With an increase in K supply, the root-shoot ratio initially increased and then decreased, and maximized under 6 mM K treatment, indicating that K deficiency and excessive K has a significant impact on root growth than that on aboveground parts of seedlings. Table 2. The root morphology of M9T seedlings was also significantly affected by different K levels Figure 1A. In and , the root length and total root surface area of seedlings were the largest under 6 mM K concentration, and the root length and surface area of seedlings under 0 mM and 12 mM K treatment were significantly lower than those of the 6 mM treatment.
The result showed that low and high K supply levels inhibited the elongation and growth of root Figures 1B,C. Figure 1. Each treatment had three biological replicates and the assays were repeated three times. As shown in Figure 1D , K levels also significantly affected root activity. The highest root activity appeared in 6 mM K treatment, and inappropriate K levels had a negative effect on root activity.
Potassium content in the roots, stems, and leaves of seedlings increased with the increasing in K supply Figure 2. The K content of all organs was the highest under K12 treatment. In K0 and K3 treatments, the K content of each organ was the highest in leaves, second-highest in the stems, and lowest in roots. Under the other K level treatments, the K content of each organ was highest in the roots and lowest in the stems.
So, K was preferentially supplied to the shoot under low K conditions. Figure 2. We monitored photosynthetic rate and gas exchange parameters to determine possible effects of different K levels. With increasing K supply, P n and G s increased first and then decreased Table 3 , reaching the maximum value in K6 treatment.
However, C i was the highest in K0 treatment and the lowest in K6 treatment. Table 3. Chlorophyll fluorescence was further investigated to understand the internal causes of the effects of different K levels on photosynthesis. This indicates that unsuitable K levels can inhibit photosynthetic electron transfer, increase heat dissipation and even damage the light system K0 treatment.
As shown in Figure 3 , after 30 days, seedlings subjected to K6 treatments acquired the highest activities of Rubisco, SPS and SS, followed by K9 treatments, and K0 treatments obtained the lowest activities. These results indicate that low or high K levels can significantly inhibit the activity of C metabolizing enzymes in leaves, and the inhibition effect is more significant under low K levels than that under high K levels.
Figure 3. The 13 C accumulation rate in all organs of seedlings under the K6 treatment were significantly higher than those under of other treatments Figure 4A. Figure 4. The distribution ratio of 13 C to each organ is related to its competitive ability but also chiefly to its transport capacity within the plant. The 13 C distribution rates for each treatment were consistent in both years, among which the leaves had the highest values followed by the stems, and roots Figure 4B.
K supply increased the 13 C distribution rate in roots, which increased first and then decreased with increasing K levels. An different trend was, however, observed for leaves. No significant effect was observed on the 13 C distribution ratio in stems under K treatments. The NO 3 — ion flow velocity in roots increased at first as K supply rose, but then decreased, which implied that a moderate K supply level will promote nitrate ions to be take up by roots Figure 5.
In and , the average NO 3 — flux rates within 10 min of seedling root exposure to K6 treatment increased by Figure 5. A Net NO 3 — fluxes in the root of apple seedlings for 10 min. B Mean rate of NO 3 — fluxes during the entire 10 min.
Compared with roots, NR activities in leaves were significantly affected by K levels Figure 6 , and NR activities in leaves under the K6 treatment were significantly higher than the other treatments for all three stages Figure 6A , which improved nitrate assimilation capacity. In contrast, NR activities in the leaves under the K0 and K12 treatments were relatively lower.
Unlike NR activities, differences in GS activities in roots was greater between different K treatments than that in leaves Figures 6C,D , and the higher values appeared in the K6 treatment. Figure 6. We compared the effects of the different K supply levels on NRT1. As expected, we found that NRT1.
Figure 7. After 30 days of treatment, the 15 N absorption rate of seedlings in K6 treatment was significantly higher than that of the other treatments, and the 2-year average was 1. Figure 8. The 15 N use efficiency was calculated from the 15 N absorption content divided by the total 15 N application rate. Potassium has a significant effect on the growth and development of plant roots. Jung et al. Therefore, plants can cope with short-term K deficiency by promoting root growth.
However, compared with the lack of N and phosphorus, the growth of plant roots is strongly inhibited under conditions of prolonged K deficiency, and the root-shoot ratio will be significantly reduced Hermans et al. However, root growth was significantly inhibited by unsuitable K supply levels, which may be due to an increase in ethylene and a decrease in indoleacetic acid IAA in the roots Zhang et al.
At the same time, the limited transport of photosynthetic products from leaves to roots may also explain why unreasonable K supply hinders root growth Figure 4B. The percentage of 15 N in each organ accounting for the total 15 N content reflects the distribution of N fertilizer in the seedlings and the migration regularity in the organs. And, the opposite trend exhibited in the leaves Figure 8B.
This suggested that the K level can affect root-to-leaf transportation. Potassium status of plants has a significant effect on the transport and distribution of photosynthetic products Pettigrew, Sufficient K supply can establish osmotic potential in the phloem and help to transfer photosynthates from source to sink organs Cakmak, However, the loading of photosynthates in phloem of K deficient plants is inhibited and the transport to roots is significantly reduced Gerardeaux et al.
In this study, the 13 C isotope labeling results showed that the 13 C assimilation rate and distribution ratio in roots were higher under an appropriate K supply level.
This indicates that insufficient or excessive K supply can inhibit the C assimilation of leaves and the photosynthetic products transport from leaves to roots. Correlation analysis also showed that the 13 C distribution ratio was positively correlated with root biomass. Meanwhile, the 13 C distribution ratio of roots was significantly positive related to photosynthesis and C metabolizing enzyme activity SS and SPS activities.
We also measured the gas exchange parameters of leaves, and found that the P n and G s of seedling decreased significantly under the treatment of low and high K supply, which indicates that inappropriate K supply would limit photosynthesis through stomatal restrictions. C i increased significantly under K0 treatment, therefore, the decrease of P n may also be related to limitations of the optical system. These results clearly show that K deficiency or excess can inhibit the photochemical efficiency and electron transfer efficiency of PSII reaction center.
Lu et al. In conclusion, we showed that K affected C assimilation and distribution by regulating photosynthesis and C metabolizing enzymes.
The increase in the distribution of photosynthetic products to the root system will promote growth and development of the root system, then improving the absorption ability of N, thus increasing NUE.
Parker and Newstead showed that NRT1. Li et al. In addition, an ideal root morphology and activity were important for nutrient absorption Sattelmacher et al. As a result, a higher 15 N absorption content appeared under appropriate K supply conditions Figure 8.
In addition, K also affected the distribution of NO 3 — between root and shoot Ruiz and Romero, Our results show that higher 15 N distribution ratio in roots were found in K deficient or excess treatments, while the highest 15 N distribution ratio in leaves appeared under appropriate K supply treatments. This suggests that appropriate K supply not only increases NO 3 — absorption in roots, but also promotes the transport from roots to shoots.
Rufty et al. So it is necessary to focus on the effect of K on N assimilation in roots and leaves. The inhibition of K deficiency on NR activity has been verified in cotton, cucumber, and Arabidopsis Ruiz and Romero, ; Balkos et al. Consistent with previous results, we also found that for a certain range, with the increase of K supply, GS activity of roots and NR activity of leaves of M9T seedlings gradually increased, which promoted the assimilation of NO 3 —.
However, when the K supply is too high, the activity of these enzymes will decrease, which may be related to the inhibition of photosynthesis and the reduction of energy supply.
The absorption and distribution of nitrate also depends on the energy and C skeleton from photosynthesis Liu et al. We found that the higher NUE was related to the improvement of the fixation rate of photosynthetic carbon and the efficiency of photosynthetic electron transfer under the appropriate K supply level.
In addition, the results of 15 N labeling showed that low or high K levels were not conducive to NO 3 — transport from root to leaf, which was consistent with previous studies Ruiz and Romero, ; Coskun et al. Han et al. Perchlik and Tegeder also reported that increasing N allocation to leaves represents an effective strategy for improving C fixation and photosynthetic nitrogen use efficiency NUE. Our findings reveal how the application of K affects the uptake, transport, and assimilation of NO 3 — , and deepens our understanding of the relationship between K supply and improved NUE.
It should be noted that our research was mainly focused on physiological mechanisms on K induces positive changes in N metabolism in M9T seedlings. Further molecular studies are needed to gain a deeper understanding of how K improves NUE.
Our results showed that M9T seedlings treated with the optimum K levels had i enhanced 13 C accumulation and 13 C transport from leaves to roots; ii increased root NO 3 — ion flow rate; iii relatively high N metabolic enzyme activities; iv up-regulated transcript levels of nitrate uptake genes NRT1.
In conclusion, optimum K levels can increase NUE by affecting root morphology and activity, the activity of enzymes involved in C and N metabolism, nitrate uptake genes, and nitrate transport. All authors contributed to the article and approved the submitted version. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Armengaud, P. Multilevel analysis of primary metabolism provides new insights into the role of potassium nutrition for glycolysis and nitrogen assimilation in Arabidopsis roots. Plant Physiol. Bai, L. Gibberellin is involved in inhibition of Cucumber growth and nitrogen uptake at Suboptimal root-Zone temperatures. PLoS One e Balkos, K.
Optimization of ammonium acquisition and metabolism by potassium in rice Oryza sativa L. Plant Cell Environ. Ben Zioni, A. So a plant must have a living, breathing, healthy root system. It builds sugars and sends them to the root system. To get the energy needed for nutrient uptake, the root system burns the sugars during cell respiration, and it needs oxygen to do that.
It is taking in carbo-hydrates and letting out carbon dioxide, and it needs oxygen to drive that process. A lack of oxygen is shutting down the metabolic processes required to take up nutrients. Managing K leaching. K can be leached out of soil by water—up to 30 lb. In an acid soil environment, there are lots of positively charged ions, such as aluminum and hydrogen, attached to soil particles, leaving no opportunity for K ions to attach, Ferrie explains.
So as K ions change from non-exchangeable to exchangeable through the weathering process and enter the soil solution, they are unable to attach to soil particles. These unattached K ions can be leached away by water. As a crop manager, recognize that your light soils with low water-holding capacity are also more subject to leaching, Ferrie advises. Split your K application by applying some with your starter fertilizer and when you sidedress nitrogen. Fight K fixation.
Soils with high CECs may have most of the K fixed to the exchange sites, leaving very little in the soil solution. In another type of tie-up, K ions may get trapped between clay lattices when soil dries out and the lattices collapse. You can band potash fertilizer in the spring, or in the fall if you strip-till. You also can add potassium to your starter and sidedress fertilizer.
K advice for all soils. In any soil, manage your pH. Either situation creates opportunities for K to be leached away by water. Be aware of and manage any soil compaction in your fields. How plants lose K. Hail followed by rain can cause heavy losses of potassium out of the plant, from the torn leaves.
If you rip a leaf and run water across it, it will actually bleed K right out on the ground. So, on tissue tests, potassium levels can drop drastically after a minor hail situation. K recommendations. There are various ways to make a K fertilizer recommendation. Some create the recommendation solely on parts per million ppm or pounds of K in the soil, as shown on a soil test. Others adjust that recommendation based on the CEC of the soil.
To do this, the CEC must be included on your soil test. Here are some common sources of organic potassium:. For healthy crops and plants or lawns first have an accurate soil sample test performed to determine what fertilizer you may need.
When looking for a fertilizer rich in nitrogen, check the middle number labeled on the fertilizer bag. Usually the bags are labeled with numbers such as or some other combination.
The first number is Nitrogen, the second is Phosphorus and the third is Potassium. Fertilizers high in Phosphorus are usually determined by a high middle number. A simple soil test will help determine exactly what is needed to give you the highest yielding crops, most delicious fruits and greenest lawn. If you are not sure about the essential elemental balance in your soil contact us today to find out how we can help.
We offer a soil test for potassium and other essential elements which is much more accurate than store bought tests. Come see why some of the largest crop producers in the state have come to count on Phoslab Environmental Service since Phoslab Blog. How does Potassium Help Plants Grow? May 13, Phoslab Agriculture , Uncategorized Potassium K is an essential element for plant growth it is important to food crops.
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