Root expansion induced by Sulfur limitation and mild heatwaves mitigated yield loss under a severe heatwave in grasslands

Grasslands, like many temperate ecosystems, are threatened by heatwaves which have been shown to be more frequent. Plant diversity can buffer yield loss due to heatwaves, but this positive effect may be modified by nutrient availability. Soil sulfur (S) has declined over the last decades and although it is crucial for coping with abiotic stresses, its role in grassland responses to heatwaves remains poorly documented. We aimed to determine how S nutrition modulates the responses of grasslands to heatwaves. Four monocultures and two mixtures were grown under two S levels and exposed to four thermoprotocols: i) control, ii) two successive mild heatwaves, iii) one severe heatwave, and iv) a recurrent sequence combining mild and severe heatwaves. We measured biomasses, leaf S compounds, {delta}13C as a proxy of water-use efficiency, leaf temperature, and photosystem II efficiency. S nutrition interacted with thermoprotocols. Under a severe heatwave, standard S promoted higher shoot production and better water-use efficiency. In contrast, under recurrent events, S limitation enhanced root:shoot ratio, water-use efficiency, shoot growth, and led to lower leaf temperature. S-containing metabolites did not vary with heatwaves, suggesting no direct metabolic. Under recurrent heatwaves, S limitation could indirectly improve tolerance to severe heatwaves. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=114 SRC="FIGDIR/small/691764v1_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@184f87borg.highwire.dtl.DTLVardef@d55d3forg.highwire.dtl.DTLVardef@1dd1426org.highwire.dtl.DTLVardef@1560116_HPS_FORMAT_FIGEXP M_FIG C_FIG