Science - USA (2020-09-04)

increasing soil age, foliar Si concentrations
showed the opposite pattern. The Jurien Bay
chronosequence is characterized by strong
turnover of plant species ( 34 ), reflecting the
expression of selective edaphic forces acting
on a species-rich regional flora over an eco-
logical time scale ( 23 ). As a result, species
adapted to older, nutrient-impoverished soils
have low foliar concentrations of rock-derived
nutrients ( 24 ) but accumulate Si in their
leaves. Increases in foliar Si concentrations
could be partly attributable to longer leaf life
spans, because Si tends to accumulate as
leaves age ( 35 ), and plants growing on nutrient-
poor soils often increase nutrient-use effi-
ciency by producing longer-lived leaves ( 36 ).
The biological control of the Si cycle during
ecosystem retrogression may also reflect im-
portant Si-based plant functions ( 4 , 5 , 10 ). Re-
duced herbivory through silica deposition
( 5 , 9 ) in plants growing on the older soils
could have adaptive value in these nutrient-
impoverished habitats by minimizing tissue
loss and therefore increasing the mean resi-
dence time of nutrients and nutrient-use ef-
ficiency ( 37 , 38 ). In addition, there is mounting
evidence that Si allows plants to withstand
phosphorus stress ( 7 ), reflected in a high foliar
Si concentration ( 8 ). Therefore, the mainte-

nance of the terrestrial Si cycle by plants in

ecosystems undergoing retrogression suggests

important, but overlooked, beneficial effects in

nutrient-poor environments.

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ACKNOWLEDGMENTS

We thank the Western Australian Department of Biodiversity,

Conservation and Attractions for permission to sample along the

Guilderton and Jurien Bay chronosequences and for access to

these rare biodiverse and outstanding ecosystems. This work

would not have been possible without the invaluable help of

J.-C. Bergen and F. Fontaine, whom we sincerely thank.

Funding:J.-T.C. and F.d.T. were supported by Fonds National de la

Recherche Scientifique of Belgium (FNRS; Research Credit Grant

for the project SiCliNG CDR J.0117.18).Author contributions:

F.d.T. and J.-T.C. formulated research questions. All the authors

designed the field approach. F.d.T., J.-T.C., and G.Z. collected soil

and plant samples. F.d.T. performed the analysis. All authors

discussed the results and contributed to writing the manuscript.

Competing interests:The authors declare that they have no

competing interests.Data and materials availability:All data

needed to evaluate the conclusions of the paper are present in the

paper and/or the supplementary materials.

SUPPLEMENTARY MATERIALS

science.sciencemag.org/content/369/6508/1245/suppl/DC1

Materials and Methods

Supplementary Text

Figs. S1 to S7

Tables S1 to S4

References ( 39 – 46 )

17 April 2020; accepted 17 July 2020

10.1126/science.abc0393

de Tombeuret al.,Science 369 , 1245–1248 (2020) 4 September 2020 4of4

Fig. 4. Mean foliar concentra-
tions of silicon, calcium,
magnesium, potassium, and
phosphorus of mature indivi-
duals of the 10 most abundant
plant species per plot along
the Jurien Bay chrono-
sequence.Points indicate
means, bars show 95% confidence
intervals (n= 5 plots). Letters
above each mean represent
Fisher’s least significant difference
groupings (P<0.05),performed
on log-transformed data for silicon,
magnesium, and phosphorus. Soil
age increases with increasing
chronosequence stage.

RESEARCH | REPORT