Foliar‐applied manganese and phosphorus in deficient barley: Linking absorption pathways and leaf nutrient status

Abstract

Foliar fertilization delivers essential nutrients directly to plant tissues, reducing excessive soil fertilizer applications that can lead to eutrophication following nutrient leaching. Foliar nutrient absorption is a dynamic process affected by leaf surface structure and composition, plant nutrient status, and ion physicochemical properties. We applied multiple methods to study the foliar absorption behaviors of manganese (Mn) and phosphorus (P) in nutrient‐deficient spring barley (Hordeum vulgare) at two growth stages. Nutrient‐specific chlorophyll a fluorescence assays were used to visualize leaf nutrient status, while laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) was used to visualize foliar absorption pathways for P and Mn ions. Rapid Mn absorption was facilitated by a relatively thin cuticle with a low abundance of waxes and a higher stomatal density in Mn‐deficient plants. Following absorption, Mn accumulated in epidermal cells and in the photosynthetically active mesophyll, enabling a fast (6 h) restoration of Mn‐dependent photosynthetic processes. Conversely, P‐deficient plants developed thicker cuticles and epidermal cell walls, which reduced the penetration of P across the leaf surface. Foliar‐applied P accumulated in trichomes and fiber cells above leaf veins without reaching the mesophyll and, as a consequence, no restoration of P‐dependent photosynthetic processes was observed. This study reveals new links between leaf surface morphology, foliar‐applied ion absorption pathways, and the restoration of affected physiological processes in nutrient‐deficient leaves. Understanding that ions may have different absorption pathways across the leaf surface is critical for the future development of efficient fertilization strategies for crops in nutrient‐limited soils.

Foliar P Application Cannot Fully Restore Photosynthetic Capacity, P Nutrient Status, and Growth of P Deficient Maize (Zea mays L.)

“…Nevertheless, CO 2 assimilation was increased by about 85%, indicating that P-deficient maize plants are not fundamentally incapable of recovering plant functionality, but that the uptake of P via the leaf is the limiting factor. In the study of Arsic et al [ 53 ], P deficient barley plants ( Hordeum vulgare ) were also unable to restore photosynthetic processes after foliar P treatment. As suggested by the authors, one reason was the altered morphology of the plant under P deficiency, which showed no influence on stomatal or trichome density, unlike in Fernández et al [ 25 ], but a thicker cuticle and epidermal cell wall with lower abundance of polysaccharides, all of which are characteristics that are connected to impaired foliar uptake [ 31 , 53 ].…”

“…In particular, the effects on biomass formation, adequate timing, as well as the optimal concentration of foliar P application were the focus of investigations. In recent years, some foliar P application studies were carried out with P deficient plant species such as wheat [ 25 , 48 , 49 , 50 , 51 , 52 ], barley [ 20 , 21 , 53 , 54 , 55 ] or maize [ 28 , 56 , 57 ]. It was shown that P deficiency can lead to alterations in the composition of plant tissues and epidermal structures such as stomata and trichomes, which ultimately affects the rate of uptake of P via foliage.…”

“…The effect of P deficiency is thereby strongly dependent on the type of crop, among other factors. While for wheat, the number of stomata and trichomes was strongly reduced and P foliar absorption no longer takes place [ 25 ], for barley mainly the tissue structure (cuticle, epidermal cell wall, polysaccharides) was changed and P continued to be absorbed, albeit at a reduced rate which could not restore functionality [ 53 ]. Foliar P application in P deficient maize plants led to an increase in P concentration and a short-term increase in biomass [ 28 , 56 , 57 ].…”

“…Foliar P application in P deficient maize plants led to an increase in P concentration and a short-term increase in biomass [ 28 , 56 , 57 ]. Using high-resolution bioimaging techniques, Arsic et al [ 53 , 54 ] recently showed that the uptake of P was mainly associated with trichomes and fiber cells, while P was subsequently translocated via bundle sheath extensions.…”

Melatonin administration decrypts the inferential determinants of idiosyncratic foliar nastic movements

“…A large number of idioblast cells filled with water in a leaf, in particular, could have several effects on leaf-water relation parameters. Idioblasts potentially alter (1) bulk leaf osmotic potential, (2) the water potential at the turgor pressure deficit loci, (3) hydraulic capacitance, (4) transpiration forces in action, and (5) the hydraulic drifts promoting water uptake in plants (Sruthi and Puthur 2020;Arsic et al 2022). Transpiration pull, water capacitance and osmotic potential are remarkably crucial for succulents.…”