Root Length Density Research Articles

Improving crop modeling in saline soils by predicting root length density dynamics with machine learning algorithms

Improving crop modeling in saline soils by predicting root length density dynamics with machine learning algorithms

Asparagus (Asparagus officinalis L.) Root Distribution: Cultivar Differences in Mature Plantings

Annual plant growth patterns and seasonal conditions have both been shown to influence asparagus (Asparagus officinalis L.) root development over time. Root biomass and distribution changes in mature asparagus cultivars are herein illustrated and described. Asparagus root length density and biomass were estimated from soil cores using a systematic field sampling approach each spring. Soil cores (0.9 m deep) were divided into 0.15 m lengths and fleshy roots collected from the soil. Root length density and dry weights were determined and root distribution maps generated from collected data. As asparagus plantings matured, the sampling year had a significant influence on root development. Fleshy roots grew deeper into the soil each year but the majority of roots of Atlas, Guelph Millennium, and Jersey Giant were found in the upper 60 cm of the soil profile. For the three cultivars evaluated, minor differences in root length and root weight occurred. By Year 6, Atlas showed a decrease in root length and weight when compared to Guelph Millennium and Jersey Giant. While spear yield differences between the varieties were not significant, Atlas tended to produce more very large and large spears compared to Guelph Millennium and Jersey Giant. These results increase our understanding of asparagus root development.

Oil radish, winter rye and crimson clover: root and shoot performance in cover crop mixtures

Abstract Purpose The current knowledge of belowground interactions in intercropping systems is limited due to methodological constraints. The current study aimed to investigate cereal-brassica and cereal-legume-brassica cover crop mixtures regarding mixture effects on root and shoot biomass as well as root traits, vertical root niche differentiation, and complementarity. Methods Sole crops and two- and three-species-mixtures of winter rye (Secale cereale L.), crimson clover (Trifolium incarnatum L.), and oil radish (Raphanus sativus L. var. oleiformis Pers.) were grown in Germany in a two-year organic field experiment. Root traits were analysed using the monolith method. For discrimination of species root mass Fourier transform infrared (FTIR) spectroscopy was used. Results Oil radish dominated mixtures above- and belowground. Oil radish and its mixtures had highest root length density (RLD) and root mass density (RMD) in subsoil. Rye had highest root biomass and RLD in topsoil. Clover was uncompetitive and had low RLD and RMD. Large but non-significant mixture effects occurred in the shoot, especially for shoot nutrient uptake. Mixture effects were positive for RLD and RMD in subsoil and positive for specific root length (SRL) throughout the whole profile. There was no clear evidence for vertical root niche differentiation and root mass complementarity. Conclusion Oil radish as a mixing partner increased rooting in subsoil. When comparing mixtures and sole crops, morphological changes, i.e. higher SRL in mixtures, were found. Contrary to expectations, changes in root allocation patterns, such as vertical niche differentiation or complementarity of root mass, were not observed.

Effects of arbuscular mycorrhizal fungi inoculation on infection and growth of rice and pearl millet in upland fields with three water regimes

ABSTRACT Inoculation with arbuscular mycorrhizal fungi (AMF) may enhance crop growth in upland fields, depending on the water regime. To quantify changes in AMF infection rate and subsequent effects on nutrient uptake and growth, we grew rice (wetland crop) and pearl millet (dryland crop) genotypes with or without the commercial inoculant Dr. Kinkon (Glomus sp. R10) in Andosol upland fields in 2020 and 2021. Root infection rates were measured in shallow (0–10 cm) and deep (20–30 cm) layers under three water regimes: well-irrigated, half-irrigated, and non-irrigated. Inoculation enhanced shoot dry weight (SDW), plant height, tiller number, phosphorus (P) uptake, leaf water potential, photosynthetic rate (measured only in 2021) and root transversal area. The increase in SDW with inoculation was higher under well-irrigated than under water-limited conditions. The increment in pearl millet SDW was related to higher P uptake associated with higher infection rates, whereas that in rice SDW was related to maintenance of leaf water potential, greater root transversal area and root length density, and higher P uptake but not to infection rate parameters. Inoculation increased mycorrhizal and vesicular infection rates with the similar tendency for arbuscular infection rate and qPCR. Infection rates were similar across water regimes in both years despite significant differences in plant growth parameters with higher rates in deep than shallow layers. AMF inoculation enhanced infection rates, mostly independent of water regime, but plant growth enhancement was greater under the well-irrigated treatment and was more directly linked with infection rates in pearl millet.

Creeping Bentgrass Nutritional, Morphological, and Putting Green Performance Response to Ca/Mg-Silicate Slag Liming Agent

While not classified as an essential plant nutrient, silicon (Si) assimilation following exogenous Si application has enhanced the wear resistance of cool-season turfgrass. Given this beneficial supplementation of lignin by Si reported in epidermal tissue of monocotyledonous plants, our research objective was to quantify root morphology, vegetative nutrition and vigor, soil chemistry, and putting green performance in response to split applications of pelletized liming agents rich in Si and/or Ca and Mg. Field evaluation of granular liming agent treatment, 2441 kg (ha year)−1, was conducted on creeping bentgrass (Agrostis stolonifera L. cv. Penn G-2) putting green maintained in the Mid-Atlantic US. Pelletized Ca/Mg-SiO3 slag or dolomitic limestone treatments were conducted in frequent split applications and incorporated into the upper 5 cm of the rootzone. Measurements of canopy color and density, shoot growth as clipping yield, soil pH, Si and nutrient content of clippings, and soil extractable Si were performed each season. Cumulative Ca/Mg-SiO3 application (kg ha−1) increased mean acetic acid (HOAc) extractable Si by 35 to 60 mg kg−1 and leaf Si content by 1.0 to 1.5 mg g−1. However, neither putting green canopy quality, shoot nutrient concentration, 5 to 15 cm depth root length density nor ball roll distance was improved by liming agent treatment. Liming agent-treated or untreated plots showed statistical, yet inconsistent, differences in clipping yield 4, 14, 15, 16, and 17 months from initiation (MFI). This thorough shuffling of treatment rank, resulting in identical experiment-wide means precludes the expectation of dependably superior vigor by any.

Effects of Root Growth of Deep and Shallow Rooting Rice Cultivars in Compacted Paddy Soils on Subsequent Rice Growth

Rice is often grown as multiple seasons in one year, alternating between flooded and upland systems. A major constraint, introduced from the flooded system, is a plough pan that may decrease rooting depth and productivity of follow-on upland rice. Roots penetrating the plough pan under flooded rice system can leave a legacy of weaker root growth pathways. Deeper rooting rice cultivars could have a bigger impact, but no direct evidence is available. To explore whether a deep rather than a shallow rooting rice cultivar grown in a flooded cropping cycle benefited deeper root growth of follow-on rice in an upland, reduced tillage cropping cycle, a simulated flooded paddy in greenhouse was planted with deep (Black Gora) and shallow (IR64) rooting cultivars and a plant-free control. Artificial plough pans were made in between the topsoil and subsoil to form different treatments with no plough pan (0.35 MPa), soft plough pan (1.03 MPa) and hard plough pan (1.70 MPa). After harvest of this ‘first season’ rice, the soil was drained and undisturbed to simulate zero-tillage upland and planted rice cultivar BRRI Dhan 28. The overall root length density (RLD), root surface area, the numbers of root tips and branching of BRRI Dhan 28 did not vary between plough pan and no plough pan treatments. Compared with the shallow rooting rice genotype, the deep rooting rice genotype as ‘first season’ crop produced 19% greater RLD, 34% greater surface area and 29% more branching of BRRI Dhan 28 in the subsoil. In the topsoil, however, BRRI Dhan 28 had 28% greater RLD, 35% greater surface area and 43% more branching for the shallow rather than deep rooting genotype planted in the ‘first season’. The results suggested that rice cultivar selection for a paddy cycle affects root growth of a follow-on rice crop grown under no-till, with benefits to subsoil access from deep rooting cultivars and topsoil proliferation for shallow rooting cultivars.

Nitrogen-fixing tree species modulate species richness effects on soil aggregate-associated organic carbon fractions

Soil aggregation is an important mechanism shaping soil organic carbon (SOC) fractions, but the effects of tree species richness on soil aggregate-associated organic carbon fractions are poorly understood. In this study, a manipulative experiment was conducted to examine whether and how tree species richness (1, 2, 4 and 6) together with or without the presence of nitrogen (N)-fixing tree species affect soil aggregate-associated organic carbon. Soil aggregates were classified into four fractions: large macroaggregates (>2 mm), small macroaggregates (0.25–2 mm), microaggregates (0.053–0.25 mm), and silt and clay (<0.053 mm). And then large and small macroaggregates were further separated into coarse (c-iPOC), fine intra-aggregate particulate organic carbon (f-iPOC) and mineral associated organic carbon (MAOC), and microaggregates were divided into f-iPOC and MAOC. We observed that the effects of tree species richness on soil aggregate-associated organic carbon fractions were depended on the presence or absence of N-fixing tree species. In the presence of N-fixing tree species, organic carbon contents of small macroaggregate, microaggregate and silt and clay fractions were increased across the gradient of tree species richness (+10.4%, +31.3% and + 26.7% from monocultures to 6-species mixture), and the similar responses occurred for c-iPOC within small macroaggregates (+42.9%) and f-iPOC within microaggregates (+50.0%). In the absence of N-fixing tree species, however, only f-iPOC within large macroaggregates (+60.0%) had a positive linear relationship with tree species richness. Structural equation modeling was then used to dissect the mechanism underlying the positive effects of tree species richness on the aggregate-associated organic carbon fractions, indicating either direct or indirect effects by increasing root length density. Our study highlights the important roles of N-fixing tree species in shaping tree species richness effects on soil aggregate-associated organic carbon fractions, and therefore, N-fixing tree species should be preferentially considered in mixed-species plantations to enhance long-term SOC stabilization.

Effects of Foliar-Applied Mixed Mineral Fertilizers and Organic Biostimulants on the Growth and Hybrid Seed Production of a Male-Sterile Inbred Maize Line.

Plants of inbred maize lines are characterized by low vigor due to their high rates of homozygosity and may, therefore, benefit from additional nutrients and biostimulants supplied via foliar spraying. The present study innovatively investigated the effects of foliar treatment with three commercial organic-mineral fertilizers/biostimulants on a male-sterile inbred line of maize at the five-leaf stage. The three fertilizers were characterized by their following content: (i) NPK + hydrolyzed animal epithelium + micronutrients (named 'NPK + Hae + micro'), (ii) NK + humified peat (named 'NK + Hp'), and (iii) PK + Ascophyllum nodosum extracts (named 'PK + An'). The resulting shoot and root growth and seed yield and quality were compared to a control (C). Both NPK + Hae + micro and PK + An treatments enhanced root growth in the top 20 cm soil layer at the ten-leaf stage: root dry biomass increased by 80 and 24%, respectively, and the volumetric root length density by 61 and 17%. The two treatments also allowed for a larger number of commercial seeds to be produced (on average +16 bags per gross hectare vs. C) owing to a better seed caliber, which consequently reduced rates of seed disposal (-11 and -20% for PK + An and NPK + Hae + micro, respectively) and, in the case of NPK + Hae + micro, due to an increment in the number of kernels per ear (+5% vs. C). These effects were not associated with any significant changes in shoot growth, height, or leaf net CO2 assimilation. In this preliminary trial, peak commercial benefit was obtained with the use of hydrolyzed epithelium together with macro- and micronutrients. Further investigation into application timing and dose, and the means by which these products alleviate the effects of low vigor and stress conditions observed particularly under mechanical emasculation is, however, necessary for their full exploitation in the production of hybrid maize seeds.

Effect of Tillage and Residue Management on Wheat Yield and Water Productivity

The present investigation was conducted in wheat at the Punjab Agricultural University, Ludhiana, to study effect of four tillage viz mould board ploughing to a depth of 25 cm followed by rotavator (PT25+R), mould board ploughing to a depth of 14 cm followed by rotavator (PT14+R), zero tillage with happy seeder (ZT) and conventional practices (CT) and three irrigation scheduling based on IW/PAN-E ratio I1 ( 0.6 ), I2 (0.8) and I3 (1.0) on soil water balance and crop growth for two consecutive years (2016-17 and 2017-18). Straw and grain yield was significantly higher in I3 over I1 and I2 by 46.05 &amp; 38.5% and 8.72% &amp; 11.30 % respectively during both years. Water productivity increased significantly in I2 over I1 and I3 by 27.38 &amp; 2.26% in 2016-17 and 27.70 &amp; 1.91% in 2017-18. During both years higher water was stored by ZT &amp; I3 over PT25+R, PT14+R, CT, I1 and I2. During both years highest water was depleted under PT14+R &amp; I1 over PT25+R, ZT, CT, I2 and I3. The overall mean number of tillers, leaf area index, root length and mass density were significantly higher under PT25+R than PT14+R, ZT and CT.

Subsoiling depth affects the morphological and physiological traits of roots in film-mulched and drip-irrigated cotton

Subsoil compaction is increasingly a problem. Subsoiling breaks up the soil, removes compaction, and improves root growth. However, it is unclear whether subsoiling depth affects root growth and physiological functioning of film-mulched and drip-irrigated cotton, which has a shallow root system (< 60 cm). A 2-year experiment (2019–2020) was performed under field conditions (soil texture was sandy loam from 0 to 40 cm and clay loam from 40 to 60 cm) to determine the morphological and physiological traits of the root system at different subsoiling depths: no subsoiling (NS, control) and subsoiling to 30 (S30), 40 (S40), and 50 (S50) cm. The root/shoot ratios were significantly higher for the S30 and S40 treatments than for the control (p < 0.05). The dry matter levels over the 2 years were 24.2% higher in S40 plants than in controls and 20.7% higher than in the others subsoiling treatments. The average 2-year yields (676.9 g m–2) were 24.3%, 11.9%, and 1.4% higher in S40 plants than in controls, S30, and S50 plants. At different soil depths of 0–60 cm, the average 2-year root length density (RLD) of all subsoiling treatments was 0.5 cm cm−3 in the top 20 cm of soil, 14.0% higher than that from 20 to 40 cm and 344.2% higher than that from 40 to 60 cm. However, RLDs of the NS and S30 treatments were highest at 0–20 cm, while S40 and S50 maximum RLDs were in the 20–40 cm layers. The RLD, average diameter of roots, and surface area density of roots were significantly higher in the S40 and S50 treatments than in the S30 and NS treatments (p < 0.05). Compared to NS, subsoiling reduced the levels of malondialdehyde and abscisic acid in roots; improved superoxide dismutase, peroxidase, and catalase activities in roots, and increased the levels of gibberellic acid and indole-3-acetic acid in roots. Our results provide evidence that could help optimize subsoiling depth in film mulching and drip-irrigated cotton in Xinjiang.

Melatonin Increases Drought Resistance through Regulating the Fine Root and Root Hair Morphology of Wheat Revealed with RhizoPot

Melatonin application has obvious improving effects on alleviating the drought-induced inhibition of plant growth. However, the root phenotypic dynamics in wheat treated with melatonin remain unknown. This study was conducted using RhizoPot, a novel and improvised in situ root observation device, with three treatments, including normal water condition (CK), drought condition (Ds, relative water content 45–50%), and 100 µM melatonin treatment under drought condition (MT). Results showed that MT application effectively improves root morphological indicators, including root (specific root) length, surface area, and volume; root length density; and the average root diameter of wheat plants. Also, the inhibitory effect of drought on shoot morphology, including plant height, dry weight, net photosynthesis, and stomatal aperture of leaves, were improved significantly through MT under drought condition. Life span and percent survival of fine root, lateral root, and root hair at different segments were also effectively improved under MT treatment. Compared with those shown under CK and Ds, the melatonin contents in leaves and roots were increased, and the expression levels of melatonin-synthesis-related genes (TaCOMT and TaTDC) were upregulated significantly under MT treatment. The findings of this study may clarify the drought resistance mechanism of wheat treated with melatonin under drought stress.

Oriental beech roots improve soil aggregate stability and reduce soil detachment rate in forest lands

In many forestlands, such as Saravan Forest Park, the high capacity of soil detachment from deforestation and subsequent ecological restoration are important issues that need detailed information about plant and tree species for the objectives of soil conservation. To determine if some species are more helpful for the stability of soil aggregates and thus reducing soil erosion, we examined Oriental beech species, compared to three other species (Crataegus ambigue, Primula heterochroma and Rubus persicus) in the Saravan forest park, and measured how root characteristics (root biomass, root length and root weight density) influenced mean weight diameter of aggregates (MWD) and soil detachment rate (Dc). For measuring Dc, undisturbed samples collected from soils under the four studied species and subjected to five slopes (from 4.8 to 31.4%) and five water discharges (from 0.26 to 0.65 l m−1 s−1) by a hydraulic flume. Results showed that Oriental beech roots can significantly influence soil aggregate stability. MWD was greater in soil under Oriental beech species characterized by high values of root biomass, root length and root weight density. Moreover, Dc was significantly lower in soils with Oriental beech species compared to three other species. Pearson's correlation matrix showed a strong positive correlation between MWD and the root characteristics (P < 0.01) (R2 = 0.8). Also, the clustering of soils among the studied species by the principal component analysis (PCA) revealed a clear difference based on the root characteristics and MWD. Generally, this study showed that, compared with other species, the root system of Oriental beech is more effective in the stabilization of slope by the binding effect on the soil, thus improving aggregate stability and reducing soil detachment rates.

Increasing root-lower characteristics improves drought tolerance in cotton cultivars at the seedling stage

Drought is an important abiotic stress factor in cotton production. The root system architecture (RSA) of cotton shows high plasticity which can alleviate drought-related stress under drought stress (DS) conditions; however, this alleviation is cultivar dependent. Therefore, this study estimated the genetic variability of RSA in cotton under DS. Using the paper-based growth system, we assessed the RSA variability in 80 cotton cultivars at the seedling stage, with 0 and 10% polyethylene glycol 6000 (PEG6000) as the control (CK) and DS treatment, respectively. An analysis of 23 above-ground and root traits in the 80 cotton cultivars revealed different responses to DS. On the 10th day after DS treatment, the degree of variation in the RSA traits under DS (5–55%) was greater than that of CK (5–49%). The 80 cultivars were divided into drought-tolerant cultivars (group 1), intermediate drought-tolerant cultivars (group 2), and drought-sensitive cultivars (group 3) based on their comprehensive evaluation values of drought resistance. Under DS, the root length-lower, root area-lower, root volume-lower, and root length density-lower were significantly reduced by 63, 71, 76, and 4% in the drought-sensitive cultivars compared to CK. Notably, the drought-tolerant cultivars maintained their root length-lower, root area-lower, root volume-lower, and root length density–lower attributes. Compared to CK, the root diameter (0–2 mm)-lower increased by 21% in group 1 but decreased by 3 and 64% in groups 2 and 3, respectively, under DS. Additionally, the drought-tolerant cultivars displayed a plastic response under DS that was characterized by an increase in the root-lower characteristics. Drought resistance was positively correlated with the root area-lower and root length density-lower. Overall, the RSA of the different cotton cultivars varied greatly under DS. Therefore, important root traits, such as the root-lower traits, provide great insights for exploring whether drought-tolerant cotton cultivars can effectively withstand adverse environments.

Nutrient Management Influences Root Characteristics and Nitrogen Use Efficiency in the Vegetable-Based Agroecosystem in the Northwestern Himalayas

Imbalanced nutrient fertilization adversely affects root growth and alters the nutrient use efficiency of a crop. This study aimed to understand the influence of integrated nutrient management on root characteristics and nitrogen use efficiency in the vegetable-based agroecosystem. The field trial was conducted at the Department of Soil Science and Water Management of Dr. Y S Parmar University of Horticulture and Forestry Nauni, Solan (HP) India in 2019 and 2020. There were nine treatments viz. T1- control, T2-100% farmyard manure (FYM; N equivalent basis), T3-100% N, T4-100% NP, T5-100% NK, T6-100% PK, T7-100% NPK, T8-100% NPK + FYM (recommended practice), and T9-150% NPK + FYM on root densities (mass, volume, and length) and N use efficiency of cauliflower and capsicum. The results observed that different treatments exert significant effects on measured as well as derivative parameters. In detail, the application of 150% NPK + FYM recorded significantly higher root-mass density (0.72 and 1.71 g m−3 × 10−3), root-volume density (4.49 and 2.52 m3 m−3 × 10−3), and root-length density (1.21 and 0.81 cm m−3 × 10−4) in cauliflower and capsicum, respectively, which was statistically at par with treatment T9 (100% NPK + FYM). Similarly, this treatment (150% NPK + FYM) resulted in a maximum positive N (774.6 kg ha−1), P (650.4 kg ha−1), and K (334.9 kg ha−1) balance of soil after the complete harvest of two cropping-sequence cycles. However, maximum agronomic N use efficiency (59.9 and 67.9 kg kg−1) and apparent recovery of N (39.3 and 59.7%) were recorded under 100% FYM (N equivalence) in cauliflower and capsicum, respectively, but this treatment produced the negative N balance (−91.7 kg ha−1) and K (−340.3 kg ha−1) in soil, whereas significant improvement in agronomic use efficiency, apparent recovery of applied N, as well as in soil, and the NPK balance was recorded under 100% NPK + FYM over the other treatment. This study recommended an integrated nutrient module that is the application of 100% NPK + FYM to ensure better root growth and positive nutrient balance in the soil.

Infiltration and shear strength characteristics of gully heads soil of typical vegetation on the gullied Loess Plateau, Northwest China.

Gully head is the main active part of gully erosion, which seriously affects the occurrence of gully headcut erosion. To investigate root distribution and soil physical and mechanical characteristics of typical vegetation gully head, we analyzed the infiltration, root distribution, physical and mechanical properties of soil-root complex of soil in different layers (0-1 m) in natural restoration gully head and artificial restoration gully head. The results showed that the variability of soil bulk and total porosity among different vegetation gully heads was low, with bulk density ranging from 1.10 to 1.37 g·cm-3 and total porosity ranging from 48.3% to 58.4%. Infiltration index of different vegetation gully heads generally decreased with increasing soil depth. The infiltration rate of different soil layers in natural restoration gully head tended to stabilize in 20-30 min, while that of artificial restoration gully head tended to stabilize in 40 min. The infiltration capacity and average infiltration rate of artificial restoration gully head were generally higher than those of natural restoration gully head in all soil layers. Root length density, root surface area density, and average diameter all tended to decrease with increasing soil depth. Except for the 20-40 cm soil layer, root length density, root surface area density and average diameter of natural restoration gully head were all lower than those of artificial restoration gully head. Root system of both vegetation gully heads mainly consisted of 0-0.5 mm roots, accounting for 84.2%-93.6% of the total root length. In the vertical depth, with the increases of water content, the cohesion force decreased linearly with the deepening of soil layer, ranging from 0.42 to 22.67 kPa. The average cohesion force of artificial restoration gully head was higher than natural restoration gully head at each level of water content. The study revealed the effects of vegetation on the gully head cut erosion, which could provide scientific basis for the effective prevention and control of soil erosion in the region.

Quantifying root-induced soil strength, measured as soil penetration resistance, from different crop plants and soil types

A common soil mechanical property for assessing soil strength is soil penetration resistance (PR) or soil cone index (CI), which is related to the undrained shear strength of saturated and cohesive soil. Plant roots can increase soil strength, but physical conditions may confound this. Pot experiments were conducted using 70 cm soil columns, three soil types (beach sand, erosion-prone soil, and two typical arable soils), and four crop plants (maize, sorghum, Napier, and vetiver grass). We tested the hypothesis that plant roots impact soil strength, measured as soil PR, and the induced soil strength differs based on plant species. The CI and root system architecture (RSA) traits were measured. Napier grass grown in arable soils recorded higher total biomass. Together with maize, Napier grass had a more significant root length density, particularly at 25–40 cm depth. The CI increased with increasing depth, with a 57–99% increase in CI in the bottom layer compared to the top layer of the soil column. The overall CI of soils grown to Napier grass (2.0 and 2.3 MPa) and maize (1.7 and 2.2 MPa) were similar, but both were higher than the soils cultivated with the other crop plants and unplanted control. The overall CI of the SEA sand of ∼2.0 MPa was 36%, higher than that for the arable soils. Soil moisture content did not significantly increase CI, but the interaction of soil bulk density and root system traits could be implicated in increased CI of root-permeated soils. It is concluded that (i) roots growing in arable soils can increase CI and hence soil strength, possibly due to the binding effect of root systems, even when the transpiration effect of plants on soil moisture is low; (ii) crop plants contribute differently to soil strength, and (iii) Napier grass could offer a rapid growth and establishment option when considering plants for soil reinforcement and stability.

Partial replacement of chemical fertilizer by manure affects maize root traits in North China Plain

AbstractIn order to achieve high yields and environmental friendliness simultaneously, the replacement of chemical fertilizers by manure has become a research hotspot in recent years. Roots absorb nitrogen, participate in its assimilation and contribute to the cereal's dry matter accumulation. A 5‐year filed experiment in the North China Plain was initiated to assess the response of root morphology and distribution of summer maize (Zea mays L.) to fertilizer application and contribution to crop yield. The treatments included CK (unfertilized control), NPK (inorganic nitrogen/phosphorus/potassium fertilizer) and NPKM (manure + 70% NPK). We determined the root biomass, root diameter, root length density (RLD) of three diameters (&gt;0.8 mm, 1stRLD; 0.2–0.8 mm, 2ndRLD; &lt;0.2 mm, 3rdRLD) and the soil chemical properties at 60 cm with 10 cm increments. At 40–60 cm, NPKM significantly decreased the root diameter than NPK. Fertilization showed no effect on total RLD, 1stRLD, 2ndRLD and 3rdRLD for a 60‐cm soil profile. At 40–50 cm, the NPKM increased the RLD compared to NPK, mainly by increasing the 2ndRLD and 3rdRLD. Under CK and NPK, root lengths of 0–20 cm made up 62% and 57% of the total root length, respectively. Under NPKM, root lengths of 40–60 cm made up 46% of the total root length. Our results indicate that maize yield was preserved after replacing 30% of N fertilizer with manure, presumably depending on the change of root vertical distribution pattern and increase of the fine root length in deeper soil.

Transpiration response to soil drying versus increasing vapor pressure deficit in crops: physical and physiological mechanisms and key plant traits.

The water deficit experienced by crops is a function of atmospheric water demand (vapor pressure deficit) and soil water supply over the whole crop cycle. We summarize typical transpiration response patterns to soil and atmospheric drying and the sensitivity to plant hydraulic traits. We explain the transpiration response patterns using a soil-plant hydraulic framework. In both cases of drying, stomatal closure is triggered by limitations in soil-plant hydraulic conductance. However, traits impacting the transpiration response differ between the two drying processes and act at different time scales. A low plant hydraulic conductance triggers an earlier restriction in transpiration during increasing vapor pressure deficit. During soil drying, the impact of the plant hydraulic conductance is less obvious. It is rather a decrease in the belowground hydraulic conductance (related to soil hydraulic properties and root length density) that is involved in transpiration down-regulation. The transpiration response to increasing vapor pressure deficit has a daily time scale. In the case of soil drying, it acts on a seasonal scale. Varieties that are conservative in water use on a daily scale may not be conservative over longer time scales (e.g. during soil drying). This potential independence of strategies needs to be considered in environment-specific breeding for yield-based drought tolerance.

Nitrogen reduction combined with ETc irrigation maintained summer maize yield and increased water and nitrogen use efficiency.

High rainfall and excessive urea application are counterproductive to summer maize growth requirements and lower grain yield and water/nitrogen (N) use efficiency. The objective of this study was to determine whether ETc irrigation based on summer maize demand and reduced nitrogen rate in the Huang Huai Hai Plain increased water and nitrogen use efficiency without sacrificing yield. To achieve this, we conducted an experiment with four irrigation levels [ambient rainfall (I0) and 50% (I1), 75% (I2), and 100% (I3) of actual crop evapotranspiration (ETc)] and four nitrogen rates [no nitrogen fertilizer (N0), recommended nitrogen rate of urea (NU), recommended nitrogen rate of blending controlled-release urea with conventional urea fertilizer (BCRF) (NC), and reduced nitrogen rate of BCRF (NR)] in 2016-2018. The results show that reduced irrigation and nitrogen rate reduced Fv/Fm, 13C-photosynthate, and nitrogen accumulation both in the kernel and plant. I3NC and I3NU accumulated higher 13C-photosynthate, nitrogen, and dry matter. However, 13C-photosynthate and nitrogen distribution to the kernel was decreased from I2 to I3 and was higher in BCRF than in urea. I2NC and I2NR promoted their distribution to the kernel, resulting in a higher harvest index. Compared with I3NU, I2NR increased root length density by 32.8% on average, maintaining considerable leaf Fv/Fm and obtaining similar kernel number and kernel weight. The higher root length density of I2NR of 40-60 cm promoted 13C-photosynthate and nitrogen distribution to the kernel and increased the harvest index. As a result, the water use efficiency (WUE) and nitrogen agronomic use efficiency (NAUE) in I2NR increased by 20.5%-31.9% and 11.0%-38.0% than that in I3NU, respectively. Therefore, 75%ETc deficit irrigation and BCRF fertilizer with 80% nitrogen rate improved root length density, maintained leaf Fv/Fm in the milking stage, promoted 13C-photosynthate, and distributed nitrogen to the kernel, ultimately providing a higher WUE and NAUE without significantly reducing grain yield.

Response of in situ root phenotypes to potassium stress in cotton.

Potassium plays a significant role in the basic functions of plant growth and development. Potassium uptake is closely associated with morphological characteristics of the roots. However, the dynamic characteristics of phenotype and lifespan of cotton (Gossypium hirsutum L.) lateral roots and root hairs under low and high potassium stress remain unclear. In this study, potassium stress experiments (low and high potassium, medium potassium as control) were conducted using RhizoPot (an in situ root observation device) to determine the response characteristics of lateral roots and root hairs in cotton under potassium stress. The plant morphology, photosynthetic characteristics, root phenotypic changes, and lifespan of lateral roots and root hairs were measured. Potassium accumulation, aboveground phenotype, photosynthetic capacity, root length density, root dry weight, root diameter, lateral root lifespan, and root hair lifespan under low potassium stress were significantly decreased compared to medium potassium treatment. However, the root hair length of the former was significantly increased than that of the latter. Potassium accumulation and the lateral root lifespan were significantly increased under high potassium treatment, while root length density, root dry weight, root diameter, root hair length, and root hair lifespan were significantly decreased compared to the medium potassium treatment. Notably, there were no significant differences in aboveground morphology and photosynthetic characters. Principal component analysis revealed that lateral root lifespan, root hair lifespan of the first lateral root, and root hair length significantly correlated with potassium accumulation. The root had similar regularity responses to low and high potassium stress except for lifespan and root hair length. The findings of this study enhance the understanding of the phenotype and lifespan of cotton's lateral roots and root hairs under low and high potassium stress.