Foliar Chlorophyll Content Research Articles

Evaluation of hydroponic systems for organic lettuce production in controlled environment.

Organic farming methods, including the use of organic substrates, fertilizers, pesticides, and biological control, are gaining popularity in controlled environment agriculture (CEA) due to economic benefits and environmental sustainability. However, despite several studies focusing on the preparation and evaluation of liquid organic fertilizers, none have explored the compatibility of these fertilizers with different hydroponic systems. Therefore, the objective of this study was to evaluate lettuce production using a liquid organic fertilizer under different hydroponic systems. Four distinct hydroponic methods were selected: nutrient film technique (NFT), deep water culture (DWC) (liquid culture systems), and Dutch bucket (DB), regular plastic container (RPC) (substrate-based systems). 'Green Butter' lettuce was grown using a liquid organic fertilizer (Espartan) for four weeks. Shoot growth parameters (e.g., shoot width, number of leaves, leaf area, foliar chlorophyll content, fresh weight, and dry weight) and root growth parameters (e.g., root length, fresh weight, and dry weight) were measured. The growth difference of lettuce under the DB and RPC systems was negligible, but the growth in RPC was 29% to 60% and 15% to 44% higher than the NFT and DWC systems, respectively, for shoot width, number of leaves, leaf area, shoot fresh weight and dry weight. Root parameters were nearly identical for the NFT and DWC systems but significantly lower (21% to 94%) than the substrate-based DB and RPC systems. Although lettuce grown in the NFT system showed the least growth, its mineral content in the leaf tissue was comparable or sometimes higher than that of substrate-based hydroponic systems. In conclusion, the tested liquid organic fertilizer is suitable for substrate-based hydroponic systems; however, further evaluation of different liquid organic fertilizers, and crop species is required.

Phyto-treatment of tannery industry effluents under combined application of citric acid and chromium-reducing bacterial strain through Lemna minor L.: A lab scale study

Contamination of agricultural soils with heavy metals (HMs) poses a significant environmental threat, especially because industrial discharges often irrigate agricultural lands. A prominent source of HM(s) pollution occurs from tannery effluents containing high concentrations of chromium (Cr) in both Cr3+ and Cr6+ forms along with other toxic materials. Cr is known for its carcinogenic and mutagenic properties in biological systems. Microbe-assisted phytoremediation has emerged as a promising and environmentally friendly approach for detoxifying Cr-contaminated environments. This study aimed to evaluate the performance of citric acid (CA) and a Cr-reducing bacterial strain (Staphylococcus aureus) on the phytoextraction potential of Lemna minor within a Constructed Wetland System treated with tannery wastewater. Various combinations of tannery wastewater (0, 50, and 100 %), CA (0, 5 and 10 mM), and microbial inoculants were applied to the test plants. The mitigative effects of Staphylococcus aureus strain K1 were examined in combination with different concentrations of CA (0, 5, 10 mM). Data on growth and yield attributes highlighted the beneficial effects of bacterial inoculation and CA in ameliorating Cr toxicity in L. minor, as evidenced by increased foliar chlorophyll and carotenoid contents, enhanced antioxidant enzyme activities (SOD, POD, APX, CAT), and improved nutrient uptake. Specifically, CA application resulted in an enhancement of Cr ranging from 12% to 15% and 23%–31% in concentration, and 134%–141% and 322%–337% in Cr accumulation, respectively. When combined with the S. aureus inoculation treatment, CA application (5 and 10 mM) further increased the concentration and accumulation of Cr in L. minor. The enhancement in Cr ranged from 12% to 23% and 27%–41% in concentration, 68%–75%, and 179%–185% in accumulation, respectively. These results demonstrated that L. minor is an effective choice for environmentally friendly Cr remediation due to its continued ability to grow in polluted wastewater. This study suggested that microbial-assisted phytoextraction combined with chelating agents such as CA could be a practical and effective approach for remediating tannery effluents.

Assessment of rice genotypes through the lens of morpho-physiological and biochemical traits in response to arsenic stress

Rice is a globally important food crop which is sensitive to the presence of a metalloid, arsenic (As). There is limited research pertaining to identifying relevant As-tolerant rice germplasm in adaptive breeding research initiatives, despite the fact that As contamination in rice has long been known. This study served to identify the growth performance of different rice genotypes under high levels of As. Rice seed germination analysis (germination percentage, GP) was performed to categorize the eight different rice genotypes and growing under varying As levels including As25, 25 μM and As50, 50 μM. The Zhenong 41 was identified as the highly tolerant genotypes with lowest decrease in GP by 87 %, plant height (PH) by 26 %, and dry weight (DW) by 16 %; while 9311 was observed to be the most sensitive genotype with highest reduction in GP by 44 %, PH by 48 % and DW by 54 % under As25 stress conditions, compared to control treatment. The higher As50 stress treatment delivered more adverse growth inhibitory effects than the rice plants cultivated under As25. Specifically, the As-sensitive rice genotype 9311 showed significantly higher decrease in foliar chlorophyll contents relative to the other genotypes, especially Zhenong 41 (As-tolerant). During exposure to high As levels, the rice genotype 9311 significantly modulated and augmented the production of MDA and H2O2 by stimulating the activities of POD, SOD, and CAT. This study revealed interesting insights into the responses of rice genotypes to variable As stresses throughout the various growth stages. Overall, the findings of this study could be harnessed to support any ongoing As-tolerant rice breeding agendas for cultivation in As-polluted environments.

Effects of biochar types on seed germination, growth, chlorophyll contents, grain yield, sodium, and potassium uptake by wheat (Triticum aestivum L.) under salt stress

Soil salinity is a significant challenge in agriculture, particularly in arid and semi-arid regions such as Pakistan, leading to soil degradation and reduced crop yields. The present study assessed the impact of different salinity levels (0, 25, and 50 mmol NaCl) and biochar treatments (control, wheat-straw biochar, rice-husk biochar, and sawdust biochar applied @ 1% w/w) on the germination and growth performance of wheat. Two experiments: a germination study and a pot experiment (grown up to maturity), were performed. The results showed that NaCl-stress negatively impacted the germination parameters, grain, and straw yield, and agronomic and soil parameters. Biochar treatments restored these parameters compared to control (no biochar), but the effects were inconsistent across NaCl levels. Among the different biochars, wheat-straw biochar performed better than rice-husk and sawdust-derived biochar regarding germination and agronomic parameters. Biochar application notably increased soil pHs and electrical conductivity (ECe). Imposing NaCl stress reduced K concentrations in the wheat shoot and grains with concomitant higher Na concentrations in both parts. Parameters like foliar chlorophyll content (a, b, and total), stomatal and sub-stomatal conductance, and transpiration rate were also positively influenced by biochar addition. The study confirmed that biochar, particularly wheat-straw biochar, effectively mitigated the adverse effects of soil salinity, enhancing both soil quality and wheat growth. The study highlighted that biochar application can minimize the negative effects of salinity stress on wheat. Specifically, the types and dosages of biochar have to be optimized for different salinity levels under field conditions.

Effects of Black Pepper-Groundnut Intercropping on Soil Total Nitrogen and the Physiological Characteristics of Black Pepper (Piper nigrum L.)

The utilisation of leguminous groundnut (Arachis hypogaea) has been recognised for its advantageouseffects, including nitrogen (N) fixation, which consequently enhances the soil N availability. The objectiveof this study was to analyse the impact of a mixed intercropping system involving pepper (Piper nigrum)and groundnut on soil total N. Additionally, the study aimed to assess the influence of N on variousparameters, including the Normalised Difference Vegetation Index (NDVI), chlorophyll content, and gasexchange rate of black pepper. The study employed a randomized complete block design in a fieldexperiment, with two treatments that were reproduced 15 times. The treatments consisted of the controlgroup (M0), which involved a pepper plot without groundnut intercropping, and the mixed intercroppingsystem (M1), which involved a pepper plot with groundnut intercropping. The soil total N content exhibiteda statistically significant increase (p < 0.05) in the context of a mixed intercropping system. Theintercropping treatment resulted in considerably higher values (p < 0.05) for pepper NDVI, foliarchlorophyll concentration, photosynthetic rates (A), stomatal conductance (gs), and transpiration (E)compared to the control treatment. Moreover, a positive correlation has been seen between the chlorophyllcontent of pepper leaves and the total N content in the soil. Similarly, a positive association has beenestablished between the A of pepper plants and the total N content in the soil. As a result, the observedelevation in A under high N circumstances was ascribed to an augmentation in chlorophyll concentration.Consequently, the integration of groundnut within pepper cultivation systems over an extended period hasthe potential to enhance crop productivity through the amelioration of soil conditions.

EFFECT OF SELENIUM ON CHLOROPHYLL CONTENT OF WHEAT PLANT (TRITICUM AESTIVUM L.)

A pot culture experiment was conducted to study the effect of various concentrations of selenium provided as di sodium selenite and di sodium selenate (0.5, 1.0, 2.0, 4.0, 8.0, 16.0 ugg-1) on chlorophyll of wheat plants (Triticum aestivum L.). Low concentration of selenium was observed to be beneficial for the test plants. A positive correlation was observed between a lower level of selenium (0.5 and 1.0 ugg-1) and foliar chlorophyll content. Higher levels of selenium (2.0 – 16.0 ugg-1) were toxic to the plants.

Field Performance of ‘Valencia’ Sweet Orange Trees Grafted onto Pummelo Interstocks and Swingle Citrumelo Rootstocks under Huanglongbing (HLB) Endemic Conditions

Interstocks have been used in fruit tree cultivation to regulate tree size and improve fruit production and quality. In this study, several Huanglongbing (HLB)-tolerant open-pollinated pummelo interstock candidates were evaluated as interstocks between the Swingle rootstock and the ‘Valencia’ scion, with Swingle serving as the control interstock. After 5 years in the field, most trees did not exhibit visual HLB symptoms, although the trees were infected with HLB, and the CaLas Ct values in the ‘Valencia’ leaves of the different interstock treatments ranged between 25.88 and 27.82. Although the foliar chlorophyll content among the interstock treatments was not highly significant (p-value = 0.0313), the foliar starch content was significantly different (p-value = 0.0018). ‘Valencia’ grafted onto 5-1-99-3 and HBJL-4 interstocks (both open pollinated seedlings of the Hirado Buntan pummelo) exhibited the highest total phenolic compound (TPC) levels (46.44 and 46.36 mg gallic acid g−1 FW). Transcripts of CsPR1 and CsPR2, two pathogenesis-related (PR) genes, were upregulated in ‘Valencia’ grafted onto open pollinated seedling selections of the red shaddock pummelo, Liang Ping Yau pummelo, and Hirado Buntan pummelo compared with ‘Valencia’ grafted onto Swingle. All interstocks influenced the tree growth rate and improved canopy volume in the field compared to the control trees without any interstocks (p-value = 0.0085). The 5-4-99-7 (red shaddock pummelo) and 8-1-99-1B (Liang Ping Yau pummelo) interstock trees had the highest canopy volume among all the treatments. We propose, based on our current results, that HLB-tolerant citrus accessions, when judiciously used as interstocks, may enhance plant defense and provide increased HLB tolerance to susceptible scions.

Foliar Spectral Signature Analysis of Three Pepper (Piper nigrum L.) Cultivars in Malaysia

Pepper (Piper nigrum L.) is an important cash crop for smallholders in the state of Sarawak, Malaysia. At present, there are more than eight pepper cultivars being planted in the state since the 1950s. In this study, the unique spectral signatures of three high yielding pepper cultivars in Malaysia were examined using a ground-based spectral sensor to detect varietal differences. Concurrent foliar spectral signatures, chlorophyll concentration, and Normalized Difference Vegetation Index (NDVI) of cultivar Kuching, Semongok Aman and Semongok Emas were recorded under normal field conditions. Foliar chlorophyll concentration and NDVI results showed that all the matured pepper vines under this assessment were in healthy condition. From a rough observation, except for a slight increase in the visible (VIS) region of the spectrum (500 to 699 nm) for cultivar Semongok Aman and Semongok Emas, spectral reflectance of all three pepper cultivars were similar in the near-infrared region (700 to 1000 nm). The results for First Derivative Curves analysis indicated that the 684.5 to 756.5 nm region showed the highest separation followed by region with the second lowest separation (504.5 to 540.5 nm). The highest value was obtained in the Red Edge Position (REP) for cultivar Kuching, Semongok Aman and Semongok Emas which were 709, 706 and 710, respectively. The highest value obtained in the VIS region for cultivar Kuching, Semongok Aman and Semongok Emas were 523, 524 and 527, respectively. These fundamental findings suggested that it is possible to discriminate pepper cultivars through field spectroscopy and first derivative analysis. In addition, this information may be used for further studies related to precision agriculture particularly in integrated nutrient and disease management.

Investigating Foliar Macro- and Micronutrient Variation with Chlorophyll Fluorescence and Reflectance Measurements at the Leaf and Canopy Scales in Potato

Vegetation indices (VIs) related to plant greenness have been studied extensively for the remote detection of foliar nitrogen content. Yet, the potential of chlorophyll fluorescence (ChlF) and photoprotection-based indices such as the photochemical reflectance index (PRI) or the chlorophyll/carotenoid index (CCI) for the detection of a wide range of nutrients remains elusive. We measured the dynamics of foliar macro- and micronutrient contents in potato plants as affected by fertilization and water stress, along with leaf and canopy level observations of spectral reflectance and ChlF (or solar-induced fluorescence). ChlF and photoprotection-related indices were more strongly related to a wide range of foliar nutrient contents compared to greenness-based indices. At the leaf level, relationships were largely mediated by foliar chlorophyll contents (Cab) and leaf morphology, which resulted in two contrasting groupings: a group dominated by macronutrients N, P, K, and Mg that decreased during canopy development and was positively correlated with Cab, and a group including Cu, Mn, Zn, and S that increased and was negatively related to Cab. At the canopy-level, spectral indices were additionally influenced by canopy structure, and so their capacity to detect foliar nutrient contents depends on the spatiotemporal covariation between foliar Cab, morphology, and canopy structure within the observations.

Alternating processes of dry and wet nitrogen deposition have different effects on the function of canopy leaves: Implications for leaf photosynthesis.

Canopy leaves are sinks of dry and wet nitrogen (N) deposition, most studies have not considered the response of canopy leaves to the alternating processes of dry and wet N deposition. We manipulated a close top chamber experiment to observe the effects of simulated N deposition with the same total deposition flux but different dry to wet ratios on leaf structure and physiology by spraying NH4Cl solution or supplying gaseous NH3 over the canopy of seedlings of three species (Betula platyphylla, Fraxinus mandshurica, Pinus koraiensis) placed in the chamber. After 32 days of N deposition and relative to the control, the leaf morphology and mesophyll tissue structure of the three species had no significant changes under all N deposition treatments. With the increase in the ratio of dry to wet N deposition, the N concentration, N metabolizing enzyme activity and soluble protein concentration in leaves of all three species increased continuously, but for the leaf light-saturated net photosynthesis rate, B. platyphylla showed a continuous increase, F. mandshurica showed a continuous decrease, and P. koraiensis showed no significant change. We found that F. mandshurica was the only species whose foliar chlorophyll and potassium concentration decreased with the increase in the ratio of dry to wet N deposition and its leaf light-saturated net photosynthesis rate was positively correlated with foliar chlorophyll and potassium concentration, respectively. Our results indicate that dry deposition is relatively more important on leaf physiological functions in alternating deposition. B. platyphylla and P. koraiensis may better acclimate to canopy NH3/NH4 + deposition than F. mandshurica. Most importantly, the results indicate that a single simulated dry and wet deposition would overestimate and underestimate the response of leaf function to atmospheric N deposition, respectively. Alternating processes of dry and wet deposition should be considered for more realistic assessments of the effects of atmospheric N deposition in forests.

IAA Plays an Important Role in Alkaline Stress Tolerance by Modulating Root Development and ROS Detoxifying Systems in Rice Plants

Auxin regulates plant growth and development, as well as helps plants to survive abiotic stresses, but the effects of auxin on the growth of alkaline-stressed rice and the underlying molecular and physiological mechanisms remain unknown. Through exogenous application of IAA/TIBA, this study explored the physiological and molecular mechanisms of alkaline stress tolerance enhancement using two rice genotypes. Alkaline stress was observed to damage the plant growth, while exogenous application of IAA mitigates the alkaline-stress-induce inhibition of plant growth. After application of exogenous IAA to alkaline-stressed rice, dry shoot biomass, foliar chlorophyll content, photosynthetic rate in the two rice genotypes increased by 12.6-15.6%, 11.7-40.3%, 51.4-106.6%, respectively. The adventitious root number, root surface area, total root length and dry root biomass in the two rice genotypes increased by 29.3-33.3%, 26.4-27.2%, 42.5-35.5% and 12.8-33.1%, respectively. The accumulation of H2O2, MAD were significantly decreased with the application of IAA. The activities of CAT, POD, and SOD in rice plants were significantly increased by exogenous application of IAA. The expression levels of genes controlling IAA biosynthesis and transport were significantly increased, while there were no significant effects on the gene expression that controlled IAA catabolism. These results showed that exogenous application of IAA could mitigate the alkaline-stress-induced inhibition of plant growth by regulating the reactive oxygen species scavenging system, root development and expression of gene involved in IAA biosynthesis, transport and catabolism. These results provide a new direction and empirical basis for improving crop alkaline tolerance with exogenous application of IAA.

Performance of Leguminous Tree Species in Sand-mined Soil Under Nursery Conditions

Early growth performance of Delonix regia, Albizia lebbeck , Albizia saman and Leuceana leucocephala in soil from an abandoned sand mining site was investigated. Using a completely randomized block design, forty seedlings from each species were transplanted into topsoil and sand-mined soil. Total height, collar diameter, and number of leaves were monitored fortnightly, for 16 weeks. Biomass accumulated by the seedlings was determined, while root nodulation and foliar chlorophyll content were assessed. Significant differences were observed in the main and interaction effects of soil type and species type on growth variables, with higher growth in topsoil. Delonix regia in topsoil had the highest total height (41.01±3.14 cm) and collar diameter (7.11±0.34 cm), while A. lebbeck had the highest number of leaves (11.39±0.37). Biomass accumulation followed the trend: D. regia>A. lebbeck> A. saman>L. leucocephala for both topsoil and sand-mined soil treatments. Highest nodulation was in A. saman (13) growing in sand-mined soil while D. regia (6.20±1.20 mg/g) in topsoil had the highest chlorophyll content. All the species survived in the sand-mined soil with D. regia and A. lebbeck out performing the other species, indicating their potential choice for rehabilitation of sand mining quarries.

Identifying and modelling key physiological traits that confer tolerance or sensitivity to ozone in winter wheat

Tropospheric ozone threatens crop production in many parts of the world, especially in highly populated countries in economic transition. Crop models suggest substantial global yield losses for wheat, but typically such models fail to address differences in ozone responses between tolerant and sensitive genotypes. Therefore, the purpose of this study was to identify physiological traits contributing to yield losses or yield stability under ozone stress in 18 contrasting wheat cultivars that had been pre-selected from a larger wheat population with known ozone tolerance. Plants were exposed to season-long ozone fumigation in open-top chambers at an average ozone concentration of 70 ppb with three additional acute ozone episodes of around 150 ppb. Compared to control conditions, average yield loss was 18.7 percent, but large genotypic variation was observed ranging from 2.7 to 44.6 percent. Foliar chlorophyll content represented by normalized difference vegetation index and net CO2 assimilation rate of young leaves during grain filling were the physiological traits most strongly correlated with grain yield losses or stability. Accumulative effects of chronic ozone exposure on photosynthesis were more detrimental for grain yield than instantaneous effects of acute ozone shocks, or accelerated senescence of older leaves represented by changes in the ratio of brown leaf area/green leaf area index. We used experimental data of two selected tolerant or sensitive varieties, respectively, to parametrize the LINTULCC2 crop model expanded with an ozone response routine. By specifying parameters representing the distinct physiological responses of contrasting genotypes, we simulated yield losses of 7 percent (tolerant) or 33 percent (sensitive). By considering genotypic differences in ozone response models, this study helps to improve the accuracy of simulation studies, estimate the effects of adaptive breeding, and identify physiological traits for the breeding of ozone tolerant wheat varieties that could deliver stable yields despite ozone exposure.

Foliar chlorophyll concentration modulates the degree of fungal exploitation in a rhizoctonia-associated orchid.

Some green orchids obtain carbon from both mycobionts and photosynthesis at the adult stage. Intriguingly, these orchids can produce albino and, in rare cases, variegated phenotypes. Here, we studied a Platanthera hondoensis population with green, variegated, and albino individuals. Although its closely related Platanthera species are usually associated with non-ectomycorrhizal rhizoctonias, and several studies have failed to find evidence of trophic plasticity in rhizoctonia-associated orchids, variegated and albino P. hondoensis must possess a higher fungal dependency than green P. hondoensis. Therefore, we investigated whether (i) P. hondoensis is associated with non-ectomycorrhizal rhizoctonias and (ii) the degree of mycoheterotrophy (using 13C abundance as a proxy) correlates with the foliar chlorophyll concentration. High-throughput DNA sequencing revealed that all P. hondoensis phenotypes were dominantly associated with a rhizoctonia from Ceratobasidiaceae belonging to a clade distinct from recognized ectomycorrhizal clades. Regression analysis revealed a positive linear relationship between foliar chlorophyll concentration and the degree of mycoheterotrophy. This study strongly suggests that rhizoctonia-associated P. hondoensis can dynamically adjust fungal exploitation in response to photosynthetic carbon levels. Since rhizoctonia is the most common orchid mycorrhizal partner, trophic plasticity may be a widespread adaptive trait in green orchids.

Climate change influences foliar nutrition and metabolism of red maple (Acer rubrum) trees in a northern hardwood forest

AbstractMean annual air temperatures are projected to increase, while the winter snowpack is expected to shrink in depth and duration for many mid‐ and high‐latitude temperate forest ecosystems over the next several decades. Together, these changes will lead to warmer growing season soil temperatures and an increased frequency of soil freeze–thaw cycles (FTCs) in winter. We took advantage of the Climate Change Across Seasons Experiment (CCASE) at the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire, USA, to determine how these changes in soil temperature affect foliar nitrogen (N) and carbon metabolism of red maple (Acer rubrum) trees in 2015 and 2017. Earlier work from this study revealed a similar increase in foliar N concentrations with growing season soil warming, with or without the occurrence of soil FTCs in winter. However, these changes in soil warming could differentially affect the availability of cellular nutrients, concentrations of primary and secondary metabolites, and the rates of photosynthesis that are all responsive to climate change. We found that foliar concentrations of phosphorus (P), potassium (K), N, spermine (a polyamine), amino acids (alanine, histidine, and phenylalanine), chlorophyll, carotenoids, sucrose, and rates of photosynthesis increased with growing season soil warming. Despite similar concentrations of foliar N with soil warming with and without soil FTCs in winter, winter soil FTCs affected other foliar metabolic responses. The combination of growing season soil warming and winter soil FTCs led to increased concentrations of two polyamines (putrescine and spermine) and amino acids (alanine, proline, aspartic acid, γ‐aminobutyric acid, valine, leucine, and isoleucine). Treatment‐specific metabolic changes indicated that while responses to growing season warming were more connected to their role as growth modulators, soil warming + FTC treatment‐related effects revealed their dual role in growth and stress tolerance. Together, the results of this study demonstrate that growing season soil warming has multiple positive effects on foliar N and cellular metabolism in trees and that some of these foliar responses are further modified by the addition of stress from winter soil FTCs.

Diverse Understory Vegetation Alleviates Nitrogen Competition with Crop Trees in Poplar Plantations

Understory vegetation plays a crucial role in nutrient turnover and cycling in plantations, but it also competes for nutrients with crop trees when only a single species is present due to its specific nutrient requirements. However, it remains unclear whether this competition can be alleviated when the species richness of understory vegetation increases. In this study, we tested different gradients of understory vegetation species richness, including understory vegetation removal (UR), the retention of a single main understory vegetation species (RS), and the retention of natural diverse understory vegetation (RD) as part of a poplar (Populus deltoides ‘Nanlin-3804′) plantation, to study their effects on poplar growth, and to evaluate nitrogen (N) usage and how this was affected by the interactions between the poplar and understory vegetation. The results showed a generally lower periodic growth, and a significant decline in the foliar chlorophyll content and glutamine synthetase activity of poplar under treatment with RS and RD compared to those under UR treatment conducted in July 2019, which clearly indicated N competition between the understory vegetation and poplar trees. However, no significant difference was detected in the foliar chlorophyll content and glutamine synthetase activity of poplar under RD and RS treatment; only the nitrate reductase activity in poplar leaves under RD treatment declined significantly, by 22.25%, in June 2019. On the contrary, the diameter at breast height (DBH) of the poplar under RD treatment showed an increase of 34.69% from July to August 2019, compared with that under RS treatment. Furthermore, the increase in the species richness of understory vegetation resulted in an increase in the δ15N values in the poplar leaves, which was strongly regulated by the NH4+-N pool in the 10–20 cm soil layer, indicating the effective coordination of N utilization between poplar and understory vegetation when diversified understory plant species were present. These findings demonstrate the essential role of understory vegetation species diversity in alleviating N competition with crop trees, and provide guidance for understory vegetation management in poplar plantations.

Effects of clonal integration on allelopathy of invasive plantWedelia trilobataunder heterogeneous light conditions

AbstractPlant invasion is one of the most serious threats to ecosystems worldwide. When invasive plants with the ability of clonal growth invading or colonizing in new habitat, their interconnected ramets may suffer from heterogeneous light. Effects of clonal integration on allelopathy of invasive plants are poorly understood under heterogeneous light conditions. To investigate the effects of clonal integration on allelopathy of invasive plant Wedelia trilobata under heterogeneous light conditions, a pot experiment was conducted by using its clonal fragments with two successive ramets. The older ramets were exposed to full light, whereas the younger ones were subjected to 20% full light. The younger ramets of each clonal fragment were adjacently grown with a target plant (one tomato seedling) in a pot. Stolon between two successive ramets was either severed or retained intact. In addition, two tomato seedlings (one as target plant) were adjacently grown in a pot as contrast. Compared with severing stolon, biomass accumulation, foliar chlorophyll and nitrogen contents, chlorophyll fluorescence parameters and net photosynthetic rates of the target plants as well as their root length and activity, were significantly decreased when stolon between interconnected ramets of W. trilobata retained intact. Under heterogeneous light conditions, transportation or sharing of carbohydrate between two successive ramets enhanced allelopathy of the young ramets subjected to 20% full light treatment. It is suggested that clonal integration may be important for invasion or colonization of invasive plants with ability of clonal growth under heterogeneous light conditions.

Aroma composition of Tempranillo grapes as affected by iron deficiency chlorosis and vine water status

Water deficit and iron nutritional deficiency (iron chlorosis) are frequent environmental stresses affecting grapevine production in the Mediterranean region. The objectives of this work were (i) to study the combined effects of both stresses on aromatic profile of Tempranillo grapes, occurring simultaneously in the vineyard, and (ii) to evaluate the viability of foliar chlorophyll content at veraison (Chl) to early assess aromatic quality potential of grapes in those conditions. Twenty non-irrigated vineyard subzones (10 m × 10 m each), affected and non-affected by iron chlorosis, were monitored in Ribera del Duero Appellation of Origin (North-Central Spain) during two consecutive seasons. Factorial ANOVA was performed to study the effects of predawn leaf water potential and Chl measured at veraison on the must composition parameters and, specifically, on the concentrations of free and bound aromatic compounds. Water deficit tended to increase color intensity and extractable anthocyanin content of the grapes, whereas the incidence of iron deficiency enhanced total phenolic compound content within subzones with better water status. More water or iron stressed subzones restricted C6-alcohols contents than less stressed subzones. Without significant effects on vine vigor, yield or berry size, the incidence of iron chlorosis increased the concentrations of some specific terpenes, C13-norisoprenoids, volatile acids and volatile phenols. These results showed that low to moderate iron stress can have positive effects on grape aromatic quality, and demonstrated that Chl can be a useful tool in precision viticulture to map the aromatic potential within rainfed vineyards affected by iron chlorosis.

Effects of activated water irrigation on growth characteristics of soybean under drought stress

To understand the effects of activated water irrigation on soybean growth under different drought conditions and explore the underlying mechanisms, an indoor pot experiment was conducted under four moisture conditions of 95%-100%, 75%-85%, 55%-65% and 35%-45% of the maximum water holding capacity (80% moisture) of the medium. Soybean was irrigated with tap water, magnetized water, aerated water, and magnetized and then aerated water, respectively. The results showed that total biomass, leaf area, root to shoot ratio, and root length of magnetized water irrigation increased by 67.6%, 23.5%, 84.6% and 122.8%, respectively compared with tap water irrigation after 30 days of growth under 35%-45% severe drought condition. All the variables were increased by 70.8%, 24.0%, 61.9% and 162.3% respectively in magnetized and aerated water treatment. There was no significant difference for foliar chlorophyll content. The values of the other water treatments were slightly lower than that of tap water. In conclusion, magnetized water irrigation effectively enhanced root growth, root-shoot ratio, and water use efficiency of soybean, and alleviated the negative effects of drought stress under severe drought condition.

Not so stressful after all: Epiphytic individuals of accidental epiphytes experience more favourable abiotic conditions than terrestrial conspecifics

Vascular epiphytes are mainly associated with tropical and subtropical forest ecosystems. However, the frequent occurrence of accidental epiphytes in temperate forests proves that epiphytic growth of vascular plants is possible in tree crowns at these latitudes. Comparing the abiotic conditions of epiphytic and terrestrial microhabitats in conjunction with intraspecific differences in functional traits of the inhabiting plants, we identified limitations to vascular epiphytism in the study area in a Central European low mountain range. We determined light availability, winter temperatures, soil moisture, nutrient concentrations, and pH of arboreal soil in crotches of broad-leaved trees and in the immediate vicinity of each tree on the ground. Similarly, we quantified total plant water content, relative foliar chlorophyll content, specific leaf area (SLA), leaf dry matter content (LDMC), root-mass fraction, and aboveground nutrient concentrations of 110 pairs of epiphytic and terrestrial conspecifics. Water and nutrient availability were generally high in crotches filled with arboreal soil, suggesting better growth conditions than on the ground. A trophic advantage of epiphytic individuals over terrestrial conspecifics can be deduced from higher plant nutrient concentrations, higher SLA, and lower LDMC. Advantageous growth conditions might even result in higher growth rates and higher fitness of epiphytic individuals. Our findings highlight that vascular epiphytism in the study area is not necessarily limited by abiotic conditions but at least partly by the availability of old and structurally diverse trees providing suitable microhabitats. Accordingly, management actions in these secondary forest ecosystems should incorporate the preservation of old and large deciduous trees in order to sustain arboreal microhabitats and the associated biota.