In my latest paper, Extensive management promotes plant and microbial nitrogen retention in temperate grassland, published in PLoS ONE last month, we show that traditionally managed, species rich haymeadows lose less nitrogen with drainage water from their soils than more intensively managed grasslands. This is important, because nitrogen that leaches from the soil can pollute ground and surface water, reduce plant species diversity, and cause problems for human health if concentrations in drinking water are getting too high.
In this paper, we used both extensive field observations and a mechanistic glasshouse experiment to show that traditional haymeadows have lower nitrogen leaching because of more uptake of available nitrogen in plant roots and in microbes. Specifically, we found that a greater biomass of soil fungi increased microbial nitrogen uptake, and that this in turn increased the retention of nitrogen retention in soil.
These results confirm an ecological theory, namely that ecosystems with a more fungal-dominated microbial community are more efficient in their nitrogen cycling, and have thus lower nitrogen losses. This is not a novel theory at all – in fact, it is often assumed to be true, but it has never before been experimentally tested. To illustrate this, in this Science paper, it is said that ‘Because fungal-based soil food webs promote less leaky nutrient cycles that are more retentive of nutrients than do bacterial-based food webs…’ and subsequently, a paper by Coleman et al. from 1983 is cited. However, on further inspection, this appears to be a review paper, which by no means proves that this theory is correct. Moreover, it is not possible to adequately test this theory, since it is not possible to take the microbial community out of its environment, and thus it is impossible to test whether it is the composition of the microbial community that is responsible for lower nitrogen leaching, or its environment, for example the amount of organic matter in the soil.
Still, I believe that the approach that we used in this paper goes a long way in confirming this theory. We showed, using a field survey across 22 grasslands in the North of England, that nitrogen leaching is lower in traditionally managed haymeadows with more fungal-dominated microbial communities than intensively managed grasslands. Then, in a glasshouse experiment, we added labelled nitrogen to intact soil columns from a subset of eight grasslands, and we traced this nitrogen into the different soil pools. Here, we found that nitrogen uptake in roots and microbes was highest in traditionally managed haymeadows. Moreover, using model selection, we found than the biomass of fungi, and the biomass of fungi relative to that of bacteria, were the best predictors for microbial nitrogen uptake, and for nitrogen leaching. That is, microbial nitrogen uptake was greater, and leaching from soil was lower, when more fungi were present.
However, in our paper we are not just trying to test an ecological theory. Knowledge on the controls of ecosystem nitrogen retention is crucial to make agriculture more sustainable; after all, we want expensive fertilisers to be taken up by the crop, and not to cause environmental problems elsewhere! Our study is a, small, but important step towards understanding the role of the microbial community in ecosystem nitrogen retention.
Importantly, the paper has received a lot of coverage on the internet, for example here, here, and here, and the BBC might potentially be interested (fingers crossed!). Moreover, the paper has been recommended by Faculty of 1000 – it received a two star rating with the tags Interesting Hypothesis and New Finding.
But, now my point: you wouldn’t believe how difficult it was to get this paper published! OK, being rejected by the big three is not necessarily too disappointing and can happen to the best. But, from the next two journals, I felt that the reviewers simply refused to believe the results. They suggested alternative mechanisms that could be playing a role – that I had tested – and they pinpointed the correlative nature of the link between fungi and N retention – which I acknowledged. Moreover, some reviews were actually quite positive, but still the editor chose to reject my paper, which makes me wonder whether the reviewers were more negative in their confidential comments to the editor. Of course, I could have challenged the decision of the editor, but with this in mind, I was wondering whether that would be a waste of energy. After all, I can find it very discouraging to get negative reviews back on a paper that you put your heart and soul in!
I have the impression that reviews are getting harsher, and I know that colleagues are feeling the same. The frequency of unreasonably harsh, and sometimes bitter, or resenting, reviewers is increasing, and I wonder why. Is it because the pressure to publish, particularly in high impact journals, is ever increasing? Is it because scientists tend to jump on hot topics, because they are more likely to get funded, or just because of being a young scientist, pissing off people who have been working in a particular area for years (why should this person publish on my topic in this high impact journal)? Anyway, this is a discussion in its own right, which I might want to expand on later. The bottom line is that my paper got published in PLoS ONE, which is a great journal, and the open access structure means that anyone – anyone! – can access and read my paper. Here.