Water, not carbon, drives drought-constraints on stem terpene defense against simulated bark beetle attack in Pinus edulis.

Drought predisposes forest trees to bark beetle-induced mortality, but the physiological mechanisms remain unclear. While drought-induced water and carbon limitations have been implicated in defensive failure and tree susceptibility, evidence demonstrating how these factors interact is scarce. We withheld water from mature, potted Pinus edulis and subsequently applied a double-stem girdle to inhibit carbohydrate transport from the crown and roots.

Local carbon reserves are insufficient for phloem terpene induction during drought in Pinus edulis in response to bark beetle-associated fungi.

Stomatal closure during drought inhibits carbon uptake and may reduce a tree's defensive capacity. Limited carbon availability during drought may increase a tree's mortality risk, particularly if drought constrains trees' capacity to rapidly produce defenses during biotic attack. We parameterized a new model of conifer defense using physiological data on carbon reserves and chemical defenses before and after a simulated bark beetle attack in mature Pinus edulis under experimental drought.

Carbon starvation following a decade of experimental drought consumes old reserves in Pinus edulis.

Shifts in the age or turnover time of non-structural carbohydrates (NSC) may underlie changes in tree growth under long-term increases in drought stress associated with climate change. But NSC responses to drought are challenging to quantify, due in part to large NSC stores in trees and subsequently long response times of NSC to climate variation. We measured NSC age (Δ C) along with a suite of ecophysiological metrics in Pinus edulis trees experiencing either extreme short-term drought (-90% ambient precipitation plot, 2020-2021) or a decade of severe drought (-45% plot, 2010-2021).

Fire intensity impacts on physiological performance and mortality in Pinus monticola and Pseudotsuga menziesii saplings: a dose-response analysis.

Fire is a major cause of tree injury and mortality worldwide, yet our current understanding of fire effects is largely based on ocular estimates of stem charring and foliage discoloration, which are error prone and provide little information on underlying tree function. Accurate quantification of physiological performance is a research and forest management need, given that declining performance could help identify mechanisms of-and serve as an early warning sign for-mortality. Many previous efforts have been hampered by the inability to quantify the heat flux that a tree experiences during a fire, given its highly variable nature in space and time.

No carbon storage in growth-limited trees in a semi-arid woodland.

Plant survival depends on a balance between carbon supply and demand. When carbon supply becomes limited, plants buffer demand by using stored carbohydrates (sugar and starch). During drought, NSCs (non-structural carbohydrates) may accumulate if growth stops before photosynthesis.

The osmotic balancing act: When sugars matter for more than metabolism in woody plants.

Sugars and other non-structural carbohydrates are known to serve as currency in plants, to either fuel metabolic activities or as storage for later use. They can also serve non-metabolic purposes of osmoregulation and cryoprotection, especially in perennial woody plants.

Death from hunger or thirst? Phloem death, rather than xylem hydraulic failure, as a driver of fire-induced conifer mortality.

Disruption of photosynthesis and carbon transport due to damage to the tree crown and stem cambial cells, respectively, can cause tree mortality. It has recently been proposed that fire-induced dysfunction of xylem plays an important role in tree mortality. Here, we simultaneously tested the impact of a lethal fire dose on nonstructural carbohydrates (NSCs) and xylem hydraulics in Pinus ponderosa saplings.

Global field observations of tree die-off reveal hotter-drought fingerprint for Earth's forests.

Earth's forests face grave challenges in the Anthropocene, including hotter droughts increasingly associated with widespread forest die-off events. But despite the vital importance of forests to global ecosystem services, their fates in a warming world remain highly uncertain. Lacking is quantitative determination of commonality in climate anomalies associated with pulses of tree mortality-from published, field-documented mortality events-required for understanding the role of extreme climate events in overall global tree die-off patterns.

Hotter droughts alter resource allocation to chemical defenses in piñon pine.

Heat and drought affect plant chemical defenses and thereby plant susceptibility to pests and pathogens. Monoterpenes are of particular importance for conifers as they play critical roles in defense against bark beetles. To date, work seeking to understand the impacts of heat and drought on monoterpenes has primarily focused on young potted seedlings, leaving it unclear how older age classes that are more vulnerable to bark beetles might respond to stress.

Foliar respiration is related to photosynthetic, growth and carbohydrate response to experimental drought and elevated temperature.

Short-term plant respiration (R) increases exponentially with rising temperature, but drought could reduce respiration by reducing growth and metabolism. Acclimation may alter these responses. We examined if species with different drought responses would differ in foliar R response to +4.

Short- and long-term effects of fire on stem hydraulics in Pinus ponderosa saplings.

Understanding tree physiological responses to fire is needed to accurately model post-fire carbon processes and inform management decisions. Given trees can die immediately or at extended time periods after fire, we combined two experiments to assess the short- (one-day) and long-term (21-months) fire effects on Pinus ponderosa sapling water transport. Native percentage loss of conductivity (nPLC), vulnerability to cavitation and xylem anatomy were assessed in unburned and burned saplings at lethal and non-lethal fire intensities.

Drought Tolerance and Competition in Eastern Redcedar () Encroachment of the Oak-Dominated Cross Timbers.

On the dry, western edge of the eastern deciduous forest of the USA (Cross Timbers), the drought-tolerant, evergreen eastern redcedar ( is encroaching into post oak- dominated woodlands. The overall goal of this study was to examine whether the drought tolerance strategies of eastern redcedar provide it a competitive advantage over post oak and whether this is a key attribute facilitating its successful establishment in the Cross Timbers. Specifically, we assessed xylem water potential and leaf gas exchange of these two species growing in single-species stands and in a mixed-species stand.

Divergences in hydraulic conductance and anatomical traits of stems and leaves in three temperate tree species coping with drought, N addition and their interactions.

Drought and nitrogen (N) addition have been shown to affect tree hydraulic traits, but few studies have been made on their interactions across species with different wood types or leaf forms. We examined the responses of hydraulic conductance and xylem anatomical traits of Quercus mongolica (ring porous with simple leaves), Fraxinus mandshurica (ring porous with compound leaves) and Tilia amurensis (diffuse porous with simple leaves) to drought, N addition and their interactions. Drought stress decreased current-year xylem-specific conductivity in stems (Ksx) and leaf hydraulic conductance (Kleaf ), but N addition affected Ksx and Kleaf differently among species and watering regimes.

Tree defence and bark beetles in a drying world: carbon partitioning, functioning and modelling.

Drought has promoted large-scale, insect-induced tree mortality in recent years, with severe consequences for ecosystem function, atmospheric processes, sustainable resources and global biogeochemical cycles. However, the physiological linkages among drought, tree defences, and insect outbreaks are still uncertain, hindering our ability to accurately predict tree mortality under on-going climate change. Here we propose an interdisciplinary research agenda for addressing these crucial knowledge gaps.

Conifers depend on established roots during drought: results from a coupled model of carbon allocation and hydraulics.

Trees may survive prolonged droughts by shifting water uptake to reliable water sources, but it is unknown if the dominant mechanism involves activating existing roots or growing new roots during drought, or some combination of the two. To gain mechanistic insights on this unknown, a dynamic root-hydraulic modeling framework was developed that set up a feedback between hydraulic controls over carbon allocation and the role of root growth on soil-plant hydraulics. The new model was tested using a 5 yr drought/heat field experiment on an established piñon-juniper stand with root access to bedrock groundwater.

Embolism recovery strategies and nocturnal water loss across species influenced by biogeographic origin.

Drought-induced tree mortality is expected to increase in future climates with the potential for significant consequences to global carbon, water, and energy cycles. Xylem embolism can accumulate to lethal levels during drought, but species that can refill embolized xylem and recover hydraulic function may be able to avoid mortality. Yet the potential controls of embolism recovery, including cross-biome patterns and plant traits such as nonstructural carbohydrates (NSCs), hydraulic traits, and nocturnal stomatal conductance, are unknown.

Belowground annual ring growth coordinates with aboveground phenology and timing of carbon storage in two tallgrass prairie forb species.

Premise Of The Study: Herb chronology, the study of belowground annual growth rings in perennial forbs, has much potential as a tool for monitoring plant growth as a function of environment. To harness this potential, understanding of the coordination between ring ontogeny, aboveground phenology, and the temporal allocation of carbon products belowground in herbaceous forbs must be improved.

Methods: We investigated these relationships in two southern United States tallgrass prairie perennial forb species, Asclepias viridis and Lespedeza stuevei, making monthly excavations for a year.

Standardized protocols and procedures can precisely and accurately quantify non-structural carbohydrates.

Non-structural carbohydrates (NSCs), the stored products of photosynthesis, building blocks for growth and fuel for respiration, are central to plant metabolism, but their measurement is challenging. Differences in methods and procedures among laboratories can cause results to vary widely, limiting our ability to integrate and generalize patterns in plant carbon balance among studies. A recent assessment found that NSC concentrations measured for a common set of samples can vary by an order of magnitude, but sources for this variability were unclear.

The sweet side of global change-dynamic responses of non-structural carbohydrates to drought, elevated CO2 and nitrogen fertilization in tree species.

Non-structural carbohydrates (NSC) play a central role in plant functioning as energy carriers and building blocks for primary and secondary metabolism. Many studies have investigated how environmental and anthropogenic changes, like increasingly frequent and severe drought episodes, elevated CO2 and atmospheric nitrogen (N) deposition, influence NSC concentrations in individual trees. However, this wealth of data has not been analyzed yet to identify general trends using a common statistical framework.

Responses of Woody Plant Functional Traits to Nitrogen Addition: A Meta-Analysis of Leaf Economics, Gas Exchange, and Hydraulic Traits.

Atmospheric nitrogen (N) deposition has been found to significantly affect plant growth and physiological performance in terrestrial ecosystems. Many individual studies have investigated how N addition influences plant functional traits, however these investigations have usually been limited to a single species, and thereby do not allow derivation of general patterns or underlying mechanisms. We synthesized data from 56 papers and conducted a meta-analysis to assess the general responses of 15 variables related to leaf economics, gas exchange, and hydraulic traits to N addition among 61 woody plant species, primarily from temperate and subtropical regions.