Potassium deficiency reduces grapevine water uptake due to lower gs and LAI
Or Sperling1*, Alon Ben-Gal2, Aviad Perry3, and Uri Hochberg2
1 - Plant Sciences, ARO-Volcani
2 - Soil and Water Sciences, ARO-Volcani
3 - Kreitman School, BGU
* Correspondence: orsp@agri.gov.il
Abstract
Potassium is one of the most abundant minerals in plants and has critical effects on plant growth and photosynthetic capacity. Specifically, potassium is associated with the regulation of plant hydraulics; however, its effects on plant transpiration have rarely been tested.
Hence, we determined the contribution of potassium to plant water use by measuring vine transpiration for three years (2020-2022) in large (2 m3) lysimeters. The vines were subjected to three fertigation applications (8, 20, or 58 mg K L-1), which complemented the investigation with field measurements to underline the physiological processes that respond to K availability. By 2022, we manipulated vine yield potential by leaving them with either 20 (low yield) or 50 (high yield) berry clusters.
We found that with 58 mg K L-1, vines transpired 65 L day-1, whereas vines with 8 mg K L-1 only transpired 48 L day-1 by midsummer. The higher leaf coverage in the 58 K fertigation mainly supported the higher transpiration rate when yields were premature and low (2020-2021). However, high-yielding vines (2022) amplified the effects of K on transpiration, independent of leaf area, as lower stomatal conductance limited transpiration in 8 K fertigation of high-yielding vines. We determined that fruits do not account for a large K sink (~21% in 8 K fertigation), which could still force a threshold on productivity under limiting K conditions.
Our findings illustrate the major effects of K on canopy development and consequential water uptake, suggesting that K nutrition should be adjusted according to vine yield projections for optimal production.
Introduction
Potassium applications that support farming productivity
Ahmad (2016) discusses the use of potassium-solubilizing bacteria to increase the availability of [1] potassium in soils. Adeoye (2001) found that farm wastes such as cocoa waste and water hyacinth can be used as a source of potassium for crop growth. Rawat (2016) highlights the importance of potassium in sustainable agriculture and the role of microbial strains in solubilizing potassium minerals. Pettigrew (2008) emphasizes the importance of potassium in crop yield and quality production, and suggests that developing plants that more efficiently use potassium could be a worthwhile goal for geneticists. Overall, the papers suggest that potassium applications can play an important role in supporting farming productivity.
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Potassium’s contribution to plants’ hydraulic regulation
El-Mesbahi 2012 found that plant potassium content modifies the effects of arbuscular mycorrhizal symbiosis on root hydraulic properties in maize plants. Shahzad 2016 found that a potassium-dependent oxygen sensing pathway regulates plant root hydraulics in Arabidopsis. Lu 2019 found that potassium mediates coordination of leaf photosynthesis and hydraulic conductance by modifications of leaf anatomy in both monocots and dicots. Kanai 2011 found that potassium deficiency affects water status and photosynthetic rate of the vegetative sink in greenhouse tomato prior to its effects on source activity. These findings suggest that potassium plays an important role in regulating plant hydraulic properties and that its deficiency can have negative effects on plant growth and productivity.
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Relations between metabolic sinks and plants’ potassium requirements
Armengaud 2009found that K deficiency affects the metabolite content of crops, with negative consequences for nutritional quality, mechanical stability, and pathogen/pest resistance. The study also identified metabolic targets and signaling components of K stress, showing that regulation of enzymes at the level of transcripts and proteins is likely to play an important role in plant adaptation to K deficiency. Barrow 1966 found that the soil’s buffering capacity affects the supply of K to plants, and a multiple regression containing terms for potential and for buffering capacity can be used to indicate the amount of K required to bring a deficient soil to a desirable status. Ashley 2006found that a low plant K status triggers expression of high affinity K+ transporters, up-regulates some K+ channels, and activates signaling cascades, some of which are similar to those involved in wounding and other stress responses. Bhandal 1988 found that K uptake is mainly metabolic at low external [K+], while it becomes increasingly nonmetabolic at higher (>1 mM) external [K+].
Hence, we set to study potassium’s contribution to vine development for multiple years at low and high fruit loads. We postulated that large metabolic sinks (i.e., fruits) would enhance vines’ K allocations and amplify the physiological limitations of K deficient vines. We studied table-grape vines for the economic importance of increasing their productivity by optimal and precise farming applications.
Methods
A graphic descriptions of the K application to the lysimeters:
K conditions for lysimeter vines:
We manually determined vines’ yield potential:
And, we mapped K allocation in vine:
Results
K applications affected soil and plant mineral status:
K availability also determined vines growth potential for multiple years:
Eventually vines’ ET changed:
LAI could not explain the changes in ET:
It probably happened because of low stomatal conductance:
