Average Root Length Density Research Articles

Fall/winter cover crop roots change soil hydrology to control the drought status of subsequent season summer maize in Ultisol

Climate change has increased drought frequency, necessitating strategies to reduce water stress, increase water use efficiency, and improve agricultural productivity. The impacts of different fall/winter cover crops on alleviating maize drought in the subsequent season by changing soil water content remain unclear in Ultisol. Our aim was to investigate whether different fall/winter cover crops (taproot and fibrous root) can improve soil water content to attenuate subsequent season maize drought and its underlying mechanism. This research compared four fall/winter cover crops (2 rapeseed cultivars, lucerne and vetiver) and fallow control (no cover crop in winter) to investigate their root traits, root effect on subsequent season soil water content (SWC), soil drought degree (D), maize leaf and root water potential (Ψl, Ψr), maize crop water stress index (CWSI), and maize growth components (aboveground plant and root parameters) in 2019 (a dry year), 2021 (a normal wet year), and 2022 (a severe dry year). The fibrous-rooted vetiver displayed higher average root diameter and higher average root length density, leading to increased SWC (17%, 15%, 15%), and lower D values in all three years. Additionally, it exhibited a more substantial gradient between Ψl, and Ψr and lower CWSI than taproot (rapeseed cultivars and lucerne) and fallow treatment. Furthermore, the cover crop treatments enhanced the gradient between maize Ψl and Ψr to varying degrees in different drought years. Ultimately, the improvement in SWC resulting from cover crop treatments increased maize aboveground growth (plant height, stem diameter, and leaf area) and maize root development, ultimately improving maize yield. This study introduces a new perspective on investigating the role of cover crops in alleviating seasonal drought in subsequent crops, especially by changing soil water properties in the subtropical climate.

Improved yield-salinity relationship considering salt and root distribution dynamics

Alternate drip irrigation of brackish and freshwater (ADI) is an effective strategy to relieve salt stress in crops and increase crop yield compared to irrigation using only brackish water (B). However, the correlation between the soil salinity as well as maize root distribution dynamics and crop yields under ADI treatment remains unknown. A three-year field experiment under ADI treatment was carried out from 2019 to 2021 to evaluate the effects of irrigation using only freshwater (F), B, or both brackish and freshwater (1B1F, 2B1F, 3B1F; after irrigating with brackish water once, twice, and thrice including alternate irrigation with freshwater) on root growth and crop yield. This study aimed to capture the dynamics of the electric conductivity of a saturated paste extract (ECe) and root length density (RLD) at different soil depths during different crop growth periods under different ADI treatments. Moreover, to unravel the two-dimensional distribution of soil salt and root growth in the soil profile, ECe and RLD in the area under plastic film mulching (the mulched area) and the no mulching area (bare area) were measured. This study also evaluated the yield-salinity relationship using salt and root distribution dynamics (Y-SI) and the response of maize crops on ECe and RLD. The result of this study demonstrated that the estimation accuracy of the Y-SI was higher than the yield-salinity relationship by the Food and Agriculture Organization of the United Nations. MRE decreased by 4.9% for the Y-SI using ECe and RLD with eight positions (Y-SI 8) compared to only one position (Y-SI 1). The salt stress level decreased with increasing soil layer, specifically in the 0–40 cm soil layer in mulched area. The higher irrigation frequency of brackish water was associated with a higher ECe, longer salt stress duration, lower RLD during the last two growth stages, and a lower maize yield. Compared with F treatment, average ECe in the 0–40 cm soil layer under 1B1F, 2B1F, 3B1F, and B treatments increased by 22.7%, 30.6%, 35.1%, and 46.5%, average proportion of high salt stress (>3.8 dS m−1 for ECe) duration increased by 8.9%, 16.9%, 21.0%, and 26.4%, average RLD decreased by 6.6%, 16.9%, 21.7%, and 26.9%, and average relative maize yield decreased by 1.9%, 4.9%, 12.2%, and 16.1%, respectively. In general, the 2B1F treatment could be recommended as the optimal irrigation strategy with a reduction of 1800 t ha–1 for freshwater irrigation compared to the B treatment, but only a 4.9% decrease for maize yield compared to the F treatment.

Optimizing the spatial distribution of roots by supplemental irrigation to improve grain yield and water use efficiency of wheat in the North China Plain

Soil moisture affects the yield and water use efficiency (WUE) of winter wheat (Triticum aestivum L.) by regulating the spatial distribution of roots. Therefore, appropriate supplemental irrigation (SI) schemes are essential to achieve high yield and high WUE of wheat by constructing a reasonable root structure. In this study, field experiments were conducted the North China Plain (NCP) from 2018 to 2020. Based on the soil moisture management at sowing on a consistent basis, four SI regimes were set up: no irrigation after seedling emergence (W0), SI at jointing (W1), SI at jointing and anthesis (W2), and SI at regreening, jointing, and anthesis (W3). The results showed that although the grain yield of wheat increased with the SI frequency, the WUE decreased with increasing SI amount. SI at jointing and anthesis significantly increased WUE without reducing or slightly reducing the grain yield. The grain yield and WUE in 2018–2019 were significantly higher than those of the corresponding treatments in 2019–2020, and the yield of Bainong 4199 was higher than that of Zhoumai 18. The grain yield and WUE in 2018–2019 were significantly higher than those of the corresponding treatments in 2019–2020. The root length density (RLD) in the 0–20-cm soil layer increased with increasing SI frequency, but the proportion of RLD in the 40–60-cm soil layer decreased. The average RLD in the 0–60-cm soil layer and grain yield of Bainong 4199 were significantly greater than that of Zhoumai 18. Correlation analysis showed that the grain yield and WUE was positively correlated with the RLD in the 0–20-cm soil layer, and reached a very significant level with RLD in the 0–20-cm soil layer between rows. W2 and W3 in terms of root vigor and the grain filling rate 30 days after anthesis were significantly higher than W1 and W0 and also increased the contribution of post-anthesis dry matter to grain, resulting in an increase in grain weight. These results demonstrated that SI at jointing and anthesis could optimize the spatial distribution of roots, maintain higher root activity and filling rate at the late stage, increase accumulation and translocation of post-anthesis dry matter, and finally improve the yield and WUE. Therefore, we propose that Bainong 4199 was the preferred cultivars for this experiment，under sufficient soil moisture conditions before sowing, SI at jointing and anthesis is the optimal irrigation scheme for wheat on the NCP.

Nitrogen application improved peanut yield and nitrogen use efficiency by optimizing root morphology and distribution under drought stress

Drought stress and nutrient deficiency are two main factors that restrict the growth and yield of peanut (Arachis hypogaea L.) in arid and semi-arid regions. However, the effects of N fertilizer on root growth and pod yield of peanut under different water conditions are unclear. The growth, root morphology, and pod yield of peanut were studied under different water and N combinations. Two soil water treatments were tested: Well-watered (WW, 80%-85% field capacity) and drought stress conditions (DS, 55%-60% field capacity). Three N treatments were tested: no N application (NN), moderate N (MN, 90 kg ha-1), and high N (HN, 180 kg ha-1). Results showed that pod yield of peanut was limited by drought and N deficiency. Compared with NN, peanut shoot DM and pod yield were improved by MN under DS, with an average increase range of pod yield of 16.2% in the 2 yr. The annual average root length density (RLD) in the deeper soil layer (40-100 cm) was 5.5% higher under DS-MN than DS-NN treatment. The N use efficiency (NUE) was 12.3% higher under WW than DS treatment, and the NUE of MN was significantly higher than that of HN under different water treatments. Root lengths in 40-60 and 60-80 cm soil layers were also positively correlated with pod yield (r = 0.66** and 0.47**, respectively) and NUE (r = 0.60* and 0.85**, respectively). In this study, root growth in deeper soil was improved by MN application under DS, thus increasing yield and NUE of DS conditions.

Natural Genotypic Variation Underpins Root System Response to Drought Stress in Bambara Groundnut [Vigna subterranea (L.) Verdc.

Bambara groundnut [Vigna subterranea (L.) Verdc.] is grown in rainfed production systems and suffers from periodic drought stress (DS), leading to yield reductions. Natural genotypic variation for root traits is essential for adaptation to water deficit conditions. However, root traits have not been fully utilised as selection criteria to improve DS in bambara groundnut. The present study explored the natural genotypic variation found in single genotypes of bambara groundnut derived from landraces to identify adaptive differences in tap root length (TRL) and root length density (RLD) in response to DS. A diverse core collection of eight bambara groundnut genotypes from various locations (namely, Gresik, LunT, IITA-686, DodR, S19-3, Tiga nicuru, and Ankpa-4, DipC1), were grown for two seasons (2018 and 2019) in polyvinyl chloride (PVC) columns with well-watered (WW) and 30-day DS treatments. Plant samples were collected at 55 days after emergence (DAE) (30 days of DS) and at 105 DAE (30 days of DS plus 50 days of recovery). Under DS, differential TRL among genotypes at 55 DAE was observed, with DodR recording the longest among genotypes with an increase (1% in 2018) in TRL under DS compared to WW, whereas LunT and IITA-686 showed significant (p < 0.001) decrease in TRL (27 and 25%, respectively, in 2018). Average RLD was observed to have the highest reduction under DS in the 90–110 cm layer (42 and 58%, respectively, in 2018 and 2019). Rainy habitat LunT had limited roots in 2018 and recorded the least (0.06 ± 0.013 cm–3) RLD in 2019. However, dry-habitat DodR showed an increase in the RLD (60–90 cm) under DS compared to WW, while dry-habitat S19-3 densely occupied all depths with RLD of 0.16 ± 0.05 and 0.18 ± 0.01 cm cm–3 in the deepest layer in both seasons, respectively. Reduced RLD under DS showed recovery when the plants were re-watered. These plants were additionally observed to have RLD that surpasses the density in WW at all soil depths at 105 DAE. Also, recovery was shown in Tiga nicuru and DodR (0–30 cm) and IITA-686 (90–110 cm) in 2019. Average RLD under DS treatment was associated with substantial grain yield advantage (R2 = 0.27 and R2 = 0.49, respectively) in 2018 and 2019. An increase in TRL allowed DodR to quickly explore water at a deeper soil depth in response to gradually declining soil water availability. High RLD in genotypes such as DodR, DipC1 and S19-3 also offered adaptive advantage over other genotypes under DS. Variation in intrinsic RLD in deeper soil depths in the studied genotypes determines root foraging capacity when facing DS. This suggests that different agroecological environments to which bambara groundnut is subjected in its natural habitat have promoted a phenotypic differentiation in root systems to adapt to ecotypic conditions, which may help offset the impact of DS. The natural genotypic variation exhibited, especially by DodR, could be exploited to identify potential quantitative trait loci (QTLs) that control deep rooting and root length density.

Spatial distribution and dynamics of cotton fine root under film-mulched drip irrigation

Fine roots distribution and dynamics (production, mortality, and longevity) significantly impact the crop soil ecosystems. However, the spatial distribution and dynamics of cotton (Gossypium hirsutum L.) fine roots under film-mulched drip irrigation are poorly understood. The present study aims to characterize these distributions and dynamics measured using a minirhizotron technique and the influence of soil conditions. The non-uniform distribution of soil moisture and salinity may lead to the differences of root length density (RLD) distribution. A clear decreased trend for the average RLD was observed in the shallow soil layer due to high localized salinity accumulated after brackish water irrigation. There existed a clear high soil moisture content strip at depth which may lead to a high RLD peak in the 95–100 cm soil layer. Average live root production was characterized by a very high rate during the initial growth stage followed by a decline after budding, which in turn was followed by a slight increase during boll opening. The average number of new roots was highest during the initial growth stages, decreasing after the budding stage. Thinner roots in the deep soil had shorter lifespans than those in shallow soil. Our study indicated that the minirhizotron technique can be used reliably as an in situ, non-destructive method for estimating cotton fine roots distribution and dynamics under film-mulched drip irrigation. To evaluate cotton fine root distribution and dynamics under film-mulched drip irrigation more accurately, a cotton root system architecture model could be parameterized in space and time based on the minirhizotron observations.

Soil reinforcement potential of cultivated cardoon (Cynara cardunculus L.): First data of root tensile strength and density

Plant roots play a key role in erosion control by increasing soil resistance to shear stress. Root tensile strength data have been published for natural systems, less is available on cultivated crops. Cardoon (Cynara cardunculus L.) is raising a growing interest as multipurpose crop for marginal lands. In this work we measured cardoon roots tensile strength, topsoil root area ratio, root length density and estimated soil reinforcement potential. Root samples were collected in late spring and at the beginning of fall and were subjected to tensile strength tests in laboratory. Tensile strength (σmax) ranged between 1.57 and 254.78 MPa, decreasing with by a power-law relationship with high determination coefficients (>0.75), with differences between summer and fall roots. We measured root length density (RLD) and root area ratio (RAR) in surface soil (top 5 cm) at different positions in the row and inter-row. RAR was used to calculate soil reinforcement potential (Cr = 1.2 * ∑σmax (kPa) * RAR (cm2 cm−2)). Average RLD was quite high 8.68 cm cm−3 with a mean value of 9.183 cm cm−3 on the row and 8.179 cm cm−3 on the inter-row, though differences between row and inter-row, were not significant. RAR was on average 0.017 cm2 cm−2. Average soil reinforcement was 194 kPa with values ranging from 67.34 kPa to 265 kPa. This is not to be interpreted as absolute reinforcement values, due to drawbacks of the simple model used, but they are useful for comparisons within the framework of crop choices. Cardoon produces a dense mat of fine roots that can contribute to increase soil cohesion, thus providing important ecosystem services.

The effects of straw mulching combined with nitrogen applications on the root distributions and nitrogen utilization efficiency of summer maize

To provide an appropriate tillage fertilization model for improving N utilization efficiency and increasing production, the field experiments were conducted to study the effects on root distributions and N utilization efficiency of summer maize involving different straw mulching modes combined with N fertilization. No (N0), low (N1), medium (N2), and high (N3) levels of N fertilization were incorporated into soil combined with the surface coverage straw (Treatment B) and the deeply buried straw (Treatment S). The traditional cultivation was used as control treatment. The results shown that treatments S had significantly promoted deep root growth, and the root length density (RLD) increased with increases in N application rate. SN2 and SN3 treatments’ average RLD were significantly increased by 67.5% and 68.1% in the greater than 40 cm soil layers. While the Treatment B had significantly increased the RLD in 0 –30 cm soil layers only. With increases in N application rate, the effect on summer maize yields increase under Treatment B were not significantly, and only BN3 increased by 0.4%, while under Treatments S were found to first increase, and then decrease. The apparent recovery efficiency of applied N, N uptake and summer maize yield of SN2 had increased by 66.8%, 20.4%, and 9.3%. Therefore the rational tillage fertilization model was deeply buried straw combined with medium N fertilizer in Hetao Irrigation District.

Structural Equation Modeling of Soil Moisture Effects on Evapotranspiration of Maize in the North China Plain

Relationships between crop evapotranspiration (ET) and soil water content (SWC) have been studied worldwide. However, traditional data processing has drawbacks in modeling the contribution of SWC to ET on a layer-to-layer basis. To address this issue, large-scale weighing lysimeters were used to monitor the real-time ET along with Insentek sensors to monitor daily SWC dynamics of summer maize at Xuchang Experimental Irrigation Station, North China Plain, in 2016 and 2017. At the vegetative stage of maize (V6 and V12), roots reached 70 cm deep, with an average root length density (RLD) of 0.55 cm cm−3. Mean RLD at reproductive stage (VT and R3) was 1.13 cm cm−3, and the roots reached 100 cm deep. Cumulative percentage of ETi to ET in topsoil (0–30 cm) was from 66% (V6) to 77% (R3), with the lowest proportion of 62% at maturity (R6), indicating > 2/3 of root mass distributed in the 0–30 cm soil layer. Principal component analysis was conducted to extract principal components of SWC. Soil moisture in the top (0–30 cm), middle (30–60 cm), and deep (60–100 cm) soil layers explained 8%, 14%, and 31% of the variances in ET (P < 0.05). Positive linear correlation was observed between ET and SWC in top and middle layers, while SWC in deep layer showed negative relationship with ET, which was mainly due to the gravitational forces acting on it. These findings support the premise that SWC in deep soil layer also has important effects on ET.

Tree and crop fine root distribution and belowground competition as affected by a climatic gradient in agroforestry parkland systems in Burkina Faso (West Africa)

This research assessed precipitation increase along a climactic gradient effect on tree and crop root length densities and belowground competition in parklands systems of Vitellaria paradoxa C. F Gaertn, Parkia biglobosa (Jacq.) Benth with Sorghum bicolor (L.) Moench for formulating parklands management options improving crop productivity. Field experiments were conducted at three sites along an increasing rainfall gradient. Soil samples were taken, roots were washed and sorted by categories and root length density was estimated using the method of Tennant. Belowground competition was assessed using the ratio method. Correlation between crop root and aboveground biomass was tested. For topsoil, higher crop root length density was at Sokouraba (0.087 ± 0.007 cm.cm -3 ). For subsoil, crop and tree average root length density was higher at Tougouri and were respectively 0.05 ± 0.009 and 0.117 ± 0.021 cm.cm -3 . Trees reduce crop root length density with precipitation increase and more under P. biglobosa. Belowground competition along a climatic gradient and its interaction with zones and tree species was not significantly different. Higher crop root length density obtained at topsoil with precipitation increase did not reduce belowground competition. Tree management options reducing tree roots should be tested on belowground competition along a climatic gradient. Key words : precipitation increase, management options, root length.

Temporal and spatial distributions of fine roots of different varieties of Camellia oleifera.

We examined fine root distribution dynamics at the depth of 0-40 cm soil profile for five varieties of Camellia oleifera, including "Ganwu 1", "Ganyong 5", "Changlin 4", "Changlin 40" and "Gan 447", in one year using minirhizotron technique. The temporal and spatial distribution characteristics of total root tip number (TRT), average root length density (ARLD) and average root diameter (ARD) were analyzed. The results showed that the TRT and ARLD changes of each variety were relatively stable in the second half of 2016, while there was a significant monthly fluctuation in the first half of 2017, especially for "Ganwu 1" and "Changlin 40". The TRT and ARLD of "Ganwu 1" peaked in May 2017, while the ARD of "Changlin 4" peaked in March 2017. The TRT and ARLD values of "Ganwu 1" and the ARD value of "Changlin 4" were significantly greater than those of other varieties during the whole observation period. The spatial distribution and monthly dynamics of fine roots varied significantly among different varieties of Camellia oleifera. The fine roots were mainly distributed at the soil layer of 0-20 cm for "Ganwu 1" and" Gan 447 ", but at 20-40 cm for " Changlin 4 "and " Changlin 40 ". The latter two varieties had relatively stable spatial distribution and monthly dynamics of fine roots when compared to others. In contrast, the root biomass of "Ganyong 5" was not significantly different between both soil layers despite a large spatial variation. The ARD of "Changlin 4" was significantly larger at the soil layer of 20-40 cm than that of 0-20 cm. There was no significant difference in ARD between both soil layers for other varieties. In conclusion, within the five varieties, "Ganwu 1" had the greatest biomass of fine roots, which were mainly distributed in the upper soil layer, while "Changlin 4" had the largest diameter of fine roots, which were mainly distributed in the lower soil layer.

Effects of Subsoiling Tillage on Soil Properties, Maize Root Distribution, and Grain Yield on Mollisols of Northeastern China

Core Ideas Subsoil tillage (∼30 cm) reduced compaction and increased moisture and N availability on Mollisols. Subsoiling increased the vertical and horizontal distribution of maize roots between rows rather than in row. Grain and dry matter yield were 6.3 and 3.7% greater under subsoiling than conventional tillage. Subsoiling increased maize yield due to improved soil conditions and roots distribution. Soil compaction creates unfavorable soil physical and nutrient conditions, restrains root penetration and distribution, and reduces crop yield. A field experiment was established to assess the effects of tillage treatments on soil properties, root distribution, and grain yield of maize (Zea mays L.) on some Mollisols of Northeastern China. The two treatments included in rotary tillage (RT) and subsoiling tillage (ST). The results showed that soil bulk density, penetration resistance, soil moisture, available nitrogen content, root distribution of maize, and grain yield were significantly affected by tillage systems. Compared with RT, ST had lower soil bulk density and penetration resistance, but greater soil moisture and available nitrogen contents, especially in subsoil layer (i.e., 15‐ to 45‐ cm). The ST practice significantly increased the average root length density by 13.0% than that of RT mainly due to better vertical and horizontal distribution between the rows. Average grain yield and dry matter weight of maize increased by 693 kg ha−1 (6.3%) and 933 kg ha−1 (3.7%), respectively, under ST compared with those under RT. These data show that subsoiling tillage can loosen the soil, fracture the plow pan, increase the availability and infiltration of soil moisture and nitrogen in subsoil layers, improve the vertical and horizontal extension of maize root system in the soil, and increase grain yield on Mollisols of Northeastern China.

Strategies of supplemental irrigation and modified planting densities to improve the root growth and lodging resistance of maize (Zea mays L.) under the ridge-furrow rainfall harvesting system

In the semi-arid area of northwest China, a ridge-furrow rainfall harvesting (RFRH) system and supplementary irrigation techniques have been implemented to increase crop yields. However, the effects of supplementary irrigation and planting density on maize root growth and lodging resistance under the RFRH system are unknown. Therefore, we conducted field trials implementing three planting densities (Low: 52,500 plants ha−1; Medium: 75,000 plants ha−1; High: 97,500 plants ha−1) and four irrigation modes (NI: no irrigation; IV: irrigation at the 11-leaf stage; IS: irrigation at the silking stage; and IVS: irrigation at the 11-leaf and silking stages) under the RFRH system. The results showed that the average root length density (RLD) and root surface area density (RSD) in the 0–100 cm soil layers increased at the silking and dough stages under medium and high densities compared with low density. However, the root weight under high density significantly decreased compared with that under low density. Increased planting density significantly increased ear height and the ear height coefficient, leading to an increased probability of maize lodging. The root and stalk lodging rates under high density were higher than those under low and medium densities. Compared with NI treatment, at the dough stage, the average RLD and RSD increased in all irrigation treatments; supplementary irrigation also increased the root weight and root shoot ratio. The results showed that the grain yield under IS and IVS treatments significantly increased compared with that under NI treatment. The total lodging rate under IVS treatment was 41.2% higher than that under IS treatment. Therefore, the IS treatment under medium density achieved a higher grain yield (13.2 t ha−1) and reduced maize lodging, which could be a suitable planting model in semi-arid areas.

Spatial distribution of soil moisture, soil salinity, and root density beneath a cotton field under mulched drip irrigation with brackish and fresh water

Root systems play a vital role in soil-plant interactions. The dynamics and distributions of soil moisture content (SMC), soil salinity, and cotton (Gossypium hirsutum L.) root density under mulched drip irrigation are complex and their interactions are not well understood. The aim of this study is to describe these dynamics and distributions and to evaluate their impacts on cotton above-ground growth and yield during two-year field experiments in a cotton field under mulched drip irrigation with brackish and fresh water. Significant differences were observed for the distributions of SMC, soil salinity, and root length density (RLD) in the root zone for brackish water irrigation treatment (BWT) and fresh water irrigation treatment (FWT). The average SMC and soil salinity in the root zone were higher for BWT than for FWT. The spacing of irrigation lines also had measurable impacts. SMC was less variable when irrigation spacing was small (narrow rows) than beneath wide rows. SMC for BWT and FWT decreased after irrigation due to root water uptake; simultaneously, salt concentration increased, especially in regions where RLD was relatively high. More roots were observed growing in the mulched narrow and wide rows than in the no-mulch zone. Roots were concentrated in the shallowest 30cm. Our study indicated that the average values of the ECe (electrical conductivity of soil saturation extract) in the root zone after BWT irrigation were higher than the published threshold value for optimal cotton yield. The average RLD, shoot dry weight and yield for BWT were observed to be lower than those of FWT as a result of the elevated soil salinity associated with BWT.

DISTRIBUIÇÃO DE RAÍZES E EXTRAÇÃO DE ÁGUA DA BANANEIRA ‘BRS PRINCESA’ SOB DIFERENTES CONFIGURAÇÕES DE IRRIGAÇÃO

No presente trabalho, objetivou-se avaliar a distribuição de raízes e a extração de água da bananeira ‘BRS Princesa’ sob diferentes configurações de irrigação em região semiárida do norte de Minas Gerais. Para a condução do experimento, foram adotadas cinco estratégias de irrigação: 50% de redução da lâmina de irrigação (LI) com frequência de alternância de lado da planta (FA) de sete dias; 50% de LI e FA de 14 dias; 50% de LI de FA de 21 dias; 50 % de LI com irrigação fixa (uma linha lateral de um só lado da planta) e irrigação plena (duas linhas laterais com registros abertos) durante todo o ciclo, com amostragens realizadas em quatro distâncias do pseudocaule (0,25; 0,50; 0,75 e 1,0 m) e cinco profundidades (0,05 a 15; 0,15 a 0,25; 0,35 a 0,45; 0,55 a 0,65 e 0,75 a 0,85 m), com as estratégias e amostragens dispostas em delineamento inteiramente casualizado em esquema fatorial 5 x 4 x 5, com três repetições. As médias de densidade de comprimento de raízes (DCR) foram similares entre os tratamentos, entretanto, quando a bananeira foi submetida à irrigação com déficit parcial, expressou tendência de maior desenvolvimento radicular; houve redução da DCR com a profundidade do solo e manutenção da distribuição de raízes com a distância do pseudocaule; as raízes muito finas a pequenas estiveram concentradas até a profundidade de 40 cm no perfil do solo e 70 a 90% destas raízes estiveram localizadas até 75 cm do pseudocaule; intervalo menor de alternância do lado irrigado na PRD possibilitou extração da água em camadas mais profundas.

Growth performance of clonal rubber rootstocks and combining ability test with the scion of clone RRIM 600

Past screening of rubber rootstocks in southern Thailand has revealed five clones that showed good plant growth with tentative tolerance to white root disease. The current study tested the combining ability of these clones with the scion of clone RRIM 600, commonly grown in Thailand. The five clonal rootstocks and the clone RRIM 600 were grown in rhizoboxes (10 × 45 × 100 cm) in a completely randomized design, consisting of six treatments each with four replicates, making a total of 24 rhizoboxes. After growing for 6 mth, each seedling (1 cm stem diameter) was bud grafted with the scion RRIM 600. Root growth of the rootstocks was assessed by scanning a glass panel in the side of each rhizobox after 3 mth. It was found that the seedlings of clone#5 exhibited significantly higher root growth with tentative high shoot growth compared with the remaining treatments. The results showed that clone#5 exhibited the highest average root length density at 1.26 cm/cm2 followed by clone#2 (0.90 cm/cm2) with a significant difference from the other clones. The investigation of graft union development showed that callus tissues developed on the graft union within 5 d after bud grafting (DAB). The graft union growth was almost fully developed over the wound areas and callus bridge formation was evident within 10 DAB. The new vascular tissues were connected with old cambium and vascular tissues of the scion and rootstocks within 20 DAB. The photosynthetic rate and stomatal conductance were assessed and showed 100% successful budding of rootstocks of clone RRIM 600 and clone#4, whereas the other clones achieved 75% success.

Root distribution and growth of cotton as affected by drip irrigation with saline water

The objective of this field experiment was to study the effects of irrigation water salinity and N rate on cotton (Gossypium hirsutum L.) growth and root distribution. A field experiment was established with a 3×2 factorial, completely randomized block design: i.e. three levels of irrigation water salinity (fresh water, brackish water, or saline water) and two rates of nitrogen (N) application (0 and 360kgN/ha). The results showed that cotton root biomass and distribution were significantly affected by water salinity and N fertilization, but not by N-salinity interaction. Between 85 and 90% of the root biomass was in the 0 to 20cm soil depth. Root biomass was higher in the fresh water (FW, 0.35dS/m) treatment than in the saline water (SW, 8.04dS/m) treatment, but was not significantly different from that in the brackish water (BW, 4.61dS/m) treatment. Nitrogen fertilizer increased total root biomass by 2 to 8% in the FW treatment, by 27 to 28% in the BW treatment and by 15 to 20% in the SW treatment. Most (83–95%) of the root length density was observed in the 0 to 60cm soil depth. Average root length density, root diameter, and root volume were not affected by water salinity, but decreased sharply as N rate increased. In the unfertilized plot, average root length density, root surface area, and root volume were all higher in the FW treatment than in either the BW or the SW treatments. In the fertilized plot, average root length density, root surface area and root volume were significantly higher in the BW and SW treatments than in the FW treatment. The root/shoot ratio increased significantly as irrigation water salinity increased. Application of N fertilizer increased N uptake, yield, and irrigation water use efficiency. However, saline water irrigation had a negative effect on N uptake, yield, and irrigation water use efficiency; moreover, N application exacerbated the negative effect. These results suggest that saline water irrigation inhibited cotton root growth, resulting in a reduction in shoot growth, N uptake, yield, and water and N use efficiency. Excessive fertilizer application may result in an increase in salt damage when cotton is irrigated with saline water.

Strategy of fine root expansion of Phyllostachys pubescens population into evergreen broad-leaved forest

Aims Roots, particularly fine roots, play an important role in interspecies competition. Our objective was to study the spatial distribution, morphological characteristics and growth rates of fine roots in both bamboo (Phyllostachys pubescens) and broad-leaved trees to better understand the mechanisms of expansion of bamboo into evergreen broad-leaved forest. Methods We continuously sampled P. pubescens forest (PPF), bamboo-broad-leaved mixed forest (BMF) and evergreen broad-leaved forest (EBF) perpendicular to a bamboo-broad-leaved forest interface on Dagang Mountain, Jiangxi Province, China. The live fine root biomass, specific root length (SRL), root length density (RLD), fine root growth and turnover rates were comparatively analyzed by soil core and ingrowth methods. Important findings Fine root biomass of PPF (1 201.60 g·m –2 ) was much larger than that of BMF (601.18 g·m –2 ) and EBF (204.88 g·m –2 ). Vertical stratification of bamboo fine roots in BMF was found to shift from lower to upper soil layers, SRL of bamboo significantly increased by 123.42% and average RLD of bamboo was 210.0% greater than that of broad-leaved trees. In addition, both growth and turnover rates of bamboo fine roots were faster than those of trees. Findings indicated that P. pubescens, with wide, precise, flexible and fast nutrient access and space-occupation abilities, would outcompete trees belowground, resulting in expansion of its population into evergreen broad-leaved forest.

DREB1A promotes root development in deep soil layers and increases water extraction under water stress in groundnut

Water deficit is a major yield-limiting factor for many crops, and improving the root system has been proposed as a promising breeding strategy, although not in groundnut (Arachis hypogaea L.). The present work was carried out mainly to assess how root traits are influenced under water stress in groundnut, whether transgenics can alter root traits, and whether putative changes lead to water extraction differences. Several transgenic events, transformed with DREB1A driven by the rd29 promoter, along with wild-type JL24, were tested in a lysimeter system that mimics field conditions under both water stress (WS) and well-watered (WW) conditions. The WS treatment increased the maximum rooting depth, although the increase was limited to about 20% in JL24, compared to 50% in RD11. The root dry weight followed a similar trend. Consequently, the root dry weight and length density of transgenics was higher in layers below 100-cm depth (Exp. 1) and below 30 cm (Exp. 2). The root diameter was unchanged under WS treatment, except a slight increase in the 60-90-cm layer. The root diameter increased below 60 cm in both treatments. In the WW treatment, total water extraction of RD33 was higher than in JL24 and other transgenic events, and somewhat lower in RD11 than in JL24. In the WS treatment, water extraction of RD2, RD11 and RD33 was higher than in JL24. These water extraction differences were mostly apparent in the initial 21 days after treatment imposition and were well related to root length density in the 30-60-cm layer (R(2) = 0.68), but not to average root length density. In conclusion, water stress promotes rooting growth more strongly in transgenic events than in the wild type, especially in deep soil layers, and this leads to increased water extraction. This opens an avenue for tapping these characteristics toward the improvement of drought adaptation in deep soil conditions, and toward a better understanding of genes involved in rooting in groundnut.

Morphological and physiological characteristics of corn (Zea mays L.) roots from cultivars with different yield potentials

Improving grain yield per unit area is needed to meet the growing demand for corn in China where the availability of fertile land is very limited. Roots are vital organs for yield improvement. A field experiment was conducted in 2009 and 2010 to compare the Morphological and physiological characteristics of the root systems of the higher-yielding corn variety DengHai 661 (DH661) and the commonly grown corn variety for northern China ZhengDan 958 (ZD958). The results clearly showed that DH661 consistently yielded higher than ZD958 in both years. The average biomass and grain yield of DH661 were 20.11% and 19.15% higher than those of ZD958. The roots DH661 grow faster than ZD98, it can get the depth to 160–200cm at VT stage, but the roots of ZD958 get that depth at R3 stage. At the same time, the maximum of root biomass and average root length density (RLD), root actively absorbing area, root TTC reducing capacity after VT stage in both years were 83.06%, 43.30%, 58.10% and 40.38% higher than those of ZD958, respectively. Which can supplying more water and nutrient for the shoot, and improve the LAI, photosynthetic rate (in the later growth stage) and longer duration of high photosynthesis, make the contribution to the shoot growth and grain filling. All the results supporting the hypothesis that greater root systems lead to higher yield.