Elevated CO2 causes different growth stimulation, water and nitrogen use efficiencies and leaf ultrastructure responses in two conifer species under intra- and interspecific competition

The continuously increasing atmospheric carbon dioxide concentration ([CO2]) has substantial effects on plant growth, and on the composition and structure of forests. However, how plants respond to elevated [CO2] (e[CO2]) under intra- and interspecific competition has been largely overlooked. In this study, we employed Abies faxoniana and Picea purpurea seedlings to explore the effects of e[CO2] (700 ppm) and plant–plant competition on plant growth, physiological and morphological traits, and leaf ultrastructure. We found that e[CO2] stimulated plant growth, photosynthesis and nonstructural carbohydrates (NSC), affected morphological traits and leaf ultrastructure, and enhanced water and nitrogen use efficiencies in A. faxoniana and P. purpurea. Under interspecific competition and e[CO2], P. purpurea showed a higher biomass accumulation, photosynthetic capacity and rate of ectomycorrhizal infection, and higher water and nitrogen use efficiencies compared with A. faxoniana. However, under intraspecific competition and e[CO2], the two conifers showed no differences in biomass accumulation, photosynthetic capacity, and water and nitrogen use efficiencies. In addition, under interspecific competition and e[CO2], A. faxoniana exhibited higher NSC levels in leaves as well as more frequent and greater starch granules, which may indicate carbohydrate limitation. Consequently, we concluded that under interspecific competition, P. purpurea possesses a positive growth and adjustment strategy (e.g., a higher photosynthetic capacity and rate of ectomycorrhizal infection, and higher water and nitrogen use efficiencies), while A. faxoniana likely suffers from carbohydrate limitation to cope with rising [CO2]. Our study highlights that plant–plant competition should be taken into consideration when assessing the impact of rising [CO2] on the plant growth and physiological performance.

Morphology, anatomy and leaf ultrastructure of Froelichia tomentosa (Mart.) Moq. (Amaranthaceae) - a critically endangered species in Brazil

In Brazil, Froelichia tomentosa (Mart.) Moq. has records of occurrence in Rio Grande do Sul (RS) and Bahia, however, in the former there are indications that its populations are extinct. In the RS, the records are restricted to the region of sandy- fields. In this region, biodiversity has been threatened by advances in agriculture and forestry that intensified in the sandy patch process. Therefore, this work aimed to describe the morphoanatomy and ultrastructure of the leaf blade in Froelichia tomentosa, seeking to correlate leaf characteristics to the environmental conditions. Individuals from different populations in the sand- fields (Pampa biome) were sampled. Leaf blade analyzes were performed by scanning electron microscopy (SEM), transmission electron microscopy (MET) and optical microscopy (MO). The following anatomical features were verified: epidermis with trichomes and stomata in the adaxial and abaxial surface, compact mesophyll, aquiferous hypodermis, Kranz anatomy, and numerous plastoglobules and peroxisomes. The presence of these characters may be related to the adaptation of this species to environment. In addition, we highlight the necessity to create conservation units in the sand-fields region, in order to preserve species as well as that of the present study.

Salinity Exacerbates Oil Contamination Effects in Mangroves

The effects of salinity (10 and 50% seawater) and oil in combination on three mangroves, Avicennia marina, Bruguiera gymnorrhiza and Rhizophora mucronata were determined. In all species, plant height, number of leaves and CO2 exchange were generally higher in 10% than in 50% seawater. Salinity and oil decreased plant height, number of leaves, chlorophyll content and CO2 exchange, with reductions being greater at the higher salinity. In a second experiment, the effects of salinity (0, 10 and 50% seawater) and oil on concentrations of ions, polycyclic aromatic hydrocarbons (PAHs), leaf ultrastructure and salt secretion in A. marina were investigated. Salinity and oil in combination increased concentrations of Na+ but decreased those of K+, Ca²+ and Mg²+. PAHs damaged cell membranes, disrupted ion concentrations and reduced salt secretion. This study demonstrated that increase in salinity reduces growth of mangroves and that salinity and oiling in combination exacerbate growth reduction. In A. marina, oil was absorbed and translocated to the leaves where it disrupted membranes, ion accumulation and salt secretion.

Ultrastructural and Histochemical Changes in Glyphosate-Tolerant Soybean Leaves Exposed to Glyphosate

Is it transgenic soy, resistant to glyphosate, does not suffer any injury or stress in contact with this herbicide? Anatomic studies of plant tissue are necessary to answer this question. This study investigated the influence of glyphosate in glyphosate-resistant soybean plants by analysis of leaf ultrastructure and histochemistry in a morphophysiological context. The experiment was carried out in a greenhouse, using RR soybean seeds (Glycine max (L.) Merrill, cultivar BRS Valiosa) in pots containing vermiculite and washed sand (1:1). Between the phenological stages V2 and V4, two treatments with glyphosate [N-(fosfonometil) glicina] were sprayed once a week: recommended dose (5.0 mg ae plant-1) and control (0.0 mg ae plant-1), with four repetitions each. Samples of midrib and internervural area of the leaves were fixed, dehydrated in ethyl series and blocks were sectioned at a 5-10 μm thickness. The material was stained with toluidine blue 0.05% and blades mounted on “Entellan”. Glyphosate decreased the thickness of the adaxial epidermis, palisade parenchyma, spongy parenchyma and total thickness of the leaf. Although, the diameter of companion cell was decreased with herbicide treatment, the diameter of the vase element increased, also increasing the size of the vascular bundle. Ultrastructural and histochemical changes caused by glyphosate can extend dysfunctions in the metabolic apparatus and plant relationship with the environment, given the inter-relation between tissue structure and its functions.

Alterations in Leaf Ultrastructure in Varieties of Sugarcane Infected by Diseases

Given the importance of viral, bacterial and fungal diseases in agriculture and their impact on crop yields, this study evaluated leaf ultrastructural changes in sugarcane varieties infected by these diseases, aiming to find morphological responses that may be associated to the decline of sugarcane yield. Three independent experiments were carried out with sugarcane varieties. In the three experiments, a randomised block design was used with 10 replications. The treatments consisted of the following diseases: mosaic from infection of variety SP86-155 by SCMV (experiment 1); stunting from infection with bacterium Leifsonia xyli subsp. xyli and smut from infection with fungus Sporisorium scitamineum (formally called Ustilago scitaminea) in the variety SP70-3370 (experiment 2); and scald from infection of variety SP78-5495 by bacterium Xanthomonas albilineans (experiment 3). The ultrastructural parameters were evaluated: mesophyll thickness, xylem diameter, phloem beam diameter, epidermal thickness of the adaxial face, epidermal thickness of the abaxial face, cuticle thickness of the adaxial face and cuticle thickness of the abaxial face. Healthy plants were controls for the three experiments. Sugarcane plants with mosaic, stunting, smut and scald diseases show deleterious changes in leaf ultrastructure.

Elevated temperature differently affects growth, photosynthetic capacity, nutrient absorption and leaf ultrastructure of Abies faxoniana and Picea purpurea under intra- and interspecific competition

There is a limited understanding of the impacts of global warming on intra- and interspecific plant competition. Resolving this knowledge gap is important for predicting the potential influence of global warming on forests, particularly on high-altitude trees, which are more sensitive to warming. In the present study, effects of intra- and interspecific competition on plant growth and associated physiological, structural and chemical traits were investigated in Abies faxoniana and Picea purpurea seedlings under control (ambient temperature) and elevated temperature (ET, 2 °C above ambient temperature) conditions for 2 years. We found that A. faxoniana and P. purpurea grown under intra- and interspecific competition showed significant differences in dry matter accumulation (DMA), photosynthetic capacity, nutrient absorption, non-structural carbohydrate (NSC) contents and leaf ultrastructure under ET conditions. ET increased leaf, stem and root DMA of both conifers under both competition patterns. Moreover, under ET and interspecific competition, P. purpurea had overall superior competitive capacity characterized by higher organ (leaf, stem and root) and total DMA, height growth rate, net photosynthetic rate, specific leaf area, water use efficiency (δ13C), leaf and root N and NSC concentrations and greater plasticity for absorption of different soil N forms. Thus, the growth of P. purpurea benefitted from the presence of A. faxoniana under ET. Our results demonstrated that ET significantly affects the asymmetric competition patterns in subalpine conifer species. Potential alteration of plant competitive interactions by global warming can influence the composition, structure and functioning of subalpine coniferous forests.