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Publications

2020
Mannerheim, N. ; Blessing, C. H. ; Oren, I. ; Grünzweig, J. ; Bachofen, C. ; Buchmann, N. Carbon allocation to the root system of tropical tree Ceiba pentandra using 13C pulse labelling in an aeroponic facility. Tree Physiol 2020, 40, 350 - 366. Publisher's VersionAbstract
Despite the important role of tropical forest ecosystems in the uptake and storage of atmospheric carbon dioxide (CO2), the carbon (C) dynamics of tropical tree species remains poorly understood, especially regarding belowground roots. This study assessed the allocation of newly assimilated C in the fast-growing pioneer tropical tree species Ceiba pentandra (L.), with a special focus on different root categories. During a 5-day pulse-labelling experiment, 9-month-old (~3.5-m-tall) saplings were labelled with 13CO2 in a large-scale aeroponic facility, which allowed tracing the label in bulk biomass and in non-structural carbohydrates (sugars and starch) as well as respiratory CO2 from the canopy to the root system, including both woody and non-woody roots. A combined logistic and exponential model was used to evaluate 13C mean transfer time and mean residence time (MRT) to the root systems. We found 13C in the root phloem as early as 2 h after the labelling, indicating a mean C transfer velocity of 2.4 ± 0.1 m h−1. Five days after pulse labelling, 27% of the tracers taken up by the trees were found in the leaves and 13% were recovered in the woody tissue of the trunk, 6% in the bark and 2% in the root systems, while 52% were lost, most likely by respiration and exudation. Larger amounts of 13C were found in root sugars than in starch, the former also demonstrating shorter MRT than starch. Of all investigated root categories, non-woody white roots (NRW) showed the largest 13C enrichment and peaked in the deepest NRW (2–3.5 m) as early as 24 ± 2 h after labelling. In contrast to coarse woody brown roots, the sink strength of NRW increased with root depth. The findings of this study improve the understanding of C allocation in young tropical trees and provide unique insights into the changing contributions of woody and non-woody roots to C sink strengths with depth.
Preisler, Y. ; Tatarinov, F. ; Grünzweig, J. ; Yakir, D. Seeking the “point of no return” in the sequence of events leading to mortality of mature trees. Plant, Cell & EnvironmentPlant, Cell & EnvironmentPlant Cell Environ 2020, n/a. Publisher's VersionAbstract
Abstract Drought-related tree mortality is increasing globally, but the sequence of events leading to it remains poorly understood. To identify this sequence, we used a 2016 tree mortality event in a semi-arid pine forest where dendrometry and sap flow measurements were carried out in 31 trees, of which seven died. A comparative analysis revealed three stages leading to mortality. First, a decrease in tree diameter in all dying trees, but not in the surviving trees, 8?months ?prior to the visual signs of mortality? (PVSM; e.g., near complete canopy browning). Second, a decay to near zero in the diurnal stem swelling/shrinkage dynamics, reflecting the loss of stem radial water flow in the dying trees, 6?months PVSM. Third, cessation of stem sap flow 3?months PVSM. Eventual mortality could therefore be detected long before visual signs were observed, and the three stages identified here demonstrated the differential effects of drought on stem growth, water storage capacity and soil water uptake. The results indicated that breakdown of stem radial water flow and phloem function is a critical element in defining the ?point of no return? in the sequence of events leading to mortality of mature trees.
2019
Bahat, I. ; Netzer, Y. ; Ben-Gal, A. ; Grünzweig, J. ; Peeters, A. ; Cohen, Y. Comparison of water potential and yield parameters under uniform and variable rate drip irrigation in a cabernet sauvignon vineyard. In Precision Agriculture 2019 - Papers Presented at the 12th European Conference on Precision Agriculture, ECPA 2019; Precision Agriculture 2019 - Papers Presented at the 12th European Conference on Precision Agriculture, ECPA 2019; 2019; pp. 125-131. Publisher's VersionAbstract
An experiment in variable-rate drip irrigation (VRDI) was aimed at reducing variance of midday stem water potential (SWP) and in yield parameters by applying VRDI in a highly variable vineyard. During 2018, irrigation was separated into VRDI and uniform irrigation (UI) blocks. Each block was delineated to 10 management cells, and results of 2018 season were compared to 2017 season under UI. Standard error (SE) of SWP in the last 3 measurements before harvest decreased in the VRDI block in 2018 compared to 2017 by 14-44%. In contrast, in the UI block, SE in 2018 was higher by 11-42% compared to 2017. SE of fruit yield showed a similar trend. Applying principles of precision irrigation may lead to a more homogeneous vineyard in the parameters described above and to improved wine quality. © Wageningen Academic Publishers 2019
Qubaja, R. ; Grünzweig, J. ; Rotenberg, E. ; Yakir, D. Evidence for large carbon sink and long residence time in semiarid forests based on 15 year flux and inventory records. Global Change Biology 2019. Publisher's VersionAbstract
The rate of change in atmospheric CO2 is significantly affected by the terrestrial carbon sink, but the size and spatial distribution of this sink, and the extent to which it can be enhanced to mitigate climate change are highly uncertain. We combined carbon stock (CS) and eddy covariance (EC) flux measurements that were collected over a period of 15 years (2001–2016) in a 55 year old 30 km2 pine forest growing at the semiarid timberline (with no irrigating or fertilization). The objective was to constrain estimates of the carbon (C) storage potential in forest plantations in such semiarid lands, which cover  18% of the global land area. The forest accumulated 145–160 g C m−2 year−1 over the study period based on the EC and CS approaches, with a mean value of 152.5 ± 30.1 g C m−2 year−1 indicating 20% uncertainty in carbon uptake estimates. Current total stocks are estimated at 7,943 ± 323 g C/m2 and 372 g N/m2. Carbon accumulated mostly in the soil ( 71% and 29% for soil and standing biomass carbon, respectively) with long soil carbon turnover time (59 years). Regardless of unexpected disturbances beyond those already observed at the study site, the results support a considerable carbon sink potential in semiarid soils and forest plantations, and imply that afforestation of even 10% of semiarid land area under conditions similar to that of the study site, could sequester  0.4 Pg C/year over several decades. © 2019 John Wiley & Sons Ltd
Halbritter, A. H. ; De Boeck, H. J. ; Eycott, A. E. ; Reinsch, S. ; Robinson, D. A. ; Vicca, S. ; Berauer, B. ; Christiansen, C. T. ; Estiarte, M. ; Grünzweig, J. ; et al. The handbook for standardized field and laboratory measurements in terrestrial climate change experiments and observational studies (ClimEx). Methods in Ecology and Evolution 2019. Publisher's VersionAbstract
Climate change is a world-wide threat to biodiversity and ecosystem structure, functioning and services. To understand the underlying drivers and mechanisms, and to predict the consequences for nature and people, we urgently need better understanding of the direction and magnitude of climate change impacts across the soil–plant–atmosphere continuum. An increasing number of climate change studies are creating new opportunities for meaningful and high-quality generalizations and improved process understanding. However, significant challenges exist related to data availability and/or compatibility across studies, compromising opportunities for data re-use, synthesis and upscaling. Many of these challenges relate to a lack of an established ‘best practice’ for measuring key impacts and responses. This restrains our current understanding of complex processes and mechanisms in terrestrial ecosystems related to climate change. To overcome these challenges, we collected best-practice methods emerging from major ecological research networks and experiments, as synthesized by 115 experts from across a wide range of scientific disciplines. Our handbook contains guidance on the selection of response variables for different purposes, protocols for standardized measurements of 66 such response variables and advice on data management. Specifically, we recommend a minimum subset of variables that should be collected in all climate change studies to allow data re-use and synthesis, and give guidance on additional variables critical for different types of synthesis and upscaling. The goal of this community effort is to facilitate awareness of the importance and broader application of standardized methods to promote data re-use, availability, compatibility and transparency. We envision improved research practices that will increase returns on investments in individual research projects, facilitate second-order research outputs and create opportunities for collaboration across scientific communities. Ultimately, this should significantly improve the quality and impact of the science, which is required to fulfil society's needs in a changing world. © 2019 The Authors. Methods in Ecology and Evolution published by John Wiley & Sons Ltd on behalf of British Ecological Society.
De Boeck, H. J. ; Bloor, J. M. G. ; Aerts, R. ; Bahn, M. ; Beier, C. ; Emmett, B. A. ; Estiarte, M. ; Grünzweig, J. ; Halbritter, A. H. ; Holub, P. ; et al. Understanding ecosystems of the future will require more than realistic climate change experiments – A response to Korell et al. Global Change Biology 2019. Publisher's Version
Sagi, N. ; Grünzweig, J. ; Hawlena, D. Burrowing detritivores regulate nutrient cycling in a desert ecosystem. Proceedings of the Royal Society B: Biological Sciences 2019, 286, 20191647. Publisher's VersionAbstract
Nutrient cycling in most terrestrial ecosystems is controlled by moisture-dependent decomposer activity. In arid ecosystems, plant litter cycling exceeds rates predicted based on precipitation amounts, suggesting that additional factors are involved. Attempts to reveal these factors have focused on abiotic degradation, soil–litter mixing and alternative moisture sources. Our aim was to explore an additional hypothesis that macro-detritivores control litter cycling in deserts. We quantified the role different organisms play in clearing plant detritus from the desert surface, using litter baskets with different mesh sizes that allow selective entry of micro-, meso- or macrofauna. We also measured soil nutrient concentrations in increasing distances from the burrows of a highly abundant macro-detritivore, the desert isopod Hemilepistus reaumuri. Macro-detritivores controlled the clearing of plant litter in our field site. The highest rates of litter removal were measured during the hot and dry summer when isopod activity peaks and microbial activity is minimal. We also found substantial enrichment of inorganic nitrogen and phosphorous near isopod burrows. We conclude that burrowing macro-detritivores are important regulators of litter cycling in this arid ecosystem, providing a plausible general mechanism that explains the unexpectedly high rates of plant litter cycling in deserts.
Oren, I. ; Mannerheim, N. ; Dumbur, R. ; Fangmeier, A. ; Buchmann, N. ; Grünzweig, J. Patterns and dynamics of canopy-root coupling in tropical tree saplings vary with light intensity but not with root depth. New Phytol 2019.Abstract
Carbon dynamics in canopy and roots influence whole tree carbon fluxes, but little is known about canopy regulation of tree-root activity. Here, we assess the patterns and dynamics of canopy-root carbon coupling in tropical trees. We used large aeroponics to directly study the root systems of Ceiba pentandra and Khaya anthotheca saplings at different light intensities. In Ceiba, root respiration (R ) co-varied with photosynthesis (A ) in large saplings (3-to-7-m canopy-root axis) at high-light, but showed no consistent pattern at low-light. At medium-light and in small saplings (c. 1-m axis), R tended to decrease transiently towards midday. Proximal roots had higher R and non-structural carbohydrate concentrations than distal roots, but canopy-root coupling was unaffected by root location. In medium-sized Khaya, no R pattern was observed, and in both species, R was unrelated to temperature. The early-afternoon increase in R suggests canopy-root coupling is based on mass flow of newly fixed carbon in the phloem, while the early-morning rise in R with A indicates an additional coupling signal that travels faster than the phloem sap. In large saplings and potentially also in higher trees, light and possibly additional environmental factors control the diurnal patterns of canopy-root coupling, irrespective of root location. This article is protected by copyright. All rights reserved.
Preisler, Y. ; Tatarinov, F. ; Grünzweig, J. ; Bert, D. ; Ogée, J. ; Wingate, L. ; Rotenberg, E. ; Rohatyn, S. ; Her, N. ; Moshe, I. ; et al. Mortality versus survival in drought-affected Aleppo pine forest depends on the extent of rock cover and soil stoniness. Functional Ecology 2019, 33, 901-912. Publisher's VersionAbstract
Abstract Drought-related tree mortality had become a widespread phenomenon in forests around the globe. This process leading to these events and its complexity is not fully understood. Trees in the dry timberline are exposed to ongoing drought, and the available water for transpiration in the soil can determine their survival chances. Recent drought years led to 5%–10% mortality in the semi-arid pine forest of Yatir (Israel). The distribution of dead trees was, however, highly heterogeneous with parts of the forest showing >80% dead trees (D plots) and others with mostly live trees (L plots). At the tree level, visible stress was associated with low pre-dawn leaf water potential at the dry season (−2.8 MPa vs. −2.3 MPa in non-stressed trees), shorter needles (5.5 vs. 7.7 mm) and lower chlorophyll content (0.6 vs. 1 mg/g dw). Trends in tree-ring widths reflected differences in stress intensity (30% narrower rings in stressed compared with unstressed trees), which could be identified 15–20 years prior to mortality. At the plot scale, no differences in topography, soil type, tree age or stand density could explain the mortality difference between the D and L plots. It could only be explained by the higher surface rock cover and in stoniness across the soil profile in the L plots. Simple bucket model simulations using the site’s long-term hydrological data supported the idea that these differences could result in higher soil water concentration (m3/m3) in the L plots and extend the time above wilting point by several months across the long dry season. Accounting for subsurface heterogeneity may therefore critical to assessing stand-level response to drought and projecting tree survival, and can be used in management strategies in regions undergoing drying climate trends. A plain language summary is available for this article.
2018
Gliksman, D. ; Haenel, S. ; Osem, Y. ; Yakir, D. ; Zangy, E. ; Preisler, Y. ; Grünzweig, J. Litter decomposition in Mediterranean pine forests is enhanced by reduced canopy cover. 2018, 422, 317 - 329. Publisher's VersionAbstract
This study investigated the impact of canopy cover and seasonality on litter decay in Mediterranean pine forests to enhance climate predictions.
Gliksman, D. ; Haenel, S. ; Grünzweig, J. Biotic and abiotic modifications of leaf litter during dry periods affect litter mass loss and nitrogen loss during wet periods. Functional Ecology 2018, 32, 831-839. Publisher's VersionAbstract
Abstract Decomposition of organic matter in semi-arid ecosystems is a key component of the terrestrial carbon (C) cycle. The well-known inaccuracies in predicting litter decay in water-limited regions were lessened by considering solar radiation as an abiotic decay driver of photodegradation. Moreover, exposure to high solar irradiance in dry periods often led to massive facilitation of litter decay in subsequent wet periods (“photoacceleration”), though in many studies this effect was absent. Recently, water vapour and dew were identified as modulators enabling substantial microbial degradation during rainless periods. Here, we investigated, (1) whether the activity of micro-organisms modifies litter traits, such as litter quality and microbial community in dry periods, consequently altering the loss of litter mass and nitrogen (N) in wet periods, and (2) whether it can co-occur with photoacceleration. By successively introducing litter to the field at the beginning and the end of the dry season, we found that microbial activity during the dry season affected litter mass and N loss during the wet season. Low microbial activity in the dry season led to inhibition of mass loss in the wet season, while high microbial activity led to facilitation of mass loss. Microbial activity during the dry season also caused strong inhibition of N loss from litter during the wet season, likely by enhancing the dry-season N loss. A microclimate manipulation experiment using radiation filters showed that microbial activity and exposure to solar radiation jointly modified the litter during the dry season and affected subsequent decay in the wet season. Knowledge of biotic and abiotic modifications of litter during dry periods and their implication for wet periods enhances our understanding of litter decay in semi-arid regions. Furthermore, it can improve biogeochemical model predictions of C and N cycling in drylands and in the many regions that are projected to experience a drier climate during the coming decades. A plain language summary is available for this article.
Gliksman, D. ; Navon, Y. ; Dumbur, R. ; Haenel, S. ; Grünzweig, J. Higher rates of decomposition in standing vs. surface litter in a Mediterranean ecosystem during the dry and the wet seasons. 2018, 428, 427 - 439. Publisher's VersionAbstract
Plant litter decomposition in drylands is not well understood, and even less is known about decay of the abundant standing dead residues. Here, we followed decomposition of standing and surface litter, and assessed the underlying drivers and mechanisms.
2017
Gliksman, D. ; Rey, A. ; Seligmann, R. ; Dumbur, R. ; Sperling, O. ; Navon, Y. ; Haenel, S. ; De Angelis, P. ; Arnone III, J. A. ; Grünzweig, J. Biotic degradation at night, abiotic degradation at day: positive feedbacks on litter decomposition in drylands. Global Change Biology 2017, 23, 1564-1574. Publisher's VersionAbstract
Abstract The arid and semi-arid drylands of the world are increasingly recognized for their role in the terrestrial net carbon dioxide (CO2) uptake, which depends largely on plant litter decomposition and the subsequent release of CO2 back to the atmosphere. Observed decomposition rates in drylands are higher than predictions by biogeochemical models, which are traditionally based on microbial (biotic) degradation enabled by precipitation as the main mechanism of litter decomposition. Consequently, recent research in drylands has focused on abiotic mechanisms, mainly photochemical and thermal degradation, but they only partly explain litter decomposition under dry conditions, suggesting the operation of an additional mechanism. Here we show that in the absence of precipitation, absorption of dew and water vapor by litter in the field enables microbial degradation at night. By experimentally manipulating solar irradiance and nighttime air humidity, we estimated that most of the litter CO2 efflux and decay occurring in the dry season was due to nighttime microbial degradation, with considerable additional contributions from photochemical and thermal degradation during the daytime. In a complementary study, at three sites across the Mediterranean Basin, litter CO2 efflux was largely explained by litter moisture driving microbial degradation and ultraviolet radiation driving photodegradation. We further observed mutual enhancement of microbial activity and photodegradation at a daily scale. Identifying the interplay of decay mechanisms enhances our understanding of carbon turnover in drylands, which should improve the predictions of the long-term trend of global carbon sequestration.
Dirks, I. ; Dumbur, R. ; Lienin, P. ; Kleyer, M. ; Grünzweig, J. Size and Reproductive Traits Rather than Leaf Economic Traits Explain Plant-Community Composition in Species-Rich Annual Vegetation along a Gradient of Land Use Intensity. Frontiers in Plant Science 2017, 8 891. Publisher's VersionAbstract
Agricultural land use imposes a major disturbance on ecosystems worldwide, thus greatly modifying the taxonomic and functional composition of plant communities. However, mechanisms of community assembly, as assessed by plant functional traits, are not well known for dryland ecosystems under agricultural disturbance. Here we investigated trait responses to disturbance intensity and availability of resources to identify the main drivers of changes in composition of semiarid communities under diverging land use intensities. The eastern Mediterranean study region is characterized by an extended rainless season and by very diverse, mostly annual communities. At 24 truly replicated sites, we recorded the frequency of 241 species and the functional traits of the 53 most common species, together with soil resources and disturbance intensity across a land use gradient ranging from ungrazed shrubland to intensively managed cropland (six land use types). Multivariate RLQ analysis (linking functional traits, sites and environmental factors in a three-way ordination) and fourth corner analysis (revealing significant relations between traits and environmental factors) were used in a complementary way to get insights into trait-environment relations. Results revealed that traits related to plant size (reflecting light absorption and competitive ability) increased with resource availability, such as soil phosphorus and water holding capacity. Leaf economic traits, such as specific leaf area (SLA), leaf nitrogen content (LNC), and leaf dry matter content showed low variation across the disturbance gradient and were not related to environmental variables. In these herbaceous annual communities where plants grow and persist for just 3–5 months, SLA and LNC were unrelated, which together with relatively high SLA values might point to strategies of drought escape and grazing avoidance. Seed mass was high both at higher and lower resource availability, whereas seed number increased with the degree of disturbance. The strong response of size and reproduction traits, and the missing response of leaf economic traits reveal light interception and resource competition rather than resource acquisition and litter decomposition as drivers of plant community composition. Deviations from trait relationships observed in commonly studied temperate ecosystems confirm that climatic conditions play a fundamental role by filtering species with particular life forms and ecological strategies.