Changes In Soil Function Research Articles

Impact of grassland degradation on soil multifunctionality: Linking to protozoan network complexity and stability

Soil protozoa, as predators of microbial communities, profoundly influence multifunctionality of soils. Understanding the relationship between soil protozoa and soil multifunctionality (SMF) is crucial to unraveling the driving mechanisms of SMF. However, this relationship remains unclear, particularly in grassland ecosystems that are experiencing degradation. By employing 18S rRNA gene sequencing and network analysis, we examined the diversity, composition, and network patterns of the soil protozoan community along a well-characterized gradient of grassland degradation at four alpine sites, including two alpine meadows (Cuona and Jiuzhi) and two alpine steppes (Shuanghu and Gonghe) on the Qinghai-Tibetan Plateau. Our findings showed that grassland degradation decreased SMF for 1–2 times in all four sites but increased soil protozoan diversity (Shannon index) for 13.82–298.01 % in alpine steppes. Grassland degradation-induced changes in soil protozoan composition, particularly to the Intramacronucleata with a large body size, were consistently observed across all four sites. The enhancing network complexity (average degree), stability (robustness), and cooperative relationships (positive correlation) are the responses of protozoa to grassland degradation. Further analyses revealed that the increased network complexity and stability led to a decrease in SMF by affecting microbial biomass. Overall, protozoa increase their diversity and strengthen their cooperative relationships to resist grassland degradation, and emphasize the critical role of protozoan network complexity and stability in regulating SMF. Therefore, not only protozoan diversity and composition but also their interactions should be considered in evaluating SMF responses to grassland degradation, which has important implications for predicting changes in soil function under future scenarios of anthropogenic change.

Increased connections among soil microbes and microfauna enhances soil multifunctionality along a long‐term restoration chronosequence

Abstract The functional role of soil microbes in the restoration of degraded lands is greatly influenced by interactions within and between microbial communities, as well as by soil organisms at higher trophic levels (microfauna). However, little is known about how changes in connection patterns among soil microbes and their co‐existing microfauna contribute to associated changes in soil function over the ecosystem restoration process. In this study, the effects of afforestation and natural regeneration approaches on connection patterns among soil microbes and their co‐existing microfauna were assessed in ex‐arable lands on the Loess Plateau in China along a 50‐year restoration chronosequence. The relationships between soil network connections, microbial functional associations, and multiple soil functions (e.g. multifunctionality) were assessed quantitatively. Although both afforestation and natural regeneration approaches enhance connections among soil microbes and their co‐existing microfauna compared to recently abandoned sites, connection trends were opposed between these two approaches across the restoration chronosequence. Afforestation resulted in a higher number of soil microbial and microfauna species with a unimodal connection pattern, while natural regeneration resulted in a continuous increase in soil network connections over the progress of succession. These increases in soil network connections, particularly those of soil microfauna‐microbe and microbial inter‐kingdom connections, corresponded to enhanced microbial functional associations. This result is corroborated by significant correlations between microbial functional genes encoding different central functional pathways, which, in turn, were positively correlated with soil multifunctionality. Synthesis and applications. Changes in the connections among soil microbes and their co‐existing microfauna were positively associated with changes in soil multifunctionality, mediated by microbial functional associations. While in the early restoration stages, soil networks following afforestation contained more connections than those following natural regeneration, in later restoration stages, the number of connections of the afforestation network declined and was eventually surpassed by those following natural regeneration. These findings raise concerns about the ecological sustainability of afforestation measures in historic grasslands on the Loess Plateau, suggesting that natural regeneration is the preferred approach to achieve long‐term ecological restoration success.

Conservation agriculture practices impact on biological and microbial diversity in earthworm cast under maize-wheat system

Soil degradation is a major global concern due to its negative impact on soil quality and the sustainability of agricultural resources. The conservation agriculture (CA) approach, which includes three key principles such as zero tillage, retention of crop residue and crop rotation has gained widespread adoption to help mitigate the climate change effects on agricultural soils and meet the growing demand for increased production. Earthworm communities, along with microbial activity and diversity, are highly sensitive to tillage practices. Additionally, microbial activity and diversity quickly respond to different cropping systems, making them effective indicators for detecting short-term changes in soil functioning. We therefore, assess the effects of CA innovative approached after 6-years on biological and microbial diversity within earthworm cast in maize-wheat system (MWS). The treatments consist of PBM-RN0/ZTW-RN0 (permanent beds No-N control-both residues removed and wheat with zero tillage); PBM+RN0/ZTW+RN0 (permanent beds No-N control-both residues retained)-50% of maize stover and 25% of wheat residue retained; PBM-RN120/ZTW- RN120 (permanent beds with 120 kg N ha-1 both residues removed wheat with zero tillage); PBM+RN120/ZTW+RN120 (permanent beds with 120 kg N ha-1 both residues retained and wheat with zero tillage) and FBM-RN120/CTW-RN120 (fresh beds in maize/CT in wheat with 120 kg N ha-1 both residues removed). The result of present study showed that activities of carbon (C) cycle-related enzymes in the cast soils viz., dehydrogenase (DHA), β-glucosidase (β-glu), cellulase, and xylanase were significantly higher under PBM+RN120/ ZTW+RN120 than under PBM-RN0/ZTW-RN0. Specifically, the activities of these enzymes were 21.5, 26.8, and 76.5% higher under the PBM+RN120/ZTW+RN120 treatment, respectively. Moreover, the Alk-P activity was found to be 1.3 times higher in the PBM+RN120/ZTW+RN120 treatment than in the PBM-RN0/ZTW-RN0 treatment. The bacterial, fungal, and actinomycete counts in the cast soil ranged from 6.87 to 7.47 CFU (colony forming units) x 106 g-1 soil, 3.87–3.30 CFU x 104 g-1 soil, and 5.09–5.67 CFU x 104 g-1 soil, respectively. Total organic carbon (TOC) showed significant increases of 34.6% under PBM+RN120/ZTW+RN120 as compared to PBM-RN0/ZTW-RN0. The less labile C (Frac. 3), total carbohydrate carbon (TCHO), phenol oxidase (PHE) and peroxidase (PER) were observed as the sensitive indicators under different tillage, rate of nitrogen and residue management practices. This study suggests that permanent beds with crop residue retention with balance fertilization practices can be recommended and popularized to the overall improvement of soil biological pools within earthworm casts in MWS.

A comparative study of soil fertility and biota population under organic, semi-organic, and conventional farming system of rice fields in Giriwoyo District, Wonogiri Regency, Indonesia

Continuous use of chemical fertilizers and farming practices in rice fields would reduce nutrient availability and biota population in the soil. Because soil biological linkages are sensitive to changes in soil function, changes in fauna and microbial populations can affect soil fertility. This study aimed to identify the condition of soil fertility and soil biota under various farming systems, namely organic, semi-organic, and conventional, and find the indicators that determine soil fertility index (SFI) in the research area. This research is a survey with the sampling method was purposive on the Land Mapping Unit (LMU) overlaid with thematic maps (land use, soil type, slope, and rainfall). The method analysis of SFI using Principal Component Analysis (PCA) and scoring methods were used for the effect of farming systems using One-way, continued by DMRT, and determinant factor using Pearson’s. Correlation. The results illustrated that soil fertility was a moderate category. The highest SFI was in organic rice fields (0.69), then in semi-organic (0.62), and the lowest fertility was in conventional (0.59). Organic farming also showed the best soil biota conditions (0.27 individuals/liter of earthworms and 0.755 µ/g of microbial C biomass) compared to semi-organic (0.15 individuals/liter, 0.508 µ/g microbial C biomass) and conventional farming (0.11 individuals/liter, microbial biomass C 0.325 µ/g). Soil fertility and soil biota are positively correlated, meaning that the higher the soil fertility, the higher the density of soil biota. The soil indicators most determining fertility are total N, P-available, K-available, CEC, and organic C.

Biochar Enhances the Resistance of Legumes and Soil Microbes to Extreme Short-Term Drought.

Short-term drought events occur more frequently and more intensively under global climate change. Biochar amendment has been documented to ameliorate the negative effects of water deficits on plant performance. Moreover, biochar can alter the soil microbial community, soil properties and soil metabolome, resulting in changes in soil functioning. We aim to reveal the extent of biochar addition on soil nutrients and the soil microbial community structure and how this improves the tolerance of legume crops (peanuts) to short-term extreme drought. We measured plant performances under different contents of biochar, set as a gradient of 2%, 3% and 4%, after an extreme experimental drought. In addition, we investigated how soil bacteria and fungi respond to biochar additions and how the soil metabolome changes in response to biochar amendments, with combined growth experiments, high-throughput sequencing and soil omics. The results indicated that biochar increased nitrites and available phosphorus. Biochar was found to influence the soil bacterial community structure more intensively than the soil fungal community. Additionally, the fungal community showed a higher randomness under biochar addition when experiencing short-term extreme drought compared to the bacterial community. Soil bacteria may be more strongly related to soil nutrient cycling in peanut agricultural systems. Although the soil metabolome has been documented to be influenced by biochar addition independent of soil moisture, we found more differential metabolites with a higher biochar content. We suggest that biochar enhances the resistance of plants and soil microbes to short-term extreme drought by indirectly modifying soil functioning probably due to direct changes in soil moisture and soil pH.

Relating Threshold Changes in Soil Function to Structural Changes in Woody Vegetation Along Herbivore Utilization Gradients with Different Management Histories in an Arid Thicket Mosaic, South Africa

The hypothesis that transformation of rangelands by domestic herbivores follows state-and-transition models predicts that vegetation communities will cross ecological thresholds when shifting from one state to another. We test this hypothesis by identifying threshold responses of soil function in Gamka Thicket, a variation of Arid Thicket in South Africa. We relate indices of soil water infiltration, nutrient cycling, and soil retention (reflecting ecosystem function) to distance from artificial watering points in four piosphere treatments differing in rangeland management history. Furthermore, we compare the pattern, extent, and variation in transformation at the end regions of our piosphere treatments to each other and to a transformed and untransformed reference site. The changes to all the indices of ecosystem function support the hypothesis that functional thresholds have been crossed. We propose a conceptual model that suggests that Arid Thicket transformation due to herbivory transcends three vegetation states. We contend that during the process of transformation the crossing of structural thresholds lead to the crossing of functional thresholds that ultimately drive the formation of new vegetation states.

Effects of Fractal Dimension and Soil Erodibility on Soil Quality in an Erodible Region: A Case Study from Karst Mountainous Areas

Soil aggregate stability and soil erodibility (k) are crucial indicators of soil quality that exhibit high sensitivity to changes in soil function. Therefore, it is of great significance to explore the quantitative relationship between these indicators and soil quality for effective ecosystem monitoring and assessment. In this study, soil samples were collected from eight altitude gradients in a karst mountainous area; we analyzed 11 soil physical, chemical, and biological properties, and assessed soil quality using the minimum data set (MDS) method. The results revealed that soil aggregate stability, bulk density (BD), pH, and fungal community diversity exhibited a unimodal altitudinal pattern, whereas the soil organic carbon (SOC), total nitrogen (TN), and C:N ratio showed an increasing trend. Among the factors considered, SOC, BD, soil pH, mechanical composition, and fungal community diversity were found to explain the most variation in soil aggregate stability and soil erodibility (k). Principal component analysis (PCA) identified soil fungal community diversity, C:N ratio, coarse sand, and macro-aggregate (MA) content as highly weighted indicators for MDS. The integrated soil quality index (SQI) values, ranging from 0.30 to 0.62 across the eight altitude gradients, also exhibited a unimodal altitudinal pattern. The analysis indicated a significant linear relationship between the fractal dimension (D) and soil erodibility of the EPIC model (Kepic) with SQI, suggesting that D and Kepic can serve as alternative indicators for soil quality. These findings further enhance our understanding of the response of soil properties to altitude changes, and provide a novel method for assessing and monitoring soil quality in karst mountainous areas.

Fungal diversities and community assembly processes show different biogeographical patterns in forest and grassland soil ecosystems.

Soil fungal community has been largely explored by comparing their natural diversity. However, there is a relatively small body of literature concerned with fungal community assembly processes and their co-occurrence network correlations carried out across large spatial-temporal scales with complex environmental gradients in natural ecosystems and different habitats in China. Thus, soil fungal community assembly processes were assessed to predict changes in soil function in 98 different forest and grassland sites from the Sichuan, Hubei, and Hebei Provinces of China using high-throughput sequencing of nuclear ribosomal internal transcribed spacer 2 (ITS-2). The 10 most abundant fungal phyla results showed that Ascomycota was the most abundant phylum in forests from Sichuan province (64.42%) and grassland habitats from Hebei province (53.46%). Moreover, core fungal taxa (487 OTUs) represented 0.35% of total fungal OTUs. We observed higher fungal Shannon diversity and richness (the Chao1 index) from diverse mixed forests of the Sichuan and Hubei Provinces than the mono-cultured forest and grassland habitats in Hebei Province. Although fungal alpha and beta diversities exhibited different biogeographical patterns, the fungal assembly pattern was mostly driven by dispersal limitation than selection in different habitats. Fungal co-occurrence analyses showed that the network was more intense at Saihanba National Forest Park (SNFP, Hebei). In contrast, the co-occurrence network was more complex at boundaries between forests and grasslands at SNFP. Additionally, the highest number of positive (co-presence or co-operative) correlations of fungal genera were inferred from grassland habitat, which led fungal communities to form commensalism relationships compared to forest areas with having higher negative correlations (mutual exclusion or competitive). The generalized additive model (GAM) analysis showed that the association of fungal Shannon diversity and richness indices with geographical coordinates did not follow a general pattern; instead, the fluctuation of these indices was restricted to local geographical coordinates at each sampling location. These results indicated the existence of a site effect on the diversity of fungal communities across our sampling sites. Our observation suggested that higher fungal diversity and richness of fungal taxa in a particular habitat are not necessarily associated with more complex networks.

Unearthing soil-plant-microbiota crosstalk: Looking back to move forward.

The soil is vital for life on Earth and its biodiversity. However, being a non-renewable and threatened resource, preserving soil quality is crucial to maintain a range of ecosystem services critical to ecological balances, food production and human health. In an agricultural context, soil quality is often perceived as the ability to support field production, and thus soil quality and fertility are strictly interconnected. The concept of, as well as the ways to assess, soil fertility has undergone big changes over the years. Crop performance has been historically used as an indicator for soil quality and fertility. Then, analysis of a range of physico-chemical parameters has been used to routinely assess soil quality. Today it is becoming evident that soil quality must be evaluated by combining parameters that refer both to the physico-chemical and the biological levels. However, it can be challenging to find adequate indexes for evaluating soil quality that are both predictive and easy to measure in situ. An ideal soil quality assessment method should be flexible, sensitive enough to detect changes in soil functions, management and climate, and should allow comparability among sites. In this review, we discuss the current status of soil quality indicators and existing databases of harmonized, open-access topsoil data. We also explore the connections between soil biotic and abiotic features and crop performance in an agricultural context. Finally, based on current knowledge and technical advancements, we argue that the use of plant health traits represents a powerful way to assess soil physico-chemical and biological properties. These plant health parameters can serve as proxies for different soil features that characterize soil quality both at the physico-chemical and at the microbiological level, including soil quality, fertility and composition of soil microbial communities.

Microplastics in agroecosystems: A review of effects on soil biota and key soil functions

AbstractContamination of soils in agroecosystems with microplastics (MPs) is of increasing concern. The contamination of the environment/farmland soils with MPs (1 µm to 5 mm sized particles) and nanoplastics (NPs; <1 µm sized particles) is causing numerous effects on ecological soil functions and human health. MPs enter the soil via several sources, either from intentional plastic use (e.g., plastic mulch, plastic greenhouses, plastic‐coated products) or indirectly from the input of sewage sludge, compost, or irrigation water that is contaminated with plastic. Once in the soil, plastic debris can have various impacts such as changes in soil functions and physicochemical properties and it affects soil organisms due to its toxic behavior. This review paper describes the different effects of plastic waste to understand the consequences for agricultural productivity. Furthermore, we identify knowledge gaps and highlight the required approaches, indicating future research directions on sources, transport, and fate of MPs in soils to improve our understanding of various unspecified abiotic and biotic impacts of MP pollution in agroecosystems.

Effects of long‐term sewage sludge application to a calcareous soil structure

AbstractSoil degradation is a growing challenge to global agriculture and the United Nations' Sustainable Development Goals (SDGs). This has prompted calls for less use of mineral fertilizer and greater reliance on organic fertilizers. However, we need to understand better the long‐term effects of organic fertilizer usage on soil structure to guide soil management practice, as many soil functions are sensitive to pore morphology and connectivity. In this study, we characterized topsoil (0–30 cm) pore architecture in relation to soil physical properties in a long‐term experiment (LTE) site where calcareous soil had received 25 years of sewage sludge application. Two dosage rates (SSa, 20 and SSe, 80 Mg ha−1) were compared to mineral fertilization treatment and a control (no fertilization) in a random factorial block design. Soil microstructure and the types of pores were characterized using micromorphological methods and image analysis, in soil thin sections. Long‐term sewage sludge SSa application improved soil microstructure (crumb and sub‐angular‐blocky type) and increased the presence of biopores, while mineral fertilized soil showed a platy to apedal microstructure, with more elongated pores and lower faunal activity. Mineral fertilized soil had the lowest total porosity values, with differences found in the aspect ratio of pores of equivalent diameter 100–200 μm. These findings suggest a relation between the different types of fertilization and soil pore shape and network. Further exploration of these changes in soil functioning is needed for a complete assessment of the consequences of SS application.

The Impact of Freeze‐Thaw History on Soil Carbon Response to Experimental Freeze‐Thaw Cycles

AbstractFreeze‐thaw is a disturbance process in cold regions where permafrost soils are becoming vulnerable to temperature fluctuations above 0°C. Freeze‐thaw alters soil physical and biogeochemical properties with implications for carbon persistence and emissions in Arctic landscapes. We examined whether different freeze‐thaw histories in two soil systems led to contrasting biogeochemical responses under a laboratory‐controlled freeze‐thaw incubation. We investigated controls on carbon composition through Fourier‐transform ion cyclotron resonance mass spectrometry (FT‐ICR‐MS) to identify nominal carbon oxidation states and relative abundances of aliphatic‐type carbon molecules in both surface and subsurface soils. Soil cores (∼60 cm‐depth) were sampled from two sites in Alaskan permafrost landscapes with different in situ freeze‐thaw characteristics: Healy (>40 freeze‐thaw cycles annually) and Toolik (<15 freeze‐thaw cycles annually). FT‐ICR‐MS was coupled with in situ temperature data and soil properties (i.e., soil texture, mineralogy) to assess (a) differences in soil organic matter composition associated with previous freeze‐thaw history and (b) sensitivity to experimental freeze‐thaw in the extracted cores. Control (freeze‐only) samples showed greater carbon oxidation in Healy soils compared with Toolik, even in lower mineral horizons where freeze‐thaw history was comparable across both sites. Healy showed the most loss of carbon compounds following experimental freeze‐thaw in the lower mineral depths, including a decrease in aliphatics. Toolik soils responded more slowly to freeze‐thaw as shown by intermediary carbon oxidation distributed across multiple carbon compound classes. Variations in the response of permafrost carbon chemistry to freeze‐thaw is an important factor for predicting changes in soil function as permafrost thaws in high northern latitudes.

Precipitation balances deterministic and stochastic processes of bacterial community assembly in grassland soils

Microbial biodiversity is crucial for maintaining ecosystem functions. As climate change progresses at both global and regional scales, there is a need to understand microbial community assembly processes and diversity to predict changes in soil function in different regions. However, our knowledge of the mechanisms that shape bacterial β diversity at multiple spatial scales with complex environmental gradients is very limited. To investigate the mechanisms driving bacterial β diversity at regional (across transects) and local (within transect) scales, soil samples were collected from 30 grassland ecosystems in three east-west transects in northern China. The regional species pools influenced β diversity by mediating rare taxa migration across the three transects. After correcting for regional differences in species, the importance of local community assembly processes in controlling bacterial diversity was independent of spatial scales. Homogeneous selection (HoS, 39%–60%) and dispersal limitation (DL, 31%–54%) proved to be the most important community assembly processes for soil bacteria. Two dominant bacterial taxa accounting for 65% of the total abundance were identified, mainly including Acidobacteria, Actinobacteria, and Proteobacteria, with 63% and 64% contributions for the HoS and DL, respectively. Mean annual precipitation (MAP) mediated the relative importance of deterministic and stochastic assembly in bacterial communities. Consistently across all spatial scales, the relative importance of DL increased with aridity, and the contribution of HoS decreased. Importantly, the relative abundance of the two dominant bacterial taxa controlled by the HoS and DL varied with MAP. Collectively, our results provide clear evidence that water availability mediates the community assembly process of soil bacteria. This conclusion is of utmost importance for predicting the dynamics of soil microbial diversity and nutrient cycling in natural ecosystems in drylands.

Conversion of grassland to cropland altered soil nitrogen-related microbial communities at large scales

Land-use changes may dramatically disturb underground microbial biodiversity, especially in the fragile ecological areas. However, the impact of conversion of grassland to cropland on soil nitrogen (N)-related microbial communities is not fully understood in the farming-pastoral ecotone of northern China. Therefore, 24 paired grassland and cropland soil samples were collected in this region to investigate the community structure and assembly processes of soil N-related microorganisms via amplicon sequencing of nifH, archaeal and bacterial amoA, and nxrB genes. The results showed higher ammonia-oxidizing bacteria (AOB) alpha diversity but a lower nitrite-oxidizing bacteria (NOB) diversity in cropland soil compared to grassland soil. Non-metric multidimensional scaling ordinations revealed that diazotroph, AOB and NOB communities differed considerably between grassland and cropland soil. Soil microbial co-occurrence networks showed that conversion of grassland to cropland significantly lowered the average degree, average clustering coefficient, total nodes and links, resulting in less complex microbial networks in cropland soil. Land-use change altered AOB community assembly processes, resulting from a stochasticity-dominated process in grassland soil to a determinism-dominated process in cropland soil. In contrast, deterministic processes were dominant in diazotroph community assembly, whereas stochastic processes were dominant in constructing ammonia-oxidizing archaea and NOB communities in both grassland and cropland soil. These results provide novel evidence that the conversion of grassland to cropland altered the diversity and assembly processes of soil microbial communities involved in soil N-cycling processes, which has important implications for the potential changes in soil functions under land-use changes.

Earthworm communities and microbial metabolic activity and diversity under conventional, feed and biogas cropping systems as affected by tillage practices

Understanding management factors driving soil biota is pivotal to improve the sustainability of cropping systems, especially given the emergence of new cropping systems induced by bioeconomy. Here, we investigated the combined effects of tillage practices (tillage versus no-tillage) and contrasted cropping systems, including conventional, feed and biogas cropping systems, on earthworm communities and microbial metabolic activity and diversity (using Biolog Ecoplate). After three years, our results revealed that tillage overrode the effect of cropping systems on soil biota while being also detrimental for both earthworm communities and microbial activity and diversity compared with no-tillage. By contrast, no-tillage had generally a beneficial effect on soil microbial activity and earthworm abundance. More importantly, under no-tillage, feed and biogas systems increased microbial activity and diversity which was likely due to the higher crop diversity and the use of digestate instead of manure and slurry compared with the conventional system. Taken together, our findings show that both earthworm communities and microbial activity and diversity are very sensitive to tillage. Moreover, microbial activity and diversity are also rapidly affected by the type of cropping system, suggesting that it would be a better indicator to detect short-term changes in soil functioning following change in land use. Our study also indicates that, provided that no-tillage is included, biogas cropping system with high crop diversity can promote soil biota compared with conventional farming practices, leading likely to the improvement of soil functioning and ecosystem service delivery.

Direct and indirect effects of global change on mycorrhizal associations of savanna plant communities

Mycorrhizal fungi are key components of whole‐plant adaptive strategies to cope with different abiotic and biotic constraints. Although they are particularly sensitive to different global change drivers, there are still many gaps on the mechanisms underpinning shifts in mycorrhizal associations under different climatic and management scenarios.We carried out a field manipulative experiment of rainfall exclusion and increased temperature aimed to evaluate the impact of forecasted warming and drying on mycorrhizal associations of savanna plant communities subjected to different grazing history. Additionally, we compiled detailed information on the abiotic and biotic environment with the final aim of disentangling the direct and indirect effects of climate change on this widespread mycorrhizal symbiosis.Our results suggest that climate change could induce relevant changes in mycorrhizal associations, primarily promoted by warming, which decreased the abundance of mycorrhizae but induced higher activity of nutrient exchange between the host–plant and the mycosymbiont. Temperature did not only affect this symbiosis in a direct way, but also exerted relevant indirect effects via changes in soil functioning and other root‐colonizing microorganisms such as dark septate endophytes. Grazing history influenced the allocation of fungal structures inside the host‐root, but its effect differed as a function of the climatic treatment.Results from this study suggest that mycorrhizal fungi might become less prevalent in plant communities inhabiting savanna ecosystems under future scenarios of increasing aridity. In agreement with this finding, higher temperatures also promoted the predominance of plants with root traits that favour efficient resource acquisition by themselves without the help of a mycorrhizal partner. Our results provide new insights into the interactive effects of the two main threats facing Mediterranean savanna ecosystems, as well as potentially useful information to be applied in ecologically‐based management strategies aimed at attenuating the potential impact of global change on mycorrhizal fungi.

Evaluation methods of heavy metal pollution in soils based on enzyme activities: A review

Soil enzyme activities have been suggested as suitable indicators for the evaluation of metal contamination because they are susceptible to microbial changes caused by heavy metal stress and are strictly related to soil nutrient cycles. However, there is a growing lack of recognition and summary of the historic advancements that use soil enzymology as the proposal of evaluation methods. Here, we review the most common methods of heavy metal pollution evaluation based on enzyme activities, which include single enzyme index, combined enzyme index, enzyme-based functional diversity index, microbiological stress index, and ecoenzymatic stoichiometry models. This review critically examines the advantages and disadvantages of these methods based on their execution complexity, performance, and ecological implications and gets a glimpse of avenues to come to improved future evaluation systems. Indices based on a single enzyme are variable and have no consistent response to soil heavy metals, and the following three composite indices are characterized by the loss of many critical microbial processes, which thus not conducive to reflect the effects of heavy metals on soil ecosystems. Considering the dexterity of ecoenzymatic stoichiometry methods in reflecting changes in soil functions under heavy metal stress, we propose that microbial metabolic limitations quantified by ecoenzymatic stoichiometry models could be promising indicators for enhancing the reality and acceptance of results and further improving the potential for actual utility in environmental decision-making.

Consequences of land-use change in Brazil’s new agricultural frontier: A soil physical health assessment

In the so-called MATOPIBA region in northeastern Brazil, large areas of the Brazilian savannah (Cerrado biome) were converted to agricultural areas (e.g., soybean and cotton production) in recent years. However, little is known about the long-term impacts of this land-use change on soil physical properties and related soil functions. We carried out a field experiment in three consolidated agricultural areas (~23 years old) across a 1000-km transect within the MATOPIBA region to quantify land-use change effects from native vegetation (NV) to agricultural areas under no-tillage (NT) on soil physical properties and associated functions; and compare the obtained results with critical values from literature considered as thresholds for soil degradation. Soil samples were collected from paired plots (NV and NT) in each location at 0–5, 5–10, 10–20, and 20–30 cm soil depth to determine key soil physical properties related to soil texture, compaction, porosity, water storage, and structural stability. Additionally, a set of soil physical indicators was added into a soil physical quality index (SPQI) as an integrated and quantitative approach for evaluating changes in soil functions. Our results indicated that conversion from NV to agriculture under NT increased the compaction process and reduced total soil porosity, unbalancing the proportion between soil water and air storage to critical levels. Besides, water infiltration within the soil profile was strongly decreased. The land-use conversion further induced changes on soil aggregate stability, decreasing large macroaggregates (>2000 µm) and increasing small macroaggregates (250–2000 µm) and the silt/clay-sized fraction (<53 µm). The SPQI was reduced by ~33% in NT, indicating detrimental effects of agriculture expansion on soil functionality. Based on the SPQI, water availability and air diffusion were the soil functions most affected by land-use change. Our results provide a quantitative assessment of soil physical properties and soil function changes as a consequence of agricultural expansion in the MATOPIBA region, indicating the need to improve NT practices towards alleviating soil compaction and improving soil structure. Best management practices are fundamental to restore soil functionality, ensuring crop yields and other ecosystem services.

Soil properties and microbial processes in response to land‐use change in agricultural highlands of the Central Andes

AbstractUnderstanding changes in soil functions in response to land‐use change is important for guiding agricultural practices towards sustainable soil management. We evaluated the differences in soil properties (soil organic matter, water extractable carbon (C) and nitrogen (N), microbial biomass, pHKCL and exchangeable cations) and microbial processes (respiration potential, net N mineralization, net nitrification and metabolic potential of soil bacteria), as well as the relative importance of soil properties in explaining changes in processes under three land uses (potato crops, fallow fields and eucalyptus plantations) in the agricultural highlands of the Central Andes. Soils under potato crops were characterized by the highest net N mineralization and net nitrification rates, and extractable phophorus (P), and the lowest microbial biomass P. Conversion to eucalyptus plantations led to an increase in soil organic matter, water extractable C and microbial biomass, and a decrease in extractable P and metabolic diversity of soil bacteria. Higher exchangeable aluminium (Al) indicated soil acidification under eucalyptus. Fallow practices did not lead to major changes in soil properties and microbial processes, indicating that fallow practices for up to 6 years were too short to substantially contribute to soil fertility restoration. Hot water extractable carbon (HWC) showed the best relationship with soil processes (respiration potential, net N mineralization and net nitrification). Our results highlight the necessity of alternative management practices for maintaining soil fertility under potato crops, the drastic modification of soil properties and processes under eucalyptus plantations, and the potential of HWC as a proxy for monitoring land‐use‐induced changes in soil functions related to C and N cycling.Highlights Effects of conversion from potato crops to eucalyptus and fallow on soil properties and processes were assessed. Under eucalyptus, soil respiration increased; metabolic diversity and N transformations decreased. Short fallow periods did not result in soil fertility restoration. Hot water extractable C was the best indicator of changes in soil processes.

Temporal changes in soil function in a wooded dryland following simulated disturbance by a vertebrate engineer

An inherent feature of arid and semiarid environments (drylands) is the importance of landscape heterogeneity in driving soil and ecological processes. Soil disturbance by organisms is an important, but often overlooked, driver of patchiness, but little is known about the temporal changes in soil and ecological processes following disturbance. We used artificial depressions, designed to mimic the foraging pits of the vertebrate marsupial, the Short-beaked echidna (Tachyglossus aculeatus), to examine temporal changes in soil labile carbon, decomposition, litter capture, and plant germination and survival, over an 18 month period. Foraging pits had a half-life of about 7 months, and trapped seven-times more litter than an equivalent area on the soil surface. Larger pits tended to trap more litter than smaller pits. Foraging pits trapped six-times more seed abundance and three-times more richness than the surface. Eighteen months after disturbance, litter decomposition was 30% greater in the pits, and labile carbon concentrations were 8% greater (622 mg kg−1) than the original undisturbed soils (578 mg kg−1). Taken together, we provide strong evidence that foraging by native animals is an important mechanism for driving spatial heterogeneity in dryland soils. Our results also suggest that simulating the activities of short-beaked echidnas may provide a mechanism for rehabilitating degraded soils.