Non-structural Carbohydrate Content Research Articles

Fine root nutrient foraging ability in relation to carbon availability along a chronosequence of Chinese fir plantations

In the quest to reveal the mechanisms of yield decline during the late growth stage of tree plantations, there remains a knowledge gap regarding the changes of the fine root nutrient foraging strategies during stand development and their underlying mechanisms. Fine root traits were studied using the soil core method in a typical chronosequence of six first-generation Chinese fir plantations: 2- (recently planted), 7- (sapling), 16- (middle-aged), 21- (pre-mature), 40- (mature), and 88-year-old (over-mature) stands. For the fine roots of the 0–1 mm diameter class, the specific root length (SRL), specific root area (SRA), and specific root tip density (SRT) decreased with stand age, indicating that the fine root nutrient foraging ability decreased in older stands. Fine root nitrogen (N) concentration decreased with stand age, but it significantly increased by the over-mature stage, likely as a result of physiological compensation for the decline in nutrient foraging ability. The concentrations of non-structural carbohydrates (NSCs), their components, and the NSC : N ratio (RNN) were lower in older stands, but the ratio of soluble sugar concentration to starch concentration (RSS) and the root δ13C values were higher. This reflected decreased carbon (C) availability and increased utilization of C reserves in the fine roots during late stand development. The root NSC concentration was positively correlated with SRL, SRT, and N concentration, indicating a positive effect of root C availability on nutrient foraging ability. The root δ13C value was positively correlated with the RSS and negatively correlated with the RNN, indicating that δ13C can accurately reflect the balance of carbohydrate supply and demand in fine roots. It was concluded that fine root nutrient foraging ability decreased in older stands, likely due to increasing fine root C limitation. These results provide a new perspective for understanding the mechanism of age-related yield decline in tree plantations.

三个亚热带森林优势种凋落物非结构性碳水化合物含量的季节动态

PDF HTML阅读 XML下载 导出引用 引用提醒 三个亚热带森林优势种凋落物非结构性碳水化合物含量的季节动态 DOI: 10.5846/stxb202103050606 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（32022056，31800521，31922052） Seasonal variations of non-structural carbohydrates in fresh litters of three dominant tree species in subtropical forests Author: Affiliation: Fund Project: National Natural Science Foundation of China (32022056, 31800521, 31922052). 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:非结构性碳水化合物（NSC）是凋落物中的易分解组分，在凋落物分解早期快速释放进入土壤并被微生物利用，参与森林土壤生物地球化学循环，因此新鲜凋落物中NSC变化规律是认识森林土壤碳和养分循环的关键之一。选取亚热带常绿阔叶林优势树种米槠（Castanopsis carlesii）和主要造林树种杉木（Cunninghamia lanceolata）、马尾松（Pinus massoniana）为研究对象，分析其新鲜凋落叶和凋落枝中NSC （可溶性糖和淀粉）含量的动态变化规律。结果表明：凋落物中NSC含量在不同月份表现出明显的时间动态，米槠、杉木和马尾松凋落叶和凋落枝中NSC含量总体上在11-12月呈上升趋势，而在2-6月呈缓慢下降趋势。不同类型的凋落物NSC含量存在显著差异，米槠、杉木和马尾松凋落叶中NSC含量分别为3.03%-3.56%、2.18%-4.37%、3.38%-4.89%，凋落枝中NSC含量分别为1.87%-4.22%、2.88%-4.28%、2.75%-5.27%，米槠和马尾松凋落叶中NSC含量高于凋落枝，而杉木凋落枝中NSC含量高于凋落叶。不同树种凋落物NSC含量差异显著，米槠和马尾松凋落叶中NSC含量显著高于杉木，而马尾松凋落枝中NSC含量显著高于米槠。这些结果表明，凋落物中NSC含量受凋落物类型、树种和凋落物生产节律的影响，且亚热带常绿阔叶林转换为杉木和马尾松人工林将改变凋落物中NSC等易分解组分归还，进而影响森林地表生物地球化学过程。 Abstract:Forests retain large amounts of organic carbon mainly through the accumulation of photosynthetic products and the sequestration of soil organic carbon. Plant litter transfers carbon from plants to soils as a more stable pool with high resistance time. Non-structural carbohydrates (NSC), such as soluble sugars and starch, are labile components in plant litter and could be released quickly from decomposing litter and utilized by soil microorganisms. Therefore, the NSC in plant litter could involve in soil biogeochemical cycles and is a key driver for carbon and nutrient cycling in forest soils. In this study, we collected monthly fresh leaf and twig litters of Castanopsis carlesii (a dominant tree species in subtropical evergreen broad-leaved forest), Cunninghamia lanceolata and Pinus massoniana (two main planted trees in subtropical China) in a natural Castanopsis carlesii forest and the Cunninghamia lanceolata and Pinus massoniana plantations over one year to assess the seasonal dynamics of the NSC (including soluble sugars and starch) in fresh litters. The results showed that the NSC content in fresh litter varied significantly among seasons for all studied litter species and between litter types (leaf versus twig). In general, the NSC content in the leaf and twig litters of Castanopsis carlesii, Cunninghamia lanceolate, and Pinus massoniana greatly increased in November and December but decreased dramatically from February to June of the following year. The NSC content differed significantly between litter types:the NSC content in leaf litters of Castanopsis carlesii, Cunninghamia lanceolata and Pinus massoniana showed average values of 3.03%-3.56%, 2.18%-4.37%, 3.38%-4.89%, respectively, while those in the twig litters were 1.87%-4.22%, 2.88%-4.28%, 2.75%-5.27%, for the three litter species, respectively. The NSC contents in leaf litters of Castanopsis carlesii and Pinus massoniana were generally higher than those in the twig litters, and the NSC content in twig litter of Cunninghamia lanceolata was higher than that in the leaf litter. The NSC content in fresh litter also varied significantly among tree species:the NSC contents in leaf litters of Castanopsis carlesii and Pinus massoniana were significantly higher than that of Cunninghamia lanceolata, and the NSC content in twig litter of Pinus massoniana was significantly higher than that of Castanopsis carlesii. The results suggest that the NSC content in fresh litter varied significantly between litter types, tree species and litterfall rhythms. The conversion of subtropical evergreen broad-leaved forests to Cunninghamia lanceolata and Pinus massoniana plantations may change the input of easily decomposable components from seasonal litterfall, and this change in labile carbon input from fresh litterfall may affect soil microbial turnover and microbially mediated biogeochemical cycles in forest soils of subtropical China. 参考文献 相似文献 引证文献

热带次生林不同林层植物叶片非结构性碳水化合物的季节变化及其对氮磷添加的响应

非结构性碳水化合物（Non-structural Carbohydrates，NSCs）是植物生长代谢过程中重要的能量来源。通过在华南热带次生林进行氮磷添加试验，探究不同林层植物叶片NSCs的季节变化及其对氮磷添加的响应，取样时间为2019年1月、4月、7月和10月。结果表明：1）植物叶片NSCs存在显著的种间差异，磷（P）添加对叶片淀粉和NSCs含量具有显著影响，且物种与磷添加的交互作用显著影响叶片淀粉含量。2）黑嘴蒲桃和紫玉盘叶片NSCs含量对氮（N）添加的响应较为敏感，而白车和竹节叶片NSCs含量对P添加的响应较为敏感，氮磷同时添加（+NP）对植物叶片NSCs的增效作用最好。3）植物叶片NSCs存在显著的季节性变化，且季节与林层间的交互作用对叶片可溶性糖和NSCs含量具有显著影响。4）不同林层植物对氮磷添加的响应不同，氮磷添加使林下层植物叶片可溶性糖含量增高，林冠层降低，在干季，N添加会使林下层植物叶片淀粉含量增高，林冠层降低。P添加的影响恰好与之相反。在湿季，氮磷添加使林下层和林冠层植物叶片的淀粉含量增加。5）林冠层植物叶片NSCs含量高于林下层，且林下层植物叶片NSCs含量和可溶性糖与淀粉的比值均表现为干季高于湿季。因此，叶片NSCs之间的变化差异反映了不同植物的碳利用策略，NSCs含量对氮磷添加的响应变化可以反映出热带森林植物在生长发育过程中碳供给和消耗的动态变化情况，为探索热带次生林植物碳利用策略及共存机制提供科学依据。;Non-structural carbohydrates (NSCs) are important energy sources in the process of plant growth and metabolism. In this paper, we conducted field-based experiment with nitrogen (N) and phosphorus (P) addition, to explore the seasonal changes of leaf NSCs in different forest layers and its response to N and P additions in a secondary tropical forest in south China. Leaf samples were conducted in January, April, July, and October 2019. The results showed that:1) There were significantly interspecific differences on the leaf NSCs. Phosphorus addition had a significant impact on starch and NSCs contents, and the interactions between species and P addition significantly affected the starch content. 2) Leaf NSCs of Syzygium bullockii and Uvaria microcarpa were sensitive to N addition, while those of Syzygium levinei and Carallia brachiate were sensitive to P addition, and N and P co-addition (+NP) had the best synergistic effect on leaf NSCs. 3) There were significantly seasonal changes on leaf NSCs, and the interaction between seasons and forest layers significantly affected soluble sugar and NSCs content. 4) The responses of plants in different forest layers to N and P addition were different. N and P additions increased the leaf soluble sugar content in the understory and decreased those in the overstory plants. In dry season, N addition increased the leaf starch contents in the understory and decreased in the overstory species. However, P addition had the opposite effect. In wet season, N and P additions increased the starch content of plant leaves in understory and overstory. 5) Leaf NSCs content in overstory was higher than that in understory. The leaf NSCs content and soluble sugar/starch ratio of understory plants were higher in the dry season than those in wet season. Therefore, the variation of NSCs in different plant leaves reflects the carbon (C) utilization strategies, and the change of NSCs content in response to N and P addition can reflect the dynamic changes of C supply and consumption during the growth and development of tropical forest plants, which provides scientific basis for exploring C utilization strategies and coexistence mechanisms of plants in secondary tropical forest.

Belowground carbon dynamics in Scots pine stands

Boreal forest soils are globally one of the most extensive carbon storages, whereas soil respiration (CO2 efflux) forms the largest carbon flux from the ecosystem to the atmosphere. Current changes in the world climate may have unpredictable effects on belowground carbon processes, and thereby, on the carbon balance of boreal forests. To better understand the various processes in soil and to quantify the potential changes in the carbon cycle, forest-floor respiration (RFF) was partitioned into five different components, and tree-root respiration (RR) was estimated, using four different methods in a mature boreal Scots pine (Pinus sylvestris L.) stand in southern Finland. Non-structural carbohydrate (NSC) concentrations in tree roots were determined, and carbon allocation to belowground by trees was estimated with the whole-tree carbon model ‘CASSIA’. In addition, RR and heterotrophic soil respiration (RH) were separated using root exclusion in seven coniferous forests along a latitudinal gradient in Northern and Central Europe. The RR comprised almost half of the RFF, the RH almost a third, and ground vegetation and respiration of mycorrhizal hyphae the remaining fifth in the boreal Scots pine stand. While the annual RR decreased throughout the first three study years, the RH increased when the mycorrhizal roots were excluded from the treatments. The RR and most of the NSC concentrations were higher in the warmer years and lower in the cooler, as estimated with most of the methods. Three methods resulted in rather similar RR estimations, while the RR estimated with root incubation was significantly lower. The RR was over 50% of the annual photosynthesis in the northernmost forest stand, whereas in the southernmost stand it was only up to 15%. Carbon allocation to the belowground, as modelled with CASSIA was a third of the annual photosynthesis on average and almost 5% for the symbiotic mycorrhizae.

Dynamics of nonstructural carbohydrates in a deciduous woody species from tropical dry forests under recurrent water deficit.

In tropical dry forests, both the dry and the short rainy seasons have become increasingly irregular. This study replicated these conditions to investigate the effects of two water deficit cycles on Cenostigma microphyllum seedlings. Impacts were assessed by measuring growth traits, water relations, gas exchange, and dynamics of nonstructural carbohydrate (NSC) content in the whole plant under greenhouse conditions in potted plants. In the first water deficit cycle, the leaf relative water content (RWC) was maintained at the expense of a rapid drop in gas exchange. Furthermore, there was a slight accumulation of NSC, mainly soluble sugars (SS) in the stem wood and roots, to the detriment of height and stem diameter growth. In the second cycle, the leaf RWC remained 40% higher than the lowest level measured in the first water deficit, and CO2 assimilation remained twice as long in previously stressed plants. The SS content of the stems and roots was strongly correlated with the predawn leaf RWC. No strong reduction was observed in the bark stock even with the gradual increase of SS in the wood. Our data suggest that under recurrent water deficit prior to leaf drop, CO2 assimilation is maintained, with the highest possible leaf RWC, under reduced stomatal conductance. This assists in SS transport to wood and root, which is no longer used to support the growth of the aboveground parts.

Combined effects of marine heatwaves and reduced light on the physiology and growth of the surfgrass Phyllospadix torreyi from Baja California, Mexico

This study aimed to elucidate for the first time the combined effects of marine heatwaves (MHWs) and light limitation simulated in mesocosm on critical physiological descriptors of the surfgrass Phyllospadix torreyi, which constitutes highly productive meadows along the intertidal and subtidal rocky shores of the Pacific coast of North America. Our results revealed that short-term exposure (~7 days) to extreme thermal anomalies of + 9 °C had positive effects on the photosynthetic capacities of P. torreyi, as indicated by increments in maximum photosynthetic rates, photosynthetic efficiency (α), maximum electron transport rate, and effective quantum yield. Despite that its photosynthetic performance was enhanced, exposure to warming caused a decrease in its internal carbon reserves (i.e. energy status), likely as a consequence of carbon mobilization/utilization to activate heat-stress responses. Plants exposed to light limitation (i.e. sub-saturating irradiance of 30 μmol photon m−2 s−1) generally exhibited an increase in α and/or a decrease in respiration, which ultimately allowed for a reduction in plant compensation irradiance. The combination of low light and seawater warming resulted in a decrease in non-structural carbohydrates content, daily net-productivity, and leaf growth rates. Gross photosynthetic rates at control saturating irradiance exhibited higher activation energy and, thus, greater responsiveness to seawater warming than plants kept under light limitation. While our results indicated that unusual warming events might favor the photosynthetic performance of P. torreyi, combining this condition with a drastic light reduction can lead to internal carbon depletion and potentially compromise plant survival in the long term.

Identification of trehalose-6-phosphate synthase (TPS)-coding genes involved in flowering induction of Lilium× formolongi

Lilium × formolongi, a facultative long-day (LD) plant, can complete the floral transition within one year after sowing under LD conditions. In addition to the photoperiod, the molecular mechanisms by which other flowering regulators, such as sugar, participate in juvenile development and flowering induction in L. × formolongi remain elusive. Therefore, based on the investigation of seedling development under different day length conditions, we explored the growth and nonstructural carbohydrate (NSC) contents of leaves and underground bulbs. Furthermore, the expression profiles of trehalose-6-phosphate synthase (TPS)-coding genes, LfTPSs, and miR156 were also determined. Three putative LfTPS genes, LfTPS1, LfTPS3 and LfTPS5, displayed high expression levels at the juvenile vegetative stage under different day length conditions. Among them, LfTPS1 maintained gradually elevated expression until the visible bud stage under short-day (SD) conditions. Additionally, the expression levels of LfTPS3 and LfTPS5 increased with the exogenous sucrose concentration. In contrast, the expression of miR156 rapidly decreased under the same sucrose treatments. Overexpression of LfTPS1/3/5 hastened flowering and the decline in miR156 expression levels to varying degrees in transgenic Arabidopsis. Taken together, the results demonstrate that LfTPS1, LfTPS3 and LfTPS5 modulate both juvenile vegetative development and flowering induction controlled by sugars in L. × formolongi.

Differential Variation in Non-structural Carbohydrates in Root Branch Orders of Fraxinus mandshurica Rupr. Seedlings Across Different Drought Intensities and Soil Substrates.

Non-structural carbohydrates (NSCs) facilitate plant adaptation to drought stress, characterize tree growth and survival ability, and buffer against external disturbances. Previous studies have focused on the distribution and dynamics of NSCs among different plant organs under drought conditions. However, discussion about the NSC levels of fine roots in different root branch orders is limited, especially the relationship between fine root trait variation and NSC content. The objective of the study was to shed light on the synergistic variation in fine root traits and NSC content in different root branch orders under different drought and soil substrate conditions. The 2-year-old Fraxinus mandshurica Rupr. potted seedlings were planted in three different soil substrates (humus, loam, and sandy–loam soil) and subjected to four drought intensities (CK, mild drought, moderate drought, and severe drought) for 2 months. With increasing drought intensity, the biomass of fine roots decreased significantly. Under the same drought intensity, seedlings in sandy–loam soil had higher root biomass, and the coefficient of variation of 5th-order roots (37.4, 44.5, and 53% in humus, loam, and sandy–loam soil, respectively) was higher than that of lower-order roots. All branch order roots of seedlings in humus soil had the largest specific root length (SRL) and specific root surface area (SRA), in addition to the lowest diameter. With increasing drought intensity, the SRL and average diameter (AD) of all root branch orders increased and decreased, respectively. The fine roots in humus soil had a higher soluble sugar (SS) content and lower starch (ST) content compared to the loam and sandy–loam soil. Additionally, the SS and ST contents of fine roots showed decreasing and increasing tendencies with increasing drought intensities, respectively. SS and ST explained the highest degree of the total variation in fine root traits, which were 32 and 32.1%, respectively. With increasing root order, the explanation of the variation in root traits by ST decreased (only 6.8% for 5th-order roots). The observed response in terms of morphological traits of different fine root branch orders of F. mandshurica seedlings to resource fluctuations ensures the maintenance of a low cost-benefit ratio in the root system development.

Effects of elevated CO2 concentration and nitrogen addition on the chemical compositions, construction cost and payback time of subtropical trees in Cd-contaminated mesocosm soil.

Rising atmospheric CO2 concentration ([CO2]) and nitrogen (N) deposition are changing plant growth, physiological characteristics and chemical compositions; however, few studies have explored such impacts in a heavy metal-contaminated environment. In this study, we conducted an open-top chamber experiment to explore the impacts of 2 years of elevated atmospheric [CO2] and N addition on the growth, physiological characteristics and chemical compositions of five subtropical tree species in a cadmium (Cd)-contaminated environment. Results showed that N addition significantly increased concentration of leaf N and protein in five tree species and also decreased payback time (PBT) and leaf carbon:nitrogen ratios and increased tree relative height growth rate (RGR-H) and basal diameter growth rate (RGR-B) in Liquidambar formosana Hance and Syzygium hainanense Chang et Miau. Elevated [CO2] increased leaf maximum photosynthetic rate (Amax) and concentration of total non-structural carbohydrates and shortened PBT to offset the negative effect of Cd contamination on RGR-B in Acacia auriculiformis A. Cunn. ex Benth. The combined effects of elevated [CO2] and N addition did not exceed their separate effects on RGR-H and RGR-B in Castanopsis hystrix Hook. f. & Thomson ex A. DC. and Cinnamomum camphora (L.) presl. The addition of N significantly increased the concentration of leaf Cd by 162.1% and 338.0%, and plant Cd bio-concentration factor by 464% and 861% in C. hystrix and C. camphora, respectively, compared with only Cd addition. Among the five tree species, the decrease in PBT and the increase in Amax, RGR-B and concentrations of leaf protein in response to N and Cd addition under elevated [CO2] were on average 86.7% higher in A. auriculiformis than other species, suggesting that the mitigation of the negative effects of Cd pollution by elevated [CO2] and N addition among five species was species-specific. Overall, we concluded that N addition and elevated [CO2] reduced Cd toxicity and increased the growth rate in A. auriculiformis, S. hainanense and L. formosana, while it maintained the growth rate in C. hystrix and C. camphora by differently increasing photosynthetic rate, altering the leaf chemical compositions and shortening PBT.

Below-Ground Growth of Alpine Plants, Not Above-Ground Growth, Is Linked to the Extent of Its Carbon Storage.

Understanding carbon allocation in plants is essential for explaining their growth strategies during environmental adaptation. However, the role of mobile carbon in plant growth and its response to habitat conditions is still disputed. In degraded meadow (alpine sandy grassland) and non-degraded meadow (typical alpine meadow and swamp meadow) on the Qinghai–Tibetan Plateau, we measured the monthly averages of above-ground biomass (AGB) and below-ground biomass (BGB) of the investigated species in each meadow and the average concentration of non-structural carbohydrates (NSCs), an indicator of carbon storage. Below-ground organs had higher concentrations and showed more seasonal variation in NSCs than above-ground organs. BGB had a positive correlation with below-ground NSCs levels. However, AGB had no clear relationship with above-ground NSCs levels. Plants in sandy grasslands had higher total NSC, soluble sugars, fructose, and sucrose concentrations and lower starch concentrations in below-ground organs than plants in alpine or swamp meadows. Overall, NSCs storage, particularly soluble sugars, is a major process underlying the pattern of below-ground growth, but not above-ground growth, in the meadow ecosystem of the Qinghai–Tibetan Plateau, and degraded meadow strengthens this process. These results suggest that the extent of carbon storage in non-photosynthetic organs of alpine herbs impacts their growth and habitat adaptation.

Nutritional considerations for the management of equine pituitary pars intermedia dysfunction

SummaryPituitary pars intermedia dysfunction (PPID) is a common endocrine disorder affecting equids. To help achieve and maintain healthy body condition, whilst reducing the risk of dietary associated laminitis, appropriate nutritional management is key. This review proposes a stepwise approach to building an individual nutritional plan for equines with PPID. Starting with considerations relating to current and desired body condition and muscle mass, it highlights the importance of providing appropriate amounts and forms of energy, carbohydrate and protein, with further practical considerations regarding the feeding of animals that are often aged and may have particular clinical sequelae to PPID. The next important step is to determine the degree of insulin dysregulation (ID), as this is a major factor associated with an increased risk of laminitis. Animals with ID should be fed low non‐structural carbohydrate (NSC) providing feeds/feedstuffs as well as fresh or preserved forage with NSC content <10‐12% on a DM basis. Finally, adjustments need to be made according to life stage and activity level.

Reduced Nitrogen Rate with Increased Planting Density Facilitated Grain Yield and Nitrogen Use Efficiency in Modern Conventional Japonica Rice

The past three decades have seen a pronounced development of conventional japonica rice from the 1990s, although little information is available on changes regarding grain yield and nutrient use efficiency during this process. Nine conventional japonica rice released during the 1990s, 2000s, and 2010s were grown under a reduced nitrogen rate, with increased planting density (RNID) and local cultivation practice (LCP) in 2017 and 2018. The rice from the 2010s had 3.6–5.5% and 7.0–10.1% higher (p < 0.05) grain yield than the 2000s and the 1990s, respectively, under RNID and LCP. The harvest index contributed more to genetic yield gain from the 1990s to the 2000s; whereas from the 2000s to 2010s, yield increase contributed through shoot biomass. Genetic improvement increased total nitrogen (N), phosphorus (P), and potassium (K) accumulation, and their use efficiencies. The rice from the 2010s showed a similar grain yield, whereas the 1990s and 2000s’ rice exhibited a lower (p < 0.05) grain yield under RNID relative to LCP. RNID increased N, P, and K use efficiencies, particularly the N use efficiency for the grain yield (NUEg) of the 2010s’ rice, compared with LCP. For three varietal types, RNID increased the panicles per m2, the filled-grain percentage, and the grain weight (p < 0.05) while decreasing spikelets per panicle of the 2010s’ rice. Compared with LCP, RNID reduced non-structural carbohydrate (NSC) content and shoot biomass, at heading and maturity, while increasing the remobilization of NSC and the harvest index, especially for the 2010s’ rice. Our results suggested the impressive progressive increase in grain yield and nutrient use efficiency of conventional japonica rice since the 1990s in east China. RNID could facilitate grain yield and NUEg for modern conventional japonica rice.

Response of four evergreen savanna shrubs to an incidence of extreme drought: high embolism resistance, branch shedding and maintenance of nonstructural carbohydrates.

Extreme drought events are becoming frequent globally, resulting in widespread plant mortality and forest dieback. Although savanna vegetation cover ~20% of the earth's land area, their responses to extreme drought have been less studied than that of forests. Herein, we quantified branch dieback, individual mortality and the associated physiological responses of four evergreen shrubs (Tarenna depauperate Hutch., Maytenus esquirolii (H. Lév.) C.Y. Cheng, Murraya exotica L., Jasminum nudiflorum Lindl.) in a savanna ecosystem in Southwest China to an incidence of extreme drought during 2019 and 2020. We found that 80-100% of the individuals of these species exhibited branch dieback, whereas individual mortality was only found in T. depauperate (4.5%). All species showed high resistance to stem embolism (P50, water potential at 50% loss of hydraulic conductivity ranged from -5.62 to -8.6MPa), whereas the stem minimum water potentials reached -7.6to ca -10.0MPa during the drought. The low water potential caused high native embolism levels (percentage loss of hydraulic conductivity (PLC) 23-65%) in terminal branches, and the remaining stems maintained 15-35% PLC at the end of the drought. Large within-individual variations in stem vulnerability to embolism were detected, and shedding of vulnerable branches could be a mechanism for shrubs to reduce water and carbon consumption. Overall, the content of total nonstructural carbohydrates (NSC) and their components in the stem were generally comparable to or higher than those in the rainy season in three of the four species. Because the leaves were turgor-less for most time during the drought, high NSC levels during the drought could be due to recycling of NSC from dead branches or translocation from roots. Our results suggest high tolerance of savanna shrub species to extreme drought, which could be facilitated by high embolism resistance in some stems and shedding of vulnerable branches to maintain individual water and carbon balance.

Comparison and Characterization of Oxidation Resistance and Carbohydrate Content in Cd-Tolerant and -Sensitive Kentucky Bluegrass under Cd Stress

Kentucky bluegrass (Poa pratensis L.), a turf grass species that is hypertolerant of cadmium (Cd), is a potential phytoremediation material for soil polluted with Cd. However, the mechanism of Cd phytotoxicity in Kentucky bluegrass is unclear. Here, we compared the phenotype, induction of oxidative stress, and structural and non-structural carbohydrate contents between a Cd-tolerant genotype (‘Midnight’, M) and Cd-sensitive genotype (‘Rugby’, R). The results showed that both genotypes accumulated more Cd in the roots, whereas the R genotype distributed more Cd into the leaves compared with the M genotype. In both genotypes, Cd inhibited the length and fresh weight of the leaves and roots; increased the peroxidase (POD) activity but inhibited ascorbate peroxidase (APX) and catalase (CAT) activity; and increased the superoxide radical (O2−), hydrogen peroxide (H2O2), and malondialdehyde (MDA) contents. However, the M genotype exhibited lower root length inhibition, and the H2O2 and MDA contents confirmed that the M genotype had increased Cd accumulation and resistance, while the R genotype exhibited a better distribution of Cd. Moreover, Cd stress significantly increased the soluble sugar, trehalose, and sucrose contents of both genotypes. Pectin, lignin, and cellulose were significantly increased to prevent the entry of Cd into the roots. The Cd-induced growth inhibition and physiological responses in Kentucky bluegrass were preliminarily explored herein, with the chelation of pectin, lignification, and antioxidant response being possible contributors to Cd detoxification in Kentucky bluegrass. In addition, the Cd-induced increase in trehalose, sucrose, and soluble sugar contents might play a pivotal role in the defense against Cd stress in Kentucky bluegrass.

Contrasting Metabolic Fingerprints and Seed Protein Profiles of Cucurbita foetidissima and C. radicans Fruits from Feral Plants Sampled in Central Mexico.

Cucurbita foetidissima and C. radicans are scarcely studied wild pumpkin species that grow in arid and semi-arid areas of Mexico and the United States. This study describes the morphological, proximal composition, metabolic finger-prints and seed protein profiles of C. foetidissima and C. radicans fruits collected in the wild during a one-year period in different locations of central-western Mexico. The results obtained complement the limited information concerning the fruit composition of C. foetidissima and greatly expand information in this respect regarding C. radicans. Morphology and proximal composition of their fruits varied significantly. Different metabolic fingerprints and seed protein profiles were detected between them and also with the chemical composition of domesticated Cucurbita fruits. The neutral lipids in seed, pulp and peels were rich in wax content and in unsaturated compounds, probably carotenoids and tocopherols, in addition to tri-, di- and mono-acylglycerols. The tri- and diacylglycerol profiles of their seed oils were different from commercial seed oils and between each other. They also showed unusual fatty acid compositions. Evidence of a possible alkaloid in the pulp and peel of both species was obtained in addition to several putative cucurbitacins. An abundance of phenolic acids was found in all fruit parts, whereas flavonoids were only detected in the peels. Unlike most cucurbits, globulins were not the main protein fraction in the seeds of C. radicans, whereas the non-structural carbohydrate and raffinose oligosaccharide content in their fruit parts was lower than in other wild cucurbit species. These results emphasize the significantly different chemical composition of these two marginally studied Cucurbita species, which was more discrepant in C. radicans, despite the notion regarding C. foetidissima as an aberrant species with no affinity to any other Cucurbita species.

Grain yield response to cultivar and harvest time of the first crop in rice ratooning in southwestern Japan

AbstractRice (Oryza sativa L.) ratooning has attracted attention due to its higher yield potential compared with conventional methods. Here, field experiments were conducted in southwestern Japan in 2019 and 2020 to determine the effects of cultivar (‘Takanari’, an indica cultivar, and ‘Koshihikari’, a japonica cultivar) and harvest time of the first crop (early and late) on the grain yields of the first and second crops in rice ratooning. For Koshihikari in 2019, grain yield of the second crop did not differ between harvest times. However, Takanari produced a lower grain yield at late harvest. Takanari had fewer spikelets, fewer filled spikelets, and a lower 1,000‐grain weight at late harvest. However, for Takanari in 2020, grain yield did not differ between harvest times. In 2019, the stubble nonstructural carbohydrate (NSC) content did not increase from early to late harvest, whereas the stubble leaf area index (LAI) decreased between harvest times; this difference was more apparent in Takanari than in Koshihikari. Contrastingly, in 2020, the NSC content increased from early to late harvest, but the stubble LAI did not differ between harvest times. Thus, the lower grain yield of late‐harvested Takanari in 2019 might be attributed to the lower stubble LAI resulting in fewer spikelets. In contrast, the maintained grain yield from early to late harvest in 2020 might be attributed to the maintenance of spikelet numbers via the higher stubble NSC content. Therefore, the sufficient stubble LAI and NSC could be essential for improving grain yield of the second crop.

Nitrogen nutrition addition mitigated drought stress by improving carbon exchange and reserves among two temperate trees

Climate change-driven increases in drought and atmospheric nitrogen (N) deposition frequency and severity across the world, and these changes have profound impacts on forest dynamics by affecting tree carbon balance. However, important knowledge gaps persist concerning the interactions between drought and N enrichment on carbon supply and reserve dynamics. We investigated gas exchange and carbohydrate reserve shifts and associated with leaf chemical composition across two temperate tree saplings coping with different levels of drought stress, N nutrition addition and their interactions. Our results showed that drought stress decreased net photosynthetic rate (A) and stomatal conductance (gs), while A and gs were increased by N addition, combined with increased gs under the interactive effects of drought and N addition, indicating that N nutrient availability had suppressing effect on drought stress and improved the drought-induced negative conditions by altering carbon exchange traits. In addition, we found that N addition reduced the concentrations of nonstructural carbohydrate (NSC) and its components in relation to foliar carbon and nitrogen changes and the fast growth of saplings. Under the interaction of drought and N nutrition addition, no variation in carbohydrate concentrations demonstrate that carbon reserves play a critical role in regulating carbon exchange and growth. Our observations provide evidence of N nutrient availability mitigated drought stress by improving carbon exchange and reserves, which is expected to contribute to the predictions of future vegetation dynamics.

Stem Photosynthesis Affects Hydraulic Resilience in the Deciduous Populusalba but Not in the Evergreen Laurus nobilis

Stem photosynthesis has been suggested to play relevant roles to cope with different biotic and abiotic stress factors, including drought. In the present study, we performed measurements of stem hydraulic conductance and non-structural carbohydrate content in the evergreen Laurus nobilis L. and the deciduous Populusalba L., subjected to inhibition of stem photosynthesis and successive exposure to a drought-recovery cycle in order to check if stem photosynthesis may be involved in allowing hydraulic recovery after drought stress relief. Stem shading affected the growth of L. nobilis but not of P. alba saplings. By contrast, inhibition of stem photosynthesis was coupled to inhibition of hydraulic recovery following embolism build-up under drought in P. alba but not in L. nobilis. The two study species showed a different content and behavior of nonstructural carbohydrates (NSCs). The differences in NSCs’ trend and embolism reversal ability led to a significant relationship between starch content and the corresponding hydraulic conductance values in L. nobilis but not in P. alba. Our findings suggest that stem photosynthesis plays a key role in the maintenance of hydraulic functioning during drought especially in the deciduous species. This, in turn, may increase their vulnerability under current global climate change scenarios.

Endogenous metabolic content of the cutting positions and ndole-3-butyric acid influence rooting of Toona ciliata var. pubescens stem cuttings

Toona ciliata var. pubescens (family Meliaceae) is an endangered species of mahogany endemic to China. It is now under Class II protection, and stem cuttings are an important means for its clonal propagation. However, the metabolic changes that occur in the cuttings during adventitious root formation and how these are influenced by indole-3-butyric acid (IBA) are still unclear. This study investigated the influence of cutting positions (top, middle and base) on the rooting ability and the associated metabolic changes during adventitious root formation. We compared treatment with 800 mg l−1 IBA with controls. The results showed that the rooting percentage, taproots per cutting, and longest root length differed significantly depending on the cutting position. Base cuttings had the best rooting ability and exhibited the highest average rooting percentage, the longest roots, and most taproots per cutting. The contents of soluble sugar, starch, non-structural carbohydrates (NSCs) and soluble proteins, and the peroxidase (POD) activity, were significantly higher in base cuttings than in middle and top cuttings; however, polyphenol oxidase (PPO) activity did not differ significantly among the positions. Metabolic changes occurred during the cutting process. The levels of POD and PPO activities increased significantly until 20 days after planting, suggesting that this period is key for the induction of adventitious rooting in this species. In the rooting process, IBA promoted an increase in the contents of soluble sugar, starch, NSCs and soluble proteins in the stem cuttings and it also increased the activities of POD and PPO. Bark-water extract from the stem cuttings inhibited the germination of Chinese cabbage seeds in a concentration-dependent manner, irrespective of the cutting position.

Effects of nitrogen fertilization for bud initiation and tiller growth on yield and quality of rice ratoon crop in central China

Rice ratooning is an ancient technology, known as harvesting twice after one sowing. In recent years, ratoon rice has drawn much attention and been widely practiced by farmers in central China because of its advantages in saving labor and increasing profit. For ratoon crop (RC), nitrogen (N) application for promoting bud initiation (Nbud) and for promoting regenerated tiller growth (Ntiller) are two common N management practices. However, it is still obscure about their effects on grain yield and quality of RC. Field experiments were conducted to compare the effects of Nbud (75 kg N ha−1 application at 12 days after heading of main crop, MC) and Ntiller (75 kg N ha−1 application at 2 days after harvesting of MC) on the grain yield and quality of RC in 2018 and 2019. Compared to Nbud, Ntiller had an evident and positive effect on grain yield, head rice percentage (HRP) and chalkiness degree (CD) of RC. Averaged across years, Nbud and Ntiller increased grain yield of RC by 5.5 % and 30.5 %, respectively. Moreover, Ntiller improved grain quality with an increase of 10.5 % in HRP and a decrease of 10.2 % in CD. Ntiller significantly increased sink size like spikelets m-2, and source ability including leaf area index, leaf N content, and crop growth rate in ratoon crop. The positive effect of Nbud on grain yield of RC was positively correlated with the increase in panicles m-2, but negatively correlated with the panicles m-2 of MC. Nbud has no effect on stubble dry weight, and significantly increased stubble N concentration, but significantly decreased stubble non-structural carbohydrate concentration at maturity in the main season. Overall, our results indicated that nutrient status of straw and panicle number in MC affected the roles of Nbud on RC yield, and more attention should be paid on Ntiller in future RC production.