Project Number: 3098-21600-001-067-N
Project Type: Non-Funded Cooperative Agreement
Start Date: May 1, 2020
End Date: Apr 30, 2024
1. Examine long-term expression of nutrient limitation in native C4 grassland by re-commencing sampling of the existing Nutrient Network site at USDA-ARS Temple, Texas. 2. Establish the DRAGNet experiment at USDA-ARS Temple, Texas.
Objective 1: Terrestrial ecosystem productivity is widely accepted to be nutrient limited, and many studies have focused on limitation by a single nutrient, nitrogen (N). However, the global extent and magnitude of multiple limitation by nutrients other than N and P remains poorly understood in grasslands. Furthermore, limitation by nutrients may vary from year to year as water availability varies with annual rainfall inputs, and water x nutrient interactions may be further contingent on the presence of abiotic drivers such as fire. Understanding the interactions of nutrient limitation and precipitation variability and the contingent effects of fire in grasslands requires long-term experiments. The GSWRL Nutrient Network experiment started in 2008 and was sampled continuously using Nutrient Network standardized protocols through 2016. The experiment used the standardized plot design, fertilization treatments, and sampling protocols designated for all Nutrient Network sites. Fertilization treatments have been applied in subsequent years even though sampling has not been conducted. Texas State University collaborators will resume sampling of the temple.us experiment in 2020, continuing the protocols used during 2008-2016 to ensure continuity of data quality. The management regime of the site containing the Nutrient Network experiment has been to mow and remove previous years senescent plant material each spring prior to active plant growth. This regime will be changed to one of spring burning during the course of this agreement. Up to three years of sampling will be conducted under the current practice, and spring burning will be implemented once all collaborators are confident that continuity of data quality has been verified by comparison of 2020 and 2021 data to the historical dataset from 2008-2016. Prescribed burning will be conducted by collaborators from Texas A&M University under terms specified in a separate agreement. Objective 2: The overarching goal of DRAGNet is to assess the generality and site-specificity of factors influencing disturbance recovery and community assembly in herbaceous-dominated ecosystems by testing whether assembly, recovery rate, or trajectory in herbaceous-dominated plant communities interacts with environmental nutrient enrichment. This experiment is widely relevant because habitat loss via land conversion for agriculture is a leading cause of extinctions, and biodiversity in grassland systems is especially vulnerable to land conversion. The DRAGNet experiment at GSWRL will be located in the same native C4 grassland as the existing Nutrient Network experiment. Plots will be defined in a randomized complete blocks design, with 3 to 5 blocks each containing five, 5 x 5 m plots. Plots will receive either long-term nutrient addition, a physical disturbance, nutrient addition combined with disturbance, short-term nutrient addition, or no treatments (controls). The experiment will receive the same regime of mowing and then burning as the NutNet experiment.