Transpiration efficiency: new insights into an old story

Abstract

Producing more food per unit of water has never been as important as it is at present, and the demand for water by economic sectors other than agriculture will necessarily put a great deal of pressure on a dwindling resource, leading to a call for increases in the productivity of water in agriculture. This topic has been given high priority in the research agenda for the last 30 years, but with the exception of a few specific cases, such as water-use-efficient wheat in Australia, breeding crops for water-use efficiency has yet to be accomplished. Here, we review the efforts to harness transpiration efficiency (TE); that is, the genetic component of water-use efficiency. As TE is difficult to measure, especially in the field, evaluations of TE have relied mostly on surrogate traits, although this has most likely resulted in over-dependence on the surrogates. A new lysimetric method for assessing TE gravimetrically throughout the entire cropping cycle has revealed high genetic variation in different cereals and legumes. Across species, water regimes, and a wide range of genotypes, this method has clearly established an absence of relationships between TE and total water use, which dismisses previous claims that high TE may lead to a lower production potential. More excitingly, a tight link has been found between these large differences in TE in several crops and attributes of plants that make them restrict water losses under high vapour-pressure deficits. This trait provides new insight into the genetics of TE, especially from the perspective of plant hydraulics, probably with close involvement of aquaporins, and opens new possibilities for achieving genetic gains via breeding focused on this trait. Last but not least, small amounts of water used in specific periods of the crop cycle, such as during grain filling, may be critical. We assessed the efficiency of water use at these critical stages.

Tolerant pearl millet (Pennisetum glaucum (L.) R. Br.) varieties to low soil P have higher transpiration efficiency and lower flowering delay than sensitive ones

“…Our findings showed that tolerant genotypes produced higher yields under combined P and water stress, had higher TE under low P conditions, while the total amount of water used was similar compared with sensitive genotypes. These results add to a recent review that argues that high TE can indeed be related to higher grain yield (Vadez et al 2014). More research would be needed to understand the mechanisms underlying the TE differences occuring Fig.…”

“…The setup allows to determine transpiration efficiency (TE, calculated as dry matter (DM) produced per kg of water transpired) to distinguish tolerant and sensitive genotypes (Ratnakumar and Vadez 2011;Vadez et al 2011a;. It is well known that TE depends on interactions between water and nutrient availability (De Wit 1958;Tanner and Sinclair 1983;Clarkson et al 2000;Vadez et al 2014), and is particularly affected by nutrient deficiency (Payne 2000). For Sahelian conditions, Sivakumar and Salaam (1999) reported a 84 % increase of water use efficiency in millet (WUE, grain yield per mm rain), of which TE is an important component, due to the addition of mineral fertilizers.…”

Modelling the effect of plant water use traits on yield and stay-green expression in sorghum

“…Aside from 'cosmetic' stay-green (retention of nonfunctional chlorophyll; see reviews (e.g. Thomas and Howarth 2000;Cha et al 2002)), there are basically two parallel streams of hypotheses explaining the maintenance of green leaves under water stress, one of which deals with the enhanced use of available N (Rajcan and Tollenaar 1999;Borrell and Hammer 2000;Borrell et al 2001;Bertheloot et al 2008;van Oosterom et al 2010b) and another one favouring an improved plant water use status Vadez et al 2011Vadez et al , 2014. Several quantitative trait loci (QTLs) contributing to stay-green phenotype expression under drought (Stages 1-4, Stages A and B) have been validated across different research groups (Tuinstra et al 1996(Tuinstra et al , 1997(Tuinstra et al , 1998Crasta et al 1999;Subudhi et al 2000;Tao et al 2000;Xu et al 2000;Kebede et al 2001;Sanchez et al 2002;Haussmann et al 2002;Hash et al 2003;Harris et al 2007).…”

Photosynthetic characteristics of peanut genotypes under excess and deficit irrigation during summer

“…The increased value of Ci in T 3 seems to be because of in-efficiency of the photosynthetic incorporation of CO 2 . A tight link has been found between large differences in TE in several crops and attributes of plants that make them restrict water losses under high vapour-pressure deficits (Vadez et al 2014).…”