Differences in Species Composition of the Soil Seed Banks among Degraded Patches in an Agro-Pastoral Transition Zone in Inner Mongolian Steppe

Degraded grasslands were distributed in patches characterized by fringed sagebrush (Artemisia frigida), narrowleaf stellera (Stellera chamaejasme), shining speargrass (Achnatherum splendens), or white swordflag (Iris lactea) at an agro-pastoral transition zone of the south Inner Mongolian steppe, which have been retrogressive from a Leymus chinensis steppe. A control patch (undegraded) was located close to the four degraded patches. We investigated the size, composition, species richness of soil seed banks, and its relation to the aboveground vegetation. The density of soil seed banks was highest in the white swordflag patch, intermediate in the shining speargrass and undegraded patches and lowest in the fringed sagebrush and narrowleaf stellera patches. The percentage of the persistent seed bank in the undegraded patch was higher than those in the four degraded patches. Similarities between the soil seed bank of the undegraded patch and degraded patches and between soil seed banks and standing vegetation of the undegraded patch were all low. The potential for in situ regeneration of the established vegetation of the undegraded patch from the soil seed bank is low in all of these four patches. We can assume that restoration of these habitats can not rely on seed banks alone

Soil biodiversity enhances the persistence of legumes under climate change

Summary: Global environmental change poses threats to plant and soil biodiversity. Yet, whether soil biodiversity loss can further influence plant community’s response to global change is still poorly understood. We created a gradient of soil biodiversity using the dilution‐to‐extinction approach, and investigated the effects of soil biodiversity loss on plant communities during and following manipulations simulating global change disturbances in experimental grassland microcosms. Grass and herb biomass was decreased by drought and promoted by nitrogen deposition, and a fast recovery was observed following disturbances, independently of soil biodiversity loss. Warming promoted herb biomass during and following disturbance only when soil biodiversity was not reduced. However, legumes biomass was suppressed by these disturbances, and there were more detrimental effects with reduced soil biodiversity. Moreover, soil biodiversity loss suppressed the recovery of legumes following these disturbances. Similar patterns were found for the response of plant diversity. The changes in legumes might be partly attributed to the loss of mycorrhizal soil mutualists. Our study shows that soil biodiversity is crucial for legume persistence and plant diversity maintenance when faced with environmental change, highlighting the importance of soil biodiversity as a potential buffering mechanism for plant diversity and community composition in grasslands

Evaluating the role of bacterial diversity in supporting soil ecosystem functions under anthropogenic stress

Ecosystem functions and services are under threat from anthropogenic global change at a planetary scale. Microorganisms are the dominant drivers of nearly all ecosystem functions and therefore ecosystem-scale responses are dependent on responses of resident microbial communities. However, the specific characteristics of microbial communities that contribute to ecosystem stability under anthropogenic stress are unknown. We evaluated bacterial drivers of ecosystem stability by generating wide experimental gradients of bacterial diversity in soils, applying stress to the soils, and measuring responses of several microbial-mediated ecosystem processes, including C and N cycling rates and soil enzyme activities. Some processes (e.g., C mineralization) exhibited positive correlations with bacterial diversity and losses of diversity resulted in reduced stability of nearly all processes. However, comprehensive evaluation of all potential bacterial drivers of the processes revealed that bacterial α diversity per se was never among the most important predictors of ecosystem functions. Instead, key predictors included total microbial biomass, 16S gene abundance, bacterial ASV membership, and abundances of specific prokaryotic taxa and functional groups (e.g., nitrifying taxa). These results suggest that bacterial α diversity may be a useful indicator of soil ecosystem function and stability, but that other characteristics of bacterial communities are stronger statistical predictors of ecosystem function and better reflect the biological mechanisms by which microbial communities influence ecosystems. Overall, our results provide insight into the role of microorganisms in supporting ecosystem function and stability by identifying specific characteristics of bacterial communities that are critical for understanding and predicting ecosystem responses to global change

Effects of perfluoroalkyl and polyfluoroalkyl substances (PFAS) on soil structure and function

Soils are impacted globally by several anthropogenic factors, including chemical pollutants. Among those, perfluoroalkyl and polyfluoroalkyl substances (PFAS) are of concern due to their high environmental persistence, and as they might affect soil structure and function. However, data on impacts of PFAS on soil structure and microbially-driven processes are currently lacking. This study explored the effects of perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and perfluorobutanesulfonic acid (PFBS) at environmental-relevant concentrations on soil health, using a 6-week microcosm experiment. PFAS (even at 0.5 ng g−1 for PFBS) significantly increased litter decomposition, associated with positive effects on β-glucosidase activities. This effect increased with PFAS concentrations. Soil pH was significantly increased, likely as a direct consequence of increased litter decomposition affected by PFAS. Soil respiration was significantly inhibited by PFAS in week 3, while this effect was more variable in week 6. Water-stable aggregates were negatively affected by PFOS, possibly related to microbial shifts. PFAS affected soil bacterial and fungal abundance, but not microbial and certain enzyme activities. Our work highlights the potential effects of PFAS on soil health, and we argue that this substance class could be a factor of environmental change of potentially broad relevance in terrestrial ecosystem functioning

Effects of Microplastic Fibers on Soil Aggregation and Enzyme Activities Are Organic Matter Dependent

Microplastic as an anthropogenic pollutant accumulates in terrestrial ecosystems over time, threatening soil quality and health, for example by decreasing aggregate stability. Organic matter addition is an efficient approach to promote aggregate stability, yet little is known about whether microplastic can reduce the beneficial effect of organic matter on aggregate stability. We investigated the impacts of microplastic fibers in the presence or absence of different organic materials by carrying out a soil incubation experiment. This experiment was set up as a fully factorial design containing all combinations of microplastic fibers (no microplastic fiber addition, two different types of polyester fibers, and polyacrylic) and organic matter (no organic matter addition, Medicago lupulina leaves, Plantago lanceolata leaves, wheat straw, and hemp stems). We evaluated the percentage of water-stable aggregates (WSA) and activities of four soil enzymes (β-glucosidase, β-D-celluliosidase, N-acetyl-b-glucosaminidase, phosphatase). Organic matter addition increased WSA and enzyme activities, as expected. In particular, Plantago or wheat straw addition increased WSA and enzyme activities by 224.77 or 281.65% and 298.51 or 55.45%, respectively. Microplastic fibers had no effect on WSA and enzyme activities in the soil without organic matter addition, but decreased WSA and enzyme activities by 26.20 or 37.57% and 23.85 or 26.11%, respectively, in the presence of Plantago or wheat straw. Our study shows that the effects of microplastic fibers on soil aggregation and enzyme activities are organic matter dependent. A possible reason is that Plantago and wheat straw addition stimulated soil aggregation to a greater degree, resulting in more newly formed aggregates containing microplastic, the incorporated microplastic fibers led to less stable aggregates, and decrease in enzyme activities This highlights an important aspect of the context dependency of microplastic effects in soil and on soil health. Our results also suggest risks for soil stability associated with organic matter additions, such as is common in agroecosystems, when microplastics are present

Excluding arbuscular mycorrhiza lowers variability in soil respiration but slows down recovery from perturbations

The role of mutualisms in mediating temporal stability in an ecosystem has been debated extensively. Here, we focus on how a ubiquitous mutualism, arbuscular mycorrhiza, influences temporal stability of a key ecosystem process, ecosystem respiration. We discriminated between two forms of temporal stability, temporal variability and resilience, and hypothesized that excluding arbuscular mycorrhiza would be detrimental for both of them. We analyzed a set of 10 parallel manipulation experiments to assess how excluding arbuscular mycorrhiza modulates temporal stability compared to other common experimental factors. We quantified the temporal variability of ecosystem respiration and the resilience to experimental perturbations (i.e., pulses, stresses, and a disturbance) following manipulations of mycorrhizal state. We observed lower temporal variability in the absence of arbuscular mycorrhiza in discord to our main hypothesis. Manipulating arbuscular mycorrhiza had a stronger impact on temporal variability than the pulse (application of urea), the stress (addition of salt), and a disturbance (experimental defoliation) but weaker than excluding primary producers or comparing across different plant species. Resilience to experimental perturbations declined in non‐mycorrhizal microcosms. We present an empirical study on how mutualisms impact temporal stability. Arbuscular mycorrhiza differentially alters temporal variability and resilience, highlighting that generalizing across different forms of temporal stability could be misleading

Model Sparsification Can Simplify Machine Unlearning

Recent data regulations necessitate machine unlearning (MU): The removal of the effect of specific examples from the model. While exact unlearning is possible by conducting a model retraining with the remaining data from scratch, its computational cost has led to the development of approximate but efficient unlearning schemes. Beyond data-centric MU solutions, we advance MU through a novel model-based viewpoint: sparsification via weight pruning. Our results in both theory and practice indicate that model sparsity can boost the multi-criteria unlearning performance of an approximate unlearner, closing the approximation gap, while continuing to be efficient. With this insight, we develop two new sparsity-aware unlearning meta-schemes, termed `prune first, then unlearn' and `sparsity-aware unlearning'. Extensive experiments show that our findings and proposals consistently benefit MU in various scenarios, including class-wise data scrubbing, random data scrubbing, and backdoor data forgetting. One highlight is the 77% unlearning efficacy gain of fine-tuning (one of the simplest approximate unlearning methods) in the proposed sparsity-aware unlearning paradigm. Codes are available at https://github.com/OPTML-Group/Unlearn-Sparse

Multiple anthropogenic pressures eliminate the effects of soil microbial diversity on ecosystem functions in experimental microcosms

Biodiversity is crucial for the provision of ecosystem functions. However, ecosystems are now exposed to a rapidly growing number of anthropogenic pressures, and it remains unknown whether biodiversity can still promote ecosystem functions under multifaceted pressures. Here we investigated the effects of soil microbial diversity on soil functions and properties when faced with an increasing number of simultaneous global change factors in experimental microcosms. Higher soil microbial diversity had a positive effect on soil functions and properties when no or few (i.e., 1–4) global change factors were applied, but this positive effect was eliminated by the co-occurrence of numerous global change factors. This was attributable to the reduction of soil fungal abundance and the relative abundance of an ecological cluster of coexisting soil bacterial and fungal taxa. Our study indicates that reducing the number of anthropogenic pressures should be a goal in ecosystem management, in addition to biodiversity conservation

Non-targeted Metabolomics Analysis of Metabolic Differences among Liuyang Douchi Fermented by Different Strains

In order to investigate the metabolic differences among Liuyang Douchi fermented by different starter cultures, the contents of total acid and amino nitrogen in Douchi fermented naturally and by using Aspergillus flavus 7214 (AF 7214), A. flavus 7622 (AF 7622), their mixture (AF 7214 + AF 7622) or A. orzyae were determined, and the difference in metabolites among these fermentation strategies was explored by liquid chromatography-mass spectrometry (LC-MS). The results showed that among the five Douchi samples, Douchi fermented by AF 7214 had the highest contents of total acid (3.52%) and amino nitrogen (1.47 g/100 g). The results of partial least squares discriminant analysis (PLS-DA) indicated that significant differences in metabolites were observed among the Douchi samples, and the composition of metabolites in Douchi fermented by AF 7622 showed the smallest difference from that in naturally fermented Douchi. Further analysis revealed that the differential metabolites between Douchi fermented naturally and by using starter cultures were mainly involved in amino acid metabolic pathways, especially arginine biosynthesis. A total of 62 key differential metabolites among the five samples were identified using variable importance in the projection (VIP) greater than 1.5 and P < 0.05 as criteria, including 26 amino acids and their derivatives such as L-lysine, L-serine and 2-methylserine, which indicated that enhanced fermentation showed the most notable influence on the metabolism of amino acids. This study has provided a new understanding of the formation of metabolites during the enhanced fermentation of Liuyang Douchi