Effects of soil physicochemical environment on the plasticity of root growth and land productivity in maize soybean relay strip intercropping system

BACKGROUND

Soil is a key foundation of crop root growth. There are interactions between root system and soil in multiple ways. The present study aimed to further explore the response of root distribution and morphology to soil physical and chemical environment under maize (Zea mays L.) soybean (Glycine Max L. Merr.) relay strip intercropping (MS) An experiment was carried out aiming to examine the effects of nitrogen (N) applications and interspecific distances on root system and soil environment in MS. The two N application levels, referred to as no N application (NN) and conventional N application (CN), were paired with different interspecific distances: 30, 45 and 60 cm (MS30, MS45 and MS60) and 100 cm of monoculture maize and soybean (MM/SS100).

RESULTS

The results demonstrated that MS45 increased the distribution of soil aggregates (> 2 mm) near the crop roots and maize soil nutrients status, which increased by 20.3% and 15.6%. Meanwhile, MS reduced soil bulk density, increased soil porosity and improved soil oxygen content. Optimization of the soil environment facilitated root growth. The MS45 achieved a better result on root distribution and morphology than the other configuration and also increased land productivity.

CONCLUSION

Relay intercropped soybean with maize in interspecific row spacing of 45 cm, improved soil physicochemical environment, reshaped root architecture and optimized root spatial distribution of crops to achieve greater land productivity. © 2024 Society of Chemical Industry.

Effects of water-nitrogen coupling on water and salt environment and root distribution in Suaeda salsa

Understanding the spatial distribution of crop roots is crucial for effectively managing crop water and fertilizer. We investigate the effects of water-nitrogen coupling on the water-salt environment and root distribution in the root zone of S. salsa. Three irrigation levels were established, calculated according to 0.35 (W1), 0.50 (W2), and 0.65 (W3) of local ET0. The three nitrogen levels were 150 (N1), 250 (N2), and 350 (N3) kg·hm-2 in a complete combination design. With the augmentation of irrigation water and nitrogen application, the total root weight density of the root system of Suaeda salsa increased from 17.18×10-3 g·cm-3 to 27.91×10-3 g·cm-3. The distribution of soil water suction significantly influences the root distribution of Suaeda salsa in saline soil, causing a transition from a narrow deep type to a wide shallow type. Under the W2 irrigation level, soil water suction ranges from 1485.60 to 1726.59 KPa, which can provide water for S. salsa.it becomes feasible to attain the necessary water and salt environment for the growth and development of S. salsa, resulting in the attainment of maximum biomass, ash content, and salt uptake. No significant differences in the biomass, ash content, and salt uptake of S. salsa was noted between N2 and N3 nitrogen application levels (p > 0.05).The optimal irrigation volume and nitrogen application level were 0.50 ET0 and 250 kg·hm-2, respectively. The results of this study provide a scientific basis for the large-scale planting of S. salsa in extreme arid areas to improve and utilize saline wastelands.

Male, female, and mixed-sex poplar plantations support divergent soil microbial communities

Males and females of dioecious plants have sex-specific adaptations to diverse habitats. The effects of inter- and intrasexual interactions in poplar plantations on composition, structure, and function of soil microbiota have not been explored in degraded areas. We conducted a series of greenhouse and field experiments to investigate how belowground competition, soil microbial communities, and seasonal variation nitrogen content differ among female, male, and mixed-sex Populus cathayana plantations. In the greenhouse experiment, female neighbors suppressed the growth of males under optimal nitrogen conditions. However, male neighbors enhanced stable isotope ratio of nitrogen (δ15 N) of females under intersexual competition. In the field, the root length density, root area density, and biomass of fine roots were lower in female plantations than in male or mixed-sex plantations. Bacterial networks of female, male, and mixed-sex plantations were characterized by different composition of hub nodes, including connectors, modules, and network hubs. The sex composition of plantations altered bacterial and fungal community structures according to Bray-Curtis distances, with 44% and 65% of variance explained by the root biomass, respectively. The total soil nitrogen content of mixed-sex plantation was higher than that in female plantation in spring and summer. The mixed-sex plantation also had a higher β-1,4-N-acetyl-glucosaminidase activity in summer and a higher nitrification rate in autumn than the other two plantations. The seasonal soil N content, nitrification rate, and root distribution traits demonstrated spatiotemporal niche separation in the mixed-sex plantation. We argue that a strong female-female competition and limited nitrogen content could strongly impede plant growth and reduce the resistance of monosex plantations to climate change and the mixed-sex plantations constitutes a promising way to restore degraded land.

Root distribution characteristics of monoculture and mixture of Pinus tabuliformis and Robinia pseudoacacia plantation

In this study, we analyzed the vertical distribution characteristics of root biomass density, root length density, root surface area density in monoculture and mixture of Pinus tabuliformis and Robinia pseudoacacia plantations in Caijiachuan small watershed of Jixian County, Shanxi. We examined their relationships with soil physical and chemical properties in different stand types. The results showed that the total root biomass density of P. tabuliformis and R. pseudoacacia in mixture was more than 75% higher than that in monoculture. Root system of P. tabuli-formis mainly distributed in shallow layer (0-40 cm), while that of R. pseudoacacia was deeper (40-80 cm). Fine roots were predominant in different diameter classes. Length density and surface area density of fine roots were in the order of R. pseudoacacia in mixture > P. tabuliformis in mixture > R. pseudoacacia stand > P. tabuliformis stand. Root biomass density of fine roots was in the order of P. tabuliformis in mixture ＞ R. pseudoacacia in mixture ＞ P. tabuliformis stand ＞ R. pseudoacacia stand. In vertical profile, the total root and fine root biomass, root length and root surface area density of P. tabuliformis stand, R. pseudoacacia stand, P. tabuliformis in mixture and R. pseudoacacia in mixture showed a rule of decreasing with the increases of soil depth. Under different stand types, fine root length density, root biomass density and total root length density were positively correlated with soil total nitrogen, soil organic carbon, and soil water contents. Total root surface area density was significantly positively correlated with soil organic carbon, soil water content, and soil total nitrogen. The distribution of roots in pure and mixed stands of P. tabuliformis and R. pseudoacacia showed different patterns. Compared with the pure stand, the mixed stand had higher root biomass, soil nutrient contents, and soil water content.

15 N labeling technology reveals enhancement of nitrogen uptake and transfer by root interaction in cotton/soybean intercropping

BACKGROUND

Biological nitrogen fixation in legumes and their transfer of nitrogen to non-legumes in legume/non-legume intercropping systems are considered to be important for the improvement of productivity. However, research on interspecific interaction and root nitrogen transfer in cotton/soybean intercropping systems has rarely been undertaken. In this study, the roots of cotton and soybean were separated with either complete root barriers (CB), using plastic film, or semi-root barriers (SB), using nylon net. No root barrier (NB) was used as the control.

RESULTS

The results showed that cotton produced more above-ground dry matter (DM) than soybean. The above-ground DM and nitrogen uptake of cotton was greatest with the NB treatment. The above-ground DM and nitrogen uptake of soybean was greatest with the CB treatment. At the harvest stage, the nitrogen transfer rate from soybean to cotton was 22.47% with the SB treatment and 40.41% with the NB treatment. Interspecific root interaction increased the nitrogen transfer amount, especially for the cotton roots in the 0-15 cm soil layer and for the soybean roots in the 0-30 cm soil layer. The root distribution of soybean was the key factor affecting nitrogen transfer amount, and nitrogen transfer amount was the key factor affecting nitrogen uptake of cotton in the cotton/soybean intercropping system.

CONCLUSION

These results indicated that nitrogen transfer from soybean to cotton through root interaction improved cotton above-ground DM and nitrogen uptake. © 2023 Society of Chemical Industry.

Effects of Salt Tolerance Training on Multidimensional Root Distribution and Root-Shoot Characteristics of Summer Maize under Brackish Water Irrigation

To investigate the impact of brackish water irrigation on the multidimensional root distribution and root-shoot characteristics of summer maize under different salt-tolerance-training modes, a micro-plot experiment was conducted from June to October in 2022 at the experimental station in Hohai University, China. Freshwater irrigation was used as the control (CK), and different concentrations of brackish water (S0: 0.08 g·L-1, S1: 2.0 g·L-1, S2: 4.0 g·L-1, S3: 6.0 g·L-1) were irrigated at six-leaf stage, ten-leaf stage, and tasseling stage, constituting different salt tolerance training modes, referred to as S0-2-3, S0-3-3, S1-2-3, S1-3-3, S2-2-3, and S2-3-3. The results showed that although their fine root length density (FRLD) increased, the S0-2-3 and S0-3-3 treatments reduced the limit of root extension in the horizontal direction, causing the roots to be mainly distributed near the plants. This resulted in decreased leaf area and biomass accumulation, ultimately leading to significant yield reduction. Additionally, the S2-2-3 and S2-3-3 treatments stimulated the adaptive mechanism of maize roots, resulting in boosted fine root growth to increase the FRLD and develop into deeper soil layers. However, due to the prolonged exposure to a high level of salinity, their roots below 30 cm depth senesced prematurely, leading to an inhibition in shoot growth and also resulting in yield reduction of 10.99% and 11.75%, compared to CK, respectively. Furthermore, the S1-2-3 and S1-3-3 treatments produced more reasonable distributions of FRLD, which did not boost fine root growth but established fewer weak areas (FLRD < 0.66 cm-3) in their root systems. Moreover, the S1-2-3 treatment contributed to increasing leaf development and biomass accumulation, compared to CK, whereas it allowed for minimizing yield reduction. Therefore, our study proposed the S1-2-3 treatment as the recommended training mode for summer maize while utilizing brackish water resources.

The impact of soil hydrological regimes and vegetation systems on plant performance and root depth distribution in bioswale microcosms

Plant rooting patterns in bioswales, raingardens and other vegetated infiltration systems are essential, as they contribute biopores which maintain the infiltration function over time. However, fluctuating hydrological conditions, ranging from flooded to drained, can have a heavy impact on plant rooting, as well as consequences for plant contributions to other ecosystem services and ecological functions. This study tested the biomass allocation to roots and the vertical root profile of four plant species, alone or in competition with a grass, and their responses to the experimental manipulation of soil hydrology in soil column microcosms. The hydrological regimes were combinations of flooded and drained conditions, respectively, including Wet cycles (72 and 96 h), Dry cycles (24 and 144 h), Wet-dry cycles (72 and 264 h), and Control group (watered twice per week). When the species were exposed to repeated wet-dry cycling hydrological regimes, we found a clear shift in vertical root distribution and shallower rooting in wetter regimes. It was also found that alongside this shallower rooting, there were no changes to total biomass and only moderate adjustments to biomass investment in roots. Overall, differences in rooting patterns between hydrological regimes and species were moderate when the dicot species were grown alone. The addition of the grass Festuca rubra contributed to a strong increase in total root mass density that evened out the differences in rooting patterns but also gave a deeper rooting. Accordingly, mixed species systems may be a robust approach to vegetated infiltration systems.

Field traffic-induced soil compaction under moderate machine-field conditions affects soil properties and maize yield on sandy loam soil

Soil compaction due to field trafficking involves a complex interplay of machine-soil properties. In contrast to previous studies simulating worst field scenarios, this two-year field experiment investigated the effects of traffic-induced compaction involving moderate machine operational specifications (axle load, 3.16 Mg; mean ground contact pressure, 77.5 kPa) and lower field moisture contents (< field capacity) at the time of trafficking on soil physical properties, spatial root distribution, and corresponding maize growth and grain yield in sandy loam soil. Two compaction levels, i.e. two (C2) and six (C6) vehicle passes, were compared with a control (C0). Two maize (Zea mays L.) cultivars, i.e. ZD-958 and XY-335, were used. Results showed topsoil (< 30 cm) compaction with increases in bulk density (BD) and penetration resistance (PR) up to 16.42% and 127.76%, respectively, in the 10-20 cm soil layer in 2017. Field trafficking resulted in a shallower and stronger hardpan. An increased number of traffic passes (C6) aggravated the effects, and the carryover effect was found. Higher BD and PR impaired root proliferation in deeper layers of topsoil (10-30 cm) and promoted shallow horizontal root distribution. However, XY-335, compared with ZD-958, showed deeper root distribution under compaction. Compaction-induced reductions in root biomass and length densities were respectively up to 41% and 36% in 10-20 cm and 58% and 42% in the 20-30 cm soil layer. Consequent yield penalties (7.6%-15.5%) underscore the detriments of compaction, even only in topsoil. In crux, despite their low magnitude, the negative impacts of field trafficking under moderate machine-field conditions after just two years of annual trafficking foreground the challenge of soil compaction.

Investigation of root traits of Dendrocalamus strictus cultivated on organically amended coalmine overburden and its potential use for slope stabilization

The active and abandoned coalmine overburden (OB) dumps are prone to slope instability under the influence of external agents. Estimating the mechanical reinforcement imparted by the grassroots on the coalmine overburden dumps is vital. This paper discusses the effect of organic amendment on the growth characteristics and root distribution of native grass Dendrocalamus strictus species (common name: Bamboo) in the Jharkhand region, India. A pot experiment was conducted wherein the OB was amended with different proportions of cow dung (OA) and garden soil (GS) to be used as growth substrates known as treatments (T1-T5). A pot having only GS (T6) was used as a control. The growth of six D. strictus saplings under each treatment was monitored for survival, shoot height, and canopy area. The root distribution, root area ratio (RAR) with depth, root tensile strength (Tr) vs. root diameter (d) relationship, and variation of additional cohesion (root cohesion, cr) with depth were studied for each species (Wu method). The pot experiment shows that the chosen grass can survive on the OB dumps with a suitable external amendment and can exhibit a well-developed root system and produce higher root reinforcement when allowed to grow under unrestricted conditions.

Can plants integrate information on above-ground competition in their directional responses below ground?

BACKGROUND AND AIMS

Light competition can induce varying above-ground responses in plants. However, very little is known regarding the effect of above-ground light competition cues on plant responses below ground. Here we asked whether light competition cues that indicate the occurrence and direction of neighbours above ground might affect directional root placemat.

METHODS

In a common-garden experiment, we examined the integrated responses of the annual procumbent plant Portulaca oleracea to light competition cues and soil nutrient distribution. Soil nutrients were distributed either uniformly or in patches, and light competition was simulated using a transparent green filter, which was spatially located either in the same or opposite direction of the soil nutrient patch.

KEY RESULTS

As predicted, root proliferation of P. oleracea increased in the direction of the enriched soil patches but was homogenously distributed under the uniform nutrient distribution. Interestingly, root distribution was also affected by the light competition cue and increased in its direction regardless of the location of the soil patches.

CONCLUSIONS

Our results provide initial support to the idea that below-ground plant responses to competition might also be regulated by above-ground neighbour cues, highlighting the need to further investigate the combined effects of both above- and below-ground competition cues on root behaviour.

Spatial-Temporal Distribution of Allelopathic Rice Roots in Paddy Soil and Its Impact on Weed-Suppressive Activity at the Seedling Stages

BACKGROUND

Allelochemicals secreted by allelopathic rice roots are transmitted to the receptor rhizosphere through the soil medium to inhibit the growth of the surrounding weeds. This research aimed to explore the relationships between the spatial-temporal distribution of rice roots in soil and weed-suppression ability at its seedling stage.

RESULTS

This study first examined the root distribution of three rice cultivars in paddy soil in both vertical and horizontal directions at 3-6 leaf stage. Then, an experiment using rice-barnyardgrass mixed culture was conducted to analyze the allelopathic potential and allelochemical content secreted by rice roots in different lateral soil layers. The results showed that allelopathic rice had a smaller root diameter and larger root length density, root surface area density, and root dry weight density than those of non-allelopathic rice, in the top 5 cm at 5- and 6-leaf stages. In particular, there were significant differences in root distribution at the horizontal distance of 6-12 cm. Besides, allelopathic rice significantly inhibited the above-ground growth of barnyardgrass co-cultured at 12 cm lateral distance in situ, and the content of benzoic acid derivatives in allelopathic rice in a 6-12 cm soil circle was higher than that observed at 0-6 cm distance. Moreover, correlation analysis confirmed that the distribution of roots in the horizontal distance was significantly correlated with weed inhibition effect and allelochemical content.

CONCLUSION

These results implied that spatial distribution of allelopathic rice roots in paddy soil, particularly at the lateral distance, appears to have important impact on its weed-suppressive activity at the seedling stage, suggesting that modifying root distribution in soil may be a novel method to strengthen the ability of rice seedlings to resist paddy weeds.

Dry Season Transpiration and Soil Water Dynamics in the Central Amazon

With current observations and future projections of more intense and frequent droughts in the tropics, understanding the impact that extensive dry periods may have on tree and ecosystem-level transpiration and concurrent carbon uptake has become increasingly important. Here, we investigate paired soil and tree water extraction dynamics in an old-growth upland forest in central Amazonia during the 2018 dry season. Tree water use was assessed via radial patterns of sap flow in eight dominant canopy trees, each a different species with a range in diameter, height, and wood density. Paired multi-sensor soil moisture probes used to quantify volumetric water content dynamics and soil water extraction within the upper 100 cm were installed adjacent to six of those trees. To link depth-specific water extraction patterns to root distribution, fine root biomass was assessed through the soil profile to 235 cm. To scale tree water use to the plot level (stand transpiration), basal area was measured for all trees within a 5 m radius around each soil moisture probe. The sensitivity of tree transpiration to reduced precipitation varied by tree, with some increasing and some decreasing in water use during the dry period. Tree-level water use scaled with sapwood area, from 11 to 190 L per day. Stand level water use, based on multiple plots encompassing sap flow and adjacent trees, varied from ∼1.7 to 3.3 mm per day, increasing linearly with plot basal area. Soil water extraction was dependent on root biomass, which was dense at the surface (i.e., 45% in the upper 5 cm) and declined dramatically with depth. As the dry season progressed and the upper soil dried, soil water extraction shifted to deeper levels and model projections suggest that much of the water used during the month-long dry-down could be extracted from the upper 2-3 m. Results indicate variation in rates of soil water extraction across the research area and, temporally, through the soil profile. These results provide key information on whole-tree contributions to transpiration by canopy trees as water availability changes. In addition, information on simultaneous stand level dynamics of soil water extraction that can inform mechanistic models that project tropical forest response to drought.

Characterization of Root System Architecture Traits in Diverse Soybean Genotypes Using a Semi-Hydroponic System

Phenotypic variation and correlations among root traits form the basis for selecting and breeding soybean varieties with efficient access to water and nutrients and better adaptation to abiotic stresses. Therefore, it is important to develop a simple and consistent system to study root traits in soybean. In this study, we adopted the semi-hydroponic system to investigate the variability in root morphological traits of 171 soybean genotypes popularized in the Yangtze and Huaihe River regions, eastern China. Highly diverse phenotypes were observed: shoot height (18.7-86.7 cm per plant with a median of 52.3 cm); total root length (208-1663 cm per plant with a median of 885 cm); and root mass (dry weight) (19.4-251 mg per plant with a median of 124 mg). Both total root length and root mass exhibited significant positive correlation with shoot mass (p ≤ 0.05), indicating their relationship with plant growth and adaptation strategies. The nine selected traits contributed to one of the two principal components (eigenvalues > 1), accounting for 78.9% of the total genotypic variation. Agglomerative hierarchical clustering analysis separated the 171 genotypes into five major groups based on these root traits. Three selected genotypes with contrasting root systems were validated in soil-filled rhizoboxes (1.5 m deep) until maturity. Consistent ranking of the genotypes in some important root traits at various growth stages between the two experiments indicates the reliability of the semi-hydroponic system in phenotyping root trait variability at the early growth stage in soybean germplasms.

Long-Term Lime and Phosphogypsum Amended-Soils Alleviates the Field Drought Effects on Carbon and Antioxidative Metabolism of Maize by Improving Soil Fertility and Root Growth

Long-term surface application of lime (L) and/or phosphogypsum (PG) in no-till (NT) systems can improve plant growth and physiological and biochemical processes. Although numerous studies have examined the effects of L on biomass and plant growth, comprehensive evaluations of the effects of this practice on net CO2 assimilation, antioxidant enzyme activities and sucrose synthesis are lacking. Accordingly, this study examined the effects of long-term surface applications of L and PG on soil fertility and the resulting impacts on root growth, plant nutrition, photosynthesis, carbon and antioxidant metabolism, and grain yield (GY) of maize established in a dry winter region. At the study site, the last soil amendment occurred in 2016, with the following four treatments: control (no soil amendments), L (13 Mg ha-1), PG (10 Mg ha-1), and L and PG combined (LPG). The long-term effects of surface liming included reduced soil acidity and increased the availability of P, Ca2+, and Mg2+ throughout the soil profile. Combining L with PG strengthened these effects and also increased SO4 2--S. Amendment with LPG increased root development at greater depths and improved maize plant nutrition. These combined effects increased the concentrations of photosynthetic pigments and gas exchange even under low water availability. Furthermore, the activities of Rubisco, sucrose synthase and antioxidative enzymes were improved, thereby reducing oxidative stress. These improvements in the physiological performance of maize plants led to higher GY. Overall, the findings support combining soil amendments as an important strategy to increase soil fertility and ensure crop yield in regions where periods of drought occur during the cultivation cycle.

[Root architecture of main tree species and the effects on soil reinforcement in typical black soil region.]

To explore root architecture and its effects on soil reinforcement of main tree species in typical black soil region, we measured root spatial distribution characteristics, root fractal characte-ristics, and geometric morphological characteristics of Amygdalus triloba, Caragana microphylla, Betula platyphylla, Acer negundo, Picea koraiensis, Pinus sylvestris var. mongolica, using whole root excavation method and WinRHIZO Pro LA2004 root analysis system. All the examined species are distributed widely in typical black soil region. The vertical uprooting force was determined by in-situ uprooting tests. The results showed that inclined roots were dominant in A. triloba, horizontal roots were dominant in C. microphylla, B. platyphylla, A. negundo and P. koraiensis, and the horizontal and vertical distribution of roots were commensurable in P. sylvestris var. mongolica. Except for the total root surface area of B. platyphylla and the total root length of P. koraiensis, the total root length and root surface area of shrub species were significantly greater than those of arbor species, while deciduous broad-leaved trees were significantly larger than coniferous evergreen trees. The total root volume of B. platyphylla was significantly larger than that of C. microphylla, A. negundo, P. koraiensis and P. sylvestris var. mongolica. The root fractal dimension and abundance of A. triloba, C. microphylla, B. platyphylla were significantly higher than those of P. koraiensis and P. sylvestris var. mongolica. The average maximum uprooting force of A. triloba, C. microphylla, and A. negundo was significantly higher than that of B. platyphylla, P. koraiensis, and P. sylvestris var. mongolica. Due to the role of total root length, total root surface area and the number of inclined roots, root system of A. triloba, C. microphylla and A. negundo showed strong soil reinforcement capacity. A. triloba, C. microphylla and A. negundo could be used as the option-preferred tree species when constructing soil and water conservation vegetation in typical black soil region.

Importance of individual root traits to understand crop root system in agronomic and environmental contexts

Resource acquisition, one of the major functions of roots, can contribute to crop growth and mitigating environmental impacts. The spatio-temporal distribution of roots in the soil in relation to the dynamics of the soil resources is critical in resource acquisition. Root distribution is determined by root system development. The root system consists of many individual roots of different types and ages. Each individual root has specific development, resource acquisition, and transport traits, which change with root growth. The integration of individual root traits in the root system could exhibit crop performance in the various environments via root distribution in the soil. However, the relationship between individual root traits and the pattern of root distribution is complicated. To understand this complicated relationship, we need to evaluate enormous numbers of individual root traits and understand the relationship between individual root development and root distribution as well as the integrated functions of individual root traits along with dynamics of resources in the soil.

Effects of Slope Aspect and Rainfall on Belowground Deep Fine Root Traits and Aboveground Tree Height

The vertical root distribution and rooting depth are the main belowground plant functional traits used to indicate drought resistance in arid and semiarid regions. The effects of the slope aspect on the aboveground traits are visible but not the belowground deep root traits. We aimed to investigate the fine root traits of the locust tree (Robinia pseudoacacia L.) planted on southerly and northerly aspects, and the variations in the rooting depth in regions with different rainfall, as well as assessing how deep rooting, might affect the response to drought in a loess region. We selected three study sites with different rainfall amounts, with six sampling plots at each site (three each with southerly and northerly aspects). Soil core samples were collected down to the depth where no roots were present. The locust trees tended to develop deeper fine roots rather than greater heights. The tree height and diameter were greater for locust trees on northerly aspects, whereas trees on southerly aspects had significantly deeper rooting depths. Fine root traits (root length, root area, and root dry weight density) were higher in the southerly aspect for both Changwu and Ansai, but lower in Suide. The ratio of the root front depth tree height ranged from 1.04 to 3.17, which was higher on southerly than northerly aspects, and it increased as the rainfall decreased. Locust tree growth traits (belowground fine root and aboveground tree height) were positively correlated with the mean annual rainfall. The soil moisture content of the topsoil decreased as the rainfall decreased, but the pattern varied in the deep layer. Our results suggest that the variations in the belowground rooting depth under different slope aspects may be related to plant survival strategies. The vertical extension of the rooting depth and tree height may be key functional traits that determine plant growth in drought-prone regions.

Variable Light Condition Improves Root Distribution Shallowness and P Uptake of Soybean in Maize/Soybean Relay Strip Intercropping System

In this study, soybean root distribution in an inter-cropping system was influenced by various environmental and biotic cues. However, it is still unknown how root development and distribution in inter-cropping responds to aboveground light conditions. Herein, soybeans were inter- and monocropped with P (phosphorus) treatments of 0 and 20 kg P ha yr⁻¹ (P0 and P20, respectively) in field experiment over 4 years. In 2019, a pot experiment was conducted as the supplement to the field experiment. Shade from sowing to V5 (Five trifoliolates unroll) and light (SL) was used to imitate the light condition of soybeans in a relay trip inter-cropping system, while light then shade from V5 to maturity (LS) was used to imitate the light condition of soybeans when monocropped. Compared to monocropping, P uptake and root distribution in the upper 0–15 cm soil layer increased when inter-cropped. Inter-cropped soybeans suffered serious shade by maize during a common-growth period, which resulted in the inhibition of primary root growth and a modified auxin synthesis center and response. During the solo-existing period, plant photosynthetic capacity and sucrose accumulation increased under ameliorated light in SL (shade-light). Increased light during the reproductive stage significantly decreased leaf P concentration in SL under both P-sufficient and P-deficient conditions. Transcripts of a P starvation response gene (GmPHR25) in leaves and genes (GmEXPB2) involved in root growth were upregulated by ameliorated light during the reproductive stage. Furthermore, during the reproductive stage, more light interception increased the auxin concentration and expression of GmYUCCA14 (encoding the auxin synthesis) and GmTIR1C (auxin receptor) in roots. Across the field and pot experiments, increased lateral root growth and shallower root distribution were associated with inhibited primary root growth during the seedling stage and ameliorated light conditions in the reproductive stage. Consequently, this improved topsoil foraging and P uptake of inter-cropped soybeans. It is suggested that the various light conditions (shade-light) mediating leaf P status and sucrose transport can regulate auxin synthesis and respond to root formation and distribution.

Impact of Irrigation Strategies on Tomato Root Distribution and Rhizosphere Processes in an Organic System

Root exploitation of soil heterogeneity and microbially mediated rhizosphere nutrient transformations play critical roles in plant resource uptake. However, how these processes change under water-saving irrigation technologies remains unclear, especially for organic systems where crops rely on soil ecological processes for plant nutrition and productivity. We conducted a field experiment and examined how water-saving subsurface drip irrigation (SDI) and concentrated organic fertilizer application altered root traits and rhizosphere processes compared to traditional furrow irrigation (FI) in an organic tomato system. We measured root distribution and morphology, the activities of C-, N-, and P-cycling enzymes in the rhizosphere, the abundance of rhizosphere microbial N-cycling genes, and root mycorrhizal colonization rate under two irrigation strategies. Tomato plants produced shorter and finer root systems with higher densities of roots around the drip line, lower activities of soil C-degrading enzymes, and shifts in the abundance of microbial N-cycling genes and mycorrhizal colonization rates in the rhizosphere of SDI plants compared to FI. SDI led to 66.4% higher irrigation water productivity than FI, but it also led to excessive vegetative growth and 28.3% lower tomato yield than FI. Our results suggest that roots and root-microbe interactions have a high potential for coordinated adaptation to water and nutrient spatial patterns to facilitate resource uptake under SDI. However, mismatches between plant needs and resource availability remain, highlighting the importance of assessing temporal dynamics of root-soil-microbe interactions to maximize their resource-mining potential for innovative irrigation systems.

Belowground interactions differ between sympatric desert shrubs under water stress

Understanding the relationships among species is central to ecological research; however, many knowledge gaps remain regarding how desert plant species interact. In the present study, we assessed the effect of rainfall on the belowground interactions and root morphology of two desert shrubs, Reaumuria soongorica (Tamaricaceae) and Salsola passerina (Chenopodiaceae), from three communities with similar landforms and soil environments. The roots of both R. soongorica and S. passerina were deeper when grown together than grown singly. Interestingly, the belowground biomass of R. soongorica was higher, but the belowground biomass of S. passerina was lower when grown together than when grown alone. This suggests that S. passerina benefitted from the association with R. soongorica. When grown together under conditions of low rainfall, the roots of R. soongorica were deeper than those of S. passerina, which suggests that R. soongorica is more robust than S. passerina when subjected to periods of decreased rainfall. We concluded that the symbiotic relationship between these two shrub species can lead to deeper roots and that the plants are affected by rainfall availability. Combined with the output results of climate change models, we speculated that the distribution area of these two species will expand to the west, which has important implications on how the interactions of other desert species may change in response to climate variability.

Nitrogen Fertilization Increases Root Growth and Coordinates the Root-Shoot Relationship in Cotton

The root system plays an important role in the growth and development of cotton, and root growth is closely related to shoot growth, both of which are affected by N availability in the soil. However, it is unknown how N affects root growth and the root-shoot relationship under various N rates in the Yellow River Basin, China. Thus, the aim of this study was to assess the impacts of the application rate of N on root growth and the root-shoot relationship, to provide insight into the N regulation of root and shoot growth and N efficiency from the perspective of the root system. A field experiment conducted in 2014 and 2015 was used to determine the effects of N rates (0, 120, 240, and 480 kg ha^-1) on root morphology, root distribution, the root-shoot relationship, and cotton yield. A moderate N fertilization rate (240 kg ha^-1) increased root length, root surface area, and root biomass in most soil layers and significantly increased total root growth and total root biomass by more than 36.06% compared to the 0 kg ha^-1 treatment. In addition, roots in the surface soil layers were more strongly affected by N fertilization than roots distributed in the deeper soil layers. Total root length, total root surface area, and root biomass in the 0-15 cm layer were significantly correlated with shoot biomass and boll biomass. In the 60-75 cm layer, total root length, total root surface area, and root length were significantly positively correlated with seed cotton yield. The application of a moderate level of N markedly increased total shoot biomass, boll biomass, and seed cotton yield. Our results show that increased shoot and boll biomasses were correlated with a significant increase in the root system especially the shallow roots in the moderate N treatment (240 kg ha^-1), leading to an increase in cotton seed yield.

[Response of distribution pattern and physiological characteristics of apple roots grown in the dry area of eastern Gansu to ground mulching]

The objective of the experiment is to ascertain the effects of different mulching materials on the distribution and physiological activity of apple roots as well as the soil physicochemical pro-perties in the rain-fed Longdong arid areas. With fourteen years old apple trees as test material, the different classes of roots were collected by using soil profile method and stratified sampling in soil profile to investigate the spatial distribution, root biomass, root length and surface area. The activity of root and antioxidant enzymes and some antioxidant indexes were measured. Soil bulk density and soil porosity in different soil layers were determined. The results indicated that ground covering treatment increased the soil moisture, porosity and organic matter content, and the amplification were 2.7%-11.6%, 3.2%-27.7%, 5.1%-36.0%, respectively compared with the control. The soil bulk density was reduced by 88.7%-96.4%. The roots of CK distributed mainly in soil layer of 0-60 cm in depth, 30-120 cm away from the trunk. However, with straw and plastic mulching the roots distributed mainly in the layer of 0-100 cm in depth, 0-150 cm and 0-60 cm away from the trunk, respectively, mostly concentrated in the 20-40 cm layer close to the ground. Plastic mul-ching made a narrower horizontal root distribution than CK and the total fine root amount was 96.4% of that of CK, and that in 0-60 cm layer accounted for 51.6% of the total fine root amount. More-over, the mulching resulted in a higher activity of root and antioxidant enzymes in 0-80 cm layer. The root activity with straw mulching was 111.3%-136.7% as much as the control. For sake of the efficacy on improving root distribution and physiological activity, the straw mulching was suggested as a better way for soil management in apple orchard in dry area of eastern Gansu.

[Water sources of dominant sand-binding plants in dry season in southern Horqin Sandy Land, China]

It's important to explore the water sources of sand-binding plants and their relationship to reveal the mechanism underling species coexistence and vegetation stability. In the present study, 12 sand-binding species in two typical habitats (fixed dune and dune slack) in southern Horqin Sandy Land were selected. The δD and δ¹⁸O values of plant water, rain water, ground water and soil water were determined, and the percentages of soil water at different depths used by plants were calculated with the IsoSource model. Our results showed that the δD and δ¹⁸O values of stem water were significantly different among various life forms in both habitats except for those of trees and shrubs in dune slack. From trees to grass, the depth of soil water contributed to main water source of plant became shallower in dune slack: trees and shrubs mainly used soil water in 50-150 cm or 30-50 cm layer, subshrubs mainly used soil water in 10-30 cm layer while grass relied on soil water of 0-10 cm layer. Shrubs mainly used soil water of 0-30 cm layer and subshrubs mainly used soil water around 50 cm at fixed dune. This study indicated that in dry season plants at fixed dune are more dependent on soil water of 0-50 cm layer compared with those in dune slack. The water sources of sand-binding plants are correlated with plant life form and root distribution range, and the later might play a more important role.

Optimizing soil-coring strategies to quantify root-length-density distribution in field-grown maize: virtual coring trials using 3-D root architecture models

BACKGROUND AND AIMS

Root distribution has a major influence on soil exploration and nutrient and water acquisition by plants. Soil coring is a well-known way to estimate root distribution. However, identifying an optimal core-sampling strategy is important if one is to strike the right balance between the high cost of making field estimates of root length density (RLD) vs. the need for accurate estimates. Virtual assessment of competing soil-coring strategies, based on three-dimensional (3-D) models of root system architecture (RSA), is a highly effective way to find that balance.

METHODS

The trajectories of the axile roots of two maize cultivars having contrasting axile root angles were measured in the field using in situ 3-D digitization. Lateral roots were also measured by recording topological and geometrical parameters. Based on the measurement dataset obtained, contrasting 3-D RSA models of individual maize plants were constructed in which the different lateral rooting angles were represented. Using these RSA models the accuracies of various core-sampling strategies for estimating RLD were assessed in a series of virtual experiments.

KEY RESULTS

Substantial biases occur if a one-core sampling strategy is used to estimate RLD. The biases largely remain for two-core sampling, although a weighting method can reduce these. However, given that identification of an optimal weighting method is difficult in practice, a new sampling strategy is proposed based on an area-weighting algorithm. In this way low deviations in RLD estimation can be achieved by sampling between rows and also by using larger-diameter (7.5 or 10 cm) cores.

CONCLUSIONS

A 3-D root architecture model based on a detailed measurement dataset provides an ideal platform for assessing a range of soil-coring strategies. The improved two-core sampling strategy, based on an area-weighting algorithm, shows considerable promise as a cost-efficient way of obtaining good quality RLD estimates for maize.

A new method for the rapid characterization of root growth and distribution using digital image correlation

Rapidly determining root growth patterns is biologically important and technically challenging. Current methods focus on direct observation of roots and require destructive excavations or time-consuming root tracing. We developed a novel methodology based on analyzing soil particle displacement, rather than direct observation of roots. This inferred root growth method uses digital image correlation (DIC) analysis, an established and high-throughput method used in many engineering and science disciplines. By applying DIC analyses to repeated images of plants grown in clear window boxes, we produced visually intuitive and quantifiable strain maps, indicating the magnitude and direction of soil movement. From this, we could infer root growth and rapidly quantify root system metrics. Strain measures were closely associated with the spatial distribution of roots and correlated with root length measured using conventional approaches. The method also allowed for the detection of root proliferation in nutrient-enriched soil patches, indicating its suitability for quantifying biological patterns. This novel application of DIC in root biology is effective, scalable, low cost, flexible and complementary to existing technologies. This method offers a new tool for answering questions in plant biology and will be particularly useful in studies involving temporal dynamics of root processes.

Lost in diversity: the interactions between soil-borne fungi, biodiversity and plant productivity

There is consensus that plant species richness enhances plant productivity within natural grasslands, but the underlying drivers remain debated. Recently, differential accumulation of soil-borne fungal pathogens across the plant diversity gradient has been proposed as a cause of this pattern. However, the below-ground environment has generally been treated as a 'black box' in biodiversity experiments, leaving these fungi unidentified. Using next generation sequencing and pathogenicity assays, we analysed the community composition of root-associated fungi from a biodiversity experiment to examine if evidence exists for host specificity and negative density dependence in the interplay between soil-borne fungi, plant diversity and productivity. Plant species were colonised by distinct (pathogenic) fungal communities and isolated fungal species showed negative, species-specific effects on plant growth. Moreover, 57% of the pathogenic fungal operational taxonomic units (OTUs) recorded in plant monocultures were not detected in eight plant species plots, suggesting a loss of pathogenic OTUs with plant diversity. Our work provides strong evidence for host specificity and negative density-dependent effects of root-associated fungi on plant species in grasslands. Our work substantiates the hypothesis that fungal root pathogens are an important driver of biodiversity-ecosystem functioning relationships.

Root Traits, Nodulation and Root Distribution in Soil for Five Wild Lentil Species and Lens culinaris (Medik.) Grown under Well-Watered Conditions

The efficient use of resources such as water and nutrients by plants is increasingly important as the world population food demand continues to grow. With the increased production of lentil in the temperate zones of North America, improvement in yield needs to be maintained. The use of wild lentil genotypes as sources of genetic diversity for introgression into cultivated lentil is an important breeding strategy, but little is known about their root systems. We evaluated the root systems of five wild lentil species and Lens culinaris under fully watered conditions. Plants were grown in 60 cm tubes containing equal volumes of soil collected from the reconstructed A, B, and C horizons. Significant differences were observed for root traits and fine root distribution between and within species and the proportion of root biomass partitioned into each soil layer was unique for each genotype. We also observed variability in nodule number and nodule shape within and between genotypes. Some genotypes more efficiently used water for either biomass or seed production. The allocation of resources to seed production also varied between genotypes. These observations could have impact on the design of future lentil breeding in the context of strategies for managing changes in rainfall amount and distribution for lentil production ecosystems.

Genotypic Variation in Yield, Yield Components, Root Morphology and Architecture, in Soybean in Relation to Water and Phosphorus Supply

Water shortage and low phosphorus (P) availability limit yields in soybean. Roots play important roles in water-limited and P-deficient environment, but the underlying mechanisms are largely unknown. In this study we determined the responses of four soybean [Glycine max (L.) Merr.] genotypes [Huandsedadou (HD), Bailudou (BLD), Jindou 21 (J21), and Zhonghuang 30 (ZH)] to three P levels [applied 0 (P0), 60 (P60), and 120 (P120) mg P kg-1 dry soil to the upper 0.4 m of the soil profile] and two water treatment [well-watered (WW) and water-stressed (WS)] with special reference to root morphology and architecture, we compared yield and its components, root morphology and root architecture to find out which variety and/or what kind of root architecture had high grain yield under P and drought stress. The results showed that water stress and low P, respectively, significantly reduced grain yield by 60 and 40%, daily water use by 66 and 31%, P accumulation by 40 and 80%, and N accumulation by 39 and 65%. The cultivar ZH with the lowest daily water use had the highest grain yield at P60 and P120 under drought. Increased root length was positively associated with N and P accumulation in both the WW and WS treatments, but not with grain yield under water and P deficits. However, in the WS treatment, high adventitious and lateral root densities were associated with high N and P uptake per unit root length which in turn was significantly and positively associated with grain yield. Our results suggest that (1) genetic variation of grain yield, daily water use, P and N accumulation, and root morphology and architecture were observed among the soybean cultivars and ZH had the best yield performance under P and water limited conditions; (2) water has a major influence on nutrient uptake and grain yield, while additional P supply can modestly increase yields under drought in some soybean genotypes; (3) while conserved water use plays an important role in grain yield under drought, root traits also contribute to high nutrient uptake efficiency and benefit yield under drought.

Rooting depth and root depth distribution of Trifolium repens × T. uniflorum interspecific hybrids

Background and aims Traits related to root depth distribution were examined in Trifolium repens × T. uniflorum backcross 1 (BC1) hybrids to determine whether root characteristics of white clover could be improved by interspecific hybridization. Methods Two white clover cultivars, two T. uniflorum accessions and two BC1 populations were grown in 1 -m deep tubes of sand culture. Maximum rooting depth and root mass distribution were measured at four harvests over time, and root distribution data were fitted with a regression model to provide measures of root system shape. Morphological traits were measured at two depths at harvest 3. Key Results Root system shape of the hybrids was more similar to T. uniflorum than to white clover. The hybrids and T. uniflorum had a higher rate of decrease in root mass with depth than white clover, which would result in higher proportions of root mass in the upper profile. Percentage total root mass at 100-200 mm depth was higher for T. uniflorum than white clover, and for Crusader BC1 than 'Crusader'. Roots of the hybrids and T. uniflorum also penetrated deeper than those of white clover. T. uniflorum had thicker roots at 50-100 mm deep than the other entries, and more of its fine root mass at 400-500 mm. The hybrids and white clover had more of their fine root mass higher in the profile. Consequently, T. uniflorum had a higher root length density at 400-500 mm than most entries, and a smaller decrease in root length density with depth. Conclusions These results demonstrate that rooting characteristics of white clover can be altered by hybridization with T. uniflorum, potentially improving water and nutrient acquisition and drought resistance. Root traits of T. uniflorum are likely to be adaptations to soil moisture and fertility in its natural environment.

[Effects of ridge-cultivation and plastic film mulching on root distribution and yield of spring maize in hilly area of central Sichuan basin, China.]

A field experiment was conducted to study the effects of planting pattern (ridge culture, flatten culture, furrow culture) and film mulching on the distribution of spring maize root system and their influence on the yield of spring maize in the hilly area of central Sichuan basin. The results showed that ridge and film mulching had great influence on root morphology and root distribution of maize. The root length, root surface area and root volume of film mulching was 42.3%, 50.0%, 57.4% higher than those of no film mulching at jointing stage. The film mulching significantly increased the dry mass of root in vertical and horizontal distribution, and increased the root allocation ratio in deeper soil layer (20-40 cm) and the allocation ratio of wide row (0-20 cm) in horizontal direction. The effects of planting pattern on root growth and root distribution differed by film mulching. With film mulching, the ridge culture significantly increased the root dry mass in each soil layer and enlarged the distribution percentage of wide row (20-40 cm) in horizontal direction, as well as the dry mass of root in horizontal distribution and the root allocation ratio of wide row. The root mass under film mulching was in the order of ridge culture>flatten culture>furrow culture. Without film mulching, the furrow culture significantly increased root dry mass of narrow row (0-40 cm), and the root mass under no film mulching was in the order of furrow culture > ridge culture >flatten culture. As for the spike characteristics and maize yield, the filming mulching mea-sures reduced the corn bald length while increased the spike length, grain number, 1000-grain mass and yield. The yield under film mulching was in the order of ridge culture>flatten culture> furrow culture, while it was furrow culture > flatten culture > ridge culture under no film mulching. The reason for yield increase under ridge culture with film mulching was that it increased root weight especially in deep soil, and promoted the root allocation ratio in deeper soil and wide row (20-40 cm) in horizontal direction. The ridge-furrow culture without film mulching was helpful to root growth and increased the maize yield.

Molecular diversity and distribution of indigenous arbuscular mycorrhizal communities colonizing roots of two different winter cover crops in response to their root proliferation

A clear understanding of how crop root proliferation affects the distribution of the spore abundance of arbuscular mycorrhizal fungi (AMF) and the composition of AMF communities in agricultural fields is imperative to identify the potential roles of AMF in winter cover crop rotational systems. Toward this goal, we conducted a field trial using wheat (Triticum aestivum L.) or red clover (Trifolium pratense L.) grown during the winter season. We conducted a molecular analysis to compare the diversity and distribution of AMF communities in roots and spore abundance in soil cropped with wheat and red clover. The AMF spore abundance, AMF root colonization, and abundance of root length were investigated at three different distances from winter crops (0 cm, 7.5 cm, and 15 cm), and differences in these variables were found between the two crops. The distribution of specific AMF communities and variables responded to the two winter cover crops. The majority of Glomerales phylotypes were common to the roots of both winter cover crops, but Gigaspora phylotypes in Gigasporales were found only in red clover roots. These results also demonstrated that the diversity of the AMF colonizing the roots did not significantly change with the three distances from the crop within each rotation but was strongly influenced by the host crop identity. The distribution of specific AMF phylotypes responded to the presence of wheat and red clover roots, indicating that the host crop identity was much more important than the proliferation of crop roots in determining the diversity of the AMF communities.

The effect of Piriformospora indica on the root development of maize (Zea mays L.) and remediation of petroleum contaminated soil

As the depth of soil petroleum contamination can vary substantially under field conditions, a rhizotron experiment was performed to investigate the influence of endophyte, P. indica, on maize growth and degradation of petroleum components in a shallow and a deep-reaching subsurface layer of a soil. For control, a treatment without soil contamination was also included. The degree in contamination and the depth to which it extended had a strong effect on the growth of the plant roots. Contaminated soil layers severely inhibited root growth thus many roots preferred to bypass the shallow contaminated layer and grow in the uncontaminated soil. While the length and branching pattern of these roots were similar to those of uncontaminated treatment. Inoculation of maize with P. indica could improve root distribution and root and shoot growth in all three contamination treatments. This inoculation also enhanced petroleum degradation in soil, especially in the treatment with deep-reaching contamination, consequently the accumulation of petroleum hydrocarbons (PAHs) in the plant tissues were increased.

A tillering inhibition gene influences root-shoot carbon partitioning and pattern of water use to improve wheat productivity in rainfed environments

Genetic modification of shoot and root morphology has potential to improve water and nutrient uptake of wheat crops in rainfed environments. Near-isogenic lines (NILs) varying for a tillering inhibition (tin) gene and representing multiple genetic backgrounds were phenotyped in contrasting, controlled environments for shoot and root growth. Leaf area, shoot and root biomass were similar until tillering, whereupon reduced tillering in tin-containing NILs produced reductions of up to 60% in total leaf area and biomass, and increases in total root length of up to 120% and root biomass to 145%. Together, the root-to-shoot ratio increased two-fold with the tin gene. The influence of tin on shoot and root growth was greatest in the cv. Banks genetic background, particularly in the biculm-selected NIL, and was typically strongest in cooler environments. A separate de-tillering study confirmed greater root-to-shoot ratios with regular tiller removal in non-tin-containing genotypes. In validating these observations in a rainfed field study, the tin allele had a negligible effect on seedling growth but was associated with significantly (P<0.05) reduced tiller number (-37%), leaf area index (-26%), and spike number (-35%) to reduce plant biomass (-19%) at anthesis. Root biomass, root-to-shoot ratio at early stem elongation, and root depth at maturity were all increased in tin-containing NILs. Soil water use was slowed in tin-containing NILs, resulting in greater water availability, greater stomatal conductance, cooler canopy temperatures, and maintenance of green leaf area during grain-filling. Together these effects contributed to increases in harvest index and grain yield. In both the controlled and field environments, the tin gene was commonly associated with increased root length and biomass, but the significant influence of genetic background and environment suggests careful assessment of tin-containing progeny in selection for genotypic increases in root growth.

Contrasting strategies to cope with drought conditions by two tropical forage C4 grasses

Drought severely limits forage productivity of C4 grasses across the tropics. The avoidance of water deficit by increasing the capacity for water uptake or by controlling water loss are common responses in forage C4 grasses. Napier grass (Pennisetum purpureum) and Brachiaria hybrid cv. Mulato II are tropical C4 grasses used for livestock production due to their reputed resistance to drought conditions. However, there is scant information on the mechanisms used by these grasses to overcome water-limited conditions. Therefore, assessments of cumulative transpired water, shoot growth, leaf rolling, leaf gas exchange, dry mass production and a number of morpho-physiological traits were recorded over a period of 21 days under well-watered or drought conditions. Drought reduced shoot dry mass of both grasses by 35 %, yet each grass exhibited contrasting strategies to cope with water shortage. Napier grass transpired most available water by the end of the drought treatment, whereas a significant amount of water was still available for Mulato II. Napier grass maintained carbon assimilation until the soil was fairly dry, whereas Mulato II restricted water loss by early stomatal closure at relatively wet soil conditions. Our results suggest that Napier grass exhibits a 'water-spending' behaviour that might be targeted to areas with intermittent drought stress, whereas Mulato II displays a 'water-saving' nature that could be directed to areas with longer dry periods.

A multi-imaging approach to study the root-soil interface

BACKGROUND AND AIMS

Dynamic processes occurring at the soil-root interface crucially influence soil physical, chemical and biological properties at a local scale around the roots, and are technically challenging to capture in situ. This study presents a novel multi-imaging approach combining fluorescence and neutron radiography that is able to simultaneously monitor root growth, water content distribution, root respiration and root exudation.

METHODS

Germinated seeds of white lupins (Lupinus albus) were planted in boron-free glass rhizotrons. After 11 d, the rhizotrons were wetted from the bottom and time series of fluorescence and neutron images were taken during the subsequent day and night cycles for 13 d. The following day (i.e. 25 d after planting) the rhizotrons were again wetted from the bottom and the measurements were repeated. Fluorescence sensor foils were attached to the inner sides of the glass and measurements of oxygen and pH were made on the basis of fluorescence intensity. The experimental set-up allowed for simultaneous fluorescence imaging and neutron radiography.

KEY RESULTS

The interrelated patterns of root growth and distribution in the soil, root respiration, exudation and water uptake could all be studied non-destructively and at high temporal and spatial resolution. The older parts of the root system with greater root-length density were associated with fast decreases of water content and rapid changes in oxygen concentration. pH values around the roots located in areas with low soil water content were significantly lower than the rest of the root system.

CONCLUSIONS

The results suggest that the combined imaging set-up developed here, incorporating fluorescence intensity measurements, is able to map important biogeochemical parameters in the soil around living plants with a spatial resolution that is sufficiently high enough to relate the patterns observed to the root system.

Belowground neighbor perception in Arabidopsis thaliana studied by transcriptome analysis: roots of Hieracium pilosella cause biotic stress

Root-root interactions are much more sophisticated than previously thought, yet the mechanisms of belowground neighbor perception remain largely obscure. Genome-wide transcriptome analyses allow detailed insight into plant reactions to environmental cues. A root interaction trial was set up to explore both morphological and whole genome transcriptional responses in roots of Arabidopsis thaliana in the presence or absence of an inferior competitor, Hieracium pilosella. Neighbor perception was indicated by Arabidopsis roots predominantly growing away from the neighbor (segregation), while solitary plants placed more roots toward the middle of the pot. Total biomass remained unaffected. Database comparisons in transcriptome analysis revealed considerable similarity between Arabidopsis root reactions to neighbors and reactions to pathogens. Detailed analyses of the functional category "biotic stress" using MapMan tools found the sub-category "pathogenesis-related proteins" highly significantly induced. A comparison to a study on intraspecific competition brought forward a core of genes consistently involved in reactions to neighbor roots. We conclude that beyond resource depletion roots perceive neighboring roots or their associated microorganisms by a relatively uniform mechanism that involves the strong induction of pathogenesis-related proteins. In an ecological context the findings reveal that belowground neighbor detection may occur independently of resource depletion, allowing for a time advantage for the root to prepare for potential interactions.

Multiple adaptive responses of Australian native perennial legumes with pasture potential to grow in phosphorus- and moisture-limited environments

BACKGROUND AND AIMS

Many Australian legumes have evolved in low-phosphorus (P) soils and low-rainfall areas. Therefore a study was made of the interaction of soil [P] and water availability on growth, photosynthesis, water-use efficiency (WUE) and P nutrition of two Australian native legumes with pasture potential, Cullen australasicum and C. pallidum, and the widely grown exotic pasture legume, lucerne (Medicago sativa).

METHODS

Plants were grown in a glasshouse at 3, 10 and 30 mg P kg(-1) dry soil for 5 months. At week 10, two drought treatments were imposed, total pot dried (all-dry) and only top soil dried (top-dry), while control pots were maintained at field capacity.

KEY RESULTS

Shoot dry weight produced by lucerne was never higher than that of C. australasicum. For C. pallidum only, shoot dry weight was reduced at 30 mg P kg(-1) dry soil. The small root system of the Cullen species was quite plastic, allowing plants to access P and moisture efficiently. Lucerne always had a higher proportion of its large root system in the top soil layer compared with Cullen species. All species showed decreased photosynthesis, leaf water potential and stomatal conductance when exposed to drought, but the reductions were less for Cullen species, due to tighter stomatal control, and consequently they achieved a higher WUE. All species showed highest rhizosphere carboxylate concentrations in the all-dry treatment. For lucerne only, carboxylates decreased as P supply increased. Citrate was the main carboxylate in the control and top-dry treatments, and malate in the all-dry treatment.

CONCLUSIONS

Multiple adaptive responses of Cullen species and lucerne favoured exploitation of low-P soils under drought. The performance of undomesticated Cullen species, relative to that of lucerne, shows their promise as pasture species for environments such as in south-western Australia where water and P are limiting, especially in view of a predicted drying and warming climate.

Modelling cereal root systems for water and nitrogen capture: towards an economic optimum

A quantitative model of wheat root systems is developed that links the size and distribution of the root system to the capture of water and nitrogen (which are assumed to be evenly distributed with depth) during grain filling, and allows estimates of the economic consequences of this capture to be assessed. A particular feature of the model is its use of summarizing concepts, and reliance on only the minimum number of parameters (each with a clear biological meaning). The model is then used to provide an economic sensitivity analysis of possible target characteristics for manipulating root systems. These characteristics were: root distribution with depth, proportional dry matter partitioning to roots, resource capture coefficients, shoot dry weight at anthesis, specific root weight and water use efficiency. From the current estimates of parameters it is concluded that a larger investment by the crop in fine roots at depth in the soil, and less proliferation of roots in surface layers, would improve yields by accessing extra resources. The economic return on investment in roots for water capture was twice that of the same amount invested for nitrogen capture.