Loss Of Photosynthetic Tissue Research Articles

Interactions between ectomycorrhizal fungi and chestnut blight (<em>Cryphonectria parasitica</em>) on American chestnut (<em>Castanea dentata</em>) used in coal mine restoration

Plant and fungal interactions drive successional trajectories within reforestation offering both mutualisms (ectomycorrhizal fungi [ECM]) and fungal pathogens. Appalachian forest and mine reclamation projects re-introducing American chestnut and chestnut hybrids will inevitably document the return of chestnut blight, resulting in cankers causing branch dieback and loss of photosynthetic tissue. Similar to herbivory, the loss of photosynthetic tissue may reduce ECM root colonization and cause changes in fungal species composition. To test this, 75 six-year-old established chestnut trees were selected to represent the following: (1) Healthy trees free of chestnut blight; (2) trees with cankers and 50% branch dieback; (3) trees that died prior to the fifth growing season. Each tree had a chestnut seed planted 24 cm from the base. ECM colonization of both the established parent trees (n = 50) and five-month-old seedlings (n = 64) were quantified and genera determined by fungal DNA sequencing of the internal transcribed (ITS) region. Healthier seven-year-old chestnuts trees had significantly more ECM roots than those trees infected with chestnut blight cankers. However, disease die-back on chestnut did not have an influence on community composition among the parent trees or the neighboring five month seedlings. Results also demonstrated that five-month-old seedlings neighboring healthy parent trees had greater ECM on roots (P = 0.002), were larger in size (P = 0.04), and had greater survival (P = 0.01). ECM genera such as Cortinarius, Russula and Scleroderma provided tree to seedling inoculation. ECM colonization by Cortinarius spp. resulted in larger chestnut plants and increased nitrogen foliar concentrations on the five month seedlings. It can be hypothesized that blight will aid in diversifying forest stand composition and these early ECM networks will help facilitate the survival of other native hardwoods that recruit into these sites over time.

Costs of induced defenses for the invasive plant houndstongue (Cynoglossum officinale L.) and the potential importance for weed biocontrol

Inducible plant defenses—those produced in response to herbivore feeding—are thought to have evolved as a cost-saving tactic that allows plants to enact defenses only when needed. The costs of defense can be significant, and loss of plant fitness due to commitment of resources to induced defenses could affect plant populations and play a role in determining the success or failure of weed biocontrol. We used methyl jasmonate (MeJA) to experimentally induce defenses without herbivores in invasive houndstongue plants (Cynoglossum officinale L.) in the field and measured resulting growth and fitness (plant size, seed number, and seed weight). MeJA-treated plants emitted large amounts of plant volatiles and produced leaves with twice as many trichomes as untreated plants. Plants with activated defenses had fewer leaves, were smaller, and produced nutlets that weighed less than plants not investing in defenses. These data indicate that herbivore-induced defenses are costly for houndstongue plants in their invaded range and represent significant indirect costs of herbivory beyond direct feeding damage (e.g., loss of photosynthetic tissue). Notably, the magnitude of defenses elicited upon feeding varies greatly by herbivore species and a better understanding of the costs of defense could help us predict which potential biocontrol herbivores are most likely to be effective.

Tempered mlo broad-spectrum resistance to barley powdery mildew in an Ethiopian landrace

Recessive mutations in the Mlo gene confer broad spectrum resistance in barley (Hordeum vulgare) to powdery mildew (Blumeria graminis f. sp. hordei), a widespread and damaging disease. However, all alleles discovered to date also display deleterious pleiotropic effects, including the naturally occurring mlo-11 mutant which is widely deployed in Europe. Recessive resistance was discovered in Eth295, an Ethiopian landrace, which was developmentally controlled and quantitative without spontaneous cell wall appositions or extensive necrosis and loss of photosynthetic tissue. This resistance is determined by two copies of the mlo-11 repeat units, that occur upstream to the wild-type Mlo gene, compared to 11–12 in commonly grown cultivars and was designated mlo-11 (cnv2). mlo-11 repeat unit copy number-dependent DNA methylation corresponded with cytological and macroscopic phenotypic differences between copy number variants. Sequence data indicated mlo-11 (cnv2) formed via recombination between progenitor mlo-11 repeat units and the 3′ end of an adjacent stowaway MITE containing region. mlo-11 (cnv2) is the only example of a moderated mlo variant discovered to date and may have arisen by natural selection against the deleterious effects of the progenitor mlo-11 repeat unit configuration.

Growth and reproductive consequences of photosynthetic tissue loss in the surface canopies of Macrocystis pyrifera (L.) C. Agardh

Macrocystis pyrifera (L.) C. Agardh provides biogenic habitat for species of significant commercial, cultural and recreational value; however, the floating surface canopies of M. pyrifera are particularly vulnerable to physical and biological disturbance (e.g., herbivory, storm events and harvesting). Given the key ecological roles of M. pyrifera, it is important to identify the impacts of photosynthetic tissue loss on growth and reproduction. I hypothesized that canopy removal would result in compensatory regeneration of the surface canopy. As life history theory posits a tradeoff between growth and reproduction, I also hypothesized that canopy removal would involve a reduction in reproductive investment, as either: (i) reduced production of reproductive structures; or (ii) changes in reproductive condition from fertile to sterile. To evaluate these hypothesizes I conducted two field experiments. In the first experiment, there was no significant difference in the generation of vegetative fronds or reproductive blades between controls (no loss of photosynthetic tissue from surface canopies) and treatments where photosynthetic tissue in surface canopies was thinned by either 30% or 70%. Relative to controls, the removal of entire surface canopies to a depth of 1.2m (i.e., simulated commercial harvesting) did not affect the generation of new vegetative fronds; however, the generation of reproductive blades was reduced by an average of 86%, suggesting that without the organic production supplied by the canopy, reproduction, but not growth, suffers. Further, the lack of evidence for compensatory growth despite reductions in reproduction suggests that M. pyrifera has little tolerance to canopy loss. The second experiment, which examined the effect of removing surface canopies on rate and longevity of changes in reproductive condition, found that although no control algae became sterile, 89% of algae with their surface canopies removed became sterile 50d after canopy removal, with effects persisting for up to 83d. As the supply of M. pyrifera propagules in the center of kelp forests can be tightly coupled to local reproductive output, induced sterility via the loss of photosynthetic tissue could affect the long-term stability of M. pyrifera beds. Further investigation into the scalability of these results and implications for long-term stability of M. pyrifera beds is warranted.

Physiological price of an induced chemical defense: photosynthesis, respiration, biosynthesis, and growth.

A recurring theme in defense allocation theories is that defenses are costly. Most studies that attempt to quantify a cost of defense seek to establish a trade-off between a component of plant fitness and the level of a constitutive defense. Such estimates are ambiguous because they cannot discount the cost of traits that are correlated with defense but are not themselves defensive. We examined the effects of damage-induced synthesis of furanocoumarins, known defense compounds, on the growth of wild parsnip. Plants that had 2% of their leaf area removed accumulated 8.6% less total biomass and 14% less root biomass than intact plants over a 4-week period. We also found that this small amount of leaf damage significantly reduced net photosynthetic rates 0.5 h after damage; the effect was temporary, as photosynthetic rates were no longer significantly different after 48 h. Lastly, we found that increases in respiration rates associated with damage coincided spatially and temporally with increases in furanocoumarin production, and that respiration increases were phenotypically correlated with furanocoumarin production. When damage-induced changes in furanocoumarin content and respiration rates were expressed in glucose equivalents and compared, the energetic cost of furanocoumarin production (12.6 μg glucose cm-2) accounted for all of the increase in respiration (12.0 μg glucose cm-2). A comparison of other secondary compounds in damaged and intact leaflets revealed that myristicin, a furanocoumarin synergist, is the only other compound aside from furanocoumarins that is inducible. The inducible defense system of wild parsnip thus appears to involve a small subset of secondary compounds. Synthesis of these compounds is tightly linked to damage-induced rates of respiration. Because the negative impact that damage had on the rate of net photosynthesis was short-lived, the impact of damage on growth observed in this study was likely due to the cost of furanocoumarin synthesis elicited by damage rather than the loss of photosynthetic tissue caused by damage.

Seedlings from Large Seeds Tolerated Defoliation Better: A Test Using Phylogeneticaly Independent Contrasts

The characteristic seed size of a plant species may reflect evolution toward an optimal compromise between size and number of seeds produced. The extent to which large seed size conveys an advantage to a seedling probably varies according to circumstances, and this may explain at least some of the great variation in seed size among species. Here we test whether large—seeded species are better able than small—seeded species to withstand defoliation at the seedling state. We compared growth and survival of seedlings of 40 species of Australian angiosperms after removing 95% of their photosynthetic tissue shortly after emergence. We accounted for effects of phylogeny by selecting pairs of species that were "phylogenetically independent contrasts." That is, the phylogenetic path connecting the two species of any pair was independent of the path connecting the two species of any other pair we used. We also selected the species so that the two members of each pair differed at least 10—fold in seed mass. Therefore, each pair provided an independent case for examining the consequences of evolutionary divergence in seed size. We found that the large seeded species survived loss of photosynthetic tissue better than the smaller seeded species in 14 of the 16 pairs for which there was a significant difference in survival. The extent to which growth of survivors was reduced by loss of photosynthetic tissue also differed in 8 pairs. With the large—seeded species being less affected in 6 of these cases. We conclude that large seed size is generally associated with greater ability of seedlings to cope with loss of photosynthetic tissue. Consequently, large seed size may be favored in any circumstances in which seedlings are likely to experience carbon deficit early in development.

LITTLE ICE AGE DECLINE OF A COLD MARGINAL PINUS SYLVESTRIS FOREST IN THE SWEDISH SCANDES

SUMMARYThe natural decline of a virgin high‐altitude Pinus sylvestris forest during the Little Ice Age (approximately AD 1300–1850) was studied in the Swedish Scandes. Methods included 14C and cross‐dating of wood remnants, soil analyses, year‐ring chronologies and age structures. A closed pine forest started a gradual decline in the 11th century or somewhat later, which proceeded until the mid‐19th century. Long‐term failure of regeneration and premature death of trees are postulated to have caused the forest dieback, mainly owing to a negative shift of the carbon budget, including weather‐induced loss of photosynthetic tissue and root disfunction. Temperature measurements on the study site stressed its current marginality. Especially thermal conditions in and close to the ground were deduced to be decisive. The decline of the forest is considered to indicate a long‐term lowering during the Little Ice Age of the summer (June‐September) mean temperature by 1°C or more, compared with the 1931–1960 mean.