Plastic response of Medicago sativa L. root system traits and cold resistance to simulated rainfall events

Abstract

Climate change (rainfall events and global warming) affects the survival of alfalfa (Medicago sativa L.) in winter. Appropriate water management can quickly reduce the mortality of alfalfa during winter. To determine how changes in water affect the cold resistance of alfalfa, we explored the root system traits under different rainfall events and the effects on cold resistance in three alfalfa cultivars. These were exposed to three simulated rainfall events (SRE) × two phases in a randomized complete block design with six replications. The three cultivars were WL168, WL353 and WL440, and the three SRE were irrigation once every second day (D2), every four days (D4) and every eight days (D8). There were two phases: before cold acclimation and after cold acclimation. Our results demonstrated that a period of exposure to low temperature was required for alfalfa to achieve maximum cold resistance. The root system tended toward herringbone branching under D8, compared with D2 and D4, and demonstrated greater root biomass, crown diameter, root volume, average link length and topological index. Nevertheless, D8 had less lateral root length, root surface area, specific root length, root forks and fractal dimensions. Greater root biomass and topological index were beneficial to cold resistance in alfalfa, while more lateral roots and root forks inhibited its ability to survive winter. Alfalfa roots had higher proline, soluble sugar and starch content in D8 than in D2 and D4. In contrast, there was lower malondialdehyde in D8, indicating that alfalfa had better cold resistance following a longer irrigation interval before winter. After examining root biomass, root system traits and physiological indexes we concluded that WL168 exhibited stronger cold resistance. Our results contribute to greater understanding of root and cold stress, consequently providing references for selection of cultivars and field water management to improve cold resistance of alfalfa in the context of changes in rainfall patterns.

Response Strategies of Root System Architecture to Soil Environment: A Case Study of Single-Species Cupressus funebris Plantations

“…Li et al ( 2020 ) argued that root systems shifted from a herringbone branching pattern to a dichotomous branching pattern when plants adjust to drought stress. More recently, Li et al ( 2021 ) also showed that a dichotomous branching pattern is beneficial to cold resistance. Yet, work by Hao et al ( 2021 ) failed to find soil texture influencing the topological index.…”

“…The TI indirectly describes the uptake efficiency of roots for water and nutrients, for which Fitter ( 1994 ) proposed two extreme branching patterns, namely, the dichotomous branching pattern ( TI = 1) to adapt to nutrient-poor soils and the herringbone branching pattern for the nutrient-rich soils ( TI = 0.5). However, due to the influences from plant growth characteristics, soil fertilities, and soil compaction, the TI values always range from 0.5 to 1 (Fitter, 1994 ; Magalhães and Seifert, 2015 ; Li et al, 2020 , 2021 ; Hao et al, 2021 ). In our study, the root system of C. funebris branching pattern changed from a herringbone branching pattern (having a small number of internal links, many external links, many secondary branches, and internal overlaps) to a dichotomous branching pattern exhibiting more internal links, fewer external links, fewer secondary branches, less overlap, and weaker internal competition ( Figures 3A–C ).…”

“…Yan et al ( 2019 ) reported that nitrogen deposition tended to decrease the number of root branches in all root orders. Li et al ( 2021 ) showed that a dichotomous branching pattern is beneficial in cold conditions. In general, there are still a few studies on RSA, and the results are still not unified.…”

Effects of Organic Base Fertilizer and Inorganic Topdressing on Alfalfa Productivity and the Soil Bacterial Community in Saline Soil of the Huanghe River Delta in China

“…We found that the root productivity in June of the planting year was significantly correlated with ANPP in both the current and following year (Table 4). Rapid growth of the root system in the early stages of plant growth is essential for alfalfa productivity, but further research is required to explore the specific mechanisms and processes involved [33].…”

Metabolomic changes in crown of alfalfa (Medicago sativa L.) during de-acclimation

“…In northern China, because of the extended periods of sub-zero air and soil temperatures, only cold tolerant cultivars can be grown. These cultivars can tolerate extremely low temperatures during winter, but they can also adapt to temperature fluctuations in spring 1 , 2 .…”