Biomass Accumulation In Seedlings Research Articles

Nitrogen addition improves drought tolerance in Camellia japonica (Naidong) seedlings

The northernmost population of Camellia japonica globally is a unique ecotype within the species. Water deficit and atmospheric nitrogen deposition are two critical environmental factors that influence plant growth and primary productivity, particularly in the context of environmental change. However, the interactive effects of drought and nitrogen deposition on the physiology and growth of Naidong seedlings have not been investigated. To address this gap, we conducted a greenhouse experiment to investigate the individual and combined influences of different water and nitrogen (N) levels on growth, leaf morphology and physiology, and biomass and carbohydrate allocation of three-year-old Naidong seedlings. The results demonstrated that drought reduced height, basal diameter, specific leaf area, biomass accumulation, net photosynthesis, and non-structural carbohydrate (NSC) pool in the root of seedlings. However, water use efficiency (WUE) increased under slight drought conditions. Moderate (6 g N m−2 year−1) nitrogen addition enhanced seedling biomass accumulation, carbon fixation capacity, and WUE. Furthermore, a significant interaction between water and nitrogen deposition on Fv/Fm, soluble sugars concentration in the stem, and starch concentration in the root of Naidong seedlings was discovered. Drought and nitrogen deposition exhibited antagonistic effects on seedling biomass accumulation and photosynthetic capacity. The adverse impact of drought on growth and physiological responses could be partially compensated by increased nitrogen availability. This study highlights the need to include more variables when assessing a species' vulnerability to shifts in environmental conditions in the context of global change studies. Furthermore, our findings provide supportive data for the survival of C. japonica under future climate scenarios.

Seed Priming Stimulates Germination and Early Seedling Establishment Of Corethrodendron Multijugum Under Drought Stress

Seed priming can alleviate the negative effects of drought stress. The present study focused on exploring the effects of seed priming, drought and their interaction on the germination characteristics of Corethrodendron multijugum. We attempted to standardise an appropriate priming method for C. multijugum seeds by comparing the effects of various priming methods and drought stress on seed germination and seedling establishment to provide theoretical basis and technical support for subsequent cultivation and production. The results indicated that seed priming, drought stress and their interaction significantly (P < 0.01) affected all seed germination parameters and seedling establishment parameters, and germination was significantly (P < 0.05) correlated with early seedling establishment under drought stress. Of the different priming agents used in this study, water, 0.5% KMnO4, 0.3% H2O2and 5% PEG-6000 significantly (P < 0.05) promoted seed germination and seedling establishment in C. multijugum. Among them, 0.5% KMnO4 was the most effective in alleviating the effects of drought stress on germination and early seedling establishment. Morphologically, the beneficial effects of priming can be attributed to increased seed germination, elongation and biomass accumulation of seedlings.

Effects of Pre-Hardening and Autumn Fertilization on Biomass Allocation and Root Morphology of Pinus koraiensis Seedlings

The effects of pre-hardening fertilization and autumn fertilization on seedling growth have been studied separately, but studies on their combined effects are relatively scarce. We studied the effects of pre-hardening fertilization type and autumn fertilization level on biomass allocation and root morphology of container-grown seedlings of Korean pine (Pinus koraiensis Sieb. et Zucc.), a valuable evergreen conifer distributed from Changbai Mountain to the Xiaoxing’an Mountains in northeastern China. Three pre-hardening fertilization types (conventional fertilization, exponential fertilization, and controlled-release fertilizer) were all applied with 72 mg of nitrogen. We also applied four nitrogen levels of autumn fertilization: 0 mg/plant, 2 mg/plant, 4 mg/plant, and 6 mg/plant. We found that autumn fertilization increased Korean pine seedling biomass accumulation and root growth by 65.91%–92.15% and 108.86%–141.48%, respectively. There was significant interaction between pre-hardening fertilization type and autumn fertilization level on biomass allocation and root morphology. Seedlings with conventional fertilization during the growing season have the best response to autumn fertilization, particularly in the 2 mg/seedling and 4 mg/seedling treatments. Autumn fertilization can be applied to the cultivation of high-quality Korean pine seedlings.

New Biostimulants Screening Method for Crop Seedlings under Water Deficit Stress

Biostimulants can be used in many crops growing under water deficit conditions at the seedling stage. This study used tomato, Solanum lycopersicum L., seedlings growing in commercial 150-cell trays as an experimental setup to reproduce mild drought stress effects. The method showed significant reductions in seedling growth and RGR (25%) after a seven-day experiment. Gas exchange parameters (Pn, Gs and E) had significantly lower values (30–50%) than the control seedlings. Stress-related metabolite, ABA, exhibited a significant accumulation in the tomato seedlings (24 h), consistent with SINCED2 gene expression. Proline levels were twice as high in the water-deficit treated seedlings, remaining at this level until the end of the experiment. However, total carbohydrates were significantly lower in water-deficit treated seedlings. Qualitative and quantitative analysis suggested that using the variable ‘seedling biomass accumulation’ could simplify the methodology. Twelve different biostimulants were assayed, implementing this simplification, and all of them showed higher biomass accumulation in the treated seedlings than in the non-treated ones under water deficit. Among them, putrescine, spermine and spermidine were the most effective. The method is adjustable to different biostimulant volumes (1, 3 and 5 mL; 1 mM BABA), with no significant differences between the treatments.

Bacillus cereus Improves Performance of Brazilian Green Dwarf Coconut Palms Seedlings With Reduced Chemical Fertilization.

Coconut production in the Amazon requires the knowledge and development of sustainable technologies to alleviate the detrimental effects of inorganic chemical fertilizers and intensive farming practices. In this study, we investigated the effects of plant growth-promoting rhizobacteria (PGPR) isolated from coconut seedlings on nutrient use efficiency (NUE) and physiological mechanisms related to biomass accumulation of seedlings grown with reduced inorganic fertilizer levels. Of the 96 PGPR isolates tested on rice plants, the isolate Bacillus cereus (UFRABC40) was selected, as it resulted in the most significant gain in growth variables. In a commercial coconut tree nursery, we subjected seedlings to two treatments, both with seven replications: control 100% NPK chemical fertilizer (CF) and B. cereus + 50% NPK CF. The results indicated that the inoculation increased phytohormone levels [190% indole acetic acid (IAA), 31% gibberellic acid GA3, and 17% gibberellic acid GA4] and leaf gas exchange [48% by assimilation of CO2 (A), 35% stomatal conductance to water vapor (gs), 33% transpiration, and 57% instantaneous carboxylation efficiency] in leaves. Furthermore, growth parameters (shoot, root, and total dry weight, height, and diameter) and macro- and micronutrient levels (95% N, 44% P, 92% K, 103 Ca, 46% Fe, 84% B) were improved. Our results show the potential ability of strain Bacillus cereus UFRABC40 to promote the growth performance of coconut seedlings under decreased application of inorganic fertilizers. The application of microbial-based products in coconut seedling production systems improves plants’ physiological performance and the efficiency of nutrient use.

Effect of sea water substitution on growth, physiological and biochemical processes of coconut (Cocos nucifera L.) seedlings—A hydroponic study

Coconut is grown along the coasts and islands that are vulnerable to climate change-induced sea level rise. Though coconut is considered moderately salt tolerant, our understanding on the growth and physiological response to sea water, either inundation or subsurface water contamination, is very limited. This understanding will enable to effectively manage coconut in coastal systems under future climatic scenarios. In this study, ten month old hydroponically grown coconut seedlings were subjected to 0, 10, 25, 50, 75 and 100 % of sea water substitution (SWS), equivalent to 2.17, 8.32, 16.32, 30.03, 42.14 and 53.69 dS m−1 EC, respectively. Substituting Hoagland solution in hydroponic system by sea water of increasing concentration (>50 % SWS) significantly changed physiological processes; Fv/Fm decreased and rs increased as early as 7 and 18 days after treatment imposition (DAT), respectively which led to significant decline in leaf area and root length expansion as early as 24 DAT. At 25 % SWS, root system (root length and root biomass) was stable but the aerial part biomass was declined by 47 %. On the other hand plant height, leaf area, collar girth and biomass accumulation of seedlings under 10 % SWS (8.32 EC) was on par with the control plants suggesting coconut seedlings could tolerate 10 % SWS. Though, PN declined by 19 % and 43 % at 10 % and 25 % SWS, respectively and a similar decline in gs without a concomitant change in leaf water potential suggested that root-generated signals regulated the stomatal movement in coconut under salinity. Still the biomass accumulation at 10 % SWS was not affected by decline in PN. Under increasing sea water treatments, most of the Na+ absorbed was compartmentalized in root and shoot, while leaf had more accumulation of K+, that ensured high K+/Na+ ratio in the leaves which is an important salinity tolerant mechanism observed in coconut. The leaf Cl− content also had strong negative correlation with [PN] (r=-0.873) and biomass (r=-0.833), therefore in addition to K+ and Na+ homeostasis, the level of tolerance to the increased Cl− content in the leaves may also play an important role in salinity tolerance of coconut. This understanding will help in making appropriate strategies for managing coconut grown at coastal systems in the face of sea level rise under climate change.

FLAME RETARDANTS EFFECTS ON THE INITIAL GROWTH OF Schizolobium amazonicum HUBER EX DUCKE

ABSTRACT Flame retardants are efficient in fighting wildfire; however, their environmental implications, especially regarding the vegetation, need to be clarified. This work aimed at assessing the effects of flame retardant on the initial growth of Schizolobium amazonicum. Treatments consisted in applying different flame retardant concentrations via substrate and leaf: Phos-Chek WD-881® (0, 3.00, 6.00, 8.00 and 10.00 mL L-1), Hold Fire® (0, 7.00, 9.00, 12.00 and 15.00 mL L-1) and water-retaining polymer Nutrigel® used as alternative retardant (0, 0.25, 0.50, 0.75 and 1.00 g L-1). Growth analyses were carried out to assess the effects of these substances (10 repetitions per treatment). The aliquot of 10.00 mL L-1 of Phos-Chek WD881 applied on the leaves led to an increase of 70% in leaf area and 15% in seedling height. The same Phos-Chek concentration favored height increase (32%) and total dry mass accumulation (33%) throughout time. The concentration of 15 mL L-1 of Hold Fire® applied on leaves, compromised 45% the accumulation of dry biomass in the seedling. Initially, 1.00 g L-1 of Nutrigel® applied via substrate led to an increase of 70% in leaf area, 29% in plant height, and 89% in leaf dry mass. Therefore, Phos-Chek applied on leaves favored shoot growth in S. amazonicum. Hold Fire® applied on leaves impaired biomass accumulation in seedlings. Nutrigel® applied on substrate does not cause long-lasting damage to the initial growth of S. amazonicum. The aliquot of 0.50 g L-1 administered via polymer leave had positive effect on seedling shoot.

EFFECTS OF LIGNOHUMATE ON THE PHYTOTOXICITY OF PHOSPHORUS-CONTAINING COMPOUNDS (MODEL EXPERIMENTS)

In conditions of chemical pollution, it is relevant to enhance the resistance of plants with substances that have a protective action. The effect of humic substance Lignohumate on the phytotoxic properties of phosphorus-containing compounds methylphosphonic acid (MPA) and sodium pyrophosphate (SPP) was studied in model experiments. Lignohumate was tested at three concentrations (0.1, 0.5, and 1 g/L) on Hordeum distichum L. of the Novichok variety. The test functions were such indicators as the germinating and sprouting ability of seeds, the growth and biomass accumulation of seedlings, and the inhibition effect. Lignohumate in the studied concentrations did not affect germination of the barley seeds, but it stimulated growth of the barley seedlings. In the conditions of MPA pollution (0.01 mol/L), Lignohumate exerted a protective effect on the plants, and the highest concentration of humic preparation (1 g/L) was the most effective. In the experiments with SPP (0.01 mol/L), Lignohumate stimulated germination the barley seeds but it did not reduce the growth inhibitory effect of SPP. The combined exposure to the studied pollutants negatively affected growth and accumulation of biomass by the barley roots. The introduction of Lignohumate weakened the combined effect but could not completely countervail it. The calculation of inhibition effect showed that the phytotoxicity of phosphorus-containing substances reduced in the order MPA (without buffer) - SPP - MPA (with buffer) - MPA+SPP . The introduction of Lignohumate to the growth medium was the most effective in experiments with low-toxic substances.

Abscisic Acid and Gibberellins Act Antagonistically to Mediate Epigallocatechin-3-Gallate-Retarded Seed Germination and Early Seedling Growth in Tomato

Germination is a crucial event in plant lifecycle mediated by a complex hormonal crosstalk. In this study, we revealed an antagonistic interaction between phytohormone abscisic acid (ABA) and gibberellins in epigallocatechin-3-gallate (EGCG)-retarded germination and early seedling growth in tomato. High concentrations of EGCG (0.5 mM and 1.0 mM) decelerated the seed germination and reduced the germination rate and biomass accumulation in seedlings. EGCG-induced inhibition in seedling growth was associated with oxidative stress and changes in antioxidant enzyme activity. Moreover, EGCG treatment increased the ABA content and decreased the GA3 content, leading to a significant reduction in the ratio of GA3/ABA in a dose-dependent manner. EGCG-induced changes in ABA and GA levels were attributed to the changes in expression levels of genes involved in their metabolism. Either exogenous GA application or endogenous ABA deficiency both alleviated EGCG-induced inhibition in early seedling growth. These results suggest that EGCG inhibits seed germination and early seedling growth by affecting the balance between ABA and GA in tomato. These findings are important to better understand the role of flavonoids in seed germination and their implications in controlling seed dormancy.

Nutrient retranslocation in Larix principis-rupprechtii Mayr relative to fertilization and irrigation

Nutrient retranslocation from senescing foliage to perennial organs is critical for nutrient conservation and a mechanism of plant adaptation to low-fertility soils. And it has been well documented for evergreen species and for deciduous broadleaf tree species. Meanwhile, subirrigation (SI) and fertilization are used to improve the production efficiency of seedlings, however, little is known about how retranslocation in deciduous conifer seedlings is affected by SI or soil fertility. We fertilized Larix principis-rupprechtii Mayr seedlings with 50, 100, and 150 mg N per seedling using SI and overhead irrigation (OI). Seedling growth and nutrient status, at both pre-senescence (T1) and post-abscission (T2) moments, and growing media electrical conductivity were measured to (1) explore relationships between foliar nutrient retranslocation and (a) growth, (b) nutrient status, and (c) media fertility, and (2) examined how these are affected by irrigation method and fertilizer rate. Fertilizer rate and irrigation method had little effect on seedling growth, with the exception of root mass, but N, P, and K concentrations increased with increasing soil fertility and both concentrations and contents were greater under SI compared to OI. Foliar N and K retranslocation was lower under SI compared to OI across all fertilizer rates, while foliar P retranslocation was lower only at the highest fertilizer rate for SI-seedlings. For OI-seedlings, retranslocation was unaffected by fertilizer rate, with average N, P, and K retranslocation efficiencies of 71%, 29%, and 55%, respectively. However, retranslocation in SI-seedlings declined as fertilizer rates increased. Foliar nutrient retranslocation directly correlated with seedling biomass accumulation over the growing season (up to T1) and inversely correlated with soil fertility, shoot biomass accumulation during hardening (from T1 to T2), and T1 nutrient concentration in roots (N, P, and K) and stems (N and K). Understanding nutrient retranslocation dynamics for deciduous woody plants informs more effective nutrient management regimes for seedling production under SI.

Florida Citrus Nursery Trends and Strategies to Enhance Production of Field-Transplant Ready Citrus Plants

The Florida citrus industry is going through major changes and considerable replanting. Many growers are planting varieties, especially rootstocks, that are potentially productive under Huanglongbing (HLB; Candidatus Liberibacter asiaticus) prevalent conditions. However, the high demand for new plant material has put tremendous pressure on citrus nurseries and has created a bottleneck in production. Often it can take more than one year to produce field-transplant ready plants in nurseries; therefore, there is a critical need to accelerate plant production. This three-part study was conducted with the following objectives: (1) determine citrus nursery trends; (2) evaluate use of compost for rootstock germination; and, (3) evaluate use of compost for rootstock seedling growth. According to the nursery survey, rootstock seed germination and seedling growth were the most time-consuming, taking 6–8 months. Moreover, it was apparent from the survey results that 44% of the citrus nurseries were experimenting with potting mixes to achieve adequate plant growth and quality. Our greenhouse study demonstrated successful use of yard waste compost in place of peat moss in a potting mix. With use of 37% to 50% of compost in the potting mix, the overall germination rate and mean emergence time were improved to 70% in less than four weeks for US-897 rootstock as compared to no compost in the potting mix. In addition, 37% to 50% compost resulted in higher biomass accumulation in seedlings. When seedlings of rootstocks C-32 and Flying Dragon were grown with 37% to 50% compost, the growth rate and, therefore, percentage of successful budding were significantly increased as compared to no compost. In addition, substrate analysis indicated that a high compost potting media was rich in mineral nutrients, hence the use of fertilizer in nurseries could be minimized. Altogether, use of compost in place of peat moss seems promising and could accelerate germination and growth of rootstocks, reducing the production time as well as cost.

The effect of red light (660 nm) on proliferative activity and growth reactions in seedlings of plants with contrast photoperiodic reaction

The results of a study of the effect of red light irradiation (660 nm) on the proliferative activity of root meristems and growth reactions of plant seedlings with contrast photoperiodic reactions are presented in this paper. Plants of the family Fabaceae contrasting in the photoperiodic reaction were used as plant material: long-day plants (LDP) of peas (Pisum sativum L.) of the Metsenat variety and short-day plants (SDP) of soybean (Glycine max (L.) Merr.) of the Korsak variety. Phytochromes were activated by irradiating the aerial part of the experimental seedlings with monochromatic red light (RL) of 660 nm using an LED matrix for 30 minutes for 5 days. The proliferative activity of meristem cells was determined by analysis of the mitotic index (MI). The growth reaction was studied by linear growth indicators: the total length of the seedling, the length of the aerial part and roots, and the integral indicator of growth and biosynthetic processes – the accumulation of biomass. According to the results of the experiments, it was shown that the mitotic activity of root meristems under the influence of red light on the aerial part in seedlings of the LDP of pea Metsenat decreased slightly – by 8 %, and in the seedlings of the SDP of soybean Korsak increased significantly – by 47 %. The linear growth and accumulation of biomass in the aerial part under the action of RL irradiation in seedlings of pea of the Metsenat variety and soybean of the Korsak variety decreased, and this effect was more pronounced in soybean than in pea. During irradiation of RL the linear root growth and their biomass accumulation in seedlings of LDP pea decreased slightly, while at the same time, these processes in the roots of soybean SDP seedlings were significantly stimulated. Under the influence of RL in pea seedlings, the growth rate did not change in the length of the aerial part, but in the roots increased, while the rate of biomass accumulation by them decreased. In soybean seedlings during RL irradiation, the growth rate of both the aerial part and the roots decreased, the biomass accumulation rate by the aerial part increased, and by the roots – decreased. LDP of pea Metsenat and SDP of soybean Korsak variety differ in the nature of the reaction of growth processes in response to irradiation of RL. The activation of the phytochrome system in the aerial part causes changes in the proliferative activity and growth processes of the roots, which indicate a systemic response of the plant organism to the action of this factor. The relationship of the photoperiodic reaction of plants with the realization of phytochrome signal in the plant by activating or inhibiting the proliferative activity of root meristems and growth reactions is discussed.

Novel haplotype combinations reveal enhanced seedling vigor traits in rice that can accurately predict dry biomass accumulation in seedlings.

Seedling vigor is of vital importance for the initial plant establishment of direct-seeded rice. Here, 166 recombinant inbred lines were employed to assess eight seedling vigor traits over the first 25 days of germination. Significant correlations were found between most traits, and statistical analysis has revealed, for the first time, a linear relationship that uses seedling height and fresh weight to accurately predict the accumulation of dry biomass. Further, a subset of 20 lines, spanning the phenotypic range of the larger population, were genotyped by using 16 simple sequence repeats (SSR) markers known to be associated with seedling vigor traits. Markers RM317 and RM348 linked with significantly different phenotypes, including seedling height and fresh weight. One combination, haplotype II-1 (RM317 (I/II) and RM348 (1/2)), consistently produced superior values for seedling height, root length, and leaf length. The new prediction tool for seedling dry weight, namely the haplotype of RM317 and RM348, will have a wide range of applications in breeding strategies by using marker-assisted selection to produce elite lines that optimize genetic composition contributing to seedling vigor.

Nitrogen supplementation improves the high-light acclimation of Guazuma ulmifolia Lam. seedlings

High nitrogen supply prevents dynamic photoinhibition in Guazuma ulmifolia seedlings and improves their morphophysiological quality during the high-light acclimation in the nursery. Acclimation under full sun is an important step in the production of tree seedlings in nurseries because it increases plant resistance to stressful conditions. Thus, the development of management techniques that improve high-light acclimation could facilitate the production of higher-quality seedlings. Given the importance of nitrogen (N) for plant growth and photosynthetic metabolism, here we evaluated whether supplementation with high N levels (HN) could positively affect the high-light acclimation of seedlings of Guazuma ulmifolia Lam., a tree species widely used in reforestation programs in the neotropics. We compared the morphophysiological parameters of seedlings transferred from the shaded sector of the nursery to full sun that were supplemented with or without HN. HN supply prevented the midday depression of both photosystem II (PSII) activity and the CO2 assimilation rate, suggesting the avoidance of dynamic photoinhibition by HN. This effect was related to HN-induced increases in the electron transport rate of PSII, carboxylation efficiency and mesophyll conductance to CO2 and not to reduced stomatal limitation. A decrease in excess excitation energy in PSII resulting from energy-demanding N assimilation, as suggested by increases in the light saturation points of the CO2 assimilation and PSII electron transport rates, might also contribute to the protective effect of N. In addition, HN treatment increased seedling biomass accumulation and stem base diameter, enhancing the Dickson quality index of the acclimated seedlings. Overall, these results indicate that HN supply during high-light acclimation in the nursery improves the morphophysiological quality of G. ulmifolia seedlings.

ВПЛИВ ПРАЙМУВАННЯ ГІБЕРЕЛІНОМ ЗА ЯРОВИЗАЦІЇ НА РІСТ ТА ВМІСТ РОЗЧИННИХ ВУГЛЕВОДІВ В ПРОРОСТКАХ ПШЕНИЦІ М’ЯКОЇ

The present study was designed to investigate the influence of gibberellin (GA) priming under vernalization on the growth response, content and fractional composition of soluble carbohydrates in seedlings of 3 varieties of winter wheat - Doridna, Statna and Alians. Modeling different levels of trophic support of the vernalization process and investigating the influence of GA, the following variants were used in the experiments: 1) grains + water (control, optimal trophic support); 2) grains + 10 mg / l GA3, (optimal trophic support); 3) isolated embryos + water (control, lack of trophic support); 4) isolated embryos + 10 mg / l GA3 (lack of trophic support). Vernalization was carried out during 45 days at 4 ° C in Petri dishes on wet filter paper. According to the results, the stimulation of growth processes was identified under the GA effect in all investigated winter wheat varieties. The stimulation occurred as linear growth and biomass accumulation of seedlings, the intensity of which depended on the level of trophic support of these processes. The GA priming in the variant with the lack of trophic support did not significantly stimulate the content of carbohydrates in the varieties Doridna and Statna. It noticeably stimulated the content of carbohydrates in the Alians variety due to changes of oligosaccharides content. The patterns of phytohormonal and trophic regulation of vernalization processes in winter wheat are discussed.

Regulating acorn germination and seedling emergence in Quercus pagoda (Raf.) as it relates to natural and artificial regeneration

Dormancy break and germination requirements for Quercus pagoda (Raf.) acorns were determined, as well as the effects of acorn pretreatment and post-germination temperatures on epicotyl emergence, seedling development, and seedling biomass accumulation. There was an inverse linear relationship between length of cold stratification (5/1 °C for 0–12 weeks) and cumulative germination percentages in all incubation temperatures (15/6, 20/10, 25/15, 30/20 °C). Acorns required 12 weeks of cold stratification to break dormancy. Gibberellic acid substituted for cold stratification; although, it was not as effective as 12 weeks cold stratification. At 16 weeks of cold stratification, 20% of acorns had germinated, and the remaining 80% of ungerminated acorns reached ≥ 97 ± 1% cumulative germination within 4 days in all incubation temperatures. Post-germination time to epicotyl emergence and to leaf flush was a function of temperature, and time decreased with increased temperatures. With light held constant (50 μmol m−2 s−1), seedlings accumulated greater biomass in temperatures > 20/10 °C. Q. pagoda acorns possess Type 2 nondeep physiological dormancy, and this allows for artificial manipulation of timing and duration of germination. Extending cold stratification 4 weeks beyond dormancy break (i.e., 16 weeks) yields more uniform germination across a range of temperatures. Epicotyl emergence, seedling development, and biomass accumulation may be regulated by manipulating growing temperature. In this study, the most uniform seedling cohort with the greatest total biomass was produced when acorns received 16 weeks of cold stratification, followed by transfer of germinants to 30/20 °C.

Emergence and biomass accumulation in seedlings of rice cultivars irrigated with saline water

ABSTRACT The objective of this study was to evaluate the performance of three rice cultivars under saline water irrigation. The experiment was carried out in full sun at the Experimental Farm of the Unilab, in Redenção, Ceará, Brazil, in January 2016. The experimental design was completely randomized (CRD), in a 5 x 3 factorial scheme [irrigation water electrical conductivity (ECw: 0.5, 1.0, 2.0, 3.0 and 4.0 dS m-1) versus three rice cultivars (C1 - Ligeirinho, C2 - Casado and C3 - Meruinho)], totaling 15 treatments, with 4 replicates of 30 seeds per cultivar. After 21 days, the following variables were evaluated: emergence percentage (EP), emergence speed index (ESI), mean time of emergence (MTE), mean speed of emergence (MSE), shoot dry matter (SDM), root dry matter (RDM) and total dry matter (TDM). The cultivar Ligeirinho showed higher tolerance to saline stress with respect to the emergence percentage, emergence speed index and mean speed of emergence. The cultivar Casado showed higher tolerance to saline stress for shoot dry matter, root dry matter and total dry matter in comparison to the other cultivars.

Responses of seedling performance to altered seasonal precipitation in a secondary tropical forest, southern China

Abstract Given the intensified global climate change, understanding the responses of seedlings in tropical forests to changing precipitation patterns is critical for predicting plant community regeneration. In a field study, we investigated the potential effects of changes in seasonal precipitation on seedling establishment and growth of Cinnamomum burmanni, a dominant tree species in a secondary tropical forest, southern China. The field precipitation treatments included ambient rainfall (CT), increased precipitation (IP) in the wet season, and extended dry (ED) season without change in annual rainfall. For the IP treatment, 25% of the mean annual precipitation was added in the wet season using pumps and sprinklers. For the ED treatment, 60% of incoming throughfall was removed in March and April to extend dry season for two months using transparent roofs, and re-added back in October and November with the total annual rainfall amount not changed. The results showed that the IP treatment increased seedling height growth in June and August when extra water was applied. By the end of experiment, stem biomass was significantly greater in IP plots than in ED plots. Precipitation treatments also affected biomass allocation. Seedlings in ED plots had a lower root/shoot ratio and root mass to total mass ratio. Compared to the control, the IP treatment significantly increased leaf and stem nitrogen concentrations of the seedlings. Nitrogen and phosphorus contents in stems and roots were much higher in IP plots than in ED plots, which might be explained by the increased NO3−-N and available phosphorus concentrations in soil. Our findings indicate that extended dry season without change in annual rainfall or increased precipitation in the wet season induced by climate change, is likely to affect soil nutrients, seedling biomass accumulation and partitioning, and nutrient uptake, and thereby impact regeneration dynamics and future community structure in tropical forests.

Selenium improves recovery of wheat seedlings at rewatering after drought stress

Rewatering after drought is beneficial to plants subjected to moderate drought stress, and selenium (Se) could increase the tolerance of plants to stressful environment. The role of Se in rewatering of drought-treated wheat seedlings (Triticum aestivum L., cv Hengmai5229) was studied. The objective was to elucidate whether Se could improve recovery of wheat seedlings at rewatering after drought stress. Drought stress induced a significant reduction in growth parameters, total chlorophyll and soluble protein contents, and increased the rate of superoxide radical (O 2 ·− ) production, MDA content, and the activities of peroxidase, catalase (CAT), and superoxide dismutase in wheat seedlings. Rewatering after drought did not significantly affect biomass accumulation of seedlings over drought treatment, although it decreased the rate of O 2 ·− production and MDA content. However, the combined treatment of rewatering and Se evidently promoted biomass accumulation of seedlings over drought treatment and rewatering alone; and the rate of O 2 ·− production, MDA content, soluble protein content and CAT activity were recovered to the control values. This indicates that Se improved recovery of wheat seedlings at rewatering after drought stress.

Belowground competitive suppression of seedling growth by grass in an African savanna

Coexistence of N2-fixing legumes and non-legume trees with grasses in African savannas results in intense competition between these life-forms. We hypothesised that belowground competition might induce different nutritional constraints in N2- versus non-N2-fixing species. A field (Hluhluwe-imFolozi nature reserve, South Africa) competition experiment with two N2-fixing legume species (Acacia burkei and Acacia karroo) and two non-N2-fixing species (Schotia brachypetala and Spirostachys africana) both with clipped grass and without grass was established. Plants were supplied with no fertilizer, or generous amounts of fertilizer (200 kg N ha−1, 100 kg P2O5 ha−1, 7.1 kg K2O ha−1) supplied as either 28–10 (N–K), P or a combination of these fertilizers (NPK). Regularly clipped grass suppressed growth (by more than 90 %) of both N2- and non-N2-fixing seedlings equally. Biomass accumulation of seedlings grown with grass and the grasses themselves responded positively to NK and/or NPK, but not P, although P-fertilization did have effects on foliar [N] and δ15N values of trees and grasses showing that plants accessed the fertilizer. Tree δ15N values and foliar [N] were also modified by NPK, demonstrating access to fertilizer. However, the ameliorative effects of NPK on grass competition-induced biomass suppression were only partial. This may be due to ‘non-resource competition’ (i.e. root gaps) imposed by dense grass roots. The fact that nutrients were able to partially ameliorate the effects of grass competition, however, indicates that such ‘non-resource competition’ may be partially overcome by even more generous supply of fertilizers.