Soil Microbial Nutrient Research Articles

Potential effect of warming on soil microbial nutrient limitations as determined by enzymatic stoichiometry in the farmland from different climate zones

The decomposition of organic matter mediated by soil enzymes is the key process that transports carbon from the soil into the atmosphere. To better understand the effect of global warming on organic matter decomposition, we evaluated the temperature sensitivity (Q10) of invertase (EC3.2.1.26), β-glucosidase (EC3.2.1.21), urease (EC3.1.1.5), acid phosphatase (EC3.1.3.2), and arylsulfatase (EC3.1.6.1) activities in red soil from the subtropical region and black soil from the mid-temperate region at 5, 15, 25, 35, and 45 °C. Further, the in-situ stoichiometry of the products released by enzymes was modelled. All of the enzyme activities in the tested soils increased with the increasing temperature (1.1–8.9 fold per 10 °C), indicating an enhanced degradation of the organic substrate with warming. In the lower temperature range (5–25 °C), Q10 of the enzyme activities in the red soil evaluated in terms of total enzyme activity index were more prominent than that in black soil (1.53 and 3.46 vs 1.16 and 3.19). Changes in the in-situ stoichiometry of enzyme products with warming indicated that, in colder months (Jan. to Apr. and Oct. to Dec.), the microbial nutrient demand in the red soil exhibited the following order, N > P > S > C. While in the black soil, it suggested that there is increasing microbial demand for only N and S. In the warmer months (May to Sep.), the microbial nutrient demands in the two soils were opposite to the colder months. The results suggested differential changes in microbial nutrient limitation with warming, which has significant implications for the carbon stocks management in farmlands under the changing global climate.

Microplastics pollution from different plastic mulching years accentuate soil microbial nutrient limitations

Microplastics (MPs) are major global environmental pollutants that have been extensively detected in agroecosystems. However, researches on their distribution and fates in farmland as well as their potential impacts on soil ecosystems are limited, especially studies on the influences of MPs on enzymes associated with carbon (C), nitrogen (N), and phosphorus (P) cycling and microbial nutrient limitations characterized by enzymatic stoichiometry are missing. In this study, we investigated the MPs characteristics under different continuous mulching management years (3, 6, 10, 15, and 20a) of tobacco fields in Enshi Prefecture, China, and identified the mechanisms of MPs pollution on soil microbial nutrient limitations. The results showed that the abundance of MPs varied from 647 to 2840 items/kg. Films, fibers and small-sized particles (0–1.0 mm) were the predominant types and size, respectively, and increased significantly with the increase of planting years. A vector analysis of enzyme activity suggested that microbial metabolism was limited both with C and P. The correlation analysis demonstrated that MPs pollution and soil properties were significantly linked to microbial nutrient limitations. Meanwhile, partial least squares path model (PLS-PM) revealed that MPs abundance exacerbated microbial limitation mainly by directly affecting soil microbial properties, followed by soil physical properties and soil nutrients, whereas MPs size and shapes indirectly exacerbated microbial nutrient limitation by significantly influencing MPs abundance. These results demonstrated that contamination of soil with MPs may have deleterious effects on soil key functions related to microbial metabolism, nutrient cycling, etc. Changes in soil properties and functions can damage plant growth and development, which may further affect crop yield and quality. This study provided a new theoretical basis for the response of soil microbial metabolism to MPs pollution and facilitated a better understanding and estimation of the environmental behavior and ecological risk of MPs in agricultural fields.

Linkage between soil ectoenzyme stoichiometry ratios and microbial diversity following the conversion of cropland into grassland

Soil ectoenzyme activities (mainly carbon [C]-, nitrogen [N]- as well as phosphorus [P]-acquiring enzymes) and their ratios are the sensitive indicators for the nutrients and energy demands for microbes. How ectoenzyme stoichiometry ratios mediate the changes in microbial community composition and diversity following the conversion of cropland into grassland remains unknown. This study assessed the effects of soil abiotic, biotic factors, and ectoenzyme stoichiometry ratios on microbial diversity (using high-throughput sequencing) following the conversion of cropland into grassland (Cropland and 5, 10, 15, 25, and 30 year natural successional grasslands). Soil ectoenzyme activities synchronously increased with the increase of bacterial and fungal alpha diversity following the conversion of cropland into grassland. Moreover, biotic and abiotic factors co-explained microbial diversity by the changes of ectoenzyme stoichiometry ratios. Specially, ectoenzyme stoichiometry ratios were strongly related to the relative abundance of predominant fungal phylum (Ascomycota, Basidiomycota) and bacterial phylum (Acidobacteria), and ultimately leading to the microbial life history strategies transiting from the oligotrophic groups with retarded growth, to the copiotrophic groups with rapid growth. These differences of microbial community composition, driven by ectoenzyme stoichiometry ratios, reflect soil microbial nutrient cycling following the conversion of cropland into grassland.

Response of root nutrient resorption strategies to rhizosphere soil microbial nutrient utilization along Robinia pseudoacacia plantation chronosequence

Understanding root nutrient resorption strategies and their drivers is essential to explore plant nutrient acquisition strategies in restored ecosystems. However, the interaction between root nutrient resorption and the nutrient utilization of rhizosphere soil microorganisms in restored ecosystems has yet to be determined. In this study, we investigated plant fine roots and rhizosphere soils in Robinia pseudoacacia plantations at four stages of forest succession (14, 20, 30, and 45 years of age) on the Loess Plateau in China. We studied the characteristics of root nitrogen and phosphorus resorption efficiencies (NRE and PRE) at different recovery stages and analyzed the relationships among nutrient resorption and rhizosphere soil variables (nutrients and microbial communities). We detected a tendency of an initial reduction and subsequent increase in root NRE and PRE with stand age (the lowest value at 30-y sites), whereas the nutrient contents of rhizosphere soil increased with stand age, and soil available nutrients initially increased and then declined. The diversity of rhizosphere soil microorganisms also showed an initial increase and subsequent decline. Proteobacteria were considered to be at an advantage during the nutrient-rich stage of restoration (30-y sites), whereas Acidobacteria were found to be dominant during the low-nutrient restoration stage (14-y sites). Furthermore, the microbial nutrient utilization ratios of soil microbial biomass carbon: soil organic carbon, microbial biomass nitrogen: soil total nitrogen, and microbial biomass phosphorus: soil total phosphorus also showed an initial increase and then decreased (with peaks at the 30-y sites). Redundancy analysis indicated that the nutrient contents of rhizosphere soil were significantly related to microbial communities and correlation analysis revealed that microbial nutrient-use efficiencies were significantly related to rhizosphere soil nutrient contents and the dominant microbial communities. We also detected a significant negative correlation between root nutrient resorption and microbial nutrient utilization. Partial least squares path modeling revealed that forest restoration influences the contents of nutrients in rhizosphere soil and the composition of microbial communities, whereas microbial biomass and nutrient utilization efficiency were shown to have a negative effect on root resorption efficiency. Based on our findings, we propose that the highly conservative nutrient utilization strategies of the rhizosphere soil microbial community may negatively drive root nutrient resorption strategies during the succession of R. pseudoacacia.

Adaptive pathways of soil microorganisms to stoichiometric imbalances regulate microbial respiration following afforestation in the Loess Plateau, China

Afforestation results in a wide range of soil resources with carbon (C), nitrogen (N), and phosphorus (P) levels that rarely meet microbial elemental demands. Such stoichiometric imbalances result in the limitation of microbial activity by nutrients, and have consequences for microbial C and nutrient use efficiency and ultimately the fate of soil C. However, how microorganisms cope with stoichiometric imbalances following afforestation and how their responses regulate microbial-driven C emissions remain unclear. We compared sites along a 42 year Robinia pseudoacacia afforestation chronosequence on the Loess Plateau of China, to quantify soil microbial nutrient limitation and explore the mechanisms underlying microbe-mediated C dynamics under conditions of stoichiometric imbalance. Soil available nutrients, potential activities of C-, N-, and P-acquiring enzymes, microbial biomass, microbial community composition and diversity, as well as microbial respiration were measured. Results showed that stoichiometric imbalances increased soil enzymatic activities targeting the mobilization of limiting nutrients at different afforestation stages. Specifically, soil microbial communities were limited by C in farmland, co-limited by N and P at the 10-year site, and became more limited by P as stand age increased. Reductions in stoichiometric imbalance along the afforestation chronosequence corresponded to an increased microbial alpha diversity and fungi-to-bacteria ratio. Stoichiometric imbalances were more strongly associated with changes in soil bacterial beta diversity than fungal beta diversity. Bacterial communities transitioned from being oligotrophic (Actinobacteria dominant) to copiotrophic (Proteobacteria dominant) during forest development, and this was significantly related to stoichiometric imbalance. However, no significant correlation was detected between stoichiometric imbalance and the dominant fungal phyla (i.e., Ascomycota, Basidiomycota, and Zygomycota). The synergistic responses of enzymatic stoichiometry and microbial community properties to stoichiometric imbalance following afforestation led to reduced microbial threshold elemental ratios, which elevated microbial C use efficiency and increased biomass turnover time, further suppressing microbial respiration. Such collaborative-adaptations imply that more C will be diverted into microbial biomass rather than losing, thus could be favorable to soil C storage. Collectively, these findings highlight the importance of stoichiometric imbalances in regulating microbial-driven C emissions and contribute to an improved understanding of how substrate quality changes induced by revegetation influences terrestrial C flows in ecologically fragile areas.

Direct and indirect influences of long-term fertilization on microbial carbon and nitrogen cycles in an alpine grassland

Beginning in the twentieth century, atmospheric deposition of N and P greatly increased in terrestrial ecosystems, including alpine grasslands. These inputs have profoundly affected soil microbial C and N cycles. Changes in the microbial environment are directly caused by changes in soil N and P availability and also indirectly through changes in vegetation in response to increased fertilization. The mechanisms involved in both the direct and indirect changes are not mutually exclusive and are poorly understood. Therefore, we investigated the responses of vegetation and soil microbes to a 9-year fertilization (N and P) experiment in an alpine grassland in the Qinghai–Tibetan Plateau in China. We found that N addition altered soil microbial community composition and processes regardless of P addition. To maintain stoichiometric homeostasis, soil microbes adjusted metabolic processes in response to changes in nutrient availability. High N availability enhanced microbial investment in C acquisition as indicated by β-1,4-Glucosidase activity. The abundance of microbial taxa that degrade labile C also increased. High N inputs also induced a proliferation of denitrifiers and increased the gaseous N loss potential. Partial least squares path modelling indicated that soil parameters (e.g., soil organic C and total N) and changes in the plant community played a key role in shaping soil microbial community structure and C and N cycling. Our results suggest that vegetation and stoichiometric differences between resource availability and soil microbial nutrient requirements collectively regulate the responses of soil microbial processes to N enrichment, which provides novel experimental insights into the mechanisms underlying the effects of nutrient inputs on microbial C and N cycles. Ultimately, our findings highlight the importance of plant traits in regulating microbial nutrient cycles, further promoting our comprehension about the mechanism of variation in the microbial nutrient cycles in an alpine grassland soils.

Effects of Biochar Application on Soil Microbial Nutrient Limitations and Carbon Use Efficiency in Lou Soil

Soil microbial metabolism is vital for nutrient cycling and stability of an ecosystem. To elucidate the long-term effects of biochar application on nutrient limitations and carbon use efficiency (CUE) of soil microbial metabolisms, biochars pyrolyzed at 450℃ from trunks and branches of fruit trees under an oxygen-limited condition were mixed with the top Lou soils (0-20 cm) with application amounts of 0, 20, 40, 60, and 80 t·hm-2 in 2012. Corn-wheat rotation was carried out afterwards for seven years. The nutrient limitations of soil microbial metabolisms were analyzed quantitatively through ecoenzymatic stoichiometry in 2019. The results indicated that:① With an increase in the biochar application amount, soil moisture, organic carbon, total nitrogen, C:N, C:P, and N:P significantly increased, whereas there were no clear patterns for the active components of carbon, nitrogen, and phosphorus, microbial biomass carbon, nitrogen, phosphorus and total phosphorus. In contrast, the activities of five extracellular enzymes (β-1,4-glucosidase, cellobiohydrolase, leucine aminopeptidase, β-1,4-N-acetylglucosaminidase, and phosphatase) were significantly reduced. ② The soil microorganisms suffered from the phosphorus limitation under all treatments in this study. In the treatments of biochar application, the carbon and phosphorus limitations of microbial metabolisms increased significantly with increasing application amount, whereas the microbial CUE decreased significantly. When the application amount was 20 t·hm-2, the carbon limitation (0.625±0.022) and phosphorus limitation (62.153°±0.892°) were lowest, and the microorganism CUE (0.511±0.007) was highest. ③ Partial least-squares path modeling (PLS-PM) showed that soil carbon, nitrogen, phosphorus, and their stoichiometry had a very direct positive effect on phosphorus limitation (P<0.01), and there was a positive correlation between carbon limitation and phosphorus limitation (R2=0.242, P<0.001); in contrast, the carbon and phosphorus limitations had a very significant negative effect on CUE (P<0.001). It was revealed that the excessive application of biochar had caused a soil element stoichiometry imbalance, which deteriorated the phosphorus limitation of the soil microbial metabolism and further led to carbon limitation and reduction of CUE. When the biochar application amount was 20 t·hm-2, C and P limitations were lowest, and microbial CUE was highest. Therefore, 20 t·hm-2 was optimal for regulating soil microbial metabolism, maintaining ecological functions, and reducing carbon dioxide emission produced by microbial metabolism.

Nitrogen and phosphorus uptake from isotope‐labeled fertilizers by sorghum and soil microorganisms

AbstractOn nutrient‐depleted Lixisols from Burkina Faso, nutrient acquisition by crops and soil microbes mainly relies on the limited amounts of mineral and organic fertilizers applied by small‐scale farmers. The objective of this study was to determine simultaneously the uptake of nitrogen (N) and phosphorus (P) contained in organic and mineral fertilizers by sorghum [Sorghum bicolor (L.) Moench ] and soil microbial biomass. Double 15N and 33P direct and indirect labeling techniques were applied in a pot experiment to determine the contributions of different fertilizers to sorghum N and P uptake during 52 d of growth. In parallel, soil respiration, available, and microbial N and P were tracked in an incubation experiment. Sorghum derived 83–90% of P from fertilizers. Nitrogen from cattle manure was poorly available, contributing only 20% of the N taken up by sorghum. Water‐soluble mineral fertilizers increased soil N and P availability, resulting in the highest total N and P uptake by sorghum from fertilizers and soil among all treatments. The application of cowpea [Vigna unguiculata (L.) Walp.] residues induced microbial N and P immobilization, reducing sorghum N and P uptake to the level of the non‐fertilized treatment. The use of double 15N and 33P labeling elucidated the impact of fertilizers on soil nutrient pools. The low plant N/P ratio suggested N limitation for sorghum in the manure treatment. Cowpea residues were inefficient for sorghum nutrition, but they increased soil microbial nutrient pools. This study gives insights on the potential effects of legume residues used as green manure to build soil fertility.

Linking soil microbial nutrient limitation to fertilizer regime and sugar beet yield

Aim Depending on the availability and stoichiometry of nutrients in soil, microbes and plants can compete for the same resources. In this study we aimed to test how microbial nutrient limitation in agricultural systems can be linked to fertilizer regimes and sugar beet yield. Methods We measured the dynamics of microbial growth responses by monitoring soil respiration after the application of carbon (C), C and nitrogen (N), C and phosphorus (P) and C, N and P to soils of an agricultural long-term fertilization experiment in Speyer (Germany). Samples were taken in February and June before harvest and in November after harvest. Results CN limitation in June was the best predictor for sugar beet yield, with increasing CN limitation there was a decreasing yield. Mineral N fertilization in May alleviated microbial N limitation in June. Over the course of the sampling, microbial nutrient limitations were highest after harvest in November. Conclusions Together, our results indicate that plants and microbes compete for the same nutrients, and that plants are more competitive at acquiring them. Measurements of microbial nutrient limitation four months before harvest successfully predicted sugar beet yield and could therefore be used as a diagnostic indicator.

Patterns of soil microbial nutrient limitations and their roles in the variation of soil organic carbon across a precipitation gradient in an arid and semi-arid region

The effects of precipitation patterns on the metabolism of soil microbes are poorly understood, especially in water-limited ecosystems where soil microorganisms play crucial roles in the turnover of soil organic carbon (SOC) and nutrients. We investigated the influence of the gradient levels of mean annual precipitation (MAP from 300 to 900 mm) on soil microbial metabolism in an arid and semi-arid grassland region located in Loess Plateau, China and identified relationships between microbial metabolic limitations and the variation of soil organic matter (SOM). Microbial metabolism in this arid and semi-arid region was limited by soil C and phosphorus (P) or nitrogen (N). Microbial C and P limitations decreased with the increase of MAP. Microbial C and P limitations were lowest in the areas with MAPs of 700–900 mm, whereas N limitation was observed in the areas with MAPs >700 mm. The results of a variation-partitioning analysis and partial least squares path modeling indicated that the microbial C and N/P limitations on regional scales were mainly determined by climate factors (MAP and mean annual temperature (MAT)), followed by vegetation biomass and soil properties. The extents of soil drying-rewetting processing caused by different MAPs directly affected microbial nutrient limitation. Our results suggested that the influence of precipitation variation on microbial metabolic limitation strongly governed SOM stability and that an increase in the rate of SOM decomposition with increasing precipitation could be caused by increased microbial nutrient limitation. SOM may be most stable at a MAP of 700 mm in the arid and semi-arid regions (300–900 mm MAP) where microbial nutrient limitation was lowest. This study provided novel insights into the responses of soil microbial metabolism to precipitation change and is an important step toward understanding the mechanisms of SOM stability in an arid and semi-arid grassland ecosystem under scenarios of precipitation variation.

Soil microbial nutrient constraints along a tropical forest elevation gradient: a belowground test of a biogeochemical paradigm

Abstract. Aboveground primary productivity is widely considered to be limited by phosphorus (P) availability in lowland tropical forests and by nitrogen (N) availability in montane tropical forests. However, the extent to which this paradigm applies to belowground processes remains unresolved. We measured indices of soil microbial nutrient status in lowland, sub-montane and montane tropical forests along a natural gradient spanning 3400 m in elevation in the Peruvian Andes. With increasing elevation there were marked increases in soil concentrations of total N, total P, and readily exchangeable P, but a decrease in N mineralization determined by in situ resin bags. Microbial carbon (C) and N increased with increasing elevation, but microbial C : N : P ratios were relatively constant, suggesting homeostasis. The activity of hydrolytic enzymes, which are rich in N, decreased with increasing elevation, while the ratio of enzymes involved in the acquisition of N and P increased with increasing elevation, further indicating an increase in the relative demand for N compared to P with increasing elevation. We conclude that soil microorganisms shift investment in nutrient acquisition from P to N between lowland and montane tropical forests, suggesting that different nutrients regulate soil microbial metabolism and the soil carbon balance in these ecosystems.

Effect of microbial organic fertilizer application on soil microbial activity

Microbial organic fertilizer (which is a typical functional fertilizer) was used in a corn pot culture under greenhouse con- dition to determine the effect of microbial organic fertilizer on soil microbial ecology via plate count and BIOLOG ECO methods. The study shows significantly enhancement in the number of soil microbes under microbial organic fertilizer compared with chemical fertilizer. AWCD values and carbon source utilization analyses show that microbial organic fertilizer noticeably increases carbon source utility by microbes, especially utility of carboxylic, amino acids, and miscellaneous carbon sources. More carbon source is used under microbial organic fertilizer application than under other treatments. Microbial organic fertilizer increases carbon source utilization, improves soil microbial nutrient level, and also increases soil microbial community activity and diversity.

Vernal nitrogen and phosphorus retention by forest understory vegetation and soil microbes

Northern hardwood forests experience annual maximal loss of nutrients during spring. The vernal dam hypothesis predicts that spring ephemeral herbs in northern hardwood forests serve as sinks for nutrients during this season and reduce the loss of nutrients from the terrestrial ecosystem. Soil microbes of northern hardwood forests also sequester nutrients during spring. We compared the vernal nutrient acquisition ability of a soil microbial community and an understory plant community with species of mixed leaf phenology. We monitored nitrogen and phosphorus pool sizes in understory vegetation and soil microbes during spring from 1999 through 2001 in a northern hardwood forest in the Catskill Mountains, New York. Vegetation nutrient content increased during two spring seasons by an average of 3.07 g N m−2 and 0.19 g P m−2 and decreased during one spring by 0.81 g N m−2 and 0.10 g P m−2. Evergreen, wintergreen, and deciduous plant species were able to sequester nutrients during spring. Soil microbial nutrient content decreased during one spring by 1.29 g N m−2 and remained constant during the other two springs. Streamwater nitrogen losses were not correlated with biotic nutrient uptake suggesting a temporal disconnect between the two processes. We conclude that understory vegetation is a larger potential sink for vernal nutrients than are soil microbes in this northern hardwood forest and understory and species representing multiple phenologies are capable of vernal nutrient uptake.