Roots at work: Root responses to heterogeneity of soil biota

Background/Question/Methods

The positive correlation between biodiversity and productivity of grasslands has so far been attributed to resource complementarity of plant species. Here, we examine whether this phenomenon of overyielding can be explained by a more recently proposed hypothesis: higher productivity of more diverse plant communities is determined, in part, by the composition of soil biota communities. An experiment using soils trained with soil biota of four different plants and a proportional mixture of these soils showed that in monocultured soils, plant productivity was reduced compared to mixture soils, but restored by soil sterilization. Particular apparent was the growth of the grass species Anthoxanthum odoratum that was substantially promoted on Leucanthemum vulgare soil, showing species specificity of soil biota. Plants create soil legacies: a patchy soil, not only with nutrients, but also with species-specific soil biota. While the influence of patchy nutrients on root growth behaviour is well studied we do not know whether roots can also choose between patches of different soil biota. To investigate this, we performed two short-term experiments in a climate chamber with non-sterilized and sterilized treatments and homogeneous and heterogeneous distributions of soil biota. 

Results/Conclusions

As in the previous experiment, plants produced more biomass when growing in sterilized compared to non-sterilized soils. Productivity was higher when plants were confronted with heterogeneous distributions of soil biota than with homogeneous distributions, while no differences in biomass occurred between these distributions if soil biota were absent. Selective placement of roots in nutrient hotspots can lead to higher productivity in soils with heterogeneous nutrient distributions. In our experiment with heterogeneous soil biota, however, no differences in rooting placement occurred, as the amount of roots was similar in all compartments. Root activity of the roots measured by rates of 15N uptake, however, did differ with, in general, higher uptake rates in compartments containing soil biota of other species.

Our results suggest that root physiological responses to distributions of species-specific soil biota are more important than morphological responses. Root activity changes locally as a result of the interaction of these roots with the species-specific soil biota present in that patch, resulting in higher plant productivity when soil biota are heterogeneously distributed.