Long-Term Grazing and Woody Plant Encroachment Alter C, N, and P Stores and the Structure and Function of Soil Microbial Communities in Juniper-Oak Savanna
Abstract
Semi-arid grasslands and savannas in the southern Great Plains, USA, are utilized extensively for livestock grazing. In this region, Juniperus (juniper) and Quercus (oak) species have increased in abundance during the past 100-150 years, likely in response to intensive livestock grazing and the concomitant decrease in fire frequency. Using a long-term (71 years) grazing experiment on the Edwards Plateau in west-central Texas, we explored the interaction between livestock herbivory (none, moderate, and heavy grazing) and vegetation cover (grassland, juniper, and oak) on concentrations of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP), as well as soil microbial community composition and predicted function. Concentrations of both SOC and TN were 50-150% greater under juniper and oak canopies compared to grasslands, and 10-30% lower in grazed treatments vs. controls. There was a significant vegetation x grazing interaction, with soils under oaks showing greater losses of SOC and TN in grazed areas than those under juniper and grassland. Soil TP was significantly higher in ungrazed controls vs. grazed areas, and higher beneath oak and juniper canopies compared to grasslands. Soil microbial DNA sequencing revealed that both bacterial and fungal community structure were significantly different between all three vegetation types. In contrast, grazing affected only bacterial communities. Non-metric multidimensional scaling indicated that SOC, TN, and TP were the vectors describing the majority of differentiation in bacterial and fungal community structure. Changes in the abundances of bacterial phyla in response to vegetation cover were linked to four key metabolic pathways: energy metabolism, carbohydrate metabolism, terpenoid/polyketide metabolism, and xenobiotic metabolism. These results are among the first to indicate that long-term livestock grazing and woody plant encroachment have both direct and interactive effects on soil C, N, and P storage, and alter the structural and functional attributes of soil microbial communities. In addition, these findings will help guide the incorporation of land cover/land use effects in dryland ecosystems into coupled biogeochemistry-climate models aimed at representing future global change scenarios.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B21K2358B
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0486 Soils/pedology;
- BIOGEOSCIENCES;
- 1622 Earth system modeling;
- GLOBAL CHANGE