Browsing by Subject "Drought"

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  • Ariza, Gloria Maria; Jacome, Jorge; Kotze, D. Johan (2021)
    The tropical dry forest (TDF) ecosystem is characterised by strong seasonality exasperated periodically by the El Nino/southern oscillation (ENSO). The environment produced by this event could constrain the survival of small organisms, such as insects. Carabid beetles were collected in a TDF in Armero, Colombia, during wet and dry seasons in both El Nino and non-El Nino periods. A series of traits linked to desiccation resistance were measured to characterise their adaptation to the TDF environment and to investigate changes experienced by carabid beetles during both episodes in quantitative (assemblage) and qualitative (traits) parameters. We found no difference in the presence of traits between El Nino and non-El Nino episodes, but carabid assemblages changed significantly in composition and assemblage structure between these episodes. During both periods, small-sized and nocturnal species dominated the assemblages, but in terms of number of individuals, medium and large-sized, and visual hunter species dominated. Calosoma alternans and Megacephala affinis were the most abundant species with high dispersal capacity. Carabid beetles exhibited morphological traits well-adapted to drought experienced in TDF, including when it is exasperated by ENSO. However, long-term studies can help to elucidate the real effects of ENSO and to confirm the adaptation of carabid beetles to cope with this extreme environment.
  • Tuure, Juuso; Korpela, Antti; Hautala, Mikko; Rautkoski, Hille; Hakojarvi, Mikko; Mikkola, Hannu; Duplissy, Jonathan; Pellikka, Petri; Petaja, Tuukka; Kulmala, Markku; Alakukku, Laura (2020)
    Passive dew collection could be a viable option as a source of irrigation water in arid areas. The plastic foil acting as a condensing surface plays a key role in the passive dew collection regime. A laboratory method for comparing various plastic foils for dew collection was prepared and tested. The focus was on creating a method for measuring the attributes affecting dew condensation and the flow of dew droplets on the measured surface. A low-density polyethylene foil designed for dew collection, white polyethylene plastic, black polyethylene plastic, and white polyvinyl chloride plastic were used as the test plastics. The laboratory dew yields were compared with model calculations. In addition, field trials were conducted in arid conditions in Maktau, Kenya, to compare with the laboratory measurement. Results from the hardware model tests were not reflected in the results obtained from the field conditions. The laboratory tests showed that the dew-harvesting quality of plastic foils is difficult to evaluate using the laboratory test rig. A more comprehensive evaluation regime requires tests performed in field conditions or further development of the test rig used here. (C) 2020 IAgrE. Published by Elsevier Ltd. All rights reserved.
  • Tuure, Juuso; Korpela, A; Hautala, Mikko; Hakojärvi, Mikko; Räsänen, Matti; Duplissy, Jonathan; Pellikka, Petri; Petäjä, Tuukka; Kulmala, Markku; Alakukku, Laura (2019)
    This study characterized different polyethylene (PE) and polyvinyl chloride (PVC) plastic foil materials effectiveness for dew collection in arid field-conditions in Kenya. Dew yields were collected daily for one year. Ten dew collectors with four different plastic foils were setup in the experimental field. The cumulated dew yields ranged from 18.9 to 25.3 mm. The greatest cumulated dew yields were 25.3 mm (nightly mean 0.096 mm) and 24.3 mm (nightly mean 0.093) measured with PVC and OPUR coated collectors respectively. The lowest cumulated dew yields 18.9 mm (nightly mean 0.075 mm) and 19.1 mm (nightly mean 0.074 mm) were measured with PVC and PE coated collectors respectively. Dew provided a continuous water source during the dry season. The type of the surface material was not found to be a determining factor for the collected dew yield. The location of the collector at the experimental field had impact on the collected dew yields. We also compared harvested dew yields to measured meteorological parameters and calculated dew yields with the use of a diffusion model using the measured surface temperatures and coefficient of mass diffusion to evaluate the dew collecting potential under the prevailing conditions.
  • Rissanen, Kaisa; Hölttä, Teemu; Bäck, Jaana; Rigling, Andreas; Wermelinger, Beat; Gessler, Arthur (2021)
    Droughts and other rapid changes in abiotic environmental conditions can predispose trees to damage by pest insects and pathogens. For survival of coniferous trees, functional resin-based defences are essential, and it is important to know how they react to changes in environmental conditions at various time scales. We studied the effects of differing water availabilities on resin-based defences in mature Scots pine (Pinus sylvestris) trees in a naturally drought-prone forest within a long-term irrigation experiment. Our objectives were to understand the effects of long-term drought on carbon allocation to resin production and to analyse its influence on resin flow and pressure in comparison to the shorter-term effects of seasonal drought. We tracked carbon allocation to resin after C-13-pulse labelling experiment in late summer 2017 and compared the observed resin dynamics between drought-exposed control trees and irrigated trees from June to August during the dry hot summer of 2018. Dry control trees showed higher allocation of labelled carbon to resin than irrigated trees. Resin pressure was higher in dry control than in irrigated trees with similar water potentials, and resin flow in June was higher in dry control than in irrigated trees with similar crown transparency. Yet, resin pressures of dry control trees in particular decreased with decreasing water availability from June to August. Resin flow was little affected by short-term changes in water availability and mostly associated with crown transparency. We suggest that because of differing timescales of direct drought effects and changes in allocation patterns, dry conditions may support resin-based defences in the long term, but a drought period decreases resin pressure in the short term.
  • Chen, Lei; Huang, Jian-Guo; Stadt, Kenneth J.; Comeau, Philip G.; Zhai, Lihong; Dawson, Andria; Alam, Syed Ashraful (2017)
    Many studies have already addressed the existence of unstable and nonlinear relationships between radial growth of white spruce (Picea glauca) and climate variables in boreal forests along the high latitudes (> 60° N). However, along the mid-latitudes, the climate-growth relationship is still poorly understood. In this study, we used a network of ring-width chronologies from 40 white spruce sites along a wide latitudinal gradients from 52° N to 58° N in Alberta, Canada and attempted to understand the complicated response of tree growth to climatic variables and to identify the main limiting factor for the radial growth of white spruce. We combined the empirical linear statistics with the process-based Vaganov-Shashkin Lite (VS-Lite) model requiring only latitude, month mean temperature, and monthly total precipitation information together to better clarify growth-climate relationship. The linear statistical methods indicated that the previous summer temperature imposed a strong negative impact on the radial growth of white spruce while the precipitation and climate moisture index in prior and current summer both had significant positive effects on the radial growth. Similarly, the VS-Lite model showed that the radial growth of white spruce was limited by soil moisture, and temperature-induced drought is the main limiting factor for the radial growth of white spruce. Furthermore, climate-growth relationship varied along different elevations, latitudes, and growing degree days (GDD > 5℃). The radial growth of white spruce in northern stands is often more strongly limited by temperature-induced drought due to the higher temperature and lower precipitation. As the global climate change is in progress, we suggest that more large-scale and continuous investigations are needed to address the spatial variation in growth-climate relationship due to the temperature-induced drought.
  • Alam, Syed Ashraful; Huang, Jianguo; Stadt, Kenneth J.; Comeau, Philip G.; Dawson, Andria; Gea-Izquierdo, Guillermo; Aakala, Tuomas; Hölttä, Teemu Samuli; Vesala, Timo Veikko; Mäkelä, Annikki; Berninger, Frank Alexander (2017)
    Understanding the complex interactions of competition, climate warming-induced drought stress, and photosynthetic productivity on the radial growth of trees is central to linking climate change impacts on tree growth, stand structure and in general, forest productivity. Using a mixed modelling approach, a stand-level photosynthetic production model, climate, stand competition and tree-ring data from mixedwood stands in western Canada, we investigated the radial growth response of white spruce (Picea glauca (Moench.) Voss) to simulated annual photosynthetic production, simulated drought stress, and tree and stand level competition. The long-term (~80-year) radial growth of white spruce was constrained mostly by competition, as measured by total basal area, with minor effects from drought. There was no relation of competition and drought on tree growth but dominant trees increased their growth more strongly to increases in modelled photosynthetic productivity, indicating asymmetric competition. Our results indicate a co-limitation of drought and climatic factors inhibiting photosynthetic productivity for radial growth of white spruce in western Canada. These results illustrate how a modelling approach can separate the complex factors regulating both multi-decadal average radial growth and interannual radial growth variations of white spruce, and contribute to advance our understanding on sustainable management of mixedwood boreal forests in western Canada.
  • Singh, Jaswinder; Cameron, Erin; Reitz, Thomas; Schädler, Martin; Eisenhauer, Nico (2021)
    Abstract The impacts of climate change on biodiversity can be modulated by other changing environmental conditions, e.g. induced by land-use change. The potential interactive effects of climate change and land use have rarely been studied for soil organisms. To test the effects of changing climatic conditions and land use on soil invertebrates, we examined earthworm communities across different seasons in different grassland-use types (intensively managed grassland, extensively managed meadow, and extensively managed sheep pasture).We predicted that the strength of climate change effects would vary with season and land use. Overall, extracted earthworm populations showed the strongest variations in response to the season, indicating major differences in activity patterns and extraction efficiency, while climate change and different grassland-use types had fewer and weaker effects. Future climate, characterized by slightly higher precipitation in spring and fall but a strong reduction during the summer, had positive effects on the abundance of extracted adult earthworms in spring but then reduced the abundance of active earthworms across the remaining seasons. In contrast, the total biomass of juveniles tended to be consistently lower under future climate conditions. Earthworm species responded differently to the climate change and different grassland management types, and these species-specific responses further varied strongly across seasons. Intensive grassland management had negative effects, due to plant community composition, while sheep grazing favoured earthworm populations, due to dung deposition. There were only limited interactive effects between climate and land use, which thus did not support our main hypothesis. Nevertheless, these results highlight the complex and context-dependent responses of earthworm communities and activity patterns to climate change, with potential consequences for long-term population dynamics and crucial ecosystem functions. This article is protected by copyright. All rights reserved.
  • Chapman, Jack (Helsingin yliopisto, 2022)
    Climate change is expected to cause long-term drying on northern peatlands due to increased evapotranspiration. Summer heatwaves and droughts are also predicted to increase with climate change. Vascular plant leaf area phenology on peatlands is affected by reduced water levels and interannual variation in weather. Nutrient rich mire types are more susceptible to both functional and compositional changes in response to long-term and short-term changes in water level. What remains unexplored is the potential for interactive effects between long-term drying and short-term drought events on leaf area phenology on varying mire types. This study quantifies the response of leaf area phenology to 20-year experimental water level drawdown (WLD) across three mire types of varying nutrient levels (mesotrophic fen, oligotrophic fen and ombrotrophic bog). Measurements were conducted in two contrasting growing seasons, 2017 a cool wet year and 2021 a hot dry year. WLD led to significantly earlier growth peaks across all sites. Community compositional changes in response to WLD were most significant at the more nutrient rich mire sites. At the mesotrophic site WLD resulted in significant reductions in peak leaf area (LAIMAX), which was not observed at the other sites. Across all the WLD plots the hot dry year 2021 resulted in significantly greater LAIMAX relative to the cool wet year 2017, this difference was not significant at any of the control plots. This suggests long-term drying alters the way mire phenology responds to short-term variations in weather. This has important implications for the ability of northern mires to function ‘normally’ under future climate conditions.
  • Grossiord, Charlotte; Sevanto, Sanna; Limousin, Jean-Marc; Meir, Patrick; Mencuccini, Maurizio; Pangle, Robert E.; Pockman, William T.; Salmon, Yann; Zweifel, Roman; McDowell, Nate G. (2018)
    Tree transpiration depends on biotic and abiotic factors that might change in the future, including precipitation and soil moisture status. Although short-term sap flux responses to soil moisture and evaporative demand have been the subject of attention before, the relative sensitivity of sap flux to these two factors under long-term changes in soil moisture conditions has rarely been determined experimentally. We tested how long-term artificial change in soil moisture affects the sensitivity of tree-level sap flux to daily atmospheric vapor pressure deficit (VPD) and soil moisture variations, and the generality of these effects across forest types and environments using four manipulative sites in mature forests. Exposure to relatively long-term (two to six years) soil moisture reduction decreases tree sap flux sensitivity to daily VPD and relative extractable water (REW) variations, leading to lower sap flux even under high soil moisture and optimal VPD. Inversely, trees subjected to long-term irrigation showed a significant increase in their sensitivity to daily VPD and REW, but only at the most water-limited site. The ratio between the relative change in soil moisture manipulation and the relative change in sap flux sensitivity to VPD and REW variations was similar across sites suggesting common adjustment mechanisms to long-term soil moisture status across environments for evergreen tree species. Overall, our results show that long-term changes in soil water availability, and subsequent adjustments to these novel conditions, could play a critical and increasingly important role in controlling forest water use in the future.
  • Heiskanen, Lauri Ilmari; Tuovinen, Juha-Pekka; Vekuri, Henriikka W; Räsänen, Aleksi; Virtanen, Tarmo; Juutinen, Sari; Lohila, Annalea Katriina; Mikola, Juha; Aurela, Mika (2023)
    The subarctic landscape consists of a mosaic of forest, peatland, and aquatic ecosystems and their ecotones. The carbon (C) exchange between ecosystems and the atmosphere through carbon dioxide (CO2) and methane (CH4) fluxes varies spatially and temporally among these ecosystems. Our study area in Kaamanen in northern Finland covered 7 km(2) of boreal subarctic landscape with upland forest, open peatland, pine bogs, and lakes. We measured the CO2 and CH4 fluxes with eddy covariance and chambers between June 2017 and June 2019 and studied the C flux responses to varying meteorological conditions. The landscape area was an annual CO2 sink of -45 +/- 22 and -33 +/- 23 g C m(-2) and a CH4 source of 3.0 +/- 0.2 and 2.7 +/- 0.2 g Cm-2 during the first and second study years, respectively. The pine forest had the largest contribution to the landscape-level CO2 sink, -126 +/- 21 and -101 +/- 19 g C m(-2), and the fen to the CH4 emissions, 7.8 +/- 0.2 and 6.3 +/- 0.3 g C m(-2), during the first and second study years, respectively. The lakes within the area acted as CO2 and CH4 sources to the atmosphere throughout the measurement period, and a lake located downstream from the fen with organic sediment showed 4-fold fluxes compared to a mineral sediment lake. The annual C balances were affected most by the rainy peak growing season in 2017, the warm summer in 2018, and a heatwave and drought event in July 2018. The rainy period increased ecosystem respiration (ER) in the pine forest due to continuously high soil moisture content, and ER was on a level similar to the following, notably warmer, summer. A corresponding ER response to abundant precipitation was not observed for the fen ecosystem, which is adapted to high water table levels, and thus a higher ER sum was observed during the warm summer 2018. During the heat wave and drought period, similar responses were observed for all terrestrial ecosystems, with decreased gross primary productivity and net CO2 uptake, caused by the unfavourable growing conditions and plant stress due to the soil moisture and vapour pressure deficits. Additionally, the CH(4 )emissions from the fen decreased during and after the drought. However, the timing and duration of drought effects varied between the fen and forest ecosystems, as C fluxes were affected sooner and had a shorter post-drought recovery time in the fen than forest. The differing CO2 flux response to weather variations showed that terrestrial ecosystems can have a contrasting impact on the landscape-level C balance in a changing climate, even if they function similarly most of the time.
  • Le Thiec, D.; Manninen, S. (Elsevier SAS., 2003)
    The effects of ambient and elevated ozone (O3) levels on photosynthesis, growth, pigment, biomass and element contents of Aleppo pine (Pinus halepensis Mill.) were studied for two growing seasons (1997, 1998). Two-year-old seedlings were exposed to elevated O3 in open-top chambers. The treatments were charcoal-filtered air and non-filtered air + 50 nl l–1 O3 (24 h per day, 7 days per week). In summer 1998, half of the seedlings were drought-stressed (leaf water potential down to approximately –2 MPa), while the other half were kept well-watered. At the beginning of the season (1998), current (c) and previous-year (c + 1) needles under O3 stress showed an increase in stomatal conductance and net photosynthesis. During the drought period, only stomatal conductance increased in both needle age-classes, whereas the net photosynthesis decreased. At the end of the measuring period, both parameters were reduced in the O3 treatment. Both O3 and drought decreased chlorophyll a and b concentrations, growth and biomass.A carry-over effect of O3 on pigments was also observed. Needle K content was increased in the O3 treatment. Drought protected Aleppo pine against O3 (less chlorotic mottle and less decrease of stem and branch biomass).
  • Abera, Temesgen Alemayehu; Heiskanen, Janne Hermanni; Pellikka, Petri Kauko Emil; Maeda, Eduardo Eiji (2018)
    Climate–vegetation interaction can be perturbed by human activities through deforestation and natural extreme climatic events. These perturbations can affect the energy and water balance, exacerbating heat stress associated with droughts. Such phenomena are particularly relevant in the Horn of Africa, given its economic and social vulnerability to environmental changes. In this paper, we used 16-year time series (2001–2016) of remotely sensed environmental data with the objective of 1) clarifying how rainfall–vegetation interaction affects land surface temperature (LST) seasonality across the Horn of Africa, and 2) evaluating how this interaction affects LST anomalies during forest loss and drought events. Our results showed that vegetation seasonality follows rainfall modality patterns in 81% of the region. On the other hand, seasonality of daytime LST was negatively related to vegetation greenness patterns across ecoregions, and rainfall modality. LST varied more strongly in grasslands and shrublands than over other vegetation classes. Comparison of LST before and after forest loss in three selected areas (two in Ethiopia and one in Kenya) revealed an annual average increase in LST of 0.7 °C, 1.8 °C, and 0.2 °C after climate variability correction, respectively. The average increase in LST was relatively high and consistent during dry months (1.5 °C, 3 °C, and 0.6 °C). As expected, the rainfall anomalies during droughts (2010/2011, 2015, and 2016) were positively correlated with vegetation greenness anomalies. Nonetheless, the degree with which vegetation cover is affected by extreme rainfall events has a strong influence in regulating the impact of droughts on temperature anomalies. This highlights the importance of vegetation resilience and land cover management in regulating the impact of extreme events.
  • Sim, Thomas G.; Swindles, Graeme T.; Morris, Paul J.; Baird, Andy J.; V. Gallego-Sala, Angela; Wang, Yuwan; Blaauw, Maarten; Camill, Philip; Garneau, Michelle; Hardiman, Mark; Loisel, Julie; Väliranta, Minna; Anderson, Lysanna; Apolinarska, Karina; Augustijns, Femke; Aunina, Liene; Beaulne, Joannie; Bobek, Premysl; Borken, Werner; Broothaerts, Nils; Cui, Qiao-Yu; Davies, Marissa A.; Ejarque, Ana; Farrell, Michelle; Feeser, Ingo; Feurdean, Angelica; Fewster, Richard E.; Finkelstein, Sarah A.; Gaillard, Marie-Jose; Gaika, Mariusz; Heffernan, Liam; Hoevers, Renske; Jones, Miriam; Juselius-Rajamäki, Teemu; Karofeld, Edgar; Knorr, Klaus-Holger; Korhola, Atte; Kupriyanov, Dmitri; Kylander, Malin E.; Lacourse, Terri; Lamentowicz, Mariusz; Lavoie, Martin; Lemdahl, Geoffrey; Lucow, Dominika; Magnan, Gabriel; Maksims, Alekss; Mansilla, Claudia A.; Marcisz, Katarzyna; Marinova, Elena; Mathijssen, Paul J. H.; Mauquoy, Dmitri; Mazei, Yuri A.; Mazei, Natalia; McCarroll, Julia; McCulloch, Robert D.; Milner, Alice M.; Miras, Yannick; Mitchell, Fraser J. G.; Novenko, Elena; Pelletier, Nicolas; Peros, Matthew C.; Piilo, Sanna R.; Pilote, Louis-Martin; Primeau, Guillaume; Rius, Damien; Robin, Vincent; Robitaille, Mylene; Roland, Thomas P.; Ryberg, Eleonor; Sannel, A. Britta K.; Schittek, Karsten; Servera-Vives, Gabriel; Shotyk, William; Slowinski, Michal; Stivrins, Normunds; Swinnen, Ward; Thompson, Gareth; Tiunov, Alexei; Tsyganov, Andrey N.; Tuittila, Eeva-Stiina; Verstraeten, Gert; Wallenius, Tuomo; Webb, Julia; Willard, Debra; Yu, Zicheng; Zaccone, Claudio; Zhang, Hui (2023)
    Northern peatlands store globally-important amounts of carbon in the form of partly decomposed plant detritus. Drying associated with climate and land-use change may lead to increased fire frequency and severity in peatlands and the rapid loss of carbon to the atmosphere. However, our understanding of the patterns and drivers of peatland burning on an appropriate decadal to millennial timescale relies heavily on individual site-based reconstructions. For the first time, we synthesise peatland macrocharcoal re-cords from across North America, Europe, and Patagonia to reveal regional variation in peatland burning during the Holocene. We used an existing database of proximal sedimentary charcoal to represent regional burning trends in the wider landscape for each region. Long-term trends in peatland burning appear to be largely climate driven, with human activities likely having an increasing influence in the late Holocene. Warmer conditions during the Holocene Thermal Maximum (similar to 9e6 cal. ka BP) were associated with greater peatland burning in North America's Atlantic coast, southern Scandinavia and the Baltics, and Patagonia. Since the Little Ice Age, peatland burning has declined across North America and in some areas of Europe. This decline is mirrored by a decrease in wider landscape burning in some, but not all sub-regions, linked to fire-suppression policies, and landscape fragmentation caused by agricultural expansion. Peatlands demonstrate lower susceptibility to burning than the wider landscape in several instances, probably because of autogenic processes that maintain high levels of near-surface wetness even during drought. Nonetheless, widespread drying and degradation of peatlands, particularly in Europe, has likely increased their vulnerability to burning in recent centuries. Consequently, peatland restoration efforts are important to mitigate the risk of peatland fire under a changing climate. Finally, we make recommendations for future research to improve our understanding of the controls on peatland fires.(c) 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (
  • Liu, Miao; Korpelainen, Helena; Li, Chunyang (2022)
  • Xia, Zhichao; He, Yue; Xu, Jiahui; Zhu, Zuodong; Korpelainen, Helena; Li, Chunyang (2023)
    How sex-related root traits and soil microbes and their interactions respond to drought remains unclear. Here, we investigated how fine root traits and the composition of rhizosphere microbial communities in Populus euphratica females and males respond to drought in concert in 17-year-old plantations. Females increased specific root length (SRL) in response to drought. However, males showed no changes in their roots but significant increases in arbuscular mycorrhizal hyphal biomass and population of Gram-negative bacteria in the rhizosphere. Also, fungal symbiotroph communities associated with root systems in males differed from those in females under drought. We further demonstrated that the Gram-positive to Gram-negative bacteria ratios positively correlated with the SRL, while fungi to bacteria ratios were negatively correlated. Meanwhile, the relative abundance of symbiotrophs was negatively correlated with the SRL, while saprotroph abundance was positively correlated. Nevertheless, the relative abundance of symbiotrophs was positively correlated with the root carbon content (RCC). These findings indicate that microbial responses to drought depend highly upon the sex of the plant and microbial group and are related to root trait adjustments to drought. This discovery also highlights the role of plant-microbial interactions in the ecosystems of P. euphratica forest plantations.
  • Xia, Zhichao; He, Yue; Zhou, Bin; Korpelainen, Helena; Li, Chunyang (2020)
    Extensive research has shown that dioecious plants exhibit sexual dimorphism under extreme environments. However, sex-specific differences in responses to drought, phosphorus (P) shortage or their combination are less known. In our study, impacts of drought, P shortage and their combination on the performance of Populus cathayana males and females were investigated. Drought and P deficiency caused a greater negative impact on female growth than on male growth. P application ameliorated the more negative effect of drought on the shoot dry matter accumulation and P concentration in male leaves, while smaller effects were observed in females. The concentration of citrate in the rhizosphere of males was higher under drought combined with P application than under adequate water availability, and the increase was greater in males than in females. Males also showed a higher abundance of main soil microbial groups, including bacteria, actinomycetes, arbuscular mycorrhizal fungi (AMF), and Gram+ and Gram- bacteria in the rhizosphere, resulting in a more resistant microhabitat. In contrast, the abundance of bacteria and AMF was less in the rhizosphere of females exposed to stress conditions, while saprophytic fungi increased significantly. P enhanced drought resistance more in stress-resistant males but less in females under relatively severe drought stress. Increased drought resistance by P in males might be associated with greater plasticity in rhizosphere processes when compared with females.
  • Junttila, Samuli; Hölttä, Teemu; Puttonen, Eetu Severi; Katoh, Masato; Vastaranta, Mikko; Kaartinen, H.; Holopainen, Markus; Hyyppä, Hannu (2021)
    During the past decades, extreme events have become more prevalent and last longer, and as a result drought-induced plant mortality has increased globally. Timely information on plant water dynamics is essential for understanding and anticipating drought-induced plant mortality. Leaf water potential (Psi(L)), which is usually measured destructively, is the most common metric that has been used for decades for measuring water stress. Remote sensing methods have been developed to obtain information on water dynamics from trees and forested landscapes. However, the spatial and temporal resolutions of the existing methods have limited our understanding of the water dynamics and diurnal variation of Psi(L) within single trees. Thus, we investigated the capability of terrestrial laser scanning (TLS) intensity in observing diurnal variation in Psi(L) during a 50-h monitoring period. We aimed to improve the understanding on how large a part of the diurnal variation in Psi(L) can be captured using TLS intensity observations. We found that TLS intensity at the 905 nm wavelength measured from a static position was able to explain 77% of the variation in Psi(L) for three trees of two tree species with a root mean square error of 0.141 MPa. Based on our experiment with three trees, a time series of TLS intensity measurements can be used in detecting changes in Psi(L), and thus it is worthwhile to expand the investigations to cover a wider range of tree species and forests and further increase our understanding of plant water dynamics at wider spatial and temporal scales.
  • Khazaei, Hamid; Street, Kenneth; Bari, Abdallah; Mackay, Michael; Stoddard, Fred (2013)
    Efficient methods to explore plant agro-biodiversity for climate change adaptive traits are urgently required. The focused identification of germplasm strategy (FIGS) is one such approach. FIGS works on the premise that germplasm is likely to reflect the selection pressures of the environment in which it developed. Environmental parameters describing plant germplasm collection sites are used as selection criteria to improve the probability of uncovering useful variation. This study was designed to test the effectiveness of FIGS to search a large faba bean (Vicia faba L.) collection for traits related to drought adaptation. Two sets of faba bean accessions were created, one from moisture-limited environments, and the other from wetter sites. The two sets were grown under well watered conditions and leaf morpho-physiological traits related to plant water use were measured. Machine-learning algorithms split the accessions into two groups based on the evaluation data and the groups created by this process were compared to the original climate-based FIGS sets. The sets defined by trait data were in almost perfect agreement to the FIGS sets, demonstrating that ecotypic differentiation driven by moisture availability has occurred within the faba bean genepool. Leaflet and canopy temperature as well as relative water content contributed more than other traits to the discrimination between sets, indicating that their utility as drought-tolerance selection criteria for faba bean germplasm. This study supports the assertion that FIGS could be an effective tool to enhance the discovery of new genes for abiotic stress adaptation.
  • Pfeifer, Marion; Gonsamo, Alemu; Woodgate, William; Cayuela, Luis; Marshall, Andrew R.; Ledo, Alicia; Paine, Timothy C. E.; Marchant, Rob; Burt, Andrew; Calders, Kim; Courtney-Mustaphi, Colin; Cuni-Sanchez, Aida; Deere, Nicolas J.; Denu, Dereje; de Tanago, Jose Gonzalez; Hayward, Robin; Lau, Alvaro; Macia, Manuel J.; Olivier, Pieter I.; Pellikka, Petri; Seki, Hamidu; Shirima, Deo; Trevithick, Rebecca; Wedeux, Beatrice; Wheeler, Charlotte; Munishi, Pantaleo K. T.; Martin, Thomas; Mustari, Abdul; Platts, Philip J. (2018)
    Background: Canopy structure, defined by leaf area index (LAI), fractional vegetation cover (FCover) and fraction of absorbed photosynthetically active radiation (fAPAR), regulates a wide range of forest functions and ecosystem services. Spatially consistent field-measurements of canopy structure are however lacking, particularly for the tropics. Methods: Here, we introduce the Global LAI database: a global dataset of field-based canopy structure measurements spanning tropical forests in four continents (Africa, Asia, Australia and the Americas). We use these measurements to test for climate dependencies within and across continents, and to test for the potential of anthropogenic disturbance and forest protection to modulate those dependences. Results: Using data collected from 887 tropical forest plots, we show that maximum water deficit, defined across the most arid months of the year, is an important predictor of canopy structure, with all three canopy attributes declining significantly with increasing water deficit. Canopy attributes also increase with minimum temperature, and with the protection of forests according to both active (within protected areas) and passive measures (through topography). Once protection and continent effects are accounted for, other anthropogenic measures (e.g. human population) do not improve the model. Conclusions: We conclude that canopy structure in the tropics is primarily a consequence of forest adaptation to the maximum water deficits historically experienced within a given region. Climate change, and in particular changes in drought regimes may thus affect forest structure and function, but forest protection may offer some resilience against this effect.