查看更多>>摘要：? 2021 Elsevier LtdSoil organic carbon (SOC) has significant implications in regulating soil health. Emerging insights emphasize the important role of microbial anabolism in SOC storage by continuously transforming plant fragments into persistent microbial residues. However, knowledge of the sequestration pathway of root versus shoot carbon (C) is under debate. While recent studies have shown that labile shoot residue is disproportionately important for stable SOC accumulation through microbial assimilation, how plant root vs. shoot residue retention impacts microbial-derived C under different soil fertility conditions remains elusive. Here, we conducted a 500-d in situ experiment using Alfisols with low fertility (LF) and high fertility (HF) amended with maize root or shoot (both stem and leaf) residues. The microbial residues (amino sugar biomarkers) and microbial communities (lipid biomarkers) were analyzed at 60, 90, 150, and 500 d after the amended materials were added. The results showed that shoot residue input facilitated microbial residue accumulation more efficiently than root input before 150 d. However, at the end of the experiment, the treatment containing added root residue accumulated more microbial residues and produced a higher proportion of microbial residue in SOC, compared with shoot treatment. These results provide novel evidence that root residue can also yield SOC efficiently through the organic substrate–microbial anabolism pathway, but it depends on the decomposition period. Moreover, soil fertility plays an important role in regulating the quantity and relative composition of microbial residues. Specifically, crop residue application greatly increased the contribution of microbial residue C to SOC in the LF treatment compared to that in the HF treatment on day 500. Meanwhile, crop residue addition had a more positive effect on fungal residue accumulation in the LF soil, while it facilitated the accumulation of bacterial residue in the HF soil. These findings highlight that crop residue addition (especially root residue) is an effective approach for improving microbial-derived C sequestration in infertile soils.
查看更多>>摘要：? 2021 Elsevier LtdSoil organic matter (SOM) plays a central role in mediating soil productivity through its impacts on nutrient cycling and retention, aggregate stability and water retention. Thus, management techniques or technologies including novel soil amendments could benefit farmers through the accumulation of carbon (C) and other nutrients in SOM. However, these same inputs can also lead to accelerated mineralization of native SOM through the process known as priming. This unresolved paradox may be due to the limited understanding of how different SOM fractions respond to priming and in which direction. In this study, we examine the response of functionally distinct SOM fractions to priming when soils are amended with lactobionate, a low molecular weight sugar acid byproduct of cheese manufacturing. Liquid-based 13C lactobionate was added to an agricultural silty loam soil to study its persistence, priming effects, and response of different SOM fractions to lactobionate over 84 days. Cumulative soil carbon dioxide (CO2) was greater in lactobionate-amended soils versus control and by the end of the experiment, 53% of added lactobionate was mineralized. In total, positive priming of 40% of extant SOM was observed from 14 to 84 days. Lactobionate-induced changes to SOM fractions were determined at days 14, 28, 56 and 84 of the incubation to examine if and how priming altered the distribution of C between fast and slow-cycling SOC fractions. In response to lactobionate, the total C content of the water extractable organic matter (WEOM) fraction initially increased by 100% from the dissolved lactobionate we added, but then declined and at a faster rate than other SOM fractions. In addition, the total C of the light-fraction particulate organic matter (LF-POM) fraction also declined. At the same time, we observed total C increases in the slower-cycling sand-sized POM (H-POM) and mineral-associated organic (MAOM) C fractions, in response to lactobionate additions. We also saw a marginal increase in total soil C in the lactobionate-amended soils. Our findings therefore suggest that the application of lactobionate to soils may induce positive priming of the faster cycling LF-POM and WEOM fractions, but also concurrent gains in the H-POM and MAOM C fractions associated with long-term persistence and relative resiliency to disturbance with no net loss of total soil carbon. Thus, the application of low-molecular weight C-based materials such as lactobionate presents an avenue to building more persistent SOM through its impacts on the internal cycling and transformation of SOM fractions.
查看更多>>摘要：? 2021 Elsevier LtdLinkages between aboveground and belowground communities are a key but globally under-researched component of responses to environmental change. Given the logistical complications to studying these relationships, much of our knowledge derives from laboratory experiments and localized field studies which have so far yielded inconsistent results. Because environmental factors may alter relationships between above- and belowground communities, there is a need for broad-scale field studies testing these interactions. The Antarctic Peninsula provides an ideal test setting, given the relatively simple communities both above- and belowground. The Peninsula is also experiencing rapid environmental changes, including alterations in species diversity and distribution both above- and belowground. Thus, an improved understanding of the broad-scale consequences of altered environments and vegetation communities for the soil microbiome is of high priority. To determine the nature and strength of the relationship between in situ plant and soil communities across a broad spatial scale and range of environmental conditions, we sampled soil communities at 9 locations (spanning 60–72°S along the Scotia Arc and Antarctic Peninsula) beneath the major aboveground habitats (moss, grass, lichen, algae and bare soil). We measured a comprehensive suite of soil physicochemical properties, microbial (bacterial and fungal) diversity and composition, and invertebrate abundance and community composition to determine the relationships between plant and soil communities. Our results suggest that, with increased environmental severity, plant cover types become more important for influencing the physicochemical soil environment, and therefore the soil microbial communities. Although we found site-specific relationships, broad-scale patterns reveal significant differences among bare soils and vegetated soils, particularly soils beneath grass and moss. This suggests that expansion of vegetation communities under current climate warming projections will be accompanied by shifts in the soil microbiome, with important implications for the ecosystem functioning with which they are associated.
查看更多>>摘要：? 2021Iron (Fe) is an essential element for almost all living organisms. In addition, microbial Fe cycling drives the biogeochemical cycles of other elements, although little is known about characteristics of Fe cycling and its driving mechanism in desert ecosystems. Here, we investigated the key microbial functional genes involved in Fe(II) oxidation and Fe(III) reduction and the associated factors affecting the soil during the development of biological soil crusts (BSCs), which are among the most important landscapes in desert ecosystems. We also analyzed the relationships among the genes involved in Fe, carbon (C), and nitrogen (N) cycling. The available Fe content and diversity of genes associated with microbial Fe cycling increased after 61 years of BSC development. Our results suggested that Fe(II) oxidation in BSCs is mainly driven by the iro gene from microaerophilic Fe oxidizing microorganisms (FeOMs), whereas Fe(III) reduction is driven mainly by c-type cytochromes through regulation by the OmcS gene. The presence of both genes significantly correlated with that of genes involved in labile organic C degradation, denitrification, and N reduction. Fungal abundance, soil nutrient content (mainly total N), and the Fe-manganese (Mn) oxide-bound fraction (RED-Fe) were the main soil factors affecting the gene profile associated with microbial Fe cycling in BSCs (explaining 74.8% of the variation). These results indicated that the main Fe cycling process in desert ecosystems can adapt to the local environment. Furthermore, the interaction between Fe and the C or N cycles, as well as the synergistic effects of soil quality improvement, actively promotes effective and dynamic Fe cycling in BSCs.
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