Browsing by Subject "water use efficiency"

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  • Belachew, Kiflemariam Y.; Nagel, Kerstin A.; Poorter, Hendrik; Stoddard, Frederick L. (2019)
    Water deficit may occur at any stage of plant growth, with any intensity and duration. Phenotypic acclimation and the mechanism of adaptation vary with the evolutionary background of germplasm accessions and their stage of growth. Faba bean is considered sensitive to various kinds of drought. Hence, we conducted a greenhouse experiment in rhizotrons under contrasting watering regimes to explore shoot and root traits and drought avoidance mechanisms in young faba bean plants. Eight accessions were investigated for shoot and root morphological and physiological responses in two watering conditions with four replications. Pre-germinated seedlings were transplanted into rhizotron boxes filled with either air-dried or moist peat. The water-limited plants received 50-ml water at transplanting and another 50-ml water 4 days later, then no water was given until the end of the experimental period, 24 days after transplanting. The well-watered plants received 100 ml of water every 12 h throughout the experimental period. Root, stem, and leaf dry mass, their mass fractions, their dry matter contents, apparent specific root length and density, stomatal conductance, SPAD value, and Fv/Fm were recorded. Water deficit resulted in 3–4-fold reductions in shoot biomass, root biomass, and stomatal conductance along with 1.2–1.4-fold increases in leaf and stem dry matter content and SPAD values. Total dry mass and apparent root length density showed accession by treatment interactions. Accessions DS70622, DS11320, and ILB938/2 shared relatively high values of total dry mass and low values of stomatal conductance under water deficit but differed in root distribution parameters. In both treatments, DS70622 was characterized by finer roots that were distributed in both depth and width, whereas DS11320 and ILB938/2 produced less densely growing, thicker roots. French accession Mélodie/2 was susceptible to drought in the vegetative phase, in contrast to previous results from the flowering phase, showing the importance of timing of drought stress on the measured response. Syrian accession DS70622 explored the maximum root volume and maintained its dry matter production, with the difference from the other accessions being particularly large in the water-limited treatment, so it is a valuable source of traits for avoiding transient drought.
  • Vesala, Timo; Sevanto, Sanna; Grönholm, Tiia; Salmon, Yann; Nikinmaa, Eero; Hari, Pertti; Hölttä, Teemu (2017)
    The pull of water from the soil to the leaves causes water in the transpiration stream to be under negative pressure decreasing the water potential below zero. The osmotic concentration also contributes to the decrease in leaf water potential but withmuch lesser extent. Thus, the surface tension force is approximately balanced by a force induced by negative water potential resulting in concavely curved water-air interfaces in leaves. The lowered water potential causes a reduction in the equilibrium water vapor pressure in internal (sub-stomatal/ intercellular) cavities in relation to that over water with the potential of zero, i.e., over the flat surface. The curved surface causes a reduction also in the equilibrium vapor pressure of dissolved CO2, thus enhancing its physical solubility to water. Although the water vapor reduction is acknowledged by plant physiologists its consequences for water vapor exchange at low water potential values have received very little attention. Consequences of the enhanced CO2 solubility to a leaf water-carbon budget have not been considered at all before this study. We use theoretical calculations and modeling to show how the reduction in the vapor pressures affects transpiration and carbon assimilation rates. Our results indicate that the reduction in vapor pressures of water and CO2 could enhance plant water use efficiency up to about 10% at a leaf water potential of -2 MPa, and much more when water potential decreases further. The low water potential allows for a direct stomatal water vapor uptake from the ambient air even at sub-100% relative humidity values. This alone could explain the observed rates of foliar water uptake by e.g., the coastal redwood in the fog belt region of coastal California provided the stomata are sufficiently open. The omission of the reduction in the water vapor pressure causes a bias in the estimates of the stomatal conductance and leaf internal CO2 concentration based on leaf gas exchange measurements. Manufactures of leaf gas exchange measurement systems should incorporate leaf water potentials in measurement set-ups.
  • Iso-Kokkila, Marijke (Helsingin yliopisto, 2020)
    Barley has been cultivated throughout the world for centuries. During that time, it has experienced different climatic conditions and selective pressure. The consecutive genetic variation gives us a valuable source to explore various components of yield and stress resilience. In this research field experiments were performed on 24 European barley cultivar and landrace genotypes, as well as laboratory experiments on 15 genotypes; 13 cultivated and 2 genetically modified genotypes. The aim of the field tests was to examine the genotypic variation in Finnish weather conditions during two growth seasons in Viikki and to find out how stomatal conductance differs between varieties and whether it can be connected to yield. The aim of the laboratory tests conducted in Tartu was to examine the genotypic variation in the ability of barley seedlings’ stomata to react to changes in environmental conditions with high vapor pressure deficit and abscisic acid treatment. The reason for this study is the ongoing climate change, which challenges breeders to create new resilient varieties for future climatic conditions. In addition to genomic data and genetic tools a wide variety of genotype data is needed to capture valuable traits that different varieties possess. The hypothesis of this study was to find differences in gas exchange, that could be useful considering breeding of resilient barley cultivars adapted to future climatic conditions. The tests conducted in field and laboratory conditions demonstrated, that genotypic variation could be found among here tested barley varieties. In the experiments we found several interesting cultivars, that could be tested further to verify their usefulness in breeding resilient barley cultivars for future climatic conditions.
  • Farzam, Neda (Helsingin yliopisto, 2015)
    This study provides the green (the share of rain water in crop production) and blue (the share of surface and groundwater in crop production) water footprint (WF) of four annual crops in Finland and five annual crops in Iran for the growing period 2007?2012. It aims to present more recent water footprint accounting on annual crops in this study. Due to the large scale water footprint accounting (country level), the calculation for grey water footprint was omitted from this study. The green and blue water footprints of barley, maize, oilseed rape, soybeans and wheat for Iran and barley, oats, oilseed rape, and wheat for Finland were calculated over the annual growing period 2007 to 2012. Crops were selected upon the availability of crop production in each country. WF values were estimated based on crop water use (CWU) and crop yield, where CWU was estimated upon the accumulative ET over the growing season of the crops. For daily evapotranspiration values AQUACROP model was used. For running the AQUACROP model, different parameters were needed such as climatic parameters (including minimum and maximum temperature, rainfall and potential evapotranspiration), soil type, land management, irrigation practice, groundwater and initial condition for sowing, sowing and harvesting dates. This data were mined from databases. Due to the fact that crop production in Finland is rain-fed, only green WF of the selected crops were calculated for Finland. In Finland oilseed rape had the highest average green water footprint per ton of production, which was 2471 m^3 t¯¹yr¯^1 and it was followed by oats (1036 m^3 t¯¹yr¯^1), wheat (944? m?^3 t¯¹yr¯^1), and barley (838? m?^3 t¯¹yr¯^1). Considering the annual crop production, the average total green water footprint of selected crops was 3669 Mm^3 yr¯^1 in Finland. Water saving through crop trade was estimated -294 Mm^3 yr¯^1. The negative saving water amount showed the virtual water loss through crop trade of selected crops in Finland. The highest export crop in Finland was oats during 2007?2012. In Iran the major share of annual crop production comes from irrigated crop lands and that shows the importance of blue water footprint accounting beside green water footprint. The sum of green and blue water footprints of the growing crops in Iran was considered as water footprint of the crops. Water footprint per ton of crops in Iran increased from maize (696 m^3 t¯¹yr¯^1), wheat (1235 m^3 t¯¹yr¯^1), barley (1350 m^3 t¯¹yr¯^1), soybeans (2210 m^3 t¯¹yr¯^1) to oilseed rape (3503 m^3 t¯¹yr¯^1). Total average water footprint of the selected crops in Iran considering their production in the country was estimated 22816? Mm?^3 yr¯^1. Regarding the crop trade balances in Iran, the country saved 8902? Mm?^3 yr¯^1 water by importing the crops. Wheat was the major import crop during 2007?2012. WF can be a strong tool for assessing the consumptive water use of the agricultural systems in place and time according to different agricultural and water managements. It can bring a ground for comparing the production sites for certain crops or products considering the lower WF of the produced items. This study aimed at producing recent calculations of water footprint of crops in Finland and Iran, using local data.
  • Gao, Yao (2016)
    Finnish Meteorological Institute Contributions 124
    Interactions between the land surface and climate are complex as a range of physical, chemical and biological processes take place. Changes in the land surface or the climate can affect the water, energy and carbon cycles in the Earth system. This thesis discusses a number of critical issues that concern land-atmospheric interactions in the boreal zone, which is characterised by vast areas of peatlands, extensive boreal forests and a long snow cover period. Regional climate modelling and land surface modelling were used as the main tools for this study, in conjunction with observational data for evaluation. First, to better describe the present-day land cover in the regional climate model, we introduced an up-to-date and high-resolution land cover map to replace the inaccurate and outdated default land cover map for Fennoscandia. Second, in order to provide background information for future forest anagement actions for climate change mitigation, we studied the biogeophysical effects on the regional climate of peatland forestation, which has been the dominant land cover change in Finland over the last century. Moreover, climate variability can influence the land surface. Although drought is uncommon in northern Europe, an extreme drought occurred in the summer of 2006 in Finland, and induced visible drought symptoms in boreal forests. Thus, we assessed a set of drought indicators with drought impact data in boreal forests in Finland to indicate summer drought in boreal forests. Finally, the impacts of summer drought on water use efficiency of boreal Scots pine forests were studied to gain a deeper understanding of carbon and water dynamics in boreal forest ecosystems. In summary, the key findings of this thesis include: 1) the updated land cover map led to a slight decrease in biases of the simulated climate conditions. It is expected that the model performance could be improved by further development in model physics. 2) Peatland forestation in Finland can induce a warming effect in the spring of up to 0.43 K and a slight cooling effect in the growing season of less than 0.1 K due to decreased surface albedo and increased evapotranspiration, respectively. Corresponding to spring warming, the snow clearance day was advanced by up to 5 days over a 15-year mean. 3) The soil moisture index SMI was the most capable of the assessed drought indicators in capturing the spatial extent of observed forest damage induced by the extreme drought in 2006 in Finland. Thus, a land surface model capable of reliable predictions of regional soil moisture is important in future drought predictions in the boreal zone. 4) The inherent water use efficiency (IWUE) showed an increase during drought at the ecosystem level, and IWUE was found to be more appropriate than the ecosystem water use efficiency (EWUE) in indicating the impacts of drought on ecosystem functioning. The combined effects of soil moisture drought and atmospheric drought on stomatal conductance have to be taken into account in land surface models at the global scale when simulating the drought effects on plant functioning.