Root Respiration Rate Research Articles

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.

Effects of controlling soil moisture regime based on root-sourced signal characteristics on yield formation and water use efficiency of winter wheat

The upper and lower limits of soil water content (SWC) determine the quota and time of regulated deficit irrigation (RDI). The drought resistance of plant varies with growth stages. Therefore, it is very difficult to determine the appropriate upper and lower limits of soil water under different growth stages. This study was first conducted to quantify the non-hydraulic root-sourced signals (nHRS), hydraulic root-sourced signals (HRS) and photosynthetic rate (PN) characteristics of winter wheat in progressively drying soil. Based on the characteristics of root-sourced signals and PN in plant, 3 water control modes were designed: CK (full irrigation, SWC when nHRS occurs was used as the lower limit of irrigation), W1 (SWCs when nHRS occurs and PN decreases significantly were used as the upper and lower limits of irrigation, respectively) and W2 (SWCs when PN decreases significantly and HRS occurs were used as the upper and lower limits of irrigation, respectively). The results showed that W1 and W2 both lowered plant height and leaf area of wheat. W1 had similar PN to CK, but W2 had significantly lower PN compared with CK. W1 and W2 lowered transpiration rates (Tr) and increased leaf instantaneous water use efficiency (WUEleaf) of plant compared with CK. After flowering, W1 lowered root respiration rate and increased accumulated dry matter after flowering (ADM) and pre-flowering dry matter remobilization (DMR) of wheat, and W2 had lower ADM compared to CK. At maturity, W1 had similar yield and higher harvest index compared to CK, but W2 reduced them. W1 significantly reduced irrigation water and improved WUE compared with W2 and CK. In conclusion, controlling suitable soil moisture (W1) based on root-sourced signal characteristics of plant helps to regulate the consumption and distribution of water and photosynthate, thus increasing water use efficiency (WUE) and irrigation water use efficiency (IWUE) of winter wheat.

Effects of nitrogen addition on tree root traits.

Atmospheric nitrogen deposition has complex effects on individual plants and terrestrial ecosystems. We synthesized results from 39 published papers (16 papers in English and 23 papers in Chinese) and conducted a meta-analysis to evaluate the general responses of tree root traits to nitrogen addition, and further analyzed the difference of N-induced results between English papers and Chinese papers. Our results showed that N addition significantly increased fine root diameter (+6.7%), fine root N content (+8.9%), and root respiration rate (+17.5%), but did not affect fine root biomass, fine root length, specific root length, fine root C content, and fine root C:N ratio. Different climatic zone and fertilizer types had different effects on the experimental results. In addition, experimental results published in English papers were generally more significant than those in Chinese papers. We summarized the general effects of N addition on tree root systems, and further analyzed the mechanisms underlying the effects of N enrichment on forest ecosystem carbon cycle.

Leaf Senescence can be Induced by Inhibition of Root Respiration

Constituting the last stage of leaf development, leaf senescence is a complicated process that involves many senescence-associated genes, and numerous factors can induce leaf senescence. To elucidate the relationship between root respiration and leaf senescence, we treated the roots of Alhagi sparsifolia with nitrogen (N2) with the purpose of inhibiting root respiration (denoted as the N2 group). The results showed that compared with the control group, N2 treatment decreased the root respiration rate, chlorophyll (Chl) a, Chl b and carotenoid (Car) contents, the Chl/Car ratio, stomatal conductance (Gs), photosynthesis rate (Pn), maximum photochemical efficiency (φPo), and performance index on absorption basis (PIabs). In contrast, it increased leaf proline (Pro), malonaldehyde (MDA), and abscisic acid (ABA) contents. Moreover, no significant decline of Chl a/b was found in the N2 group. The results of the present work implied that leaf senescence can be induced by root respiration inhibition. Root respiration inhibition may result in ABA accumulation in leaves and thus induce leaf senescence. Another mechanism may be that root respiration inhibition resulted in the decrease of root water uptake, which subsequently led to water stress-induced leaf senescence. Root respiration inhibition-induced leaf senescence is a highly regulated process that is similar to natural senescence. In this process, no significant decline of Chl a/b was found. Root respiration inhibition-induced senescence is a “mild” process, in which most of the function of the photosynthetic apparatus performed well. Carotenoids play a key photoprotective role in leaf senescence. Overall, root respiration inhibition accelerated leaf senescence. In both types of senescence (root respiration induced senescence and natural senescence), the photosynthetic apparatus maintains a good performance until the last stage of senescence.

LeNRT1.1 Improves Nitrate Uptake in Grafted Tomato Plants under High Nitrogen Demand.

Grafting has become a common practice among tomato growers to obtain vigorous plants. These plants present a substantial increase in nitrogen (N) uptake from the root zone. However, the mechanisms involved in this higher uptake capacity have not been investigated. To elucidate whether the increase in N uptake in grafted tomato plants under high N demand conditions is related to the functioning of low- (high capacity) or high-affinity (low capacity) root plasma membrane transporters, a series of experiments were conducted. Plants grafted onto a vigorous rootstock, as well as ungrafted and homograft plants, were exposed to two radiation levels (400 and 800 µmol m−2 s−1). We assessed root plasma membrane nitrate transporters (LeNRT1.1, LeNRT1.2, LeNRT2.1, LeNRT2.2 and LeNRT2.3) expression, Michaelis‒Menten kinetics parameters (Vmax and Km), root and leaf nitrate reductase activity, and root respiration rates. The majority of nitrate uptake is mediated by LeNRT1.1 and LeNRT1.2 in grafted and ungrafted plants. Under high N demand conditions, vigorous rootstocks show similar levels of expression for LeNRT1.1 and LeNRT1.2, whereas ungrafted plants present a higher expression of LeNRT1.2. No differences in the uptake capacity (evaluated as Vmax), root respiration rates, or root nitrate assimilation capacity were found among treatments.

Effect of temperature on growth of roots of juvenile asparagus (Asparagus officinalis L.) plants

It is difficult to observe the growth of root system and to measure its morpho-physiological parameters when asparagus is grown in the open field. Therefore, different from that cultivation method, juvenile asparagus plants were cultivated in aeroponics in greenhouse in this study. Under such conditions, investigation on the growth of roots became easier since it allowed nondestructive observation and examination of root system of asparagus. Seven asparagus cultivars from countries differing in climatic conditions were used in the study. When stems of juvenile plants were fully developed, their storage roots were taken for root respiration rate (R(r)) measurement at three temperatures: 10, 20 and 30°C. Regressions between R(r) and temperatures were analyzed for each cultivar. From these results, soil temperature was estimated based on the standard root respiration rate (R(rs)) observed from the experiment. Significant difference was found on R(r) of juvenile plants among cultivars at three temperatures. Reaction of roots to temperature changes also varied at different degrees among cultivars. Some cultivars were shown to be more suitable for growing at higher soil temperatures, indicating that the others should be cultivated in much lower soil temperature if R(r) needed to be equal to R(rs).

Relationship of root biomass and soil respiration in a stand of deciduous broadleaved trees\u2014a case study in a maple tree

BackgroundIn ecosystem carbon cycle studies, distinguishing between CO2 emitted by roots and by microbes remains very difficult because it is mixed before being released into the atmosphere. Currently, no method for quantifying root and microbial respiration is effective. Therefore, this study investigated the relationship between soil respiration and underground root biomass at varying distances from the tree and tested possibilities for measuring root and microbial respiration.MethodsSoil respiration was measured by the closed chamber method, in which acrylic collars were placed at regular intervals from the tree base. Measurements were made irregularly during one season, including high temperatures in summer and low temperatures in autumn; the soil’s temperature and moisture content were also collected. After measurements, roots of each plot were collected, and their dry matter biomass measured to analyze relationships between root biomass and soil respiration.ResultsApart from root biomass, which affects soil’s temperature and moisture, no other factors affecting soil respiration showed significant differences between measuring points. At each point, soil respiration showed clear seasonal variations and high exponential correlation with increasing soil temperatures. The root biomass decreased exponentially with increasing distance from the tree. The rate of soil respiration was also highly correlated exponentially with root biomass. Based on these results, the average rate of root respiration in the soil was estimated to be 34.4% (26.6~43.1%).ConclusionsIn this study, attempts were made to differentiate the root respiration rate by analyzing the distribution of root biomass and resulting changes in soil respiration. As distance from the tree increased, root biomass and soil respiration values were shown to strongly decrease exponentially. Root biomass increased logarithmically with increases in soil respiration. In addition, soil respiration and underground root biomass were logarithmically related; the calculated root-breathing rate was around 44%. This study method is applicable for determining root and microbial respiration in forest ecosystem carbon cycle research. However, more data should be collected on the distribution of root biomass and the correlated soil respiration.

PGPR Reduce Root Respiration and Oxidative Stress Enhancing Spartina maritima Root Growth and Heavy Metal Rhizoaccumulation.

The present study aims to unravel ecophysiological mechanisms underlying plant-microbe interactions under natural abiotic stress conditions, specifically heavy metal pollution. Effect of plant growth promoting rhizobacteria (PGPR) bioaugmentation on Spartina maritima in vivo root respiration and oxidative stress was investigated. This autochthonous plant is a heavy metal hyperaccumulator cordgrass growing in one of the most polluted estuaries in the world. The association with native PGPR is being studied with a view to their biotechnological potential in environmental decontamination. As a novelty, the oxygen-isotope fractionation technique was used to study the in vivo activities of cytochrome oxidase (COX) and alternative oxidase (AOX) pathways. Inoculated plants showed decreased antioxidant enzymatic activities and in vivo root respiration rates. The reduction in respiratory carbon consumption and the stress alleviation may explain the increments observed in S. maritima root biomass and metal rhizoaccumulation after inoculation. For the first time, plant carbon balance and PGPR are interrelated to explain the effect of rhizobacteria under abiotic stress.

Effect of Carnauba Wax–Based Coating Containing Glycerol Monolaurate on Decay and Quality of Sweet Potato Roots during Storage

Because of high water loss and rot observed in postharvest sweet potato ( Ipomoea batatas (L.) Lam.) roots, a carnauba wax (CW)-based nanoemulsion without or with glycerol monolaurate (CW-GML) was developed by a high-energy emulsification approach. The effects of the two coatings on decay, respiration rate, weight loss, surface color, total soluble sugar, and starch content as well as the sensory quality of sweet potato roots were investigated during storage at 20°C for 50 days. Compared with the control treatment (water) and CW coating alone, CW-GML coating exhibited higher emulsion stability and antifungal activity, and treatment resulted in a uniform and continuous coating on roots. The CW-GML and CW coatings both effectively reduced root weight loss and respiration rate and inhibited decay incidence compared with control roots during storage. The CW-GML coating showed markedly stronger inhibition of root rot than the CW coating. Both the CW-GML and CW coatings promoted an increase in root sweetness but did not negatively impact perceived flavor. The overall results demonstrate that the CW-GML coating holds great promise as an effective postharvest technology to preserve food quality and extend shelf life of sweet potato roots.

Increased soil respiration in response to experimentally reduced snow cover and increased soil freezing in a temperate deciduous forest

Winter snowpack in seasonally snow-covered regions plays an important role in moderating ecosystem processes by insulating soil from freezing air temperatures. However, climate models project a decline in snowpack at mid and high latitudes over the next century. We conducted a snow removal experiment in a temperate deciduous forest at Harvard Forest in Massachusetts, USA to quantify the effects of a reduced winter snowpack and increased soil freezing on total soil respiration and its bulk (i.e. heterotrophic) and root-rhizosphere components. Snow removal increased soil freezing severity by more than three-fold, which resulted in a 27.6% increase in annual total soil respiration (p = 0.058). Across our plots and years of this study, we found that the severity, rather than simply the presence of soil freezing, was the primary driver of the soil respiration response to reduced winter snowpack. Bulk soil respiration made the largest contribution to total soil respiration with root-rhizosphere respiration contributing up to 26.1 ± 6.5% of total soil respiration across plot types and years. Snow removal significantly increased fine root mortality (p = 0.03), which was positively correlated with soil frost depth and duration (p = 0.068, $${\text{R}}_{{{\text{LMM}}(m)}}^{ 2}$$ = 0.46), rates of total soil respiration (p = 0.075; $${\text{R}}_{{{\text{LMM}}(m)}}^{ 2}$$ = 0.27) and the contribution of root-rhizosphere respiration to total soil respiration (p = 0.004; $${\text{R}}_{{{\text{LMM}}(m)}}^{ 2}$$ = 0.58). We conclude that increased rates of soil respiration in response to soil freezing are driven by plant-mediated processes, whereby soil frost-induced root mortality stimulates respiration through decomposition of root necromass with additional enhancements possibly related to priming of soil organic matter decomposition and elevated rates of root respiration associated with growth.

Tillage and deficit irrigation strategies to improve winter wheat production through regulating root development under simulated rainfall conditions

Knowledge of rooting systems and soil water status across rooting zones is important for stabilizing agricultural productivity in the semi-arid regions of China. In the present study, a mobile rainproof shelter trial was performed to find out the effects of cultivation mode on the temporal and spatial root growth distribution, soil water content, root respiration rate, and grain yield during 2015–2016 and 2016–2017 growing seasons. The two cultivation modes were: (1) the ridge furrow (RF) rainfall harvesting technique; and (2) traditional flat planting (TF). In addition, three simulated rainfall (1: 275, 2: 200, 3: 125 mm) and two deficit irrigation (150, 75 mm) levels were used. Our results showed that different cultivation modes with simulated precipitation levels significantly improved moisture content for wheat growth, improved root growth, and provided favourable conditions for higher wheat production. The RF150 treatment with 200 mm rainfall significantly increased morphology of the wheat rooting system, especially in the top 40 cm soil layer compared with TF cultivation. The RF150 treatment significantly increased root dry weight (47%), root tissue density (6.7%), root fineness (4.8%), root length ratio (20.3%), root mass ratio (27.3%), and grain yield (18.9%) of wheat at 200 mm rainfall than that of TF2150 treatment. Root weight density, root length density, root surface area density, and root diameter were significantly higher under RF150 treatment with 200 mm and 275 mm precipitation in the 40 cm soil layer and reached maximum values at the flowering stage. The root dry weight, root respiration rate, and grain yield were significantly improved under RF2150 treatment, but there were no significant differences when the rainwater increased from 200 to 275 mm under both cultivation modes. Therefore, we suggested that the RF2150 treatment is a suitable water saving strategy to improve temporal and spatial root growth distribution, resulting in higher grain yield in a dry-land farming system.

Differential effect of the nitrogen form on the leaf gas exchange, amino acid composition, and antioxidant response of sweet pepper at elevated CO2

It is well known that NH4+ used as the sole N source is toxic, and that the degree of toxicity depends on environmental factors. However, far too little is known about the effect of the use of different NO3−/NH4+ ratios when the CO2 concentration [CO2] is high. Therefore, this work evaluates the extent to which the optimal form of the N-supply can increase growth at elevated CO2. Sweet pepper plants (Capsicum annuum L., cv. Melchor) were grown at ambient or elevated [CO2] (400 or 800 µmol mol−1) with a nutrient solution containing different NO3−/NH4+ ratios (concentration percentages of 100/0, 100/0 plus foliar urea (100/U), 90/10, 50/50, or 25/75). The results show that a low dose of NH4+ (90/10) in combination with the elevated [CO2] had beneficial effects on the plants. These plants had greater growth, root respiration rates, water-use efficiency, and chlorophyll fluorescence. Additionally, total phenolic compounds and ascorbate peroxidase activity were affected differentially, while the amino acid profile was also altered. This study reveals the strong interaction between the N form and the [CO2] in relation to the uptake of N, which requires further analysis to establish better nutritional strategies for the future.

Taxonomic and Functional Responses of Soil Microbial Communities to Annual Removal of Aboveground Plant Biomass.

Clipping, removal of aboveground plant biomass, is an important issue in grassland ecology. However, few studies have focused on the effect of clipping on belowground microbial communities. Using integrated metagenomic technologies, we examined the taxonomic and functional responses of soil microbial communities to annual clipping (2010–2014) in a grassland ecosystem of the Great Plains of North America. Our results indicated that clipping significantly (P < 0.05) increased root and microbial respiration rates. Annual temporal variation within the microbial communities was much greater than the significant changes introduced by clipping, but cumulative effects of clipping were still observed in the long-term scale. The abundances of some bacterial and fungal lineages including Actinobacteria and Bacteroidetes were significantly (P < 0.05) changed by clipping. Clipping significantly (P < 0.05) increased the abundances of labile carbon (C) degrading genes. More importantly, the abundances of recalcitrant C degrading genes were consistently and significantly (P < 0.05) increased by clipping in the last 2 years, which could accelerate recalcitrant C degradation and weaken long-term soil carbon stability. Furthermore, genes involved in nutrient-cycling processes including nitrogen cycling and phosphorus utilization were also significantly increased by clipping. The shifts of microbial communities were significantly correlated with soil respiration and plant productivity. Intriguingly, clipping effects on microbial function may be highly regulated by precipitation at the interannual scale. Altogether, our results illustrated the potential of soil microbial communities for increased soil organic matter decomposition under clipping land-use practices.

Soil respiration versus vegetation degradation under the influence of three grazing regimes in the Songnen Plain

AbstractUnderstanding the effects of ongoing vegetation degradation (due to grazing pressure) on soil respiration provides a basis for managing grazing to improve sustainability of grassland ecosystems in the context of climate change. In a 2‐year field experiment in a meadow ecosystem, vegetation, soil properties, and root and microbial respiration of 2 dominant communities (Leymus chinensis and Chloris virgata) were examined along a vegetation degradation sequence caused by varying grazing pressures. Aboveground biomass, belowground net primary productivity, litter mass, and microbial biomass carbon significantly decreased as ground cover was reduced. For 2 community types, from light degradation to severe degradation (SD), soil organic carbon (SOC), soil total nitrogen, and total phosphorus concentrations decreased by 14.1–15.4%, 10.9–12.3%, and 10.7–11.9%, respectively; and soil bulk density and pH increased by 9.1–9.3% and 4.6–5.2%, respectively. Over 2 years, from light degradation to SD in 2 communities, annual mean root and microbial respiration rate significantly decreased by 35.9–43.5% and 28–34.4%, respectively. Root respiration was more sensitive to vegetation degradation in C. virgata communities compared with L. chinensis communities. However, temperature sensitivity (Q10) for root and microbial respiration did not significantly change as vegetation degraded. These results indicated that (a) vegetation degradation could drive significant soil degradation in this meadow; (b) vegetation degradation restrained soil CO2 efflux, but more largely decreased biomass carbon input into soil, which finally reduced SOC concentration; and (c) vegetation degradation would not change the response of soil CO2 efflux to climate change. To increase SOC storage and maintain grassland sustainability, grazing exclusion was suggested for restoring vegetation in SD sites, with a stocking rate &lt; 2 sheep·ha−1 or rotational grazing recommended. Finally, overseeding with L. chinensis and legumes should enhance forage and livestock production, and soil carbon and nitrogen sequestration, thus preserving grassland sustainability in this meadow ecosystem.

INCREASED CARBON LOSS VIA ROOT RESPIRATION AND IMPAIRED ROOT MORPHOLOGY UNDER FREE-AIR OZONE ENRICHMENT ADVERSELY AFFECT RICE (ORYZA SATIVA L.) PRODUCTION

SUMMARYThe increasing tropospheric ozone concentration [O3] strongly affects plant growth. However, the response of belowground processes in rice (Oryza sativa L.) systems to higher O3 is not well understood. The grain production, belowground biomass partitioning, root morphology and activity of rice (cv. Shanyou 63) were investigated in a free-air O3 enrichment platform at four key growth stages. Elevated O3 (EO3, 50% above the ambient O3) significantly decreased the grain yield and total biomass at the grain milky mature stage, root biomass at the tillering stage and root to shoot ratios (RRS) at the flowering and grain filling stages. The effects of EO3 on root morphology and activity varied among rice growth stage. EO3 significantly decreased root length, density, area, diameter and volume at the flowering stage, but EO3 significantly decreased various root morphological indices at the tillering, grain filling and milky mature stages. EO3 significantly increased the specific root respiration rate (root activity) and root respiration rate (autotrophic respiration) at grain filling and milky mature stages. Higher root autotrophic respiration and lower RRS in response to EO3 would reduce allocation of assimilated carbon to root growth, adversely affecting rice productivity. Our findings are critical for understanding the O3-induced impairment of belowground processes and carbon cycling in rice cropping systems and breeding of O3-tolerant cultivars under higher [O3] scenarios.

Effects of different phosphorus application rates on growth, 15N-urea absorption, and utilization characteristics of pear rootstocks.

Three kinds of potted one-year-old pear rootstocks (Pyrus calleryana, P. pashia, and P. xerophila) and 15N trace technique were used to examine the effects of different phosphorus application rates (P0, P1, P2, P3 and P4 equivalent to 0, 50, 100, 150 and 200 kg·hm-2 P2O5, respectively) on plant growth and the characteristics of 15N-urea absorption and utilization. The results showed that, with the increases of phosphorus levels, plant height, ground diameter, dry mass, root surface area, root length, number of root tips, root activity, root respiration rate, Ndff values, and nitrogen use efficiency of rootstocks first increased and then decreased. However, the range of rise and fall of different rootstocks were distinct, and each index reached the highest level at different phosphorus levels. The plant height, diameter, dry mass of P. xerophila were the highest under the same phosphorus level, followed by P. pashia, and P. calleryana was the lowest. The root architecture parameters and root respiration rate showed the same trend, but Ndff values and nitrogen use efficiency performed different. Under different phosphorus levels, each index of P. xerophila reached the highest level at P3, but those of P. pashia and P. calleryana appeared at P2 and P1 rates, respectively. The Ndff values in stem were the highest among different organs of rootstocks at diffe-rent phosphorus levels, and the highest nitrogen use efficiency of P. xerophila, P. pashia and P. calleryana was 9.6%, 8.9% and 8.3%, respectively. The variations of plant growth and N absorption and utilization of different pear rootstocks across different phosphorus levels indicated that phosphorus fertilizer should be carry out reasonably in practice and give full consideration of phosphorus demands of plants.

Multi‐dimensional patterns of variation in root traits among coexisting herbaceous species in temperate steppes

Abstract Characterizing patterns of variation in plant traits across species and environmental gradients is critical for understanding performance of species in ecosystems. One‐dimensional pattern of variation has been demonstrated in leaf traits, which is known as the leaf economic spectrum. However, it is unclear whether such a spectrum exists for root traits. For roots of 15 species from temperate grasslands, we determined respiration rate, relative growth rate, life span and 10 morphological, chemical and anatomical root traits. We further evaluated pairwise and multiple‐trait relationships by Pearson's correlation and principle component analysis including phylogenetic contrasts. We found that root functions were related to three clusters of variation. Root respiration rate and relative growth rate were positively correlated with average root diameter (AD), but they were negatively correlated with specific root length (SRL). In contrast, root life span was not correlated with AD, but it was positively correlated with SRL. These results are inconsistent with the presumption of the root economic spectrum. The principle components analysis revealed a multi‐dimensional pattern of variation in root traits among the 15 coexisting herbaceous species. Moreover, species within the same phylogenetic clades tended to have similar root trait syndromes. Most of the root traits exhibited a significant phylogenetic signal. Synthesis. Our results do not support a one‐dimensional root economic spectrum in the coexisting herbaceous species of temperate grasslands. In contrast, the pattern of variation in root traits was multi‐dimensional. We further demonstrated that species in different phylogenetic clades possess diverse root trait syndromes for efficient resource acquisition. Our findings provide a next step in understanding root functions and plant strategies in temperate grasslands.

Effect of sowing time and seeding rate on yield components and water use efficiency of winter wheat by regulating the growth redundancy and physiological traits of root and shoot

A field experiment was conducted to explore the effect of different sowing time and seeding rate on yield components and water use efficiency (WUE) of winter wheat by regulating the growth redundancy and physiological traits of root and shoot. Winter wheat sowing was performed on Oct.12 (T1), Oct.22 (T2), Nov.3 (T3), respectively. There were three treatments of different seeding rates, i.e. 112.5 kg hm−2 (D1), 150 kg hm−2 (D2) and 225 kg hm−2(D3) in each sowing time. The results showed that sowing time and seeding rate significantly influenced the morphological and physiological characteristics of winter wheat. Plant height, ineffective tiller number, leaf area and root biomass decreased significantly along with the delay of sowing date. Plant height, ineffective tiller number and root biomass increased significantly and leaf area decreased significantly with increasing seeding rate. Under the same seeding rate condition, T1 had the highest number of ineffective tiller, and T3 had the lowest one. Delayed sowing (T2 and T3) increased significantly root activities and leaf photosynthetic rate (Pn) in the late growing stage, and decreased significantly root respiration rate (Rroot) per unit area of wheat. In the same sowing time treatment, root activities and leaf Pn decreased significantly and Rroot increased significantly with the increase of seeding rate; however, seeding rate had no effect on root activity and leaf Pn in T3 treatment. Grain yield decreased significantly in T1 and increased significantly in T3 with the increase of seeding rate, and it was the highest in D2 and the lowest in D1 in T2 treatment. Delayed sowing lowered significantly soil water consumption of crop. Under the same sowing time condition, soil water consumption increased significantly as seeding rate increased. WUE decreased significantly with the increase of seeding rate in T1and T2 treatments. In two test years, T2D2 had highest grain yield and WUE, and T3D1 had lowest grain yield and WUE. The interaction of sowing time and seeding rate also had significant effect on soil water consumption, grain yield and WUE. It is clear that appropriate sowing time and seeding rate (T2 Treatmeat) can increase grain yield and WUE of winter wheat by regulating the growth redundancy and physiological traits of root and shoot, but excessive reduction of vegetative organs (T3 Treatmeat) can affect crop production.

Nitrogen addition decreased soil respiration and its components in a long-term fenced grassland on the Loess Plateau

Knowledge of the impact of N enrichment on soil respiration components is critical for understanding carbon (C) cycling and its feedback processes with climate change. We conducted three N level addition experiments, control (CK, 0 g N m−2yr−1), low nitrogen addition (LN, 10 g N m−2yr−1), and high nitrogen addition (HN, 20 g N m−2yr−1)) to investigate the response of microbial and root respiration to N enrichment in a long-term fenced grassland on the Loess Plateau of China. Compared to the control, both the LN and HN treatments generally decreased soil respiration and its two components for both years. Under N addition, the decreased rates of root respiration and microbial respiration were significantly and positively correlated with the monthly root production and soil microbial biomass C, respectively. Nitrogen addition decreased the Q10 values of root and microbial respiration, with the reduction more pronounced in root respiration. Overall, our results suggest that N enrichment may reduce the soil C loss through CO2 emissions. With global warming, soil C loss will be less due to the lower Q10 values of root and microbial respiration on the Loess Plateau of China under future scenarios of N deposition.

Effects of soil warming on specific respiration rate and non-structural carbohydrate concentration in fine roots of Chinese fir seedlings

A field mesocosm experiment with Chinese fir (Cunninghamia lanceolata) seedlings was conducted in Chenda State-Owned Forest Farm, Sanming, Fujian Province. The effects of soil warming (ambient +5 ℃) on specific respiration rates and nonstructural carbohydrate (NSC) concentrations in fine roots were measured by the ingrowth core method, to reveal the belowground responses and the adaptability of Chinese fir to global warming. The results showed that soil warming caused significant changes of fine root NSC in the second year. The NSC and starch concentrations in 0-1 mm fine roots, and the NSC and sugar concentrations in 1-2 mm fine roots decreased signifi-cantly in January. The NSC, sugar and starch concentrations in 0-1 mm roots and the starch concentration in 1-2 mm roots increased in July. Soil warming had no significant effect on fine root NSC in the third year. The specific root respiration rate of the 0-1 mm roots significantly increased in July of the second year but significantly decreased in July of the third year in the warmed plots. Compared with the 0-1 mm roots, soil warming had no significant effect on the specific root respiration rate of the 1-2 mm roots. In conclusion, the responses of fine root respiration to soil warming depended on the duration of warming. Fine root respiration partly acclimated to soil warming with increasing duration of soil warming, which kept fine root NSC being relatively stable.