LB 7-59 - Soil chemistry and function in a tallgrass prairie restoration

Background/Question/Methods:

Historical land uses can have long lasting impacts on ecosystem functioning including altering local soil nutrient cycling and loss of native biodiversity. Restoration practices are often hindered by these legacy effects which can take decades to remedy. To investigate how tallgrass prairie restoration impacts soil chemistry and function, we examined soil nutrients and function in an experiment at the Morton Arboretum that includes 127 tallgrass prairie species planted in both polycultures and monocultures. Polycultures were planted with varying levels of both plant phylogenetic and trait diversity. We hypothesized that polycultures would increase soil carbon more quickly than monocultures and would have increased soil function due to the increased diversity of carbon inputs to the soil. Within monoculture plots, we hypothesized that different plant groups would vary significantly in their N use strategies due to the wide range of life histories represented in the monocultures.

Results/Conclusions:

Plots differed in total carbon (TOC) and nitrogen (TN) and inorganic N pools (p >0.05). Polycultures had higher TOC pools whereas monocultures had larger TN pools. They differed in N mineralization and nitrification rates (p >0.05) with monocultures having larger TN and inorganic N pools as well as faster N mineralization and nitrification rates. Polycultures had no differences with varying phylogenetic nor trait diversities. Monocultures were subdivided into three groups, graminoids, legumes and forbs. TOC varied by group (p >0.05), with graminoids and legumes being similar and forbs varying widely. No N measure varied by group which was contrary to our hypothesis. All other measures, with the exception of organic N, varied by plant family in monoculture plots (p >0.05). This could mean that the idea of functional redundancy within plant communities is overstated and a wider variety of plant species will create better ecosystem functioning. Increased N pools in monocultures suggests that polycultures are relatively more N limited, which could be caused by increased competition. Higher TOC in polycultures suggests that increased diversity of C inputs increases soil C stores faster than monocultures, which could overcome land use legacy effects faster than single species restorations.