. However, data also suggest that simultaneous changes in the availability of multiple resources may be necessary to affect a response in these low-resource systems, offering an opportunity to test patterns and controls of co-limitation, serial limitation, and individual limitation in soil environments. While drylands may play a governing role in key aspects of Earth's C cycle, and while an improved understanding of resource limitation could substantially improve our forecasts of dryland responses to change, our understanding of interacting controls on soil C cycle processes remains notably poor in these dry systems. Here, we address multiple fundamental hypotheses of resource controls over ecosystem function to test how water, C, N, and P regulate soil C cycling individually and interactively in a dryland ecosystem on the Colorado Plateau. Using a series of laboratory incubations, we found that while water, C, and N limited C cycling through serial limitation, water alone resulted in an extremely small respiratory response from target organisms, whereas water + C resulted in a dramatic increase in soil C cycling, suggesting a degree of functional co-limitation. Nitrogen additions alone resulted in no changes to soil C cycling, but when N was added in concert with water and C, N greatly increased soil C cycling rates relative to additions of water and C without N. Phosphorus additions had no effect on the C cycle either alone or synergistically. These patterns were consistent with the stoichiometry of the system, and interactions among resources were surprising in ways that inform our understanding of critical theories in ecology, such as the Transient Maxima Hypothesis, supporting the suggestion that multiple resource limitation explains pulse-dynamic C cycling in drylands better than water limitation alone.

Functional Genetic Diversity and Plant Growth Promoting Potential of Polyphosphate Accumulating Bacteria in Soil

Polyphosphate (polyP) accumulation is an important trait of microorganisms. Implication of polyP accumulating bacteria (PAB) in enhanced biological phosphate removal, heavy metal sequestration, and dissolution of dental enamel is well studied. Phosphorous (P) accumulated within microbial biomass also regulates labile P in soil; however, abundance and diversity of the PAB in soil is still unexplored. Present study investigated the genetic and functional diversity of PAB in rhizosphere soil. Here, we report the abundance of Pseudomonas spp. as high PAB in soil, suggesting their contribution to global P cycling. Additional subset analysis of functional genes i.e., polyphosphate kinase (ppk) and exopolyphosphatase (ppx) in all PAB, indicates their significance in bacterial growth and metabolism. Distribution of functional genes in phylogenetic tree represent a more biologically realistic discrimination for the two genes. Distribution of ppx gene disclosed its phylogenetic conservation at species level, however, clustering of ppk gene of similar species in different clades illustrated its environmental condition mediated modifications. Selected PAB showed tolerance to abiotic stress and strong correlation with plant growth promotary (PGP) traits viz. phosphate solubilization, auxin and siderophore production. Interaction of PAB with A. thaliana enhanced the growth and phosphate status of the plant under salinity stress, suggestive of their importance in P cycling and stress alleviation.

IMPORTANCE Study discovered the abundance of Pseudomonas genera as a high phosphate accumulator in soil. The presence of functional genes (polyphosphate kinase [ppk] and exopolyphosphatase [ppx]) in all PAB depicts their importance in polyphosphate metabolism in bacteria. Genetic and functional diversity reveals conservation of the ppx gene at species level. Furthermore, we found a positive correlation between PAB and plant growth promotary traits, stress tolerance, and salinity stress alleviation in A. thaliana.

Technologies and perspectives for achieving carbon neutrality

Global development has been heavily reliant on the overexploitation of natural resources since the Industrial Revolution. With the extensive use of fossil fuels, deforestation, and other forms of land-use change, anthropogenic activities have contributed to the ever-increasing concentrations of greenhouse gases (GHGs) in the atmosphere, causing global climate change. In response to the worsening global climate change, achieving carbon neutrality by 2050 is the most pressing task on the planet. To this end, it is of utmost importance and a significant challenge to reform the current production systems to reduce GHG emissions and promote the capture of CO2 from the atmosphere. Herein, we review innovative technologies that offer solutions achieving carbon (C) neutrality and sustainable development, including those for renewable energy production, food system transformation, waste valorization, C sink conservation, and C-negative manufacturing. The wealth of knowledge disseminated in this review could inspire the global community and drive the further development of innovative technologies to mitigate climate change and sustainably support human activities.

C:N:P stoichiometry responses to 10 years of nitrogen addition differ across soil components and plant organs in a subtropical Pleioblastus amarus forest

How stoichiometry in different ecosystem components responds to long-term nitrogen (N) addition is crucial for understanding within-ecosystem biogeochemistry cycling processes in the context of global change. To explore the effects of long-term N addition on nutrient stoichiometry in soil and plant components in forest ecosystem, a 10-year N addition experiment using ammonium nitrate (NH₄NO₃) was conducted in a bamboo forest in the Rainy Zone of West China, where the background N deposition is the highest in the world. Four N treatment levels (+0, +50, +150, +300 kg N ha^-1 yr^-1) (CK, LN, MN, HN) were applied monthly since November 2007, and then, the C:N:P stoichiometry of soil, microbial biomass, and enzymes in rhizosphere soil and bulk soil, and plant organs were measured. N addition decreased the stoichiometry of C:N:P of soil, microbial biomass, and enzymes. Soil C:N:P change under N addition treatments was stronger in bulk soil, while C:N:P changes for microbial biomass and enzyme activity were significant in rhizosphere soil. N addition significantly decreased TOC in bulk soil. Changes in MBC:MBN:MBP in rhizosphere and bulk soil were mainly caused by MBN and MBP, and MBP performance was consistent with that of AP. The main variable leading to the change of enzyme C:N:P in rhizosphere soil was BG and AP, and in bulk soil was LAP + NAG activity. Plant root C:P and N:P increased with N addition, while those for leaves and twigs did not. N addition significantly reduced the pH of both rhizosphere and bulk soils. These results suggest that the stoichiometry responses of rhizosphere and bulk soils were different due to the influence of plant roots. Soil acidification, enhanced aluminum toxicity potential, decreased root biomass and enhanced microbial P limitation caused by N addition were the important mechanisms that promoted stoichiometry changes in this ecosystem. Under the chronic input of N deposition, the stoichiometry between plant and soil evolved in different directions, which may lead to the decoupling of plants from soils.

Preferred reporting items for systematic reviews and meta-analyses in ecology and evolutionary biology: a PRISMA extension

Since the early 1990s, ecologists and evolutionary biologists have aggregated primary research using meta-analytic methods to understand ecological and evolutionary phenomena. Meta-analyses can resolve long-standing disputes, dispel spurious claims, and generate new research questions. At their worst, however, meta-analysis publications are wolves in sheep's clothing: subjective with biased conclusions, hidden under coats of objective authority. Conclusions can be rendered unreliable by inappropriate statistical methods, problems with the methods used to select primary research, or problems within the primary research itself. Because of these risks, meta-analyses are increasingly conducted as part of systematic reviews, which use structured, transparent, and reproducible methods to collate and summarise evidence. For readers to determine whether the conclusions from a systematic review or meta-analysis should be trusted - and to be able to build upon the review - authors need to report what they did, why they did it, and what they found. Complete, transparent, and reproducible reporting is measured by 'reporting quality'. To assess perceptions and standards of reporting quality of systematic reviews and meta-analyses published in ecology and evolutionary biology, we surveyed 208 researchers with relevant experience (as authors, reviewers, or editors), and conducted detailed evaluations of 102 systematic review and meta-analysis papers published between 2010 and 2019. Reporting quality was far below optimal and approximately normally distributed. Measured reporting quality was lower than what the community perceived, particularly for the systematic review methods required to measure trustworthiness. The minority of assessed papers that referenced a guideline (~16%) showed substantially higher reporting quality than average, and surveyed researchers showed interest in using a reporting guideline to improve reporting quality. The leading guideline for improving reporting quality of systematic reviews is the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement. Here we unveil an extension of PRISMA to serve the meta-analysis community in ecology and evolutionary biology: PRISMA-EcoEvo (version 1.0). PRISMA-EcoEvo is a checklist of 27 main items that, when applicable, should be reported in systematic review and meta-analysis publications summarising primary research in ecology and evolutionary biology. In this explanation and elaboration document, we provide guidance for authors, reviewers, and editors, with explanations for each item on the checklist, including supplementary examples from published papers. Authors can consult this PRISMA-EcoEvo guideline both in the planning and writing stages of a systematic review and meta-analysis, to increase reporting quality of submitted manuscripts. Reviewers and editors can use the checklist to assess reporting quality in the manuscripts they review. Overall, PRISMA-EcoEvo is a resource for the ecology and evolutionary biology community to facilitate transparent and comprehensively reported systematic reviews and meta-analyses.

The Exudation of Surplus Products Links Plant Functional Traits and Plant-Microbial Stoichiometry

The rhizosphere is a hot spot of soil microbial activity and is largely fed by root exudation. The carbon (C) exudation flux, coupled with plant growth, is considered a strategy of plants to facilitate nutrient uptake. C exudation is accompanied by a release of nutrients. Nitrogen (N) and phosphorus (P) co-limit the productivity of the plant-microbial system. Therefore, the C:N:P stoichiometry of exudates should be linked to plant nutrient economies, plant functional traits (PFT) and soil nutrient availability. We aimed to identify the strongest links in C:N:P stoichiometry among all rhizosphere components. A total of eight grass species (from conservative to exploitative) were grown in pots under two different soil C:nutrient conditions for a month. As a result, a wide gradient of plant–microbial–soil interactions were created. A total of 43 variables of plants, exudates, microbial and soil C:N:P stoichiometry, and PFTs were evaluated. The variables were merged into four groups in a network analysis, allowing us to identify the strongest connections among the variables and the biological meaning of these groups. The plant–soil interactions were shaped by soil N availability. Faster-growing plants were associated with lower amounts of mineral N (and P) in the soil solution, inducing a stronger competition for N with microorganisms in the rhizosphere compared to slower-growing plants. The plants responded by enhancing their N use efficiency and root:shoot ratio, and they reduced N losses via exudation. Root growth was supported either by reallocated foliar reserves or by enhanced ammonium uptake, which connected the specific leaf area (SLA) to the mineral N availability in the soil. Rapid plant growth enhanced the exudation flux. The exudates were rich in C and P relative to N compounds and served to release surplus metabolic products. The exudate C:N:P stoichiometry and soil N availability combined to shape the microbial stoichiometry, and N and P mining. In conclusion, the exudate flux and its C:N:P stoichiometry reflected the plant growth rate and nutrient constraints with a high degree of reliability. Furthermore, it mediated the plant–microbial interactions in the rhizosphere.

Effects of rhizosphere fungi on the chemical composition of fruits of the medicinal plant Cinnamomum migao endemic to southwestern China

BACKGROUND

This study examined how rhizosphere fungi influence the accumulation of chemical components in fruits of a small population species of Cinnamomum migao.

RESULTS

Ascomycota and Basidiomycota were dominant in the rhizosphere fungal community of C. migao. Pestalotiopsis and Gibellulopsis were associated with α-Terpineol and sabinene content, and Gibellulopsis was associated with crude fat and carbohydrate content. There were significant differences in rhizosphere fungal populations between watersheds, and there was no obvious change between fruiting periods. Gibberella, Ilyonectria, Micropsalliota, and Geminibasidium promoted sabinene accumulation, and Clitocybula promoted α-Terpineol accumulation.

CONCLUSION

The climate-related differentiation of rhizosphere fungal communities in watershed areas is the main driver of the chemical composition of C. migao fruit. The control of the production of biologically active compounds by the rhizosphere fungal community provides new opportunities to increase the industrial and medicinal value of the fruit of C. migao.

A holistic framework integrating plant-microbe-mineral regulation of soil bioavailable nitrogen

Soil organic nitrogen (N) is a critical resource for plants and microbes, but the processes that govern its cycle are not well-described. To promote a holistic understanding of soil N dynamics, we need an integrated model that links soil organic matter (SOM) cycling to bioavailable N in both unmanaged and managed landscapes, including agroecosystems. We present a framework that unifies recent conceptual advances in our understanding of three critical steps in bioavailable N cycling: organic N (ON) depolymerization and solubilization; bioavailable N sorption and desorption on mineral surfaces; and microbial ON turnover including assimilation, mineralization, and the recycling of microbial products. Consideration of the balance between these processes provides insight into the sources, sinks, and flux rates of bioavailable N. By accounting for interactions among the biological, physical, and chemical controls over ON and its availability to plants and microbes, our conceptual model unifies complex mechanisms of ON transformation in a concrete conceptual framework that is amenable to experimental testing and translates into ideas for new management practices. This framework will allow researchers and practitioners to use common measurements of particulate organic matter (POM) and mineral-associated organic matter (MAOM) to design strategic organic N-cycle interventions that optimize ecosystem productivity and minimize environmental N loss.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10533-021-00793-9.

Excessive nitrogen addition accelerates N assimilation and P utilization by enhancing organic carbon decomposition in a Tibetan alpine steppe

High amounts of deposited nitrogen (N) dramatically influence the stability and functions of alpine ecosystems by changing soil microbial community functions, but the mechanism is still unclear. To investigate the impacts of increased N deposition on microbial community functions, a 2-year multilevel N addition (0, 10, 20, 40, 80 and 160 kg N ha^-1 year^-1) field experiment was set up in an alpine steppe on the Tibetan Plateau. Soil microbial functional genes (GeoChip 4.6), together with soil enzyme activity, soil organic compounds and environmental variables, were used to explore the response of microbial community functions to N additions. The results showed that the N addition rate of 40 kg N ha^-1 year^-1 was the critical value for soil microbial functional genes in this alpine steppe. A small amount of added N (≤40 kg N ha^-1 year^-1) had no significant effects on the abundance of microbial functional genes, while high amounts of added N (>40 kg N ha^-1 year^-1) significantly increased the abundance of soil organic carbon degradation genes. Additionally, the abundance of microbial functional genes associated with NH₄⁺, including ammonification, N fixation and assimilatory nitrate reduction pathways, was significantly increased under high N additions. Further, high N additions also increased soil organic phosphorus utilization, which was indicated by the increase in the abundance of phytase genes and alkaline phosphatase activity. Plant richness, soil NO₂^-/NH₄⁺ and WSOC/WSON were significantly correlated with the abundance of microbial functional genes, which drove the changes in microbial community functions under N additions. These findings help us to predict that increased N deposition in the future may alter soil microbial functional structure, which will lead to changes in microbially-mediated biogeochemical dynamics in alpine steppes on the Tibetan Plateau and will have extraordinary impacts on microbial C, N and P cycles.

Interactive Effects of Light and Nitrogen on Pakchoi (Brassica chinensis L.) Growth and Soil Enzyme Activity in an Underground Environment

Light conditions and nitrogen fertilizer are crucial for plant growth, especially in the underground situations without sunlight and nitrogen deposition. In this paper, the effects of photoperiod (12 h and 16 h lighting time per day), light intensity (200, 300 and 400 μmol m−2 s−1) and nitrogen addition (0, 0.15, 0.3 and 0.45 g N kg−1 soil) on pakchoi growth and specific soil enzyme activity were investigated. The results demonstrated that there were strong interactive effects of light intensity and nitrogen addition on plant yield. The plant yield changed parabolically with increasing nitrogen addition when a light intensity was given between 200 and 300 μmol m−2 s−1, while the yield decreased linearly with increasing nitrogen application under the light intensity of 400 μmol m−2 s−1. The combination of 16 h photoperiod, 300 μmol m−2 s−1 light intensity and 0.3 g N kg−1 soil nitrogen addition was the best for pakchoi growth. The investigation of soil enzyme showed that the activity of urease responded negatively to nitrogen addition, whereas the activity of phosphatase had positive correlation with light intensity but was not affected by nitrogen addition. Our results suggested that the toxic effect of excessive nitrogen was a better explanation for the interactive effects of light and nitrogen than the plant-microbe interaction framework. The critical toxicity level of nitrogen for pakchoi was determined and showed negative correlation with light intensity.

Quasi-steady uptake and bacterial community assembly in a mathematical model of soil-phosphorus mobility

We mathematically model the uptake of phosphorus by a soil community consisting of a plant and two bacterial groups: copiotrophs and oligotrophs. Four equilibrium states emerge, one for each of the species monopolising the resource and dominating the community and one with coexistence of all species. We show that the dynamics are controlled by the ratio of chemical adsorption to bacterial death permitting either oscillatory states or quasi-steady uptake. We show how a steady state can emerge which has soil and plant nutrient content unresponsive to increased fertilization. However, the additional fertilization supports the copiotrophs leading to community reassembly. Our results demonstrate the importance of time-series measurements in nutrient uptake experiments.

Yeast strain Debaryomyces hansenii for amelioration of arsenic stress in rice

Arsenic (As) is a serious threat for environment and human health. Rice, the main staple crop is more prone to As uptake. Bioremediation strategies with heavy metal tolerant rhizobacteria are well known. The main objective of the study was to characterize arsenic-resistant yeast strains, capable of mitigating arsenic stress in rice. Three yeast strains identified as Debaryomyces hansenii (NBRI-Sh2.11), Candida tropicalis (NBRI-B3.4) and Candida dubliniensis (NBRI-3.5) were found to have As reductase activity. D. hansenii with higher As tolerance has As expulsion ability as compared to other two strains. Inoculation of D. hansenii showed improved detoxification through scavenging of reactive oxygen species (ROS) by the modulation of SOD and APX activity under As stress condition in rice. Modulation of defense responsive gene (NADPH, GST, GR) along with arsR and metal cation transporter are the probable mechanism of As detoxification as evident with improved membrane (electrolyte leakage) stability. Reduced grain As (~40% reduction) due to interaction with D. hansenii (NBRI-Sh2.11) further validated it's As mitigation property in rice. To the best of our knowledge D. hansenii has been reported for the first time for arsenic stress mitigation in rice with improved growth and nutrient status of the plant.

Microbial carbon limitation: The need for integrating microorganisms into our understanding of ecosystem carbon cycling

Numerous studies have demonstrated that fertilization with nutrients such as nitrogen, phosphorus, and potassium increases plant productivity in both natural and managed ecosystems, demonstrating that primary productivity is nutrient limited in most terrestrial ecosystems. In contrast, it has been demonstrated that heterotrophic microbial communities in soil are primarily limited by organic carbon or energy. While this concept of contrasting limitations, that is, microbial carbon and plant nutrient limitation, is based on strong evidence that we review in this paper, it is often ignored in discussions of ecosystem response to global environment changes. The plant-centric perspective has equated plant nutrient limitations with those of whole ecosystems, thereby ignoring the important role of the heterotrophs responsible for soil decomposition in driving ecosystem carbon storage. To truly integrate carbon and nutrient cycles in ecosystem science, we must account for the fact that while plant productivity may be nutrient limited, the secondary productivity by heterotrophic communities is inherently carbon limited. Ecosystem carbon cycling integrates the independent physiological responses of its individual components, as well as tightly coupled exchanges between autotrophs and heterotrophs. To the extent that the interacting autotrophic and heterotrophic processes are controlled by organisms that are limited by nutrient versus carbon accessibility, respectively, we propose that ecosystems by definition cannot be 'limited' by nutrients or carbon alone. Here, we outline how models aimed at predicting non-steady state ecosystem responses over time can benefit from dissecting ecosystems into the organismal components and their inherent limitations to better represent plant-microbe interactions in coupled carbon and nutrient models.

Global meta-analysis shows pervasive phosphorus limitation of aboveground plant production in natural terrestrial ecosystems

Phosphorus (P) limitation of aboveground plant production is usually assumed to occur in tropical regions but rarely elsewhere. Here we report that such P limitation is more widespread and much stronger than previously estimated. In our global meta-analysis, almost half (46.2%) of 652 P-addition field experiments reveal a significant P limitation on aboveground plant production. Globally, P additions increase aboveground plant production by 34.9% in natural terrestrial ecosystems, which is 7.0–15.9% higher than previously suggested. In croplands, by contrast, P additions increase aboveground plant production by only 13.9%, probably because of historical fertilizations. The magnitude of P limitation also differs among climate zones and regions, and is driven by climate, ecosystem properties, and fertilization regimes. In addition to confirming that P limitation is widespread in tropical regions, our study demonstrates that P limitation often occurs in other regions. This suggests that previous studies have underestimated the importance of altered P supply on aboveground plant production in natural terrestrial ecosystems.

Plants are thought to be limited by phosphorus (P) especially in tropical regions. Here, Hou et al. report a meta-analysis of P fertilization experiments to show widespread P limitation on plant growth across terrestrial ecosystems modulated by climate, ecosystem properties, and fertilization regimes