This study was a really good example of a home-away growth experiment, and showed some really striking results. Seeds from Pinus contorta trees of known provenance were collected in Sweden, and then grown in soil from their native Canadian sites and their introduced
Swedish sites to look for differences in aboveground and belowground biomass. Sounds simple? It would be, but they didn’t just compare fresh soils containing whatever biota could contend with the 2mm sieve. They also used sterilised soils from both countries, sterilised soils which had been cross-inoculated with soils from the opposite country, and included a fertilisation element to make it more interesting.
So what was the take-home message? The clue is in the title, but the short version is that it’s all about the soil biota. Seedlings grown in Swedish soils had much higher biomass (around 43% higher) than those grown in native their native Canadian soils, despite the Swedish soils having lower pH and nutrient availability. When seedlings were grown in sterilised soils, the soil origin had no effect on biomass. When seedlings were grown in sterilised soil from either country, but inoculated with soil biota from Sweden, biomass was again much greater than when sterilised soils were inoculated with Canadian soil biota. The effect of soil biota was even greater than the effect of fertiliser on biomass.
Considering these different trials together, it becomes clear that not only did the Swedish biota have a strong positive effect on P. contorta seedling biomass, but that the Canadian biota actually had a negative effect on biomass. This provides evidence that better growth in soils from outside of the native range is probably down to a combination of pathogen release and positive biotic associations.
However, this evidence also highlights the gap in this paper – analysis of the soil biota itself. We see the effects, but what are the actual differences in the bacterial, fungal, and/or mesofaunal communities? Are there differences in community structure? Abundances or biomass? Activity? All of these? It would be great to see data on this, especially regarding known pathogens or ectomycorrhizal fungi associates. I hope/suspect there may be another paper on the way exploring some this.
Overall, this was a really nicely designed project that asked interesting questions and addressed them in a very straightforward way. The paper itself was well written. It flows nicely and is easy to follow and understand even on a quick reading. The methods made no attempt to disguise the logistical issues associated with transporting soils half way around the world, and the data analysis and presentation was simple and direct with no unnecessary frills or risk of misinterpretation. All of these are elements that we should expect of any paper, but sometimes experiments are complex and difficult to describe, methodological detail gets glossed over in an attempt to meet word counts, and data are not easy to interpret. While it is not possible to answer all questions with a glasshouse study, or to present all data with bar graphs, it is a nice reminder of the clarity with which we should try to communicate our work.
So now that I’ve had my say, exposing my soil ecology and science communication biases, we’d love to hear what you thought about the paper. Was there anything you would have done differently? What do you think the next steps should be? What did you think of the tree provenance element of the study? It didn’t show a significant effect here, but would it be worth pursuing in other systems? How well do you think the results of this glasshouse study represent what’s happening in the natural communities?
You can let us know your take on this either in the comments or via twitter using the hashtag #psejclub. We’d also love to hear from you If you have a suggestion for a paper you’d like us to discuss, or if you want to write a post yourself!