Bison grazing increases grass foliar nutrients and drought tolerance at fine spatial scales

Abstract Aims The American bison is often recognized as an ecological engineer because their grazing and wallowing behavior increases plant diversity and productivity. These disturbances increase spatial heterogeneity and can alter plant nutrient and water dynamics. We assessed how bison grazing and wallowing affect grass chemistry and physiology, and whether grass evolutionary legacies mediate species-specific responses. Methods We measured grass drought tolerance, photosynthetic activity, and foliar and soil chemistry in four grass species at Konza Prairie Biological Station (Kansas, USA). Species included two dominant C 4 panicoids, one C 3 panicoid, and one C 4 chloridoid species that becomes dominant in grazed areas. We sampled grasses in grazed areas near and away from bison wallows and adjacent fenced areas that have excluded bison for over 30 years. We assessed intra-annual changes in turgor loss point, maximum leaf electron transport rate, foliar δ 13 C, and C, N, P, and K content. Results Soil nutrient concentrations did not vary across locations, but foliar P, K, and N content was highest near bison wallows. Higher foliar N in bison grazed areas was correlated with higher electron transport rate. The chloridoid species showed the greatest response to bison wallows, with lower turgor loss point and higher foliar nutrients near wallows than in adjacent grazed prairie. Conclusion Our results demonstrate that bison grazing creates fine-scale heterogeneity that alters plant nutrient dynamics, photosynthetic capacity, and drought tolerance. These findings suggest that bison engineer ecosystems not only through changes in plant communities but also through the physiological responses of dominant grass species.