Leaf Water Relations in Lime Trees Grown under Shade Netting and Open-Air

Abstract

Physiological plant water status indicators are useful for managing precision irrigation in regions with limited water resources. The aim of this work was to evaluate the effect of shade netting on the diurnal and seasonal variations of several plant water status indicators in young lime trees (Citrus latifolia Tan., cv. Bearss), grown at the CEBAS-CSIC experimental station in Murcia, Spain. Stem water potential (Ψ stem ), leaf gas exchange (net photosynthesis (P n ) and stomatal conductance (g s )), and canopy temperature (T c ) were measured on representative days of winter and summer. The Ψ stem daily pattern was quite similar in both seasons under both conditions. However, the circadian rhythm of leaf gas exchange was affected by shade conditions, especially in summer, when shaded leaves showed maximum g s values for a longer time, allowing higher net photosynthesis (37%). Canopy temperature behaved similarly in both conditions, nevertheless, lower values were recorded in open-air than in shaded trees in the two seasons. The canopy-to-air temperature difference (T c − T a ), however, was lower in shaded trees during the daylight hours, indicating the higher degree of leaf cooling that was facilitated by high g s values. The possibility of continuously recording T c makes it (or the proposed canopy thermal index, CTI) a promising index for precise irrigation scheduling. Shade netting was seen to favour gas exchange, suggesting that it may be considered alternative to open-air for use in semi-arid areas threatened by climate change.Plants 2020, 9, 510 2 of 14 that integrates the soil and atmosphere water status, as well as measuring the physiological response to the water available in the soil. The most commonly used are the conventional, non-automated methods for measuring leaf or stem water potential, stomatal conductance or photosynthesis, and automated methods for measuring sap flow, canopy temperature, trunk diameter, or leaf turgor pressure [6]. Canopy temperature is one of the plant water status indicators that has recently become popular due to the development of infrared thermometry [6,7]. In the last few years, the use of canopy temperature for irrigation scheduling has been tested in several fruit tree crops, including cherry [8,9] avocado [10], almond [11], nectarine [12], peach [13] and also citrus trees such as lemon [14,15]. However, less information is available concerning lime.Shading, which aims to protect crops against abiotic stresses such as high air temperature or excessive solar radiation, is regarded as a good cropping technique to cope with climatic change. This is likely due to the net increases light scattering, thus reducing radiation and creating an optimal microclimate for crop development [16]. As several studies have pointed out [17,18], shaded conditions affect agrometeorological variables, such as relative humidity, wind velocity and canopy and soil temperatures. Additionally, changes in the microclimate can modify physiological water status indicators. Many authors have pointe...

Effects of Postharvest Water Deficits on the Physiological Behavior of Early-Maturing Nectarine Trees

“…Similarly, automated irrigation has been demonstrated as suitable efficient irrigation scheduling of early-maturing Prunus sp. trees [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. In plum trees, the automated system based on soil moisture sensors proposed by Millán et al [ 32 ] was able to establish a regulated deficit irrigation strategy based on 40% ETc.…”

“…Agro-meteorological conditions in the study area were typical for a Mediterranean climate with dry summers and mild–wet winters [ 17 , 39 ]. During the experimental period, rainfall amounted to 71 mm and ET 0 1017.6 mm ( Table 1 ).…”

“…Regarding plant water status, the T–C treatment showed an average Ψ stem value of about −0.80 MPa ( Figure 2 A), which is symptomatic of non-limiting soil water conditions in clay–loam soils [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 ]. In this sense, Abrisqueta et al [ 30 ] affirmed that a Ψ stem value above −0.9 MPa during the summer is an indicator of water stress initiation in early-maturing peach trees.…”

“…Plant physiological processes are directly affected by the amount of water that plants can extract from the soil [ 17 ]. Water stress limits plant growth and crop production more than any other environmental factor.…”

“…Previous studies have shown that continuous real-time measurements based on soil water content (θ v ) with capacitance probes indicated accurately the impact of different irrigation events on the stored soil water. This provided useful information concerning the advance of the wetted front, the depth of the root system activity, and the fate of the applied water [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. These θ v -based data allowed an optimal soil moisture range to be set for the crop.…”