NR 402 Final - Short Answer
what is the function of abscisic acid in protecting plants from environmental stress? why does activation of this hormonal pathway lead to increased plant susceptibility to biotic attack?
-ABA is a general response to envm stress -shuts down general pathways of secondary chemical production -this activation leads to susceptibility of attack because it depresses two key pathways of induced chemical defense -ABA does not support growth or defense
what is the function of abscisic acid in protecting plants from environmental stress? why does activation of this hormonal pathway lead to increased plant susceptibility to biotic attack?
-ABA is a general response to envm stress -shuts down general pathways of secondary chemical production -this activation leads to susceptibility of attack because it depresses two key pathways of induced chemical defense -ABA does not support growth or defense
how do beetles vector fungal pathogens? what morphological adaptations aid in transmission?
-acquire the pathogen from an infected host -most to another host and deliver the pathogen morphological adaptations: -mycangium (pockets in their bodies or mouthparts evolved to help carry fungal spores or biomass) -mycangium fungi help decompose woody structures and increase insects nutritional value
how does armillaria persist within stands following cutting?
-because it persists in the roots and on stumps -additionally, it can live on dead tissue
describe the growth differentiation balance hypothesis in the context of gypsy moth dynamics
-competition becomes the primary threat to plant survival in non-outbreak years -oaks respond to outbreaks through induced defenses (tannins) -in outbreak years, GDB shifts towards defense (induced senescence) -in non outbreak years, GDB shifts towards growth, leaving them open to attack
how does environmental stress influence the capacity of plants to defend themselves? justify your answer in terms of physical damage to plant tissues and defensive plant responses
-environmental stress reduces the plants capacity to defend themselves -focus on growth instead of defense (growth differentiation balance hypothesis) -will suffer -reduction in carbon resources available for defense -physical damage to plant vascular tissue
how does environmental stress influence the capacity of plants to defend themselves? justify your answer in terms of physical damage to plant tissues and defensive plant responses
-environmental stress reduces the plants capacity to defend themselves -focus on growth instead of defense (growth differentiation balance hypothesis)
what characteristic of p. cinnamon causes it to have a remarkably strong capacity to persist within a stand? hows does this give manages an easy way to prevent spreading?
-has a broad host range and asymmetric impacts (can survive in extreme temps) -root disease -can't sporulate above ground, soil drenching management can control the spread
what characteristic is essential to creating "disease of the site" and how does this influence the duration of disease in a particular location?
-if they can persist at the individual site (grow to large biomasses) -legacy effects
at what point during stand development in a second growth stand would you expect armillaria inoculum will be at its greatest levels?
-in high input production sysems -after being built up on buried root and stump -on a tree that was recently cut -recently disturbed forest
how do concepts of value at the individual level differ among fields of health
-individual plants are likely to be attacked during their lifespan -best known advances in medicine improve the health of individuals -agriculture -value of the individual varies between industry (high value in humans and animals) (value of plants depends on how they interest with environment) pg 14
how do volatile organic chemicals fit into the lifecycle or day-to-day lives of insects?
-insects are good at detecting volatile chemicals to find susceptible plants, track pheromone trails and find prey -can signal susceptibility of host trees -can use to assemble large group of insects to overwhelm a plant (mass attack)
oaks respond to gypsy moth attack by increasing foliar phenolic concentrations (tannins) which are usually not toxic identify how these compounds influence insect development times and susceptibility to nuclear polyhedrosis virus
-interfere's with protein absorption in insect's gut -slows nutrient absorption, insect development and quenches outbreaks -NVP
oaks respond to gypsy moth attack by increasing foliar phenolic concentrations (tannins) which are usually not toxic identify how these compounds influence insect development times and susceptibility to nuclear polyhedrosis virus
-interfere's with protein absorption in insect's gut -slows nutrient absorption, insect development and quenches outbreaks -NVP
identify how forest managers can limit eastern spruce budworm impacts silviculturally?
-look at the stand composition -the development and fitness of budworm are increased by local density of firs and spruce -if you have more fir, you have more outbreak -clear out more forests, reduce the stand density
what changes in the environment will cause an increase in swiss needle cast severity? what land use or management factors will increase disease severity?
-precipitation makes swiss needle cast worse -timber/logging will make the disease worse (disturbance will help it spread) -silviculture management
heart rot does not attack living tissue, by what mechanism can these tissues then be protected?
-prevent the initial attack -helpful fungi that will defend against the infection (tissue is already dead)
mineral resources can limit many aspects of plant productivity, why then is the CN balance hypothesis so inadequate as an explanatory model?
-says that N-rich defense will be suppressed at low nutrient levels and C-based will be tied to light limitation -said defensive responses should shift based on CN status but these might not be the best ways plants defend themselves -herbivory can alter plant nutritional status to benefit the attacker -plants should focus on defending first instead of outgrowing neighbors when it comes to scarce resources
identify the mechanism by which plants shutdown secondary defensive chemical pathways and under the environmental conditions when this can occur
-temperature and moisture stress induces abscisic acid signaling -depresses salicylic acid and jasmoic acid under secondary chemical synthesis (two key pathways of secondary chemical defense) -signaling pathways
describe the degree of damage caused by emerald ash borer in its native range
-virtually unknown in its native range of China -big deal in the US, selectively kills larger trees
identify a pathway by which wind can cause increase susceptibility (as opposed to transmission) to infection by pathogens?
-wind exposure (wind makes the canopies of trees rougher, easier for insects) -soil anchorage (wind uproots trees and makes them less stable, pathogens can get in and reduce stability even more) -resistance to stem breakage (pathogens again decrease stability)
what are the three primary classes of plant-microbial interactions? how are these characteristics defined or structured?
1) Pathogenic -causes harm to host plant -effects dispersal, growth, etc of trees 2) Sapotrophic -most independent of host plant of the 3 interaction types -breaks down of organic matter -can brea k down cellulose, hemicellulose and lignin 3) Mutualistic -benefits host plant directly
what two factors tend to dampen gypsy moth outbreaks?
1) defoliated oaks -host defensive response -slows nutrient absorption and insect development 2) NPV -native pathogen -kills gypsy moth -insects consume NPV and then transmit it
identify the three main genera of bark beetles in western conifer forests and rank them according to their capacity to cause mortality of coniferous species
1) dendroctonus 2) scolytus 3) ips
describe the transmission dynamics for Heterbasidion root disease at the stand scale between the two principle species that affect californian forests?
1)irregulare: pines -rapidly kills trees -large disease center -easier to control 2) occidentale: firs -slowly kills trees -smaller (but more frequent) disease centers both are persistent
American chestnut is a transformed species in eastern forests. In locations impacted by Cryphonectria parasitica (chestnut blight), describe the canopy position and average tree size for surviving individuals. Describe the effects on chestnut for piedmont forests invaded by Phytophthora cinnamomi?
In surviving individuals, the American chestnut has been reduced to an understory shrub, with stems no wider than 10cm, rarely fruiting Cinnamomi completely kills chestnuts in the lowland forests
describe the relationship of the oomycota to other fungi including the relative relationship to the other two principle groups of fungi (identify them as well)
Pythium: -diverse, widespread collection of soil fungi -causes damping off disease -major causes of seedling mortality Phytophthora: -many agricultural crops (potato famine) oomycota: -many can be considered aquatic pathogens -persist as saprotrophs on dead organic matter -cause the most devastating diseases
identify two principle groups of mistletoes and state their relative capacity to cause diesease
dwarf: -parasitize nutrients, water and carbon -causes serious damage and mortality leafy: -parasitize nutrients and water but not carbon -relatively less damaging
how does generalist vs specificity affect the ability of insects to control outbreak? Which characteristic would you select for biocontrol program?
generalist: affects many different kinds of plants specialists: can only infect one or few plants -bark beetles, hypoxolon cankers
describe the patterns of insect decline across Europe what type of ecosystems have shown insect population declines
all types of flying insects pristine areas (areas without direct spraying over herbicides or pesticides, without direct habitat loss)
is Asscomycota or basidiomycota more important for forest health?
basidiomycota -most familiar and economically important fungi group -most of organism is hidden within the host/underground -large and obvious -armillaria -just want to disperse spores ascomycota -sac like structure -penicillum -pitch canker -critically important diseases to crops -less showy more slimy bas - better for nutrient cycling, fuel removal, putting organic matter back in soil bc they persist a long time
contrast resource acquisition between biotrophic (A) and necrotrophic (B) pathogens identifying the status of tissue where these pathogens will be found in an infected plant
biotrophic -live within living tissue but kill and feed off of the adjacent dead tissue -found in living tissue necrothrophic -pathogens kill tissue and acquire nutrients from dead organic matter -more likely to be saprotrophs -found in dead tissue
where do parasitoid insects complete their life cycle? how could this benefit forest management?
can complete life cycle in predators, herbivores, detribores and even other parasitoids we can come up with many different ways to kill them
contrast induced and constitutive plant defenses to biotic attack
constitutive: -produced and maintained continuously -thorns, hairs, waxy leaf coatings -significant energy cost to produce but durable induced: -temporary -only come up when needed -more unpredictable for insect
bark beetle outbreaks can influence fire intensity but this effect has some important context describe when outbreak is likely to cause hazardous fuel conditions (time or stand condition)
during stressful environmental events -prolonged/severe drought -heat event -stand previously weakened (bark beetle numbers are allowed to climb)
insects are poikilothermic animals, what does this mean for their thermo regulation? Identify one adaptation or action insects use to limit excessively high and low temperatures
high temperatures -large dorsal fins to rapidly pump water through the insect low temperatures -torpor (depression of body temperature to converse energy)
define the following descriptions of host range and identify one example of generalist and specialist biotic agents
host range: -the environment where something (like a pathogen or tree species) can survive and thrive -the number or diversity of suitable hosts for a particular microbe generalist: -much easier to establish -broad prey/host range -cannot control specific prey they attack -some of most dangerous are generalists specialist: -have very specific host range
-its a loss of abundance in all species instead of just a loss in diversity -loss of abundance causes a trophic cascade, where the ecosystem can't function -trophic cascades also occur in extinctions
how are declines in insect biomass different than extinctions? how are the impacts to ecosystems similar?
describe the impacts of Phellinus weirrii in Douglas fir forests of the PNW including impact on hosts, the timing or stand conditions conductive to transmission, and management responses to limit spread
impacts on hosts: - impacts on timing: - impacts on stand conditions conductive to transmission: -root to root contact management responses: -
for spruce budworm, what part of the insect's life stage is problematic
larval stage -attacks buds and the foliage of conifers
describe the impacts of hemlock woolly adelgid in its native range contrast these impacts with the impacts of the insect in western hemlock forests where it is exotic
native range: -relatively unimportant source of mortality exotic range: -attacks leaf tissue -range is determined by temp and predators that we release -much larger impact
describe the mode of action by which swiss needle cast damages host tissue
pathogen biomass clogs the stomata, thereby disrupting the carbon acquisition
contrast parasitoids with predators which is more effective for controlling insect outbreak?
predators: -insects eat other insects -beetles/wasps/flies/hemiptera -have masticating insect bodies and piercing sucking mouthparts parasitoids: -wasps and flies with specialized body parts for attacking eggs on a host -have adaptations rendering hosts incapable of defense
when and where is Phellinus weirii most likely to be a management problem?
when: -in times of high nutrient availability, changes its biogeochemical cycles -disease intensifies with root to root contact that comes with canopy closure and increased tree mortality where: -doug fir areas (Pacific Northwest) -landscape level disease -south of the Oregon-California border
contrast the two principle types of wood rot fungi in terms of the wood components they degrade identify the residual compounds for each
white rot -attacks lignin -unprotected cellulose is white brown rot -attacks cellulose -leftover lignin oxidizes