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The effects of localized fertilizer (LF) application on changes in root system architecture (RSA) of upland rice seedlings under upland condition were evaluated, and root traits important for deep root development were identified using three root box experiments (Exps). Fertilizer was homogeneously mixed and broadcasted on the soil surface in two control treatments, while in three LF treatments, it was point-placed at 2.5, 7.5 and 12.5 cm below the soil surface. Nitrogen (N) fertilizer in Exp. 1, phosphorus (P) fertilizer in Exp. 2 and compound fertilizer with nitrogen, phosphorus and potassium (NPK) in Exp. 3 were used to compare the effects of LF. Localized N and NPK application altered the RSA through root proliferation and increasing root length percentage around the fertilizer-applied area, whereas localized P application had no effect on both root and shoot development. Deep root and shoot development were decreased with localized NPK application compared to homogeneously mixed control treatment but were maintained with localized N application, when applied at deeper soil depths. Furthermore, the increase in deep root length (DRL) was closely related to the increase in both total root length (TRL) and deep root length ratio (DRR). DRR increased with TRL in Exps. 2 and 3, while it was independent from TRL in Exp. 1, suggesting that DRL can be promoted by increasing DRR regardless of TRL. These results showed that localized N application at deeper soil depths could modify RSA of upland rice seedlings grown under upland condition without affecting shoot growth.

The effects of localized fertilizer (LF) application on changes in root system architecture (RSA) of upland rice seedlings under upland condition were evaluated, and root traits important for deep root development were identified using three root box experiments (Exps). Fertilizer was homogeneously mixed and broadcasted on the soil surface in two control treatments, while in three LF treatments, it was point-placed at 2.5, 7.5 and 12.5 cm below the soil surface. Nitrogen (N) fertilizer in Exp. 1, phosphorus (P) fertilizer in Exp. 2 and compound fertilizer with nitrogen, phosphorus and potassium (NPK) in Exp. 3 were used to compare the effects of LF. Localized N and NPK application altered the RSA through root proliferation and increasing root length percentage around the fertilizer-applied area, whereas localized P application had no effect on both root and shoot development. Deep root and shoot development were decreased with localized NPK application compared to homogeneously mixed control treatment but were maintained with localized N application, when applied at deeper soil depths. Furthermore, the increase in deep root length (DRL) was closely related to the increase in both total root length (TRL) and deep root length ratio (DRR). DRR increased with TRL in Exps. 2 and 3, while it was independent from TRL in Exp. 1, suggesting that DRL can be promoted by increasing DRR regardless of TRL. These results showed that localized N application at deeper soil depths could modify RSA of upland rice seedlings grown under upland condition without affecting shoot growth. [ABSTRACT FROM AUTHOR]

Background and aims: Root distribution over the soil profile is important for crop resource uptake. Using machine learning (ML), this study investigated whether measured square root of planar root length density (Sqrt_pRLD) at different soil depths were related to uptake of isotope tracer (15N) and drought stress indicator (13C) in wheat, to reveal root function. Methods: In the RadiMax semi-field root-screening facility 95 winter wheat genotypes were phenotyped for root growth in 2018 and 120 genotypes in 2019. Using the minirhizotron technique, root images were acquired across a depth range from 80 to 250 cm in May, June, and July and RL was extracted using a convolutional neural network. We developed ML models to explore whether the Sqrt_pRLD estimates at different soil depths were predictive of the uptake of deep soil nitrogen - using deep placement of 15N tracer as well as natural abundance of 13C isotope. We analyzed the correlations to tracer levels to both a parametrized root depth estimation and an ML approach. We further analyzed the genotypic effects on root function using mediation analysis. Results: Both parametrized and ML models demonstrated clear correlations between Sqrt_pRLD distribution and resource uptake. Further, both models demonstrated that deep roots at approx. 150 to 170 cm depth were most important for explaining the plant content of 15N and 13C isotopes. The correlations were higher in 2018. Conclusions: The results demonstrated that, parametrized models and ML-based analysis provided complementary insight into the importance of deep rooting for water and nitrogen uptake. [ABSTRACT FROM AUTHOR]

Abstract Water‐use efficiency (WUE) is an under‐researched but very important drought tolerance trait in forage breeding. This research estimated quantitative genetic parameters of morpho‐physiological traits linked to agronomic water‐use efficiency (WUEA) and its proxy measures based on δ13C (WUEi) or gas exchange (evapotranspiration, WUEAET, or stomatal conductance WUEASC) of genotypes from half‐sib families of Lolium perenne L. (PRG) in a simulated summer drought cycle. Principal component analysis (PCA) of trait data distinguished a group of PRG genotypes where high WUEA and dry matter yield was associated with deep rooting, leaf hydration at more negative leaf osmotic and water potential, and reduced soil moisture depletion. Plants with this trait association sustained net assimilation and postdefoliation regrowth in drought. However, WUEi, WUEASC, and WUEAET were poorly correlated with most traits of interest at p 0.7;p

Abstract Background Deep rooting is an important factor affecting rice drought resistance. However, few genes have been identified to control this trait in rice. Previously, we identified several candidate genes by QTL mapping of the ratio of deep rooting and gene expression analysis in rice. Results In the present work, we cloned one of these candidate genes, OsSAUR11, which encodes a small auxin-up RNA (SAUR) protein. Overexpression of OsSAUR11 significantly enhanced the ratio of deep rooting of transgenic rice, but knockout of this gene did not significantly affect deep rooting. The expression of OsSAUR11 in rice root was induced by auxin and drought, and OsSAUR11-GFP was localized both in the plasma membrane and cell nucleus. Through an electrophoretic mobility shift assay and gene expression analysis in transgenic rice, we found that the transcription factor OsbZIP62 can bind to the promoter of OsSAUR11 and promote its expression. A luciferase complementary test showed that OsSAUR11 interacts with the protein phosphatase OsPP36. Additionally, expression of several auxin synthesis and transport genes (e.g., OsYUC5 and OsPIN2) were down-regulated in OsSAUR11-overexpressing rice plants. Conclusions This study revealed a novel gene OsSAUR11 positively regulates deep rooting in rice, which provides an empirical basis for future improvement of rice root architecture and drought resistance.

Water‐use efficiency (WUE) is an under‐researched but very important drought tolerance trait in forage breeding. This research estimated quantitative genetic parameters of morpho‐physiological traits linked to agronomic water‐use efficiency (WUEA) and its proxy measures based on δ13C (WUEi) or gas exchange (evapotranspiration, WUEAET, or stomatal conductance WUEASC) of genotypes from half‐sib families of Lolium perenne L. (PRG) in a simulated summer drought cycle. Principal component analysis (PCA) of trait data distinguished a group of PRG genotypes where high WUEA and dry matter yield was associated with deep rooting, leaf hydration at more negative leaf osmotic and water potential, and reduced soil moisture depletion. Plants with this trait association sustained net assimilation and postdefoliation regrowth in drought. However, WUEi, WUEASC, and WUEAET were poorly correlated with most traits of interest at p <.05. Another PCA revealed a weak association between WUEA and its proxy measures under conditions tested. Quantitative genetic parameters including high estimates of narrow‐sense heritability (hn2>0.7;p<.05) of WUEA and related traits emphasized the genetic potential of the key trait combination for selecting PRG for improved drought tolerance. Research findings highlight the relative importance of WUEA and its proxy measures in the broad definition of PRG drought tolerance for breeding purposes. [ABSTRACT FROM AUTHOR]

Background: Deep rooting is an important factor affecting rice drought resistance. However, few genes have been identified to control this trait in rice. Previously, we identified several candidate genes by QTL mapping of the ratio of deep rooting and gene expression analysis in rice. Results: In the present work, we cloned one of these candidate genes, OsSAUR11, which encodes a small auxin-up RNA (SAUR) protein. Overexpression of OsSAUR11 significantly enhanced the ratio of deep rooting of transgenic rice, but knockout of this gene did not significantly affect deep rooting. The expression of OsSAUR11 in rice root was induced by auxin and drought, and OsSAUR11-GFP was localized both in the plasma membrane and cell nucleus. Through an electrophoretic mobility shift assay and gene expression analysis in transgenic rice, we found that the transcription factor OsbZIP62 can bind to the promoter of OsSAUR11 and promote its expression. A luciferase complementary test showed that OsSAUR11 interacts with the protein phosphatase OsPP36. Additionally, expression of several auxin synthesis and transport genes (e.g., OsYUC5 and OsPIN2) were down-regulated in OsSAUR11-overexpressing rice plants. Conclusions: This study revealed a novel gene OsSAUR11 positively regulates deep rooting in rice, which provides an empirical basis for future improvement of rice root architecture and drought resistance. [ABSTRACT FROM AUTHOR]

Phragmites australis (or common reed), one of the most widespread invasive species in wetlands of North America, has a high nitrogen (N) demand compared to native species. However, it is unclear how P. australis is able to meet this N demand, especially in systems with low soil N and limited N inputs. We evaluated whether deep rooting could be a mechanism by which P. australis accesses otherwise unused N pools, allowing it to circumvent nutrient competition and acquire the "missing N" needed to meet its N demand. We examined above and belowground N pools, as well as depth profiles of belowground biomass (to 3 m), in native and P. australis-dominated plant communities in two brackish marshes of the Chesapeake Bay. To evaluate whether deep roots contribute to P. australis meeting its high N demand, we amended soil porewater with 15N at four soil depths (10, 20, 40, and 80 cm) and measured the rate of 15N assimilation into plant biomass. We found that P. australis had 6–8 × the aboveground standing stock N, 2–3 × the total belowground biomass, and roots up to 3 × deeper than native plant communities (some exceeding 3 m). Our 15N tracer study demonstrated that P. australis acquired N from all measured soil depths, whereas N uptake by native plants was minimal below 20 cm. Our results demonstrate that deep rooting is a mechanism by which P. australis can access previously buried N pools, helping to satisfy its high N demand and thus fuel its invasion. Moreover, these results fundamentally challenge our understanding of biogeochemical processes deep within the soil profile given the presence of active roots at depths where they were previously thought to be largely inert. [ABSTRACT FROM AUTHOR]

Deep rooting is an important trait in rice drought resistance. Genetic resources of deep-rooting varieties are valuable in breeding of water-saving and drought-resistant rice. In the present study, 234 BC2F7 backcross introgression lines were derived from a cross of Dongye 80 (an accession of Dongxiang wild rice as the donor parent) and R974 (an indica restorer line as the recurrent parent). A genetic linkage map containing 1 977 bin markers was constructed by ddRADSeq for QTL analysis. Thirty-one QTLs for four root traits (the number of deep roots, the number of shallow roots, the total number of deep roots and the ratio of deep roots) were assessed on six rice chromosomes in two environments (2020 Shanghai and 2021 Hainan). Two of the QTLs, qDR5.1 and qTR5.2, were located on chromosome 5 in a 70-kb interval. They were detected in both environments. qDR5.1 explained 13.35% of the phenotypic variance in 2020 Shanghai and 12.01% of the phenotypic variance in 2021 Hainan. qTR5.2 accounted for 10.88% and 10.93% of the phenotypic variance, respectively. One QTL (qRDR2.2) for the ratio of deep roots was detected on chromosome 2 in a 210-kb interval and accounted for 6.72% of the phenotypic variance in 2020. The positive effects of these three QTLs were all from Dongxiang wild rice. Furthermore, nine and four putative candidate genes were identified in qRDR2.2 and qDR5.1/qTR5.2, respectively. These findings added to our knowledge of the genetic control of root traits in rice. In addition, this study will facilitate the future isolation of candidate genes of the deep-rooting trait and the utilization of Dongxiang wild rice in the improvement of rice drought resistance.

The objective of this study was to evaluate the usage of species with coloured roots to study root growth patterns during intercropping. Red beet (Beta vulgaris L. cv. Detroit), having clear red roots, was used in a semi-field and field experiment to allow identification and quantification of roots of the individual species in the mixture. In the field experiment, red beet was strip intercropped with lucerne (Medicago sativa L. cv. Creno) and kale (Brassica oleracea L. var. Sabellica), respectively while the red beet-lucerne intercropping was conducted in large rhizoboxes where root growth distribution and 15N isotope uptake was determined. The study confirmed that the direct visual measurement of root growth using species with coloured roots and indirect tracer uptake measurements contributed to the success of studying root growth dynamics in intercropping systems. Red beet root intensity was not considerably affected by the strip intercropping when the crops were established at the same time, but when established between existing lucerne strips, a reduction in roots at the border row was shown. Lucerne and kale were both observed to be able to exploit the deep soil layers beneath the red beet border row.

Drought stress severely affects plant growth and development, causing significant yield loss in rice. This study demonstrates the relevance of water use efficiency with deeper rooting along with other root traits and gas exchange parameters. Forty-nine rice genotypes were evaluated in the basket method to examine leaf-level water use efficiency (WUEi) variation and its relation to root traits. Significant variation in WUEi was observed (from 2.29 to 7.39 µmol CO2 mmol−1 H2O) under drought stress. Regression analysis revealed that high WUEi was associated with higher biomass accumulation, low transpiration rate, and deep rooting ratio. The ratio of deep rooting was also associated with low internal CO2 concentration. The association of deep rooting with lower root number and root dry weight suggests that an ideal drought-tolerant genotype with higher water use efficiency should have deeper rooting (>30% RDR) with moderate root number and root dry weight to be sustained under drought for a longer period. The study also revealed that, under drought stress conditions, landraces are more water-use efficient with superior root traits than improved genotypes. [ABSTRACT FROM AUTHOR]

Deep rooting is an important trait in rice drought resistance. Genetic resources of deep-rooting varieties are valuable in breeding of water-saving and drought-resistant rice. In the present study, 234 BC 2 F 7 backcross introgression lines were derived from a cross of Dongye 80 (an accession of Dongxiang wild rice as the donor parent) and R974 (an indica restorer line as the recurrent parent). A genetic linkage map containing 1 977 bin markers was constructed by ddRADSeq for QTL analysis. Thirty-one QTLs for four root traits (the number of deep roots, the number of shallow roots, the total number of deep roots and the ratio of deep roots) were assessed on six rice chromosomes in two environments (2020 Shanghai and 2021 Hainan). Two of the QTLs, qDR5.1 and qTR5.2 , were located on chromosome 5 in a 70-kb interval. They were detected in both environments. qDR5.1 explained 13.35% of the phenotypic variance in 2020 Shanghai and 12.01% of the phenotypic variance in 2021 Hainan. qTR5.2 accounted for 10.88% and 10.93% of the phenotypic variance, respectively. One QTL (qRDR2.2) for the ratio of deep roots was detected on chromosome 2 in a 210-kb interval and accounted for 6.72% of the phenotypic variance in 2020. The positive effects of these three QTLs were all from Dongxiang wild rice. Furthermore, nine and four putative candidate genes were identified in qRDR2.2 and qDR5.1 / qTR5.2 , respectively. These findings added to our knowledge of the genetic control of root traits in rice. In addition, this study will facilitate the future isolation of candidate genes of the deep-rooting trait and the utilization of Dongxiang wild rice in the improvement of rice drought resistance. [ABSTRACT FROM AUTHOR]

The response of plant growth and development to nutrient and water availability is an important adaptation for abiotic stress tolerance. Roots need to intercept both passing nutrients and water while foraging into new soil layers for further resources. Substantial amounts of nitrate can be lost in the field when leaching into groundwater, yet very little is known about how deep rooting affects this process. Here, we phenotyped root system traits and deep 15N nitrate capture across 1.5 m vertical profiles of solid media using tall mesocosms in switchgrass (Panicum virgatum L.), a promising cellulosic bioenergy feedstock. Root and shoot biomass traits, photosynthesis and respiration measures, and nutrient uptake and accumulation traits were quantified in response to a water and nitrate stress factorial experiment for switchgrass upland (VS16) and lowland (AP13) ecotypes. The two switchgrass ecotypes shared common plastic abiotic responses to nitrogen (N) and water availability, and yet had substantial genotypic variation for root and shoot traits. A significant interaction between N and water stress combination treatments for axial and lateral root traits represents a complex and shared root development strategy for stress mitigation. Deep root growth and 15N capture were found to be closely linked to aboveground growth. Together, these results represent the wide genetic pool of switchgrass and show that deep rooting promotes nitrate capture, plant productivity, and sustainability. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the usage of species with coloured roots to study root growth patterns during intercropping. Red beet (Beta vulgaris L. cv. Detroit), having clear red roots, was used in a semi-field and field experiment to allow identification and quantification of roots of the individual species in the mixture. In the field experiment, red beet was strip intercropped with lucerne (Medicago sativa L. cv. Creno) and kale (Brassica oleracea L. var. Sabellica), respectively while the red beet-lucerne intercropping was conducted in large rhizoboxes where root growth distribution and 15N isotope uptake was determined. The study confirmed that the direct visual measurement of root growth using species with coloured roots and indirect tracer uptake measurements contributed to the success of studying root growth dynamics in intercropping systems. Red beet root intensity was not considerably affected by the strip intercropping when the crops were established at the same time, but when established between existing lucerne strips, a reduction in roots at the border row was shown. Lucerne and kale were both observed to be able to exploit the deep soil layers beneath the red beet border row. [ABSTRACT FROM AUTHOR]

Changes in root development and growth in upland rice receiving subsurface irrigation were evaluated using root box experiments. Irrigated water was independently applied every day to depths of 0, 5, 10 and 20 cm from the ground surface, and root morphology and aboveground growth were determined after 2 weeks of treatment. Plant length, stem number and leaf age significantly increased along with the irrigation depth, and the aboveground dry weights of rice grown at 5-, 10- and 20-cm depths were significantly greater than those grown at 0 cm. Root surface area significantly increased along with the irrigation depth, which was attributed to the increasing lengths and branch numbers of roots. Subsurface irrigation significantly increased root lengths in deep layers (below 15 cm) and increased the deep layers’ distribution ratios by 1.2 to 5.7 times as the surface layer ratio decreased. This was accompanied with a decrease in the root diameter. This may be associated with the increase in the numbers of branches and the decrease in the numbers of thick nodal roots. These results indicate that subsurface irrigation increases root length and branching in the deep soil layers, inducing deep rooting, even with same amount of irrigation.

Abstract Background Deep rooting is one of the most promising plant traits for improving crop yield under water-limited conditions. Most root phenotyping methods are designed for laboratory-grown plants, typically measuring very young plants not grown in soil and not allowing full development of the root system. Results This study introduced the 15N tracer method to detect genotypic variations of deep rooting and N uptake, and to support the minirhizotron method. The method was tested in a new semifield phenotyping facility on two genotypes of winter wheat, seven genotypes of spring barley and four genotypes of ryegrass grown along a drought stress gradient in four individual experiments. The 15N labeled fertilizer was applied at increasing soil depths from 0.4 to 1.8 m or from 0.7 to 2.8 m through a subsurface tracer supply system, and sampling of aboveground biomass was conducted to measure the 15N uptake. The results confirm that the 15N labeling system could identify the approximate extension of the root system. The results of 15N labeling as well as root measurements made by minirhizotrons showed rather high variation. However, in the spring barley experiment, we did find correlations between root observations and 15N uptake from the deepest part of the root zone. The labeled crop rows mostly had significantly higher 15N enrichment than their neighbor rows. Conclusion We concluded that the 15N tracer method is promising as a future method for deep root phenotyping because the method will be used for phenotyping for deep root function rather than deep root growth. With some modifications to the injection principle and sampling process to reduce measurement variability, we suggest that the 15N tracer method may be a useful tool for deep root phenotyping. The results demonstrated that the minirhizotrons observed roots of the tested rows rather than their neighboring rows.

Drought stress severely affects plant growth and development, causing significant yield loss in rice. This study demonstrates the relevance of water use efficiency with deeper rooting along with other root traits and gas exchange parameters. Forty-nine rice genotypes were evaluated in the basket method to examine leaf-level water use efficiency (WUEi) variation and its relation to root traits. Significant variation in WUEi was observed (from 2.29 to 7.39 µmol CO2 mmol−1 H2O) under drought stress. Regression analysis revealed that high WUEi was associated with higher biomass accumulation, low transpiration rate, and deep rooting ratio. The ratio of deep rooting was also associated with low internal CO2 concentration. The association of deep rooting with lower root number and root dry weight suggests that an ideal drought-tolerant genotype with higher water use efficiency should have deeper rooting (>30% RDR) with moderate root number and root dry weight to be sustained under drought for a longer period. The study also revealed that, under drought stress conditions, landraces are more water-use efficient with superior root traits than improved genotypes.

Aims: Diversity of root systems among genetic resources can contribute to optimize water and nutrient uptake. Topsoil exploitation vs. deep soil exploration represent two contrasting ideotypes in relation to resource use. Our study reveals how rooting patterns changed between wheat wild progenitors and landraces in regard to these ideotypes. Methods: Root (partitioning, morphology, distribution, elongation, anatomy) and shoot traits (dry-matter, leaf area, assimilation) of durum landraces, wild emmer and wild einkorn from Iran, Syria, Turkey and Lebanon were phenotyped using the GrowScreen-Rhizo platform. Distinctive rooting patterns were identified via principal component analysis and relations with collection site characteristics analyzed. Results: Shoot trait differentiation was strongly driven by seed weight, leading to superior early vigor of landraces. Wild progenitors formed superficial root systems with a higher contribution of lateral and early-emerging nodal axes to total root length. Durum landraces had a root system dominated by seminal axes allocated evenly over depth. Xylem anatomy was the trait most affected by the environmental influence of the collection site. Conclusions: The durum landrace root system approximated a deep soil exploration ideotype which would optimize subsoil water uptake, while monococcum-type wild einkorn was most similar to a topsoil exploiting strategy with potential competitive advantages for subsistence in natural vegetation. [ABSTRACT FROM AUTHOR]

Keywords: abiotic stress; metabolic changes; gene regulation; protein regulation; root architecture; root plasticity; deep rooting; yield EN abiotic stress metabolic changes gene regulation protein regulation root architecture root plasticity deep rooting yield N.PAG N.PAG 4 01/20/21 20210115 NES 210115 The unfavorable soil (low supply of nutrients, high levels of toxic elements, salinity, compaction) and climatic (drought, waterlogging, high temperature, low temperature) conditions reduce plant and crop productivity (Pereira, [11]). Multiple Stress Tolerance in Acid Soils On tropical, acidic soils, Al toxicity, low P availability and drought stress are the major limitations to yield stability. The authors suggested that the NudC genes could be considered as potentially important target genes in breeding more resilient crops with improved root architecture under abiotic stress. Abiotic stress, metabolic changes, gene regulation, protein regulation, root architecture, root plasticity, deep rooting, yield. [Extracted from the article]

Changes in root development and growth in upland rice receiving subsurface irrigation were evaluated using root box experiments. Irrigated water was independently applied every day to depths of 0, 5, 10 and 20 cm from the ground surface, and root morphology and aboveground growth were determined after 2 weeks of treatment. Plant length, stem number and leaf age significantly increased along with the irrigation depth, and the aboveground dry weights of rice grown at 5-, 10- and 20-cm depths were significantly greater than those grown at 0 cm. Root surface area significantly increased along with the irrigation depth, which was attributed to the increasing lengths and branch numbers of roots. Subsurface irrigation significantly increased root lengths in deep layers (below 15 cm) and increased the deep layers' distribution ratios by 1.2 to 5.7 times as the surface layer ratio decreased. This was accompanied with a decrease in the root diameter. This may be associated with the increase in the numbers of branches and the decrease in the numbers of thick nodal roots. These results indicate that subsurface irrigation increases root length and branching in the deep soil layers, inducing deep rooting, even with same amount of irrigation. [ABSTRACT FROM AUTHOR]

In the quest for sustainable intensification of crop production, we discuss the option of extending the root depth of crops to increase the volume of soil exploited by their root systems. We discuss the evidence that deeper rooting can be obtained by appropriate choice of crop species, by plant breeding, or crop management and its potential contributions to production and sustainable development goals. Many studies highlight the potentials of deeper rooting, but we evaluate its contributions to sustainable intensification of crop production, the causes of the limited research into deep rooting of crops, and the research priorities to fill the knowledge gaps. Recent studies have documented highly significant differences among current and potential crops, as well as genotypic differences, in the ability for deep rooting. Results have shown significant effects of deep roots on deep soil water and nutrient uptake. Technological improvements of nondestructive methods, such as rhizotron and image analysis based root observations, soil water sensors, and isotope tracers for uptake studies, allow combined and dynamic studies of root development and function. The quest for sustainable intensification of crop production promotes the interest in understanding and exploiting the potential contribution by deeper soil layers. Deep layers may contribute to resource supply for crop growth, reducing losses to the environment and deep C sequestration to mitigate climate change. [ABSTRACT FROM AUTHOR]

Background: Deep rooting is one of the most promising plant traits for improving crop yield under water-limited conditions. Most root phenotyping methods are designed for laboratory-grown plants, typically measuring very young plants not grown in soil and not allowing full development of the root system. Results: This study introduced the 15N tracer method to detect genotypic variations of deep rooting and N uptake, and to support the minirhizotron method. The method was tested in a new semifield phenotyping facility on two genotypes of winter wheat, seven genotypes of spring barley and four genotypes of ryegrass grown along a drought stress gradient in four individual experiments. The 15N labeled fertilizer was applied at increasing soil depths from 0.4 to 1.8 m or from 0.7 to 2.8 m through a subsurface tracer supply system, and sampling of aboveground biomass was conducted to measure the 15N uptake. The results confirm that the 15N labeling system could identify the approximate extension of the root system. The results of 15N labeling as well as root measurements made by minirhizotrons showed rather high variation. However, in the spring barley experiment, we did find correlations between root observations and 15N uptake from the deepest part of the root zone. The labeled crop rows mostly had significantly higher 15N enrichment than their neighbor rows. Conclusion: We concluded that the 15N tracer method is promising as a future method for deep root phenotyping because the method will be used for phenotyping for deep root function rather than deep root growth. With some modifications to the injection principle and sampling process to reduce measurement variability, we suggest that the 15N tracer method may be a useful tool for deep root phenotyping. The results demonstrated that the minirhizotrons observed roots of the tested rows rather than their neighboring rows. [ABSTRACT FROM AUTHOR]

Background Deep roots are critical for the survival of Populus euphratica seedlings on the floodplains of arid regions where they easily suffer drought stress. Drought typically suppresses root growth, but P. euphratica seedlings can adjust phenotypically in terms of root-shoot allocation and root architecture and morphology, thus promoting deep rooting. However, the root phenotypic changes undertaken by P. euphratica seedlings as a deep rooting strategy under drought conditions remain unknown. Methods We quantified deep rooting capacity by the relative root depth (RRD), which represents the ratio of taproot length to plant biomass and is controlled by root mass fraction (RMF), taproot mass fraction (TRMF), and specific taproot length (STRL). We recorded phenotypic changes in one-year-old P. euphratica seedlings under control, moderate and severe drought stress treatments and assessed the effects of RMF, TRMF, and STRL on RRD. Results Drought significantly decreased absolute root depth but substantially increased RRD via exerting positive effects on TRMF, RMF, and STRL. Under moderate drought, TRMF contributed 55%, RMF 27%, and STRL 18% to RRD variation. Under severe drought, the contribution of RMF to RRD variation increased to 37%, which was similar to the 41% for TRMF. The contribution of STRL slightly increased to 22%. Conclusion These results suggest that the adjustments in root architecture and root-shoot allocation were predominantly responsible for deep rooting in P. euphratica seedlings under drought conditions, while morphological changes played a minor role. Moreover, P. euphratica seedlings rely mostly on adjusting their root architecture to maintain root depth under moderate drought conditions, whereas root-shoot allocation responds more strongly under severe drought conditions, to the point where it plays a role as important as root architecture does on deep rooting.

Highlights • Critical moisture for crop in each phenological stage was added as the lowest limit of LLWR. • Water uptake in soil profile improved with deep tillage, intercropping and additional gypsum. • Soil physico-chemical conditioning was important to maintain plant water status. • Unlike plants aerial growth, average yield of first years are the same among management systems. • Intercropping with Brachiaria reduces soil moisture but not lead water stress to Coffee plants. Abstract Water determines the success of coffee farming, since it influences the phenology of the plant and, consequently, its productivity, product quality and commercial viability. The Least Limiting Water Range (LLWR) associated with the monitoring of soil water content (θ) distinguishes management systems as to their effectiveness in supplying water to plants. The need for developing better management systems –in Brazilian rainfed farming– that promote water uptake by coffee plant radicular systems at lower soil depths where water is more available, inspired this study. This work had as an objective to evaluate the availability of water in soil through LLWR limits in association with leaf water potential, as well as growth and yield of coffee plants, in the Cerrado region of Southeastern Brazil over 4 years. The management systems evaluated were: CV-0 (conventional management with coffee interrow maintained with bare soil); G-28 (conservation management, with maintenance of Brachiaria in interrow, ridging and additional application of 28 Mg ha−1 gypsum applied in the rows) and G-7 (same as G-28, except for an additional application of 7 Mg ha−1 of gypsum). θ was monitored every 15 days. Critical moisture for coffee crop in each phenological stage was added as the lowest limit of LLWR. In all evaluated management systems, θ was below the critical moisture as measured at the soil depths of 0.20 m and 0.60 m. At 1.00 m depth in the CV-0 management system, the greatest value of θ was found, which caused the assumption of smaller water uptake. Regardless of the management adopted, the leaf water potential reached -1.16 MPa in August 2010, but that did not cause water stress high enough to reduce productivity. At 0.60 m depth, the lowest value for θ between rows was observed for the G-28 management system. Plants showed a more accentuated initial growth in the CV-0 management system. Each management system showed distinct behavior regarding productivity of the evaluated crops: in 2011, CV-0 had the highest productivity, but, in 2012, productivity was greater for G-7 and G-28. [ABSTRACT FROM AUTHOR]

The plasticity in root system development (RSD) is a key trait for the adaptation of rice to mild drought. However, the enhanced RSD due to the plasticity may not be always a sole function of promoted lateral root (LR) production, but also of the integrated responses of nodal root (NR) development. In this study, we aimed to evaluate the effects of mild drought intensities on the development of the NR and LR, and their contribution to the entire RSD. We used six genotypes including KDML105 (indica, lowland adapted), a high lateral rooting ability genotype. The plants were grown up to heading or maturity stage for two years under soil with limited soil depth (20 cm) assuming the presence of the hardpan and at different moisture gradients generated by the line source sprinkler system. The effects of drought intensities generally differed between the development of NR and LR. In both years, all genotypes showed highest LR development under mild drought stress intensities. However, in some genotypes including KDML105, NR development was maintained in a limited soil moisture range only, which was narrower and wetter than that in which LR plasticity was expressed. Furthermore, the entire RSD was maintained only when both the NR and LR were simultaneously promoted or maintained. These results suggest that the NR have less plasticity than the LR in response to drought and the contribution of the plasticity in LR development to the entire RSD is dependent on both the soil moisture and nodal rooting ability.

In this study, to identify deep rooting accessions, we assessed the differences in root depth based on the length of the longest primary root among 586 different rice accessions: 511 Oryza sativa and 75 O. glaberrima. Malagkit Pirurutong and Binicol were identified as the two rice accessions with deepest roots through four field experiments conducted at two different locations in West Africa. For these two accessions, root depths reached 35.6 and 41.4 cm, respectively, in the first experiment at Bamako; on the other hand, their depths only reached 22.6 and 18.6 cm, respectively, in the second and third experiments at Ibadan, leading to inconsistent genotypic ranking based on root depth between the two locations. However, Malagkit Pirurutong was identified as deep rooting in both locations; in addition, it showed deep rooting in the fourth experiment in a 20-mm irrigation treatment, even when compared with the deep rooting reference Azucena. Nonetheless, this pattern was not found under a 10-mm irrigation treatment. Malagkit Pirurutong kept developing deep roots even following 60 days after sowing (DAS), whereas other shallower rooting accessions ceased deepening by 60 DAS. The longer period for deepening roots would be beneficial for terminal drought stress.

Characterizing the morphological variability in root system architecture (RSA) during the sensitive pre-flowering growth stage is important for crop performance. To assess this variation, eight bambara groundnut single genotypes derived from landraces of contrasting geographic origin were selected for root system architecture and rooting distribution studies. Plants were grown in a polyvinyl chloride (PVC) column system under controlled water and nutrient availability in a rainout shelter. Days to 50% plant emergence was characterized during the first two weeks after sowing, while taproot length (TRL), root length (RL), root length density (RLD), branching number (BN), branching density (BD) and intensity (BI), surface area (SA), root volume (RV), root diameter (RDia), root dry weight (RDW), shoot dry weight (SDW), and shoot height (SH) were determined at the end of the experiment, i.e., 35 days after emergence. Genotypes S19-3 and DipC1 sourced from drier regions of sub-Saharan Africa generally had longer taproots and greater root length distribution in deeper (60 to 90 cm) soil depths. In contrast, bambara groundnut genotypes from wetter regions (i.e., Gresik, Lunt, and IITA-686) in Southeast Asia and West Africa exhibited relatively shallow and highly branched root growth closer to the soil surface. Genotypes at the pre-flowering growth stage showed differential root foraging patterns and branching habits with two extremes, i.e., deep-cheap rooting in the genotypes sourced from dry regions and a shallow-costly rooting system in genotypes adapted to higher rainfall areas with shallow soils. We propose specific bambara groundnut genotype as donors in root trait driven breeding programs to improve water capture and use efficiency.

Drought is the most serious abiotic stress limiting rice production, and deep root is the key contributor to drought avoidance. However, the genetic mechanism regulating the development of deep roots is largely unknown. In this study, the transcriptomes of 74 root samples from 37 rice varieties, representing the extreme genotypes of shallow or deep rooting, were surveyed by RNA-seq. The 13,242 differentially expressed genes (DEGs) between deep rooting and shallow rooting varieties (H vs. L) were enriched in the pathway of genetic information processing and metabolism, while the 1,052 DEGs between the deep roots and shallow roots from each of the plants (D vs. S) were significantly enriched in metabolic pathways especially energy metabolism. Ten quantitative trait transcripts (QTTs) were identified and some were involved in energy metabolism. Forty-nine candidate DEGs were confirmed by qRT-PCR and microarray. Through weighted gene co-expression network analysis (WGCNA), we found 18 hub genes. Surprisingly, all these hub genes expressed higher in deep roots than in shallow roots, furthermore half of them functioned in energy metabolism. We also estimated that the ATP production in the deep roots was faster than shallow roots. Our results provided a lot of reliable candidate genes to improve deep rooting, and firstly highlight the importance of energy metabolism to the development of deep roots.

* Background and Aims The genetic basis of increased rooting below the plough layer, post-anthesis in the field, of an elite wheat line (Triticum aestivum 'Shamrock') with recent introgression from wild emmer (T. dicoccoides), is investigated. Shamrock has a non-glaucous canopy phenotype mapped to the short arm of chromosome 2B (2BS), derived from the wild emmer. A secondary aim was to determine whether genetic effects found in the field could have been predicted by other assessment methods. * Methods Roots of doubled haploid (DH) lines from a winter wheat ('Shamrock' x 'Shango') population were assessed using a seedling screen in moist paper rolls, in rhizotrons to the end of tillering, and in the field postanthesis. A linkage map was produced using single nucleotide polymorphism markers to identify quantitative trait loci (QTLs) for rooting traits. * Key Results Shamrock had greater root length density (RLD) at depth than Shango, in the field and within the rhizotrons. The DH population exhibited diversity for rooting traits within the three environments studied. QTLs were identified on chromosomes 5D, 6B and 7B, explaining variation in RLD post-anthesis in the field. Effects associated with the non-glaucous trait on RLD interacted significantly with depth in the field, and some of this interaction mapped to 2BS. The effect of genotype was strongly influenced by the method of root assessment, e.g. glaucousness expressed in the field was negatively associated with root length in the rhizotrons, but positively associated with length in the seedling screen. * Conclusions To our knowledge, this is the first study to identify QTLs for rooting at depth in field-grown wheat at mature growth stages. Within the population studied here, our results are consistent with the hypothesis that some of the variation in rooting is associated with recent introgression from wild emmer. The expression of genetic effects differed between the methods of root assessment. [ABSTRACT FROM AUTHOR]

Drought is the major abiotic stress factor limiting yield of common bean (Phaseolus vulgaris L.) in smallholder systems in Latin America and eastern and southern Africa; where it is a main source of protein in the daily diet. Identification of shoot and root traits associated with drought resistance contributes to improving the process of designing bean genotypes adapted to drought. Field and greenhouse studies were conducted at the International Center for Tropical Agriculture (CIAT), Palmira, Colombia to determine the relationship between grain yield and different shoot and root traits using a recombinant inbred lines (RILs) population (MD23-24 x SEA 5) of common bean. The main objectives of this study were to identify: (i) specific shoot and root morpho-physiological traits that contribute to improved resistance to drought and that could be useful as selection criteria in breeding beans for drought resistance; and (ii) superior genotypes with desirable shoot and root traits that could serve as parents in breeding programs that are aimed at improving drought resistance. A set of 121 bean genotypes (111 RILs, 2 parents, 8 checks) belonging to the Mesoamerican gene pool and one cowpea variety were evaluated under field conditions with two levels of water supply (irrigated and rainfed) over three seasons. To complement field studies, a greenhouse study was conducted using plastic cylinders with soil inserted into PVC pipes, to determine the relationship between grain yield obtained under field conditions with different root traits measured under greenhouse conditions. Resistance to drought stress was positively associated with a deeper and vigorous root system, better shoot growth, and superior mobilization of photosynthates to pod and seed production. The drought resistant lines differed in their root characteristics, some of them with a vigorous and deeper root system while others with a moderate to shallow root system. Among the shoot traits measured, pod harvest index, and seed number per area could serve as useful selection criteria for assessing sink strength and for genetic improvement of drought resistance in common bean. [ABSTRACT FROM AUTHOR]

Climate models predict that the frequency, intensity and duration of drought events will increase in tropical regions. Although water withdrawal from deep soil layers is generally considered to be an efficient adaptation to drought, there is little information on the role played by deep roots in tropical forests. Tropical Eucalyptus plantations managed in short rotation cycles are simple forest ecosystems that may provide an insight into the water use by trees in tropical forests., The contribution made by water withdrawn from deep soil layers to the water required for evapotranspiration was quantified daily from planting to harvesting age for a Eucalyptus grandis stand using a soil water transfer model coupled with an ecophysiological forest model ( MAESPA). The model was parameterized using an extensive data set and validated using time series of the soil water content down to a depth of 10 m and water-table level, as well as evapotranspiration measured using eddy covariance., Fast root growth after planting provided access to large quantities of water stored in deep soil layers over the first 2 years. Eucalyptus roots reached the water-table at a depth of 12 m after 2 years. Although the mean water withdrawal from depths of over 10 m amounted to only 5% of canopy transpiration from planting to a harvesting age of 5 years, the proportion of water taken up near the water-table was much higher during dry periods. The water-table rose from 18 to 12 m below-ground over 2 years after the harvest of the previous stand and then fell until harvesting age as evapotranspiration rates exceeded the annual rainfall., Deep rooting is an efficient strategy to increase the amount of water available for the trees, allowing the uptake of transient gravitational water and possibly giving access to a deep water-table. Deep soil layers have an important buffer role for large amounts of water stored during the wet season that is taken up by trees during dry periods. Our study confirms that deep rooting could be a major mechanism explaining high transpiration rates throughout the year in many tropical forests. [ABSTRACT FROM AUTHOR]

Root growth into deep soil is an important factor for stable production in wheat under drought conditions. Root penetrating capacity (RP) shown by pot experiments with a paraffin-Vaseline layer (PV layer) may be a useful indicator estimating deep rooting ability of wheat genotypes. Previously, we identified genotypes of durum wheat (Triticum turgidum L. var. durum) and bread wheat (T. aestivum L.) with diverse RP by the pot experiments. In this study, we investigated the root distribution of three Ethiopian landraces of durum wheat with high RP, three recent cultivars of durum wheat with low RP and one Japanese cultivar of bread wheat ‘Haruyutaka’ with low RP using: (1) pots with a PV layer, (2) root boxes, (3) artificial field and (4) a normal field to analyze the relationship between RP estimated by pot experiment and root development in the field. In the pot experiments, RP was evaluated by the number of roots penetrating through the PV layer (NRP). In the root-box and field experiments, the root distribution was evaluated by the number of roots on the vertical surface of soil as the root frequency (RF: root number cm-1 soil surface). Ethiopian landraces had a significantly larger NRP than recent cultivars in the pot experiment. The root box and field experiments showed that Ethiopian landraces tended to have a higher RF than recent cultivars in deep soil layer. We concluded that RP estimated by pot experiments with a PV layer is a useful indicator of deep rooting ability under field conditions.

The plasticity in root system development (RSD) is a key trait for the adaptation of rice to mild drought. However, the enhanced RSD due to the plasticity may not be always a sole function of promoted lateral root (LR) production, but also of the integrated responses of nodal root (NR) development. In this study, we aimed to evaluate the effects of mild drought intensities on the development of the NR and LR, and their contribution to the entire RSD. We used six genotypes including KDML105 (indica, lowland adapted), a high lateral rooting ability genotype. The plants were grown up to heading or maturity stage for two years under soil with limited soil depth (20 cm) assuming the presence of the hardpan and at different moisture gradients generated by the line source sprinkler system. The effects of drought intensities generally differed between the development of NR and LR. In both years, all genotypes showed highest LR development under mild drought stress intensities. However, in some genotypes including KDML105, NR development was maintained in a limited soil moisture range only, which was narrower and wetter than that in which LR plasticity was expressed. Furthermore, the entire RSD was maintained only when both the NR and LR were simultaneously promoted or maintained. These results suggest that the NR have less plasticity than the LR in response to drought and the contribution of the plasticity in LR development to the entire RSD is dependent on both the soil moisture and nodal rooting ability. [ABSTRACT FROM AUTHOR]

As the first organ in plants to sense water-deficit in the soil, roots have important roles for improving crop adaption to water limited environments. Stem water soluble carbohydrates (WSC) are a major carbon source for grain filling under drought conditions. The contributions of root WSC during grain filling under drought has not been revealed. Wheat parental lines of Westonia, Kauz and their derived four double haploid (DH) lines, namely, DH 125, DH 139, DH 307, and DH 338 were used in a field drought experiment with four replications. Through measurements of the root and stem WSC components, and the associated enzyme activities during grain filling, we identified that the levels of root WSC and fructan were one third of the levels in stems. In particular, root glucose and 6-kestose levels were one third of the stem, while the root fructose and bifurcose level were almost half of the stem and sucrose level was two third of the stem. The accumulation and the degradation patterns of root fructan levels were similar to that in the stem, especially under drought. Correlations between root fructan levels and grain assimilation were highly significant, indicating that under terminal drought, root WSC represents a redistributed carbon source for grain filling rather than deep rooting. The significantly higher root sucrose levels under drought suggest that sucrose may act as a signal under drought stress. As compared with stem fructose levels, the earlier increased root fructose levels in DH 307, DH 139, and DH 338 provided agile response to drought stress. Our root results further confirmed that β-(2-6) linkages predominate in wheat with patterns of 6-kestose being closely correlated with overall fructan patterns. Further research will focus on the roles of 6-FEH during fructan remobilization in stems. [ABSTRACT FROM AUTHOR]

In this study, to identify deep rooting accessions, we assessed the differences in root depth based on the length of the longest primary root among 586 different rice accessions: 511Oryza sativaand 75O. glaberrima.Malagkit Pirurutong and Binicol were identified as the two rice accessions with deepest roots through four field experiments conducted at two different locations in West Africa. For these two accessions, root depths reached 35.6 and 41.4 cm, respectively, in the first experiment at Bamako; on the other hand, their depths only reached 22.6 and 18.6 cm, respectively, in the second and third experiments at Ibadan, leading to inconsistent genotypic ranking based on root depth between the two locations. However, Malagkit Pirurutong was identified as deep rooting in both locations; in addition, it showed deep rooting in the fourth experiment in a 20-mm irrigation treatment, even when compared with the deep rooting reference Azucena. Nonetheless, this pattern was not found under a 10-mm irrigation treatment. Malagkit Pirurutong kept developing deep roots even following 60 days after sowing (DAS), whereas other shallower rooting accessions ceased deepening by 60 DAS. The longer period for deepening roots would be beneficial for terminal drought stress. [ABSTRACT FROM AUTHOR]

The total water supply (irrigation plus rainfall) would determine biomass production. This study aimed to elucidate the effects of water supply and cultivar differences on the dry matter production of rice grown under upland conditions. Three rice cultivars ('Yumeno-hatamochi ', YHM; 'Lemont ', LMT; 'Nipponbare ', NPB) were used on an upland site with three water regimes (rain-fed, RU; irrigated, IU; water deficit during the panicle-formation stage, WD) and in a flooded lowland (FL) in Japan from 2001 to 2003. The total amount of aboveground dry matter (TDM) of NPB in RU (1101 g m-2) was 15% lower than that in FL (1302 g m-2) in 2001, when dry spells occurred frequently, but was comparable to FL in 2003 (1313 vs. 1324 g m-2) under favorable soil water conditions with ample rainfall before heading. The nitrogen (N) content of the aboveground part at maturity in RU in 2003 was similar to that in FL, but the growth duration was 9 days longer in RU. The amount of total water supply during the crop growth differed greatly (419 to 1132 mm) among water regimes and years under upland conditions, where TDM and aboveground N content generally increased with increasing water supply. We detected a cultivar – water regime interaction in TDM at maturity in both 2002 and 2003. In FL and under the upland conditions with adequate water supply in 2003, TDM was the largest for NPB, but it was the smallest in this cultivar in 2002 when rainfall was less frequent. The small TDM of NPB in 2002 resulted from asmaller amount of N uptake associated with shallower root system development. In contrast, YHM had a deeper root system and thus the amount of N uptake was larger and TDM was smaller under upland conditions with limited water supply. Our results indicate that the three cultivars responded differently to the water conditions, and that the total water supply greatly affected TDM in uplands through its effects on the amount of N uptake, which was associated with the depth of root development.

Aims: Root angles are widely recognized to play an important role in determining rooting depth and drought tolerance in crop plants. But there has been no report revealing any association between root angle and yield performance under drought conditions in maize. There is also no simple method available to screen root angles. The objectives of this study were to evaluate genetic variation in seminal and nodal root angles in maize in greenhouse condition and their association with drought tolerance in field condition. Methods: Eighteen hybrids, of which nine were higher-yielding and nine were lower-yielding under water-stressed condition in field, were evaluated for root angle variation. Root angle was estimated as the distance between the horizontal soil surface line and slope of the root at 2 cm position from root base using a protractor. Results: Significant phenotypic variation was observed among hybrids for seminal and nodal root angles and primary root diameter. These root traits showed strong positive correlations with grain yield under drought condition. All the higher-yielding hybrids had steeper root growth angle than the lower-yielding hybrids. A strong correlation between seminal and nodal root angles was observed. A strong correlation was also observed between 5th and 4th node nodal root angles. Conclusion: Either seminal or nodal root angle could be used for selection for the improvement drought tolerance. The current screening system for root angle is simple and inexpensive, and could be used for screening a large number of genotypes. [ABSTRACT FROM AUTHOR]

Deep penetration of an axile root is one of the important factors that allow crops to form deep root systems. In this study, the nodes from which the deepest penetrated roots had emerged were examined at the heading stage in upland rice and maize grown in large root boxes and in the field. Both experiments were designed to measure the direction, length, and rooting nodes of each root. In maize, the growth angles of axile roots increased with vertical elongation as rooting nodes acropetally advanced. The roots that emerged from the lower nodes, namely from coleoptilar to the second node, exhibited conspicuously horizontal elongation in the field, reaching 2.3 m in width at the maximum. The roots that emerged from higher than the fifth node were too short to penetrate deeply. Thus, these roots became the deepest root in less or no probability under field conditions. On the other hand, the fourth nodal root, which had an intermediate growth angle and length, had the highest probability. In upland rice, the deepest roots emerged from the nodes lower than the forth node on the main stem in the root boxes. In the field, however, the deepest roots emerged at later stages, that is, the roots from the middle nodes on the main stem and from the low nodes on the primary and secondary tillers were the deepest roots. Five out of nine of the deepest roots were from the prophyll nodes in three field-grown upland rice. The deepest roots from the same plant were estimated to have emerged and grown at approximately the same stage.

Despite a vast amount of data on the effect of tillage on crop productivity, surprisingly there is little detailed information available on the influence on below and aboveground crop growth dynamics. Such information is essential for developing sustainable cropping systems. The objective of this study was to investigate the effect of tillage intensity on crop growth dynamics and soil structure. A tillage experiment was established in autumn 2002 on two Danish sandy loams (Foulum and Flakkebjerg) in a cereal-based crop rotation. The tillage systems included in this study were direct drilling (D), harrowing 8–10 cm (H8-10), and ploughing (P). A single-disc drill was used in the H8-10 and D treatments and a traditional seed drill in the P treatment. Measurements were carried out in 2004–05 and 2005–06 and winter wheat was grown in both years (first and second year winter wheat). Shoot and root growth was followed during the growing seasons using spectral reflectance and mini-rhizotron measurements, respectively. A range of soil physical properties were measured. We found decreased early season shoot and root growth with decreasing tillage intensity. Differences diminished later in the growing season, although significant treatment effects were observed throughout the growing season for the second year winter wheat. The formerly ploughed layer in the D and H8-10 treatments was noticeably compacted as indicated by increases in both penetration resistance and bulk density. Nitrate leaching increased with decreasing tillage intensity for the first year winter wheat at Foulum. In general ploughing resulted in the highest grain yields. This study highlights the important interaction between soil structure and crop growth dynamics. [ABSTRACT FROM AUTHOR]

Variation in stable nitrogen isotope ratios (δ15 N) was assessed for plants comprising two wetland communities, a bog-fen system and a flood plain, in central Japan. δ15 N of 12 species from the bog-fen system and six species from the flood plain were remarkably variable, ranging from -5.9 to +1.1‰ and from +3.1 to +8.7‰, respectively. Phragmites australis exhibited the highest δ15 N value at both sites. Rooting depth also differed greatly with plant species, ranging from 5 cm to over 200 cm in the bog-fen system. There was a tendency for plants having deeper root systems to exhibit higher δ15 N values; plant δ15 N was positively associated with rooting depth. Moreover, an increasing gradient of peat δ15 N was found along with depth. This evidence, together with the fact that inorganic nitrogen was depleted under a deep-rooted Phragmites australis stand, strongly suggests that deep-rooted plants actually absorb nitrogen from the deep peat layer. Thus, we successfully demonstrated the diverse traits of nitrogen nutrition among mire plants using stable isotope analysis. The ecological significance of deep rooting in mire plants is that it enables those plants to monopolize nutrients in deep substratum layers. This advantage should compensate for any consequential structural and/or physiological costs. Good evidence of the benefits of deep rooting is provided by the fact that Phragmites australis dominates as a tall mire grass. [ABSTRACT FROM AUTHOR]