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Drylands comprise one-third of Earth's terrestrial surface area and support over two billion people. Most drylands are projected to experience altered rainfall regimes, including changes in total amounts and fewer but larger rainfall events interspersed by longer periods without rain. This transition will have ecosystem-wide impacts but the long-term effects on microbial communities remain poorly quantified. We assessed belowground effects of altered rainfall regimes (+ 65% and -65% relative to ambient) at six sites in arid and semi-arid Australia over a period of three years (2016–2019) coinciding with a significant natural drought event (2017–2019). Microbial communities differed significantly among semi-arid and arid sites and across years associated with variation in abiotic factors, such as pH and carbon content, along with rainfall. Rainfall treatments induced shifts in microbial community composition only at a subset of the sites (Milparinka and Quilpie). However, differential abundance analyses revealed that several taxa, including Acidobacteria, TM7, Gemmatimonadates and Chytridiomycota, were more abundant in the wettest year (2016) and that their relative abundance decreased in drier years. By contrast, the relative abundance of oligotrophic taxa such as Actinobacteria, Alpha-proteobacteria, Planctomycetes, and Ascomycota and Basidiomycota, increased during the prolonged drought. Interestingly, fungi were shown to be more sensitive to the prolonged drought and to rainfall treatment than bacteria with Basidiomycota mostly dominant in the reduced rainfall treatment. Moreover, correlation network analyses showed more positive associations among stress-tolerant dominant taxa following the drought (i.e., 2019 compared with 2016). Our result indicates that such stress-tolerant taxa play an important role in how whole communities respond to changes in aridity. Such knowledge provides a better understanding of microbial responses to predicted increases in rainfall variability and the impact on the functioning of semi-arid and arid ecosystems. [ABSTRACT FROM AUTHOR]

Populations from different climates often show unique growth responses to temperature, reflecting temperature adaptation. Yet, whether populations from different climates differ in physiological temperature acclimation remains unclear. Here, we test whether populations from differing thermal environments exhibit different growth responses to temperature and differences in temperature acclimation of leaf respiration. We grew tropical and subtropical populations of two mangrove species (Avicennia germinans and Rhizophora mangle) under ambient and experimentally warmed conditions in a common garden at the species' northern range limit. We quantified growth and temperature responses of leaf respiration (R) at seven time points over ~10 months. Warming increased productivity of tropical populations more than subtropical populations, reflecting a higher temperature optimum for growth. In both species, R measured at 25 °C declined as seasonal temperatures increased, demonstrating thermal acclimation. Contrary to our expectations, acclimation of R was consistent across populations and temperature treatments. However, populations differed in adjusting the temperature sensitivity of R (Q 10) to seasonal temperatures. Following a freeze event, tropical Avicennia showed greater freeze damage than subtropical Avicennia , while both Rhizophora populations appeared equally susceptible. We found evidence of temperature adaptation at the whole-plant scale but little evidence for population differences in thermal acclimation of leaf physiology. Studies that examine potential costs and benefits of thermal acclimation in an evolutionary context may provide new insights into limits of thermal acclimation. [ABSTRACT FROM AUTHOR]

Aridity shapes species distributions and plant growth and function worldwide. Yet, plant traits often show complex relationships with aridity, challenging our understanding of aridity as a driver of evolutionary adaptation. We grew nine genotypes of Eucalyptus camaldulensis subsp. camaldulensis sourced from an aridity gradient together in the field for ~650 days under low and high precipitation treatments. Eucalyptus camaldulesis is considered a phreatophyte (deep‐rooted species that utilizes groundwater), so we hypothesized that genotypes from more arid environments would show lower aboveground productivity, higher leaf gas‐exchange rates, and greater tolerance/avoidance of dry surface soils (indicated by lower responsiveness) than genotypes from less arid environments. Aridity predicted genotype responses to precipitation, with more arid genotypes showing lower responsiveness to reduced precipitation and dry surface conditions than less arid genotypes. Under low precipitation, genotype net photosynthesis and stomatal conductance increased with home‐climate aridity. Across treatments, genotype intrinsic water‐use efficiency and osmotic potential declined with increasing aridity while photosynthetic capacity (Rubisco carboxylation and RuBP regeneration) increased with aridity. The observed clinal patterns indicate that E. camaldulensis genotypes from extremely arid environments possess a unique strategy defined by lower responsiveness to dry surface soils, low water‐use efficiency, and high photosynthetic capacity. This strategy could be underpinned by deep rooting and could be adaptive under arid conditions where heat avoidance is critical and water demand is high. [ABSTRACT FROM AUTHOR]

Leaf hydraulic traits characterize plant drought tolerance and responses to climate change. Yet, plant hydraulics are biased towards northern hemisphere woody species. We collected rhizomes of several perennial grass species along a precipitation gradient in eastern Australia and grew them in an experimental pot study to investigate potential trade‐offs between drought tolerance and plant morphology.We measured the following leaf hydraulic traits: the leaf water potential (Ψleaf) at 50% and 88% loss of leaf hydraulic conductance (P50Kleaf and P88Kleaf), the Ψleaf at 50% loss of stomatal conductance (P50gs), leaf turgor loss point (TLP), leaf dry matter content (LDMC), leaf modulus of elasticity (ε), and the slope of the relationship between predawn and midday Ψleaf. We also measured basal area, tiller density, seed head density, root collar diameter, plant height, and aboveground biomass of each individual.As expected, grass species varied widely in leaf‐level drought tolerance, with loss of 88% hydraulic conductance occurring at a Ψleaf ranging from −1.52 to −4.01 MPa. However, all but one species lost leaf turgor, and most reached P50gs before this critical threshold. Taller more productive grass species tended to have drought vulnerable leaves characterized by low LDMC and less negative P88Kleaf. Species with greater tiller production experienced stomatal closure and lost turgor at more negative Ψleaf. Although our sample size was limited, we found no relationships between these species' traits and their climate of origin.Overall, we identified important hydraulic and morphological trade‐offs in Australian grasses that were surprisingly similar to those observed for woody plants: (1) xylem of taller species was less drought tolerant and (2) turgor loss occurs and stomatal closure begins before significant loss of Kleaf. These data build upon a small yet growing field of grass hydraulics and may be informative of species responses to further drought intensification in Australia. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Nutrient enrichment is a major driver of environmental change in mangrove ecosystems. Yet, nutrient enrichment impacts on physiological processes that regulate CO2 and water fluxes between mangrove vegetation and the atmosphere remain unclear. We measured peak growing season photosynthesis (A) and respiration (R) in black mangrove (Avicennia germinans) leaves that had been subjected to long-term (8-year) nutrient enrichment (added N, added P, control) in north Florida. Previous results from this site indicated that Avicennia productivity was N-limited, but not P-limited. Thus, we expected that N addition would increase light saturated net photosynthesis at ambient CO2 (Anet), intrinsic water-use efficiency (iWUE), maximum rate of Rubisco carboxylation (Vcmax), and leaf dark respiration (R), while P addition would have little effect on any aspect of photosynthesis or respiration. We expected that increased photosynthesis and respiration would be most apparent immediately after N addition and in newly formed leaves. Indeed, Anet and Vcmax increased just after N addition in the N addition treatment; these increases were limited to leaves formed just after N addition. Nonetheless, over time, photosynthetic parameters and iWUE were similar across treatments. Interestingly, R measured at 25 °C increased with N addition; this effect was consistent across time points. P addition had little effect on R. Across treatments and time points, Vcmax,25 (Vcmax standardized to 25 °C) showed no relationship with R at 25 °C, but the maximum rate of electron transport for RuBP regeneration standardized to 25 °C (Jmax,25) increased with R at 25 °C. We conclude that N addition may have small, short-lived effects on photosynthetic processes, but sustained effects on leaf R in N-limited mangrove ecosystems. [ABSTRACT FROM AUTHOR]

Grassland biomass production is strongly linked with the timing and intensity of precipitation events. While the direct effects of precipitation patterns on grasses are well‐studied, less is known regarding plant–plant interactions during different phases of drought (i.e., dry down vs. recovery). Here, we examined how the intensity and timing of drought affected biomass production, traits related to growth rate and competitive vigor (specific leaf area [SLA], leaf dry matter content [LDMC], and height [HT]), and competitive effects in three common pasture grasses. Each species was grown alone (one individual per 45‐L planter) or with competition (one individual of each species per 45‐L planter) under three different drought types: (1) "short‐term" drought where water was withheld until the first species reached stomatal closure; (2) "prolonged" drought where water was withheld until all three species reached stomatal closure; and (3) "repeated" short‐term drought where water was withheld until the first species reached stomatal closure, plants were rewatered to capacity, and then, the drought was repeated. In all three drought types, replicates were assessed for biomass and traits pre‐ and post‐rewatering to represent the "resistance" and "recovery" phases of drought, respectively. Overall, we found (1) competitive interactions during phases of drought were primarily mediated by plant HT and LDMC, not SLA; (2) the severity and frequency of drought were key factors in describing plant–plant interactions during phases of drought; and (3) interspecific differences in traits and trait responses to drought phases were key in predicting plant–plant competition. Such shifts in competition interactions associated with interspecific trait responses to drought and during recovery from drought are likely to have significant effects on the productivity and composition of multispecies, grass‐dominated plant communities. [ABSTRACT FROM AUTHOR]

Climate warming could shift some subtropical regions to a tropical climate in the next 30 years. Yet, climate warming impacts on subtropical species and ecosystems remain unclear. We conducted a passive warming experiment in a subtropical forest in Florida, USA, to determine warming impacts on four species differing in their climatic distribution, growth form, and functional type: Serenoa repens (palm), Andropogon glomeratus (C4 grass), Pinus palustris (needled evergreen tree), and Quercus laevis (broadleaved deciduous tree). We hypothesized that warming would have neutral‐positive effects on photosynthetic processes in monocot species with warmer climatic distributions or adaptations to warmer temperatures, but negative effects on photosynthesis in tree species. We also hypothesized that periods of low soil moisture would alter photosynthetic responses to warming. In both monocot species, warming had no significant effect on net photosynthesis (A) or stomatal conductance (gs) measured at prevailing temperatures, or photosynthetic capacity measured at a common temperature. In P. palustris, warming reduced A (−15%) and gs (−28%), and caused small reductions in Rubisco carboxylation and RuBP regeneration. Warming had little effect on photosynthetic processes in Q. laevis. Interestingly, A. glomeratus showed little sensitivity to reduced soil moisture, and all C3 species reduced A and gs as soil moisture declined and did so consistently across temperature treatments. In subtropical forests of the southeastern US, we conclude that climate warming may have neutral or slightly positive effects on the performance of grasses and broadleaved species but negative effects on P. palustris seedlings, foreshadowing possible changes in community and ecosystem properties. [ABSTRACT FROM AUTHOR]

Temperature acclimation of leaf respiration (R) is an important determinant of ecosystem responses to temperature and the magnitude of temperature‐CO2 feedbacks as climate warms. Yet, the extent to which temperature acclimation of R exhibits a common pattern across different growth conditions, ecosystems, and plant functional types remains unclear. Here, we measured the short‐term temperature response of R at six time points over a 10‐month period in two coastal wetland species (Avicennia germinans [C3 mangrove] and Spartina alterniflora [C4 marsh grass]) growing under ambient and experimentally warmed temperatures at two sites in a marsh–mangrove ecotone. Leaf nitrogen (N) was determined on a subsample of leaves to explore potential coupling of R and N. We hypothesized that both species would reduce R at 25°C (R25) and the short‐term temperature sensitivity of R (Q10) as air temperature (Tair) increased across seasons, but the decline would be stronger in Avicennia than in Spartina. For each species, we hypothesized that seasonal temperature acclimation of R would be equivalent in plants grown under ambient and warmed temperatures, demonstrating convergent acclimation. Surprisingly, Avicennia generally increased R25 with increasing growth temperature, although the Q10 declined as seasonal temperatures increased and did so consistently across sites and treatments. Weak temperature acclimation resulted in reduced homeostasis of R in Avicennia. Spartina reduced R25 and the Q10 as seasonal temperatures increased. In Spartina, seasonal temperature acclimation was largely consistent across sites and treatments resulting in greater respiratory homeostasis. We conclude that co‐occurring coastal wetland species may show contrasting patterns of respiratory temperature acclimation. Nonetheless, leaf N scaled positively with R25 in both species, highlighting the importance of leaf N in predicting respiratory capacity across a range of growth temperatures. The patterns of respiratory temperature acclimation shown here may improve the predictions of temperature controls of CO2 fluxes in coastal wetlands. [ABSTRACT FROM AUTHOR]

Summary: Nighttime stomatal conductance (gsn) varies among plant functional types and species, but factors shaping the evolution of gsn remain unclear. Examinations of intraspecific variation in gsn as a function of climate and co‐varying leaf traits may provide new insight into the evolution of gsn and its adaptive significance.We grew 11 genotypes of Panicum virgatum (switchgrass) representing differing home‐climates in a common garden experiment and measured nighttime and daytime leaf gas exchange, as well as stomatal density (SD) and size during early‐, mid‐, and late‐summer. We used piecewise structural equation modelling to determine direct and indirect relationships between home‐climate, gas exchange, and stomatal traits.We found no direct relationship between home‐climate and gsn. However, genotypes from hotter climates possessed higher SD, which resulted in higher gsn. Across genotypes, higher gsn was associated with higher daytime stomatal conductance and net photosynthesis.Our results indicate that higher gsn may arise in genotypes from hotter climates via increased SD. High SD may provide benefits to genotypes from hotter climates through enhanced daytime transpirational cooling or by permitting maximal gas exchange when conditions are suitable. These results highlight the role of climate and trait coordination in shaping genetic differentiation in gsn. [ABSTRACT FROM AUTHOR]

Temperature and salinity are important regulators of mangrove range limits and productivity, but the physiological responses of mangroves to the interactive effects of temperature and salinity remain uncertain. We tested the hypothesis that salinity alters photosynthetic responses to seasonal changes in temperature and vapor pressure deficit (D), as well as thermal acclimation _of leaf respiration in black mangrove (Avicennia germinans). To test this hypothesis, we grew seedlings of A. germinans in an outdoor experiment for ~ 12 months under four treatments spanning 0 to 55 ppt porewater salinity. We repeatedly measured seedling growth and in situ rates of leaf net photosynthesis (A sat) and stomatal conductance to water vapor (g s) at prevailing leaf temperatures, along with estimated rates of Rubisco carboxylation (V cmax) and electron transport for RuBP regeneration (J max), and measured rates of leaf respiration at 25 °C (R area25). We developed empirical models describing the seasonal response of leaf gas exchange and photosynthetic capacity to leaf temperature and D , and the response of R area25 to changes in mean daily air temperature. We tested the effect of salinity on model parameters. Over time, salinity had weak or inconsistent effects on A sat, g s and R area25. Salinity also had little effect on the biochemical parameters of photosynthesis (V cmax, J max) and individual measurements of A sat, g s, V cmax and J max showed a similar response to seasonal changes in temperature and D across all salinity treatments. Individual measurements of R area25 showed a similar inverse relationship with mean daily air temperature across all salinity treatments. We conclude that photosynthetic responses to seasonal changes in temperature and D , as well as seasonal temperature acclimation of leaf R , are largely consistent across a range of salinities in A. germinans. These results might simplify predictions of photosynthetic and respiratory responses to temperature in young mangroves. [ABSTRACT FROM AUTHOR]

Aims: Precipitation and soil nutrients play an important role in regulating grassland productivity. However, little is known regarding the sensitivity of grasslands to changes in water and nutrient availability and the mechanisms driving productivity responses. Methods: We examined the effects of extreme drought (65% rainfall reduction) and phosphorus fertilization on aboveground net primary production (ANPP) and plant functional traits (PFTs) of four dominant mesic grassland species in a semi-natural grassland in southeast Australia. We used piecewise structural equation modelling to determine which PFTs contribute to the treatment effects on ANPP. Results: Reduced rainfall decreased ANPP by 29% while P addition increased ANPP by 62% at the community-level. Significant drought-related reductions in ANPP were apparent for Setaria parviflora, while Cynodon dactylon was the only species exhibiting increased ANPP under P addition. There was no interaction between rainfall and P addition. Structural equation modelling indicated specific root length was a key trait underpinning community-level ANPP responses to P; this was, however, primarily driven by a single dominant (~61% of community biomass) species (Cynodon). Conclusions: Our results indicate the negative impacts of drought on ANPP – driven primarily by Setaria– were not ameliorated by P addition. The positive effect of P addition on community-level ANPP was attributed to the response of the most dominant species, Cynodon, and mediated by changes in specific root length. This study highlights the importance of understanding the link between belowground traits and ANPP for predicting dominant species' response to global change drivers. [ABSTRACT FROM AUTHOR]

Classifying “urban” and “rural” environments is a challenge in understanding urban climate, specifically urban heat islands (UHIs). Stewart and Oke developed the “local climate zone” (LCZ) classification system to clarify these distinctions using 17 unique groups. This system has been applied to many areas around the world, but few studies have attempted to utilize them to detect UHI effects in smaller cities. Our aim was to use the LCZ classification system 1) to detect UHI in two small cities in Alabama and 2) to determine whether similar zones experienced similar intensity or magnitude of UHIs. For 1 week, we monitored hourly temperature in two cities, in four zones: compact low-rise, open low-rise, dense forests, and water. We found that urban zones were often warmer for overall, daytime, and nighttime temperatures relative to rural zones (from −0.1° to 2.8°C). In addition, we found that temperatures between cities in similar zones were not very similar, indicating that the LCZ system does not predict UHI intensity equally in places with similar background climates. We found that the LCZ classification system was easy to use, and we recognize its potential as a tool for urban ecologists and urban planners. [ABSTRACT FROM AUTHOR]

Abstract: Plant traits can be used to predict ecosystem responses to environmental change using a response–effect trait framework. To do this, appropriate traits must be identified that explain a species' influence on ecosystem function (“effect traits”) and the response of those species to environmental change (“response traits”). Response traits are often identified and measured along gradients in plant resources, such as water availability; however, precipitation explains very little variation in most plant traits globally. Given the strong relationship between plant traits and ecosystem functions, such as net primary productivity (NPP), and between NPP and precipitation, the lack of correlation between precipitation and plant traits is surprising. We address this issue through a systematic review of >500 published studies that describe plant trait responses to altered water availability. The overarching goal of this review was to identify potential causes for the weak relationship between commonly measured plant traits and water availability so that we may identify more appropriate “response traits.” We attribute weak trait–precipitation relationships to an improper selection of traits (e.g., nonhydraulic traits) and a lack of trait‐based approaches that adjust for trait variation within communities (only 4% of studies measure community‐weighted traits). We then highlight the mechanistic value of hydraulic traits as more appropriate “response traits” with regard to precipitation, which should be included in future community‐scale trait surveys. Trait‐based ecology has the potential to improve predictions of ecosystem responses to predicted changes in precipitation; however, this predictive power depends heavily on the identification of reliable response and effect traits. To this end, trait surveys could be improved by a selection of traits that reflect physiological functions directly related to water availability with traits weighted by species relative abundance. A plain language summary is available for this article. [ABSTRACT FROM AUTHOR]

Seedlings from four families of loblolly pine (Pinus taeda L.) were grown in capped open-top chambers and exposed to three different weekly moisture regimes for 13 weeks. Moisture regimes varied in intensity and frequency of simulated rainfall (irrigation) events; however, the total amounts were comparable. These simulated treatments were chosen to simulate expected changes in rainfall variability associated with climate change. Seedlings were inoculated with two root-infecting ophiostomatoid fungi associated with Southern Pine Decline. We found susceptibility of loblolly pine was not affected by water stress; however, one family that was most sensitive to inoculation was also most sensitive to changes in moisture availability. Many studies have examined the effects of drought (well-watered vs. dry conditions) on pine physiology and host-pathogen interactions but little is known about variability in moisture supply. This study aimed to elucidate the effects of variability in water availability, pathogen inoculation and their interaction on physiology of loblolly pine seedlings. [ABSTRACT FROM AUTHOR]