Archive for the ‘Publications’ Category

PhytoSim was used to study crop load effects in peach trees

Monday, September 15th, 2014

On August 22th 2014 a paper was published which used a model, implemented in PhytoSim, to assess the effects of crop load on stem diameter variations and fruit growth of peach trees.

Reference:

De Swaef T., Mellisho C.D., Baert A., De Schepper V., Torrecillas A., Conejero W. and Steppe K. (2014) Model-assisted evaluation of crop load effects on stem diameter variations and fruit growth in peach. Trees.

http://link.springer.com/article/10.1007/s00468-014-1069-z

Abstract:

Stem diameter (D stem) variations have extensively been applied in optimisation strategies for plant-based irrigation scheduling in fruit trees. Two D stem derived water status indicators, maximum daily shrinkage (MDS) and daily growth rate (DGR), are however influenced by other factors such as crop load, making it difficult to unambiguously use these indicators in practical irrigation applications. Furthermore, crop load influences the growth of individual fruits, because of competition for assimilates. This paper aims to explain the effect of crop load on DGR, MDS and individual fruit growth in peach using a water and carbon transport model that includes simulation of stem diameter variations. This modelling approach enabled to relate differences in crop load to differences in xylem and phloem water potential components. As such, crop load effects on DGR were attributed to effects on the stem phloem turgor pressure. The effect of crop load on MDS could be explained by the plant water status, the phloem carbon concentration and the elasticity of the tissue. The influence on fruit growth could predominantly be explained by the effect on the early fruit growth stages.

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PhytoSim used to study stem diameter variation patterns in different mangrove species

Tuesday, September 9th, 2014

On February 16th 2014 a paper was published which used a model, implemented in PhytoSim, to study stem diameter variation patterns in different mangrove species.

Reference:

Vandegehuchte M.W., Guyot A., Hubeau M., De Swaef T., Lockington D.A. and Steppe K. (2014). Modelling reveals endogenous osmotic adaptation of storage tissuewater potential as an important driver determining different stem diameter variation patterns in the mangrove species Avicennia marina and Rhizophora stylosa. Annals of Botany, 114(4), 667-676.
http://aob.oxfordjournals.org/content/114/4/667.abstract.html?etoc

Abstract:

Background Stem diameter variations are mainly determined by the radial water transport between xylem and storage tissues. This radial transport results from the water potential difference between these tissues, which is influenced by both hydraulic and carbon related processes. Measurements have shown that when subjected to the same environmental conditions, the co-occurring mangrove species Avicennia marina and Rhizophora stylosa unexpectedly show a totally different pattern in daily stem diameter variation.

Methods Using in situ measurements of stem diameter variation, stem water potential and sap flow, a mechanistic flow and storage model based on the cohesion–tension theory was applied to assess the differences in osmotic storage water potential between Avicennia marina and Rhizophora stylosa.

Key results Both species, subjected to the same environmental conditions, showed a resembling daily pattern in simulated osmotic storage water potential. However, the osmotic storage water potential ofR. stylosa started to decrease slightly after that of A. marina in the morning and increased again slightly later in the evening. This small shift in osmotic storage water potential likely underlaid the marked differences in daily stem diameter variation pattern between the two species.

Conclusions The results show that in addition to environmental dynamics, endogenous changes in the osmotic storage water potential must be taken into account in order to accurately predict stem diameter variations, and hence growth.

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PhytoSim used to analyse the effect of mistletoe on Scots pine

Wednesday, July 3rd, 2013

on January 20th 2012 a paper was published that used a model, implemented in PhytoSim, to analyse the effect of mistletoe on Scots pine.

Reference:

Zweifel R., Bangerter S., Rigling A. and Sterck F.J. (2012). Pine and mistletoes: how to live with a leak in the water flow and storage system? Journal of Experimental Botany, 63(7), 2565-2578.
http://jxb.oxfordjournals.org/content/63/7/2565.abstract

Abstract:

The mistletoe, Viscum album, living on Scots pine (Pinus sylvestris) has been reported barely to regulate its transpiration and thus heavily to affect the gas exchange of its host. The extent of this mistletoe effect and its underlying mechanism has, so far, only been partially analysed. In this study, pine branches with different mistletoe infestation levels were investigated by sap flow gauges and analysed with a modelling approach to identify the mistletoe-induced stomatal regulation of pine and its consequences for the water and carbon balances of the tree. It was found that Viscum album barely regulates its stomata and that pines consequently compensate for the additional water loss of mistletoes by closing their own stomata. Despite the reduced stomatal aperture of the needles, the total water loss of branches with mistletoes increased. Furthermore, the increasingly closed stomata reduced carbon assimilation for the pine. Such a negative effect of the mistletoes on pine’s stomatal conductance and carbon gain was particularly strong during dry periods. Our study therefore suggests that mistletoe-induced stomatal closure is a successful mechanism against dying from hydraulic failure in the short term but increases the risk of carbon starvation in the long term. With the current conditions in Valais, Switzerland, a tree with more than about 10–20% of its total leaf area attributable to mistletoes is at the threshold of keeping a positive carbon balance. The currently increasing mistletoe abundance, due to increasing mean annual temperatures, is therefore accelerating the ongoing pine decline in many dry inner-Alpine valleys.

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PhytoSim used in sap flow research

Tuesday, October 2nd, 2012

In a recently published paper about a new sap flow measurement technique (Sapflow+) PhytoSim was used to develop, simulate and calibrate the Sapflow+ model. Besides that, the PhytoSim sensitivity and identifiability analysis was also used to determine if the heat velocity, volumetric heat capacity and thermal conductivities could be estimated from the measured data.

Reference:

Vandegehuchte M.W. and Steppe K. (2012). Sapflow+: a four-needle heat-pulse sap flow sensor enabling nonempirical sap flux density and water content measurements. New Phytologist, 196(1), 306-317. http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2012.04237.x/abstract

Abstract:

  • To our knowledge, to date, no nonempirical method exists to measure reverse, low or high sap flux density. Moreover, existing sap flow methods require destructive wood core measurements to determine sapwood water content, necessary to convert heat velocity to sap flux density, not only damaging the tree, but also neglecting seasonal variability in sapwood water content.
  • Here, we present a nonempirical heat-pulse-based method and coupled sensor which measure temperature changes around a linear heater in both axial and tangential directions after application of a heat pulse. By fitting the correct heat conduction–convection equation to the measured temperature profiles, the heat velocity and water content of the sapwood can be determined.
  • An identifiability analysis and validation tests on artificial and real stem segments of European beech (Fagus sylvatica L.) confirm the applicability of the method, leading to accurate determinations of heat velocity, water content and hence sap flux density.
  • The proposed method enables sap flux density measurements to be made across the entire natural occurring sap flux density range of woody plants. Moreover, the water content during low flows can be determined accurately, enabling a correct conversion from heat velocity to sap flux density without destructive core measurements.
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PhytoSim used in wood thermal diffusivity research

Tuesday, September 18th, 2012

A recently published paper on wood thermal diffusivity used PhytoSim to calibrate a theoretical model in order to determine both axial and tangential diffusivity in sapwood. The PhytoSim sensitivity and identifiability analysis was also used to better understand the model and learn which parameters most influenced the end-results.

Reference:

Vandegehuchte M.W. and Steppe K. (2012). A triple-probe heat-pulse method for measurement of thermal diffusivity in trees. Agricultural and Forest Meteorology, 160, 90–99.
http://www.sciencedirect.com/science/article/pii/S0168192312000998

Abstract:

Although thermal diffusivity is a crucial parameter for sap flow calculations in both the heat field deformation and the heat ratio method, it is seldom measured on a routine basis. This paper presents a theory based on thermodynamic principles to determine both axial and tangential diffusivity in sapwood. By measuring the temperature response after application of a heat pulse at a short axial and tangential distance from a line heater, axial and tangential thermal conductivity as well as volumetric heat capacity of the sapwood can be derived from a theoretical model. From these parameters, axial and tangential diffusivity can easily be determined. Sensitivity analysis and results of an experiment on European beech (Fagus sylvatica L.) confirm the applicability of the method. The obtained thermal diffusivities ranged from 2.7 × 10−7 m2 s−1 to 2.2 × 10−7 m2 s−1 for a relative water content (moisture per dry weight) ranging from 0.47 to 0.90, respectively. This was on average 22% lower than when applying the common methodology based on wood core sampling.

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PhytoSim used in leaf temperature modelling research

Tuesday, September 4th, 2012

A recently published paper on leaf temperature monitoring and modelling used PhytoSim as the main modelling and simulation software. The PhytoSim built-in sensitivity, identifiability and uncertainty analysis was used to help construct a model for online plant stress detection at the leaf level.

Reference:

Vermeulen K, Aerts J-M, Dekock J, Bleyaert P, Berckmans D, Steppe K. (2012). Automated leaf temperature monitoring of glasshouse tomato plants by using a leaf energy balance model. Computers and Electronics in Agriculture 87: 19–31. http://www.sciencedirect.com/science/article/pii/S0168169912001172

Abstract:

In order to detect biotic and abiotic stress at leaf level thermal indices based on leaf temperature measurements have been commonly used. The application of these indices within glasshouse crops is, however, restricted due to the specific humid conditions and the large spatial variability of irradiance and air temperature inside a glasshouse. In this study, a novel diagnostic algorithm is proposed as an alternative method to automatically monitor the leaf temperature of a glasshouse tomato crop based on the ecophysiological interactions between a leaf and its surrounding microclimate. Given that this algorithm is intended to be implemented as a software tool in glasshouse climate control systems, a critical overview of all relevant equations found in literature was first given. Next, the most appropriate equations were selected by using two objective criteria, i.e. the commonly used R2 and the less conventional Young Information Criterion, which also takes into account the complexity of an algorithm, so that the most feasible algorithm for automated monitoring purposes was built. Our results also showed that an in situ calibration of the selected algorithm was needed, for which a novel procedure was proposed. Once calibrated, this algorithm successfully simulated the leaf temperature of a well-watered tomato plant during several days given that the environmental conditions in its microclimate were accurately measured. Finally, the 95% confidence limits on the leaf temperature simulations provided the requested dynamic thresholds necessary for an effective automated monitoring tool. It was demonstrated that by using this novel diagnostic algorithm unexpected and likely harmful stomatal closure can be detected before visual signs of turgidity loss are observed.

 

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Phyto-IT co-authors a paper comparing several sap flow sensors

Friday, May 7th, 2010

A paper about the comparison of several sap flow sensors, co-authored by Dirk De Pauw (Phyto-IT), was published in Agriculture and Forest Meteorology. A laboratory test and field evaluation were conducted to determine the accuracy of the three commonly used techniques for measuring sap flux density in trees: heat pulse velocity, thermal dissipation and heat field deformation. In the laboratory test a constant flow rate of water was maintained through freshly cut stem segments of diffuse-porous Fagus grandifolia trees. The three sensor types were measured simultaneously and compared against gravimetric measurements. All three techniques substantially underestimated sap flux density. It is concluded that a species-specific calibration is necessary when using any of these techniques to insure that accurate estimates of sap flux density are obtained, at least until a physical basis for an error correction can be proposed.

Full reference details:

    Steppe K., De Pauw D.J.W., Doody T.M. and Teskey R.O. (2010). A comparison of sap flux density using thermal dissipation, heat pulse velocity and heat field deformation methodsAgricultural and Forest Meteorology150(7-8), 1046-1056. 
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Phyto-IT co-authors a paper on Sap Flow Tool

Wednesday, November 11th, 2009

A paper on the use of Phyto-IT’s Sap Flow Tool, co-authored by Dirk De Pauw (Phyto-IT), has been published. This work was presented at the 7th International Workshop on Sap Flow which which was held in Seville, Spain from October 21th-24th 2008. The paper deals with the measurement, calculation and analysis of radial sap flow profiles.

Full reference details:

    Steppe K., De Pauw D.J.W., Saveyn A., Tahon P., Nadezhdina N., Cermak J. and Lemeur R. (2009). Radial Sap Flux Profiles and Beyond: an Easy Software Analysis ToolActa Horticulturae846, 85-92. 
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Phyto-IT co-authors a paper on hydraulic redistribution

Wednesday, November 11th, 2009

A paper dealing with hydraulic redistribution in trees, co-authored by Dirk De Pauw (Phyto-IT), was published in New Phytologist. During a dry period, a 53-year-old Douglas-fir tree was subjected to localized irrigation on one side of the tree. This created heterogeneous soil water conditions which resulted in a stem-mediated hydraulic redistribution of the water to the other (non-irrigated) side of the tree. In addition, bidirectional flow in the dry root was also observed. This illustrates that water can simultaneously flow in opposite directions in the same part of a tree.

Full reference details:

    Nadezhdina N., Steppe K., De Pauw D.J.W., Bequet R., Cermak J. and Ceulemans R. (2009). Stem-mediated hydraulic redistribution in large roots on opposing sides of a Douglas-fir tree following localized irrigationNew Phytologist184(8), 932-943.
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Paper about on-line plant stress monitoring

Saturday, March 14th, 2009

A paper dealing with on-line plant stress monitoring, co-authored by Dirk De Pauw (Phyto-IT), was published today. Continuous monitoring of stem diameter variations combined with Unfold Principal Component Analysis (UPCA) allowed for successful on-line stress detection, days before the appearance of visible symptoms. The technique was applied successfully to two plant species: young apple trees and truss tomato plants.

Full reference details:

    Villez K., Steppe K. and De Pauw D.J.W. (2009). Use of Unfold PCA for on-line plant stress monitoring and sensor failure detectionBiosystems Engineering,103(1), 23-34. 
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