Root Respiration Rate Research Articles

Spatiotemporal responses of rice root architecture and anatomy to drought

AimsGrowth reductions and yield losses from drought could be mitigated by developing rice genotypes with more efficient root systems. We examined spatiotemporal responses to drought in order to determine whether roots developing in upper vs. deeper soil layers respond differently to drought stress.MethodsRoot anatomical and architectural phenotypes of two rice genotypes, Azucena (drought tolerant) and IR64 (drought susceptible), were measured weekly in well-watered and vegetative-stage drought stress treatments in solid medium with stratified moisture availability. Basal and apical segments were collected from older, deeper nodal roots and apical segments from younger, shallow roots for assessment of anatomy and lateral rooting phenotypes. The relationship between root anatomy and root respiration rates was tested in solution culture and solid medium.ResultsCompared to IR64, Azucena had deeper root systems and larger diameter roots in both treatments but reduced its living tissue area in response to drought, while IR64 roots exhibited less plasticity in root diameter. Root respiration rates were positively correlated with root diameter and living tissue area, providing evidence that root anatomy affects the metabolic cost of tissues. In response to drought, Azucena showed reduced theoretical axial hydraulic conductance in shallow roots and at the base of deep roots but slightly greater conductance at the tip of deep roots, while IR64 displayed low plasticity in metaxylem phenotypes.ConclusionWe propose that the plasticity of root phenotypes in Azucena contributes to its drought tolerance by reducing the metabolic cost of soil exploration and improving the efficiency of water transport.

Newly developed sugarbeet lines with altered postharvest respiration rates differ in transcription factor and glycolytic enzyme expression

AbstractRespiration is the principal cause for postharvest sucrose loss in sugarbeet (Beta vulgaris L.) roots. Although reductions in respiration rate could mitigate these losses, developing sugarbeet cultivars and storage procedures that reduce respiration are hindered by a lack of knowledge of the genetic and metabolic factors that control storage respiration rate. Research was conducted to identify genes and gene products that affect storage respiration rate by creating two sugarbeet lines that differ in respiration rate and characterizing gene expression differences between these lines. Sugarbeet lines F1056 and F1057, which differ by up to 42% in respiration rate, were created by divergent selection of a sugarbeet population using root respiration rate after 30 d in storage as the principal selection criterion. RNA sequencing identified 287 differentially expressed genes (DEGs) between these lines on the day of harvest and after 28‐d storage. Of these DEGs, nine encoded transcription factors and five encoded enzymes involved in the respiratory pathway. Other DEGs contributed to a variety of biological and molecular functions based on gene ontology classifications. Of respiratory pathway DEGS, genes for NAD+‐ and NADP+‐dependent forms of glyceraldehyde‐3‐phosphate dehydrogenase were of note due to their high upregulation in the high respiring line and for their established role in glycolysis, a pathway identified as a likely bottleneck in respiratory substrate production. Overall, lines F1056 and F1057 provide new tools for investigating genetic and physiological differences in storage respiration rate, and their DEGs identify candidates for genes affecting sugarbeet root respiration rate.

Shift from Acquisitive to Conservative Root Resource Acquisition Strategy Associated with Increasing Tree Age: A Case Study of Fraxinus mandshurica

Tree age has an important effect on the form and function of fine roots. Previous studies have focused on the variations in root morphological and chemical traits among tree ages, while less attention has been given to the physiological traits, impeding a full understanding of the relationship between root resource acquisition strategy and tree age. Here, we measured root morphological (diameter, specific root length, specific root area and tissue density), chemical (nitrogen concentration) and physiological (respiration and exudation rate) traits of young, middle-aged and mature trees of Fraxinus mandshurica in a temperate secondary forest in northeastern China. Our overall aim was to determine how root traits and related resource acquisition strategy change with tree age. The results showed that from young to mature trees, root diameter gradually increased, but specific root length, specific root area, root nitrogen concentration, respiration and exudation rates all decreased, and the significant differences were mainly found between young and mature trees. Pearson’s correlation analysis revealed that the relationships of root respiration and exudation rates to root morphological and chemical traits depended on tree age and the specific traits examined, but these correlations were all significant except for root tissue density when the data were pooled across all tree age classes. Principal component analysis (PCA) showed that the conservative traits represented by root diameter, and the acquisitive traits such as root respiration and exudation rates and related morphological and chemical traits, occupied two ends of the first axis, respectively, while root tissue density occupied one end of the second axis, partially confirming the conceptual framework of “root economics space”. Standardized major axis (SMA) analysis of root exudation and respiration rates showed that young trees allocated more root carbon flux to the formation of root exudation, compared to middle-aged and mature trees. Our findings suggest that root resource acquisition strategy in F. mandshurica appears to shift from an absorptive to conservative strategy associated with increasing tree age, which may have substantial consequences for individual growth and interspecific competition, as well as belowground carbon allocation in ecosystems.

Responses of fine root exudation, respiration and morphology in three early successional tree species to increased air humidity and different soil nitrogen sources.

Global climate change scenarios predict an increase in air temperature, precipitation and air humidity for northern latitudes. Elevated air humidity may significantly reduce the water flux through forest canopies and affect interactions between water and nutrient uptake. However, we have limited understanding of how altered transpiration would affect root respiration and carbon (C) exudation as fine root morphology acclimates to different water flux. We investigated the effects of elevated air relative humidity (eRH) and different inorganic nitrogen sources (NO3- and NH4+) on above and belowground traits in hybrid aspen (Populus × wettsteinii Hämet-Ahti), silver birch (Betula pendula Roth.) and Scots pine (Pinus sylvestris L.) grown under controlled climate chamber conditions. The eRH significantly decreased the transpiration flux in all species, decreased root mass-specific exudation in pine, and increased root respiration in aspen. eRH also affected fine root morphology, with specific root area increasing for birch but decreasing in pine. The species comparison revealed that pine had the highest C exudation, whereas birch had the highest root respiration rate. Both humidity and nitrogen treatments affected the share of absorptive and pioneer roots within fine roots; however, the response was species-specific. The proportion of absorptive roots was highest in birch and aspen, the share of pioneer roots was greatest in aspen and the share of transport roots was greatest in pine. Fine roots with lower root tissue density were associated with pioneer root tips and had a higher C exudation rate. Our findings underline the importance of considering species-specific differences in relation to air humidity and soil nitrogen availability that interactively affect the C input-output balance. We highlight the role of changes in the fine root functional distribution as an important acclimation mechanism of trees in response to environmental change.

Growth, root respiration and photosynthesis of a root-sprouting short-lived herb after severe biomass removal

The predominance of short-lived species in disturbed habitats supports the view that generative regeneration is an advantageous strategy under these conditions. However, there are short-lived species that survive the destruction of aboveground biomass and resprout from roots. Yet, there is only limited knowledge on the effect of injury on the plant growth of individuals regrowing from roots, and nearly no research has been conducted on the physiological regulation of root-sprouting.We experimentally tested the effect of total shoot biomass removal on the growth, root respiration and photosynthesis of the short-lived, root-sprouting herb Barbarea vulgaris (Brassicaceae) to assess the efficiency and importance of the root sprouting ability.Regenerating plants compensated for the loss of photosynthetic area by producing a higher number of leaves with higher SLA, but we did not observe compensatory photosynthesis, which could potentially counterbalance the loss of photosynthetic area and allow accelerated growth. The root respiration rate significantly decreased immediately after injury and then slightly and consequentially increased. The belowground biomass of the injured plants decreased by more than four times a month after the injury comparing to the biomass measured immediately after the disturbance. This result suggests the intensive consumption of reserves located in roots, although the root respiration values did not indicate it.Although we found physiological constraints that limited more vigorous resprouting, we conclude that the root-sprouting ability of short-lived species represents a useful strategy for population persistence in frequently disturbed habitats, in places lacking seed banks or when disturbances occur during less-than-suitable germination conditions.

Effects of Trichoderma harzianum Fertilizer on the Soil Environment of Malus hupehensis Rehd. Seedlings under Replant Conditions

A pot experiment was performed to investigate the effects of Trichoderma harzianum on the root morphology of Malus hupehensis Rehd. seedlings and their soil environment under replant conditions. The experiment consisted of four treatments: continuously cropped soil (CK1), methyl bromide fumigation (CK2), carrier substrate control (T1), and T. harzianum fertilizer (T2). Plant growth parameters, soil phenolic acid content, abundance of soil microorganisms, and root respiration rate were measured. Compared with CK1, plant height, basal diameter, and fresh weight were 34.58%, 27.55%, and 32.91% greater in T2; 11.35%, 12.10%, and 18.33% greater in T1; and 54.34%, 57.64%, and 45.74% greater in CK2. These metrics were significantly higher in the CK2 treatment than in the other treatments. The second highest values were recorded in the T2 treatment. Differences in root architecture were consistent with differences in biomass. Application of T. harzianum fertilizer was associated with increases of 45.45%, 120.06%, 86.44%, and 268.29% in the activities of the antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), respectively, and there was little difference between T2 and CK2. The contents of phlorizin and phloretin were 39.39% and 51.70% less in T2, respectively, and 17.85% and 18.14% less in T1, respectively, compared with CK1. Trichoderma harzianum fertilizer increased the abundance of bacteria and actinomycetes while decreasing that of fungi. The gene copy numbers of Fusarium oxysporum and Fusarium moniliforme were 64.30% and 49.35% less, respectively, in the T2 treatment. The fungus population and the gene copy number of Fusarium oxysporum and Fusarium moniliforme was the least in CK2 because of the good sterilization effect. The T. harzianum fertilizer showed satisfactory effects in promoting the root growth of M. hupehensis, increasing the root resistance, decreasing the soil phenolic acid content, and significantly reducing the gene copy number of F. oxysporum and F. moniliforme. In summary, T. harzianum fertilizer is an effective and green alternative for the prevention and control of apple replant disease (ARD).

Root Functional Trait and Soil Microbial Coordination: Implications for Soil Respiration in Riparian Agroecosystems.

Predicting respiration from roots and soil microbes is important in agricultural landscapes where net flux of carbon from the soil to the atmosphere is of large concern. Yet, in riparian agroecosystems that buffer aquatic environments from agricultural fields, little is known on the differential contribution of CO2 sources nor the systematic patterns in root and microbial communities that relate to these emissions. We deployed a field-based root exclusion experiment to measure heterotrophic and autotrophic-rhizospheric respiration across riparian buffer types in an agricultural landscape in southern Ontario, Canada. We paired bi-weekly measurements of in-field CO2 flux with analysis of soil properties and fine root functional traits. We quantified soil microbial community structure using qPCR to estimate bacterial and fungal abundance and characterized microbial diversity using high-throughput sequencing. Mean daytime total soil respiration rates in the growing season were 186.1 ± 26.7, 188.7 ± 23.0, 278.6 ± 30.0, and 503.4 ± 31.3 mg CO2-C m–2 h–1 in remnant coniferous and mixed forest, and rehabilitated forest and grass buffers, respectively. Contributions of autotrophic-rhizospheric respiration to total soil CO2 fluxes ranged widely between 14 and 63% across the buffers. Covariation in root traits aligned roots of higher specific root length and nitrogen content with higher specific root respiration rates, while microbial abundance in rhizosphere soil coorindated with roots that were thicker in diameter and higher in carbon to nitrogen ratio. Variation in autotrophic-rhizospheric respiration on a soil area basis was explained by soil temperature, fine root length density, and covariation in root traits. Heterotrophic respiration was strongly explained by soil moisture, temperature, and soil carbon, while multiple factor analysis revealed a positive correlation with soil microbial diversity. This is a first in-field study to quantify root and soil respiration in relation to trade-offs in root trait expression and to determine interactions between root traits and soil microbial community structure to predict soil respiration.

Methyl jasmonate effects on sugarbeet root responses to postharvest dehydration.

BackgroundSugarbeet (Beta vulgaris L.) roots are stored under conditions that cause roots to dehydrate, which increases postharvest losses. Although exogenous jasmonate applications can reduce drought stress in intact plants, their ability to alleviate the effects of dehydration in postharvest sugarbeet roots or other stored plant products is unknown. Research was conducted to determine whether jasmonate treatment could mitigate physiological responses to dehydration in postharvest sugarbeet roots.MethodsFreshly harvested sugarbeet roots were treated with 10 µM methyl jasmonate (MeJA) or water and stored under dehydrating and non-dehydrating storage conditions. Changes in fresh weight, respiration rate, wound healing, leaf regrowth, and proline metabolism of treated roots were investigated throughout eight weeks in storage.ResultsDehydrating storage conditions increased root weight loss, respiration rate, and proline accumulation and prevented leaf regrowth from the root crown. Under dehydrating conditions, MeJA treatment reduced root respiration rate, but only in severely dehydrated roots. MeJA treatment also hastened wound-healing, but only in the late stages of barrier formation. MeJA treatment did not impact root weight loss or proline accumulation under dehydrating conditions or leaf regrowth under non-dehydrating conditions. Both dehydration and MeJA treatment affected expression of genes involved in proline metabolism. In dehydrated roots, proline dehydrogenase expression declined 340-fold, suggesting that dehydration-induced proline accumulation was governed by reducing proline degradation. MeJA treatment altered proline biosynthetic and catabolic gene expression, with greatest effect in non-dehydrated roots. Overall, MeJA treatment alleviated physiological manifestations of dehydration stress in stored roots, although the beneficial effects were small. Postharvest jasmonate applications, therefore, are unlikely to significantly reduce dehydration-related storage losses in sugarbeet roots.

Amygdalin and Benzoic Acid on the Influences of the Soil Environment and Growth of Malus hupehensis Rehd. Seedlings.

Crop rotation in fruit trees is an effective approach for addressing some of the problems of continuous cropping. To determine whether aged peach orchard soil is suitable for planting apple trees, we studied the effects of two substances abundant in aged peach orchard soil—amygdalin and benzoic acid—on the soil microbial community structure, soil enzyme activity, and the growth of Malus hupehensis Rehd. seedlings. Soils treated with amygdalin (T1), benzoic acid (T2), and a mixed solution of amygdalin and benzoic acid (T3) were used to plant M. hupehensis Rehd. seedlings. Compared with fallow (control) soil, the soil microbial community structure, soil enzyme activities, and root protective enzyme activities, leaf chlorophyll content, and net photosynthetic rate decreased in the three treatments. The biomass and root index of M. hupehensis Rehd. seedlings significantly decreased. Compared with T3, the plant height, ground diameter, fresh weight, dry weight, root length, root surface area, root volume, and root respiration rate of M. hupehensis Rehd. seedlings in T2 in 2015 (2016 in parentheses) decreased by 19.3% (12.6%), 8.7% (7.1%), 21.2% (13.3%), 9.1% (19.6%), 7.9% (25.3%), 40.7% (28.8%), 46.2% (21.1%), and 44.2% (27.5%), respectively. Compared with T3, the same variables in T1 in 2015 (2016 in parentheses) decreased by 34.9% (16.7%), 27.6% (9.8%), 53.6% (19.4%), and 50% (20.5%), 24.1% (31.4%), 55.1% (37.6%), 63.2% (28.2%), and 47.0% (28.7%), respectively. Thus, the inhibitory effect of T3 was the strongest, followed by T2 and T1. In sum, amygdalin and benzoic acid are harmful substances in aged peach orchard soil that inhibit the growth of M. hupehensis Rehd. seedlings.

Effects of Different Fumigants on the Replanted Soil Environment and Growth of Malus hupehensis Rehd. Seedlings

Apple replant disease (ARD) has been reported in all major fruit-growing regions of the world and is often caused by biotic factors (pathogen fungi) and abiotic factors (phenolic compounds). Soil chemical fumigation can kill soil pathogenic fungi; however, the traditionally used fumigant methyl bromide has been banned because of its ozone-depleting effects. There is thus a need to identify greener fumigant candidates. We characterized the effects of different fumigants on the replanted soil environment and the growth characteristics of Malus hupehensis Rehd. seedlings. All five experimental treatments [treatment 1 (T1), metham-sodium; treatment 2 (T2), dazomet; treatment 3 (T3), calcium cyanamide; treatment 4 (T4), 1,3-dichloropropene; and treatment 5 (T5), methyl bromide] promoted significantly the biomass, root growth, and root respiration rate of M. hupehensis seedlings and the ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3–-N) contents of replanted soil. Metham sodium (T1) and dazomet (T2) had stronger effects compared with 1,3-dichloropropene (T4) and calcium cyanamide (T3). At 172 days after T1, the height, root length, and root respiration rate of Malus hupehensis Rehd. seedlings, and the NH4+-N and NO3–-N contents of replanted soil increased by 91.64%, 97.67%, 69.78%, 81.98%, and 27.44%, respectively, compared with the control. Thus, dazomet and metham sodium were determined to be the optimal fumigants for use in practical applications.

Fine root trait-function relationships affected by mycorrhizal type and climate

Root respiration is a critical function of root carbon cycling and accounts for a major component of the global carbon budget. However, the insufficient understanding of the global scaling relationships between root traits and respiration rate (Rr) impedes the accurate prediction of carbon effluxes from roots. Here, we analyzed a dataset of 138 species to unravel and quantify the effects of mycorrhizal type, climate, soil, and phylogenetic structure of species on fine root trait-function relationships. Four commonly measured traits were included: root nitrogen content (RNC), specific root length (SRL), root diameter, and root tissue density. We found that mycorrhizal type and climate affected the relationships between fine root traits and Rr. Specifically, the slopes of SRL-Rr and RNC-Rr relationships for ectomycorrhizal (EM) plants were significantly greater than those for arbuscular mycorrhizal (AM) plants, irrespective of the phylogenetic conservatism or plant growth forms. This finding suggested that EM plants consumed more carbon than AM plants for constructing root tissue structures. In a warmer environment, the SRL-Rr relationship was stronger while the RNC-Rr relationship was weaker, possibly because Rr was limited by enzyme activity at low temperature and by substrate supply at high temperature. Our results highlighted the importance of mycorrhizas in influencing the root trait-function relationships. Thus, incorporating mycorrhizal types into trait-based terrestrial biosphere models may help to more accurately predict the future carbon-climate change feedback.

Effects of dazomet fumigation on growth, biological characteristics of Malus hupehensis seedlings and soil environment

In this study, we examined the effects of dazomet fumigation with different concentrations (0, 0.1, 0.2, 0.4 g·kg-1) on the microbial characteristics of continuous cropping soil and growth of Malus hupehensis seedling in greenhouse and open-field pot. The results showed that all the treatment of dazomet fumigation could promote the growth of M. hupehensis seedlings in continuous cropping soil, with 0.2 g·kg-1 treatment showing the strongest effect. Compared to the control, plant height, stem diameter, dry weight of M. hupehensis seedlings in 0.2 g·kg-1 dazomet fumigation were increased by 192.9% and 91.8%, 72.8% and 60.1%, 196.8% and 195.0%, 138.5% and 130.7%, respectively in greenhouse and open-field. The root related indices (root length, root area, root volume, root respiration rate) were significantly promoted. The activities of SOD, POD, CAT in roots were increased by 114.6% and 118.5%, 123.5% and 107.6%, 164.6% and 175.6% respectively compared with the control, whereas the content of malondialdehyde was significantly lowered. Soil bacterial content, fungal content, copy number of Fusarium oxysporum gene and soil enzyme activity were significantly decreased with the increasing dazomet concentrations. In conclusion, 0.2 g·kg-1 dazomet fumigation could increase the biomass of M. hupehensis seedlings in continuous cropping, improve soil environment, and effectively alleviate the continuous cropping obstacle. Therefore, 0.2 g ·kg-1 dazomet fumigation could be given priority during the reconstruction of old apple orchards.

Specific root respiration of three plant species as influenced by storage time and conditions

AimsSpecific root respiration (RRS) is a key root trait, determining i.e. nutrient foraging and uptake efficiencies. However, a considerable uncertainty exists regarding the effects of storage time and conditions on RRS measurements.MethodsFine root CO2 efflux rates of three plant types (tree seedling Carpinus betulus, legume Pisum sativum, grass Lolium perenne) were measured as depending on storage time (30–1440 min post-rinsing) and conditions (i.e. attached to plant, warm and cold water storage, and storage under dry conditions).ResultsShort-term storage conditions (30 min) had a significant effect on measured RRS rates, in specific, RRS rates of all three species were significantly lower under dry storage. Irrespective of plant species or temperature, storage of excised roots in water did not affect RRS for 300 min,. RRS measurements remained stable for 1 day if roots were stored cold.ConclusionsOur results have important implications on measurement routines of RRS—a generally understudied root trait. Henceforth it seems reasonable to collect roots in the field and transport them, hydrated but even uncooled, to the laboratory for subsequent measurements for at least 300 min post-rinsing.

Effects of Nitrogen Concentration on Root Respiration Rate and Nonstructural Carbohydrates of Walnut Seedlings

Effects of Nitrogen Concentration on Root Respiration Rate and Nonstructural Carbohydrates of Walnut Seedlings

Heterogeneity in short-term allocation of carbon to roots of Pinus tabuliformis seedlings and root respiration under drought stress

The purpose of this study was to investigate the drought response mechanisms that underlie carbon allocation and carbon demand in roots. The correlations between root traits and the amount of carbon (C) allocated to different orders of roots were tested using 13C pulse labeling. The amount of 13C was measured by quantifying the CO2 emitted from respiring roots of Pinus tabuliformis excised 0, 1, 3, 9, 21, 81 and 120 days after labeling. 1) Moderate drought stress significantly increased the root to shoot biomass ratio, the biomass ratio of the first three orders to the 4th- and 5th-order roots, and the cumulative root length and root area of the 1st-order roots. 2) 120 days after labeling, 13C amount allocated to 1st- and 2nd-order roots was significantly higher in all drought stress treatments than adequate water supply treatment, with the exception of 13C in 1st-order roots undergoing the severe drought stress treatment. Root respiration was significantly and positively correlated with 13C in the 1st- and 2nd-order roots in all drought stress treatments. 3) The 13C ratios of all the droughted treatments vs water supply treatment were significantly higher in the 1st- and 2nd-order roots than in the 4th- and 5th-order roots, with the exception of the 1st-order roots in the most severe drought treatment. Drought stress elevated C demand in lower-order roots by increasing the lower-order root respiration rate and by expanding the photosynthate allocation to the fine roots to enhance their structural growth.

Unraveling response mechanism of photosynthetic metabolism and respiratory metabolism to uranium-exposure in Vicia faba

As a natural radionuclide, uranium (U) has obvious phytotoxicity, the purpose of this study is to unravel the response mechanism of U on photosynthetic and respiratory metabolism in plants. Therefore, 14-day-old Vicia faba seedlings were exposed to 0–25 μM U during 72 h. U effects on growth parameters, physiological parameters of plants, and potential phytotoxicity mechanism were investigated by physiological analysis, and metabolome and transcriptome data. U significantly inhibited photosynthesis and respiration of plants. In metabolome analysis, 53 metabolites related to carbohydrate metabolism were identified (13 up-regulated, 12 down-regulated). In transcriptome analysis, U significantly inhibited the expression of photoreactive electron transport chain (up: 0; down: 31), Calvin cycle (up: 0; down: 12) and photorespiration pathway genes (up: 0; down: 8). U significantly inhibited the expression of cellular energy metabolic pathways genes (e.g., glycolysis, TCA cycle, and oxidative phosphorylation pathways) (up 8, down 18). We concluded that U inhibited the expression of genes involved in the photosynthetic metabolic pathway, which caused the decrease of photosynthetic rate. Meanwhile, U inhibited the expression of the electron transport chain genes in the mitochondrial oxidative phosphorylation pathway, which leads to the abnormal energy supply of cells and the inhibition of root respiration rate.

Dehydration during storage affects carbohydrate metabolism and the accumulation of non-sucrose carbohydrates in postharvest sugarbeet roots

Sugarbeet roots produced in cold climates are stored in large piles prior to processing and are cooled by ambient winter air. These storage conditions dehydrate roots, causing root respiration rate and sucrose loss in storage to increase. Dehydration likely alters carbohydrate metabolism due to a greater demand for respiratory substrates and may affect the accumulation of non-sucrose carbohydrates that impede processing. However, effects of dehydration on carbohydrate metabolism of postharvest sugarbeet roots have not been studied. Research, therefore, was conducted to determine the effect of mild and severe dehydration on concentrations of the non-sucrose carbohydrates, glucose, fructose, and raffinose, their biosynthetic precursors, and the concentrations of metabolites that are intermediates in respiratory sucrose catabolism through glycolysis and the TCA cycle. Roots were stored at 85 and 40% relative humidity for up to 28 d to generate mildly and severely dehydrated roots typical of roots in the interior and exterior of storage piles. Severe dehydration was associated with reductions in raffinose, galactinol, glucose 6-phosphate, fructose 6-phosphate, phosphoenolpyruvate, and pyruvate concentrations, and increases in inositol and malate concentrations, while mild dehydration was associated with increased raffinose concentration. Concentrations of other glycolytic and TCA cycle intermediates, as well as the invert sugars, glucose and fructose, were largely unaffected by dehydration. From these results, it is concluded that raffinose accumulation and biosynthesis is highly sensitive to root dehydration and that carbohydrate metabolism through glycolysis is altered by dehydration, presumably to provide increased substrates for respiration. Overall, this research provides new insight into the impact of environmental conditions within storage piles on raffinose accumulation and the mechanisms by which dehydration accelerates sucrose loss in stored sugarbeet roots. • Raffinose accumulates in roots stored under mildly dehydrating conditions. • Raffinose content declines in roots stored under severely dehydrating conditions. • Severe dehydration alters flux through glycolysis to support elevated respiration. • Invert sugar concentration is not significantly altered by dehydration in storage.

Effects of residual apple fermentation products on continuous cropping soil environment and the growth of Malus hupehensis Rehd. Seedlings

Effects of fermented apple products on the growth of continuous cropping Malus hupehensis Rehd. seedlings and soil environment were examined in a pot experiment to provide theoretical basis for apple replant disease. There were four treatments, the replanted soil (control, CK), sterilized replant soil (T1), replanted soil applied with apple fermentation products (T2), and replanted soil applied with sterilized apple fermentation products (T3). The results showed that T1, T2 and T3 significantly promoted seedlings growth, with better performance of T1 and T2. T1 increased root respiration rate, plant height, ground diameter, fresh weight, and dry weight by 107.3%, 50.6%, 42.4%, 171.7%, 225.3%, while T3 increased them by 104.4%, 50.6%, 42.3%, 171.8%, 225.5%, respectively over CK. T2 and T3 increased the activities of nutrient conversion-related enzymes in continuous cropping soil. T2 increased the activities of catalase, urease, neutral phosphatase and sucrase by 44.5%, 169.5%, 23.4%, 169.3%, while T3 increased them by 23.7%, 72.6%, 1.5%, 121.5%, respectively. Catalase and sucrase activities under T1 treatment did not differ from that in CK, whereas their urease and neutral phosphatase activities were reduced by 40.8% and 41.6%, respectively. The contents of ammonium, nitrate, available phosphorus and available potassium in T2 soil were increased by 18.6%, 50.6%, 14.0% and 36.7% respectively. T3 only increased the content of available nitrogen, with ammonium and nitrate being increased by 7.0% and 23.6% respectively. The content of available nutrients of T1 decreased compared with CK. T1 and T2 significantly reduced the abundance of actinomycetes and fungi in soil and increased that of bacteria. The abundance of bacteria, actinomycetes and fungi in T3 treatment were all significantly decreased. Results of real-time fluorescence quantitative PCR analysis showed that the gene copies of Fusarium proliferaturn, F. moniliforme, F. solani and F. oxysporum in T1, T2 and T3 were ecreased to different degrees. Apple fermented product could inhibit soil pathogen in replanted orchard soil, improve soil environment, and promote seedling growth, which could be used to alleviate the apple replant disease.

Root respiration and its temperature sensitivity at various growth stages of winter wheat in the Loess Plateau, Northwest China

Understanding the effects of crop growth stage on root respiration (RA) and its temperature sensitivity (Q10) has important theoretical and practical significance for enriching the carbon cycle theory of cropland. In a rain-fed agricultural ecosystem on the Loess Plateau, soil respiration rates were in situ measured in adjacent bare soil (soil microbial respiration, RH) and non-fertilized winter wheat (soil respiration, RS=RA+RH) with an automated CO2 flux system from 2009 to 2014 to investigate the effect of growth stage on RA and Q10. The results showed that net photosynthetic rate in the seedling, elongating, filling, and the ripening stage was 5.9, 14.4, 12.0, and 4.4 μmol·m-2·s-1, and the corresponding root activity was 51.0, 100.8, 84.4, and 31.8 μg·g-1·h-1, respectively. RA differed significantly among different growth stages, which was 0.26, 0.67, 0.91, and 0.56 μmol·m-2·s-1. The variation of RA was closely related with soil moisture, soil temperature, net photosynthetic rate, and root activity, which presented parabolic, exponential, linear, and linear models respectively. Furthermore, Q10 in each stage was 2.61, 4.88, 2.26, and 6.93, respectively, the variation of which was closely related with net photosynthetic rate, root activity, and soil moisture, with the contribution rate of root respiration being 29%, 53%, 46% and 31%, respectively. In conclusion, in addition to environmental factors, growth period of winter wheat was an important factor affecting RA and Q10.

Does plant biomass partitioning reflect energetic investments in carbon and nutrient foraging?

Abstract Studies of plant resource‐use strategies along environmental gradients often assume that dry matter partitioning represents an individual's energy investment in foraging for above‐ versus below‐ground resources. However, ecosystem‐level studies of total below‐ground carbon allocation (TBCA) in forests do not support the equivalency of energy (carbon) and dry matter partitioning, in part because allocation of carbon to below‐ground pools and fluxes that are not accounted for by root biomass (e.g., mycorrhizal hyphae, rhizodeposition; root and soil respiration) can be substantial. Here, we apply this reasoning to individual plants in controlled environments and ask whether dry matter partitioning below‐ground (root mass fraction, RMF) accurately reflects TBCA in studies of optimal partitioning theory. We quantified the relationship between RMF and TBCA in individual plants, using 311 observations from 51 studies that simultaneously measured both allocation variables. Our analysis included tests of whether the RMF‐TBCA relationship depended on mutualist soil microbes, plant growth form, age and study methodology including isotopic pulse–chase duration. We found that RMF was a poor proxy for below‐ground energy investment. This disconnect of RMF and TBCA was driven in part by plants of low RMF (<0.4) exhibiting significantly higher rates of root and soil respiration per unit root mass than plants of high RMF. Root colonization by mutualist microbes, including arbuscular mycorrhizal fungi and nitrogen‐fixing bacteria, increased TBCA by 5%–7%, and TBCA was lower in grasses than other species by 9%–16%. These patterns were evident for relationships assessed both within and between species. We conclude that optimal partitioning studies of plants along environmental gradients are likely to underestimate plant energy allocation below‐ground if the C costs of root and soil respiration are ignored, especially under conditions favouring low RMF. Because energy rather than biomass better reflects how assimilated C supports fitness, this omission of respired C suggests existing studies misrepresent the significance of below‐ground processes to plant function. A free Plain Language Summary can be found within the Supporting Information of this article.