Biology and Fertility of Soils最新文献

Intercropping is a powerful practice to alter the allocation of photosynthetic carbon (C) to belowground ecosystems via promotion of diversified plant communities. The feedback of soil C stability to intercropping is controlled by microbial C use efficiency (CUE). Despite its significance, there is currently insufficient evidence to decipher how soil microbial CUE reacts to intercropping. By combining a 10-year-long intercropping experiment with a substrate-independent ¹⁸O-H₂O labelling approach and high-throughput sequencing, we elucidated the performance of intercropping on soil C pool and microbial metabolic traits as well as their relationships with soil microbial communities. Compared with monoculture, maize intercropping with peanut and soybean significantly increased soil C storage, soil mineral-associated organic C (MAOC), soil dissolved organic (DOC), and soil microbial biomass (MBC) contents at maize four growth stages. Soil microbial CUE increased significantly, especially at maize flowering and mature stages, as a consequence of enhanced microbial growth and biomass turnover rate after maize intercropping with peanut and soybean. Soil C storage and accessibility indicators (e.g., MAOC, DOC, and MBC contents) could significantly predict the changes of soil microbial diversity and core taxa. Meanwhile, the beta-diversity (community composition) of soil bacteria, fungi, saprotroph and protists, as well as rare fungal taxa were positively correlated with soil microbial CUE, and these indicators showed a high prediction of the microbial CUE. Soil C storage and accessibility indicators directly and indirectly influenced soil microbial CUE by regulating microbial diversity and key taxa. Soil microbial diversity and core taxa directly and indirectly influenced microbial CUE by mediating microbial respiration, growth, biomass, and enzyme activity, which mediated by soil C storage and accessibility. These findings provide an evidence for the associations between microbial diversity, CUE, and soil C stability, highlighting the importance of intercropping-driven soil microbiome to enhance soil microbial CUE.

Abstract

Climate change has been intensifying soil drying and rewetting cycles, which can alter the soil microbiome structure and activity. Here we hypothesized that a soil drying-rewetting cycle enhances biodegradation and, hence, decreases the effectiveness of nitrification inhibitors (NIs). The effectiveness of DMPP (3,4-Dimethylpyrazole phosphate) and MP + TZ (3-Methylpyrazol and Triazol) was evaluated in 60-day incubation studies under a drying and rewetting cycle relative to constant low and high soil moisture conditions (40% and 80% water-holding capacity, WHC, respectively) in two different textured soils. The measurements included (i) daily and cumulative N₂O-N emissions, (ii) soil NH₄⁺-N and NO₃⁻-N concentrations, and (iii) the composition of bacterial soil communities. Application of DMPP and MP + TZ reduced the overall N₂O-N emissions under drying-rewetting (-45%), as well as under 40% WHC (-39%) and 80% WHC (-25%). DMPP retarded nitrification and decreased N₂O-N release from the sandy and silt loam soils, while MP + TZ mitigated N₂O-N production only from the silt loam soil. Unexpectedly, between days 30 and 60, N₂O-N emissions from NI-treated soils increased by up to fivefold relative to the No-NI treatment in the silt loam soil at 80% WHC. Likewise, the relative abundance of the studied nitrifying bacteria indicated that the NIs had only short-term effectiveness in the silt loam soil. These results suggested that DMPP and MP + TZ might trigger high N₂O-N release from fine-textured soil with constant high moisture after this short-term inhibitory effect. In conclusion, DMPP and MP + TZ effectively reduce N₂O-N emissions under soil drying and rewetting.

Manure-derived biochars have a fertilizer potential as pyrolysis concentrates non-volatile nutrients. The addition of magnesium (Mg) to poultry manure enhances its Mg/Ca ratio and could increase soluble P by phosphate-solubilizing bacteria (PSB). Our objective was to assess the potential of PSB strains to solubilize P from both unenriched and Mg-enriched biochar and to evaluate the growth of maize in an Oxisol fertilized with biochar (100 mg kg⁻¹ total P) to satisfy plant P needs. We examined the strains: Paraburkholderia fungorum UFLA 04–155, Pseudomonas anuradhapurensis UFPI B5-8A, Paenibacillus chondroitinus UFLA 03–116, Acinetobacter pittii UFLA 03–09, and Rhizobium tropici CIAT 899. Biochar was made from poultry manure at temperatures of 350 °C, 500 °C, and 650 °C. Maize growth and P uptake were assessed in plants after 15 and 30 days under greenhouse conditions. The strain P. anuradhapurensis UFPI B5-8A significantly released more P from Mg-biochar (82% of the total P added) than from the unenriched biochar (74% of the total P added). Furthermore, this strain released tartaric and gluconic acids when mixed with the Mg-biochar, whereas malic acid was primarily exuded when applied to unenriched biochar. Similarly, P. anuradhapurensis UFPI B5-8A inoculation or Mg enrichment resulted in a 20% increase in P uptake by maize compared to unenriched biochar. Therefore, a synergistic approach using Mg-biochar and inoculation with PSB increases phosphate availability from poultry manure and maize P use efficiency.

This study presents a novel plant-soil mesocosm system designed for cultivating plants over periods ranging from days to weeks while continuously measuring fluxes of N₂, N₂O and CO₂. For proof of concept, we conducted a 33-day incubation experiment using six soil mesocosms, with three containing germinated wheat plants and three left plant-free. To validate the magnitude of N₂ and N₂O fluxes, we used ¹⁵N-enriched fertilizer and a ¹⁵N mass balance approach. The system inherent leakage rate was about 55 µg N m^− 2 h^− 1 for N₂, while N₂O leakage rates were below the detection limit (< 1 µg N m^− 2 h^− 1). In our experiment, we found higher cumulative gaseous N₂ + N₂O losses in sown soil (0.34 ± 0.02 g N m^− 2) as compared to bare soil (0.23 ± 0.01 g N m^− 2). N₂ fluxes accounted for approximately 94–96% of total gaseous N losses in both planted and unplanted mesocosms. N losses, as determined by the ¹⁵N mass balance approach, were found to be 1.7 ± 0.5 g N m^− 2 for the sown soil and 1.7 ± 0.6 g N m^− 2 for the bare soil, indicating an inconsistency between the two assessment methods. Soil respiration rates were also higher in sown mesocosms, with cumulative soil and aboveground biomass CO₂ respiration reaching 4.8 ± 0.1 and 4.0 ± 0.1 g C m^− 2 over the 33-day incubation period, in sown and bare soil, respectively. Overall, this study measured the effect of wheat growth on soil denitrification, highlighting the sensitivity and utility of this advanced incubation system for such studies.

Essential soil functions such as plant productivity, C storage, nutrient cycling and the storage and purification of water all depend on soil biological processes. Given this insight, it is remarkable that in modeling of these soil functions, the various biological actors usually do not play an explicit role. In this review and perspective paper we analyze the state of the art in modeling these soil functions and how biological processes could more adequately be accounted for. We do this for six different biologically driven processes clusters that are key for understanding soil functions, namely i) turnover of soil organic matter, ii) N cycling, iii) P dynamics, iv) biodegradation of contaminants v) plant disease control and vi) soil structure formation. A major conclusion is that the development of models to predict changes in soil functions at the scale of soil profiles (i.e. pedons) should be better rooted in the underlying biological processes that are known to a large extent. This is prerequisite to arrive at the predictive models that we urgently need under current conditions of Global Change.

Grasslands store large amounts of C; however, the underlying mechanisms of soil C sequestration after grazing exclusion are not well known. This study aimed to elucidate the drivers of soil organic C (SOC) sequestration from plant and microbial residues in temperate grasslands after long-term (~ 40 years) grazing exclusion. We conducted in situ ¹³C-CO₂ labelling experiments in the field and traced ¹³C in plant-soil systems paired with biomarkers to assess the C input from plants into soils. Long-term grazing exclusion increased all plant and soil pools including shoots, roots, microbial biomass and necromass. ¹³C allocation in these pools also increased, whereas ¹³C was lost via respiration as CO₂ from soils decreased. ¹³C incorporation into the soil and microbial biomass increased with ¹³C allocation into the roots. Grazing exclusion for over 40 years increased the total SOC content by 190%, largely due to increases in fungal necromass C, and there was a minor contribution of lignin phenols to SOC accrual (0.8%). Consequently, grazing exclusion boosts not only aboveground biomass, but also larger roots and rhizodeposition, leading to microbial biomass and necromass formation. Microbial necromass and lignin phenols contribute to SOC accrual under grazing exclusion, and microbial necromass, especially fungal necromass, makes a larger contribution than lignin phenols.

Microorganisms regulate soil organic matter (SOM) formation through accumulation and decomposition of microbial necromass, which is directly and indirectly affected by elevated CO₂ and N fertilization. We investigated the role of microorganisms in SOM formation by analyzing ¹³C recovery in microorganisms and carbon pools in paddy soil under two CO₂ levels, with and without N fertilization, after continuous ¹³CO₂ labelling was stopped. Microbial turnover transferred ¹³C from living microbial biomass (determined by the decrease in phospholipid fatty acids) to necromass (determined by the increase in amino sugars). ¹³C incorporation in fungal living biomass and necromass was higher than that in bacteria. Bacterial turnover was faster than necromass decomposition, resulting in net necromass accumulation over time; fungal necromass remained stable. Elevated CO₂ and N fertilization increased the net accumulation of bacterial, but not fungal, necromass. CO₂ levels, but not N fertilization, significantly affected ¹³C incorporation in SOM pools. Elevated CO₂ increased ¹³C in particulate organic matter via the roots, and in the mineral-associated organic matter (MAOM) via bacterial, but not fungal, necromass. Overall, bacterial necromass plays a dominant role in the MAOM formation response to elevated CO₂ because bacteria are sensitive to elevated CO₂.

Abstract

Biochars produced from different feedstocks and at different pyrolysis temperatures may have various chemical and physical properties, affecting their potential use as alternative microbial carrier materials. In this study, biochars were produced from pine wood and oak feedstocks at various temperatures (400°C, 500°C, 600°C, 700°C and 800°C), characterized, and assessed for their potential as carriers for Bradyrhizobium japonicum (CB1809) strain. The biochars were then stored at two different storage temperatures (28°C and 38°C) for up to 90 days. Furthermore, the study also explored the role of potentially ideal carriers as inoculants in the growth of Glycine max L. (soybean) under different moisture levels i.e., 55% water holding capacity (WHC) (D0), 30% WHC (D1) and, 15% WHC (D2) using a mixture of 50% garden soil and 50% sand. The results were compared to a control group (without inoculants) and a peat inoculant. Among all the materials derived from pine wood and oak, pine wood biochar pyrolyzed at 400℃ (P-BC400) exhibited the highest CFU count, with values of 10.34 and 9.74 Log 10 CFU g^− 1 after 90 days of storage at 28℃ and 38℃, respectively. This was notably higher compared to other biochars and peat carriers. Significant (p < 0.05) increases in plant properties: shoot and root dry biomass (174% and 367%), shoot and root length (89% and 85%), number of leaves (71%), membrane stability index (27%), relative water content (26%), and total chlorophyll (140%) were observed in plants treated with P-BC400 carrier inoculant compared to the control at D2; however, lower enrichment of δ¹³C (37%) and δ¹⁵N (108%) with highest number of root nodules (8.3 ± 1.26) and nitrogenase activity (0.869 ± 0.04) were observed under D2, as evident through PCA analysis, showing more nitrogen (N) fixation and photosynthetic activity. Overall, this experiment concluded that biochar pyrolyzed at lower temperatures, especially P-BC400, was the most suitable candidate for rhizobial inoculum and promoted soybean growth.

The ¹⁵N gas flux (¹⁵NGF) method allows for direct in situ quantification of dinitrogen (N₂) emissions from soils, but a successful cross-comparison with another method is missing. The objectives of this study were to quantify N₂ emissions of a wheat rotation using the ¹⁵NGF method, to compare these N₂ emissions with those obtained from a lysimeter-based ¹⁵N fertilizer mass balance approach, and to contextualize N₂ emissions with ¹⁵N enrichment of N₂ in soil air. For four sampling periods, fertilizer-derived N₂ losses (¹⁵NGF method) were similar to unaccounted fertilizer N fates as obtained from the ¹⁵N mass balance approach. Total N₂ emissions (¹⁵NGF method) amounted to 21 ± 3 kg N ha^− 1, with 13 ± 2 kg N ha^− 1 (7.5% of applied fertilizer N) originating from fertilizer. In comparison, the ¹⁵N mass balance approach overall indicated fertilizer-derived N₂ emissions of 11%, equivalent to 18 ± 13 kg N ha^− 1. Nitrous oxide (N₂O) emissions were small (0.15 ± 0.01 kg N ha^− 1 or 0.1% of fertilizer N), resulting in a large mean N₂:(N₂O + N₂) ratio of 0.94 ± 0.06. Due to the applied drip fertigation, ammonia emissions accounted for < 1% of fertilizer-N, while N leaching was negligible. The temporal variability of N₂ emissions was well explained by the δ¹⁵N₂ in soil air down to 50 cm depth. We conclude the ¹⁵NGF method provides realistic estimates of field N₂ emissions and should be more widely used to better understand soil N₂ losses. Moreover, combining soil air δ¹⁵N₂ measurements with diffusion modeling might be an alternative approach for constraining soil N₂ emissions.

Dioecious species have secondary trait dimorphism in resource acquisition, allocation, and a skewed sex ratio. Yet, it is unclear how their sex-specific nutrient acquisition strategy affects the contributions of inorganic and organic phosphorus (P) soil pools to plant-available P. Here, the contribution of inorganic and organic P sources to available P in soil and sex-specific P acquisition during the whole growing season (from June to October) was assessed in a 20-year-old Populus euphratica plantation via analysing the transformation of soil P pools. Poplar females obtain available inorganic P by increasing specific root length (by 71% compared with males) and releasing organic acids to mobilise P from precipitated P (HCl-P), thus obtaining higher P than males during the mid-growing season (June). The increased mobilisation of moderately precipitated P in the rhizosphere was more significant in females during the whole growing season. During the late-growing season, males showed increased alkaline phosphatase activities (by 25% compared with females) and maintained a higher abundance of arbuscular mycorrhiza fungi to obtain P via higher consumption of organic and residual P (decreased by 68% and 24% from June to October). These changes in P acquisition strategies reflect the temporal niche differentiation: females acquire inorganic P mainly during the beginning and middle of the season, whereas males take up organic P and HCl-P, preferably in the second half of the season. The strategic adjustment of sex-specific P acquisition modulated the transformation of organic and inorganic P sources in soil towards plant-available P, increasing resource niche partitioning between two poplar sexes to maintain P supply.