Comparison of the current study (VFE) with the Park Grass experiment.

<p>Details of the Park Grass experiment as from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177208#pone.0177208.ref009" target="_blank">9</a>].</p

Multiple regression of the phytomass of the seven most common species against soil and light parameters across all plots.

<p>(a) Soil nitrogen, pH, soil microbial respiration, organic carbon and PAR. (b) The same variables as well as species richness and biomass per plot. β values are standardized coefficients. The absolute value of β coefficients are an index of the importance of that variable as long as it is significant. The r² values are coefficients of determination of all the variables. ΔAIC = change in AIC from multiple regression containing soil and light variables only. Note that there is an increase in the r² value in all cases in (b) relative to (a) for each species. ΔAIC < 2 in the cases of <i>E</i>. <i>curvula</i> and <i>E</i>. <i>plana</i> (Table 4b), which is conventionally viewed as an insufficient improvement over the models in Table 4a (Burnham & Anderson 2002). PAR = photosynthetically active radiation.</p

There was a significant effect of nitrogen form and level of nitrogen application on species richness.

<p>There was a more negative effect on species richness of acidic ammonium sulphate fertilization (NH4—solid circles •) with increasing level of fertilization than for LAN (X). Highest species richness was for the control (no treatment—open square □).</p

There were significant correlations between phytomass of <i>Panicum maximum</i> per plot and ANPP, species richness and photosynthetically active radiation.

<p>a) There was a significant positive correlation (r = 0.87) between phytomass of <i>Panicum maximum</i> per plot and total biomass (ANPP) across all plots. b) There was a significant negative correlation (r = -0.38) between phytomass of <i>Panicum maximum</i> per plot and species richness. c) There was a significant negative correlation (r = -0.61) between phytomass of <i>Panicum maximum</i> per plot and photosynthetically active radiation (PAR), measured as % sunlight reaching just above the substrate.</p

There was a significant additive effect on mean (± 95% C.I.) Aboveground Net Primary Production (ANPP) of nitrogen and phosphorus fertilization.

<p>N+P = nitrogen + phosphorus fertilization.</p

Generalized linear model analyses of effects of fertilizer.

<p>These fertilizers are nitrogen form (control, limestone ammonium nitrate (LAN) and ammonium sulphate), nitrogen level (0 (control), 7.1, 14.1 and 21.2 g m^-2), phosphorus (0 (control), 33.6 g m^-2) and lime (0 (control), 225 g m^-2) on (a) Aboveground Net Primary Production (ANPP), (b) species richness, and (c) species diversity (Shannon-Wiener H’). Nitrogen level was nested {} within nitrogen form.</p

There was a significant interaction effect between nitrogen form and lime application on species richness.

<p>The effect of lime (X) was to increase species richness relative to the nitrogen form (particularly noticeable with the ammonium sulphate (NH4) fertilization). However, the control (no treatment) had the highest species richness. LAN = limestone ammonium nitrate. Control lime is indicated by solid circles (•).</p

Generalized linear model analysis of fertilizers on the phytomass of the seven most abundant species.

<p>We measured the effects of nitrogen form (Control, LAN and ammonium sulphate), nitrogen level (0, 7.1, 14.1 and 21.2 g m^-2), phosphorus (0 (control), 33.6 g m^-2) and lime (0 (control), 225 g m^-2) and their interactions on phytomass (k ha^-1) of the seven most abundant grass species, <i>Themeda triandra</i>, <i>Tristachya leucothrix</i>, <i>Setaria sphacelata</i>, <i>Eragrostis curvula</i>, <i>E</i>. <i>plana</i>, <i>Panicum maximum</i> and <i>Aristida junciformis</i>. {} = nested factor. χ² = Wald’s χ².</p

There was a significant positive relationship between species richness and soil pH.

<p>However, this relationship was better explained by a piecewise regression. We have used a LOWESS plot here, with a threshold at a pH of about 4.5.</p

There was a significant interaction effect between nitrogen form and phosphorus fertilization on mean (± 95% C.I.) Aboveground Net Primary Production (ANPP).

<p>Nitrogen forms were control, limestone ammonium nitrate (LAN) and ammonium sulphate (NH4). Control phosphorus is indicated by solid circles (•) and the phosphorus fertilization by X.</p