Abstract. Subsoil carbon (C) stocks are a prime target for efforts to increase soil C storage for climate change mitigation. However, subsoil C dynamics are not well understood, especially in soils under long-term intensive agricultural management. We compared subsoil C storage and soil organic matter (SOM) composition in tomato–corn rotations after 25 years of differing C and nutrient management in the California Central Valley: CONV (mineral fertilizer), CONV+WCC (mineral fertilizer and cover crops), and ORG (composted poultry manure and cover crops). The cover crop mix used in these systems is a mix of oat (Avena sativa L.), faba bean (Vicia faba L.), and hairy vetch (Vicia villosa Roth). Our results showed a ∼19 Mg ha−1 increase in soil organic C (SOC) stocks down to 1 m under ORG systems, no significant SOC increases under CONV+WCC or CONV systems, and an increased abundance of carboxyl-rich C in the subsoil (60–100 cm) horizons of ORG and CONV+WCC systems. Our results show the potential for increased subsoil C storage with compost and cover crop amendments in tilled agricultural systems and identify potential pathways for increasing C transport and storage in subsoil layers.

Nowadays, plant invasion has become a global ecological threat to local biodiversity and ecosystem stability. Spartina alterniflora encroaches on the ecological niches of local species and changes the soil’s nutrient cycle. However, few comprehensive assessments focus on the effects of S. alterniflora invasion. Here, we investigated how soil sulfur changed with spatiotemporal variation and life forms of native species after S. alterniflora invasion and speculated the possible mechanism of the sulfur increase based on the references. The invasion of S. alterniflora increased soil total sulfur by 57.29% and phytotoxic sulfide by 193.29%. In general, the invasion of S. alterniflora enhanced the total plant biomass and soil nutrients, e.g., soil organic carbon, total nitrogen, and soil microbial biomass carbon, further increasing soil sulfur content. The sulfur accumulation caused by S. alterniflora might result in the poisoning of native species. Thus, we hypothesized that the success of S. alterniflora invasion was closely connected with soil sulfur, especially toxic sulfide. Our study suggests that researchers should give more attention to the correlation between S. alterniflora invasion and the soil sulfur increase. More research is needed to investigate the mechanisms of the successful invasion by accumulating phytotoxic sulfide.

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Background and Aims Spartina alterniflora (S. alterniflora) is an invasive plant widely distributed in coastal areas of China, and the invasion has caused the accumulation of soil sulfur contents, while sulfide can accumulate to phytotoxic levels. It has been verified that S. alterniflora is more tolerant to sulfide than Scirpus mariqueter (S. mariqueter). Therefore, sulfide may play an important role in invading S. alterniflora, but the specific mechanism awaits further investigation. Methods Through experiments with situ rhizoboxes in the Jiuduansha Wetland, we conducted field investigations to analyze soil sulfur (sulfate and sulfide) contents, iron (Fe(II) and Fe(III)) contents, and physicochemical properties. Lab-scale experiment with high-resolution (HR) diffusive gradients in thin films (DGT) was conducted to investigate the distribution of oxygen, sulfide, and iron concentrations in the microenvironment of two species. Meanwhile, the effect of roots on soil bacterial communities and sulfur cycle-related microorganisms was investigated. Results The soil sulfur (sulfide and sulfate) contents in S. alterniflora were higher than in S. mariqueter. In the rhizoboxes of S. alterniflora, the contents of soil sulfide were significantly lower in the rhizosphere, while oxygen contents in the rhizosphere were higher than in bulk soil. The iron contents in S. alterniflora were significantly higher than in S. mariqueter, especially the Fe(III) contents were higher in the rhizosphere. Conclusion The S. alterniflora may gain an advantage in the invasion process by oxidizing the sulfide through radial oxygen loss and by enriching iron to mitigate high concentrations of sulfide in the rhizosphere.

Advanced oxidation processes (AOPs) have become a favored approach in wastewater treatment due to the high efficiency and diverse catalyzed ways. Iron-based materials were the commonly used catalyst due to their environmental friendliness and sustainability in the environment. We collected the published papers relative to the application of the modified iron-based materials in AOPs between 1999 and 2020 to comprehensively understand the related mechanism of modified materials to improve the catalytic performance of iron-based materials in AOPs. Related data of iron-based materials, modification types, target pollutants, final removal efficiencies, and rate constants were extracted to reveal the critical process of improving the catalytic efficiency of iron-based materials in AOPs. Our results indicated that the modified materials through various mechanisms to enhance the catalytic performance of iron-based materials. The principal aim of iron-based materials modification in AOPs is to increase the content of available Fe2+ and enhance the stability of Fe2+ in the system. The available Fe2+ is elevated by the following mechanisms: (1) modified materials accelerate the electron transfer to promote the Fe3+/Fe2+ reaction cycle in the system; (2) modified materials form chelates with iron ions and bond with iron ions to avoid Fe3+ precipitation. We further analyzed the effect of different modifying materials in improving these two mechanisms. Combining the advantages of different modified materials to develop iron-based materials with composite modification methods can enhance the catalytic performance of iron-based materials in AOPs for further application in wastewater treatment.