Nitrogen and phosphorus availability alter tree-grass competition intensity in savannas

Plant essential macronutrients like nitrogen (N) and phosphorus (P) can limit savanna tree growth and are important determinants of savanna vegetation dynamics, along with rainfall, fire, and herbivory. How nitrogen and phosphorus shape tree-grass competition and their coexistence remain unclear, hindering our ability to predict how savannas may respond to altered nutrient cycling.
Here, we evaluate (1) if trees and grasses respond differently to N vs. P availability, or (2) if grasses are more competitive in low nutrient environments while trees are more competitive in high nutrient environments. To do this, we grew saplings of 6 tree and 1 grass species from Kruger National Park, South Africa, for 16 weeks under fully factorial nutrient and competition treatments (with/without competitors, low/high rate of N supply, and low/high rate of P supply) under a watering regime designed to mimic wet season rainfall in a mesic savanna.
Trees and grasses foraged most aggressively for nitrogen a..., The primary goal of the experiment was to understand how trees and grasses respond to different nutrient and competition regimes. Six tree species and one grass species were selected based on phylogenetic diversity and nitrogen fixation ability for this experiment (Table 1). The grass species chosen for this experiment was Melinis repens, the only annual grass species common in Kruger National Park (Wigley-Coetsee and Staver 2020), one of the largest natural reserves that is situated in the low-lying savannas of South Africa.
Plants were grown in a full-factorial nutrient-addition experiment with water availability held constant across treatments. Each pot was watered three times a day for a total of 400 mL per day, designed to mimic a wet growing season in the Pretoriuskop region of Kruger National Park, which receives about 750 mm of rainfall per year. The four nutrient treatments were (1) low N and P (), (2) high N and low P (), (3) low N and high P (), and (4) high N and P (). These..., , # Nitrogen and phosphorus availability alter tree-grass competition intensity in savannas

## Description of the data and file structure

There are two files: treedata.csv and grassdata.csv. The tree data file contains all data for tree species in the experiment while the grass data contains all data for grass species.

## Tree Data Column Names

Pot = pot number in experiment

Species = Species Code

Block = Block in the randomized block design

NTrt = nutrient treatment. C = low N + low P, N = high N + low P, P = low N + high P, NP = high N + high P

GTrt = grass treatment. G- = without grass, G+ = with grass

Sample_ID = sample ID used for phosphatase enzyme assays

RSDiam = Basal diameter of tree (in cm)\
Diam10cm = tree diameter at 10 cm (if tall enough) in cm

StemHt = stem height in cm

RootLn = root length in cm

RootDiam = root diameter in cm

FPARBase = FPAR (nm of light) at the base of the tree

FPARTree = FPAR at tree canopy height

FPARGrass = FPAR at grass sward height

...