Publications

Can the reductive dissolution of ferric iron in paddy soils compensate phosphorus limitation of rice plants and microorganisms?

Biogeochemical cycles of phosphorus (P) and iron (Fe) are tightly interlinked, especially in highly weathered acidic subtropical and tropical soils rich in iron (oxyhydr)oxides (Fe(III)). The quantitative contribution of the reductive dissolution of Fe(III)-bound inorganic P (Pi) (Fe–P) in low-redox paddy soils may cover the demands of rice plants (Oryza sativa L.) and microorganisms. We hypothesized that microbially-driven Fe(III) reduction and dissolution can cover the P demand of microorganisms but not of the young rice plants when the plants’ P demand is high but their root systems are not sufficiently developed. We grew pre-germinated rice plants for 33 days in flooded rhizoboxes filled with a paddy soil of low P availability. 32P-labeled ferrihydrite (30.8 mg kg−1) was supplied either (1) in polyamide mesh bags (30 μm mesh size) to prevent roots from directly mobilizing Fe–P (pellets-in-mesh bag treatment), or (2) in the same pellet form but without a mesh bag to enable roots accessing the Fe–P (pellets-no-mesh bag treatment). Without mesh bags, Pi was more available leading to increases in microbial biomass carbon (MBC) by 18–55% and nitrogen (MBN) by 4–108% in rooted soil as compared to Pi pellets not directly available to roots. The maximum enzyme activities (Vmax) of phosphomonoesterase and β-glucosidase followed this pattern. During rice root growth, day 10 to day 33, MBC and microbial biomass phosphorus (MBP) contents in both rooted and bottom bulk (15–18 cm) soil gradually decreased by 28–56% and 47–49%, respectively. In contrast to our hypothesis, the contribution of Fe–P to MBP remarkably decreased from 4.5% to almost zero from 10 to 33 days after rice transplantation, while Fe–P compensated up to 16% of the plant P uptake at 33 days after rice transplantation, thus outcompeting microorganisms. Although both plants and microorganisms obtained Pi released by Fe(III) reductive dissolution, this mechanism was not sufficient for the demand of either organism groups.

Nitrogen pools and cycles in Tibetan Kobresia pastures depending on grazing

Atomization of yttrium, lanthanum, and neodymium in acetylene-nitrous oxide flame

The degree of atomization of the element is the principal factor defining the sensitivity of the atomic-absorption determination. An attempt is made in this paper to establish its values for yttrium, lanthanum, and neodymium by the method of linear absorption, and also to estimate the effect of the degree of dissociation of the compounds, the degree of ionization, and the relative population of the ground energy level of the atoms on the efficiency of atomization of these elements.

Microbial communities overwhelm environmental controls in explaining nitrous oxide emission in acidic soils

Intensively fertilized acidic soils are global hotspots of nitrous oxide (N2O) emissions, contributing to net agronomic greenhouse gas outcomes. Identifying the key drivers of soil N2O emissions is hampered by the synergistic or antagonistic effects of multiple factors. Within a framework based on the predominant role of microbial communities producing N2O, the N2O emissions are affected either by proximal regulators: temporary soil property fluctuations affect N2O production transcriptionally, or by distal regulators: persistent genetic rearrangements in local microbial communities. The proximal regulators, individually or together, may spontaneously impact distal regulators. Here, we use acidic soils from tea (Camellia sinensis L.) plantations on a broader geographic scale as a model system. Based on amplicon sequencing and properties of 195 acidic (average pH = 5.0) soils, we determined the importance of proximal and distal regulation to N2O emissions. Microbial phylogenetic diversity as a distal regulator overwhelms mineral N content as a proximal regulator in explaining high N2O emissions. Low-abundance, diverse prokaryotic communities (e.g., Acidothermu) and specialized denitrifying fungal communities (e.g., Fusarium) were associated with high N2O emissions. Revisiting the impact of proximal regulators on distal regulators revealed that soil pH is the sole proximal regulator influencing the prokaryotic rare taxa that correlated with high N2O emissions. When considering proximal regulators together (here soil properties compiled as soil fertility index), the microbial diversity were independent of soil fertility. The microbial assembly was dominated by stochastic processes. Consequently, proximal regulators have a limited impact on distal regulators of N2O emissions from acidic soils. In conclusion, the framework underscored the importance of in situ microbial communities as distal regulators in explaining high N2O emissions from acidic soils.

Decoding soil health constraints in regional agroecosystems: Machine learning reveals microbial enzymatic thresholds and drivers

Effects of Elevated CO2 in the Atmosphere on Soil C and N Turnover

Rising atmospheric carbon dioxide (CO2) concentration affects various soil processes especially related to carbon (C) and nutrient turnover. The methods to study the effects of elevated CO2 (eCO2) were shortly presented. All effects of eCO2 on soil are indirect: by plants through increased net primary production and belowground C inputs due to higher photosynthesis under eCO2. We summarized the impacts of eCO2 on (1) cycling of C and nitrogen (N), (2) microbial growth and enzyme activities, (3) turnover of soil organic matter and induced priming effects including N mobilization/immobilization processes, and (4) associated nutrient mobilization from organic sources. Higher C input from plants under eCO2 leads to faster C turnover due to high microbial activities including respiration, enzymatic activities, and priming effect of soil organic matter. Comparing the effects of eCO2 on changes in pools with that in fluxes we conclude that eCO2 in the atmosphere will have small (or no) effects on the C pools but will strongly increase the fluxes. The stable pools but intensified fluxes will accelerate biogeochemical cycles under elevated CO2.

Temperature sensitivity of soil organic matter decomposition was strongly affected by land use under low temperature

No abstract is provided for this article.

Benefits and limitations of biochar for climate-smart agriculture: a review and case study from China

Biochar has gained significant attention in agricultural and environmental research over the last two decades. This comprehensive review evaluates the effects of biochar on soil organic carbon (SOC), emission of non-CO 2 greenhouse gases, and crop yield, including related mechanisms and major influencing factors. The impacts of biochar on SOC, methane and nitrous oxide emissions, and crop yield are controlled by biochar and soil properties and management practices. High-temperature biochar produced from lignin-rich feedstocks may decrease methane and nitrous oxide emissions in acidic soils and strengthen long-term carbon sequestration due to its stable aromatic structure. In contrast, low-temperature biochar from manure may increase crop yield in low-fertility soils. Applying biochar to farmlands in China can increase SOC content by 1.9 Pg C and reduce methane and nitrous oxide emissions by 25 and 20 Mt CO 2 -eq year −1 , respectively, while increasing crop yields by 19%. Despite the increasing evidence of the positive effects of biochar, future research needs to explore the potential factors that could weaken or hinder its capacity to address climate change and secure crop production. We conclude that biochar is not a universal solution for global cropland; however, targeted applications in fields, landscapes, or regional scales, especially in low fertility and sandy soils, could realize the benefits of biochar as a climate-smart measure. Highlights The findings of research on biochar's effects on soil C sequestration, GHG mitigation, and crop production were summarized. The factors influencing the impact of biochar on soil functioning were reviewed. The effects of biochar on soil C sequestration and GHG mitigation in farmlands of China were quantified. Graphical Abstract

Plant‒Soil-Microbial Interactions Mediate Vegetation Succession in Retreating Glacial Forefields

Global warming is accelerating glacial retreat and vegetation succession in young developing soils. Soil microbial communities interact with plants, and they are key to vegetation succession, but the specific microbial groups that control plant‒soil feedback (PSF) are unclear. Vegetation and microbial successions were investigated in young soils after a glacial retreat in the Gongga Mountains. The direction and intensity of PSF were quantified by comparing the biomass of pioneer plants in early- (5-10 years), mid- (30-40 years) and late- (80-100 years) succession soils. The plant‒soil interactions shifted from negative feedback between plants and microorganisms in the early stages to positive feedback in the middle and late stages of soil development in the glacial retreat area. In early-stage soils, microorganisms nearly impaired the growth of pioneer plants present in all successional stages, showing negative biotic legacies. PSF and biotic legacies facilitated plant competitiveness. Poplar trees, which have strong competitive abilities, grow well in the soils of all succession stages because their rapid growth and rapid retrieval of soil nutrients prevents the invasion of other pioneer plants. The strongest drivers of soil legacy changed i) from saprophytic fungal specialists during the early stage, ii) to generalists and specialists of bacteria and arbuscular mycorrhizal fungi (AMF) in the middle stage, iii) to ectomycorrhizal fungal specialists in the late stage. The turnover of AMF and fungal pathogens across successional stages contributed to PSF. The effects of biotic legacies and microbial turnover accelerated primary succession and intensified PSF in the young soils of the glacial retreat area.

Rhizosphere bacteriome structure and functions

Microbial composition and functions in the rhizosphere—an important microbial hotspot—are among the most fascinating yet elusive topics in microbial ecology. We used 557 pairs of published 16S rDNA amplicon sequences from the bulk soils and rhizosphere in different ecosystems around the world to generalize bacterial characteristics with respect to community diversity, composition, and functions. The rhizosphere selects microorganisms from bulk soil to function as a seed bank, reducing microbial diversity. The rhizosphere is enriched in Bacteroidetes, Proteobacteria, and other copiotrophs. Highly modular but unstable bacterial networks in the rhizosphere (common for r -strategists) reflect the interactions and adaptations of microorganisms to dynamic conditions. Dormancy strategies in the rhizosphere are dominated by toxin–antitoxin systems, while sporulation is common in bulk soils. Functional predictions showed that genes involved in organic compound conversion, nitrogen fixation, and denitrification were strongly enriched in the rhizosphere (11–182%), while genes involved in nitrification were strongly depleted.

Carbon and nitrogen availability in paddy soil affects rice photosynthate allocation, microbial community composition, and priming: combining continuous 13C labeling with PLFA analysis

Carbon (C) and nitrogen (N) availability in soil change microbial community composition and activity and so, might affect soil organic matter (SOM) decompo

The adaptability of plants to phosphorus deficiency shapes the bacterial community and the spatial patterns of enzyme activities in the rhizosphere

Carbon sequestration and turnover in soil under the energy crop <i>Miscanthus</i>: repeated ¹³C natural abundance approach and literature synthesis

The stability and turnover of soil organic matter ( SOM ) are a very important but poorly understood part of carbon (C) cycling. Conversion of C 3 grassland to the C 4 energy crop Miscanthus provides an ideal opportunity to quantify medium‐term SOM dynamics without disturbance (e.g., plowing), due to the natural shift in the δ 13 C signature of soil C. For the first time, we used a repeated 13 C natural abundance approach to measure C turnover in a loamy Gleyic Cambisol after 9 and 21 years of Miscanthus cultivation. This is the longest C 3 –C 4 vegetation change study on C turnover in soil under energy crops. SOM stocks under Miscanthus and reference grassland were similar down to 1 m depth. However, both increased between 9 and 21 years from 105 to 140 mg C ha −1 ( P &lt; 0.05), indicating nonsteady state of SOM . This calls for caution when estimating SOM turnover based on a single sampling. The mean residence time ( MRT ) of old C (&gt;9 years) increased with depth from 19 years (0–10 cm) to 30–152 years (10–50 cm), and remained stable below 50 cm. From 41 literature observations, the average SOM increase after conversion from cropland or grassland to Miscanthus was 6.4 and 0.4 mg C ha −1 , respectively. The MRT of total C in topsoil under Miscanthus remained stable at ~60 years, independent of plantation age, corroborating the idea that C dynamics are dominated by recycling processes rather than by C stabilization. In conclusion, growing Miscanthus on C‐poor arable soils caused immediate C sequestration because of higher C input and decreased SOM decomposition. However, after replacing grasslands with Miscanthus , SOM stocks remained stable and the MRT of old C 3 ‐C increased strongly with depth.

Comparative efficacy of ZnSO4 and Zn-EDTA application for fertilization of rice (<b><i>Oryza sativa</i></b>L.)

Widespread Zn deficiency for rice crop has been reported from different parts of the world, including India. To correct such deficiency, Zn is often applied to the soil as fertilizer. Its concentration in soil solution and its availability to crops is controlled by sorption – desorption reactions at the surfaces of soil colloidal materials. The objective of this study was to compare the availability and relative effectiveness of Zn from Zn-EDTA and ZnSO4 sources by applying different Zn levels to a calcareous soil in field experiments through soil application. The uses of Zn-EDTA also increase the yield of rice dry matter yield and grain yield. Regarding maintenance of Zn in soil, it has been observed that the amount of Zn content was recorded higher with the split application of Zn-EDTA as compared to ZnSO4 with the simultaneous 26.1% increase in the yield of rice. Keywords: RiceZn fertilizers (ZnSO4 and Zn-EDTA)extractable ZnZn uptakeyield

Labile carbon inputs offset nitrogen-induced soil aggregate destabilization via enhanced growth of saprophytic fungi in a meadow steppe

The formation and stability of soil aggregates affect plant growth, carbon sequestration, and many other physiological and biogeochemical processes. Aggregates may be destabilized by nitrogen (N) deposition due to decreased inputs of binding materials; however, the legacy effects of which are unknown. An increase in labile carbon (C) input could mitigate the negative impacts of N addition on soil aggregate stability through the improvement of soil physical, chemical and biological conditions. Using a field experiment with the addition of NH4NO3 at multiple levels in a meadow steppe, we terminated the addition of N at the sixth year and shifted to applying labile C in the form of sucrose at three levels (C-0, C-200, and C-2000 g C m−2 y−1) to soil for two years. Then we examined the aggregate size distribution and the associated soil properties. The high historical N addition rates decreased the proportion of macroaggregates (>2000 μm) and increased microaggregates (<250 μm), leading to a reduction in the mean weight diameter (MWD), an index of soil aggregation stability. Labile C input offset the legacy effects of N addition on soil aggregates hierarchy and reversed the N-induced changes in MWD. Labile C input did not affect soil pH and exchangeable Ca2+, but increased the microbial biomass carbon (MBC) and the relative abundance of soil saprotrophic fungi (SSF); whilst the C-200 increased the relative abundance of arbuscular mycorrhizal fungi (AMF) only at low N addition rates (<N20) in comparison with that of the C-0. Analysis with the structural equation model (SEM) revealed the positive effects of labile C input on soil aggregate stability mainly by increasing the relative abundance of SSF across all N addition rates. The results of this study clearly demonstrate the effective role of short-term (2 years) labile C input in offsetting the N-caused soil aggregate instability in the meadow steppe by promoting soil microbial activity.

Invasive plant competitivity is mediated by nitrogen use strategies and rhizosphere microbiome

Three‐source partitioning of CO₂ efflux from maize field soil by ¹³C natural abundance

Abstract A natural‐ 13 C‐labeling approach—formerly observed under controlled conditions—was tested in the field to partition total soil CO 2 efflux into root respiration, rhizomicrobial respiration, and soil organic matter (SOM) decomposition. Different results were expected in the field due to different climate, site, and microbial properties in contrast to the laboratory. Within this isotopic method, maize was planted on soil with C 3 ‐vegetation history and the total CO 2 efflux from soil was subdivided by isotopic mass balance. The C 4 ‐derived C in soil microbial biomass was also determined. Additionally, in a root‐exclusion approach, root‐ and SOM‐derived CO 2 were determined by the total CO 2 effluxes from maize ( Zea mays L.) and bare‐fallow plots. In both approaches, maize‐derived CO 2 contributed 22% to 35% to the total CO 2 efflux during the growth period, which was comparable to other field studies. In our laboratory study, this CO 2 fraction was tripled due to different climate, soil, and sampling conditions. In the natural‐ 13 C‐labeling approach, rhizomicrobial respiration was low compared to other studies, which was related to a low amount of C 4 ‐derived microbial biomass. At the end of the growth period, however, 64% root respiration and 36% rhizomicrobial respiration in relation to total root‐derived CO 2 were calculated when considering high isotopic fractionations between SOM, microbial biomass, and CO 2 . This relationship was closer to the 50% : 50% partitioning described in the literature than without fractionation (23% root respiration, 77% rhizomicrobial respiration). Fractionation processes of 13 C must be taken into account when calculating CO 2 partitioning in soil. Both methods—natural 13 C labeling and root exclusion—showed the same partitioning results when 13 C isotopic fractionation during microbial respiration was considered and may therefore be used to separate plant‐ and SOM‐derived CO 2 sources.

CaCO 3 recrystallization in saline and alkaline soils

Are desert ecosystems a stable sink for atmospheric CO2? Although the uptake of atmospheric CO2 by soil during the nighttime is detected in deserts and some semi-deserts, the underlying mechanisms remain elusive. In order to determine the factors affecting the CO2 fluxes into soil and to reveal the relationship between CO2 fluxes and carbonate formation and recrystallization in saline and alkaline soils, four soils with contrasting salinity from two sites, Aksu and Yingbazar, along the Tarim River were analysed. Soils were incubated in 14CO2 labelled atmosphere for 90days at three CO2 concentrations: 0.04%, 0.4% and 4%. The 14C activity was measured in soil water and air, as well as in carbonates after 2, 14 and 90days. The 14C incorporation in CaCO3 increased with corresponding 14C decrease remaining in the CO2. The highest 14C incorporation into CaCO3 (54%) was observed in the Yingbazar saline soil. The carbonate recrystallization rates increased logarithmically (r2 >0.97) with the CO2 concentration. The average carbonate recrystallization rate from three sampling times was highest in the Yingbazar saline soil under 4% CO2 (8.45×10−6 day−1) and lowest in the Aksu alkaline soil under 0.04% CO2 (0.03×10−6 day−1). The average carbonate recrystallization rate increased with electric conductivity (corresponding to soil salinity) but decreased with pH (R 2 =0.99 for 4% CO2). The alkaline soils incorporated less 14C into CaCO3 than the saline soils. At the highest CO2 concentration of 4%, the full recrystallization period of the remaining primary carbonates was 10- to 100-fold shorter than at the lower CO2 concentrations. Therefore, besides soil chemical parameters (e.g. pH, CaCO3 content), CO2 concentration (respiration of microorganisms and roots) is an important factor for CaCO3 recrystallization and formation of pedogenic carbonates in desert soils. It is the most important factor for CaCO3 recrystallization and so, for the formation of pedogenic carbonates.

Pasture degradation modifies soil organic matter properties and biochemical functioning in Tibetan grasslands

No abstract is provided for this article.