Soil organic matter and ammonium affect potassium retention in soil microaggregates under long--term fertilization

The adsorption and fixation of potassium in agricultural soils are important as they influence K availability for crops. Soil organic matter (SOM) and ammonium (NH4+) exist in soils and play indispensable roles in soil fertility and crop yield; however, the effects of SOM and NH4+ on K retention in soil aggregate remains unclear. This study aimed to evaluate the effects of SOM and NH4+ on K adsorption and fixation in soil microaggregates (<0.25 mm). Soil microaggregates were extracted from three long-term fertilization treatments under rice-wheat rotations: no fertilizer (CK), fertilized with inorganic NPK (NPK), and inorganic NPK fertilizers combined with straw return (NPKS). Long-term fertilization, particularly the application of inorganic NPK combined with straw return, significantly improved the SOM content in microaggregates. Both NPK and NPKS treatments increased K adsorption but decreased K fixation, and SOM oxidation of microaggregates reduced K adsorption but increased K fixation in all treatments, indicating the positive and inhibitory effects of SOM on K adsorption and fixation, respectively. NH4+ significantly inhibited K adsorption and fixation, and this inhibitory effect was more significant in microaggregates with a higher SOM content. Although NH4+ reduced the positive effect of SOM on K adsorption, it enhanced the inhibitory effect of SOM on K fixation. Conclusionally, long-term fertilization increases K adsorption but reduces K fixation by improving SOM content, where NH4+ enhances SOM inhibited K retention in soil microaggregates, which is considered to improve K availability in soils amended with K fertilizers. Keywords: soil organic matter, NH4+, K, adsorption, fixation

Halophytic Hordeum brevisubulatum HbHAK1 Facilitates Potassium Retention and Contributes to Salt Tolerance

Potassium retention under saline conditions has emerged as an important determinant for salt tolerance in plants. Halophytic Hordeum brevisubulatum evolves better strategies to retain K+ to improve high-salt tolerance. Hence, uncovering K+-efficient uptake under salt stress is vital for understanding K+ homeostasis. HAK/KUP/KT transporters play important roles in promoting K+ uptake during multiple stresses. Here, we obtained nine salt-induced HAK/KUP/KT members in H. brevisubulatum with different expression patterns compared with H. vulgare through transcriptomic analysis. One member HbHAK1 showed high-affinity K+ transporter activity in athak5 to cope with low-K+ or salt stresses. The expression of HbHAK1 in yeast Cy162 strains exhibited strong activities in K+ uptake under extremely low external K+ conditions and reducing Na+ toxicity to maintain the survival of yeast cells under high-salt-stress. Comparing with the sequence of barley HvHAK1, we found that C170 and R342 in a conserved domain played pivotal roles in K+ selectivity under extremely low-K+ conditions (10 μM) and that A13 was responsible for the salt tolerance. Our findings revealed the mechanism of HbHAK1 for K+ accumulation and the significant natural adaptive sites for HAK1 activity, highlighting the potential value for crops to promote K+-uptake under stresses.

Hyperkalemia in chronic kidney disease

SUMMARY Hyperkalemia is a frequent finding in patients with chronic kidney disease (CKD). This increase in serum potassium levels is associated with decreased renal ion excretion, as well as the use of medications to reduce the progression of CKD or to control associated diseases such as diabetes mellitus and heart failure. Hyperkalemia increases the risk of cardiac arrhythmia episodes and sudden death. Thus, the control of potassium elevation is essential for reducing the mortality rate in this population. Initially, the management of hyperkalemia includes orientation of low potassium diets and monitoring of patients' adherence to this procedure. It is also important to know the medications in use and the presence of comorbidities to guide dose reduction or even temporary withdrawal of any of the potassium retention-related drugs. And finally, the use of potassium binders is indicated in both acute episodes and chronic hyperkalemia.

Renal and colonic potassium transporters in the pregnant rat

Gestational potassium retention, most of which occurs during late pregnancy, is essential for fetal development. The purpose of this study was to examine mechanisms underlying changes in potassium handling by the kidney and colon in pregnancy. We found that potassium intake and renal excretion increased in late pregnancy while fecal potassium excretion remained unchanged and that pregnant rats exhibited net potassium retention. By quantitative PCR we found markedly increased H+-K+-ATPase type 2 (HKA2) mRNA expression in the cortex and outer medullary of late pregnant vs. virgin. Renal outer medullary potassium channel (ROMK) mRNA was unchanged in the cortex, but apical ROMK abundance (by immunofluorescence) was decreased in pregnant vs. virgin in the distal convoluted tubule (DCT) and connecting tubule (CNT). Big potassium-α (BKα) channel-α protein abundance in intercalated cells in the cortex and outer medullary collecting ducts (by immunohistochemistry) fell in late pregnancy. In the distal colon we found increased HKA2 mRNA and protein abundance (Western blot) and decreased BKα protein with no observed changes in mRNA. Therefore, the potassium retention of pregnancy is likely to be due to increased collecting duct potassium reabsorption (via increased HKA2), decreased potassium secretion (via decreased ROMK and BK), as well as increased colonic reabsorption via HKA2.

Hydroxyl radical scavenging by cerium oxide nanoparticles improves Arabidopsis salinity tolerance by enhancing leaf mesophyll potassium retention

Nanoceria ROS scavenging is a key tool for understanding and improving plant tolerance to salinity, a stress that severely limits crop yield worldwide.