The effect of biochar and its interaction with the earthworm Pontoscolex corethrurus on soil microbial community structure in tropical soils.

Jorge Paz-Ferreiro,Shenglei Fu,Chenfei Liang,Ana Mendez,Gabriel Gasco,Dafeng Hui

doi:10.1371/journal.pone.0124891

Abstract

Biochar effects on soil microbial abundance and community structure are keys for understanding the biogeochemical cycling of nutrients and organic matter turnover, but are poorly understood, in particular in tropical areas. We conducted a greenhouse experiment in which we added biochars produced from four different feedstocks [sewage sludge (B1), deinking sewage sludge (B2), Miscanthus (B3) and pine wood (B4)] at a rate of 3% (w/w) to two tropical soils (an Acrisol and a Ferralsol) planted with proso millet (Panicum milliaceum L.). The interactive effect of the addition of earthworms was also addressed. For this purpose we utilized soil samples from pots with or without the earthworm Pontoscolex corethrurus, which is a ubiquitous earthworm in tropical soils. Phospholipid fatty acid (PLFA) measurements showed that biochar type, soil type and the presence of earthworms significantly affected soil microbial community size and structure. In general, biochar addition affected fungal but not bacterial populations. Overall, biochars rich in ash (B1 and B2) resulted in a marked increase in the fungi to bacteria ratio, while this ratio was unaltered after addition of biochars with a high fixed carbon content (B3 and B4). Our study remarked the contrasting effect that both, biochar prepared from different materials and macrofauna, can have on soil microbial community. Such changes might end up with ecosystem-level effects.

Highlights

Seeking for new technologies to improve agricultural systems and contributing to sustainable resource management has led to a number of creative ideas, including the pyrolysis of biomass residues and their addition to the soil system
The use of tropical soils for agriculture is constrained by low organic matter contents, CEC and nutrient contents, in particular for Acrisols and Ferralsols [6], and this can be improved with biochar addition
The CO2 evolved in 10 days from 25 g soil samples incubated at 60% water holding capacity (WHC) and at 25°C was collected in 10 ml of a 1 M NaOH solution, which was titrated with HCl

Summary

Introduction

Seeking for new technologies to improve agricultural systems and contributing to sustainable resource management has led to a number of creative ideas, including the pyrolysis of biomass residues (biochar) and their addition to the soil system. As a consequence of the beneficial role of biochar in Amazonian Dark Earths, there was an increasing interest on biochar research in the last years, mainly fuelled by its significance with respect to the abatement of carbon emissions [1], increase in agricultural yields [2] and improvement in the utilisation of wastes [3]. Several studies have shown how a general improvement in soil physical, chemical and biological activities can be expected from the use of different biochars [4, 5]. The use of tropical soils for agriculture is constrained by low organic matter contents, CEC and nutrient contents, in particular for Acrisols and Ferralsols [6], and this can be improved with biochar addition. Some pioneer studies have demonstrated that biochar could increase soil enzymatic activity [4] but, in the particular case of tropical soils, this increase is very specific and depends on the soil type, biochar and enzyme activity studied [5]

Methods

Results

Discussion

Conclusion