Dear Dr. Liu and co-authors,

Your manuscript presents a robust and much needed meta-analysis of the effect of allelopathy in plant-plant interactions. The manuscript is clearly written, the statistics are appropriate, biases are tested for. The findings, that allelopathy can have fairly strong negative effects on plants, argue for more research evaluating the importance of allelopathy in plant communities. I encourage you and your co-authors authors to provide more detail on the kind of approaches and evidence that would be most important to advance the discipline.

My additional suggestions come from my own direct experience working in this field, and as such, I’ve signed this review. In the introduction, the authors suggest that the publication rate might have dropped recently because of concerns linked to the challenging technical issues, citing a paper on which I am a co-author (Blair et al. 2009). I would encourage the authors to also cite Lau et al. 2008, New Phytologist (again, on which I am a co-author), which covers the challenges associated with activated carbon to study allelopathy, and to include a discussion of that issue in their interpretation of their findings.

Furthermore, I think it is highly likely that the number of fairly high-profile retractions and corrections associated with a scientific fraud investigation may have also contributed to a decrease in research on allelopathic interactions in plant community ecology. Your manuscript is an importance place to mention those problems for full transparency. For example, see https://retractionwatch.com/2016/03/03/sample-tampering-leads-to-plant-scientists-7th-retraction/ about catechin, and https://retractionwatch.com/2015/09/02/nsf-investigation-of-high-profile-plant-retractions-ends-in-two-debarments/ about catechin as well as other research. For papers to cite to back up a few sentences regarding scientific fraud in the field, the ones by Laura Perry mentioned in the retraction watch article, as well as Blair et al. 2005 Ecology Letters (again, on which I am a co-author) would be appropriate. I feel strongly that the issues in some of the research on allelopathy are by no means only technical, as you currently imply.

While I think the above suggestions and comments are important in revising the paper to have the most impact on the discipline, I think that the modifications should be fairly easy to make.

I firmly believe that there is sound scientific evidence that allelopathy is an important plant-plant interaction. By addressing the issues that have occurred directly, if briefly, questions and concerns can be allayed, and the sound scientific evidence will carry the weight it is due.

Best wishes, and thanks for a really nice, clear and compelling read.
Ruth Hufbauer