Grassland community dynamics are altered within the same growing season following nutrient addition and disturbance

Authors: Rowley, David; FAY, PHILIP - Retired ARS Employee; Flynn, Kyle; MARTINA, JASON - Texas State University; TREADWELL, MORGAN - Agrilife Research; ROGERS, WILLIAM - Texas A&M University

Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 11/8/2022
Publication Date: 2/14/2023
Citation: Rowley, D.W., Fay, P.A., Flynn, K.C., Martina, J.P., Treadwell, M.L., Rogers, W.E. 2023. Grassland community dynamics are altered within the same growing season following nutrient addition and disturbance [abstract]. Society for Range Management Meeting Abstracts, Boise, ID, February 12-16, 2023.

Interpretive Summary: Global change drivers are reducing grassland plant diversity and altering community dynamics. Environmental nutrient influx and disturbance from changing land use practices are two prominent and pervasive drivers of change in grassland systems. We quantified the effect of these mechanisms on grassland community assembly and productivity by setting up an experimental Disturbance and Resources Across Global Grasslands (DRAGNet) site at the Grassland Soil and Water Research Laboratory (GSWRL – Temple, TX USA). The field site consists of 25, 5 m x 5 m plots, arranged in a 5 x 5 Latin square design. Treatments included: (1) Control (C), (2) nitrogen, phosphorus, potassium, and micronutrients addition (NPKµ), (3) disturbance (D), (4) NPKµ + D, and (5) NPKµ cessation (not used in this analysis). The disturbance treatment was carried out in January 2022, while nutrient addition was administered in April 2022. Precent cover surveys were taken monthly in all plots between March – September 2022, and biomass clippings were collected once in June and once in October 2022. Nonparametric multidimensional scaling (NMDS) analysis indicated treatments were significantly dissimilar to each other, and community composition was dependent on treatment type. Total diversity decreased across all treatments relative to the control. Productivity was highest in both nutrient addition treatments (NPKµ and NPKµ+D) but was significantly reduced in the disturbance (D) treatment. Nutrient addition alone resulted in increased cover and productivity in grasses - primarily from an increase in invasive Sorghum halepense cover. Paired nutrient addition and disturbance caused total species turnover and significant reduction in grass and legume cover, but significantly increased the cover and productivity of noxious Ambrosia trifida. Our results indicate grassland plant community dynamics, both cover and productivity, can quickly respond to environmental changes in nutrients and disturbance.

Technical Abstract: Global change drivers are reducing grassland plant diversity and altering community dynamics. Environmental nutrient influx and disturbance from changing land use practices are two prominent drivers of change in grassland systems. We anlayzed the effect of these managements on grassland community assembly and productivity. Treatments included: (1) Control (C), (2) nitrogen, phosphorus, potassium, and micronutrients addition (NPKµ), (3) disturbance (D), (4) NPKµ + D, and (5) NPKµ cessation (not used in this analysis). Precent cover surveys were taken monthly in all plots between March – September 2022, and biomass clippings were collected once in June and once in October 2022. Treatments were significantly dissimilar to each other, and community composition was dependent on treatment type. Total diversity decreased across all treatments relative to the control. Productivity was highest in both nutrient addition treatments (NPKµ and NPKµ+D) but was significantly reduced in the disturbance (D) treatment. Nutrient addition alone resulted in increased cover and productivity in grasses - primarily from an increase in invasive Sorghum halepense cover. Paired nutrient addition and disturbance caused total species turnover and significant reduction in grass and legume cover, but significantly increased the cover and productivity of noxious Ambrosia trifida. Our results indicate grassland plant community dynamics, both cover and productivity, can quickly respond to environmental changes in nutrients and disturbance.