Water for agriculture: more crop per drop.

Global crop production in agriculture depends on water availability. Future scenarios predict increasing occurrence of flash floods and rapidly developing droughts accompanied by heatwaves in humid regions that rely on rain-fed agriculture. It is challenging to maintain high crop yields, even in arid and drought-prone regions that depend on irrigation. The average water demand of crops varies significantly, depending on plant species, development stage, and climate. Most crops, such as maize and wheat, require relatively more water during the vegetative phase compared to the ripening phase. In this review, we explain WUE and options to improve water use and thus crop yield. Nutrient management might represent another possibility to manipulate water uptake and use by plants. An emerging topic involves agroforest co-cultivation, where trees in the system facilitate water transfer through hydraulic lift, benefiting neighbouring crops. Other options to enhance crop yield per water use are discussed.

Drought and crop yield.

Episodes of water shortage occur in most agricultural regions of the world. Their durations and intensities increase, and their seasonal timing alters with changing climate. During the ontogenic cycle of crop plants, each development stage, such as seed germination, seedling establishment, vegetative root and shoot growth, flowering, pollination and seed and fruit development, is specifically sensitive to dehydration. Desiccation threatens yield and leads to specific patterns, depending on the type of crop plant and the harvested plant parts, e.g. leafy vegetables, tubers, tap roots or fruits. This review summarizes the effects of drought stress on crop plants and relates the dehydration-dependent yield penalty to the harvested organ and tissue. The control of shoot transpiration and the reorganization of root architecture are of core importance for maintaining proper plant water relationships. Upon dehydration, the provision and partitioning of assimilates and the uptake and distribution of nutrients define remaining growth activity. Domestication of crops by selection for high yield under high input has restricted the genetic repertoire for achieving drought stress tolerance. Introgression of suitable alleles from wild relatives into commercial cultivars might improve the ability to grow with less water. Future research activities should focus more on field studies in order to generate more realistic improvements to crops. Robotic field phenotyping should be integrated into genetic mapping for the identification of relevant traits.

Salinity and crop yield.

Thirty crop species provide 90% of our food, most of which display severe yield losses under moderate salinity. Securing and augmenting agricultural yield in times of global warming and population increase is urgent and should, aside from ameliorating saline soils, include attempts to increase crop plant salt tolerance. This short review provides an overview of the processes that limit growth and yield in saline conditions. Yield is reduced if soil salinity surpasses crop-specific thresholds, with cotton, barley and sugar beet being highly tolerant, while sweet potato, wheat and maize display high sensitivity. Apart from Na+ , also Cl- , Mg2+ , SO4 2- or HCO3 - contribute to salt toxicity. The inhibition of biochemical or physiological processes cause imbalance in metabolism and cell signalling and enhance the production of reactive oxygen species interfering with cell redox and energy state. Plant development and root patterning is disturbed, and this response depends on redox and reactive oxygen species signalling, calcium and plant hormones. The interlink of the physiological understanding of tolerance processes from molecular processes as well as the agronomical techniques for stabilizing growth and yield and their interlinks might help improving our crops for future demand and will provide improvement for cultivating crops in saline environment.

Early changes of the pH of the apoplast are different in leaves, stem and roots of Vicia faba L. under declining water availability.

Changes in pH of the apoplast have recently been discussed as an important factor in adjusting transpiration and water relations under conditions of drought via modulatory effect on abscisic acid (ABA) concentration. Using Vicia faba L., we investigated whether changes in the root, shoot and leaf apoplastic pH correlated with (1) a drought-induced reduction in transpiration and with (2) changes in ABA concentration. Transpiration, leaf water potential and ABA in leaves were measured and correlated with root and shoot xylem pH, determined by a pH microelectrode, and pH of leaf apoplast quantified by microscopy-based in vivo ratiometric analysis. Results revealed that a reduction in transpiration rate in the early phase of soil drying could not be linked with changes in the apoplastic pH via effects on the stomata-regulating hormone ABA. Moreover, drought-induced increase in pH of xylem or leaf apoplast was not the remote effect of an acropetal transport of alkaline sap from root, because root xylem acidified during progressive soil drying, whereas the shoot apoplast alkalized. We reason that other, yet unknown signalling mechanism was responsible for reduction of transpiration rate in the early phase of soil drying.