Meta-Analysis of the Effects of Biochar Application on the Diversity of Soil Bacteria and Fungi

Abstract

Biochar is increasingly being used for soil improvement, but the effects on microbial diversity in soil are still ambiguous due to contrasting results reported in the literature. We conducted a meta-analysis to clarify the effect of biochar addition on soil bacterial and fungal diversity with an increase in Shannon or Chao1 index as the outcome. Different experimental setups, quantitative levels of biochar addition, various biochar source materials and preparation temperatures, and the effect of natural precipitation in field experiments were the investigated variables. From a total of 95 publications identified for analysis, 384 datasets for Shannon index and 277 datasets for Chao1 index were extracted that described the bacterial diversity in the soils, of which field experiments and locations in China dominated. The application of biochar in soil significantly increased the diversity of soil bacteria but it had no significant effect on the diversity of fungi. Of the different experimental setups, the largest increase in bacterial diversity was seen for field experiments, followed by pot experiments, but laboratory and greenhouse settings did not report a significant increase. In field experiments, natural precipitation had a strong effect, and biochar increased bacterial diversity most in humid conditions (mean annual precipitation, MAP > 800 mm), followed by semi-arid conditions (MAP 200–400 mm). Biochar prepared from herbaceous materials was more effective to increase bacterial diversity than other raw materials and the optimal pyrolysis temperature was 350–550 °C. Addition of biochar at various levels produced inconclusive data for Chao1 and Shannon indices, and its effect was less strong than that of the other assessed variables.

Biochar modifies soil physical properties mostly through changes in soil structure rather than through its internal porosity

“…Regarding the latter, biochar particles can fill and clog the voids in between the mineral grains, especially in coarse‐textured soils (Edeh et al., 2020), take up space previously occupied by mineral particles or organo‐mineral micromass, or improve soil structure and soil aggregation by acting as an additional binding agent in the soil (Burgeon et al., 2021; Du et al., 2017). This latter mechanism is similar to the aggregating effect of uncharred organic matter and it cannot be dissociated from an indirect impact of biochar on uncharred organic matter (Burgeon et al., 2021; Hardy et al., 2016; Hernandez‐Soriano et al., 2015; Kerré et al., 2016) or on soil biology (Li et al., 2020; Wang et al., 2023; Zhang et al., 2018).…”

“…Following the addition of biochar to soil, soil porosity may be modified () through the intrinsic porosity of biochar particles (Brewer et al., 2014; Hyväluoma et al., 2018; Lehmann & Joseph, 2009; Yi et al., 2020) or (2) through its location and interaction with soil structure by (2a) filling voids in between mineral grains, especially in coarse‐textured soils (Edeh et al., 2020), (2b) occupying space previously occupied by mineral particles or organo‐mineral micromass, or (2c) acting as an additional binding agent resulting in a soil structuring effect similar to the addition of uncharred organic matter (Burgeon et al., 2021; Du et al., 2017). Through indirect effects on soil biology (Li et al., 2020; Wang et al., 2023; Zhang et al., 2018) and uncharred organic matter content (Burgeon et al., 2021; Hardy et al., 2016; Hernandez‐Soriano et al., 2015; Kerré et al., 2016), biochar addition to soil may also result in a structuring effect, although this effect cannot be isolated from the direct effects of biochar addition to soils.…”

Biochar modification methods and mechanisms for salt‐affected soil and saline‐alkali soil improvement: A review

“…BC can provide nutrients, including a source of carbon and N, directly to soil microorganisms, improving the physical and chemical properties of the soil and forming a new layered structure in the soil, which is beneficial for water‐holding capacity (Wang, Gao, et al., 2022). Additionally, ‘Charsphere’ may be created when BC is added to the soil, promoting microbial growth and allowing microorganisms to directly reproduce within the pores of the BC and avoid natural predators (Lee et al., 2022; Luo et al., 2013; Wang et al., 2007, 2023; Yang et al., 2015). Introducing nutrients directly into the soil and enhancing the high‐salinity environment, which restricts the survival of microorganisms, can accelerate the circulation of soil nutrients, making the salt‐affected soil more fertile and enhancing the growth environment of microorganisms (Duan et al., 2023; Kolton et al., 2016).…”

Ameliorant application promotes growth performances of Calliandra calothyrsus Meissn. planted on post-coal mining land

“…Biochar has the potential to be derived from various organic waste materials, such as agricultural waste [15], forestry waste, livestock waste [16,17], and settlement waste. Biochar can improve soil quality [18,19], increase soil retention of water and nutrients [20], increase pH and soil organic matter content [21], boost nutrient usage efficiency [22,23], and promote soil microorganism activity [24,25]. Furthermore, biochar can reduce possible erosion rates even at low application rates [26].…”

“…The use of solid decanters and biochar will improve the retention and availability of nutrients and groundwater. High nutrient levels in solid decanter become a source of energy for microbes and plants, while biochar acts as a provider of microbial habitat [24,25], so applying both simultaneously is expected to efficiently use nutrients in solid decanter so that the function of soil as a growing medium will last a long time.…”