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The connection between soil nitrogen availability, leaf nitrogen, and photosynthetic capacity is not perfectly understood. Because these three components tend to be positively related over large spatial scales, some posit that soil nitrogen positively drives leaf nitrogen, which positively drives photosynthetic capacity. Alternatively, others posit that photosynthetic capacity is primarily driven by aboveground conditions. Here, we examined the physiological responses of a non nitrogen-fixing plant (Gossypium hirsutum) and a nitrogen-fixing plant (Glycine max) in a fully factorial combination of light by soil nitrogen availability to help reconcile these competing hypotheses. Soil nitrogen stimulated leaf nitrogen in both species, but the relative proportion of leaf nitrogen used for photosynthetic processes was reduced under elevated soil nitrogen in all light availability treatments due to greater increases in leaf nitrogen content than chlorophyll and leaf biochemical process rates. Leaf nitrogen content and biochemical process rates in G. hirsutum were more responsive to changes in soil nitrogen than G. max, likely due to strong G. max investments in root nodulation under low soil nitrogen. Nonetheless, whole plant growth was significantly enhanced by increased soil nitrogen in both species. Light availability consistently increased relative leaf nitrogen allocation to leaf photosynthesis and whole plant growth, a pattern that was similar between species. These results suggest that the leaf nitrogen-photosynthesis relationship varies under different soil nitrogen levels and that these species preferentially allocated more nitrogen to plant growth and non-photosynthetic leaf processes, rather than photosynthesis, as soil nitrogen increased.

Representations of interactions between the C and N cycles in terrestrial ecosystems are now implemented in a majority of state-of-the-art Dynamic Global Vegetation Models (C-N models). Standard models for simulating the response of individual processes to changes in N availability have not yet emerged and widely used models have not been tested against the full diversity of empirical data. Large remaining model structural uncertainty has important implications for projections and hindcasts of the land C uptake.Here, we summarise the current state of global land C balance simulations by comparing C-N models to C-only models; summarise data from field surveys and experiments to elucidate the role of soil N in controlling photosynthesis and its acclimation, stoichiometry, allocation, and growth; and demonstrate how optimality principles can guide the representation of acclimation and allocation for simulating ecosystem responses to experimental treatments of CO2 and soil N – consistent with observations. Promising model results are achieved by assuming that the atmospheric environment, including CO2, is the principal driver for photosynthetic capacities and leaf N following optimality theory of photosynthetic acclimation (Prentice et al., 2014). In turn, the functional balance hypothesis (Bloom et al., 1985) yields accurate predictions for how soil N availability and CO2 influence allocation and growth in different tissues.Our results show how confronting new theoretical approaches to simulating ecosystem C-N interactions against the collective constraints from diverse types of observations can guide model development and potentially reduce the large uncertainty in global carbon cycle projections.ReferencesBloom, Arnold J, F Stuart Chapin, and Harold A Mooney. “Resource Limitation in Plants--An Economic Analogy” Annual Review of Ecology and Systematics, 16, no. 1 (1985): 363–92. https://doi.org/10.1146/annurev.es.16.110185.002051.Prentice, I. Colin, Ning Dong, Sean M. Gleason, Vincent Maire, and Ian J. Wright. “Balancing the Costs of Carbon Gain and Water Transport: Testing a New Theoretical Framework for Plant Functional Ecology.” Ecology Letters 17, 1 (2014): 82–91. https://doi.org/10.1111/ele.12211.

Terrestrial ecosystems regulate Earth's climate through water, energy, and biogeochemical transformations. Despite a key role in regulating the Earth system, terrestrial ecology has historically been underrepresented in the Earth system models (ESMs) that are used to understand and project global environmental change. Ecology and Earth system modeling must be integrated for scientists to fully comprehend the role of ecological systems in driving and responding to global change. Ecological insights can improve ESM realism and reduce process uncertainty, while ESMs offer ecologists an opportunity to broadly test ecological theory and increase the impact of their work by scaling concepts through time and space. Despite this mutualism, meaningfully integrating the two remains a persistent challenge, in part because of logistical obstacles in translating processes into mathematical formulas and identifying ways to integrate new theories and code into large, complex model structures. To help overcome this interdisciplinary challenge, we present a framework consisting of a series of interconnected stages for integrating a new ecological process or insight into an ESM. First, we highlight the multiple ways that ecological observations and modeling iteratively strengthen one another, dispelling the illusion that the ecologist's role ends with initial provision of data. Second, we show that many valuable insights, products, and theoretical developments are produced through sustained interdisciplinary collaborations between empiricists and modelers, regardless of eventual inclusion of a process in an ESM. Finally, we provide concrete actions and resources to facilitate learning and collaboration at every stage of data-model integration. This framework will create synergies that will transform our understanding of ecology within the Earth system, ultimately improving our understanding of global environmental change and broadening the impact of ecological research. Accepted version

Earlier spring phenological events have been widely reported in plants under global warming. Recent studies reported a slowdown in the warming-induced advanced spring phenology in temperate regions. However, previous research mainly focused on daily mean temperature, thus neglecting the asymmetric phenological responses to daytime and nighttime temperature. Using long-term records of leaf unfolding in eight deciduous species at 1300 sites across central Europe, we assessed and compared the effects of daytime temperature, nighttime temperature, and photoperiod on leaf unfolding during 1951-1980 and 1981-2013. Although leaf unfolding was advanced by daytime warming during 1951-2013, the advancing responses of leaf unfolding significantly decreased from 1951-1980 to 1981-2013 due to a lower accumulation of chilling units by daytime warming. Nighttime warming delayed leaf unfolding during 1951-1980 but advanced it during 1981-2013 due to a higher accumulation of chilling units by nighttime warming. In contrast, critical daylength and plasticity of leaf unfolding dates remained unchanged between 1951 and 2013. Our study provided evidence that daytime warming instead of nighttime warming accounts for the slowdown in the advancing spring phenology and implied that nighttime warming-induced earlier spring phenology may be buffering the slowdown of the advanced spring phenology by daytime warming. The response of spring phenology to nighttime temperature may override that to daytime temperature under the actual trends in global warming.

Irrigation of farmlands in xeric areas can increase soil salinity, reducing their suitability for food and fiber crops. One way to repurpose these lands is to convert them for use in grazing. To choose the best forage species, it is important to understand the impact of soil salinity on the growth and nutritional quality of potential forage grasses. Here, we grew four perennial C4 grasses: blue grama (Bouteloua gracilis), sideoats grama (Bouteloua curtipendula), little bluestem (Schizachyrium scoparium), and bermudagrass (Cynodon dactylon) in soil treated with four different concentrations (0, 8, 16, and 24 dS/m) of sodium chloride salt (NaCl). We then determined the effects of soil salinity on germination, biomass production, and plant tissue nitrogen content (an indicator of nutritional quality). We found a high degree of variability in salinity responses among species. S. scoparium performed poorly relative to the other species across all metrics. C. dactylon showed high biomass and low sensitivity to soil salinity for each index but had the lowest shoot nitrogen concentration of all species tested. This indicated a tradeoff of tissue quality for quantity. On the other hand, the two Bouteloua species showed opposite results, falling on the shoot quality end of the quantity-quality spectrum and even showing increased nitrogen concentration with increasing soil salinity. Given their complimentary traits, C. dactylon and Bouteloua spp. may be good candidates for interseeding on saline lands. These results indicate that species choice can help mitigate negative impacts of soil salinity on forage production and quality and should be carefully considered by land managers.

Black orthorhombic (B-γ) CsSnI3 with reduced biotoxicity and environmental impact and excellent optoelectronic properties is being considered as a promising eco-friendly candidate for high-performing perovskite solar cells (PSCs). A major challenge in a large-scale implementation of CsSnI3 PSCs includes the rapid transformation of Sn2+ to Sn4+ (within a few minutes) under an ambient-air condition. Here, we demonstrate that ambient-air stable B-γ CsSnI3 PSCs can be fabricated by incorporating N,N'-methylenebis(acrylamide) (MBAA) into the perovskite layer and by using poly(3-hexylthiophene) as the hole transporting material. The lone electron pairs of -NH and -CO units of MBAA are designed to form coordination bonding with Sn2+ in the B-γ CsSnI3, resulting in a reduced defect (Sn4+) density and better stability under multiple conditions for the perovskite light absorber. After a modification, the highest power conversion efficiency (PCE) of 7.50% is documented under an ambient-air condition for the unencapsulated CsSnI3-MBAA PSC. Furthermore, the MBAA-modified devices sustain 60.2%, 76.5%, and 58.4% of their initial PCEs after 1440 h of storage in an inert condition, after 120 h of storage in an ambient-air condition, and after 120 h of 1 Sun continuous illumination, respectively.

Leaf dark respiration (Rd) accounts for approximately 50% of plant respiration. The acclimation of plant respiration to temperature weakens the positive feedback to global warming. Most existing land surface models (LSMs) adopt an empirical leaf respiration scheme with a constant Rd25 (leaf dark respiration rate at 25°C) for each vegetation type, since there is no acceptable theory of Rd acclimation and how it varies temporally and spatially. Here we propose that Rd25 adjusts to prior nighttime temperature (Tnight) to maintain the ratio of Rd to photosynthesis capacity (Vcmax) approximately constant. To test this hypothesis and explore the time scale of acclimation, we predict Rd25 over different time windows and evaluate these predictions using data from 14 sites from two datasets (Boreal Forest Warming at an Ecotone in Danger (B4WarmED) experiment and Leaf Carbon Exchange dataset (LCE)), one of which provides measurements through time and the other across spatial gradients. Predictions that account for the combined effects of Vcmax and Tnight have better predictive power for all species (mean R2=0.4) than considering the effect of one factor alone. Predictions of acclimation on different timescales show that Vcmax and Tnight averaged over the past fortnight explain the most variation in observed Rd25. These results could provide an alternative solution to the leaf respiration schemes used in LSMs.

Nitrogen (N) limitation has been considered as a constraint on terrestrial carbon uptake in response to rising CO2 and climate change. By extension, it has been suggested that declining carboxylation capacity (Vcmax ) and leaf N content in enhanced-CO2 experiments and satellite records signify increasing N limitation of primary production. We predicted Vcmax using the coordination hypothesis and estimated changes in leaf-level photosynthetic N for 1982-2016 assuming proportionality with leaf-level Vcmax at 25°C. The whole-canopy photosynthetic N was derived using satellite-based leaf area index (LAI) data and an empirical extinction coefficient for Vcmax , and converted to annual N demand using estimated leaf turnover times. The predicted spatial pattern of Vcmax shares key features with an independent reconstruction from remotely sensed leaf chlorophyll content. Predicted leaf photosynthetic N declined by 0.27% yr-1 , while observed leaf (total) N declined by 0.2-0.25% yr-1 . Predicted global canopy N (and N demand) declined from 1996 onwards, despite increasing LAI. Leaf-level responses to rising CO2 , and to a lesser extent temperature, may have reduced the canopy requirement for N by more than rising LAI has increased it. This finding provides an alternative explanation for declining leaf N that does not depend on increasing N limitation.

Under global warming, advances in spring phenology due to rising temperatures have been widely reported. However, the physiological mechanisms underlying the advancement in spring phenology still remain poorly understood. Here, we investigated the effect of temperature during the previous growing season on spring phenology of current year based on the start of season extracted from multiple long-term and large-scale phenological datasets between 1951 and 2018. Our findings indicate that warmer temperatures during previous growing season are linked to earlier spring phenology of current year in temperate and boreal forests. Correspondingly, we observed an earlier spring phenology with the increase in photosynthesis of the previous growing season. These findings suggest that the observed warming-induced earlier spring phenology is driven by increased photosynthetic carbon assimilation in the previous growing season. Therefore, the vital role of warming-induced changes in carbon assimilation should be considered to accurately project spring phenology and carbon cycling in forest ecosystems under future climate warming.

Global warming has been linked to declines in tree growth. However, it is unclear how the asymmetry in daytime and nighttime warming influences this response. Here, we use 2947 residual tree-ring width chronologies covering 32 species at 2493 sites, between 1901 and 2018, across the Northern Hemisphere, to analyze the effects of daytime and nighttime temperatures, precipitation, and drought stress on the radial growth of trees. We show that drought stress was primarily triggered by daytime rather than nighttime warming. The radial growth of trees was more sensitive to drought stress in warm regions than in cold regions, especially for angiosperms. Our study provides robust evidence that daytime warming is the primary driver of the observed declines in forest productivity related to drought stress and that daytime and nighttime warming should be considered separately when modelling forest-climate interactions and feedbacks in a future, warmer world.

A warmer world could extend the growing seasons for plants. Changes in spring phenology have been studied, yet autumn phenology remains poorly understood. Using >500,000 phenological records of four temperate tree species between 1951 and 2013 in Europe, we show that leaf senescence in warm autumns exhibits stronger climate responses, with a higher phenological plasticity, than in cold autumns, indicating a nonlinear response to climate. The onset of leaf senescence in warm autumns was delayed due to the stronger climate response, primarily caused by night-time warming. However, daytime warming, especially during warm autumns, imposes a drought stress which advances leaf senescence. This may counteract the extension of growing season under global warming. These findings provide guidance for more reliable predictions of plant phenology and biosphere–atmosphere feedbacks in the context of global warming. Autumn leaf senescence has later onset, higher phenological plasticity and a stronger climatic response under warm compared to cold autumns. While night-time warming delays senescence, drought induced by daytime warming advances it, which may lead to loss in growing season under global warming.

The mechanisms responsible for photosynthetic acclimation are not well understood, effectively limiting predictability under future conditions. Least-cost optimality theory can be used to predict the acclimation of photosynthetic capacity based on the assumption that plants maximize carbon uptake while minimizing the associated costs. Here, we use this theory as a null model in combination with multiple datasets of C3 plant photosynthetic traits to elucidate the mechanisms underlying photosynthetic acclimation to elevated temperature and carbon dioxide (CO2 ). The model-data comparison showed that leaves decrease the ratio of the maximum rate of electron transport to the maximum rate of Rubisco carboxylation (Jmax /Vcmax ) under higher temperatures. The comparison also indicated that resources used for Rubisco and electron transport are reduced under both elevated temperature and CO2 . Finally, our analysis suggested that plants underinvest in electron transport relative to carboxylation under elevated CO2 , limiting potential leaf-level photosynthesis under future CO2 concentrations. Altogether, our results show that acclimation to temperature and CO2 is primarily related to resource conservation at the leaf level. Under future, warmer, high CO2 conditions, plants are therefore likely to use less nutrients for leaf-level photosynthesis, which may impact whole-plant to ecosystem functioning.

Plants utilizing C3 physiology have a more difficult time establishing in rooftop environments than plants with more heat and drought adapted constitutions, such as species that employ crassulacean acid metabolism (CAM). CAM species are much less susceptible to limitations of shallow, infertile soil-less media under abiotic and biotic stress. It is thought that soil amendments might improve rooftop media in a way that allows for C3 species to prosper in rooftop environments. While compost is typically added to media to achieve this goal, we hypothesized that the addition of an anthropogenic pyrogenic carbon (PyC) supplement, instead, would enable better organic and mineral sorption and water retention, resulting in improved physiological performance of C3 species. To test this, we grew a C3 legume species, wild indigo (Baptisia tinctoria L R.Br. ex), in control compost-amended media and media amended by PyC on a rooftop in Massachusetts, USA. We found PyC-amended media had greater mean organic and mineral nutrient sorption. We also found 16% greater soil water holding capacity (GWL/ψg) than control media. In addition, wild indigo photosynthetic intrinsic water use efficiency (iWUE) was significantly increased by 19% when grown in PyC-amended as compared to control media. We conclude that amending green roof media with PyC provides greater benefits than compost amendments for colonization of a C3 legume, wild indigo. Our results gathered over seven years suggest that PyC from converted waste stream cardboard could be used to improve the rooftop performance of other leguminous species, including agricultural crops.

Nitrogen (N) limitation has been considered as a constraint on terrestrial carbon uptake in response to rising CO

The maximum rate of Rubisco carboxylation (Vcmax) determines leaf photosynthetic capacity and is a key parameter for estimating the terrestrial carbon cycle, but its spatial information is lacking, hindering global ecological research. Here, we convert leaf chlorophyll content (LCC) retrieved from satellite data to Vcmax, based on plants' optimal distribution of nitrogen between light harvesting and carboxylation pathways. We also derive Vcmax from satellite (GOME-2) observations of sun-induced chlorophyll fluorescence (SIF) as a proxy of leaf photosynthesis using a data assimilation technique. These two independent global Vcmax products agree well (r2=0.79,RMSE=15.46µmol m−2 s−1, P<0.001) and compare well with 3672 ground-based measurements (r2=0.69,RMSE=13.8µmol m−2 s−1 and P<0.001 for SIF; r2=0.55,RMSE=18.28µmol m−2 s−1 and P<0.001 for LCC). The LCC-derived Vcmax product is also used to constrain the retrieval of Vcmax from TROPical Ozone Mission (TROPOMI) SIF data to produce an optimized Vcmax product using both SIF and LCC information. The global distributions of these products are compatible with Vcmax computed from an ecological optimality theory using meteorological variables, but importantly reveal additional information on the influence of land cover, irrigation, soil pH, and leaf nitrogen on leaf photosynthetic capacity. These satellite-based approaches and spatial Vcmax products are primed to play a major role in global ecosystem research. The three remote sensing Vcmax products based on SIF, LCC, and SIF+LCC are available at https://doi.org/10.5281/zenodo.6466968 (Chen et al., 2022), and the code for implementing the ecological optimality theory is available at https://github.com/SmithEcophysLab/optimal_vcmax_R and https://doi.org/10.5281/zenodo.5899564 (last access: 31 August 2022) (Smith et al., 2022).

Under global warming, advances in spring phenology due to the rising temperature have been widely reported. However, the physiological mechanisms underlying the warming-induced earlier spring phenology remain poorly understood. Here, using multiple long-term and large-scale phenological datasets between 1951 and 2018, we show that warmer temperatures during the previous growing season between May and September led to earlier spring phenology in the Northern Hemisphere. We also found that warming-induced increases in maximum photosynthetic rate in the previous year advanced spring phenology, with an average of 2.50 days °C-1. Furthermore, we found a significant decline in the advancing effect of warming during the previous growing season on spring phenology from cold to warm periods over the past decades. Our results suggest that the observed warming-induced earlier spring phenology may be driven by increased photosynthetic carbon assimilation in the previous season, while the slowdown in the advanced spring phenology arise likely from decreased carbon assimilation when warming exceeding the optimal temperatures for photosynthesis. Our study highlights the vital role of photosynthetic carbon assimilation during growing season in spring phenology under global warming.

Co/Pd thin film multilayers show large Perpendicular Magnetic Anisotropy (PMA) which is useful in MRAM devices for perpendicular magnetic recording. Co/Pd systems have been studied extensively through the use of ultrafast optical pump-probe methods in order to measure the Time Resolved Photo-excited Precession of Magnetization (TRPEPM). Most studies have been conducted at high laser fluence (> 1 mJ/cm2), where heating near the curie temperature occurs. In this study, we present low fluence measurements between 0.42 to 3.14 μJ/cm2 in Co/Pd systems with differing Co thickness between 0.4 to 0.74 nm to probe the role of interface anisotropy in low-power excitation.

SummaryShifts in plant phenology under ongoing warming affect global vegetation dynamics and carbon assimilation of the biomes. The response of leaf senescence to climate is crucial for predicting changes in the physiological processes of trees at ecosystem scale. We used long-term ground observations, phenological metrics derived from PhenoCam, and satellite imagery of the Northern Hemisphere to show that the timings of leaf senescence can advance or delay in case of warming occurring at the beginning (before June) or during (after June) the main growing season, respectively. Flux data demonstrated that net photosynthetic carbon assimilation converted from positive to negative at the end of June. These findings suggest that leaf senescence is driven by carbon assimilation and nutrient resorption at different growth stages of leaves. Our results provide new insights into understanding and modelling autumn phenology and carbon cycling under warming scenarios.

Arid ecosystems are an important component of the global carbon cycle. In these ecosystems, plant functional types are particularly important in realizing many ecosystem processes such as the dynamics and regulations of net ecosystem exchange of CO2 (NEE) to the changing environment. Here, we measured the diurnal dynamics of NEE in patches of succulent and non-succulent shrubs over two growing seasons (2012 and 2013) in the Alxa Desert, located in northern China. We find that the interannual difference of NEE was greater for the non-succulent shrub than that for he succulent shrub species. Diurnal NEE changes were similar for all species and were more strongly influenced by soil moisture than by temperature. Nonetheless, these environmental factors had a greater influence on non-succulent shrubs than succulent shrubs. Our findings highlight that species with different life history traits have different NEE dynamics and vary by time scales. These dynamics are strongly tied to water availability and plant type-specific water storage capacity, with plants possessing large water storage organs maintaining their physiological functioning better under stressful conditions. Our findings on the interaction between plant type and environment could be used to improve estimates of terrestrial carbon uptake in critical desert ecosystems.

Extracellular matrix (ECsM) bioscaffolds have been successfully used to treat five esophageal adenocarcinoma (EAC) patients following resection of neoplastic mucosal tissue. The present study evaluated the in vitro effect of ECM harvested from nonmalignant, decellularized tissue on EAC cell phenotype to understand the molecular mechanisms underlying the clinical findings. Nonmalignant (Het-1A), metaplastic (CP-A), and neoplastic (SK-GT-4, OE33) esophageal epithelial cells were exposed to ECM degradation products (250 μg/mL) prepared from heterologous urinary bladder tissue or homologous esophageal mucosa tissue, and evaluated for cell morphology, cell function, and EAC signaling pathways. Both the ECM sources downregulated neoplastic cell phenotype, but had distinctive tissue-specific effects. Urinary bladder ECM decreased OE33 and SK-GT-4 metabolism and increased CP-A apoptosis. Esophageal ECM decreased SK-GT-4, CP-A, and Het-1A proliferation; robustly downregulated PI3K-Akt-mTOR, cell cycle/DNA replication signaling, and upregulated autophagy signaling in OE33 cells; and increased cell cycle/DNA replication signaling in Het-1A cells. Both ECM sources decreased OE33 proliferation and phosphorylated AKT in OE33 cells, and in contrast, increased phosphorylated AKT in Het-1A cells. The results support the concept that the biochemical signals in nonmalignant ECM can downregulate neoplastic cell phenotype with minimal, and sometimes opposite, effects on normal cells. PI3K-Akt signaling has been implicated in EAC progression and these ECM-mediated effects may be favorable for an esophageal therapy following cancer resection. IMPACT STATEMENT: Extracellular matrix (ECM) biomaterials were used to treat esophageal cancer patients after cancer resection and promoted regrowth of normal mucosa without recurrence of cancer. The present study investigates the mechanisms by which these materials were successful to prevent the cancerous phenotype. ECM downregulated neoplastic esophageal cell function (proliferation, metabolism), but normal esophageal epithelial cells were unaffected in vitro, and suggests a molecular basis (downregulation of PI3K-Akt, cell cycle) for the promising clinical results. The therapeutic effect appeared to be enhanced using homologous esophageal ECM. This study suggests that ECM can be further investigated to treat cancer patients after resection or in combination with targeted therapy.

Earth system models (ESMs) use photosynthetic capacity, indexed by the maximum Rubisco carboxylation rate (V cmax), to simulate carbon assimilation and typically rely on empirical estimates, including an assumed dependence on leaf nitrogen determined from soil fertility. In contrast, new theory, based on biochemical coordination and co‐optimization of carboxylation and water costs for photosynthesis, suggests that optimal V cmax can be predicted from climate alone, irrespective of soil fertility. Here, we develop this theory and find it captures 64% of observed variability in a global, field‐measured V cmax dataset for C3 plants. Soil fertility indices explained substantially less variation (32%). These results indicate that environmentally regulated biophysical constraints and light availability are the first‐order drivers of global photosynthetic capacity. Through acclimation and adaptation, plants efficiently utilize resources at the leaf level, thus maximizing potential resource use for growth and reproduction. Our theory offers a robust strategy for dynamically predicting photosynthetic capacity in ESMs.

Nitrogen (N) limitation constrains the magnitude of terrestrial carbon uptake in response to CO2 fertilization and climate change. However, the trajectory of N demand, and how it is influenced by continuing changes in CO2 and climate, is incompletely understood. We estimate recent changes in global canopy N demand based on a well-tested optimality hypothesis for the control of photosynthetic capacity (Vcmax). The predicted global pattern of optimal leaf-level Vcmax is similar to the pattern derived from remotely sensed chlorophyll retrievals. Over the period from 1982 to 2015, rising CO2­ and warming both contributed to decreasing leaf-level N demand. Widespread increases in green vegetation cover over the same period (especially in high latitudes) imply increasing total canopy N demand. The net global trend is, nonetheless, a decrease in total canopy N demand. This work provides a new perspective on the past, present and future of the global terrestrial N cycle.

Plant nitrogen acquisition requires carbon to be allocated belowground to build roots and sustain microbial associations. This carbon cost to acquire nitrogen varies by nitrogen acquisition strategy; however, the degree to which these costs vary due to nitrogen availability or demand has not been well tested under controlled conditions. We grew a species capable of forming associations with nitrogen-fixing bacteria (Glycine max) and a species not capable of forming such associations (Gossypium hirsutum) under four soil nitrogen levels to manipulate nitrogen availability and four light levels to manipulate nitrogen demand in a full-factorial greenhouse experiment. We quantified carbon costs to acquire nitrogen as the ratio of total root carbon to whole-plant nitrogen within each treatment combination. In both species, light availability increased carbon costs due to a larger increase in root carbon than whole-plant nitrogen, while nitrogen fertilization generally decreased carbon costs due to a larger increase in whole-plant nitrogen than root carbon. Nodulation data indicated that G. max shifted relative carbon allocation from nitrogen fixation to direct uptake with increased nitrogen fertilization. These findings suggest that carbon costs to acquire nitrogen are modified by changes in light and nitrogen availability in species with and without associations with nitrogen-fixing bacteria.

Despite widespread evidence that biological invasion influences both the biotic and abiotic soil environments, the extent to which these two pathways underpin the effects of invasion on plant traits and performance remains unknown. Leveraging a long-term (14-year) field experiment, we show that an allelochemical-producing invader affects plants through biotic mechanisms, altering the soil fungal community composition, with no apparent shifts in soil nutrient availability. Changes in belowground fungal communities resulted in high costs of nutrient uptake for native perennials and a shift in plant traits linked to their water and nutrient use efficiencies. Some plants in the invaded community compensate for the disruption of nutritional symbionts and reduced nutrient provisioning by sanctioning more nitrogen to photosynthesis and expending more water, which demonstrates a trade-off in trait investment. For the first time, we show that the disruption of belowground nutritional symbionts can drive plants towards alternative regions of their trait space in order to maintain water and nutrient economics.

Despite widespread evidence that biological invasion influences both the biotic and abiotic soil environments, the extent to which these two pathways underpin the effects of invasion on plant traits and performance is unknown. Leveraging a long-term (14-yr) field experiment, we show that an allelochemical-producing invader affects plants through biotic mechanisms, altering the soil fungal community composition, with no apparent shifts in soil nutrient availability. Changes in belowground fungal communities result in high costs of nutrient uptake for native perennials and a shift in functional traits linked to their water and nutrient use efficiencies. Some species in the invaded community compensate for high nutrient costs by reducing nutrient uptake and maintaining photosynthesis by expending more water, which demonstrates a trade-off in trait investment. For the first time, we show that the disruption of belowground nutritional symbionts can drive native plants toward novel regions in order to maintain their water and nutrient economics.

Past research has shown that plants possess the capacity to alter their instantaneous response of photosynthesis to temperature in response to a longer-term change in temperature (i.e. acclimate). This acclimation is typically the result of processes that influence net photosynthesis (Anet), including leaf biochemical processes such as the maximum rate of Rubisco carboxylation (Vcmax) and the maximum rate of photosynthetic electron transport (Jmax), stomatal conductance (gs) and dark respiration (Rd). However, these processes are rarely examined in the field or in concert with other environmental factors, such as precipitation amount. Here, we use a fully factorial warming (active heating up to +4 °C; mean = +3.1 °C) by precipitation (−50 % ambient to 150 % ambient) manipulation experiment in an old-field ecosystem in the north-eastern USA to examine the degree to which Ulmus americana saplings acclimate through biochemical and stomatal adjustments. We found that rates of Anet at ambient CO2 levels of 400 µmol mol−1 (A400) did not differ across climate treatments or with leaf temperatures from 20 to 30 °C. Canopy temperatures rarely reached above 30 °C in any treatment, suggesting that seasonal carbon assimilation was relatively homeostatic across all treatments. Assessments of the component processes of A400 revealed that decreases in gs with leaf temperature from 20 to 30 °C were balanced by increases in Vcmax, resulting in stable A400 rates despite concurrent increases in Rd. Photosynthesis was not affected by precipitation treatments, likely because the relatively dry year led to small treatment effects on soil moisture. As temperature acclimation is likely to come at a cost to the plant via resource reallocation, it may not benefit plants to acclimate to warming in cases where warming would not otherwise reduce assimilation. These results suggest that photosynthetic temperature acclimation to future warming will be context-specific and that it is important to consider assimilatory benefit when assessing acclimation responses.

Climate change and land management are altering forest fire frequency and intensity worldwide. In some Northeast U.S. forests, pitch pine (Pinus rigida Miller) is not suffering from presence but rather a lack of wildfire events. In their absence, prescribed fire is being used to diminish fuel loads, open canopies and reduce competition. Pyrogenic carbon (PyC) produced by the fires may also improve soil moisture retention and plant physiological processes. Where the application of prescribed fire is not feasible due to nearby human populations, we reason prescribed fire PyC could be replaced by anthropogenic PyC product to provide similar soil benefits. We tested this hypothesis with pitch pine seedlings at a site absent overstory planted in submerged tree pots with control and PyC-imbued soils. Investigators found anthropogenic and forest PyC fostered similar growth, soil moisture retention and photosynthetic intrinsic water use efficiency, both significantly higher than unamended soils. We conclude anthropogenic subsurface PyC soil amendment provides a conservation management tool for enhancing benefits in ecosystems where prescribed fire is not a viable option in northerly forests in the U.S.

The mechanisms responsible for photosynthetic acclimation are not well understood, effectively limiting predictability under future conditions. Least-cost optimality theory can be used to predict the acclimation of photosynthetic capacity based on the assumption that plants maximize carbon uptake while minimizing the associated costs. Here, we use this theory as a null model in combination with multiple datasets of C

Photosynthetic 'least-cost' theory posits that the optimal trait combination for a given environment is that where the summed costs of photosynthetic water and nutrient acquisition/use are minimised. The effects of soil water and nutrient availability on photosynthesis should be stronger as climate-related costs for both resources increase. Two independent datasets of photosynthetic traits, Globamax (1509 species, 288 sites) and Glob13C (3645 species, 594 sites), were used to quantify biophysical and biochemical limitations of photosynthesis and the key variable Ci /Ca (CO2 drawdown during photosynthesis). Climate and soil variables were associated with both datasets. The biochemical photosynthetic capacity was higher on alkaline soils. This effect was strongest at more arid sites, where water unit-costs are presumably higher. Higher values of soil silt and depth increased Ci /Ca , likely by providing greater H2 O supply, alleviating biophysical photosynthetic limitation when soil water is scarce. Climate is important in controlling the optimal balance of H2 O and N costs for photosynthesis, but soil properties change these costs, both directly and indirectly. In total, soil properties modify the climate-demand driven predictions of Ci /Ca by up to 30% at a global scale.

Realistic representations of plant carbon exchange processes are necessary to reliably simulate biosphere-atmosphere feedbacks. These processes are known to vary over time and space, though the drivers of the underlying rates are still widely debated in the literature. Here, we measured leaf carbon exchange in >500 individuals of 98 species from the Neotropics to high boreal biomes to determine the drivers of photosynthetic and dark respiration capacity. Covariate abiotic (long- and short-term climate) and biotic (plant type, plant size, ontogeny, water status) data were used to explore significant drivers of temperature-standardized leaf carbon exchange rates. Using model selection, we found the previous week's temperature and soil moisture at the time of measurement to be a better predictor of photosynthetic capacity than long-term climate, with the combination of high recent temperatures and low soil moisture tending to decrease photosynthetic capacity. Non-trees (annual and perennials) tended to have greater photosynthetic capacity than trees, and, within trees, adults tended to have greater photosynthetic capacity than juveniles, possibly as a result of differences in light availability. Dark respiration capacity was less responsive to the assessed drivers than photosynthetic capacity, with rates best predicted by multi-year average site temperature alone. Our results suggest that, across large spatial scales, photosynthetic capacity quickly adjusts to changing environmental conditions, namely light, temperature, and soil moisture. Respiratory capacity is more conservative and most responsive to longer-term conditions. Our results provide a framework for incorporating these processes into large-scale models and a data set to benchmark such models.

Understanding the drivers of plant phenology is critical to predict the impact of future warming on terrestrial ecosystem carbon cycling and feedbacks to climate. Using indoor growth chambers, air humidity is reported to influence spring phenology in temperate trees. However, previous studies have not investigated the effect of air humidity on the spring phenology using long-term and large-scale ground observations. Therefore, the role of humidity in spring phenology in temperate trees still remains poorly understood. Here, we synthesized 229,588 records of leaf unfolding dates in eight temperate tree species, including four early-successional and four late-successional species, at 1716 observation sites during 1951–2015 in Europe, and comprehensively analyzed the effect of humidity on the spring phenology. We found that rising humidity significantly delayed spring leaf unfolding for all eight temperate tree species. Leaf unfolding was more sensitive to humidity in early-successional species compared to late-successional species. In addition, the delaying effect of humidity on leaf unfolding increased as temperature warmed over the past 65 years. Our results provide evidence that spring leaf unfolding of temperate trees was significantly delayed by rising humidity. The delaying effect of humidity may restrict earlier spring phenology induced by warming, especially for early-successional species, under future climate warming scenarios in temperate forests.

Improving plant water use efficiency (WUE) has the potential to lower plant susceptibility to drought. Amending soils with biochar has been suggested as a way to improve WUE, as it has been shown t...

Soil respiration is an important component of terrestrial carbon cycling and is sensitive to environmental change. Most previous studies focus on the effect of soil temperature and moisture on soil respiration, whereas the impact of spatial heterogeneity (e.g., microtopography) is seldom studied. To test the impact of microtopography on soil respiration, we performed a field investigation to examine soil respiration, soil temperature, soil water content, soil total porosity, soil organic content, and plant biomass at a hummock site (composed of grass hummocks and inter-hummock areas) and an adjacent flat meadow of the Qinghai-Tibetan plateau. Similar seasonal dynamics of soil respiration in the grass hummocks, inter-hummock areas, and flat meadow were found in the alpine meadow of the Qinghai-Tibetan plateau. However, soil respiration of the grass hummocks was 79.3% and 413.9% higher than that of the flat meadow during the growing (April, June, August) and non-growing seasons (October, December, February), respectively. Although there was no difference in soil respiration between the inter-hummock areas and the flat meadow during the non-growing season, soil respiration was 42.5% higher at the inter-hummock areas than the flat meadow during growing season. Larger soil porosity, greater surface area, and more substrate supply, but not more root growth, likely contributed to the higher soil respiration of grass hummocks. Our findings suggest that the impact of spatial heterogeneity on soil respiration should be taken into consideration to facilitate the accurate estimation of soil carbon fluxes at ecosystem and regional scales.

Investigation of post-amendment biochar impact on low clay soil moisture provides agriculture professionals with much needed data. While laboratory testing is available, we propose inexpensive containers, tools and measuring devices to enable agriculture professionals to directly assess biochar impact on gravimetric water content, shrinkage, and release at point of soil rupture. Sandy loam, silty loam and loamy sand soils are amended (10% ) with lignocellulosic (oak) and hemicellulosic (cardboard) biochars in cup, plug and roll experiments. Cups with oak and cardboard biochar addition produced 76.32% and 75.72% H2O retention respectively, compared to 67.75% (67.75 g H2O 100 g−1 H2O) for controls. Cardboard and oak biochar limited diametric shrinkage to 2.95% (1.29 mm) and 3.75% (1.65 mm) respectively; controls shrunk 6.96% (3.06 mm). Oak and cardboard biochar limited depth shrinkage to 2.95% (0.38 mm) and 2.99% (0.38 mm) respectively; control depth shrinkage is 3.64% (0.47 mm). In roll tests, cardboard and oak biochar treatment yielded 28.07% (1.37 g H2O), and 26.69% (1.3 g H2O) moisture at rupture, respectively, compared with 11.98% (0.58 g) for controls. Significant (p ≤ 0.001) differences in moisture retention, shrinkage and available moisture at rupture confirm biochar contributions to improved moisture performance. Physico-chemical analyses complemented experimental findings. We find study methods suit the needs of agricultural professionals to measure moisture while working with biochar to amend soils.

Photosynthetic temperature acclimation is a commonly observed process that is increasingly being incorporated into Earth System Models (ESMs). While short-term acclimation has been shown to increase carbon storage in the future, it is uncertain whether acclimation will directly influence simulated future climate through biophysical mechanisms. Here, we used coupled atmosphere-biosphere simulations using the Community Earth System Model (CESM) to assess how acclimation-induced changes in photosynthesis influence global climate under present-day and future (RCP 8.5) conditions. We ran four 30 year simulations that differed only in sea surface temperatures and atmospheric CO2 (present or future) and whether a mechanism for photosynthetic temperature acclimation was included (yes or no). Acclimation increased future photosynthesis and, consequently, the proportion of energy returned to the atmosphere as latent heat, resulting in reduced surface air temperatures in areas and seasons where acclimation caused the biggest increase in photosynthesis. However, this was partially offset by temperature increases elsewhere, resulting in a small, but significant, global cooling of 0.05°C in the future, similar to that expected from acclimation-induced increases in future land carbon storage found in previous studies. In the present-day simulations, the photosynthetic response was not as strong and cooling in highly vegetated regions was less than warming elsewhere, leading to a net global increase in temperatures of 0.04°C. Precipitation responses were variable and rates did not change globally in either time period. These results, combined with carbon-cycle effects, suggest that models without acclimation may be overestimating positive feedbacks between climate and the land surface in the future.

Thermal acclimation of plant respiration is highly relevant to climate projections; when included in models, it reduces the future rate of atmospheric CO2 rise. Although all living plant tissues respire, few studies have examined differences in acclimation among tissues, and leaf responses have received greater attention than stems and roots. Here, we examine the short-term temperature acclimation of leaf, stem and root respiration within individuals of eight disparate species acclimated to five temperatures, ranging from 15 to 35 °C. To assess acclimation, we measured instantaneous tissue temperature response curves (14–50 °C) on each individual following a 7-day acclimation period. In leaves and photosynthetic stems, the acclimation temperature had little effect on the instantaneous tissue temperature response of respiration, indicating little to no thermal acclimation in these tissues. However, respiration did acclimate in non-photosynthetic tissues; respiratory rates measured at the acclimation temperature were similar across the different acclimation temperatures. Respiratory demand of photosynthetic tissue increased with acclimation temperature as a result of increased photosynthetic demands, resulting in rates measured at the acclimation temperature that increased with increasing acclimation temperature. In non-photosynthetic tissue, the homeostatic response of respiration suggests that acclimation temperature had little influence on respiratory demand. Our results indicate that respiratory temperature acclimation differs by tissue type and that this difference is the consequence of the coupling between photosynthesis and respiration in photosynthetic, but not non-photosynthetic tissue. These insights provide an avenue for improving the representation of respiratory temperature acclimation in large-scale models., Our study found that temperature acclimation of respiration differs by tissue type (i.e. leaves, stems and roots). Tissue that does not photosynthesize was found to have more homeostatic responses to temperature than photosynthetic tissue. This was found due to the strong linkage between photosynthetic biochemistry and respiration fluxes. These results suggest that plant respiratory responses to changing temperatures, such as future warming, will be tissue type-specific. The link to photosynthesis found in our study provides an avenue for improving the representation of these responses in carbon cycle models.

Plant respiration is an important contributor to the proposed positive global carbon-cycle feedback to climate change. However, as a major component, leaf mitochondrial ('dark') respiration (Rd ) differs among species adapted to contrasting environments and is known to acclimate to sustained changes in temperature. No accepted theory explains these phenomena or predicts its magnitude. Here we propose that the acclimation of Rd follows an optimal behaviour related to the need to maintain long-term average photosynthetic capacity (Vcmax ) so that available environmental resources can be most efficiently used for photosynthesis. To test this hypothesis, we extend photosynthetic co-ordination theory to predict the acclimation of Rd to growth temperature via a link to Vcmax , and compare predictions to a global set of measurements from 112 sites spanning all terrestrial biomes. This extended co-ordination theory predicts that field-measured Rd and Vcmax accessed at growth temperature (Rd,tg and Vcmax,tg ) should increase by 3.7% and 5.5% per degree increase in growth temperature. These acclimated responses to growth temperature are less steep than the corresponding instantaneous responses, which increase 8.1% and 9.9% per degree of measurement temperature for Rd and Vcmax respectively. Data-fitted responses proof indistinguishable from the values predicted by our theory, and smaller than the instantaneous responses. Theory and data are also shown to agree that the basal rates of both Rd and Vcmax assessed at 25°C (Rd,25 and Vcmax,25 ) decline by ~4.4% per degree increase in growth temperature. These results provide a parsimonious general theory for Rd acclimation to temperature that is simpler-and potentially more reliable-than the plant functional type-based leaf respiration schemes currently employed in most ecosystem and land-surface models.

The ability to measure mutations in plasma cell-free DNA (cfDNA) has the potential to revolutionize cancer surveillance and treatment by enabling longitudinal monitoring not possible with solid tumor biopsies. However, obtaining sufficient quantities of cfDNA remains a challenge for assay development and clinical translation; consequently, large volumes of venous blood are typically required. Here, we test proof-of-concept for using smaller volumes via fingerstick collection. Matched venous and fingerstick blood were obtained from seven patients with metastatic breast cancer. Fingerstick blood was separated at point-of-care using a novel paper-based concept to isolate plasma centrifuge-free. Patient cfDNA was then analyzed with or without a new method for whole genome amplification via rolling-circle amplification (WG-RCA). We identified somatic mutations by targeted sequencing and compared the concordance of mutation detection from venous and amplified capillary samples by droplet-digital PCR. Patient mutations were detected with 100% concordance after WG-RCA, although in some samples, allele frequencies showed greater variation likely due to differential amplification or primer inaccessibility. These pilot findings provide physiological evidence that circulating tumor DNA is accessible by fingerstick and sustains presence/absence of mutation detection after whole-genome amplification. Further refinement may enable simpler and less-invasive methods for longitudinal or theranostic surveillance of metastatic cancer.

Plant productivity and tissue chemistry in temperate ecosystems are largely driven by water and nitrogen (N) availability. Although changes in rainfall patterns may influence nutrient limitation, few studies have considered how these two global change factors could interact to influence terrestrial ecosystem productivity and stoichiometry. Here, we examined the influence of experimentally-increased intra-annual rainfall variability and low-level nitrogen addition on aboveground productivity, C and N pools, and C:N ratios in a restored tallgrass prairie across two growing seasons. In the drier first year of the experiment, increased rainfall variability boosted productivity and C pools. In the wetter second year, aboveground productivity and C pools increased with N addition, suggesting a switch in primary resource limitation from water to N. Increased rainfall variability also reduced aboveground N pools in the second year. Community-level C:N increased under increased rainfall variability in the wetter second year and N addition slightly reduced community C:N in both years. These changes in element pools and stoichiometry were mostly a result of increased forb dominance in response to both treatments. Overall, our findings from a restored prairie indicate that increased rainfall variability and N addition can enhance aboveground productivity and C pools, but that N pools may not have a consistent response to either global change factor. Our study also suggests that these effects are dependent on growing season precipitation patterns and are mediated by shifts in plant community composition.

Summary 1. Climate change is expected to bring fewer, larger rainfall events and prolonged droughts (i.e. increased rainfall variability). Concurrently, the burning of fossil fuels and reliance on nitrogen (N) fertilizers are expected to continue to increase N availability in many ecosystems. These changes in water and N availability have the potential to alter plant community composition and structure. 2. We manipulated rainfall variability and N inputs in a restored tallgrass prairie over the course of two growing seasons. 3. Greater rainfall variability led to wetter soils throughout the majority of both growing seasons and provided punctuated relief from a severe drought that occurred during the first three months of the experiment. 4. Both rainfall variability- and fertilization-induced increases in resource availability favoured fast-growing, deeply rooted C3 forbs, particularly the dominant Solidago canadensis, at the expense of species adapted to low resource conditions, particularly C4 grasses and N-fixing forbs. 5. This change in community composition decreased plant community diversity and evenness in plots receiving both supplemental N and more variable rainfall. 6. Synthesis and applications. These results suggest that future increases in rainfall variability and nitrogen (N) deposition could synergistically alter the structure of prairie restorations and jeopardize restoration targets related to increasing floral diversity. Mitigating N availability in restoration sites may help to maintain prairie diversity as rainfall patterns become more variable.

Incorporating temperature acclimation of photosynthesis and foliar respiration into Earth system models improves their ability to reproduce observed net ecosystem exchange of CO2, and reduces the temperature sensitivity of terrestrial carbon exchange.