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Low temperature driven carbon shortage is often assumed to explain slow growth and treeline formation at high elevations. To test this hypothesis, we analysed mobile carbon pools in Pinus cembra across the treeline ecotone in the Swiss Alps. Concentrations of non-structural carbohydrates (NSC) in needles, branches, stems and roots, as well as lipids (acylglycerols) in all woody tissues were measured throughout the growing season. Starch was the most prominent non-structural carbon compound in needles, whereas lipids represented 50-75% of the mobile carbon compounds in wood. The relative seasonal variation of the lipid fraction was very small, but due to the high absolute amount of lipids, the annual variability of carbon in lipids exceeded that of NSC in woody tissues. Mobile carbon compounds were highly abundant throughout the year and were never significantly depleted. Across a 110 m altitudinal transect from timberline to the uppermost site of tree existence, NSC and lipid concentrations generally increased. This trend became even more pronounced when the increasing structural density of tissues at higher elevations was accounted for. An estimation of the whole tree mobile carbon concentration (fraction of mobile carbon compounds within the whole tree biomass) also revealed an increasing trend of NSC and lipid pools with elevation. We therefore conclude that carbon limitation is unlikely to be responsible for reduced tree growth at the alpine treeline studied. Increased concentrations of NSC and lipids at the upper tree limit rather suggest that sink activity is limited. Hence, treeline formation is most likely the result of a direct thermal restriction of tissue formation (investment in structures) under otherwise sufficient carbon assimilation during the growing season.

▪ Abstract  Contaminated soils and waters pose a major environmental and human health problem, which may be partially solved by the emerging phytoremediation technology. This cost-effective plant-based approach to remediation takes advantage of the remarkable ability of plants to concentrate elements and compounds from the environment and to metabolize various molecules in their tissues. Toxic heavy metals and organic pollutants are the major targets for phytoremediation. In recent years, knowledge of the physiological and molecular mechanisms of phytoremediation began to emerge together with biological and engineering strategies designed to optimize and improve phytoremediation. In addition, several field trials confirmed the feasibility of using plants for environmental cleanup. This review concentrates on the most developed subsets of phytoremediation technology and on the biological mechanisms that make phytoremediation work.

We described the in vitro antioxidant and antimicrobial activities of ethanol, acetone, and water extracts of beet root pomace. Total contents of phenolics (316.30-564.50 mg GAE/g of dry extract), flavonoids (316.30-564.50 mg RE/g of dry extract), betacyanins (18.78-24.18 mg/g of dry extract), and betaxanthins (11.19-22.90 mg/g of dry extract) after solid-phase extraction were determined spectrophotometrically. The antioxidant activity was determined by measuring the reducing power and DPPH scavenging activity by spectrometric method, and hydroxyl and superoxide anion radical scavenging activity by ESR spectroscopy. In general, the reducing power of all the beet root pomace extracts increased with increasing concentrations. The DPPH-free radical scavenging activity of the extracts, expressed as EC50, ranged from 0.133 mg/mL to 0.275 mg/mL. Significant correlation was observed between all phytochemical components and scavenging activity. Ethanol extract (0.5 mg/mL) completely eliminated hydroxyl radical which had been generated in Fenton system, while the same concentration of this extract scavenged 75% of superoxide anion radicals. In antibacterial tests, Staphylococcus aureus and Bacillus cereus showed higher susceptibility than Escherichia coli and Pseudomonas aeruginosa.

Global biogeochemical models have improved dramatically in the last decade in their representation of the biosphere. Although leaf area data are an important input to such models and are readily available globally, global root distributions for modeling water and nutrient uptake and carbon cycling have not been available. This analysis provides global distributions for fine root biomass, length, and surface area with depth in the soil, and global estimates of nutrient pools in fine roots. Calculated root surface area is almost always greater than leaf area, more than an order of magnitude so in grasslands. The average C:N:P ratio in living fine roots is 450:11:1, and global fine root carbon is more than 5% of all carbon contained in the atmosphere. Assuming conservatively that fine roots turn over once per year, they represent 33% of global annual net primary productivity.

Organic acids, such as malate, citrate and oxalate, have been proposed to be involved in many processes operating in the rhizosphere, including nutrient acquisition and metal detoxification, alleviation of anaerobic stress in roots, mineral weathering and pathogen attraction. A full assessment of their role in these processes, however, cannot be determined unless the exact mechanisms of plant organic acid release and the fate of these compounds in the soil are more fully understood. This review therefore includes information on organic acid levels in plants (concentrations, compartmentalisation, spatial aspects, synthesis), plant efflux (passive versus active transport, theoretical versus experimental considerations), soil reactions (soil solution concentrations, sorption) and microbial considerations (mineralization). In summary, the release of organic acids from roots can operate by multiple mechanisms in response to a number of well-defined environmental stresses (e.g., Al, P and Fe stress, anoxia): These responses, however, are highly stress-and plant-species specific. In addition, this review indicates that the sorption of organic acids to the mineral phase and mineralisation by the soil's microbial biomass are critical to determining the effectiveness of organic acids in most rhizosphere processes.

For 76 annual, biennial, and perennial species common in the grasslands of central Minnesota, USA, we determined the patterns of correlations among seven organ-level traits (specific leaf area, leaf thickness, leaf tissue density, leaf angle, specific root length, average fine root diameter, and fine root tissue density) and their relationships with two traits relating to growth form (whether species existed for part of the growing season in basal, non-caulescent form and whether species were rhizomatous or not). The first correlation of traits showed that grasses had thin, dense leaves and thin roots while forbs had thick, low-density leaves and thick roots without any significant differences in growth form or life history. The second correlation of traits showed a gradient of species from those with high-density roots and high-density erect leaves to species with low-density roots and low-density leaves that were held parallel to the ground. High tissue density species were more likely to exist as a basal rosette for part of the season, were less likely to be rhizomatous, and less likely to be annuals. We examined the relationships between the two axes that represent the correlations of traits and previously collected data on the relative abundance of species across gradients of nitrogen addition and disturbance. Grasses were generally more abundant than forbs and the relative abundance of grasses and forbs did not change with increasing nitrogen addition or soil disturbance. High tissue density species became less common as fertility and disturbance increased.

Phosphorus deficiency-induced metabolic changes related to exudation of carboxylic acids and protons were compared in roots of wheat (Triticum aestivum L. cv Haro), tomato (Lycopersicon esculentum L., cv. Moneymaker), chickpea (Cicer arietinum) and white lupin (Lupinus albus L. cv. Amiga), grown in a hydroponic culture system. P deficiency strongly increased the net release of protons from roots of tomato, chickpea and white lupin, but only small effects were observed in wheat. Release of protons coincided with increased exudation of carboxylic acids in roots of chickpea and white lupin, but not in those of tomato and wheat. P deficiency-induced exudation of carboxylic acids in chickpea and white lupin was associated with a larger increase of carboxylic acid concentrations in the roots and lower accumulation of carboxylates in the shoot tissue compared to that in wheat and tomato. -Citric acid was one of the major organic acids accumulated in the roots of all investigated species in response to P deficiency, and this was associated with increased activity and enzyme protein levels of PEP carboxylase, which is required for biosynthesis of citrate. Accumulation of citric acid was most pronounced in the roots of P-deficient white lupin, chickpea and tomato. Increased PEP carboxylase activity in the roots of these plants coincided with decreased activity of aconitase, which is involved in the breakdown of citric acid in the TCA cycle. In the roots of P-deficient wheat plants, however, the activities of both PEP carboxylase and aconitase were enhanced, which was associated with little accumulation of citric acid. The results suggest that P deficiency-induced exudation of carboxylic acids depends on the ability to accumulate carboxylic acids in the root tissue, which in turn is determined by biosynthesis, degradation and partitioning of carboxylic acids or related precursors between roots and shoot. In some plant species such as white lupin, there are indications for a specific transport mechanism (anion channel), involved in root exudation of extraordinary high amounts of citric acid.

Herbivore attack is widely known to reduce food quality and to increase chemical defenses and other traits responsible for herbivore resistance. Inducible defenses are commonly thought to allow plants to forgo the costs of defense when not needed; however, neither their defensive function (increasing a plant's fitness) nor their cost-savings function have been demonstrated in nature. The root-produced toxin nicotine increases after herbivore attack in the native, postfire annual Nicotiana attenuata and is internally activated by the wound hormone, jasmonic acid. I treated the roots of plants with the methyl ester of this hormone (MeJA) to elicit a response in one member of each of 745 matched pairs of plants growing in native populations with different probabilities of attack from herbivores, and measured the lifetime production of viable seed. In populations with intermediate rates of attack, induced plants were attacked less often by herbivores and survived to produce more seed than did their uninduced counterparts. Previous induction did not significantly increase the fitness of plants suffering high rates of attack. However, if plants had not been attacked, induced plants produced less seed than did their uninduced counterparts. Jasmonate-induced responses function as defenses but are costly, and inducibility allows this species to forgo these costs when the defenses are unnecessary

In plants, potassium serves an essential role as an osmoticum and charge carrier. Its uptake by roots occurs by poorly defined mechanisms. To determine the role of potassium channels in planta, we performed a reverse genetic screen and identified an Arabidopsis thaliana mutant in which the AKT1 channel gene was disrupted. Roots of this mutant lacked inward-rectifying potassium channels and displayed reduced potassium (rubidium-86) uptake. Compared with wild type, mutant plants grew poorly on media with a potassium concentration of 100 micromolar or less. These results and membrane potencial measurements suggested that the AKT1 channel mediates potassium uptake from solutions that contain as little as 10 micromolar potassium

The Mi locus of tomato confers resistance to root knot nematodes. Tomato DNA spanning the locus was isolated as bacterial artificial chromosome clones, and 52 kb of contiguous DNA was sequenced. Three open reading frames were identified with similarity to cloned plant disease resistance genes. Two of them, Mi-1.1 and Mi-1.2, appear to be intact genes; the third is a pseudogene. A 4-kb mRNA hybridizing with these genes is present in tomato roots. Complementation studies using cloned copies of Mi-1.1 and Mi-1.2 indicated that Mi-1.2, but not Mi-1.1, is sufficient to confer resistance to a susceptible tomato line with the progeny of transformants segregating for resistance. The cloned gene most similar to Mi-1.2 is Prf, a tomato gene required for resistance to Pseudomonas syringae. Prf and Mi-1.2 share several structural motifs, including a nucleotide binding site and a leucine-rich repeat region, that are characteristic of a family of plant proteins, including several that are required for resistance against viruses, bacteria, fungi, and now, nematodes