Plant sizes and shapes above and belowground and their interactions with climate

Joswig J.S., Wirth C., Schuman M.C., Kattge J., Reu B., Wright I.J., Sippel S.D., Rüger N., Richter R., Schaepman M.E., van Bodegom P.M., Cornelissen J.H., Díaz S., Hattingh W.N., Kramer K., et. al.

AbstractPlant functional traits can predict community assembly and ecosystem functioning and are thus widely used in global models of vegetation dynamics and land–climate feedbacks. Still, we lack a global understanding of how land and climate affect plant traits. A previous global analysis of six traits observed two main axes of variation: (1) size variation at the organ and plant level and (2) leaf economics balancing leaf persistence against plant growth potential. The orthogonality of these two axes suggests they are differently influenced by environmental drivers. We find that these axes persist in a global dataset of 17 traits across more than 20,000 species. We find a dominant joint effect of climate and soil on trait variation. Additional independent climate effects are also observed across most traits, whereas independent soil effects are almost exclusively observed for economics traits. Variation in size traits correlates well with a latitudinal gradient related to water or energy limitation. In contrast, variation in economics traits is better explained by interactions of climate with soil fertility. These findings have the potential to improve our understanding of biodiversity patterns and our predictions of climate change impacts on biogeochemical cycles.

Freschet G.T., Pagès L., Iversen C.M., Comas L.H., Rewald B., Roumet C., Klimešová J., Zadworny M., Poorter H., Postma J.A., Adams T.S., Bagniewska‐Zadworna A., Bengough A.G., Blancaflor E.B., Brunner I., et. al.

In the context of a recent massive increase in research on plant root functions and their impact on the environment, root ecologists currently face many important challenges to keep on generating cutting-edge, meaningful and integrated knowledge. Consideration of the below-ground components in plant and ecosystem studies has been consistently called for in recent decades, but methodology is disparate and sometimes inappropriate. This handbook, based on the collective effort of a large team of experts, will improve trait comparisons across studies and integration of information across databases by providing standardised methods and controlled vocabularies. It is meant to be used not only as starting point by students and scientists who desire working on below-ground ecosystems, but also by experts for consolidating and broadening their views on multiple aspects of root ecology. Beyond the classical compilation of measurement protocols, we have synthesised recommendations from the literature to provide key background knowledge useful for: (1) defining below-ground plant entities and giving keys for their meaningful dissection, classification and naming beyond the classical fine-root vs coarse-root approach; (2) considering the specificity of root research to produce sound laboratory and field data; (3) describing typical, but overlooked steps for studying roots (e.g. root handling, cleaning and storage); and (4) gathering metadata necessary for the interpretation of results and their reuse. Most importantly, all root traits have been introduced with some degree of ecological context that will be a foundation for understanding their ecological meaning, their typical use and uncertainties, and some methodological and conceptual perspectives for future research. Considering all of this, we urge readers not to solely extract protocol recommendations for trait measurements from this work, but to take a moment to read and reflect on the extensive information contained in this broader guide to root ecology, including sections I-VII and the many introductions to each section and root trait description. Finally, it is critical to understand that a major aim of this guide is to help break down barriers between the many subdisciplines of root ecology and ecophysiology, broaden researchers' views on the multiple aspects of root study and create favourable conditions for the inception of comprehensive experiments on the role of roots in plant and ecosystem functioning.

Carmona C.P., Bueno C.G., Toussaint A., Träger S., Díaz S., Moora M., Munson A.D., Pärtel M., Zobel M., Tamme R.

Plant traits determine how individual plants cope with heterogeneous environments. Despite large variability in individual traits, trait coordination and trade-offs1,2 result in some trait combinations being much more widespread than others, as revealed in the global spectrum of plant form and function (GSPFF3) and the root economics space (RES4) for aboveground and fine-root traits, respectively. Here we combine the traits that define both functional spaces. Our analysis confirms the major trends of the GSPFF and shows that the RES captures additional information. The four dimensions needed to explain the non-redundant information in the dataset can be summarized in an aboveground and a fine-root plane, corresponding to the GSPFF and the RES, respectively. Both planes display high levels of species aggregation, but the differentiation among growth forms, families and biomes is lower on the fine-root plane, which does not include any size-related trait, than on the aboveground plane. As a result, many species with similar fine-root syndromes display contrasting aboveground traits. This highlights the importance of including belowground organs to the GSPFF when exploring the interplay between different natural selection pressures and whole-plant trait integration. The authors analyse the coordination and trade-off of the aboveground and fine-root traits of vascular plants using global trait databases.

Stocker B.D., Tumber-Dávila S.J., Konings A.G., Anderson M.B., Hain C., Jackson R.B.

AbstractThe rooting zone water storage capacity (S0) extends from the soil surface to the weathered bedrock (the Critical Zone) and determines land-atmosphere exchange during dry periods. Despite its importance to land-surface modeling, variations of S0 across space are largely unknown as they cannot be observed directly. We developed a method to diagnose global variations of S0 from the relationship between vegetation activity (measured by sun-induced fluorescence and by the evaporative fraction) and the cumulative water deficit (CWD). We then show that spatial variations in S0 can be predicted from the assumption that plants are adapted to sustain CWD extremes occurring with a return period that is related to the life form of dominant plants and the large-scale topographical setting. Predicted biome-level S0 distributions, translated to an apparent rooting depth (zr) by accounting for soil texture, are consistent with observations from a comprehensive zr dataset. Large spatial variations in S0 across the globe reflect adaptation of zr to the hydroclimate and topography and implies large heterogeneity in the sensitivity of vegetation activity to drought. The magnitude of S0 inferred for most of the Earth’s vegetated regions and particularly for those with a large seasonality in their hydroclimate indicates an important role for plant access to water stored at depth - beyond the soil layers commonly considered in land-surface models.

Iversen C.M., McCormack M.L.

Freschet G.T., Roumet C., Comas L.H., Weemstra M., Bengough A.G., Rewald B., Bardgett R.D., De Deyn G.B., Johnson D., Klimešová J., Lukac M., McCormack M.L., Meier I.C., Pagès L., Poorter H., et. al.

The effects of plants on the biosphere, atmosphere and geosphere are key determinants of terrestrial ecosystem functioning. However, despite substantial progress made regarding plant belowground components, we are still only beginning to explore the complex relationships between root traits and functions. Drawing on the literature in plant physiology, ecophysiology, ecology, agronomy and soil science, we reviewed 24 aspects of plant and ecosystem functioning and their relationships with a number of root system traits, including aspects of architecture, physiology, morphology, anatomy, chemistry, biomechanics and biotic interactions. Based on this assessment, we critically evaluated the current strengths and gaps in our knowledge, and identify future research challenges in the field of root ecology. Most importantly, we found that belowground traits with the broadest importance in plant and ecosystem functioning are not those most commonly measured. Also, the estimation of trait relative importance for functioning requires us to consider a more comprehensive range of functionally relevant traits from a diverse range of species, across environments and over time series. We also advocate that establishing causal hierarchical links among root traits will provide a hypothesis-based framework to identify the most parsimonious sets of traits with the strongest links on functions, and to link genotypes to plant and ecosystem functioning.

Singh C., Wang-Erlandsson L., Fetzer I., Rockström J., van der Ent R.

Climate change and deforestation have increased the risk of drought-induced forest-to-savanna transitions across the tropics and subtropics. However, the present understanding of forest-savanna transitions is generally focused on the influence of rainfall and fire regime changes, but does not take into account the adaptability of vegetation to droughts by utilizing subsoil moisture in a quantifiable metric. Using rootzone storage capacity (Sr), which is a novel metric to represent the vegetation's ability to utilize subsoil moisture storage and tree cover (TC), we analyze and quantify the occurrence of these forest-savanna transitions along transects in South America and Africa. We found forest-savanna transition thresholds to occur around a Sr of 550-750 mm for South America and 400-600 mm for Africa in the range of 30-40% TC. Analysis of empirical and statistical patterns allowed us to classify the ecosystem's adaptability to droughts into four classes of drought coping strategies: lowly water-stressed forest (shallow roots, high TC), moderately water-stressed forest (investing in Sr, high TC), highly water-stressed forest (trade-off between investments in Sr and TC) and savanna-grassland regime (competitive rooting strategy, low TC). The insights from this study are useful for improved understanding of tropical eco-hydrological adaptation, drought coping strategies, and forest ecosystem regime shifts under future climate change.

Lepik A., Abakumova M., Davison J., Zobel K., Semchenko M.

When foraging and competing for below-ground resources, plants have to coordinate the behaviour of thousands of root tips in a manner similar to that of eusocial animal colonies. While well described in animals, we know little about the spatial behaviour of plants, particularly at the level of individual roots. Here, we employed statistical methods previously used to describe animal ranging behaviour to examine root system overlap and the efficiency of root positioning in eight grassland species grown in monocultures and mixtures along a gradient of neighbour densities. Species varied widely in their ability to distribute roots efficiently, with the majority of species showing significant root aggregation at very fine spatial scales. Extensive root system overlap was observed in species mixtures, indicating a lack of territoriality at the level of whole root systems. However, with increasing density of competitors, several species withdrew roots from the periphery of foraging ranges and increased intraplant root aggregation in the remaining area, which may indicate consolidation of foraging areas under competitive pressure. Several species exhibited responses consistent with resource contest in species mixtures where encounters with competitors’ roots triggered increased root aggregation at the expense of foraging efficiency. Such responses only occurred in mixtures of species with comparable competitive abilities but were absent in asymmetric species combinations. Synthesis. Combining fine-scale measurement of plant root distributions with spatial statistics yields new insights into plant behavioural strategies with significant potential to impact resource foraging efficiency and productivity.

Guerrero‐Ramírez N.R., Mommer L., Freschet G.T., Iversen C.M., McCormack M.L., Kattge J., Poorter H., Plas F., Bergmann J., Kuyper T.W., York L.M., Bruelheide H., Laughlin D.C., Meier I.C., Roumet C., et. al.

Motivation: Trait data are fundamental to the quantitative description of plant form and function. Although root traits capture key dimensions related to plant responses to changing environmental conditions and effects on ecosystem processes, they have rarely been included in large-scale comparative studies and global models. For instance, root traits remain absent from nearly all studies that define the global spectrum of plant form and function. Thus, to overcome conceptual and methodological roadblocks preventing a widespread integration of root trait data into large-scale analyses we created the Global Root Trait (GRooT) Database. GRooT provides ready-to-use data by combining the expertise of root ecologists with data mobilization and curation. Specifically, we (a) determined a set of core root traits relevant to the description of plant form and function based on an assessment by experts, (b) maximized species coverage through data standardization within and among traits, and (c) implemented data quality checks. Main types of variables contained: GRooT contains 114,222 trait records on 38 continuous root traits. Spatial location and grain: Global coverage with data from arid, continental, polar, temperate and tropical biomes. Data on root traits were derived from experimental studies and field studies. Time period and grain: Data were recorded between 1911 and 2019. Major taxa and level of measurement: GRooT includes root trait data for which taxonomic information is available. Trait records vary in their taxonomic resolution, with subspecies or varieties being the highest and genera the lowest taxonomic resolution available. It contains information for 184 subspecies or varieties, 6,214 species, 1,967 genera and 254 families. Owing to variation in data sources, trait records in the database include both individual observations and mean values. Software format: GRooT includes two csv files. A GitHub repository contains the csv files and a script in R to query the database.

Kattge J., Bönisch G., Díaz S., Lavorel S., Prentice I.C., Leadley P., Tautenhahn S., Werner G.D., Aakala T., Abedi M., Acosta A.T., Adamidis G.C., Adamson K., Aiba M., Albert C.H., et. al.

AbstractPlant traits—the morphological, anatomical, physiological, biochemical and phenological characteristics of plants—determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits—almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives.

Tumber‐Dávila S.J., Malhotra A.

Wang P., Huang K., Hu S.

Precipitation is one of the most important factors that determine productivity of terrestrial ecosystems. Precipitation across the globe is predicted to change more intensively under future climate change scenarios, but the resulting impact on plant roots remains unclear. Based on 154 observations from experiments in which precipitation was manipulated in the field and root biomass was measured, we investigated responses in fine-root biomass of herbaceous and woody plants to alterations in precipitation. We found that root biomass of herbaceous and woody plants responded differently to precipitation change. In particular, precipitation increase consistently enhanced fine-root biomass of woody plants but had variable effects on herb roots in arid and semi-arid ecosystems. In contrast, precipitation decrease reduced root biomass of herbaceous plants but not woody plants. In addition, with precipitation alteration, the magnitude of root responses was greater in dry areas than in wet areas. Together, these results indicate that herbaceous and woody plants have different rooting strategies to cope with altered precipitation regimes, particularly in water-limited ecosystems. These findings suggest that root responses to precipitation change may critically influence root productivity and soil carbon dynamics under future climate change scenarios.

Verbeeck H., Bauters M., Jackson T., Shenkin A., Disney M., Calders K.

We argue that tree and crown structural diversity can and should be integrated in the whole-plant economics spectrum. Ecologists have found that certain functional trait combinations have been more viable than others during evolution, generating a trait trade-off continuum which can be summarized along a few axes of variation, such as the “worldwide leaf economics spectrum” and the “wood economics spectrum”. However, for woody plants the crown structural diversity should be included as well in the recently introduced “global spectrum of plant form and function”, which now merely focusses on plant height as structural factor. The recent revolution in terrestrial laser scanning (TLS) unlocks the possibility to describe the three dimensional structure of trees quantitatively with unprecedented detail. We demonstrate that based on TLS data, a multidimensional structural trait space can be constructed, which can be decomposed into a few descriptive axes or spectra. We conclude that the time has come to develop a “structural economics spectrum” for woody plants based on structural trait data across the globe. We make suggestions as to what structural features might lie on this spectrum and how these might help improve our understanding of tree form-function relationships.

Jin Y., Qian H.

We present V.PhyloMaker, a freely available package for R designed to generate phylogenies for vascular plants. The mega‐tree implemented in V.PhyloMaker (i.e. GBOTB.extended.tre), which was derived from two recently published mega‐trees and includes 74 533 species and all families of extant vascular plants, is the largest dated phylogeny for vascular plants. V.PhyloMaker can generate phylogenies for very large species lists (the largest species list that we tested included 314 686 species). V.PhyloMaker generates phylogenies at a fast speed, much faster than other phylogeny‐generating packages. Our tests of V.PhyloMaker show that generating a phylogeny for 60 000 species requires less than six hours. V.PhyloMaker includes an approach to attach genera or species to their close relatives in a phylogeny. We provide a simple example in this paper to show how to use V.PhyloMaker to generate phylogenies.

Smith M.N., Stark S.C., Taylor T.C., Ferreira M.L., de Oliveira E., Restrepo‐Coupe N., Chen S., Woodcock T., dos Santos D.B., Alves L.F., Figueira M., de Camargo P.B., de Oliveira R.C., Aragão L.E., Falk D.A., et. al.

Seasonal dynamics in the vertical distribution of leaf area index (LAI) may impact the seasonality of forest productivity in Amazonian forests. However, until recently, fine-scale observations critical to revealing ecological mechanisms underlying these changes have been lacking. To investigate fine-scale variation in leaf area with seasonality and drought we conducted monthly ground-based LiDAR surveys over 4 yr at an Amazon forest site. We analysed temporal changes in vertically structured LAI along axes of both canopy height and light environments. Upper canopy LAI increased during the dry season, whereas lower canopy LAI decreased. The low canopy decrease was driven by highly illuminated leaves of smaller trees in gaps. By contrast, understory LAI increased concurrently with the upper canopy. Hence, tree phenological strategies were stratified by height and light environments. Trends were amplified during a 2015-2016 severe El Niño drought. Leaf area low in the canopy exhibited behaviour consistent with water limitation. Leaf loss from short trees in high light during drought may be associated with strategies to tolerate limited access to deep soil water and stressful leaf environments. Vertically and environmentally structured phenological processes suggest a critical role of canopy structural heterogeneity in seasonal changes in Amazon ecosystem function.

Zhang L., Guo L., Yu K., Cui X., Cao X., Chen X., Shen M., Chen J.

Matthus E., Zwetsloot M., Delory B.M., Hennecke J., Andraczek K., Henning T., Mommer L., Weigelt A., Bergmann J.

Abstract Background and aims Fine roots and their traits determine resource uptake from the soil, thus being fundamental for plant and ecosystem functioning. It has been five years since the concept of the root economics space (RES) has been developed to describe multidimensional fine-root trait coordination. The RES proposed a novel fungal collaboration gradient in addition to the established fast-slow gradient of resource conservation. This review addresses both researchers already using the RES and those newly introduced to the concept. Our objective is to evaluate the empirical support for the concept, explore trait extensions and implications for ecosystem functioning, and examine future prospects of the RES. Scope/Results We conducted a literature review of 134 papers working with the RES to quantitatively assess support for the concept and its two trait gradients. The RES, particularly the collaboration gradient, is widely supported across organizational levels, habitats and study designs. Multidimensionality in the trait space appears to be a universal pattern. We further map traits that have been added to the RES concept and discuss the special role of legumes and ecto- versus arbuscular mycorrhizal fungi. Conclusions We conclude that the RES is a powerful concept to understand fine-root functional variation. Moving forward, we emphasize the need to integrate additional traits to develop a more comprehensive framework for understanding plant and ecosystem functioning.

Liu Y., Xiao J., Li X., Li Y.

Abstract. Critical soil moisture (CSM), a tipping point of soil moisture (SM) at which surface fluxes shift from the energy-limited regime to the water-limited regime, is essential for the vegetation state and the corresponding land–atmosphere coupling. However, detecting CSM and attributing water–energy limit shifts to climate and ecosystem variables are challenging as in situ observations of water, carbon fluxes, and soil moisture (SM) are sparse. In this study, CSM was assessed over China using two satellite-based methods: (i) the difference between the correlation between SM and evapotranspiration (ET) and the correlation between vapor pressure deficit (VPD) and ET and (ii) the covariance between VPD and gross primary production (GPP). ET and GPP products were based on the Penman–Monteith–Leuning (PML) ET and GPP, Global LAnd Surface Satellite (GLASS) ET and GPP, Collocation-Analyzed Multi-source Ensembled Land Evapotranspiration (CAMELE) ET, Surface Energy Balance Algorithm for Land (SEBAL) ET, two-leaf light use efficiency (TL-LUE) GPP, and solar-induced chlorophyll fluorescence (SIF)-based (GOSIF) GPP. At flux sites, ET and GPP products were evaluated by eddy-covariance-based measurements; CSM values using two satellite-based methods were assessed using the soil moisture–evaporative fraction method. Their consistency at site scales demonstrated reliable results and applicability to regional scales. Through intercomparison, the spatial pattern of CSM from multi-source ET and GPP datasets was consistent and robust in eastern and southern China. Generally, CSM decreased from south to north. The Pearl River basin and Southeastern River basin displayed a relatively high CSM for clay-rich soils (e.g., 0.39 m3 m−3 using PML ET and 10 cm depth SM) and forests (e.g., 0.35 m3 m−3 using PML ET and 10 cm depth SM). Since CSM values were higher than the average SM at four soil layers, grassland and clay were water-limited. Thus, with increased water demand, western grasslands were more susceptible to water stress. These findings highlight the variability in CSM and the primary determinants of water–energy limit shifts, offering valuable insights into the potential water limitations on ecosystems under comparable SM circumstances.

Du S., Jiang S., Ren L., Zhu Y., Cui H., He M., Xu C.

An X., Liu S., He C., Yang R., Guo B., Li X., Chen C., Wang H.

Yin H., Ma X., Wang W., Xu C., Xiang X., Li W., Li J., Li Y., Tran L.P., Zhang B.

Liu Y., Hu Y., Yang L., Zhao T., Zheng S., Peng X.

Liu G.

Abstract Tropical cyclones pose significant threats to coastal populations, causing destruction and loss of life. Precisely forecasting the frequency and arrival dates is still a challenge. This research presents a technique for feature extraction and integration using a random forest (RF) model with a cascaded convolutional neural network. The approach combines different meteorological maps and uses a feature fusion technique to improve prediction accuracy. The RF model is optimized by a grid search algorithm. The results show that the proposed model outperforms conventional models to achieve a mean absolute error of 0.48 and a mean relative error of 14.14%.

Verma A., Khadke L., Eldhose E., Ghosh S.

AbstractNet Ecosystem Exchange (NEE) is crucial for understanding the carbon balance in ecosystems, indicating whether they act as carbon sinks or sources. While the impact of hydrometeorological factors on NEE at daily and monthly scales has been well‐researched, the significance of sub‐daily variability and the influence of memory in micrometeorological variables remain understudied. This study addresses this gap by analyzing the temporal dynamics of NEE using half‐hourly data from 29 FLUXNET sites over at least 6 years. We found that sub‐daily variability of NEE contributes 10%–55% of 13‐day NEE variability, depending on seasonal cycles and biome characteristics. Using an information theory based transfer entropy (TE) approach, we identified the causal drivers of NEE variability at sub‐daily scales within a 6‐hr memory. Our results show that the memory of micrometeorological variables significantly impacts NEE, surpassing their instantaneous effects. Temperature (TA), vapor pressure deficit (VPD), and soil water content (SWCMean) consistently affect NEE within this 6‐hr memory, whereas the influence of sensible heat (H) and incoming shortwave radiation (SWIN) diminishes at higher lags. While the magnitude of average TE from micrometeorological variables to NEE exhibits notable seasonal variations, the temporal structure of how information is transferred does not significantly differ across seasons, as reflected by the shape of TE values over various time lags. SWCMean, VPD, and TA impact NEE jointly, while H and SWIN have overlapping effects. Additionally, precipitation influences NEE indirectly through SWCMean. Our findings highlight the importance of accounting for high‐frequency NEE variability and its underlying drivers when investigating the ecohydrological interactions, shedding light on the role of memory in carbon‐water interactions.

Cármen de Faria Melo C., Silva Amaral D., de Mello Prado R.

Aubin I., Deschênes É., Santala K., Emilson E.J., Schoonmaker A.L., McIntosh A.C., Bourgeois B., Cardou F., Dupuch A., Handa I.T., Lapointe M., Lavigne J., Maheu A., Nadeau S., Naeth M.A., et. al.

Restoration is moving towards a more mechanistic approach that emphasizes restoration of ecosystem services. Trait-based approaches provide links between species identity and ecosystem functions and have been suggested as a promising way to formally integrate ecosystem services in the design of restoration programs. While practitioners have been routinely using informal knowledge on plant traits in their practices, these approaches are underutilized as operationalization remains challenging. The goal of this paper is to provide guidance for applied scientists and restoration practitioners looking to apply a trait-based approach to restore forest ecosystems. We present a five-step framework: (1) selection of services to be restored, (2) trait selection, (3) data acquisition, (4) analytical planning, and (5) empirical testing and monitoring. We use three Canadian case studies to illustrate the applicability of our framework and the variety of ways trait-based approaches can inform restoration practices: (1) restoration of urban woodlots after an insect outbreak, (2) restoration of a smelter-damaged landscape surrounding an urban area, and (3) reclamation of remote upland forests after oil- and gas-related disturbances. We describe the major mechanisms and traits that determine vegetation effects on ecosystem services of importance in each case study. We then discuss data availability, methodological constraints, comparability issues, analytical methods, and the importance of empirical testing and monitoring to ensure realistic prediction of service restoration. By outlining issues and offering practical information, we aim to contribute to a more robust use of traits in ecological restoration.

Billings S.A., Sullivan P.L., Hirmas D., Nippert J.B., Richter D.D., Brecheisen Z., Cook C.W., Hauser E.

Long before the term ‘critical zone’ (CZ) was coined to encompass Earth’s biological and geological features from the top of the vegetative canopy to the depths of circulating groundwater, many scientists have recognized that both biotic and abiotic actors are centrally important for understanding many of Earth’s most fundamental processes. Contemporary CZ scientists continue this legacy. We describe findings that emphasize how life, emphasizing vegetation and microbes, responds to and shapes the physical environment in which it persists, yielding feedbacks for Earth’s climate, primarily through modifications to hydrologic functioning. We focus on the interactions of biota and the physical and chemical features of soil pedons and landscapes as they drive ecosystem-scale hydrologic fluxes. We focus on hydrologically-relevant features because of the long history of individual disciplines telling us about the large-scale importance of these processes, and because of emerging research highlighting the importance of the intersection of these disciplines for projecting future ecosystem functioning on a rapidly changing Earth. The knowledge we spotlight reveals Earth’s CZ as a fundamentally ecological problem.

Hirano Y., Todo C., Tanikawa T., Yamase K., Ohashi M., Dannoura M., Okamoto Y., Doi R., Yoshida G., Ikeno H.

Campioli M., Marchand L.J., Zahnd C., Zuccarini P., McCormack M.L., Landuyt D., Lorer E., Delpierre N., Gričar J., Vitasse Y.

To synthesize new information regarding the environmental sensitivity and impact of climate change on leaf-, wood-, phloem- and root phenology of deciduous forests of the temperate (and boreal) zone, comprising overstory and understory, and both woody and herbaceous species. The environmental sensitivity and impact of climate change on spring leaf phenology are relatively well understood, with ongoing efforts focusing on the spatial and temporal variability in both overstory and understory. Autumn leaf phenology and cambial phenology have received increasing attention in recent years. The drivers of senescence progression are well understood (current temperature), while the drivers of the onset of senescence are still uncertain but likely relate to spring temperature, water availability and light conditions. Studies on cambial phenology of angiosperm trees have focused on the variability across populations and years, while studies on phloem remain scarce and synthesis studies are unavailable. For fine root phenology, asynchronicity with leaf phenology and high variability among species have been demonstrated, but large uncertainty remains regarding the drivers of the onset and cessation of their growth. Studies on woody and herbaceous understory highlight the importance of microclimate differences within the stand. Future phenology research should focus on (i) onset of leaf senescence, (ii) fine roots, (iii) the relationships between overstory and understory species not only regarding leaves, but also wood and fine roots, (iv) variability across multiples scales (e.g. individuals, stands), and (v) interannual legacy effects and connections among phenophases of different organs and forest compartments.

Bayala J., Wilson J., Muthuri C., Bargués-Tobella A., Jackson N.A., van Noordwijk M.