Spatial and temporal changes of charosphere hotspots with or without nitrogen additions

Abstract

The charosphere is a thin soil one surrounding the biochar with highly active biochemical functions. Yet, little is known about the spatial and temporal distribution of charosphere hotspots. In this study, repacked soil cores were incubated with a central layer of biochar (pristine or acid-modified) with or without nitrogen (N) additions for 30 days and sliced at the millimeter scale for analyzing soil pH, mineral N, bacterial and fungal communities as well as the putative functions. We aimed to determine gradient distributions (in millimeter scale) of charosphere affected by biochar under different N additions. Our results showed narrower gradient changes (3 mm) of microbial community composition and wider shifts (6 mm) in pH and inorganic N contents in charosphere. The pristine biochar increased the soil pH up to 1.5 units in the charosphere, and subsequently boosted the relative abundance of Proteobacteria, Acidobacteria, and Zygomycota. With N addition, both the biochar site and charosphere were observed with decreased complexity of microbial networks, which might imply the limited microbial functionality of charosphere. These results will advance the understanding and prediction of biochar’s environmental impacts in soil.

Highlight

•	The charosphere hotspots of soil pH and mineral N content reached 6 mm.
•	Soil microbial compositions fluctuated within 3 mm of charosphere.
•	Pristine biochar site fostered higher fungal diversity than that in bulk soils.
•	Lower bacterial diversity in pristine biochar site was found.
•	The microbial network complexity declined with N addition in charosphere.

Funding

National Natural Science Foundation of China(42177311)

2115 Talent Development Program of China Agricultural University

Scholarship of the ‘National Thousand (Young) Talents Program’ of China

National Key Research and Development Program of China(2022YFE0115300)