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.