Compost may affect volatile and semi-volatile plant emissions through nitrogen supply and chlorophyll fluorescence

The use of composted biosolids as an amendment for forest regeneration in degraded ecosystems is growing since sewage–sludge dumping has been banned in the European Community. Its consequences on plant terpenes are however unknown. Terpene emissions of both Rosmarinus officinalis (a terpene-storing species) and Quercus coccifera (a non-storing species) and terpene content of the former, were studied after a middle-term exposure to compost at intermediate (50 t ha−1: D50) and high (100 t ha−1: D100) compost rates, in a seven-year-old post-fire shrubland ecosystem. Some chlorophyll fluorescence parameters (Fv/Fm, ETR, ΦPSII), soil and plant enrichment in phosphorus (P) and nitrogen (N) were monitored simultaneously in amended and non-amended plots in order to establish what factors were responsible for possible compost effect on terpenes. Compost affected all studied parameters with the exception of Fv/Fm and terpene content. For both species, mono- and sesquiterpene basal emissions were intensified solely under D50 plots. On the contrary leaf P, leaf N levels reached in D50 were partly responsible of terpene changes, suggesting that optimal N conditions occurred therein. N also affected ETR and ΦPSII which were, in turn, robustly correlated to terpene emissions. These results imply that emissions of terpene-storing and non-storing species were under nitrogen and chlorophyll fluorescence control, and that a correct management of compost rates applied on soil may modify terpene emission rate of plants, which in turn has consequences in air quality and plant defense mechanisms.