Nitrogen (N) loss is a worldwide problem in crop production. Apart from reasonable N fertilizer application, breeding N efficient cultivars provides an alternative way. Root architecture is an ...important factor determining N acquisition. However, little is known about the molecular genetic basis for root growth in relation to N supply. In the present study, an F₈ maize (Zea may L.) recombinant inbred (RI) population consisting of 94 lines was used to identify the QTLs for root traits under different nitrate levels. The lateral root length (LRL), axial root length (ARL), maximal axial root length (MARL), axial root number (ARN) and average axial root length (AARL) were evaluated under low N (LN) and high N (HN) conditions in a hydroponics system. A total of 17 QTLs were detected among which 14 loci are located on the same chromosome region as published QTLs for root traits. A major QTL on chromosome 1 (between bnlg1025 and umc2029) for the AARL under LN could explain 43.7% of the phenotypic variation. This QTL co-localizes with previously reported QTLs that associate with root traits, grain yield, and N uptake. Our results indicate that longer axial roots are important for efficient N acquisition and the major QTL for AARL may be used as a marker in breeding N efficient maize genotypes.
Main conclusion
In response to low nitrogen stress, multiple hormones together with nitric oxide signaling pathways work synergistically and antagonistically in crop root elongation.
Changing root ...morphology allows plants to adapt to soil nutrient availability. Nitrogen is the most important essential nutrient for plant growth. An important adaptive strategy for crops responding to nitrogen deficiency is root elongation, thereby accessing increased soil space and nitrogen resources. Multiple signaling pathways are involved in this regulatory network, working together to fine-tune root elongation in response to soil nitrogen availability. Based on existing research, we propose a model to explain how different signaling pathways interact to regulate root elongation in response to low nitrogen stress. In response to a low shoot nitrogen status signal, auxin transport from the shoot to the root increases. High auxin levels in the root tip stimulate the production of nitric oxide, which promotes the synthesis of strigolactones to accelerate cell division. In this process, cytokinin, ethylene, and abscisic acid play an antagonistic role, while brassinosteroids and auxin play a synergistic role in regulating root elongation. Further study is required to identify the QTLs, genes, and favorable alleles which control the root elongation response to low nitrogen stress in crops.
Aims
This paper aims to investigate the adaptation of maize root system architecture (RSA) in response to increasing planting densities.
Methods
A three-year field study was conducted with three ...planting densities (40,000, 70,000, and 90,000 plants per ha, which are abbreviated as D40000, D70000 and D90000, respectively). The dynamic change of root morphological traits and the 3-dimensional RSA were quantified.
Results
The grain yield per ha increased with increasing plant density from D40000 to D70000, and then decreased at D90000. Compared to D70000, high planting density of D90000 did not changed the total root biomass per ha but increased shoot biomass per ha by 4 to 8% in two of the three experimental years. Grain yield per plant and plant NPK concentration decreased with increasing planting density. Total accumulation of P and K per ha also decreased at D90000 compared to D70000. Root to shoot ratio was reduced at high planting density beginning 50 days after emergence. Compared to the control (D70000), total root length (TRL) per plant was reduced by 18 to 30% at D90000 and increased by 43 to 56% at D40000, root biomass per plant was reduced by 23 to 34% at D90000 and increased by 66 to 75% at D40000. High plant density reduced the number of nodal roots, lateral root density (LRD) and the average lateral root (LR) length, but with less effect on the length of axial roots. The RSA is characteristic of “intra-row contraction and inter-row extension”. Vertically, root growth in top soil layer (0- to 36- cm) was enhanced under supra-optimal plant density, but had a negligible effect in deep soil layers (36- to 60- cm).
Conclusions
To adapt to the limited photosynthesis capacity in the roots under high planting density, maize plants tend to reduce nodal root number and inhibit lateral root growth. They maintain nodal root length to explore a larger soil space, and adjust root growth in the intra-row and inter-row direction to avoid root-to-root competition.
Root and rhizosphere research has been conducted for many decades, but the underlying strategy of root/rhizosphere processes and management in intensive cropping systems remain largely to be ...determined. Improved grain production to meet the food demand of an increasing population has been highly dependent on chemical fertilizer input based on the traditionally assumed notion of ‘high input, high output’, which results in overuse of fertilizers but ignores the biological potential of roots or rhizosphere for efficient mobilization and acquisition of soil nutrients. Root exploration in soil nutrient resources and root-induced rhizosphere processes plays an important role in controlling nutrient transformation, efficient nutrient acquisition and use, and thus crop productivity. The efficiency of root/rhizosphere in terms of improved nutrient mobilization, acquisition, and use can be fully exploited by: (1) manipulating root growth (i.e. root development and size, root system architecture, and distribution); (2) regulating rhizosphere processes (i.e. rhizosphere acidification, organic anion and acid phosphatase exudation, localized application of nutrients, rhizosphere interactions, and use of efficient crop genotypes); and (3) optimizing root zone management to synchronize root growth and soil nutrient supply with demand of nutrients in cropping systems. Experiments have shown that root/rhizosphere management is an effective approach to increase both nutrient use efficiency and crop productivity for sustainable crop production. The objectives of this paper are to summarize the principles of root/rhizosphere management and provide an overview of some successful case studies on how to exploit the biological potential of root system and rhizosphere processes to improve crop productivity and nutrient use efficiency.
•Net remobilization from the total vegetative organs was shown in N, P, K, Mn and Zn.•The mobility of the nutrients is organ-specific and vulnerable to weather conditions.•Low-N did not improve grain ...nutrient concentration.
The introduction of new hybrids and integrated crop-soil management has been causing maize grain yield to increase. However, less attention has been paid on the nutrient concentration of the grain; this aspect is of great importance to supplying calories and nutrients in the diets of both humans and animals worldwide. Increasing the retranslocation of nutrients from vegetative organs to grain can effectively increase the nutrient concentration of grain and general nutrient use efficiency. The present study involved monitoring the dynamic change of macro- and micronutrients in different organs of maize during the grain filling stage. In addition, the mobility of different elements and their contribution to grain nutrient content were evaluated in a 2-year experiment under low (LN, no N supplied) and high N (HN, 180kgNha−1) supply. Under HN supply, the net remobilization efficiency (RE) of the vegetative organs as a whole (calculated as nutrient remobilization amount divided by nutrient content at silking) of N, P, K, Mn, and Zn were 44%, 60%, 13%, 15%, and 25%, respectively. The other nutrients (Mg, Ca, Fe, Cu, and B) showed a net accumulation in the vegetative organs as a whole during the grain filling stage. Among the different organs, N, P, and Zn were remobilized more from the leaves (RE of 44%, 51% and 43%, respectively) and the stalks (including leaf sheaths and tassels) (RE of 48%, 71% and 43%, respectively). K was mainly remobilized from the leaves with RE of 51%. Mg, Ca, Fe, Mn, and Cu were mostly remobilized from the stalks with the RE of 23%, 9%, 10%, 42%, and 28%, respectively. However, most of the remobilized Mg, Ca, Fe, Mn, Cu, and Zn were translocated to the husk and cob, which seemingly served as the buffer sink for these nutrients. The REs of all the nutrients except for P, K, and Zn were vulnerable to variations in conditions annually and were reduced when the grain yield and harvest index were lower in 2014 compared with 2013. Under LN stress, the RE was reduced in P and Zn in 2013, increased in Cu and unchanged in other nutrients. The concentration of these nutrients in the grain was either unchanged (P, K, Ca, Zn, and B) or decreased (N, Mg, Fe, Mn, and Cu). It is concluded that grain N, P, K, Mn, and Zn, but not Mg, Ca, Fe, Cu, and B concentration, can be improved by increasing their remobilization from vegetative organs. However, enhancing the senescence of maize plant via LN stress seems unable to increase grain mineral nutrient concentration. Genetic improvement aiming to increase nutrient remobilization should take into account the organ-specific remobilization pattern of the target nutrient.
Nitrogen (N) plays a vital role in photosynthesis and crop productivity. Maize plants may be able to increase physiological N utilization efficiency (NUtE) under low-N stress by increasing ...photosynthetic rate (P n) per unit leaf N, that is, photosynthetic N-use efficiency (PNUE). In this study, we analyzed the relationship between PNUE and N allocation in maize ear-leaves during the grain-filling stage under low N (no N application) and high N (180 kg N ha(-1)) in a 2-year field experiment. Under low N, grain yield decreased while NUtE increased. Low-N treatment reduced the specific N content of ear leaves by 38% without significant influencing P n, thereby increasing PNUE by 54%. Under low-N stress, maize plants tended to invest relatively more N into bioenergetics to sustain electron transport. In contrast, N allocated to chlorophyll and light-harvesting proteins was reduced to control excess electron production. Soluble proteins were reduced to shrink the N storage reservoir. We conclude that optimization of N allocation within leaves is a key adaptive mechanism to maximize P n and crop productivity when N is limited during the grain-filling stage in maize under low-N conditions.
Nitrogen is a major limiting factor for crop productivity. The relationship between photosynthesis and nitrogen nutrition has been widely studied. However, the molecular response of leaf ...photosynthesis to low nitrogen supply in crops is less clear. In this study, RNA sequencing technology (RNA-Seq) was used to investigate the gene expressions related to photosynthesis in maize in response to low nitrogen supply. It was found that low nitrogen supply down-regulated the expression of genes involved in photosystem I (PSI) and photosystem II (PSII). Thus, low nitrogen supply down-regulated the expression of genes related to the antenna system, reduced light absorption, light transport, and electron transport. Correspondingly, the parameters related to chlorophyll fluorescence were very sensitive to nitrogen deficiency. Under low nitrogen supply, leaf chlorophyll content, actual quantum yield of PSII photochemistry, photochemical quenching, and electron transport rate, were reduced. However, the thermal diffusion and chlorophyll fluorescence were increased. RNA-Seq was used to analyze the genes involved in the response of leaf photosynthesis to low nitrogen supply in maize. These results highlight the possibility of utilizing chlorophyll fluorescence parameters, and the related genes, as indicators for plant nitrogen nutrition. This could lead to the development of new tools to make precise nitrogen fertilizer recommendations and select nitrogen-efficient genotypes.
The impact of global changes on food security is of serious concern. Breeding novel crop cultivars adaptable to climate change is one potential solution, but this approach requires an understanding ...of complex adaptive traits for climate‐change conditions. In this study, plant growth, nitrogen (N) uptake, and yield in relation to climatic resource use efficiency of nine representative maize cultivars released between 1973 and 2000 in China were investigated in a 2‐year field experiment under three N applications. The Hybrid‐Maize model was used to simulate maize yield potential in the period from 1973 to 2011. During the past four decades, the total thermal time (growing degree days) increased whereas the total precipitation and sunshine hours decreased. This climate change led to a reduction of maize potential yield by an average of 12.9% across different hybrids. However, the potential yield of individual hybrids increased by 118.5 kg ha−1 yr−1 with increasing year of release. From 1973 to 2000, the use efficiency of sunshine hours, thermal time, and precipitation resources increased by 37%, 40%, and 41%, respectively. The late developed hybrids showed less reduction in yield potential in current climate conditions than old cultivars, indicating some adaptation to new conditions. Since the mid‐1990s, however, the yield impact of climate change exhibited little change, and even a slight worsening for new cultivars. Modern breeding increased ear fertility and grain‐filling rate, and delayed leaf senescence without modification in net photosynthetic rate. The trade‐off associated with delayed leaf senescence was decreased grain N concentration rather than increased plant N uptake, therefore N agronomic efficiency increased simultaneously. It is concluded that modern maize hybrids tolerate the climatic changes mainly by constitutively optimizing plant productivity. Maize breeding programs in the future should pay more attention to cope with the limiting climate factors specifically.
The effects of 13 plant growth–promoting rhizobacteria (PGPR) from the maize rhizosphere and a model PGPR strain
Azospirillum brasilense
Az39 on maize growth were monitored in a 3-year field ...inoculation experiment (from 2018 to 2020) with low-nitrogen (N) (N input reduced by 50%) and low-phosphorus (P) (no P supply) soils in Northeast China. The effects of four efficient PGPR that stably promoted maize plant growth and affected on the composition and function of the rhizobacterial community were further investigated in 2019 and 2020. On average,
Sinorhizobium
sp. A15,
Bacillus
sp. A28,
Sphingomonas
sp. A55, and
Enterobacter
sp. P24 stably increased grain yield by 8.1–17.8% and 11.0–20.1% in low-N and low-P soil, respectively. Inoculation of these four strains increased the abundance and species richness of rhizobacteria, enriched special beneficial bacteria such as
Chloroflexia
_KD4-96 and
Bacilli
, and decreased bacterial functions related to soil-N loss. We conclude that some PGPR can N- and P-use efficiency and maize yield through reshaping the rhizobacterial community.
To understand how root growth responds to temperature, we used kinematic analysis to quantify division and expansion parameters in the root of Arabidopsis thaliana. Plants were grown at temperatures ...from 15 to 30 °C, given continuously from germination. Over these temperatures, root length varies more than threefold in the wild type but by only twofold in a double mutant for phytochrome‐interacting factor 4 and 5. For kinematics, the spatial profile of velocity was obtained with new software, Stripflow. We find that 30 °C truncates the elongation zone and curtails cell production, responses that probably reflect the elicitation of a common pathway for handling severe stresses. Curiously, rates of cell division at all temperatures are closely correlated with rates of radial expansion. Between 15 to 25 °C, root growth rate, maximal elemental elongation rate, and final cell length scale positively with temperature whereas the length of the meristem scales negatively. Non‐linear temperature scaling characterizes meristem cell number, time to transit through either meristem or elongation zone, and average cell division rate. Surprisingly, the length of the elongation zone and the total rate of cell production are temperature invariant, constancies that have implications for our understanding of how the underlying cellular processes are integrated.
How temperature affects growth components in roots has been little studied. Based on new software for determining the velocity profile, we present a kinematic analysis of growth parameters for the Arabidopsis thaliana root for seedlings grown continuously at temperatures ranging from 15 to 30 °C. A notable finding is that, between 15 and 25 °C, the cumulative rate of cell production is temperature invariant, implying the existence of hitherto unsuspected mechanisms for temperature compensation.
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