Understanding and optimizing plant growth in water-limited environments: ‘growth versus defence’ or ‘growth versus risk mitigation’?

The concept of a 'growth versus defence' antagonism is sometimes applied as a framework to explain plant responses to drought and other abiotic stress. However, for drought stress, reduced growth to conserve water is a major part of the defence against further drying. This intertwined nature of growth and defence during drought makes it both conceptually and practically problematic to analyse them as two competing processes. Furthermore, physiological analysis of plants experiencing moderate severity water limitation, where turgor is maintained but growth is reduced, finds that the reduced growth is generally not due to resource limitation, as is sometimes assumed in the 'growth versus defence' model. For studies of more severe water limitation, where plants fall below the point of turgor loss, growth is not possible and therefore there can be no trade-off with defence. It is proposed that the concept of 'growth versus risk mitigation' provides a more useful framework for understanding the relationship between drought stress and growth. The 'growth versus risk mitigation' concept clarifies both the reasons why growth is actively suppressed during moderate severity water limitation and the conditions under which it may be useful to remove such growth restraints.This article is part of the theme issue 'Crops under stress: can we mitigate the impacts of climate change on agriculture and launch the 'Resilience Revolution'?'.