Research Article Volume 2 Issue 3 - September 2016 Agri Res & Tech: Open Access J Copyright © All rights are reserved by E Kullaj Modeling Hydraulic Dynamics at Different Levels of Fruit Tree Canopies under Abiotic Stress E Kullaj 1 *, L Lepaja 1 , V Avdiu 2 and F Thomaj 1 1 Department of Horticulture and Landscape Architecture, Agricultural University of Tirana, Albania 2 Department of Fruit Trees and Viticulture, University of Pristina, Kosove Submission: August 06, 2016; Published: September 06, 2016 *Corresponding author: E Kullaj, Department of Horticulture and Landscape Architecture, Agricultural University of Tirana, Kodër-Kamëz, 1010, Albania. Introduction Fruit production provides an important contribution in the agricultural sector in Albania, providing about 20 percent of the total agriculture output. Apple is not only the main fruit produced in Albania, but its production has marked the highest growth by quadrupling between 1985 (18200 tons) and 2012 (71300 tons). Use of sap flow for either studying plant water relations or plant water use has received particular research and practical importance [1,2]. Various methods have been conceived attempting to increase the accuracy of measurement in a wide variety of species, organs and climatic or technological conditions. Climatic variables like solar radiation (Rs), air temperature (Ta), canopy temperature (Tc), vapour pressure difference (VPD) and reference evapotranspiration (ET0) drive or relate to sap flow. Solar radiation within the 400–700 nm wavebands (photosynthetic photon flux, PPF) drives the photosynthetic process, and global radiation (300–2500 nm waveband) provides the energy for transpiration activity [3]. The relationship is positive because increasing the radiation load on the leaf results in an increase in the dissipation of sensible heat and latent heat, even at constant levels of Ta and VPD [4-6]. Plant canopy geometry determines the spatial and temporal interaction between incoming radiation flux and foliage, and therefore plays a central role in quantifying the driving force for leaf physiological processes [7-10]. Effect of air temperature (and obviously canopy temperature) on SF is even higher and proportional. Varying levels of the latest influences relative humidity (RH) and consequently changes VPD altering the transpiration flow (and sap flow rates). Most these variables change significantly within fruit tree canopies and depending on the level of canopy, their effect on sap flow could be different [11]. The purpose of the research presented here was to unravel the relationship between sap flow and the above (micro) meteorological variables at various levels of a tree canopy to demonstrate which of them better predicts sap flow and at what respective canopy level. Models that predict sap flow and therefore transpiration have important applications in many areas including agricultural production, automated irrigation, tree ecophysiology, climate change, hydrology, etc. Agri Res & Tech: Open Access J 2(3): ARTOAJ.MS.ID.555586 (2016) 001 Abstract Tree canopy microclimate, influenced mainly by radiation, air temperature and wind affects both the vegetative and reproductive behaviour with a striking influence on both quantity and quality of production. The present study uses experimental data to model the xylem flows at various levels of canopy. The study was conducted on two commercial orchards with a central leader system from 2011 to 2012. Sap flow sensors based on SHB (stem heat balance) method were installed on shoots (10 - 12 mm) of five 8-years old trees of ‘Golden Delicious’ at different levels of the canopy (upper, middle, lower). Quantum sensors and infrared radiometers continuously measured PAR (photosynthetically active radiation) levels and canopy temperature at these three levels of the canopy. Stomata conductance was measured using a leaf porometer. A portable meteorological station measured meteorological variables enabling the calculation of VPD (vapour pressure deficit) and PET (potential evapotranspiration). Additionally, length, diameter TCSA (trunk cross-sectional area) and leaf area of shoots was measured too. The model was implemented in Mini32 software. A linear regression analysis was performed to study different regression models predicting the xylem flows based on measured environmental variables indicating which variable better predicts xylem flow at each canopy level. Results showed that xylem flows were better predicted by changes in ET (evapotranspiration) for the central and lower part of the canopy (R 2 = 0.95) while canopy temperature better predicted the flows of shoots at the upper part of the canopy (R 2 = 0.90). Keywords: Canopy; Apple; Sap flow; Transpiration