Abstract
We compared the results of a long-term (65 years) experiment in a South African grassland with the world’s longest-running ecological experiment, the Park Grass study at Rothamsted, U.K. The climate is warm and humid in South Africa and cool and temperate in England. The African grassland has been fertilized with two forms of nitrogen applied at four levels, phosphorus and lime in a crossed design in 96 plots. In 1951, about 84% of plant cover consisted of Themeda triandra, Tristachya leucothrix and Setaria nigrirostris. Currently, the dominant species are Panicum maximum, Setaria sphacelata and Eragrostis curvula, making up 71% of total biomass. As in the Park Grass experiment, we found a significant (additive) interaction effect on ANPP of nitrogen and phosphorus, and a (marginally significant) negative correlation between ANPP and species richness. Unlike the Park Grass experiment, there was no correlation between ANPP and species richness when pH was included as a covariate. There was also a significant negative effect of nitrogen amount and nitrogen form and a positive effect of lime on species richness and species diversity. Soil pH had an important effect on species richness. Liming was insufficient to balance the negative effects on species richness of nitrogen fertilization. There was a significant effect of pH on biomass of three abundant species. There were also significant effects of light on the biomass of four species, with only Panicum maximum having a negative response to light. In all of the abundant species, adding total species richness and ANPP to the model increased the amount of variance explained. The biomass of Eragrostis curvula and P. maximum were negatively correlated with species richness while three other abundant species increased with species richness, suggesting that competition and facilitation were active. Consistent with the results from the Park Grass and other long-term fertilization experiments of grasslands, we found a positive effect of soil pH and a negative effect of nitrogen amount on species richness, a more acutely negative effect on species richness of acidic ammonium sulphate fertilizer than limestone ammonium nitrate, a negative relationship between species richness and biomass, and a positive effect on species richness of lime interacting with nitrogen.
Highlights
Priority effects may play a large role in plant communities [1,2,3,4]
Some of the most important results from these last-mentioned studies include the additive response of biomass to fertilization with nitrogen and phosphorus, a negative relationship between species richness and biomass, a negative relationship between species richness and level of nitrogen fertilization, a more negative influence of acidic ammonium sulphate than sodium nitrate fertilization, a strong influence of soil pH on species richness, and the positive effect of liming on species richness
We found a significant effect on species richness of nitrogen form, nitrogen level (Fig 3) and lime (Table 2b) and a significant nitrogen form X lime interaction (Fig 4)
Summary
Priority effects may play a large role in plant communities [1,2,3,4]. The relationships among functional traits, composition and diversity in short-term studies may not reflect vegetation processes in the long-term, because traits of the initial dominants may be unrelated to the long-term outcome of competition [2]. Storkey et al [27] found that the number of species occurring on plots that stopped receiving N fertiliser in 1989 recovered from the negative effects of N fertilization, which was facilitated by liming While some of these results are not unique to the Park Grass experiment [7, 10, 11, 28,29,30,31,32,33,34,35,36,37,38], seldom have all the variables been tested in a single study, and most of these experiments [10, 33, 37, 39] were based on a far shorter time-frame of experimentation
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