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
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
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.
Burrowing detritivores regulate nutrient cycling in a desert ecosystem
. Proceedings of the Royal Society B: Biological Sciences 2019
, 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.
Patterns and dynamics of canopy-root coupling in tropical tree saplings vary with light intensity but not with root depth
. New Phytol 2019
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.
Mortality versus survival in drought-affected Aleppo pine forest depends on the extent of rock cover and soil stoniness
. Functional Ecology 2019
, 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.