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, P - 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: 8/25/2022
Publication Date: 10/20/2022
Citation: Rowley, D.W., Fay, P.A., Flynn, K.C., Martina Jason, P., Treadwell, M.L., Rogers, W.E. 2022. Grassland community dynamics are altered within the same growing season following nutrient addition and disturbance. Society for Range Management Meeting Abstracts [abstract], Denton, TX, October 19-21, 2022.

Interpretive Summary: Global change is reducing grassland plant diversity and altering community dynamics. Elemental nutrient influx and land disturbance are two prominent and pervasive drivers of change in grasslands. We quantified the affects of these mechanisms on grassland community assembly and trajectory 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). Treatments included: (1) Control (C), (2) nitrogen (N), phosphorus (P), potassium (K), and micronutrients (µ) addition (NPKµ), (3) disturbance (D), and (4) NPKµ + D. Precent cover surveys of each species in a 1m2 subplot were taken 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. Our results indicate grassland plant communities may be extremely susceptible to changes in nutrients and disturbance, and these changes can occur within the same growing season.

Technical Abstract: Global change is reducing grassland plant diversity and altering community dynamics. Elemental nutrient influx and land disturbance are two prominent and pervasive drivers of change in grasslands. We quantified the affects of these mechanisms on grassland community assembly and trajectory 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 (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. Precent cover surveys 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 nearly created monocultures of Ambrosia trifida. Our results indicate grassland plant communities may be extremely susceptible to changes in nutrients and disturbance, and these changes can occur within the same growing season.