Contrasting xylem vessel constraints on hydraulic conductivity between native and non-native woody understory species

We examined the hydraulic properties of 82 native and non-native woody species common to forests of Eastern North America, including several congeneric groups, representing a range of anatomical wood types. We observed smaller conduit diameters with greater frequency in non-native species, corresponding to lower calculated potential vulnerability to cavitation index. Non-native species exhibited higher vessel-grouping in metaxylem compared with native species, however, solitary vessels were more prevalent in secondary xylem. Higher frequency of solitary vessels in secondary xylem was related to a lower potential vulnerability index. We found no relationship between anatomical characteristics of xylem, origin of species and hydraulic conductivity, indicating that non-native species did not exhibit advantageous hydraulic efficiency over native species. Our results confer anatomical advantages for non-native species under the potential for cavitation due to freezing, perhaps permitting extended growing seasons

Commercial Bioinoculants Increase Root Length Colonization and Improve Petiole Nutrient Concentration of Field-grown Grapevines

Agricultural bioinoculants containing arbuscular mycorrhizal fungi represent a potential opportunity to reduce the dependence of grapevines (Vitis) on agrochemicals. This field study assessed the ability of four commercial bioinoculants to colonize grapevine roots and their effects on petiole nutrient concentration, berry composition, and root morphology of ‘Pinot noir’ (Vitis vinifera) grafted onto rootstock ‘Couderc 3309’ (Vitis riparia × Vitis rupestris) and ‘Riesling’ (V. vinifera) grafted onto ‘Couderc 3309’ and Selection Oppenheim four (Vitis berlandieri × V. riparia). Three bioinoculants increased root mycorrhizal colonization; however, regardless of the treatment, mycorrhizal fungal structures were enhanced. Grapevine petiole nutrient concentration was improved by bioinoculants. Root diameter, root length density, and specific root length increased with greater mycorrhizal root colonization. Using bioinoculants to reduce chemical fertilizers may be a good strategy to improve grapevine productivity and health in cool climates; however, the impact of mycorrhizal bioinoculants in the vineyard may differ among scion–rootstocks, edaphoclimatic conditions, and vineyard soil microbiomes

Carbon allocation to root exudates is maintained in mature temperate tree species under drought

- Carbon (C) exuded via roots is proposed to increase under drought and facilitate important ecosystem functions. However, it is unknown how exudate quantities relate to the total C budget of a drought-stressed tree, that is, how much of net-C assimilation is allocated to exudation at the tree level. - We calculated the proportion of daily C assimilation allocated to root exudation during early summer by collecting root exudates from mature Fagus sylvatica and Picea abies exposed to experimental drought, and combining above- and belowground C fluxes with leaf, stem and fine-root surface area. - Exudation from individual roots increased exponentially with decreasing soil moisture, with the highest increase at the wilting point. Despite c. 50% reduced C assimilation under drought, exudation from fine-root systems was maintained and trees exuded 1.0% (F. sylvatica) to 2.5% (P. abies) of net C into the rhizosphere, increasing the proportion of C allocation to exudates two- to three-fold. Water-limited P. abies released two-thirds of its exudate C into the surface soil, whereas in droughted F. sylvatica it was only one-third. - Across the entire root system, droughted trees maintained exudation similar to controls, suggesting drought-imposed belowground C investment, which could be beneficial for ecosystem resilience

Dynamics of initial carbon allocation after drought release in mature Norway spruce—Increased belowground allocation of current photoassimilates covers only half of the carbon used for fine‐root growth

After drought events, tree recovery depends on sufficient carbon (C) allocation to the sink organs. The present study aimed to elucidate dynamics of tree-level C sink activity and allocation of recent photoassimilates (C$_{new}$) and stored C in c. 70-year-old Norway spruce (Picea abies) trees during a 4-week period after drought release. We conducted a continuous, whole-tree $^{13}$C labeling in parallel with controlled watering after 5 years of experimental summer drought. The fate of C$_{new}$ to growth and CO$_{2}$ efflux was tracked along branches, stems, coarse- and fine roots, ectomycorrhizae and root exudates to soil CO$_{2}$ efflux after drought release. Compared with control trees, drought recovering trees showed an overall 6% lower C sink activity and 19% less allocation of C$_{new}$ to aboveground sinks, indicating a low priority for aboveground sinks during recovery. In contrast, fine-root growth in recovering trees was seven times greater than that of controls. However, only half of the C used for new fine-root growth was comprised of C$_{new}$ while the other half was supplied by stored C. For drought recovery of mature spruce trees, in addition to C$_{new}$, stored C appears to be critical for the regeneration of the fine-root system and the associated water uptake capacity

Data from: A global analysis of plant recovery performance from water stress

Plant post-drought recovery performance is essential to predict shifts in ecosystem dynamics and production during frequent climate change-driven drought events. Yet, it is not clear how post-drought recovery is related to evolutionary and geographic variations in plants. In this study, we generated a global data set of post-drought recovery performance in 140 plant species from published studies. We quantified the plant post-drought recovery performance by calculating a recovery index for multiple plant physiological and hydraulic parameters, including leaf water potential, net photosynthetic rate, leaf hydraulic conductance, and shoot biomass. The magnitude of recovery among four plant functional types (deciduous angiosperms, evergreen angiosperms, gymnosperms, and crops), two plant growth forms (shrubs and trees), two water management strategies (isohydric and anisohydric), four xylem porosity types (diffuse, ring, semi-ring, and tracheid), and four major biomes (dry sclerophyll forest, boreal forest, temperate forest, and tropical/subtropical forest) were compared. We found the inability to completely recover immediately after severe water stress is ubiquitous across all plant functional types and growth forms, while the rate and magnitude of post-drought recovery varied greatly across different plant taxonomic categories and geographic ranges. In general, plant hydraulic architecture, leaf anatomy and physiology affect plants’ propensity towards recovery, and reflect evolutionary consequences of plant adaptation to their habitat. Due to the essential role of plant functional traits in regulating carbon storage in each biome, a better understanding plant post-drought recovery performance could improve our predictions on ecosystem productivity in a rapidly changing climate

Repetitive seasonal drought causes substantial species-specific shifts in fine-root longevity and spatio-temporal production patterns in mature temperate forest trees

Temperate forest ecosystems are exposed to a higher frequency, duration and severity of drought. To promote forest longevity in a changing climate, we require a better understanding of the long-term impacts of repetitive drought events on fine-root dynamics in mature forests. Using minirhizotron methods, we investigated the effect of seasonal drought on fine-root dynamics in single-species and mixed-species arrangements of Fagus sylvatica (European beech) and Picea abies (Norway spruce) by means of a 4-yr-long throughfall-exclusion experiment. Fine-root production of both species decreased under drought. However, this reduction was not evident for P. abies when grown intermixed with F. sylvatica. Throughfall-exclusion prolonged the lifespan of P. abies roots but did not change the lifespan of F. sylvatica roots, except in 2016. Fagus sylvatica responded to drought by reducing fine-root production at specific depths and during roof closure. This is the first study to examine long-term trends in mature forest fine-root dynamics under repetitive drought events. Species-specific fine-root responses to drought have implications for the rate and depth of root-derived organic matter supply to soil. From a root dynamics perspective, intermixing tree species is not beneficial to all species but dampens drought impacts on the belowground productivity of P. abies

A new currency for mutualism? : Fungal endophytes alter antioxidant activity in hosts responding to drought

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Phenolic root exudate and tissue compounds vary widely among temperate forest tree species and have contrasting effects on soil microbial respiration

Root-soil interactions fundamentally affect the terrestrial carbon (C) cycle and thereby ecosystem feedbacks to climate change. This study addressed the question whether the secondary metabolism of different temperate forest tree species can affect soil microbial respiration. We hypothesized that phenolics can both increase and decrease respiration depending on their function as food source, mobilizer of other soil resources, signaling compound, or toxin. We analyzed the phenolic compounds from root exudates and root tissue extracts of six tree species grown in a greenhouse using high-performance liquid chromatography (HPLC). We then tested the effect of individual phenolic compounds, representing the major identified phenylpropanoid compound classes, on microbial respiration through a five-day soil incubation. Phenolic root profiles were highly species-specific. Of the eight classes identified, flavonoids were the most abundant with flavanols being the predominating sub-class. Phenolic effects on microbial respiration ranged from a 26% decrease to a 46% increase, with reduced respiration occurring in the presence of compounds possessing a catechol ring. Tree species variation in root phenolic composition influences the magnitude and direction of root effects on microbial respiration. Our data support the hypothesis that functional group rather than biosynthetic class determines the root phenolic effect on soil C cycling.We are grateful for the support from the Cornell IGERT Cross-Scale Biogeochemistry and Climate program, David R. Atkinson Center Sustainable Biodiversity Fund, Kieckhefer Adirondack Fellowship, Bartlett Tree Foundation, and Andrew W. Mellon Foundation. We also thank Daniel Buckley, Tim Fahey, Jed Sparks and Kyle Wickings for their advice, Adrian Powell and Tara Webster for discussing HPLC analysis, Leah Rae McEwen for her help with Bio_Rad KnowItAll® 2017 Spectroscopy Software, Stephen Parry from Cornell Statistical Consulting Unit, and Cornell Nutrient Analysis Laboratories (CNAL) and Cornell University Stable Isotope Laboratory (COIL) for soil analysis. Lastly, we thank Juana Muñoz Ucros, Max Heitner, Cari Gostic and Andrew Harner for their help with root exudate collection and respiration measurements

Data from: Xylem vessel traits predict the leaf phenology of native and non-native understory species of temperate deciduous forests

Non-native understorey woody species have been shown to extend leaf display and inhabit vacant phenological niches in early spring and late autumn when growing with native counterparts in temperate deciduous forests across the world. Despite the potential competitive advantages, extended leaf duration also subjects non-native species to possible hydraulic risks associated with maintaining leaves during periods of increased frost probability. It remains unclear how non-native species are able to maintain xylem function within this context. Leaf phenology in temperate deciduous trees has been shown to be a function of xylem anatomy, with earlier bud break associated with smaller xylem vessels due to the presumed resistance of smaller vessels to freezing-induced cavitation. We examined relationships between leaf phenology and xylem vessel traits across 82 native and non-native understorey deciduous woody species common to eastern U.S. deciduous forests. We hypothesized that non-native species possess xylem vessel traits associated with maximum hydraulic safety during frost-prone spring and autumn leaf display without compromising rapid growth rate. Larger metaxylem vessels in non-native species were associated with both faster spring growth and delayed autumn leaf fall compared to native species. Non-native species also had smaller latewood vessel diameter, latewood vessel area percentage and a higher proportion of solitary vessels in the entire secondary xylem cross section compared to natives, potentially increasing their resistance to freezing- and/or drought-induced cavitation in autumn, thus allowing for delayed autumn leaf fall. Native and non-native species exhibited similar dates of spring bud break and leaf emergence, consistent with similar xylem vessel size and vessel area percentage within metaxylem and earlywood. Within both groups, species with earlier bud and leaf emergence had a higher total percentage of vessel area within metaxylem and earlywood. This suggests understorey species need sufficient water to support their early spring growth at the risk of freezing-induced cavitation. Our study suggests xylem vessel properties, along with cross-sectional spatial xylem vessel distribution, reflect the capacity of non-native plants to thrive in a new environment and deepen our understanding of the physiological mechanisms of successful invasions of non-native understorey woody plant species