Root Water Content Research Articles

Effects of NaCl Stress on the Growth and Physiological Changes in Oat (<i>Avena sativa</i>) Seedlings

The oat (Avena sativa) is a kind of cereal grain, which has high saline-alkali tolerance. This experiment was carried out to investigate and compare the growth and physiological changes of oat seedling. Oat was grown under five concentrations of NaCl stress (48, 72, 96, 120 and 144 mmolL-1). The results showed that NaCl stress had no effect on the survival rate and organic acids. With the increasing of the NaCl concentration, tiller number, the chlorophyll, K+, Ca2+, NO3-, H2PO4- contents, shoot length, the shoot biomass, and shoot water content were decreased significantly. However, the Cl-, Na+, Na+/K+, SO42- and proline contents were extremely increased. K+, Ca2+, dry weight, and water content of shoots changed greater than that of roots. While Na+ and Na+/K+ of shoots changed less than that of roots. When NaCl concentration was less than 96 mmolL-1, the length, dry weight, and water content of roots had no significant changes. Based on this investigation, it can be concluded that oat seedlings accumulated more proline, Cl- and SO42- to maintaining osmotic and ion balance. In addition, NaCl stress had no significant effect on the growth of roots, and the roots can play the interceptive and protective role with a stronger salt tolerance. The roots can change the distribution of Na+, then it decreased the harm on the shoots and increased the tolerance of oat seedling.

ECO-physiological response of S. vulgaris to CR(VI): Influence of concentration and genotype

ABSTRACTThe objective of this work is to study the response of Silene vulgaris to a range of environmentally relevant concentrations of Cr(VI) in order to evaluate its potential use in the phytomanagement of Cr polluted sites. Cuttings of six homogenous genotypes from Madrid (Spain) have been used as plant material. The eco-physiological response of S. vulgaris to Cr(VI) changed with the genotype. The yield dose-response curve was characterized by stimulation at low doses of Cr(VI). The effects of metal concentration were quantified on root dry weight, water content and chlorophyll content, determined by SPAD index. The response was not homogeneous for all studied genotypes. At high doses of Cr(VI), plants increased micronutrient concentration in dry tissues which suggested that nutrient balance could be implicated in the alleviation of Cr toxicity. This work highlights the importance of studying the eco-physiological response of metallophytes under a range of pollutant concentrations to determine the most favorable traits to be employed in the phytomanagement process.

Performance of ground penetrating radar in root detection and its application in root diameter estimation under controlled conditions

A plant is stabilized by its root system. In congested urban cities such as Hong Kong, ground trenching is frequently seen due to the installation of utility lines along the roadside. Soil nailing, which involves soil coring in slopes, is a common solution to improve the slope stability. However, both activities inevitably pose a risk to the integrity of any root systems present, and thus reduce the root anchorage. To prevent or minimize such damage, a careful design of the excavation/drilling location is of prime importance. Ground penetrating radar(GPR) provides a non-destructive method for locating roots by examining the contrast between the dielectric properties of the roots and the surrounding soil. To examine the performance of GPR and promote its use in Hong Kong, a test bed was prepared using local materials to create a controlled environment in which to conduct a series of systematic tests evaluating the performance of a 900 MHz GPR. The reflected radargrams were subject to the influence of the following factors:size and depth of roots, horizontal distance between roots, and contrast between the root and soil water content. Correlations between root size and a number of waveform parameters were also explored. Limiting values for root size, root embedded depth, horizontal separation distance between roots, and water content contrast between root and soil were obtained. A significant correlation was found between the root diameter and time travel parameter T 2 ( p <0.001, r=0.795). Because GPR root detection is highly site-specific, this study provides a local reference for GPR performance in the Hong Kong environment. The findings demonstrate that the 900 MHz GPR is applicable in Hong Kong for the detection of main roots.

MODEL SIMULASI PERKEMBANGAN, PERTUMBUHAN DAN NERACA AIR TANAMAN KENTANG PADA DATARAN TINGGI DI INDONESIA

&lt;div data-canvas-width="788.5249999999997"&gt;This research aims to construct a simulation model of development, growth and waterbalance of potato crop. Reasearch&lt;/div&gt;&lt;div data-canvas-width="802.7183333333334"&gt;also predicts climate change impact on potato productivity in several potato production center in Indonesia. The crop&lt;/div&gt;&lt;div data-canvas-width="802.6816666666664"&gt;model being constructed explains process mechanism of development and growth during crop life cycle as a response&lt;/div&gt;&lt;div data-canvas-width="802.7166666666672"&gt;to fluctuation of climatic. Three field experiments were conducted at three locations at Pacet and Galudra in West Java&lt;/div&gt;&lt;div data-canvas-width="802.7066666666665"&gt;Province, and at Kerinci in Jambi Province, to support the model development; for model calibration (Pacet) and model&lt;/div&gt;&lt;div data-canvas-width="802.6899999999999"&gt;validation (Galudra and Kerinci). Paired t-test between model predictions of Granola variety with observations showed&lt;/div&gt;&lt;div data-canvas-width="802.7116666666665"&gt;that there were not significant differences (P&amp;gt; 0,05) on all variables tested, except leaf biomass. In Atlantic variety, there&lt;/div&gt;&lt;div data-canvas-width="802.6650000000001"&gt;were not significant differences (P&amp;gt; 0,05) on root, tuber biomass and soil water content. Based on graphical test showed&lt;/div&gt;&lt;div data-canvas-width="244.87999999999997"&gt;coefficient of determination were (R&lt;/div&gt;&lt;div&gt;2&lt;/div&gt;&lt;div data-canvas-width="552.9633333333334"&gt;) greater than 0,80 for all variables.Generally, results on validation suggested that&lt;/div&gt;&lt;div data-canvas-width="802.6866666666666"&gt;model predictions were not significantly different with field measurements at Galudra (Granola variety) and Kerinci&lt;/div&gt;&lt;div data-canvas-width="802.6966666666668"&gt;(Atlantis and Granola variety) for variable of plant ages, biomass of root, stem, leaf and tuber, leaf area index, and soil&lt;/div&gt;&lt;div data-canvas-width="98.58333333333331"&gt;water content. &lt;/div&gt;

Effects of Sowing Methods on the Quality and Quantity Traits of Three Annual Medicago Species

ABSTRACT- Annual Medicago species (Medicago spp.) are native to the Mediterranean region and widely used in fields and pastures in Iran. There are several methods of sowing annual Medicago species, each with different effects on the performance. However, there is currently no sufficient information about the appropriate methods for sowing Medicago species. In order to evaluate methods of sowing (broadcast planting and row planting) on qualitative and quantitative traits of three annual Medicago species (M. rigidula, M. polymorpha and M. scutellata), a 2-yr field study was conducted in Shiraz, Iran during the growing season 2010-2011. This study was carried out as a split plot experiment based on a randomized complete block (RCB) design with three replications. The results showed that there were no significant differences for most traits between the two years. Medicago planted in the row method had more root dry weight, ash, extract ether, natural detergent fiber (NDF) and nitrogen free extract (NFE). It was also demonstrated that shoot to root weight ratio, water content, organic matter, metabolic energy (ME) and digestibility (DE) were higher in Medicago plants that were planted by the broadcast method. All quantitative traits and ash of M. polymorpha were greater than those of the other two species. M. scutellata had higher percentage of organic matter, extract ether and crude fiber; M. rigidula also had a higher content of calcium, phosphorous, crude protein, NDF, NFE, ME and DE. Higher forage production was observed in M. polymorpha planted by the row method in both years, but this was especially evident in 2011. Overall, these results indicated that the row method was a more suitable method for planting M. polymorpha. Furthermore, broadcast planting was identified as a better method for planting M. scutellata and M. rigidula.

Combined effects of arbuscular mycorrhizal fungi and exogenous cytokinins on pomegranate (Punica granatum) under two contrasting water availability conditions

To our knowledge, there are no studies on the interactive effects of inoculation with arbuscular mycorrhizal fungi and cytokinin addition to plants under drought stress. We investigated the potential protective effect of arbuscular mycorrhizae on pomegranate plants, combined with exogenous cytokinin addition, under two contrasting soil water availability regimes. Our results showed that exogenous cytokinin addition enhances plant biomass, shoot to root ratio and water content, as well as increasing the anthocyanin content. However, a combination of AM fungal inoculation and cytokinin addition did not result in a synergistic protective effect against water stress. Plants were equally well protected against this stress by cytokinin spraying alone. The improvement of pomegranate growth was due mainly to exogenous cytokinin addition. Photosynthesis was promoted both by mycorrhizal inoculation alone and by exogenous cytokinin addition. The main protection against oxidative stress caused by drought was via enhanced accumulation of anthocyanins when the plants were sprayed with cytokinins. When cytokinins were used, the photosynthesis apparatus was also protected.

Supplementary calcium ameliorates ammonium toxicity by improving water status in agriculturally important species.

Fertilization of agricultural plants with ammonium [Formula: see text] is often desirable because it is less susceptible to leaching than nitrate [Formula: see text] reducing environmental pollution, risk to human health and economic loss. However, a number of important agricultural species exhibit a reduction in growth when fertilized with [Formula: see text] and increasing the tolerance to [Formula: see text] may be of importance for the establishment of sustainable agricultural systems. The present study explored the feasibility of using calcium (Ca) to increase the tolerance of bell pepper (Capsicum annuum) to [Formula: see text] fertilization. Although [Formula: see text] at proportions ≥25 % of total nitrogen (N) decreased leaf dry mass (DM), supplementary Ca ameliorated this decrease. Increasing [Formula: see text] resulted in decreased root hydraulic conductance (Lo) and root water content (RWC), suggesting that water uptake by roots was impaired. The [Formula: see text]-induced reductions in Lo and RWC were mitigated by supplementary Ca. Ammonium induced increased damage to the cell membranes through lipid peroxidation, causing increased electrolyte leakage; Ca did not reduce lipid peroxidation and resulted in increased electrolyte leakage, suggesting that the beneficial effects of Ca on the tolerance to [Formula: see text] may be more of a reflection on its effect on the water status of the plant. Bell pepper plants that received [Formula: see text] had a low concentration of [Formula: see text] in the roots but a high concentration in the leaves, probably due to the high nitrate reductase activity observed. Ammonium nutrition depressed the uptake of potassium, Ca and magnesium, while increasing that of phosphorus. The results obtained in the present study indicate that [Formula: see text] caused growth reduction, nutrient imbalance, membrane integrity impairment, increased activity of antioxidant enzymes and affected water relations. Supplementary Ca partially restored growth of leaves by improving root Lo and water relations, and our results suggest that it may be used as a tool to increase the tolerance to [Formula: see text] fertilization.

Pearl millet growth and biochemical alterations determined by mycorrhizal inoculation, water availability and atmospheric CO2 concentration

Pearl millet (Pennisetum glaucum L.) is an important fodder and is a potential feedstock for fuel ethanol production in dry areas. Our objectives were to assess the effect of elevated CO2 and/or reduced irrigation on biomass production and levels of sugars and proteins in leaves of pearl millet and to test whether mycorrhizal inoculation could modulate the effects of these abiotic factors on growth and metabolism. Results showed that mycorrhizal inoculation and water regime most influenced biomass of shoots and roots; however, their individual effects were dependent on the atmospheric CO2 concentration. At ambient CO2, mycorrhizal inoculation helped to alleviate effects of water deficit on pearl millet without significant decreases in biomass production, which contrasted with the low biomass of mycorrhizal plants under restricted irrigation and elevated CO2. Mycorrhizal inoculation enhanced water content in shoots, whereas reduced irrigation decreased water content in roots. The triple interaction between CO2, arbuscular mycorrhizal fungi (AMF) and water regime significantly affected the total amount of soluble sugars and determined the predominant soluble sugars in leaves. Under optimal irrigation, elevated CO2 increased the proportion of hexoses in pearl millet that was not inoculated with AMF, thus improving the quality of this plant material for bioethanol production. By contrast, elevated CO2 decreased the levels of proteins in leaves, thus limiting the quality of pearl millet as fodder and primary source for cattle feed.

Evaluation of biological endpoints in crop plants after exposure to non‐steroidal anti‐inflammatory drugs (NSAIDs): Implications for phytotoxicological assessment of novel contaminants

Human pharmaceuticals have been detected in the terrestrial environment at µg to mgkg−1 concentrations. Repeated application of sewage sludge (biosolids) and increasing reclaimed wastewater use for irrigation could lead to accumulation of these novel contaminants in soil systems. Despite this, potential phytotoxicological effects on higher plants have rarely been evaluated. These studies aimed to test effects upon germination, development, growth and physiology of two crop plants, namely radish (Raphanus sativus Spakler 3) and lettuce (Lactuca sativa All Year Around), after exposure to different, but structurally related non-steroidal anti-inflammatory drugs (NSAIDs) at environmentally relevant concentrations. A range of biological endpoints comprising biomass, length, water content, specific root and shoot length, root to shoot ratio, daily progress of stages of cell elongation and organ emergence (primary root, hypocotyl elongation, cotyledon emergence, cotyledon opening, and no change), as well as photosynthetic measurements were evaluated. Compounds from the fenamic acid class were found to affect R. sativus root endpoints (root length and water content), while ibuprofen affected early root development of L. sativa. In general, phytotoxicological effects on root endpoints demonstrated that impacts upon higher plants are not only compound specific, but also differ between plant species. It was found that the usage of a wide range of biological endpoints (all simple, cost-effective and ecologically relevant) were beneficial in detecting differences in plant responses to NSAID exposure. Due to paucity and discrepancy within the few previously available phytotoxicological studies with pharmaceuticals, it is now essential to allocate time and resources to consider development of suitable chronic toxicity tests, and some suggestions regarding this are presented.

Effect of short-term water deficit stress on antioxidative systems in cucumber seedling roots.

BackgroundCucumber is one of the most popular vegetables, and have little tolerance for water stress. The antioxidant defense system is one of major drought defense and adaptive mechanisms in plants, however, relatively few data are available regarding antioxidant systems in responses of cucumber to water deficit. The effect of short-term drought stress on the antioxidant system, lipid peroxidation and water content in cucumber seedlings roots was investigated.ResultsThe results showed that polyethylene glycol (PEG) induced water stress markedly decreased water content of cucumber seedling roots after treatment of 36 h, and caused excessive generation of reactive oxygen species (ROS) including superoxide (O2.−), hydrogen peroxide (H2O2). Meanwhile, malondialdehyde (MDA) content increased. Antioxidant enzymes including superoxide dismutases (SOD), peroxidases (POD), catalase (CAT) and ascorbate peroxidase (APX) activities increased in different time and different extent under water stress, while ascorbate (AsA) and glutathione (GSH) content, glutathione reductase (GR), dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) activities all decreased when compared to control.ConclusionsTherefore, it can be concluded that water stress strongly disrupted the normal metabolism of roots and restrained water absorption, and seemingly enzymatic system played more important roles in protecting cucumber seedling roots against oxidative damage than non-enzymatic system in short-term water deficit stress.Electronic supplementary materialThe online version of this article (doi:10.1186/s40529-014-0046-6) contains supplementary material, which is available to authorized users.

Modeling potato root growth and water uptake under water stress conditions

Potato (Solanum tuberosum L.) is considered a drought sensitive crop. Accurate simulation of root growth is critical for estimating water uptake dynamics. However, data required to build and test advanced potato root simulation approaches is lacking. Previously unpublished data from our soil–plant–atmosphere-research (SPAR) chambers was used to evaluate a new two-dimensional diffusive root growth module linked to the existing potato model SPUDSIM. The root module consisted of diffusive parameters controlling the direction of root growth in horizontal and vertical directions, and an additional convective term for vertical growth within the soil. This modified SPUDSIM was tested against observed SPAR data which consisted of root distribution in the soil profile and organ dry weights (DW) at harvest, plus daily water uptake patterns for each of six different irrigation treatments. The difference between simulated and observed DW data was within two standard errors for most plant organs—root DW was over-predicted for well-watered plants. Spatial and temporal patterns of root distribution and water contents were reproduced well. However, the model tended to over-estimate water uptake from soil layers closer to the surface. Differences in simulated root growth patterns among irrigation treatments were the result of fluctuations in soil water status, bulk density, and root density which, in turn, affected the amount of carbon allocated to the roots in different soil layers and the value of the convective term. These results suggest the new module will provide more reliable predictions of potato water uptake for improved agricultural decision support tools.

An Important Role of Carotenoids in Protection of Photosynthetic Apparatus under VAM Inoculation on Momordica charantia

The effect of mixed inoculums of VAM (Vesicular Arbuscular Mycorrhizas) fungi on seed growth and photosynthetic apparatus in green house was monitored. The plants were watered daily with tap water. Plants were cultivated in natural environment in mid of March (2011). A direct relation between root length and water contents suggests a defense mechanism of MP (microrihzal plants) against the fungal stress. It was also supported by the fact that the leaf area of MP was much greater as compared to the NMP (non microrihzal plants) with elevated concentration of all chlorophyllus pigments in 30 days. An increase in the surface area of the leaf and concentration of the pigments, may be for an acceleration in absorption of CO₂ for reduction of it into glucose through oxidation of water molecule. The non-significant decline in glucose contents support the above hypothesis of rapid redox reaction mechanism which was established to overcome the stress. The positive effects of mycorrhizal which were already mentioned in the literature were reported in this article in relations of survival strategies of the plant, adapted in stress conditions. An increase in the chlorophyll contents (30 d) and leaf area of plants possibly attributed with absorption of solar radiation for the protection of plants. It was also supported by the higher concentration of carotenoids (30 d) that may have an additional function of regulation of certain developmental responses and screening of light to save the plants from stress conditions.

Impact of Salinity on Tolerance, Vigor, and Seedling Relative Water Content of Haricot Bean (Phaseolus Vulgaris L.) Cultivars

A laboratory experiment was undertaken to evaluate the impact of salinity on seedling tolerance and vigor indices, phytotoxicity, and relative water content of haricot bean cultivars. Two haricot bean cultivars (Lehade and Chercher) and five salinity levels (0, 2, 4, 8, and 16mM) were factorialy arranged in Completely Randomized Design with three replications. The result of the study revealed that no significant interaction effect between cultivars vs salinity treatments (p<0.05). However, cultivars differ significantly (p<0.05) on seedling and root vigor indices, shoot phytotoxicity, and relative water content of shoot and root. Lehade gave higher seedling, shoot and root vigor indices; whereas, Chercher gave relatively higher seedling tolerance index, and lower shoot and root phytotoxicity. The highest relative shoot and root water contents were recorded on Chercher compared to Lehade. The increase in NaCl concentrations significantly (p<0.05) decreased seedling, shoot, and root vigor indices; and the lowest vigor indices were observed on 16mM NaCl concentration. However, the phytotoxicity of shoot and root increased as the concentrations of NaCl increased; and the lowest value of phytotoxicity observed at control treatment and 2 mM, while the highest on 16mM. Significant negative relationships were observed between relative shoot (R2 = 0.896) and root (R² = 0.904) water contents, and salinity concentrations. In conclusion, cultivars varied genetically for their tolerance, and relative water content. The increase in salinity decreased vigor and tolerance indices, and relative water content; however increased phytotoxicity percentage of root and shoot of haricot bean.

Effect of urea and ammonium sulphate on some physiological aspects and&lt;br&gt;chemical compositions of Pennisetum glaucum plants

A research experiment was carried out to study the effect of soil application of urea and/or ammonium sulphate on some physiological aspects and biochemical composition of pearl millet (Pennisetum glaucum) plants during the vegetative growth period. The parameters analyzed were dry weight, water content, polysaccharides, total carbohydrates, phosphorus content, nitrogenous content and proline in roots and shoots as well as photosynthetic pigments content in the leaves. The results for roots indicated significant increases in dry weight, water content and direct reducing value due to the combination of urea with ammonium sulphate at 0.5% during the first and second periods and urea with ammonium sulphate at 0.3% in the third one. Total carbohydrates significantly increased due to application of ammonium sulphate at 0.5% in the second and third samples. Organic and total phosphorus significantly increased due to application of urea at 0.3% in the first and second samples. Applying urea at 0.5% achieved the highest value in total soluble N, protein-N, total-N and proline in first sample. Meanwhile, the combination of urea and ammonium sulphate at 0.3% resulted in high increases in total- N and protein - N in the second and third samples. Likewise, application of urea with ammonium sulphate at 0.5% caused the highest significant value in total soluble - N in the second sample compared with control and other treatments in roots.

New insights into domestication of carrot from root transcriptome analyses.

BackgroundUnderstanding the molecular basis of domestication can provide insights into the processes of rapid evolution and crop improvement. Here we demonstrated the processes of carrot domestication and identified genes under selection based on transcriptome analyses.ResultsThe root transcriptomes of widely differing cultivated and wild carrots were sequenced. A method accounting for sequencing errors was introduced to optimize SNP (single nucleotide polymorphism) discovery. 11,369 SNPs were identified. Of these, 622 (out of 1000 tested SNPs) were validated and used to genotype a large set of cultivated carrot, wild carrot and other wild Daucus carota subspecies, primarily of European origin. Phylogenetic analysis indicated that eastern carrot may originate from Western Asia and western carrot may be selected from eastern carrot. Different wild D. carota subspecies may have contributed to the domestication of cultivated carrot. Genetic diversity was significantly reduced in western cultivars, probably through bottlenecks and selection. However, a high proportion of genetic diversity (more than 85% of the genetic diversity in wild populations) is currently retained in western cultivars. Model simulation indicated high and asymmetric gene flow from wild to cultivated carrots, spontaneously and/or by introgression breeding. Nevertheless, high genetic differentiation exists between cultivated and wild carrots (Fst = 0.295) showing the strong effects of selection. Expression patterns differed radically for some genes between cultivated and wild carrot roots which may be related to changes in root traits. The up-regulation of water-channel-protein gene expression in cultivars might be involved in changing water content and transport in roots. The activated expression of carotenoid-binding-protein genes in cultivars could be related to the high carotenoid accumulation in roots. The silencing of allergen-protein-like genes in cultivated carrot roots suggested strong human selection to reduce allergy. These results suggest that regulatory changes of gene expressions may have played a predominant role in domestication.ConclusionsWestern carrots may originate from eastern carrots. The reduction in genetic diversity in western cultivars due to domestication bottleneck/selection may have been offset by introgression from wild carrot. Differential gene expression patterns between cultivated and wild carrot roots may be a signature of strong selection for favorable cultivation traits.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-895) contains supplementary material, which is available to authorized users.

Water heterogeneous affects water storage in two rhizomatous clonal plants Leymus secalinus and Calamagrostis pseudophragmites

Aims Essential resources for plant growth are heterogeneously distributed in natural systems, and clonal plants can efficiently use heterogeneously distributed resources. Many studies have addressed effects of heterogeneous water supply on the growth, morphology and physiology of clonal plants, but few have tested effects of water heterogeneity on the ability of clonal plants to store water. Methods We grew ramets of two rhizomatous clonal plants Leymus secalinus and Calamagrostis pseudophrag- mites under both homogeneous and heterogeneous water supply. The experiment was conducted from 15 August to 14 October 2010 under a rain shelter at Ordos Sandland Ecological Station (39°29′ N, 110°11′ E). Water content and biomass of roots, shoots, spacers (rhizomes) and buds were measured. Important findings Spacer water content, shoot water content and root water content were significantly higher under the heterogeneous water condition than under the homogeneous water condition in both species, suggesting that clonal plants could increase the ability to store water when growing in heterogeneous water conditions. Leymus secalinus decreased single ramet biomass and increased bud number to adapt to water heterogeneity, while C. pseudophragmites increased belowground biomass, including rhizome biomass, root biomass and bud biomass, to deal with water heterogeneity. Increasing water storage may increase the ability of clonal plants to adapt to unpredictable water conditions.

Water heterogeneous affects water storage in two rhizomatous clonal plants Leymus secalinus and Calamagrostis pseudophragmites

Aims Essential resources for plant growth are heterogeneously distributed in natural systems, and clonal plants can efficiently use heterogeneously distributed resources. Many studies have addressed effects of heterogeneous water supply on the growth, morphology and physiology of clonal plants, but few have tested effects of water heterogeneity on the ability of clonal plants to store water. Methods We grew ramets of two rhizomatous clonal plants Leymus secalinus and Calamagrostis pseudophrag- mites under both homogeneous and heterogeneous water supply. The experiment was conducted from 15 August to 14 October 2010 under a rain shelter at Ordos Sandland Ecological Station (39°29′ N, 110°11′ E). Water content and biomass of roots, shoots, spacers (rhizomes) and buds were measured. Important findings Spacer water content, shoot water content and root water content were significantly higher under the heterogeneous water condition than under the homogeneous water condition in both species, suggesting that clonal plants could increase the ability to store water when growing in heterogeneous water conditions. Leymus secalinus decreased single ramet biomass and increased bud number to adapt to water heterogeneity, while C. pseudophragmites increased belowground biomass, including rhizome biomass, root biomass and bud biomass, to deal with water heterogeneity. Increasing water storage may increase the ability of clonal plants to adapt to unpredictable water conditions.

Do elevations in temperature, CO2, and nutrient availability modify belowground carbon gain and root morphology in artificially defoliated silver birch seedlings?

Climate warming increases the risk of insect defoliation in boreal forests. Losses in photosynthetically active surfaces cause reduction in net primary productivity and often compromise carbon reserves of trees. The concurrent effects of climate change and removal of foliage on root growth responses and carbohydrate dynamics are poorly understood, especially in tree seedlings. We investigated if exposures to different combinations of elevated temperature, CO2, and nutrient availability modify belowground carbon gain and root morphology in artificially defoliated 1-year-old silver birches (Betula pendula). We quantified nonstructural carbohydrates (insoluble starch as a storage compound; soluble sucrose, fructose, and glucose) singly and in combination in fine roots of plants under winter dormancy. Also the total mass, fine root proportion, water content, and length of roots were defined. We hypothesized that the measured properties are lower in defoliated birch seedlings that grow with ample resources than with scarce resources. On average, fertilization markedly decreased both the proportion and the carbohydrate concentrations of fine roots in all seedlings, whereas the effect of fertilization on root water content and dry mass was the opposite. However, defoliation mitigated the effect of fertilization on the root water content, as well as on the proportion of fine roots and their carbohydrate concentrations by reversing the outcomes. Elevation in temperature decreased and elevation in CO2 increased the absolute contents of total nonstructural carbohydrates, whereas fertilization alleviated both these effects. Also the root length and mass increased by CO2 elevation. This confirms that surplus carbon in birch tissues is used as a substrate for storage compounds and for cell wall synthesis. To conclude, our results indicate that some, but not all elements of climate change alter belowground carbon gain and root morphology in defoliated silver birch seedlings.

Forward simulation of root’s ground penetrating radar signal: simulator development and validation

Background and aims It remains unclear how the limiting factors (e.g., root size, root water content, spacing between roots, and soil water content) affect root investigation using ground penetrating radar (GPR). The objective of this study is to develop a theoretical forward simulation protocol of synthesizing root’s GPR signal and test the feasibility of our proposed simulation protocol in evaluating the impacts of limiting factors on GPR-based root detection and quantification. Methods The proposed forward simulation protocol was developed by integrating several existing numerical models, such as the Root Composition Model, the Root Dielectric Constant Model, the Root Electrical Conductivity Model, the Soil Dielectric Constant Model, the Soil Electrical Conductivity Model, and a newly-established model (Root Length-Biomass Model). Resolution and GPR index obtained from both field collected radargrams and corresponding simulations were compared to validate the accuracy of simulation. Results Simulated radargrams exhibit similar resolution with that of the in situ collected. The same trends of root radar signals against different levels of root size, root water content, interval between roots, root depth, and antenna frequency were observed on both in situ radargrams and simulated radargrams. Strong correlations (correlation coefficients ranging from 0.87 to 0.96) were found between GPR indices extracted from the simulated data and those from the field collected data. Conclusions Our proposed forward simulation is effective for assessing the impacts of limiting factors on root detection and quantification using GPR. This forward simulation protocol can be used to provide guidance for in situ GPR root investigation and can predict the accuracy of GPR-based root quantification under site-specific conditions.

Impact of root water content on root biomass estimation using ground penetrating radar: evidence from forward simulations and field controlled experiments

The GPR indices used for predicting root biomass are measures of root radar reflectance. However, root radar reflectance is highly correlated with root water content. The objectives of this study are to assess the impact of root water content on GPR-based root biomass estimation and to develop more reliable approaches to quantify root biomass using GPR. Four hundred nine roots of five plant species in a sandy area of northern China were examined to determine the general water content range of roots in sandy soils. Two sets of GPR simulation scenarios (including 492 synthesized radargrams in total) were then conducted to compare the changes of root radar signal and the accuracies of root biomass estimation by GPR at different root gravimetric water content levels. In the field, GPR transects were scanned for Ulmus pumila roots buried in sandy soils with three antenna center frequencies (0.5, 0.9, and 2.0 GHz). The performance of two new GPR-based root biomass quantification approaches (one using time interval GPR index and the other using a non-linear regression model) was then tested. All studied roots exhibited a broad range of gravimetric water content (>125 %), with the water contents of most roots ranging from 90 % to 150 %. Both field experiments and forward simulations indicated that 1) waveforms of root radar reflection, radar-reflectance related GPR indices, and root biomass estimation accuracy were all affected by root water content; and 2) using time interval index and establishing a nonlinear regression model of root biomass on GPR indices improved the accuracy of root biomass estimation, decreasing the prediction error (RMSE) by 4 to 30 % under field conditions. The magnitude of GPR indices depends on both root biomass and root water content, and root water content affects root biomass estimation using GPR indices. Using a linear regression model of root biomass on radar-reflectance related GPR index for root biomass estimation would only be feasible for roots with a relative narrow range of water content (e.g., when gravimetric water contents of studied roots vary within 20 %). Appropriate GPR index and regression models should be selected based on the water content range of roots. The new protocol of root biomass quantification by GPR presented in this study improves the accuracy of root biomass estimation.