Biology and Fertility of Soils最新文献

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.

Rhizobium is well-documented for its symbiotic relationship with legume plants, where it plays a crucial role in biological nitrogen-(N)-fixation within their root nodules. However, the isolation, identification, and association of Rhizobium as a free-living diazotroph with potato plants remain relatively less explored. The present study reports the isolation and characterization of free-living Rhizobium strain from the rhizosphere of potato plants and its potential for promoting growth and N-fixation. Diazotrophic strain (TN04) was isolated from rhizosphere of potato plants on nitrogen-free media and identified on the basis of 16S rRNA gene sequence (Accession number: LN833444). TN04 strain also contained nifH gene and showed N-fixation potential (151.70 nmolmg/protein/h) through ARA activity, indicating its ability to fix atmospheric nitrogen. TN04 exhibited potential for phosphate solubilization (272.5 µg/mL) and produced indole acetic acid at concentration of 3.50 µg/mL. To assess the N-fixing ability of TN04 diazotroph, a ¹⁵N dilution experiment was conducted in pots using sterilized sand and sterilized soil under various fertilizer doses. The results of pot experiments demonstrated significant improvement in N content and growth parameters of inoculated potato plants compared to un-inoculated controls, suggesting that diazotrophic strain effectively fixed atmospheric N through isotopic dilution. Moreover, Rhizobium sp. TN04 remarkably improved plant growth and agronomic parameters under field conditions. Significant improvements were observed in N uptake, N utilization, and N use efficiency in field trails. In addition, microscopic analysis using transmission electron and confocal laser scanning microscopy provided insights into the colonization patterns of TN04 strain at the junctions between the secondary and primary roots, forming strong association with potato roots. Our study presents novel insights into the presence and interaction of Rhizobium with non-host plants, shedding light on its N-fixing capabilities in non-leguminous crops. These findings pave the way for developing strategies to explore microbiome of non-leguminous crops and exploit the N-fixation of Rhizobium in non-host crops.

Diversification of agricultural practices, including changes in crop rotation, intercropping or cover cropping, influence the soil microbiome. Here the impact of tillage and crop diversification on the soil microbiome is reported, being one of the few boreal studies. The field experiment consisted of four treatments with four replications all having a short cereal rotation practice namely an oat (Avena sativa) – spring barley (Hordeum vulgare) – wheat (Triticum aestivum) rotation for the past 10 years until spring 2018. During that period two of the treatments were conventionally tilled with moldboard ploughing whereas the other two were no-tillage treatments. From the growing season 2018 until fall 2020 the main crop in all treatments was spring barley. The first conventional tillage treatment was diversified with English ryegrass (Lolium perenne) as an undersown cover crop for the next three growing seasons. The first no-tillage treatment continued with spring barley only. The second conventional tillage and no-tillage treatment had winter rapeseed in rotation in 2019. Bulk soils were sampled in May 2018 before diversification and then in October 2018, 2019, and 2020. The results showed a clear effect of tillage on the beta-diversity of the soil microbiome and an increase in fungal richness. Barley monoculture interrupted with winter rapeseed resulted in a minor change of the fungal and bacterial community composition. Other fungal and bacterial alpha diversity measures did not react to tillage or diversification nor did the gene copy abundances involved in the N cycle. In conclusion tillage had a profound effect on the soil microbiome hindering impact of the diversification.

The combination of conservation tillage (non-inversion and no-till) with organic farming is rare due to weed problems. However, both practices have the potential to improve soil quality and increase soil organic C (SOC). This study investigated the changes in SOC, microbial biomass, and microbial composition during the transition from conventional to organic farming (from 2014 to 2020) in a long-term tillage trial established in 1999. Non-inversion minimum tillage to a depth of 10 cm (MT) resulted in SOC stratification, whilst conventional soil tillage with 25-cm-deep mouldboard ploughing (CT) maintained an even SOC distribution in the plough layer. After 12 years of contrasting tillage in 2011, the uppermost soil layer under MT had a 10% higher SOC content (1.6% w/w) than CT (1.45% w/w). This difference became even more pronounced after introducing organic farming in 2014. By the fall of 2020, the SOC content under MT increased to 1.94%, whilst it decreased slightly to 1.36% under CT, resulting in a 43% difference between the two systems. Conversion to organic farming increased microbial biomass under both tillage systems, whilst SOC remained unchanged in CT. Abundances of total bacterial and Crenarchaeal 16S rRNA and fungal ITS genes indicated shifts in the microbial community in response to tillage and depth. Fungal communities under MT were more responsive to organic farming than bacterial communities. The improved soil quality observed under MT supports its adoption in both organic and conventional systems, but potentially large yield losses due to increased weed cover discourage farmers from combining MT and organic farming.