Elsevier

Plant Science

Volume 226, September 2014, Pages 108-119
Plant Science

Opportunities for improving leaf water use efficiency under climate change conditions

https://doi.org/10.1016/j.plantsci.2014.04.007Get rights and content

Highlights

  • A new WUEi dataset of 237 species/varieties was analyzed considering gm and Vcmax.

  • gm/gs and Vcmax/gs ratios are correlated with WUEi along the plant kingdom.

  • The relationship between A and R appears as an emergent opportunity to improve WUEi.

  • New technologies as the UAVs are promising approaches for crop water management.

Abstract

WUEi (intrinsic water use efficiency) is a complex (multi)-trait, that depends on several physiological processes, driving plant productivity and its relation with a changing environment. Climatic change predictions estimate increases in temperature and drought in the semi-arid regions, rendering improved water use efficiency is a mandatory objective to maintain the current global food supply. The aims of this review were (i) to identify through a meta-analysis the leaf traits mostly related to intrinsic water use efficiency (WUEi, the ratio between A – net photosynthesis and gs – stomatal conductance), based on a newly compiled dataset covering more than 200 species/varieties and 106 genus of C3 plants (ii) to describe the main potential targets for WUEi improvement via biotechnological manipulations and (iii) to introduce emergent and innovative technologies including UAVs (Unmanned Aerial Vehicles) to scale up levels from leaf to whole plant water status. We confirmed that increases in gm/gs and Vcmax/gs ratios are systematically related with increases in WUEi maintained across species, habitats, and environmental conditions. Other emergent opportunities to improve WUEi are described such as the relationship between photosynthesis and respiration and their link with metabolomics. Finally, we outline our hypothesis that we are observing the advent of a “smart” agriculture, wherein new technologies, such as UAVs equipped with remote sensors will rapidly facilitate an efficient water use regulating the irrigation schedule and determination, under field conditions, of cultivars with improved water use efficiency. We, therefore, conclude that the multi-disciplinary challenge toward WUE has only just begun.

Section snippets

WUE in the era of climate change: the problem of water

The need for increasing food production driven by the exponential growth of the human population is clear from any perspective. The human water consume is mainly driven (around 70%) by its need for food production [1]. When combined an increased global water demand from agriculture and associated agro-industries can be anticipated. Water resources are already limited, however irrigated lands even though they represent only 18% of world cultivated areas produce around 45% of global food [2].

Definition of WUE at different spatial and time scales

The term water use efficiency (WUE) reflects the balance between carbon gains and the associated costs in water. This balance can be measured at different spatial and temporal scales [8], [9], [14]. The different spatial scales depend if carbon and water fluxes are considered from the leaf scale, whole plant, the canopy or crop parcel and finally at the biome or the ecosystem. Each scale involves specific methods and approaches that comprise satellites or aircraft imaging, eddy-covariance

Potential biotechnological approaches to enhance intrinsic water use efficiency

As was described in previous section, the WUEi can be partitioned into several fluxes and diffusional components. First, net CO2 assimilation rate (A) and stomatal conductance (gs) define the net carbon gain and water loss components since the ratio WUEi = A/gs. Moreover, it is now widely accepted that A is influenced by one of its diffusional components, namely the mesophyll conductance [19]. Finally, there is an important dependency of WUEi on the biochemical properties of important enzymes

New directions to identify potential targets to improve WUE

In the previous section we have reviewed the possibilities for improving leaf WUE based on the traits that were highlighted using the meta-analysis of the available parameters in the dataset. All them were directly related to either photosynthetic or transpiratory fluxes. However, other parameters may be considered as potential targets for biotechnological improvement which were not reflected in our database. In this section we propose two different approaches to identify such parameters.

New Technologies for smart agriculture

Previously described genetic and biotechnological approaches should lead to novel crop varieties with enhanced WUE, however a long-term investment is necessary to achieve those goals. Another way to improve WUE is to more precisely control the irrigation schedule and dosage. Any improvements in this area can be translated to the field in a shorter term thus contributing more immediately to the improvement of the WUE and the reduction of water consumption.

We are probably at the advent of a

Conclusions and future remarks

The constant increase of human population had dramatically increased the need for more food and fuel, promoting large increases in water consumption. Climatic change predictions suggest reductions in water availability for important croplands that will impose a new challenge for society and the scientific community to maintain or enhance the current food production. One approach to achieve this has been summarized as “more crop per drop”, or in other words increasing water use efficiency.

The

Acknowledgements

This work was partly supported by the Plan Nacional, Spain, contracts AGL2009-11310 (A. Díaz-Espejo), BFU2011-23294 (J. Flexas and J. Gago), contracts AGL2009-07999 (J. Galmés), BFU2011-26989 (F. Morales), FPI grant from AGL2008-04525-C02-01, AGL2011-30408-C04-01, (S. Martorell), the project AGL2011-30408/C04-01 CICYT-FEDER financed by the Spanish government (H. Medrano and J. Escalona).

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