Larger Root Surface Area Research Articles

Cloning and Functional Study of AmGDSL1 in Agropyron mongolicum.

Agropyron mongolicum Keng is a diploid perennial grass of triticeae in gramineae. It has strong drought resistance and developed roots that can effectively fix the soil and prevent soil erosion. GDSL lipase or esterases/lipase has a variety of functions, mainly focusing on plant abiotic stress response. In this study, a GDSL gene from A. mongolicum, designated as AmGDSL1, was successfully cloned and isolated. The subcellular localization of the AmGDSL1 gene (pCAMBIA1302-AmGDSL1-EGFP) results showed that the AmGDSL1 protein of A. mongolicum was only localized in the cytoplasm. When transferred into tobacco (Nicotiana benthamiana), the heterologous expression of AmGDSL1 led to enhanced drought tolerance. Under drought stress, AmGDSL1 overexpressing plants showed fewer wilting leaves, longer roots, and larger root surface area. These overexpression lines possessed higher superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and proline (PRO) activities. At the same time, the malondialdehyde (MDA) content was lower than that in wild-type (WT) tobacco. These findings shed light on the molecular mechanisms involved in the GDSL gene's role in drought resistance, contributing to the discovery and utilization of drought-resistant genes in A. mongolicum for enhancing crop drought resistance.

PagMYB151 facilitates proline accumulation to enhance salt tolerance of poplar

Poplar is one of the main urban and rural greening and shade tree species in the northern hemisphere, but its growth and development is always restricted by salt stress. R2R3-MYB transcription factor family is commonly involved in many biological processes during plant growth and stress endurance. In this study, PagMYB151 (Potri.014G035100) one of R2R3-MYB members related to salt stress and expressed in both nucleus and cell membrane was cloned from Populus alba × P. glandulosa to perfect the salt tolerance mechanism. Morphological and physiological indexes regulated by PagMYB151 were detected using the PagMYB151 overexpression (OX) and RNA interference (RNAi) transgenic poplar lines. Under salt stress conditions, compared with RNAi and the non-transgenic wild-type (WT) plants, the plant height, both aboveground and underground part fresh weight of OX was significantly increased. In addition, OX has a longer and finer root structure and a larger root surface area. The root activity of OX was also enhanced, which was significantly different from RNAi but not from WT under salt treatment. Under normal conditions, the stomatal aperture of OX was larger than WT, whereas this phenotype was not obvious after salt stress treatment. In terms of physiological indices, OX enhanced the accumulation of proline but reduced the toxicity of malondialdehyde to plants under salt stress. Combing with the transcriptome sequencing data, 6 transcription factors induced by salt stress and co-expressed with PagMYB151 were identified that may cooperate with PagMYB151 to function in salt stress responding process. This study provides a basis for further exploring the molecular mechanism of poplar PagMYB151 transcription factor under abiotic stress.

Root System Architecture Differences of Maize Cultivars Affect Yield and Nitrogen Accumulation in Southwest China

Root system architecture (RSA) plays a critical role in the acquisition of water and mineral nutrients. In order to understand the root characteristics that contribute to enhanced crop yield and N accumulation high-yielding and N efficient cultivars under N-stressed conditions. Here, grain yield, N accumulation and RSA traits of six dominant maize cultivars (CD30, ZH311, ZHg505, CD189, QY9 and RY1210) grown in the Southwestern part of China were investigated in field experiment under three different N regimes in 2019–2020; N300 (300 kg N ha−1), N150 (150 kg N ha−1) and N0 (no N supplied). Using Root Estimator for Shovelomics Traits (REST) for the quantitative analysis of maize root image obtained in the field, RSA traits including total root length (RL), root surface area (RA), root angle opening (RO), and root maximal width (RMW) were quantified in this study. The results showed that Yield, N accumulation and RSA were significantly affected by N rates, cultivars and their interactions. Grain yield, N accumulation and root weight showed a similar trend under N300 and N150 conditions compared to N0 conditions. With the input of N fertilizer, the root length, surface area, and angle increase, but root width does not increase. Under the N300 and N150 condition, RL, RA, RO and RMW increased by 17.96%, 17.74%, 18.27%, 9.22%, and 20.39%, 18.58%, 19.92%, 16.79%, respectively, compared to N0 condition. CD30, ZH505 and RY1210 have similar RO and RMW, larger than other cultivars. However, ZH505 and RY1210 have 13.22% and 19.99% longer RL, and 11.41% and 5.17% larger RA than CD30. Additionally, the grain yield of ZH505 and RY1210 is 17.57% and 13.97% higher compared with CD30. The N accumulation of ZH505 and RY1210 also shows 4.55% and 9.60% higher than CD30. Correlation analysis shows that RL, RA, RO and RMW have a significant positive correlation with grain yield while RO and RMW have a significant positive correlation with N accumulation. Linear plus plateau model analysis revealed that when the RO reaches 99.53°, and the RMW reaches 15.18 cm, the N accumulation reaches its maximum value under 0–300 kg N ha−1 conditions. Therefore, selecting maize cultivars with efficient RSA suitable for different soil N inputs can achieve higher grain yield and N use efficiency.

Determination of Suitable Deficit Irrigation Stage in Potato Production

Water deficiency is the major limiting factor for potato yield promotion. Increasing tuber yield and decreasing consumption of water at the same time are a challenge in development of new potato cultivar. Deficit irrigation is regarded as one of the promising approaches to solve this problem, however no practical technique has been proposed in potato production as yet. By setting different deficient irrigation regimes and investigating potato growth and water use efficiency, we found that only application of deficit irrigation at the seedling stage could achieve the goal of increasing water use efficiency and maintaining marketable tuber yield at the same time. Almost half of the normal full irrigation doubled promotion effects on water efficiency and yield, especially the marketable tuber yield. This may be mainly attributed to establishment of a strong root system, including longer root length and larger root surface area under water deficit at the seedling stage. Based on such a root system at the early development stage, leaf area index and dry matter accumulation were optimized at the later developmental stages. Thus, maintaining water deficit at the seedling stage with enough water supplied at the tuber initiation and bulking stages should be practiced in potato production in water limited areas.

Effects of biochar, compost and straw input on root exudation of maize (Zea mays L.): From function to morphology

Returning crop straw, such as biochar, into the field is increasingly recognized as a valid, environmentally-friendly agricultural strategy to improve soil quality, increase crop yields, and reduce combustion-induced air pollution. Root exudation has potential importance for plant performance, rhizosphere function and plant–soil interactions; however, the effects of crop straw input on maize root exudation remain unclear. After three seasons of a field experiment, a mesh bag experiment was conducted in situ in the fourth season to study the effects of three straw incorporation treatments (chopped maize straw, SD; compost produced by maize straw, SC; biochar produced by maize straw, BC) and control (no straw, CK) on root exudation and their underlying mechanisms in a maize cropping system. Discrimination in the metabolic profiling of the root exudates between the CK and all the straw-incorporated samples was clear, but the separation between the samples from the three different straw strategies was limited. Among the 32 assigned components of maize root exudates, the fluctuations in organic acids (up to 16-fold) were stronger than those in sugars and amino acids when straw was incorporated. The response of the organic acid exudates was linked to the transcript levels of the ZmMATE1 and ZmMATE2 genes, which are associated with root exudation (Spearman correlations, P < 0.05). Straw incorporation influenced the root phenotypic appearance and morphology, which are characterized by longer and thinner root, larger root surface area, and more root tips in BC treatment, whereas shorter and thicker root, and fewer root tips in SD treatment. The changes in the root morphology and metabolomes were responsible for the responses of the maize root exudates to straw incorporation. Regulation of genes (ZmCycD2; 2a, ZmEXPB8, ZmXTH1, and ZmARF1) that associated with root growth and development, and changes in the viability and anatomical structure of root tips were involved in the modifications of root morphology. This information will be useful for modulating rhizosphere processes and soil fertility, and for guiding and recommending residue management practices in crop production with relatively larger yields.

Influence of Biochar on Nitrogen Use Efficiency and Root Morphology of Rice-Seedling in Two Contrasting Paddy Soils

Biochar may affect the root morphology and nitrogen (N) use efficiency (NUE) of rice at seedling stage, which has not been clearly verified until now. To clarify it, we conducted a pot experiment regarding to two soil types (Hydragric Anthrosol and Haplic Acrisol), two biochar application rates (0.5 wt% and 1.5 wt %) and two rice varieties (common rice var. Xiushui134 and hybrid super rice var. Zhongkejiayou12-6) meanwhile. Seedling NUE of common rice Xiuhui134 was significantly increased (p < 0.05) by 78.2% in Hydragric Anthrosol and by 91.4% in Haplic Acrisol following biochar addition with 1.5 wt%. However, biochar addition exerted no influence on seedling NUE of super rice Zhongkejiayou12-6 in both soils. Overall, 0.09–0.10 units higher soil pH and 105– 116% higher soil NH4+ -N were observed in Xiushui134 growing two soils with 1.5 wt% biochar. In addition, improved root morphology (including longer root length, larger root surface area, bigger root volume, and more root tips) contributed to the higher seedling NUE of Xiushui134 in two soils. The soil pH and NH4+ -N content, also the root morphology were influenced by biochar, which though could not thoroughly explained the NUE of Zhongkejiayou12-6. In conclusion, biochar application to paddy soil changed soil pH and NH4+ -N content, root growth, and the consequent seedling NUE of rice, which effects are relative with rice cultivar, biochar addition rate, and soil type.

Characterizing the Role of TaWRKY13 in Salt Tolerance.

The WRKY transcription factor superfamily is known to participate in plant growth and stress response. However, the role of this family in wheat (Triticum aestivum L.) is largely unknown. Here, a salt-induced gene TaWRKY13 was identified in an RNA-Seq data set from salt-treated wheat. The results of RT-qPCR analysis showed that TaWRKY13 was significantly induced in NaCl-treated wheat and reached an expression level of about 22-fold of the untreated wheat. Then, a further functional identification was performed in both Arabidopsis thaliana and Oryza sativa L. Subcellular localization analysis indicated that TaWRKY13 is a nuclear-localized protein. Moreover, various stress-related regulatory elements were predicted in the promoter. Expression pattern analysis revealed that TaWRKY13 can also be induced by polyethylene glycol (PEG), exogenous abscisic acid (ABA), and cold stress. After NaCl treatment, overexpressed Arabidopsis lines of TaWRKY13 have a longer root and a larger root surface area than the control (Columbia-0). Furthermore, TaWRKY13 overexpression rice lines exhibited salt tolerance compared with the control, as evidenced by increased proline (Pro) and decreased malondialdehyde (MDA) contents under salt treatment. The roots of overexpression lines were also more developed. These results demonstrate that TaWRKY13 plays a positive role in salt stress.

EFFECT OF BIO-FERTILIZERS AND MOLYBDENUM ON GROWTH AND YIELD OF GREEN BEAN

This experiment was carried out at the fields of the Department of Horticulture and Landscape Gardening, College of Agriculture, University of Baghdad, during the spring season of 2015 to study the effect of nitrogen fixing bacterial bio-fertilizers including Rhizobium phaseoli, Azotobacter chroococcum, and Azospirillum brasilense and molybdenum on growth and yield of green beans. The experiment was conducted according to the randomized complete block design (RCBD) with three replications each included 11 treatments represent the interactions between nitrogen fixing bacteria strains, molybdenum solo application, molybdenum and bacteria strains interactions, in addition to the recommended nitrogen application and control treatment. Results were analyzed using the least significant differences (LSD) test at 5% level of significance. Results showed significant effect of the treatment that included all bacteria strains and Mo (T11) on increasing plant macro elements (N, P, and K) which gave 2.39%, 0.49%, and 2.92%, respectively and Fe and Mo concentrations of 269.67 mg.L-1 and 0.69 mg.L-1, respectively and protein percentage in the pods of 13.98%. in addition, treatment of both R. phaseoli and A. chroococcum (T5) gave the most significant main root length of 36.56 cm while R. phaseoli and A. chroococcum and Mo (T9) gave the largest root surface area of 115.00 cm2 and the highest number of root nods that reached 5.33 nod.plant-1. Moreover, T5 significantly increased plant height, leaf number, shoot dry weight, and pod’s length that reached 54.67 cm, 30.22 leaf.plant-1, 65.56 g.plant-1, and 13.62 cm, respectively. As for the T9, results showed significant increase in the number of pods per plant and plant yield of 51.61 pod.plant-1 and 262.03 g.plant-1, respectively.

Nitrogen uptake and metabolism of Populus simonii in response to PEG-induced drought stress

In the present study, changes in nitrogen uptake, assimilation and the transcript abundance of associated genes were investigated in Populus simonii seedlings treated with 5% polyethylene glycol (PEG)-induced drought stress under hydroponic culture conditions with low and normal nitrogen levels (0.01mM NH4NO3 and 1mM NH4NO3, respectively). Drought stress negatively affected plant growth at both low and normal nitrogen levels. NH4+ and NO3− concentrations were significantly decreased in the roots and leaves of PEG-treated P. simonii seedlings; however, the ratio of NH4+ and NO3− was increased in these plants. Drought stress also decreased NR and GOGAT activity in roots and leaves, irrespective of the nitrogen levels. However, the NH4+ concentrations and NR activity in roots and leaves were increased in response to 1mM NH4NO3 under drought stress. PEG-treated plants also showed better growth at normal nitrogen level (1mM NH4NO3), with increased biomass, total fine root length and larger root surface area. Most genes related to nitrate uptake, reduction and N metabolism were down-regulated; however, two ammonium transporter genes closely related to NH4+ uptake (AMT1;2 and AMT1;6) were up-regulated in response to drought stress. These results suggested that increased N nutrition may have contributed to drought tolerance in P. simonii by increasing NH4+ uptake and decreasing nitrogen metabolism.

Relations of fine-root morphology on 137Cs uptake by fourteen Brassica species

Fourteen Brassica species consisting of seven leafy vegetables and seven root vegetables were examined for 137Cs uptake differences in relation to their fine-root morphological characters. A pot experiment was conducted from November 2014 to February 2015 in a Phytroton using a contaminated soil of Fukushima prefecture. Leafy vegetables showed bigger root diameters, larger root surface area and larger root volume. Consequently, leafy vegetables had higher 137Cs uptake compared to root vegetables. Among the three fine-root parameters, only root surface area was observed as a significant contributing factor to higher 137Cs uptake in terms of transfer factor (TF, dry weight basis). Kakina exhibited higher 137Cs TF value (0.20) followed by Chinese cabbage (0.18) and mizuna (0.17). Lower TF values were observed in turnip (0.059), rutabaga (Kitanoshou) (0.062) and radish (Ha daikon) (0.064).

Seasonal variation in plant hydraulic traits of two co‐occurring desert shrubs, Tamarix ramosissima and Haloxylon ammodendron, with different rooting patterns

AbstractEffective hydraulic responses to varying soil moisture and evaporative demand are crucial to plant survival in arid ecosystems. This study was carried out during two growing seasons (2004–2005) on two typical desert shrub species, Tamarix ramosissima and Haloxylon ammodendron, co‐occurring in the Gurbantonggut Desert (Central Asia), to investigate their hydraulic responses to seasonal variations in water availability. The root distribution was studied by excavating the intact root systems. Leaf‐specific apparent hydraulic conductance (Kl) for the two species was calculated based on leaf water potential (ψl) and transpiration rate (Tr), which were monitored during the growing seasons. T. ramosissima had a deeper taproot (3.1 vs. 2.6 m) and a larger root surface area (3.02 vs. 1.28 m2) than H. ammodendron. Combined with a higher ψl, this meant that it maintained a better water status in general. For the deep‐rooting T. ramosissima, the seasonal pattern of its predawn leaf water potential (ψpd) was in high accordance with the seasonal changes in soil moisture at a depth of 2.6–2.8 m, which was largely influenced by the upflow of groundwater through capillary ascent, and barely responded to rain events. For the shallow‐rooting H. ammodendron, the seasonal pattern of ψpd was closely related to soil moisture in the upper layer at a depth of 0–0.2 and 0.6–0.8 m, which was recharged periodically by rain events and responded acutely to rainfall above 5 mm. The two species differed in their maximum transpiration rates (Trmax) and ψpd: in T. ramosissima, Trmax gradually dropped with decreasing ψpd; in H. ammodendron, Trmax showed no significant response to ψpd. For T. ramosissima, the major water resource was groundwater and vadose zone water, and ψl contributed significantly to transpiration regulation. For H. ammodendron, the primary water resource was precipitation input, which was not sufficient to keep the ψl for this species outside the critical range of leaf shedding in summer. Thus, for these two representative species that share the same habitat, contrasting response strategies to water limitation were observed in relation to water acquisition and root distribution characteristics.

Rooting systems of oilseed and pulse crops. II: Vertical distribution patterns across the soil profile

Root distribution patterns in the soil profile are the important determinant of the ability of a crop to acquire water and nutrients for growth. This study was to determine the root distribution patterns of selected oilseeds and pulses that are widely adapted in semiarid northern Great Plains. We hypothesized that root distribution patterns differed between oilseed, pulse, and cereal crops, and that the magnitude of the difference was influenced by water availability. A field experiment was conducted in 2006 and 2007 near Swift Current (50°15′N, 107°44′W), Saskatchewan, Canada. Three oilseeds [canola ( Brassica napus L.), flax ( Linum usitatissimum L.), mustard ( Brassica juncea L.)], three pulses [chickpea ( Cicer arietinum L.), field pea ( Pisum sativum L.), lentil ( Lens culinaris)], and spring wheat ( Triticum aestivum L.) were hand-planted in lysimeters of 15 cm in diameter and 100 cm in length which were pushed into soil with a hydraulic system. Crops were evaluated under low- (natural rainfall) and high- (rainfall + irrigation) water conditions. Vertical distribution of root systems was determined at the late-flowering stage. A large portion (>90%) of crop roots was mainly distributed in the 0–60 cm soil profile and the largest amount of crop rooting took place in the top 20 cm soil increment. Pulses had larger diameter roots across the entire soil profile than oilseeds and wheat. Canola had 28% greater root length and 110% more root tips in the top 10 cm soil and 101% larger root surface area in the 40 cm soil under high-water than under low-water conditions. In 2007, drier weather stimulated greater root growth for oilseeds in the 20–40 cm soil and for wheat in the 0–20 cm soil, but reduced root growth of pulses in the 0–50 cm soil profile. In semiarid environments, water availability did not affect the vertical distribution patterns of crop roots with a few exceptions. Pulses are excellent “digging” crops with a strong “tillage” function to the soil due to their larger diameter roots, whereas canola is more suitable to the environment with high availability of soil water that promotes canola root development.

A comparative study on the growth and nitrogen and phosphorus uptake characteristics of 15 wetland species

The biomass, root morphology and nutrient uptake capacities of 15 species of local wetland plants were investigated in hydroponic culture. The wetland plants were exposed to 38.5 mg·L−1 of NH-N, 132.8 mg·L−1 of NO-N and 10 mg·L−1 of dissolved inorganic P for 28 days. Mean total biomass of the 15 species ranged from 1.2 to 21.6 g plant−1, with above/below ground ratios (AG:BG) in the range 1.7–5.5. Mean NH-N, NO-N uptake rates ranged from 3.7 to 14.3 mg N·day−1 (accounting for 8.0–49.4% of the NH-N supply) and 17.8 to 59.4 mg N·day−1 (17.8–59.6% of the NO-N supply). Mean P uptake rate ranged from 1.71 to 4.61 mg P·day−1 (24.1–61.5% of the P supply). The N and P concentrations in plant tissues ranged from 28.2 to 606.1 mg N·plant−1 and 4.1 to 53.1 mg P·plant−1, with AG:BG ratio in the range 1.7–7.0 and 1.6–4.6, respectively. The accumulation of N and P in plant tissues was both significantly correlated with plant biomass and root surface area. Among the different species, Canna generalis, Typha latifolia, Thalia dealbata and Lythrum salicaria had greater above- and below-ground biomass, larger root surface area, and greater nutrient uptake and storage rates than the other plants. Our results suggest (or indicate) that the selection of plant species suitable for constructed wetlands can be based on plant biomass and root surface area.

Characterization of a rice variety with high hydraulic conductance and identification of the chromosome region responsible using chromosome segment substitution lines

The rate of photosynthesis in paddy rice often decreases at noon on sunny days because of water stress, even under submerged conditions. Maintenance of higher rates of photosynthesis during the day might improve both yield and dry matter production in paddy rice. A high-yielding indica variety, 'Habataki', maintains a high rate of leaf photosynthesis during the daytime because of the higher hydraulic conductance from roots to leaves than in the standard japonica variety 'Sasanishiki'. This research was conducted to characterize the trait responsible for the higher hydraulic conductance in 'Habataki' and identified a chromosome region for the high hydraulic conductance. Hydraulic conductance to passive water transport and to osmotic water transport was determined for plants under intense transpiration and for plants without transpiration, respectively. The varietal difference in hydraulic conductance was examined with respect to root surface area and hydraulic conductivity (hydraulic conductance per root surface area, L(p)). To identify the chromosome region responsible for higher hydraulic conductance, chromosome segment substitution lines (CSSLs) derived from a cross between 'Sasanishiki' and 'Habataki' were used. The significantly higher hydraulic conductance resulted from the larger root surface area not from L(p) in 'Habataki'. A chromosome region associated with the elevated hydraulic conductance was detected between RM3916 and RM2431 on the long arm of chromosome 4. The CSSL, in which this region was substituted with the 'Habataki' chromosome segment in the 'Sasanishiki' background, had a larger root mass than 'Sasanishiki'. The trait for increasing plant hydraulic conductance and, therefore, maintaining the higher rate of leaf photosynthesis under the conditions of intense transpiration in 'Habataki' was identified, and it was estimated that there is at least one chromosome region for the trait located on chromosome 4.

Creeping Bentgrass Putting Green Turf Responses to Two Summer Irrigation Practices: Rooting and Soil Temperature

Light and frequent (LF) and deep and infrequent (DI) irrigation are two common practices for golf course managers. Few studies have compared the effects of these two opposing irrigation practices on summer root performance in creeping bentgrass (Agrostis stolonifera L.). The objectives of this field study were to quantify summer root development and longevity in response to LF vs. DI irrigation in ‘Providence’ creeping bentgrass grown on a sand‐based rootzone. The LF plots were irrigated daily to moisten the upper 4 to 6 cm of soil, whereas DI plots were irrigated at leaf wilt to wet soil to a depth ≥24 cm. Root measurements were obtained using the minirhizotron imaging technique and included total root count, total root length (TRL), total root surface area (TRSA), and average root diameter. When averaged over the entire 0‐ to 24‐cm rootzone depth, DI‐irrigated creeping bentgrass produced a greater number of roots, longer root lengths, and a larger root surface area than LF‐irrigated turf. Average root diameters were smaller in DI‐irrigated creeping bentgrass in the summer of 2007. Compared with data collected in 2006, the 2‐yr‐old turf had 55 and 32% fewer roots in LF‐ and DI‐irrigated bentgrass by September 2007, respectively. There were similar reductions in TRL and TRSA between years in both irrigation regimes. Deep and infrequent irrigation stimulated root growth throughout the 0‐ to 24‐cm rootzone in May and June and promoted root longevity in summer.

Growth, biomass allocation and nutrient use efficiency in Cladium jamaicense and Typha domingensis as affected by phosphorus and oxygen availability

The effects of phosphorus (P) and oxygen availability on growth, biomass allocation and nutrient use efficiency in Cladium jamaicense Crantz and Typha domingensis Pers. were studied in a growth facility equipped with steady-state hydroponic rhizotrons. The treatments included four P concentrations (10, 40, 80 and 500 μg l −1) and two oxygen concentration (8.0 and <0.5 mg O 2 l −1) in the culture solutions. In Cladium, no clear relationship was found between P availability and growth rate (19–37 mg g −1 d −1), the above to below ground biomass ratio ( A/ B) (mean=4.6), or nitrogen use efficiency (NUE) (mean=72 g dry weight g −1 N). However, the ratio between root supported tissue (leaves, rhizomes and ramets) and root biomass ( S/ R) (5.6–8) increased with P availability. In contrast, the growth rate (48–89 mg g −1 d −1) and the biomass ratios A/ B (2.4–6.1) and S/ R (5.4–10.3) of Typha increased with P availability, while NUE (71–30 g dry weight g −1 N) decreased. The proportion of root laterals was similar in the two species, but Typha had thinner root laterals (diameter=186 μm) than Cladium (diameter=438 μm) indicating a larger root surface area in Typha. The two species had a similar P use efficiency (PUE) at 10 μg P l −1 (mean=1134 g dry weight g −1 P) and at 40 and 80 μg P l −1 (mean=482 dry weight g −1 P) but the N/P ratio indicated imbalances in nutrient uptake at a higher P concentration (40 μg P l −1) in Typha than in Cladium (10 μg P l −1). The two species had similar root specific P accumulation rate at the two lowest P levels, whereas Typha had 3–13-fold higher P uptake rates at the two highest P levels, indicating a higher nutrient uptake capacity in Typha. The experimental oxygen concentration in the rhizosphere had only limited effect on the growth of the two species and had little effect on biomass partitioning and nutrient use efficiency. The aerenchyma in these species was probably sufficient to maintain adequate root oxygenation under partially oxygen depleted conditions. Cladium had characteristics typical for plants from nutrient poor habitats, which included slow growth rate, low capacity for P uptake and relatively inflexible biomass partitioning in response to increased P availability. In contrast, Typha demonstrated a high degree of flexibility in growth, biomass partitioning, and nutrient accumulation to P availability, similar to species from nutrient rich habitats. Although the N/P ratio indicated that Typha was more nutrient stressed at the low P levels, Typha had a higher capacity for P uptake and was more competitive than Cladium at the applied P concentrations.

Rol-Transgenic Populus tremula: root development, root-borne bud regeneration and in vitro propagation efficiency

The potential use of the rol genes from Agrobacterium rhizogenes to improve the root system horticultural characteristics was evaluated in transgenic aspen (Populus tremula) plants, harboring the rol genes under their native promoters. Southern blot and RT-PCR analyses confirmed the presence and expression of A. rhizogenesrolC and rolB genes in four different phenotypically selected transgenic clones. Several of the observed phenotypic modifications were related to rol-gene expression and included, in particular, modified root systems. All in vitro-cultured rol-transgenic plants exhibited extensive root formation in a hormone-free medium, as well as a larger root surface area and mass, as compared to a uidA (β-glucuronidase-encoding)-transgenic aspen line and control (non-transformed) plants. Adventitious root formation in stem segments of rol-transgenic plants exhibited very rapid kinetics, resulting in a much shorter rooting time for rol-transgenic stem segments (e.g. 10 days for 80% rooting in rol-transgenic lines T-26 and T-27, as compared to more than 18 days for control non-transformed or uidA-transgenic aspen plants). rol-Transgenic plants maintained the capacity for 100% rooting throughout the year, versus 70–80% rooting in non-transformed plants during the winter. The four rol-transgenic lines exhibited differences in root development; in two of them enhanced root development was accompanied by increased shoot fresh weight. The root:shoot fresh weight ratio was always higher in rol-transgenic lines than in non-transformed plants. In the T-27 rol-transgenic line, the propagation coefficient of shoot-bud regeneration in liquid root culture was almost three times higher than in non-transformed plants. To the best of our knowledge this is the first report on quantitative phenotypic alterations in rol-transgenic woody plants.

Large Headsetts and Improved Cultivar Enhance Growth and Development of Taro (Colocasia esculents [L.] Schott) During Establishment

AbstractSmall, medium and large headsetts of a traditional (Nine) and an improved (Alafua Sunrise) cultivar of taro were grown for 33 days in pots in a screenhouse.Differences between the cultivars were greatest in root growth where density of root primordia, number of primary roots and root surface area at the final harvest were 53, 82, and 60 % greater respectively in the improved over the traditional variety. Relative rate of leaf elongation and leaf appearance rate were about 30 % faster in the improved variety. Correlation between leaf area and root surface area was cultivar dependent.Large headsetts produced more primary roots and a larger root surface area than small headsetts. They also produced 46 % more leaf area than small headsetts because of larger individual leaves, but not the rate of leaf appearance.Dry matter and nitrogen content declined in petioles, remained relatively constant in corm and accumulated in new shoot and root during establishment. Losses of N were similar but accumulation was greater in new growth of Alafua Sunrise than Niue.We conclude that differences in productivity between the improved and traditional cultivars used in this experiment are at least partly attributable to differences in rate of development of new shoot and root during establishment. Previously reported correlations between corm yield and size of planting material are probably due to large headsetts producing a greater area of leaf and root than small headsetts during early growth.