Effects of anabolic and catabolic nutrients on woody plant encroachment after long-term experimental fertilization in a South African savanna
Date
2017-06-29
Journal Title
Journal ISSN
Volume Title
Publisher
Public Library of Science
Abstract
The causes of the worldwide problem of encroachment of woody plants into grassy vegetation
are elusive. The effects of soil nutrients on competition between herbaceous and woody
plants in various landscapes are particularly poorly understood. A long-term experiment of
60 plots in a South African savanna, comprising annual applications of ammonium sulphate
(146±1166 kg ha-1 yr-1) and superphosphate (233±466 kg ha-1 yr-1) over three decades, and
subsequent passive protection over another three decades, during which indigenous trees
encroached on different plots to extremely variable degrees, provided an opportunity to
investigate relationships between soil properties and woody encroachment. All topsoils
were analysed for pH, acidity, EC, water-dispersible clay, Na, Mg, K, Ca, P, S, C, N, NH4,
NO3, B, Mn, Cu and Zn. Applications of ammonium sulphate (AS), but not superphosphate
(SP), greatly constrained tree abundance relative to control plots. Differences between control
plots and plots that had received maximal AS application were particularly marked (16.3
± 5.7 versus 1.2 ± 0.8 trees per plot). Soil properties most affected by AS applications
included pH (H2O) (control to maximal AS application: 6.4 ± 0.1 to 5.1 ± 0.2), pH (KCl) (5.5 ±
0.2 to 4.0 ± 0.1), acidity (0.7 ± 0.1 to 2.6 ± 0.3 cmol kg-1), acid saturation (8 ± 2 to 40 ± 5%),
Mg (386 ± 25 to 143 ± 15 mg kg-1), Ca (1022 ± 180 to 322 ± 14 mg kg-1), Mn (314 ± 11 to 118
± 9 mg kg-1), Cu (3.6 ± 0.3 to 2.3 ± 0.2 mg kg-1) and Zn (6.6 ± 0.4 to 3.7 ± 0.4 mg kg-1). Magnesium,
B, Mn and Cu were identified using principal component analysis, boundary line
analysis and Kruskal-Wallis rank sum tests as the nutrients most likely to be affecting tree
abundance. The ratio Mn/Cu was most related to tree abundance across the experiment,
supporting the hypothesis that competition between herbaceous and woody plants depends
on the availability of anabolic relative to catabolic nutrients. These findings, based on more
than six decades of experimentation, may have global significance for the theoretical understanding
of changes in vegetation structure and thus the practical control of invasive woody
plants.
Description
CITATION: Mills, A. J., et al. 2018. Effects of anabolic and catabolic nutrients on woody plant encroachment after long-term experimental fertilization in a South African savannah. PLoS ONE, 12(6):e0179848, doi:10.1371/journal.pone.0179848.
The original publication is available at https://journals.plos.org/plosone/
The original publication is available at https://journals.plos.org/plosone/
Keywords
Woody plants -- South Africa, Savanna ecology, Woody plants -- Ecology -- South Africa, Plants -- Effect of minerals on, Chemical reactions -- Analysis, Anabolic nutrients, Catabolic nutrients
Citation
Mills, A. J., et al. 2018. Effects of anabolic and catabolic nutrients on woody plant encroachment after long-term experimental fertilization in a South African savannah. PLoS ONE, 12(6):e0179848, doi:10.1371/journal.pone.0179848