Summary1. The classical model of long-term ecosystem development suggests that primary productivity is limited by nitrogen (N) on young substrates and phosphorus (P) on older substrates. Measurements of foliar and soil nutrients along soil chronosequences support this model, but direct tests through nutrient-addition experiments are rare. 2. We conducted a nutrient-limitation bioassay using phytometer species grown in soils from five stages of a >2-million-year dune chronosequence in south-western Australia. This long-term chronosequence is located within a region of exceptionally high plant species diversity and has not been previously studied in the context of ecosystem development. 3. Growth of unfertilized phytometers, a proxy for primary productivity, peaked on young soils (hundreds to a few thousand years) and then declined steadily on older soils. This decline was linked to P limitation, and its rapid appearance (<7000 years) compared to other sequences reflects the low P concentration in the parent material. As predicted, growth of canola was N-limited on the youngest soil (stage 1), co-limited by multiple nutrients in stage 2 and increasingly P-limited thereafter. 4. Growth of wheat was P-limited from stage 2 onwards, yet on the youngest soil it was co-limited by potassium (K) and micronutrients -most likely iron (Fe). Nitrogen addition also decreased the root:shoot ratio of wheat such that shoot growth was higher than in the control. We attribute these responses to a parent material that is very low in K and N and strongly alkaline (pH [H 2 O] > 9), being of a marine origin (i.e. carbonate dunes). Fe is poorly soluble at high pH and K likely plays a role in the secretion of Fe-mobilizing exudates from wheat roots. 5. Synthesis. Our results provide strong support for the long-term ecosystem-development model, particularly with regard to the appearance of P limitation and associated declines in productivity. However, our study also shows that N cannot be assumed to invariably be the most important limiting nutrient in young soils, and it is unlikely to be the only limiting nutrient in calcareous soils. This south-western Australian long-term chronosequence provides an excellent opportunity to explore edaphic controls over plant species diversity.

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Introduction Fine lavender and lavandin are perfume and medicinal plants widely cultivated in Provence (south-east of France) for their essential oil and for the production of honey. The lavender monocultures are affected by a severe decline in France, due to the propagation of the yellow decline disease. This disease is caused by the Stolbur phytoplasma, a bacterium transmitted by a sap-sucking insect, Hyalesthes obsoletus. Objectives Main objective was to develop an untargeted metabolomic approach to highlight changes in the volatiles organic compounds produced by asymptomatic (“healthy”) and symptomatic (“infected”) plants. Methods Samples from fine lavender and lavandin aerial parts were collected in the field, then stored volatile compounds were extracted in the laboratory by ultrasound assisted extraction and analyzed by gas chromatography–mass spectrometry. Afterwards, multivariate statistical analysis has been performed using principal component analysis and partial least square regression as well as a multiblock statistical analysis by orthogonal partial least squares discriminant analysis to compare VOCs from fine lavender (variety 7713) and lavandin (variety abrial).Results Fifty stored VOCs, mainly oxygenated monoterpenes, from lavender and lavandin leaves and blooming head of the inflorescences were identified. Metabolism of several compounds were found to be altered by yellow decline such as β-farnesene overexpressed by symptomatic plants. Conclusion The developed metabolomic approach allowed the identification of specific volatile compounds produced by asymptomatic and symptomatic plants in a complex field environment.

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