NUT01 Nutrient Network: Investigating the roles of nutrient availability and vertebrate herbivory on grassland structure and function at Konza Prairie


The goals and focal research questions are copied below from the Nutrient Network website. More information can be found at nutnet.org.

NutNet focal research questions: (1) How general is our current understanding of productivity-diversity relationships? (2) To what extent are plant production and diversity co-limited by multiple nutrients in herbacoues-dominated communities? (3) Under what conditions do grazers or fertilization control plant biomass, diversity, and composition?

NutNet goals: (1) To collect data from a broad range of sites in a consistent manner to allow direct comparisons of environment-productivity-diversity relationships among systems around the world. This is currently occurring at each site in the network and, when these data are compiled, will allow us to provide new insights into several important, unanswered questions in ecology. (2) To implement a cross-site experiment requiring only nominal investment of time and resources by each investigator, but quantifying community and ecosystem responses in a wide range of herbaceous-dominated ecosystems (i.e., desert grasslands to arctic tundra).

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The NutNet methods used at Konza are copied below, modified from the Nutrient Network website. More information can be found at nutnet.org/methods.

1. Site Selection: The Konza NutNet site was selected to be relatively homogeneous (i.e., not encompassing large gradients), dominated by herbaceous vegetation, and representative of the tallgrass prairie ecosystem.

2. Observational Study: The observational data is composed of the pre-treatment sampling of all 30 experimental plots described below. At Konza, this data was collected in 2007.

3. Experimental Design: The core experiment was set up in a completely randomized block (environmental gradient) design with three blocks, 10 treatments per block, and three replicates per treatment (N=30 total experimental units). Each experimental unit are 5 x 5 m in size, with 1-m walkways between plots and 2-m walkways between blocks. The corners of the plots are permanently marked.

Experimental units are subdivided into 4 2.5 x 2.5 m subplots (designated A,B,C,D). These four subplot are assigned to be used for the core sampling, site-specific studies, or one of two possible future studies. Each of the four 2.5 x 2.5 m subplots is further subdivided into 4 1 x 1 m sub-subplots (1,2,3,4). Thus a specific location in the plot is designated by number, letter, number combination (e.g., 21A2, 13B4, etc).

To assess multiple resource limitation, three nutrient addition treatments (Nitrogen, Phosphorus, Potassium plus Other nutrients), each with two levels (Control, Added), are crossed in a factorial design, for a total of 8 treatment combinations. Nitrogen was added in the form of ammonium nitrate in 2008 and time-released urea thereafter. Phosphorus is added in the form of super phosphate, and potassium is added in the form of potassium sulfate. Each nutrient is applied at 10 g m-2 in the spring of each year.

In addition, there is an herbivore fencing treatment, in which the entire 5 x 5 m plot will be fenced to exclude most herbivores. This treatment is crossed with the Control and NPK+ treatments to assess top-down vs. bottom-up effects on community structure and function.

4. Core Sampling Methodology - The core sampling 2.5 x 2.5 m subplot is divided into four 1 x 1 m permanent subplots, surrounded by a 0.25 m buffer. One of these permanent 1-m2 subplots is designated for plant species composition sampling and the other three for destructive sampling. Core sampling includes aboveground standing crop (sorted to at least three functional groups), percent cover of all plant species, and light availability measurements. All of these core measurements was collected from all plots prior to initiation of the experiment and in each year of the experiment, using the same methodology as all NutNet sites.

Nut011- Plant Species Composition

Percent aerial cover was estimated in one permanently marked 1-m2 subplot within the core-sampling subplot. Aerial cover was estimated for each plant species separately using a modified Daubenmire method (Daubenmire 1959), in which cover is estimated to the nearest 1% percent for each species rooted within the plot. Percent cover was also estimated for bare soil, animal diggings/disturbance, and rocks if present. Note that total cover will typically exceed 100% because species cover is estimated independently for each species.

Within-season sampling frequency was adjusted based on the phenology of the component species in order to capture the maximum cover of each species. Species composition was measured in the spring (late-May) and again in the fall (late-Aug) to capture maximum relative cover of early-season C3 forb and grass species and late-season C4 forb and grass species, respectively.

NUT012 - Aboveground Standing Crop

Aboveground standing crop was estimated destructively by clipping at ground level all aboveground biomass of individual plants rooted within a 0.2 m2 (two 20 x 50 cm strips) area. Biomass was clipped within the 1-m2 subplots designated for destructive sampling within the core sampling subplot. Location of the quadrats was noted to prevent resampling during the duration of the study. For shrubs and subshrubs rooted within the quadrat, leaves and current year’s woody growth were collected.

Standing crop was separated into the following categories: 1. previous year's dead, 2. current year's graminoid (grasses, sedges, rushes), 3. current year's forbs, and 4. current year's woody growth. All biomass was dried at 60oC for 48hrs prior to weighing to the nearest 0.01 g.

Notes: 2013 biomass data are not available due to sample mixed up.

NUT013 - Light Availability

Light availability was measured using a light meter (1-m length ceptometer) capable of integrated measures of photosynthetically active radiation (PAR, mol m-2 sec-1). Light availability was measured at the same time and in the same 1-m2 subplot used for the species composition measurements. Light readings were taken on a cloudless day as close to solar noon as possible (i.e., 11 am to 2 pm). For each subplot, two light measurements at ground level (at opposite corners of the 1-m2 plot, diagonal to each other) and one to two above the canopy were taken. Light availability was calculated as the ratio of PAR below and above the canopy.

Notes: light data are not collected for year of 2011-2013, and 2015-2018.

For list of Species code used, please check species list in Excel version
For the NutNet Experiment treatment map, please check NutNet Treatment
For additional metadata information see: http://lter.konza.ksu.edu/sites/default/files/DC.pdf
For additional methods information see: http://lter.konza.ksu.edu/sites/default/files/MM.pdf

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