Immediate changes to grassland community composition after disturbance and nutrient addition

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: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/11/2022
Publication Date: 8/23/2022
Citation: Rowley, D.W., Fay, P.A., Flynn, K.C., Martina, J.P., Treadwell, M.L., Rogers, W.E. 2022. Immediate changes to grassland community composition after disturbance and nutrient addition [abstract], North Platte, NE, August 23-25, 2022.

Interpretive Summary: Global grassland plant diversity is declining in part from chronic elemental nutrient influx and large-scale disturbances via changing land use practices. To better understand the mechanisms and trajectory of change, we set up an experimental disturbance and nutrient management study at the Grassland Soil and Water Research Laboratory (GSWRL – Temple, TX USA). Treatments analyzed included: (1) Control (C), (2) nitrogen (N), phosphorus (P), potassium (K), and micronutrients (µ) addition (NPKµ), (3) disturbance (D), and (4) NPKµ + D. The disturbance treatment was carried out in January 2022, while nutrient addition was administered in April 2022. Species composition surveys, precent cover of each species, were collected monthly in all plots between March – September 2022. Diversity in C, NPKUµ, and D treatments peaked in May, whereas diversity in the NPKµ+D treatment peaked in June. Total diversity decreased across all treatments relative to the control. C3 grass and legume cover decreased in all treatments. Nutrient addition alone resulted in increased C4 grass cover. Paired nutrient addition and disturbance caused total species turnover, complete loss of C3 grasses, significant reduction in C4 grass and legume cover. Our results indicate grassland plant communities may be extremely susceptible to changes in nutrients and disturbance, and these changes can take place in a single growing season.

Technical Abstract: Global grassland plant diversity is declining in part from chronic elemental nutrient influx and large-scale disturbances via changing land use practices. To better understand the mechanisms and trajectory of change, we set up an experimental Disturbance and Resources Across Global Grasslands (DRAGNet) field 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 (N), phosphorus (P), potassium (K), and micronutrients (µ) 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. Species composition surveys, precent cover of each species in a 1m2 subplot, were taken monthly in all plots between March – September 2022. Nonparametric multidimensional scaling (NMDS) analysis indicated treatments were significantly dissimilar to each other and community composition was dependent on treatment type. Diversity in C, NPKUµ, and D treatments peaked in May, whereas diversity in the NPKµ+D treatment peaked in June. Total diversity decreased across all treatments relative to the control. C3 grass and legume cover decreased in all treatments. Nutrient addition alone resulted in increased C4 grass cover - primarily from an increase in invasive Sorghum halepense cover. Disturbance alone increased both Sorghum halepense and noxious Ambrosia trifida cover. Paired nutrient addition and disturbance caused total species turnover, complete loss of C3 grasses, significant reduction in C4 grass and legume cover, and created near monocultures of Ambrosia trifida. Our results indicate grassland plant communities may be extremely susceptible to changes in nutrients and disturbance, and these changes can take place in a single growing season.