Decreased Plant Biomass Research Articles

The paradoxical effects of beneficial bacteria on Solanum lycopersicum under Cd stress.

This study investigated the complex interactions between a novel consortium and tomato seedlings under cadmium (Cd) stress. The consortium consists of two bacteria, Pseudomonas sp. HS4 and Paenarthrobacter sp. AS8, both with proven plant growth-promoting (PGP) properties, isolated from Cd hyperaccumulators. Our research highlights the paradoxical effects of these bacteria, revealing their dual role in reducing Cd uptake while simultaneously inducing oxidative stress in plants. Hydroponic experiments showed that the consortium reduced Cd accumulation in tomato shoots by 52% compared to uninoculated controls. However, this reduction was accompanied by decreased plant biomass and increased oxidative stress, with malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) levels up to 80% and 160% higher, respectively, in inoculated plants. Root H₂O₂ production increased by 38% under 50 μM Cd without a corresponding rise in catalase (CAT) activity. Despite Cd exposure, the consortium promoted chlorophyll and carotenoid synthesis, restoring pigment levels to those of unstressed controls. Gene expression analysis revealed a complex impact on stress responses, with inoculation suppressing Sl1 gene expression in roots and upregulating the oxidative stress-related GR-1 gene in shoots. These findings highlight the complex and multifaceted relationship between beneficial bacteria and plant fitness under heavy metal stress, with significant implications for sustainable agriculture. The study raises new questions regarding the broader physiological and ecological impacts of applying hyperaccumulator-associated bacteria in crop management, emphasizing the necessity for deeper mechanistic insights into these interactions to fully harness their potential in improving crop resilience and productivity.

Consecutive annual mowing reduces soil respiration and increases the proportion of autotrophic component in a meadow steppe

BcakgroundSoil respiration (Rs), as the second largest CO2 emissions of terrestrial ecosystems, is sensitive to disturbance and consequent environmental changes. Mowing is strategically implemented as an management approach and has the potential to influence carbon cycling in meadow steppes. However, it remains unclear how and why Rs and its heterotrophic (Rh) and autotrophic (Ra) components respond to consecutive mowing and associated ecological consequences. Here, we conducted a field mowing experiment in a meadow steppe in 2018 and monitored Rs, Rh, and Ra from 2019 to 2022.ResultsWe observed a significant reduction in Rs by 4.8% across four years, primarily attributed to a decrease in Rh. This decline in Rs intensified over time, indicating an accumulative effect of mowing. In addition, mowing induced an generally increasing Ra/Rs ratio over the experimental years with a simultaneous increase in the ratio of belowground to aboveground biomass (BGB/AGB). Furthermore, structural equation modeling results revealed that the decline in Rs was largely ascribed to reduced microbial biomass carbon (MBC) under mowing, while the increased Ra/Rs was primarily explained by the enhanced BGB/AGB. Partial regression analysis suggested that the biotic factor of microbial biomass dominated changes in soil respiration induced by mowing rather than abiotic soil temperature.ConclusionsOur findings showed that consecutive mowing decreased Rs and raised Ra/Rs in meadow steppe by decreasing plant biomass and altering the proportion of biomass allocation. This observed decline in Rs would help to reduce CO2 concentration in atmosphere as well as alleviate global warming. However, considering the concurrent lower microbial biomass, the potential positive impacts of mowing on climate and ecosystem function should be reevaluated in future grassland management practices.

Sweet Cherry Plants Prioritize Their Response to Cope with Summer Drought, Overshadowing the Defense Response to Pseudomonas syringae pv. syringae.

Disease severity and drought due to climate change present significant challenges to orchard productivity. This study examines the effects of spring inoculation with Pseudomonas syringae pv. syringae (Pss) on sweet cherry plants, cvs. Bing and Santina with varying defense responses, assessing plant growth, physiological variables (water potential, gas exchange, and plant hydraulic conductance), and the levels of abscisic acid (ABA) and salicylic acid (SA) under two summer irrigation levels. Pss inoculation elicited a more pronounced response in 'Santina' compared to 'Bing' at 14 days post-inoculation (dpi), and those plants inoculated with Pss exhibited a slower leaf growth and reduced transpiration compared to control plants during 60 dpi. During differential irrigations, leaf area was reduced 14% and 44% in Pss inoculated plants of 'Bing' and 'Santina' respectively, under well-watered (WW) conditions, without changes in plant water status or gas exchange. Conversely, water-deficit (WD) conditions led to gas exchange limitations and a 43% decrease in plant biomass compared to that under WW conditions, with no differences between inoculation treatments. ABA levels were lower under WW than under WD at 90 dpi, while SA levels were significantly higher in Pss-inoculated plants under WW conditions. These findings underscore the influence on plant growth during summer in sweet cherry cultivars that showed a differential response to Pss inoculations and how the relationship between ABA and SA changes in plant drought level responses.

Effects of Cadmium Stress on Tartary Buckwheat Seedlings.

Cadmium (Cd) is a naturally occurring toxic heavy metal that adversely affects plant germination, growth, and development. While the effects of Cd have been described on many crop species including rice, maize, wheat and barley, few studies are available on cadmium's effect on Tartary buckwheat which is a traditional grain in China. We examined nine genotypes and found that 30 µM of Cd reduced the root length in seedlings by between 4 and 44% and decreased the total biomass by 7 to 31%, compared with Cd-free controls. We identified a significant genotypic variation in sensitivity to Cd stress. Cd treatment decreased the total root length and the emergence and growth of lateral roots, and these changes were significantly greater in the Cd-sensitive genotypes than in tolerant genotypes. Cd resulted in greater wilting and discoloration in sensitive genotypes than in tolerant genotypes and caused more damage to the structure of root and leaf cells. Cd accumulated in the roots and shoots, but the concentrations in the sensitive genotypes were significantly greater than in the more tolerant genotypes. Cd treatment affected nutrient uptake, and the changes in the sensitive genotypes were greater than those in the tolerant genotypes, which could maintain their concentrations closer to the control levels. The induction of SOD, POD, and CAT activities in the roots and shoots was significantly greater in the tolerant genotypes than in the sensitive genotypes. We demonstrated that Cd stress reduced root and shoot growth, decreased plant biomass, disrupted nutrient uptake, altered cell structure, and managed Cd-induced oxidative stress differently in the sensitive and tolerant genotypes of Tartary buckwheat.

Differential growth and metal uptake efficiency of castor bean genotypes on a lead contaminated soil

<p>Present study investigated the unknown responses of five castor bean genotypes to lead (Pb) contaminated soil, focusing on their growth and metal uptake efficiency. A unique aspect is the simultaneous assessment of multiple genotypes, offering a holistic view of their reactions to soil contamination. Five castor genotypes (NIAB Gold, NIAB Spineless, NIAB-2020, DS-30, and C-3) were grown in pots filled with soil spiked with varying concentrations of Pb (0, 100, 200, 400, and 800 mg kg-1). Results have shown that increasing Pb concentrations led to a general decrease in plant biomass and photosynthetic pigments in all castor genotypes, however NIAB-2020 and DS-30 showcased remarkable resilience. Interestingly, the activities of antioxidant enzymes revealed a contrasting pattern. While superoxide dismutase and peroxidase activity declined, catalase and ascorbate peroxidase activity increased with higher Pb levels. Notably, DS-30 and NIAB-2020 exhibited the maximum catalase and ascorbate peroxidase activity at highest Pb concentration. Furthermore, these genotypes displayed impressive Pb uptake, particularly in their roots, exceeding the other tested genotypes. With metal translocation factor less than 1, NIAB-2020 and DS-30 showed promising potential for phytostabilization through efficient Pb accumulation, coupled with strengthened antioxidant defense mechanisms and restricted translocation, making them compelling candidates for eco-friendly remediation strategies.</p>

Tomato plant growth promotion and drought tolerance conferred by three arbuscular mycorrhizal fungi is mediated by lipid metabolism

Arbuscular mycorrhizal fungi (AMF) can promote plant growth and enhance plant drought tolerance with varying effect size among different fungal species. However, the linkage between the variation and the lipid metabolism, which is exclusively derived from plants, has been little explored thus far. Here, we established AM symbiosis between tomato (Solanum lycopersicum) plants and three AMF species (Rhizophagus intraradices, Funneliformis mosseae, Rhizophagus irregularis) under well watered (WW) or drought stressed (DS) conditions in pot experiment. The plant biomass, chlorophyll fluorescence Fv/Fm, shoot P content and mycorrhizal colonization were determined. Meanwhile, fatty acid (FA) profiles and relative expression of genes encoding for nutrition exchange (SlPT4, SlPT5, RAM2, STR/STR2) in roots were also monitored. DS significantly decreased plant biomass while AMF significantly increased it, with three fungal species varying in their growth promoting capacity and drought tolerance capacity. The growth promoting effect of R. irregularis was lower than those of R. intraradices and F. mosseae, and was associated with higher mycorrhizal colonization and more consumption of lipids. However, the drought tolerance capacity of R. irregularis was greater than those of R. intraradices and F. mosseae, and was associated with less decrease in mycorrhizal colonization and lipid content. We also found that AMF mediated plant drought tolerance via regulating both AM specific FAs and non-AM specific FAs in a complementary manner. These data suggest that lipid metabolism in AM plays a crucial role in plant drought tolerance mediated by AMF.

Effects of multi-plant harvesting on nitrogen removal and recovery in constructed wetlands

The harvesting of plants is considered an effective method for nutrient recovery in constructed wetlands (CWs). However, excessive plant harvesting can lead to a decrease in plant biomass. It remains unclear what harvesting frequency can optimize plant nutrient uptake and pollutant removal. In this study, CWs planted with Myriophyllum aquaticum were constructed, and three different frequencies of plant harvesting (high: 45 days/time; low: 90 days/time; none: CK) were set to investigate nitrogen removal and its influencing mechanism, as well as the capacity for plant nutrient recovery. The results showed that the average removal efficiencies of ammonia nitrogen (NH4+-N) at 45 days/time, 90 days/time, and CK were 90.3%, 90.8%, and 88.3% respectively, while the corresponding total nitrogen (TN) were 61.2%, 67.4%, and 67.4%. Dissolved oxygen (DO) concentration and water temperature were identified as the main environmental factors affecting nitrogen removal efficiency. Low harvest frequency (90 days/time) increased DO concentration and NH4+-N removal efficiency without impacting TN removal. Additionally, TN recovery from plants under high and low harvest was found to be approximately 9.21–9.32 times higher than that from no harvest conditions. The above studies indicated that a harvest frequency of every 90 days was one appropriate option for M. aquaticum, which not only increased NH4+-N removal efficiencies but also facilitated more efficient nitrogen recovery from the wetland system.

Exogenous glycine betaine alleviates water-deficit stress in Indian pennywort (Centella asiatica) under greenhouse conditions.

Centella asiatica (Indian pennywort) is a green leafy vegetable containing centelloside' (triterpenoid), a key phytochemical component in traditional medicine. Being a glycophytic species, they exhibit decline in growth performance and yield traits when subjected to water-deficit (WD) conditions. Glycine betaine (GB) is a low molecular-weight organic metabolite that plays a crucial role in abiotic stress conditions in higher plants. The objective of this study was to investigate the potential of GB in alleviating water-deficit stress (in terms of morphological and physiological responses) in two different genotypes of Indian pennywort, "Nakhon Pathom" (NP; high centelloside-yielding genotype) and "Pathum Thani" (PT; low centelloside-yielding genotype). The genotypes of Indian pennywort were propagated by stolon cutting and transplanted into plastic bags containing 2kg of garden soil. At the flower-initiation stage (30days after transplantation), uniform plant material was treated exogenously with 0 (control), 25, and 50mMGB at 100mL per plant (one-time foliar spray) and then divided into two groups, 1) well watered (WW; irrigated daily with 400mL fresh water; 98% field capacity) and 2) water deficit (WD; withheld water for 14days; 72% field capacity). Foliar application of GB (25mM) significantly improved leaf osmotic potential in NP under WD conditions via osmotic adjustment by free proline and fructose. Differences in leaf temperature (Tleaf) between WD and WW in NP were maximized (+ 1.93°C) and the gap of Tleaf was reduced in the case of 25-50mMGB application. Similarly, crop water stress index (CWSI) in NP and PT plants under WD condition was significantly increased by 1.95- and 1.86-fold over the control, respectively; however, it was significantly decreased by exogenous GB application. Increasing Tleaf and CWSI in drought-stressed plants was closely related to stomatal closure, leading to reduced gas exchange parameters, i.e., stomatal conductance (gs), transpiration rate (E), net photosynthetic rate (Pn), and intercellular CO2 concentration (Ci), and consequently decreased plant biomass and total centelloside yield. Overall physiological, morphological, and secondary metabolite traits were enhanced in NP under WD conditions using 25mMGB exogenous application compared with the control. The study highlights the significance of GB in Indian pennywort production under limited water irrigation (water deficit) with higher vegetable yield and phytochemical stabilization.

Plant–plant interactions affect seasonal nitrogen uptake of subalpine conifer seedlings by altering root traits and soil nitrogen availabilities

AbstractAlthough it is known that plant–plant interaction is an important factor influencing plant nitrogen (N) uptake and biomass productivity, its effects on seasonal inorganic N uptake, preference, and allocation remain unclear. In this study, two conifer species (Picea asperata and Abies faxoniana) were planted in three different planting modes (i.e., single, intraspecific, and interspecific interaction). Using 15N stable isotope tracer, we quantified plant biomass, ammonium (NH4+), and nitrate (NO3−) uptake rate (mass) and allocation in the middle (July) and the end (September) of the growing season, respectively, followed by analyses of root traits and soil properties so as to explore the underlying mechanism. Across the two seasons, intraspecific interaction decreased plant biomass and inorganic N‐uptake rate, which triggered intense competition for both species. Intraspecific competition of P. asperata was stronger than that of A. faxoniana. In contrast, interspecific interaction revealed significant facilitative effects on A. faxoniana, particularly in September. From the middle to the late growing season, the inorganic N‐uptake rate of P. asperata reduced, whereas that of A. faxoniana increased under interspecific interaction. The seasonal variation in plant N uptake was regulated by changes in root traits (such as root nitrogen concentration, specific root length, and branching intensity) and soil N availabilities. Both species indicated a preference for NO3− across seasons. Furthermore, we observed that 15N allocation to shoots of A. faxoniana under interspecific interaction was higher than that of P. asperata and declined from July to September. These findings on how plant–plant interactions affect plant N uptake seasonally can facilitate our understanding of species co‐existence and community assembly in forest ecosystems.

Multi-objective optimization of saline water irrigation in arid oasis regions: Integrating water-saving, salinity control, yield enhancement, and CO2 emission reduction for sustainable cotton production

Brackish water stands as a promising alternative to mitigate freshwater scarcity in arid regions. However, its application poses potential threats to agricultural sustainability. There is a need to establish a clear understanding of the economic and ecological benefits. We conducted a two-year (2021−2022) field experiment to investigate the effects of four different irrigation water salinity levels on soil electrical conductivity, cotton yield, water use efficiency, CO2 emissions, and carbon sequestration. The salinity levels were designated as CK (0.85 g L−1), S1 (3 g L−1), S2 (5 g L−1), and S3 (8 g L−1). Results indicated that using irrigation water with high salinity (≥5 g L−1) led to the accumulation of salt in the soil, and a decrease in plant biomass and seed cotton yield. Compared to CK, the S3 treatment decreased by 18.72 % and 20.10 % in the respective two years. Interestingly, using brackish water (3 L−1 and 5 g L−1) decreased the rate and cumulative CO2 emissions, and increased the carbon emission efficiency and carbon sequestration by 0.098–0.094 kg kg−1 and 871–1859 kg ha−1 in 2021, 0.098–0.094 kg kg−1 and 617–1995 kg ha−1 in 2022, respectively. To comprehensively evaluate the tradeoff between economic and ecological benefits, we employed the TOPSIS method, and S1 was identified as the optimal irrigation salinity. Through fitting analysis, the most suitable irrigation salinity levels for 2021 and 2022 were determined as 3.52 g L−1 and 3.31 g L−1, respectively. From the perspective of water conservation, salinity management, yield improvement, and reduction of CO2 emissions, it is feasible to utilize brackish water for irrigation purposes, as long as the salinity does not exceed 3.52 g L−1 (first year) and 3.31 g L−1 (second year).

Dueling Plant Phosphorus Acquisition Strategies Over a Geochemical Gradient: A Biogeochemistry Experiment Approach

Plants are likely to be phosphorus (P)-limited because of low availability of P to roots or mycorrhizae due to slow diffusion and high sorption in soils. Phosphorus sub-cycles (inorganic versus organic) also tend to vary predictably over gradients (Fig. 1A,B). Plant responses to mycorrhizal fungi also vary by plant species and grassland type (Reinhart et al. 2017). Mycorrhizae can scavenge nutrients (i.e. orthophosphate, organic-P); however, if they cannot solubilize calcium bound P, then geochemical gradients may constrain plant-mycorrhizal interactions (Fig. 1C). Calcareous soils are found in >30% of soils and are common in arid, semiarid, and semi-humid systems (e.g. grasslands, shrublands). We used geochemical and biogeochemical experiments to test hypotheses on P limitation and acquisition (Lajtha and Schlesinger 1988). Hypothesis: an increase in soil calcium carbonate (CaCO3) will 1) reduce soil P bioavailability (geochemical exp.), 2) reduce plant biomass and phosphorus uptake (biogeochemical exp.), and 3) shift P acquisition strategies (i.e. root mining, mycorrhizal scavenging) (biogeochemical exp., Fig. 1C). Experiments had a replacement series (CaCO3 to silica sand) geochemical treatment (CaCO3 additions: 0, 0.02, 0.10, and 0.30 [g × 100 g-1]) to simulate soil properties over natural grassland gradients. The biogeochemistry experiment was a completely randomized design with the geochemical and mycorrhizal fungi treatments (+, -) (4 × 2 factorial), 8 plant species, and 8 replications. Geochemical exp.’s response variables were soil extractable nutrients and pH. Biogeochemistry exp.’s response variables were nutrient uptake and plant performance. The geochemical experiment confirmed that increasing CaCO3 increased pHwater of subsurface soil (7.6 to 8.5), reduced the intensity of available P (assessed by anion exchange membranes) in treated soils by as much as 57%, and had no obvious effect on accessible P (Olsen-P). In other words, metaphorical cups of P (with straws) had similar amounts of accessible P per cup; however, additions of CaCO3 effectively reduced the straws’ diameter and limited (re-)supply of available P. On average, large additions of CaCO3 reduced plant biomass by 20% and plant uptake of P by 15% for the biogeochemistry experiment. On average, mycorrhizal fungi increased plant biomass by 6%. Rarely did mycorrhizal fungi and geochemical treatments interact and affect plant biomass. When they did interact, mycorrhizae benefited plants in pots with greater levels of P intensity (i.e. no or little added CaCO3) thereby suggesting mycorrhizae may not help to solubilize calcium bound P. These findings confirm CaCO3 in subsoils reduced the intensity of bioavailable P, which consequently decreased plant biomass and P uptake. However, we cannot rule out that CaCO3 additions may have additionally impacted plants response due to changes in micronutrient solubility (i.e. zinc), etc. (Lajtha and Schlesinger 1988). While plants tended to benefit from mycorrhizae, we found no evidence to support a prediction of the nutritional mutualisms hypothesis—that benefits are greatest under P-limitation. On the contrary, our data suggest that plants will rely more on root mining P acquisition strategies than mycorrhizal scavenging (Albornoz et al. 2020) where the inorganic-P sub-cycle dominates and P solubility is limited due to calcium-phosphate formation (Fig. 1C).

Overexpressing Ugp1 promotes phosphate uptake and accumulation in rice (Oryza sativa)

Plant responses to phosphate (Pi) starvation stress involve an array of adaptive strategies including enhanced accumulation and shoot-to-root transport of carbohydrates required for activating the plant Pi starvation signaling. However, the contribution of carbohydrate biosynthesis genes to maintaining phosphorus (P) homeostasis remains unknown, and the functional characterization of sugar metabolism genes is often impeded or compromised due to the loss of fertility of the null mutants. Here, a highly expressed gene encoding UDP-glucose pyrophosphorylase in rice (Oryza sativa), Ugp1, was functionally characterized. Ugp1 was transcriptionally induced in leaf blades by Pi starvation. As a link between sucrose (Suc) and P, we assumed that overexpression of Upg1 would alter the Suc concentration. Given that Suc is a signaling molecule, such concentration changes would affect the P deficiency signal transduction, thereby altering the homeostasis of endogenous P. The results showed that, overexpression of Ugp1 decreased plant biomass, increased sucrose content, and promoted Pi accumulation. The elevated Pi accumulation in Ugp1-OX plants was accompanied by the up-regulation of Pi-starvation-induced genes. Taken together, these results demonstrate that Ugp1 is a positive regulator of sucrose accumulation, and is required for maintaining P homeostasis in rice. Ugp1 thus represents a novel entry point to dissect the mechanisms underlying the carbon-P crosstalk.

Polystyrene microplastics accumulation in lab-scale vertical flow constructed wetlands: impacts and fate

Microplastics (MPs) are ubiquitous pollutants that significantly threaten organisms and ecosystems. Constructed wetlands (CWs), a nature-based treatment technology, can effectively remove MPs from wastewater. However, the responses of CWs when exposed to MPs remain unclear. In this study, lab-scale vertical flow constructed wetlands (VFCWs) were installed for receiving polystyrene (PS) MPs at concentrations of 100 μg/L and 1000 μg/L. The results showed that exposure to PS-MPs has no effects on COD and TP removal in VFCWs, but TN removal decreased by 3.69–5.37 %. Further investigation revealed that PS-MPs significantly impacted microbial communities and metabolic functions. The abundances of predominant nitrifiers (Nitrospira and Nitrosomonas) and denitrifiers (Nakamurella, Bradyrhizobium, and Bacillus) in VFCWs were significantly reduced, aligning with the responses of key enzymes. The presence of PS-MPs also decreased nitrogen removal by plant uptake, leading to decreased plant biomass and chlorophyll by 39.32–48.75 % and 5.92–32.19 %, respectively. Notably, > 90 % removal rates were observed for PS-MPs within VFCWs. In addition to PS-MPs interception by VFCWs substrate, the increase of released benzenes indicated that the PS-MPs biodegradation occurred. Such insights are vital for developing sustainable solutions to mitigate MPs' adverse effects on ecosystems.

Cupriavidus metallidurans bacteria enhance sodium uptake by plants

Here we report that Cupriavidus metallidurans bacteria increase sodium (Na+) accumulation in Arabidopsis thaliana and quinoa (Chenopodium quinoa). Given the metal mobilizing feature of the bacteria, we tested this hypothesis that the bacteria can increase the uptake of Na+, a metal ion, by plants. In agar plate assays under salinity conditions, the bacterial inoculation significantly decreased plant biomass by 280% and 20% in Arabidopsis and quinoa, respectively. In pot experiments under the salinity conditions, the bacterial inoculation resulted in about 60% loss of the quinoa plant biomass. We detected a significant high accumulation of Na+ in the leaf and stem tissues of the bacteria-inoculated quinoa plants, suggesting an association between increased Na+ accumulation and bacteria-mediated growth retardation in the plants. Altogether we report a novel phenomenon, in which bacteria increase Na+ uptake by plants.

Effects of foraging tunnels created by plateau zokors on plant above‐ground biomass and species richness of graminoids and forbs in alpine grasslands

AbstractQuestionForaging‐tunnel disturbances created by herbivorous mammals can influence the above‐ground plant biomass of grassland communities. The plateau zokor (Eospalax baileyi) was considered a focal animal for investigating the effect of foraging‐tunnel disturbances created by herbivorous mammals on the above‐ground biomass and species richness of graminoids and forbs. Here, we ask how foraging‐tunnel disturbances created by plateau zokors influences above‐ground plant biomass and species richness of graminoids and forbs in alpine grasslands.LocationThe study was conducted at three sites of alpine grasslands in the Qinghai‐Tibetan Plateau, China.MethodsIn this study, all vascular plants were divided into graminoids and forbs, and 30 paired quadrats were randomly selected from each site. In total, 90 tunnel quadrats and 90 non‐tunnel quadrats were surveyed and sampled.ResultsThis study showed that foraging‐tunnel disturbances decreased the plant species richness of the grassland community and forbs by 16.5% and 17.7% respectively, whereas the response of graminoid species richness to foraging‐tunnel disturbance was different among the three sites, in which foraging‐tunnel disturbance decreased the graminoid species richness at Maqu and Xiahe sites and had no impact on the graminoid species richness at Tianzhu site. Regarding forbs, some legumes identified in the non‐tunnel quadrats were not observed in the tunnel quadrats. The foraging‐tunnel disturbances resulted in an above‐ground plant biomass decrease of 21.9% in the grassland community, 27.3% in forbs, and 17.2% in graminoids respectively. The percentage of graminoids in the above‐ground plant biomass increased from 50.4% in non‐tunnel quadrats to 55.5% in tunnel quadrats, a relative increase of 10.1% from the initial percentage.ConclusionsThese results indicate that the foraging‐tunnel disturbances seemed to improve the forage availability for livestock in tunnel quadrats due to a higher relative proportion of graminoids in the grassland plant community, despite a decrease in graminoid biomass. However, the tunnels not only decreased the above‐ground plant biomass and species richness of forbs, but also might have a negative impact on soil nitrogen input because of the absence of some legumes. The findings of this study suggest that reseeding some legumes is an effective approach to maintaining plant diversity and soil fertility, which can compensate for the negative effect of foraging‐tunnel disturbance on alpine grasslands.

Arbuscular mycorrhizal symbiosis alleviates ozone injury in ozone-tolerant poplar clone but not in ozone-sensitive poplar clone

Tropospheric ozone (O3) is a typical air pollutant with harmful effects on plants, whereas arbuscular mycorrhizal (AM) fungi are ubiquitous plant symbionts that enhance plant resistance to various abiotic stresses. However, whether AM symbiosis decreases plant O3 sensitivity and what the underlying mechanisms are remain unclear. In this study, O3-tolerant poplar clone 107 and O3-sensitive poplar clone 546 were used as test plants. An open-top chamber experiment was conducted to investigate the effects of AM inoculation on plant growth and physiological parameters under O3 enrichment. The results showed that O3 enrichment significantly decreased plant biomass and net photosynthetic rate and increased the leaf shedding rate and malondialdehyde concentration of clone 546. Generally, clone 107 was less responsive to O3 enrichment than clone 546 was. Differences in antioxidant enzyme activity, rather than in specific leaf weight or stomatal conductance, were responsible for the differences in O3 sensitivity between the two clones. AM inoculation significantly increased the biomass and decreased the leaf shedding rate and malondialdehyde concentration of clone 107 but had no significant effect on almost all the indexes of clone 546, suggesting a species-specific mycorrhizal effect on plant O3 sensitivity. Mechanistically, AM symbiosis did not significantly affect nutrient uptake, stomatal conductance, or specific leaf weight of poplar but did significantly increase antioxidant enzyme activity. Linear regression analysis of antioxidant enzyme activities and the effect of O3 on growth and physiological parameters showed that AM symbiosis mediated antioxidant enzyme activities to mitigate O3 injury to the two poplar clones. This study improved the understanding of the protective effects of AM fungi on plants against O3 pollution.

Nitrogen uptake preference and allocation in Populus cathayana in response to drought stress

The preference for different nitrogen (N) forms may enhance plant survival and fitness. However, little information is known about how soil water availability, N addition, and their interaction dynamically impact plant N uptake preference and allocation. Here, we conducted a pot experiment using Populus cathayana cuttings, consisting of soil water regime (well watering control/mild drought/intensive drought: 80/60/40 % of field capacity) combined with N addition (N0 as control/N4/N8: 0/4/8 g N m−2 yr−1) treatments based on 15N isotope tracer technology. Two tracer solution (15NH4NO3/NH415NO3, both at 10.2 atom%) were used in N4/N8 treatments. Root, stem and leaf were collected at 6 h, 1, 3, 7, 14, and 31 days after labeling. Results showed that N addition significantly increased plant biomass and N accumulation, and decreased N allocation to leaf. Drought significantly decreased plant biomass, N accumulation, and N uptake (indicated by δ15N), and intensive drought reduced more than mild drought did. Nitrogen allocation to leaf was increased by drought. NO3- uptake by P. cathayana (indicated by δ15N in NH415NO3 treatment) was correlated significantly positively with total root length (TRL), total root surface area (TRA), specific root length (SRL), specific root area (SRA), root vitality, and root nitrate reductase (NR) activity. Intensive drought significantly reduced TRL, TRA, SRL, SRA, root vitality, and root NR activity under N4 and N8 treatments, which resulted δ15N in NH415NO3 treatment reduction and lower than in 15NH4NO3 treatment, so P. cathayana exhibited ammonium preference under intensive drought treatment. Our study provides an essential insight into how plants adapt and prefer different N forms under drought stress in nature.

5-Aminolevulinic Acid Induces Chromium [Cr(VI)] Tolerance in Tomatoes by Alleviating Oxidative Damage and Protecting Photosystem II: A Mechanistic Approach.

Chromium [Cr(VI)] pollution is a major environmental risk, reducing crop yields. 5-Aminolevunic acid (5-ALA) considerably improves plant abiotic stress tolerance by inducing hydrogen peroxide (H2O2) and nitric oxide (NO) signalling. Our investigation aimed to uncover the mechanism of tomato tolerance to Cr(VI) toxicity through the foliar application of 5-ALA for three days, fifteen days before Cr treatment. Chromium alone decreased plant biomass and photosynthetic pigments, but increased oxidative stress markers, i.e., H2O2 and lipid peroxidation (as MDA equivalent). Electrolyte leakage (EL), NO, nitrate reductase (NR), phytochelatins (PCs), glutathione (GSH), and enzymatic and non-enzymatic antioxidants were also increased. Foliar application of 5-ALA before Cr treatment improved plant growth and photosynthetic pigments, diminished H2O2, MDA content, and EL, and resulted in additional enhancements of enzymatic and non-enzymatic antioxidants, NR activity, and NO synthesis. In Cr-treated tomato seedlings, 5-ALA enhanced GSH and PCs, which modulated Cr sequestration to make it nontoxic. 5-ALA-induced Cr tolerance was further enhanced by sodium nitroprusside (SNP), a NO donor. When sodium tungstate (ST), a NR inhibitor, was supplied together with 5-ALA to Cr-treated plants, it eliminated the beneficial effects of 5-ALA by decreasing NR activity and NO synthesis, while the addition of SNP inverted the adverse effects of ST. We conclude that the mechanism by which 5-ALA induced Cr tolerance in tomato seedlings is mediated by NR-generated NO. Thus, NR and NO are twin players, reducing Cr toxicity in tomato plants via antioxidant signalling cascades.

Towards greenhouse cultivation of Artemisia annua: The application of LEDs in regulating plant growth and secondary metabolism.

Artemisinin is a sesquiterpene lactone produced in glandular trichomes of Artemisia annua, and is extensively used in the treatment of malaria. Growth and secondary metabolism of A. annua are strongly regulated by environmental conditions, causing unstable supply and quality of raw materials from field grown plants. This study aimed to bring A. annua into greenhouse cultivation and to increase artemisinin production by manipulating greenhouse light environment using LEDs. A. annua plants were grown in a greenhouse compartment for five weeks in vegetative stage with either supplemental photosynthetically active radiation (PAR) (blue, green, red or white) or supplemental radiation outside PAR wavelength (far-red, UV-B or both). The colour of supplemental PAR hardly affected plant morphology and biomass, except that supplemental green decreased plant biomass by 15% (both fresh and dry mass) compared to supplemental white. Supplemental far-red increased final plant height by 23% whereas it decreased leaf area, plant fresh and dry weight by 30%, 17% and 7%, respectively, compared to the treatment without supplemental radiation. Supplemental UV-B decreased plant leaf area and dry weight (both by 7%). Interestingly, supplemental green and UV-B increased leaf glandular trichome density by 11% and 9%, respectively. However, concentrations of artemisinin, arteannuin B, dihydroartemisinic acid and artemisinic acid only exhibited marginal differences between the light treatments. There were no interactive effects of far-red and UV-B on plant biomass, morphology, trichome density and secondary metabolite concentrations. Our results illustrate the potential of applying light treatments in greenhouse production of A. annua to increase trichome density in vegetative stage. However, the trade-off between light effects on plant growth and trichome initiation needs to be considered. Moreover, the underlying mechanisms of light spectrum regulation on artemisinin biosynthesis need further clarification to enhance artemisinin yield in greenhouse production of A. annua.

An Analysis of the Reaction of Frogbit (Hydrocharis morsus-ranae L.) to Cadmium Contamination with a View to Its Use in the Phytoremediation of Water Bodies

Macrophytes play an important role in assessing the condition of aquatic ecosystems. The aim of the study was to assess the effectiveness of cadmium uptake by frogbit (Hydrocharis morsus-ranae) for the phytoremediation of aquatic ecosystems. The study examined cadmium (Cd) uptake by frogbit grown under conditions of low and high fertilizer dose and three cadmium dose levels over three- and six-week exposure times. Cadmium uptake was found to be influenced by water reactivity, mineral nutrient abundance, and exposure time. Its accumulation in frogbit is hence a good bioindicator of cadmium pollution in water bodies. Where the plant had greater access to phosphorus, nitrogen, potassium (PNK) compounds, i.e., high fertilizer level, a higher pH level (7.6) was associated with increased cadmium uptake and decreased plant biomass. A higher PNK level was also associated with greater tolerance to cadmium, while at lower PNK levels, more efficient cadmium uptake was noted after three weeks. Hydrocharis morsus-ranae can be used for water and wastewater treatment in the final stage of phytoremediation, but in combination with other species of pleustophytes that represent different biosorption sites.