Paired comparisons of native and commercial inoculants, bacteria and fungi, and single and multi-strain microorganisms show equal effects on plant growth in dryland ecosystems.

Identifying an efficient microbial inoculant to promote plant growth is a key pillar in microbial ecology. A wide variety of microbial inoculants have been developed worldwide mostly driven by agricultural demand to define the best inocula. However, the efficacy and comparisons of different microbial inoculants used in dryland ecosystems have rarely been tested. Here, we provide the first quantitative comparison of the effects of commercial versus native inoculants and single versus multiple strain inoculants as well as bacteria versus fungi inoculants on plant growth under field conditions in dryland ecosystems. We used a global meta-analysis of 62 dryland studies to compare the performance of different inocula type on plant growth. We found that microbial inoculation increased plant growth by 43% (CI = 29.69% - 58%) on average in dryland ecosystems, however the magnitude of effect was statistically similar between native (53%, CI = 31% - 80%) and commercial inoculants (40%, CI = 9% - 78%), or between single (39%, CI = 24% - 55%) and multiple strain inoculants (49% , CI = 32% - 68%) or between fungi (39% , CI = 28% - 61%) or bacteria inoculants 43% (CI = 23% - 58%). Our results confirm an assumption that, microorganisms do not usually follow macro-ecological theories and that the choice of an inoculant should be tailored to the purpose and design of the project. In drylands. The result is not only beneficial for agricultural practices in dryland ecosystems, but it is very crucial in dryland restoration projects, especially when the soil system is severely degraded and microbial inoculation is integrated as a plant growth promoter.