Importance of tree height and social position for drought-related stress on tree growth and mortality

Key message

A higher mortality of dominant trees under drought stress is explained by impacts of tree size, canopy- and root structure and the hydraulic transport system.

Abstract

Drought stress can trigger tree mortality but the impact depends on stress intensity (water demand and availability) and on the vulnerability of the individual. Therefore, most research focusses on the species-specific properties such as water use efficiency or hydraulic conductivity that determine vulnerability. At the ecosystem scale, however, tree properties that have been found important for drought sensitivity or resistance vary with individual size and resource availability within a forest—also within the same species. This is caused by different environmental conditions for each tree and hence different growth histories of individuals generating specific anatomical and physiological features. Individual drought stress sensitivity might thus be considerably different from stand scale sensitivity. Indeed, empirical evidence shows that drought stress impact depends on tree social position which can be defined in degrees of suppression but correlated to resource availability, stress sensitivity and stress exposure. In this review, we collect such evidence and discuss the role of microclimate and soil water distribution as well as anatomical and physiological adjustments, which might serve as foundation for better-adapted management strategies to mitigate drought stress impacts. Finally, we define model requirements aiming to capture stand-scale drought responses or management impacts related to drought stress mitigation.

     

Pre-treatment with salicylic acid induces phenolic responses of Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis>) bark to bark beetle (<Emphasis Type="Italic">Ips typographus</Emphasis>) attack

Keymessage

The temporal gradations of the investigated phenolics in Norway spruce bark after bark beetle (Ips typographus) attack followed the general eco-physiological concept. Treatment with salicylic acid inhibits bark beetle colonisation, alleviates the phenolic responses and activates the synthesis of condensed tannins on later sampling dates.

Abstract

Conifer bark is the target of numerous organisms due to its assimilated transport and nutrient storage functions. In the presented study, 100 mM salicylic acid (SA) was applied onto Norway spruce stems prior to being infested with bark beetles (Ips typographus L.), to study the temporal gradation of changes in condensed tannins (CT) and total phenolics (tPH) and their significance for mediating stress-tolerance. A significant accumulation of CT was monitored in untreated trees in response to progressive bark beetle infestation occurring from May onwards. In SA-treated infested trees, the CT values remained at control levels until May, but after the re-treatment of infested trees in June, the concentrations of CT rose significantly in comparison to the controls. The tPH values dropped 16 days after SA-treatment, independent of infestation, and later on remained at control level until July. In contrast, tPH contents accumulated in untreated infested trees in May, eased in June and increased again in July, when the trees were affected by the second generation of bark beetles. To sum up, in May and July when the highest beetle-flight activity was monitored the metabolic shift of phenolics within untreated infested trees differed significantly from the response of SA-treated trees. In addition, on SA-treated trees less entrance holes were monitored over the whole period of sampling when compared to untreated infested trees. These results provide evidence that SA-treatment alleviates the phenolic responses, activates the synthesis of condensed tannins and inhibits bark beetle colonisation.

     

Protective effects of C-phycocyanin on alcohol-induced subacute liver injury in mice

Excessive and long-term alcohol consumption leads to liver disease and low immunity. Extensive evidence suggests that C-phycocyanin (C-PC), a chromophore phycocyanobilin derived from Arthrospira (Spirulina) platensis, exerts protective effects against chemical-induced organ damage and improves immunity. In this study, we investigated whether C-PC could protect against ethanol-induced subacute liver injury and improve immunity. KM mice with ethanol-induced liver injury were established, and animals were divided into three groups that were treated with high, medium, and low doses of C-PC. Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), triglyceride (TG), total cholesterol (CHOL), low-density lipoprotein (LDL), total bilirubin (TBIL), liver homogenate malondialdehyde (MDA), and superoxide dismutase (SOD) levels were measured. In addition, the number of thymus T cell subsets was assessed, and liver sections were examined pathologically. C-PC exhibited obvious inhibitory effects on serum ALT, AST, TG, CHOL, LDL, and MDA levels and increased SOD content significantly in the liver. C-PC also increased serum CD3+ and CD4+ cell activation and T cell proliferation significantly compared with the model group. The structure of the hepatic lobules was clear, the liver sinus returned to normal, and the liver cell cords were arranged in neat rows. Therefore, C-PC could protect against ethanol-induced subacute liver injury significantly.     

Microalgal industry in China: challenges and prospects

Over the past 15 years, China has become the major producer of microalgal biomass in the world. Spirulina (Arthrospira) is the largest microalgal product by tonnage and value, followed by Chlorella, Dunaliella, and Haematococcus, the four main microalgae grown commercially. China’s production is estimated at about two-thirds of global microalgae biomass of which roughly 90 % is sold for human consumption as human nutritional products (‘nutraceuticals’), with smaller markets in animal feeds mainly for marine aquaculture. Research is also ongoing in China, as in the rest of the world, for other high-value as well as commodity microalgal products, from pharmaceuticals to biofuels and CO₂ capture and utilization. This paper briefly reviews the main challenges and potential solutions for expanding commercial microalgae production in China and the markets for microalgae products. The Chinese Microalgae Industry Alliance (CMIA), a network founded by Chinese microalgae researchers and commercial enterprises, supports this industry by promoting improved safety and quality standards, and advancement of technologies that can innovate and increase the markets for microalgal products. Microalgae are a growing source of human nutritional products and could become a future source of sustainable commodities, from foods and feeds, to, possibly, fuels and fertilizers.     

Two-tier vessel for photoautotrophic high-density cultures

Two-tier vessels, developed for culturing of microalgae and cyanobacteria at high cell density on a shaken platform, were assembled from a flat lower chamber to be filled with a CO₂ buffer and an upper flat sterile chamber for the culture that was separated from the lower chamber by a porous polypropylene membrane. Diffusive gas exchange with the atmosphere was controlled by the O₂ outlet channel. Referred to surface area, rates of CO₂ transfer to a shaken weakly alkaline buffer solution across the membrane were higher than those reached on the conventional pathway through the free upper liquid surface. Membrane-mediated CO₂ supply enabled rapid growth of Synechocystis sp. PCC 6803 and Synechococcus sp. PCC 7002 up to ultrahigh cell density. The biomass (dry weight) concentration of Synechococcus cultures reached more than 30 g L^?1 on a buffered medium with adequate concentrations of mineral nutrients. An increase of 15 to 20 g L^?1 was observed during repeated two-day cycles. Separate pathways for CO₂ supply and oxygen outlet prevented significant loss of CO₂. Convective gas flow through the oxygen outlet channel enabled the estimation of the O₂ generation rate. The permeability of the channel for diffusive O₂/N₂ exchange limited the O₂ concentration to a moderate value. It is concluded that shaken flat cultures using CO₂ supply through a porous hydrophobic membrane and diffusive release of O₂ through a separate pathway are promising for research on microalgae and cyanobacteria.     

Phylogenetic characterization and morphological and physiological aspects of a novel acidotolerant and halotolerant microalga <Emphasis Type="Italic">Coccomyxa onubensis</Emphasis> sp. nov. (Chlorophyta,Trebouxiophyceae)

The genus Coccomyxa comprises green microalgae, which can be found worldwide in remarkably versatile aquatic and terrestrial ecosystems including symbiotic associations with a number of different hosts. In this study, we describe a new species, Coccomyxa onubensis, based on 18S and ITS ribosomal DNA (rDNA) sequence data. Coccomyxa onubensis was isolated from acidic water, and its ability to adapt to a wide range of acidic and alkaline pH values and to high salinity was analyzed. The long-term adaptation capacity of the microalga to such extreme conditions was evaluated by performing continuous repeated batches at selected salt concentrations and pH values. Adapted cultures of C. onubensis were found to yield high biomass productivities from pH 2.5 to 9, with maximum yields at acidic pH between 2.5 and 4.5. Moreover, C. onubensis was also found to adapt to salinities as high as 0.5 M NaCl, reaching biomass productivities that were similar to those of control cultures. Ultrastructural analysis by transmission electron microscopy of C. onubensis cells adapted to high salinity showed a robust response to hyperosmotic shock. Thus, C. onubensis was found to be acidotolerant and halotolerant. High biomass productivity over a wide range of pH and salinities denotes C. onubensis as an interesting candidate for various biotechnological applications including outdoor biomass production.     

Culture medium influence on growth,fatty acid,and pigment composition of <Emphasis Type="Italic">Choricystis minor</Emphasis> var. <Emphasis Type="Italic">minor</Emphasis>: a suitable microalga for biodiesel production

The purposes of this study were to assess the influence of culture medium on biomass production, fatty acid, and pigment composition of Choricystis minor var. minor and to evaluate the use of this microalga as a source of fatty raw material for biodiesel production. Cultures of C. minor var. minor were grown using WC (Wright’s cryptophyte) and BBM (Bold’s Basal medium) media. BBM medium produced more biomass (984.3 mg L^?1) compared to the WC medium (525.7 mg L^?1). Despite this result, WC medium produced a higher methyl ester yield for biodiesel production than the BBM medium (170.0 and 90.2 mg g^?1 of biomass, respectively). The average percentage of fatty acids obtained using the WC medium (17.0 %) was similar to soybean (18.0 %) and with similar biomass fatty acid profile. However, for pigment production, carotenoids and chlorophyll concentrations were twice as high when using the BBM medium.     

Relation between light absorption measured by the quantitative filter technique and attenuation of <Emphasis Type="Italic">Chlorella fusca</Emphasis> cultures of different cell densities: application to estimate the absolute electron transport rate (ETR)

In order to estimate microalgal carbon assimilation or production of Chlorella fusca cultures based on electron transport rate (ETR) as in vivo chlorophyll a fluorescence, it is necessary to determine the photosynthetic yield and the absorbed quanta by measuring the incident irradiance and the fraction of absorbed light, i.e., absorptance or absorption coefficient in the photosynthetic active radiation (PAR) region of the spectra. Due to difficulties associated with the determination of light absorption, ETR is commonly expressed as relative units (rETR) although this is not a good estimator of the photosynthetic production since photobiological responses depend on the absorbed light. The quantitative filter technique (QFT) is commonly used to measure the absorbed quanta of cells retained on a filter (AbQ_f) as estimator of the absorbed quanta of cell suspensions (AbQ_s) determined by using integrating spheres. In this study, light attenuation of thin-layer cell suspensions is determined by using a measuring system designed to reduce the scattering. The light attenuation is related to the absorptance as the fraction of absorbed light by both indoor and outdoor C. fusca cultures of different cell densities. A linear relation between AbQ_f and AbQ_s (R ²?=?0.9902, p?<?0.01) was observed, AbQ_f?=?1.98?×?AbQ_s, being 1.98 an amplification factor to convert AbQ_s values into AbQ_f ones. On the other hand, depending on the culture system, the convenience of the use of the absorptance, light absorption or specific light absorption coefficient expressed per area (thin-layer cascade or flat panel cultivators), volume (cylindrical and tubular photobioreactors), or chlorophyll units (any type of cultivation system) is discussed. The procedure for the measurement of light absorption presented in this study for C. fusca could be applied in other phytoplankton groups. The absorbed quanta as determined in this study can be used to express absolute ETR instead of relative ETR, since the first one provides much more relevant photobiological information of microalgae culture systems.