Unveiling herbaceous plant responses to future triple interaction of drought and elevated temperature and [CO₂]:...

During the last decades, the breeding of major crops is growing at a slower rate than desirable to meet future food demands in many agro-environments. Moreover, extreme climatic conditions, and particularly, drought impairments associated with climate change, are limiting the genetic gains of crops in temperate areas, especially in the Mediterranean basin. Drought events and atmospheric air temperatures and CO₂ concentrations are increasing at an accelerating pace. Unfortunately, not all breeding programmes have been oriented towards developing climate-resilient crops to cope with future climate predictions, so it is unclear how crops will respond under future multiple stress conditions. In this regard, special attention should be paid to the triple interaction effect of drought, elevated temperature and CO₂ concentration on plant responses. Our aim was i) to perform a systematic review of the existing literature on the physiological and agronomic responses of herbaceous plants, mainly grasses, legumes, and forbs to this triple interaction, and ii) elucidate general responses through a meta-analysis. The analysis of the literature unveils the great heterogeneity that exists in the experimental designs carried out to date to study multiple stress conditions in herbaceous plants, making it difficult to extrapolate general responses. A meta-analysis of a subset of studies that met the criteria of having grown plants under elevated CO₂ concentrations along the whole experiment suggests that the negative effects of drought on plant performance will be mitigated under future climate conditions, although the responses depend on the severity of the stressors and the experimental variables measured.