Effects of root-zone warming, nitrogen supply and their interactions on root-shoot growth, nitrogen uptake and photosynthetic physiological characteristics of maize.

In the context of climate change, the impact of root-zone warming (RW) on crop nutrient absorption and utilization has emerged as a significant concern that cannot be overlooked. Nitrogen (N) is an essential element for crop growth and development, particularly under stress. The comprehensive effect and relationship between RW and N level remains unclear. The objective of this experiment was to investigate the impact of RW on root-shoot growth and photosynthetic physiological characteristics of maize seedlings under varying N levels. The results demonstrated that optimal RW was beneficial to the growth of maize, while excessive root-zone temperature (RT) significantly impeded N uptake in maize. Under low N treatment, the proportion of N distribution in roots increased, and the root surface area increased by 41 %. Furthermore, under low N levels, the decline in root vitality and the increase in root MDA caused by high RT were mitigated, resulting in an enhancement of the root's ability to cope with stress. For the above-ground part, under the double stress of high RT and low N, the shoot N concentration, leaf nitrate reductase, leaf glutamine synthase, chlorophyll content, net photosynthetic rate and shoot dry matter accumulation decreased by 86 %, 60 %, 35 %, 53 %, 64 % and 59 %, respectively. It can be reasonably concluded that reasonable N management is an important method to effectively reduce the impact of high RT stress.

Soil cooling can improve maize root-shoot growth and grain yield in warm climate.

Global warming causes topsoil temperatures to increase, which potentially leads to maize yield loss. We explored the effects of soil warming/cooling on root-shoot growth and maize grain yields by performing pot experiments with a heat-sensitive maize hybrid (HS208) and a normal maize hybrid (SD609) in warm temperate climate in 2019 and 2020. Our results reveal, for the first time, differences in root characteristics, leaf photosynthetic physiology, and yield responses to soil warming and cooling between normal and heat-sensitive maize varieties under a warm temperate climate. Soil warming (+2 and 4 °C) inhibited whole root growth by decreasing root length, volume, and dry mass weight, which indirectly reduced leaf photosynthetic capacity and decreased grain yield/plant by 15.10-24.10% versus control plants exposed to ambient temperature. Soil cooling (-2 °C) promoted root growth and leaf photosynthesis, and significantly increased grain yield of HS208 by 12.61%, although no significant change was found with SD609. It can be seen that under unfavorable conditions of global warming, selection of excellent stress-resistant hybrids plays an important role in alleviating the soil heat stress of maize in warm temperate climate regions.

Root zone temperature regulates potassium absorption and photosynthesis in maize (Zea mays).

Affected by climate warming, the impact of crop root zone warming (RZW) on maize seedling growth and nutrient uptake deserve attention. The characteristics of K uptake in maize under root zone warming and the combined impacts of potassium deficiency and RZW are still unclear. The present study aimed to investigate the effects of RZW on potassium absorption and photosynthesis of maize seedlings under the difference in potassium. The results showed that RZW and low potassium treatment significantly affected root shoot development and photosynthetic physiological characteristics of maize seedlings. Moreover, the interaction of RZW and potassium content had striking influence on maize seedlings. Under the normal potassium with root zone medium temperature treatment, the development of maize was the most vigorous. Under the dual stress of high root zone temperature and low potassium, the root absorption area, total potassium content and root activity were significantly reduced, which then influenced the light energy use efficiency and dry matter accumulation. Securing the supply of potassium fertilizer under high root zone temperature stress is useful to alleviate the impact of high temperature stress.

Negative effects of soil warming, and adaptive cultivation strategies of maize: A review.

Temperature is a key factor in regulating and controlling several ecological processes. As there is a feedback relationship between many biogeochemical processes and climate change, their response to temperature changes is particularly important. Previously, a large volume of literature has extensively explored the impact of rising air temperature on shoot growth and maize yield, from enzymatic responses within the leaf to grain yield. As the global temperature continues to increase and the frequency, duration, and/or intensity of heat wave events increases, the soil temperature of the tilth is likely to rise sharply. As one of the most widely planted food crops in the world, maize may be subjected to additional soil temperature pressure. However, as a nutrient organ in direct contact with soil, the root plays a key role in adapting the whole plant to excessive soil temperature. Little research has been done on the effect of the soil microenvironment induced by higher soil temperature on maize root growth and root to shoot communication regulation. Therefore, this review summarizes (1) the effects of excessive soil temperature on the soil microenvironment, including soil respiration, microbial community composition, carbon mineralization, and enzyme activity; (2) the negative response of absorption of water and nutrients by roots and maize root-shoot growth to excessive soil temperature; and (3) potential cultivation strategies to improve maize yield, including improving tillage methods, adding biochar amendments, applying organic fertilizers, optimizing irrigation, and farmland mulching.

Genome-Wide Association Studies of Maize Seedling Root Traits under Different Nitrogen Levels.

Nitrogen (N) is one of the important factors affecting maize root morphological construction and growth development. An association panel of 124 maize inbred lines was evaluated for root and shoot growth at seedling stage under normal N (CK) and low N (LN) treatments, using the paper culture method. Twenty traits were measured, including three shoot traits and seventeen root traits, a genome-wide association study (GWAS) was performed using the Bayesian-information and Linkage-disequilibrium Iteratively Nested Keyway (BLINK) methods. The results showed that LN condition promoted the growth of the maize roots, and normal N promoted the growth of the shoots. A total of 185 significant SNPs were identified, including 27 SNPs for shoot traits and 158 SNPs for root traits. Four important candidate genes were identified. Under LN conditions, the candidate gene Zm00001d004123 was significantly correlated with the number of crown roots, Zm00001d025554 was correlated with plant height. Under CK conditions, the candidate gene Zm00001d051083 was correlated with the length and area of seminal roots, Zm00001d050798 was correlated with the total root length. The four candidate genes all responded to the LN treatment. The research results provide genetic resources for the genetic improvement of maize root traits.

Effects of Root Zone Warming on Maize Seedling Growth and Photosynthetic Characteristics Under Different Phosphorus Levels.

Phosphorus content and root zone temperature are two major environmental factors affecting maize growth. Both low phosphorus and root zone high temperature stress significantly affect the growth of maize, but the comprehensive effects of phosphorus deficiency and root zone warming are less studied. This study aimed to explore the effects of phosphorus deficiency and root zone warming on the root absorption capacity, total phosphorus content, and photosynthetic fluorescence parameters of maize seedlings. The results showed that maize shoots and roots had different responses to root zone warming and phosphorus deficiency. Properly increasing the root zone temperature was beneficial to the growth of maize seedlings, but when the root zone temperature was too high, it significantly affected the root and shoot development of maize seedlings. The root zone warming had a more significant impact on the root system, while phosphorus deficiency had a greater impact on the shoots. Phosphorus content and root zone warming had a strong interaction. Under the comprehensive influence of normal phosphorus supply and medium temperature in the root zone, the growth of maize seedlings was the best. Under the combined effects of low phosphorus and high temperature in the root zone, the growth was the worst. Compared with the combination of normal phosphorus and root zone medium temperature treatment, the dry mass of the low-phosphorus root zone high temperature treatment was decreased by 55.80%. Under the condition of low-phosphorus too high root zone temperature reduced root vitality, plant phosphorus content, which in turn affected plant growth and light energy utilization efficiency. In the case of sufficient phosphate fertilizer supply, appropriately increasing the soil temperature in the root zone is beneficial to increase the absorption and utilization of phosphorus by plants and promote the growth and development of maize seedlings.