By Josh Friell, Ph.D. candidate
It seems nowadays that we are bombarded with messages about the need to maintain ecosystem services and function…that we need to maintain biodiversity because it’s good for the ecosystem being studied. In fact, it probably seems like they’re so ubiquitous that they’ve become just more buzz words used to grab attention or sell a product. But what does that really mean? Are these things actually being measured, and if so what is the measurement? Well, I suppose that depends. One of the benefits of turfgrass that we often tout is its ability to significantly reduce soil erosion – that is, perform an ecosystem service. But what types of data support that? Certainly there are measurements of soil loss from plots through runoff, but that’s just the result of erosion that has already occurred. Erosion is actually a function of soil aggregation and deflocculation – that is, how well the soil particles stick together or how quickly they fall apart. The greater the aggregate strength, the less soil erosion we tend to see. So does increasing biodiversity really improve this ecosystem service? That’s exactly what the authors of a recent study – Mechanisms linking plant community properties to soil aggregate stability in an experimental grassland plant diversity gradient1 – set out to show.
To accomplish this, plots were planted with a random combination of 1, 4, or 16 species. The plant species used were categorized into one of four plant functional groups including grasses, small herbs, tall herbs, and legumes. Soil samples were taken that could be analyzed for aggregate stability using a number of wetting methods including fast wetting, slow wetting, and wetting with shaking to simulate the mechanical wear induced by raindrop impact. Earthworm biomass, root biomass, soil organic carbon, and soil microbial biomass were considered in the analysis, but the primary factor of interest was plant species richness.
By and large, the factors affecting soil aggregate stability were consistent across all measures of stability. In addition, it was evident that the presence of grasses in the mixtures significantly increased soil aggregate stability while the presence of legumes generally decreased stability. Although the affect of grass species diversity was not evaluated, it can be generalized from the data that increased diversity of any type is good in one way or another. The effect of grass on aggregate stability was primarily attributed to an increase in root biomass, but their diversity is also known to increase microbial populations and diversity and likely affects extracellular enzyme concentrations and function.
In this study it was shown that grasses can indeed lead to a decrease in soil erosion by acting at the aggregate level. This has a number of implications for our industry. First and foremost it lends further credence to our continuing claim that we can reduce soil erosion by establishing turfgrass. Also, it highlights the clear lack of specific scientific knowledge pertaining to the effect of turf sward species richness on ecosystem service provision. Future work in this area, in combination with other recent studies surrounding microbial populations and alternative species use can provide a direction for future research towards identifying improved turfgrass ecology practices.