Differential effects of soil water deficit on the basic plant functions and their significance to analyse crop responses to water deficit in indeterminate plants

Abstract

On the basis of a large set of experiments conducted on legumes, cotton, and vineyards, we propose a framework to analyse the functioning of an indeterminate crop in response to soil water deficit. Indicators of basic plant functions (e.g. leaf carbon exchange rate as an indicator of production of assimilates) have been correlated with soil water status in the root zone (quantified with the fraction of transpirable soil water, FTSW), across a range of soil water deficit. Leaf area development was the most sensitive process to soil water deficits, with branching being more sensitive than leaf emission and growth on the main stem. Net carbon exchange rate and the various steps of reproductive development were less sensitive to drought, thereby explaining why grain/fruit yield can be increased by a moderate drought in indeterminate plants. Other traits of plant adaptation to drought at the crop level, such as reduction of flowering duration and increase of harvest index (in case of early drought), can be explained by the observed differential effects of soil dehydration on the various plant functions. These results have been used to develop regulated deficit irrigation strategies using tensiometers and tools for in-field diagnosis, especially for seed production and grape production.