Opportunities for improving leaf water use efficiency under climate change conditions
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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