Abstract
Potassium (K) is an indispensable nutrient element in the development of fruit trees in terms of yield and quality. It is unclear how a stable or unstable supply of K affects plant growth. We studied the root morphology and physiological and molecular changes in the carbon and nitrogen metabolism of M9T337 apple rootstock under different K levels and supply methods using hydroponics. Five K supply treatments were implemented: continuous low K (KL), initial low and then high K (KLH), appropriate and constant K (KAC), initial high and then low K (KHL), and continuous high K (KH). The results showed that the biomass, root activity, photosynthesis, and carbon and nitrogen metabolism of the M9T337 rootstocks were inhibited under KL, KH, KLH and KHL conditions. The KAC treatment promoted root growth by optimizing endogenous hormone content, enhancing carbon and nitrogen metabolism enzyme activities, improving photosynthesis, optimizing the distribution of carbon and nitrogen, and upregulating the transcription levels of nitrogen assimilation-related genes (nitrate reductase, glutamine synthetase, glutamate synthase, MdNRT1.1, MdNRT1.2, MdNRT1.5, MdNRT2.4). These results suggest that an appropriate and constant K supply ensures the efficient assimilation and utilization of nitrogen and carbon.
Highlights
Potassium (K) is an essential nutrient element for higher plant cells
Further morphological analysis showed that KAC treatment, followed by KHL treatment, produced the best root development and the largest root length and root surface area
The level and mode of K supply affected the growth of apple rootstocks
Summary
K plays an important role in maintaining the cell membrane potential gradient, promoting intracellular enzyme activity, regulating photosynthesis, and altering carbon (C) and nitrogen (N) metabolism (Marschner, 2012; Oosterhuis et al, 2014). Soil K is the primary source of K absorbed by plants, but most of this. The available K which is directly absorbed and utilized by plants only accounts for only 0.1–2% of the total K content in the soil (Chérel et al, 2014). According to the previous investigations of fertilization in different appleproducing areas in China, the orchard managers generally apply N but ignore phosphorus (P) and K applications (Zhu et al, 2018). With the rapid development of the apple industry and the resulting economic benefits, orchard managers have realized the importance of K input. The effects on the growth and metabolism of fruit trees remain unclear
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