Trunk Diameter Variation Research Articles

Relating microtensiometer-based trunk water potential with sap flow, canopy temperature, and trunk and fruit diameter variations for irrigated ‘Honeycrisp’ apple

Instrumentation plays a key role in modern horticulture. Thus, the microtensiomenter, a new plant-based sensor that continuously monitors trunk water potential (Ψtrunk) can help in irrigation management decisions. To compare the response of the Ψtrunk with other continuous tree water status indicators such as the sap flow rate, the difference between canopy and air temperatures, or the variations of the trunk and fruit diameter, all the sensors were installed in 2022 in a commercial orchard of ‘Honeycrisp’ apple trees with M.9 rootstocks in Washinton State (USA). From the daily evolution of the Ψtrunk, five indicators were considered: predawn, midday, minimum, daily mean, and daily range (the difference between the daily maximum and minimum values). The daily range of Ψtrunk was the most linked to the maximum daily shrinkage (MDS; R2 = 0.42), the canopy-to-air temperature (Tc-Ta; R2 = 0.32), and the sap flow rate (SF; R2 = 0.30). On the other hand, the relative fruit growth rate (FRGR) was more related to the minimum Ψtrunk (R2 = 0.33) and the daily mean Ψtrunk (R2 = 0.32) than to the daily range of Ψtrunk. All indicators derived from Ψtrunk identified changes in tree water status after each irrigation event and had low coefficients of variation and high sensitivity. These results encourage Ψtrunk as a promising candidate for continuous monitoring of tree water status, however, more research is needed to better relate these measures with other widely studied plant-based indicators and identify good combinations of sensors and threshold values.

Development and application of an inexpensive open-source dendrometer for detecting xylem water potential and radial stem growth at high spatial and temporal resolution.

There is currently a need for inexpensive, continuous, non-destructive water potential measurements at high temporal resolution (<1min). We describe here the development and testing of an entirely open-source dendrometer that, when combined with periodic Scholander pressure chamber measurements, provides sub-minute resolution estimates of water potential when placed on tissues exhibiting little or no secondary growth (petioles, monocotyledon stems). The dendrometer can also be used to measure radial growth of stems and branches when placed on dicotyledon and gymnosperm species. The dendrometer can be interfaced directly with a computer in real time in the lab or greenhouse, or connected to a datalogger for long periods of use in the field on batteries. We tested this device on a herbaceous dicotyledon (Helianthus annuus) (petioles and stems) and a monocotyledon (Zea mays) species (stems) for 1 week during dehydration and re-watering treatments under laboratory conditions. We also demonstrated the ability of the device to record branch and trunk diameter variation of a woody dicotyledon (Rhus typhina) in the field. Under laboratory conditions, we compared our device (hereafter 'contact' dendrometer) with modified versions of another open-source dendrometer (the 'optical' dendrometer). Overall, contact and optical dendrometers were well aligned with one another, with Pearson correlation coefficients ranging from 0.77 to 0.97. Both dendrometer devices were well aligned with direct measurements of xylem water potential, with calibration curves exhibiting significant non-linearity, especially at water potentials near the point of incipient plasmolysis, with pseudo R2 values (Efron) ranging from 0.89 to 0.99. Overall, both dendrometers were comparable and provided sufficient resolution to detect subtle differences in stem water potential (ca. 50 kPa) resulting from light-induced changes in transpiration, vapour pressure deficit and drying/wetting soils. All hardware designs, alternative configurations, software and build instructions for the contact dendrometers are provided.

Physiological and Structural Responses to Prolonged Water Deficit in Young Trees of Two Olive Cultivars.

This study aimed to characterize the physiological and structural responses of potted one-year-old olive trees belonging to two olive cultivars—‘Nocellara del Belice’ and ‘Cerasuola’—exposed to prolonged drought under greenhouse conditions. Two irrigation treatments based on evapotranspiration (ET) were imposed for 69 days, i.e., well-watered (WW, 100% ET) and drought-stressed (DS, 10–30% ET). Leaf stomatal conductance (gs), stem water potential (Ψstem), transpiration (E), photosynthetic capacity (Amax), water use efficiency (WUE), stem (Kstem) and root (Kroot) hydraulic conductance, trunk diameter variations (TDV), and leaf patch attenuated pressure fluctuations (pp, a proxy of the inverse of leaf turgor pressure) were measured in WW and DS trees at different stages of the experiment. Leaf gs did not significantly differ between cultivars under DS, whereas differences in Ψstem only became significant at the end of prolonged drought, when ‘Nocellara del Belice’ experienced Ψstem < −4 MPa. ‘Cerasuola’ trees expressed the best WUE under drought, although they were more susceptible to photoinhibition under optimal plant water status. Both cultivars tended to increase their Kstem at the end of the drought period. A marked reduction in Kroot occurred in ‘Cerasuola’ plants after prolonged drought; however, a similar mechanism was not observed in ‘Nocellara del Belice’. The ratio between Kstem and Kroot exponentially increased towards the end of the prolonged drought period in both cultivars, but more markedly in ‘Cerasuola’. TDV and pp trends suggested that ‘Cerasuola’ plants keep better plant water status under severe drought compared to ‘Nocellara del Belice’ by maintaining high leaf turgor and reduced trunk diameter fluctuations. These responses may be related to reduced cell wall elasticity and xylem vessel size and/or wall thickness—drought avoidance mechanisms. The Kstem/Kroot ratio can serve as an indicator of drought stress avoidance mechanisms to compare genotype-specific responses to drought stress.

Detecting tree water stress using a trunk relative water content measurement sensor

Irrigation water management in tree crops requires timely and accurate determination of crop water status for making irrigation scheduling decisions. However, commonly used techniques for measuring tree water statuses, such as stem water potential measured with pressure chambers or leaf stomatal conductance measured with porometers, are manually operated and lack the timeliness for making irrigation decisions in real-time. The objective of this research was to develop and field test a new electronic sensor system capable of continuously monitoring tree trunk relative water content. Replicated sensors were installed in experimental orchards planted with pomegranate and nectarine trees. Data collected from the sensor readings were compared with periodic trunk diameter, stem water potential, and leaf stomatal conductance measurements. Strong linear correlations were observed between sensor readings and tree trunk diameter variations but with a 3–4-hour phase lag. Sensor readings were also strongly correlated to stem water potential (R2 = 0.58-0.85) and leaf stomatal conductance (R2 = 0.60-0.84) for both pomegranate and nectarine trees. The next step is to further validate the sensors in commercial orchards and apply the sensors for making real-time irrigation water management decisions.

Axial pulmonary trunk diameter variations during the cardiac cycle.

Previous studies have shown a correlation between axial pulmonary trunk diameter (PTD) on chest computed tomography (CT) and pulmonary artery pressure. However, it is not known whether the PTD slices measured on chest CT have been recorded during the systolic or diastolic phase. The aim of this study was to demonstrate the variations in PTD during the cardiac cycle by measuring coronary CT angiography (CCTA) images. A retrospective analysis was made of 101 patients who underwent CCTA for coronary artery disease assessment. CCTA images were reconstructed during a full cardiac cycle and measurements were taken of the systolic and diastolic PTD and ascending aorta diameter (AAD) from the same slice by two independent observers. Inter-observer agreement wasexcellent (intraclass correlation coefficient = 0.99) for all CT measurements. The mean systolic PTD of all patients was 26.3 ± 3.6mm and the mean diastolic PTD was 22.8 ± 3.2mm (p < 0.001). The mean difference between systole and diastole was found to be 3.5 ± 1.2mm for PTD, 1.2 ± 0.7mm for AAD, and 0.1 ± 0.04 for the PTD/AAD ratio (p values < 0.001). There was no statistical significance of PTD variations according to gender, age, height, weight, body mass index, and body surface area. When an increased PTD is detected in a chest CT compared to normal limits or a previous CT scan, this may be the result of the variation in PTD due to the cardiac cycle.

Irrigation of ‘Hass’ avocado: effects of constant vs. temporary water stress

The main objectives of the present study were to assess the water demand for heavy fruit load of ‘Hass’ avocado throughout the growth periods and to investigate the effects of deficit irrigation during sensitive phenological phases on yield. The experimental set-up allowed the comparison between trees responses to three irrigation strategies during the entire growth period (no water stress; excessive irrigation; constant water stress) as well as the comparison between regulated deficit irrigation (RDI) managements applied during the early or the late growth period. The yield of no water stress treatments during three experimental years was very high (25–31 t ha−1) while the yields of water-stressed trees were significantly lower (16–21 t ha−1). More importantly, the yield of no water stress trees was not susceptible to alternate bearing while the yield of water-stressed trees was considerably reduced during off-crop years. Irrigation rates and the actual evapotranspiration coefficient KL = ET/ET0 for the no water stress treatment may serve as a reasonable guide for irrigation management. Fruit load should be taken into account while planning irrigation and fertilization management and plant-based methods should be used for controlling the irrigation management (scheduling and quantities). Analyses of trunk diameter variation data that lead to evaluation of trunk growth rate and maximum daily shrinkage reflect phenological stages and periodicity of shoot, fruit and root growth, and also may provide an integrative, “holistic viewpoint” of overall tree status.

Design, fabrication and testing of a low cost Trunk Diameter Variation (TDV) measurement system based on an ATmega 328/P microcontroller

A fast-responding inexpensive dendrometer is needed for measuring daily or hourly plant growth responses to water stress. This study reports on a low-cost microcontroller driven Trunk Diameter Variations (TDV) measurement system that was designed and constructed for automating the measurement and recording of plant stem diameter. The TDV system comprises of an ATmega 328/P microcontroller, which forms the heart of the controlling circuit, a real time clock for time stamping measurements, liquid crystal display for displaying purposes and an external secure digital card and shield for storing measured data. The stem diameter variations are measured by a caliper-type sensor based on a full bridge strain gauge that is attached to a flexible arm of mild steel. When bearing bending strain, the excited full bridge strain gauge outputs a voltage directly proportional to the bending strain, hence linear displacement. The TDV sensor displacement calibration procedure was carried out using an inside micrometer from a calibration kit. The calibration of the sensor indicated a linear relationship between the displacement and the sensor’s output voltage with a high coefficient of determination value of 0.998, calibration multiplier of 0.426 mm V−1 and an offset output voltage of 0.688 V. The TDV sensor was mounted on a smooth cylindrical dried wood away from direct sunlight and rain while air temperature was measured close to the TDV installation. Temperature sensitivity test results show that the accuracy of the sensor above 20 °C is 0.031 mm and for temperatures below 20 °C the accuracy is above 0.050 mm. The TDV system was tested on a tomato plant for 42 days, Fountain tree for three weeks and on a Citrus tree for one week under greenhouse and open-field conditions in order to evaluate its performance and suitability under different plant species and climatic conditions. The TDV system proved to be robust and produced valid results on the plant’s physiological measurements, with a good storage of the measured data over the experimental period. We concluded that the TDV system is suitable for stem diameter variations measurements and water and fertilizer stress monitoring on herbaceous and woody stem plants due to its fast response (hourly or less), ease of construction and installation, and low cost (<US$60).

Stomatal oscillations in olive trees: analysis and methodological implications.

Stomatal oscillations have long been disregarded in the literature despite the fact that the phenomenon has been described for a variety of plant species. This study aims to characterize the occurrence of oscillations in olive trees (Olea europaea L.) under different growing conditions and its methodological implications. Three experiments with young potted olives and one with large field-grown trees were performed. Sap flow measurements were always used to monitor the occurrence of oscillations, with additional determinations of trunk diameter variations and leaf-level stomatal conductance, photosynthesis and water potential also conducted in some cases. Strong oscillations with periods of 30-60 min were generally observed for young trees, while large field trees rarely showed significant oscillations. Severe water stress led to the disappearance of oscillations, but moderate water deficits occasionally promoted them. Simultaneous oscillations were also found for leaf stomatal conductance, leaf photosynthesis and trunk diameter, with the former presenting the highest amplitudes. The strong oscillations found in young potted olive trees preclude the use of infrequent measurements of stomatal conductance and related variables to characterize differences between trees of different cultivars or subjected to different experimental treatments. Under these circumstances, our results suggest that reliable estimates could be obtained using measurement intervals below 15 min.

Financial assessment of adopting irrigation technology for plant-based regulated deficit irrigation scheduling in super high-density olive orchards

Hedgerow orchards with high plant densities, or super high-density (SHD) orchards, are considered to be amongst the most profitable management systems for most fruit-tree species. Regulated deficit irrigation (RDI) strategies are recommended for SHD olive orchards, especially when scheduled from automatic and continuous measurements of plant water stress. There is a lack of information, however, on the profitability of this approach. In this work we analysed the financial feasibility of using three different systems for monitoring water stress in an ‘Arbequina’ SHD olive orchard under a RDI strategy recommended for the experimental area (SW Spain). The systems were based on sap flow (SF), trunk diameter variation (TDV) and leaf turgor pressure (TP) related measurements. We first compared their equivalent annual cost (EAC), resulting the TP based technology as that with the greatest potential to be adopted by farmers. We then used Discounted Cash Flow Analysis (DCFA) to compare the financial feasibility of an RDI treatment scheduled from TP related measurements and providing 45% of the crop water needs (45RDITP) with both a similar treatment but scheduled with the crop coefficient approach (45RDICC) and a fully irrigated (FI) treatment. Our results from two irrigation seasons demonstrated that the 45RDI strategy guarantees the profitability of SHD olive orchards in the long-term, with both 45RDICC and 45RDITP showing positive Net Present Value and Internal Rate of Return above the interest on capital. All the financial indicators suggested higher financial performance of 45RDITP as compared to 45RDICC, but differences were not significant, likely because of the high variability among replicates. The financial impact of Common Agricultural Policy payments as well as varying olive oil and irrigation water prices on the irrigation treatments was discussed.

Responses of several soil and plant indicators to post-harvest regulated deficit irrigation in olive trees and their potential for irrigation scheduling

The response of olive trees to deficit irrigation during post-harvest has been little evaluated because low rainfall often precludes the need to irrigate at this phenological stage in the Mediterranean Basin where olive is mostly cultivated. In many growing areas of Argentina, the lower latitude and continental climate leads to harvesting table olives in mid-summer when evapotranspiration is still high and rainfall is low. We assessed the responses of soil moisture and several plant-based indicators to post-harvest regulated deficit irrigation (RDI) in two growing seasons in order to: 1) determine the responses of the indicators to a range of irrigation levels; 2) elucidate the relationships between the different soil and plant variables; and 3) evaluate the appropriateness of the indicators for scheduling irrigation. Three RDI treatments (66, 33, 0% crop evapotranspiration; ETc) and a control (100% ETc) were applied for 75days from mid-summer to mid-fall in a cv. ‘Manzanilla fina’ orchard during 2009 and 2010. The treatments received irrigation equivalent to the control during the rest of the season. Soil relative extractable water (REW%), midday stem water potential (Ψs), leaf conductance (gl), sap flow, and trunk diameter variations were the variables evaluated. The RDI treatments generated a wide range of REW values (0–125%) with all of the plant indicators being affected to some degree. Midday stem water potential increased linearly with REW until it reached a break point at 48% REW, above which Ψs maintained a plateau at −1.75MPa. The increase in maximum trunk diameter (MXTD) showed strong relationships with REW, Ψs, and gl. Trunk growth rate (TGR) showed a very early response to water-withholding in both seasons, and trunk growth decreased along with Ψs until it reached a constant negative growth rate of −12μmd−1at a Ψs of −2.7MPa. Trunk maximum daily shrinkage was much less responsive to irrigation than either MXTD or TGR. Our results during post-harvest RDI in an arid region suggest that automated soil moisture sensors can be used to schedule irrigation at different water stress levels if reliable soil moisture values can be measured, and indicate that a continuous recording of trunk diameter has sufficient enough potential for irrigation scheduling that further investigation of MXTD and TGR is warranted.

Using sap flow measurements to estimate net assimilation in olive trees under different irrigation regimes

The measurement of bulk net assimilation (A) in fruit tree species is hindered by the need for sophisticated and complex instrumentation. The aim of this study is to present a simple alternative for estimating A from sap flow measurements and meteorological records. The proposed method was tested in a mature hedgerow olive orchard of 22.2 ha. Within the orchard, an irrigation experiment was established in a small plot including three treatments: a full irrigated control (CI), regulated deficit irrigation (DI) and a treatment mimicking customary orchard irrigation management (FI). Determinations of sap flow, water potential (Ψ) and trunk diameter variations (TDV) were conducted in the three treatments for 3 years. Also, measurements of net ecosystem exchange (NEE) were performed with an eddy covariance system in the centre of the orchard for the first season. The validity of the method was supported by the fact that estimates of A were consistent with both the measured values of NEE and published data regarding the same species under similar environmental and management conditions. Also, differences in A between irrigation treatments were generally in agreement with irrigation applied, transpiration (E p ), Ψ and TDV. It is concluded that the proposed sap flow-based method represents a user-friendly approach to estimate A at the canopy level with potential to study the effects of DI on biomass accumulation.

BEHAVIOUR OF APPLE CULTIVARS UNDER A HIGH RADIATION AND TEMPERATURE REGIME OF WESTERN PLAIN IN ALBANIA

Due to a high market demand, apple cultivation in Albania is spreading outside its typical and optimal cultivation area, towards the warm, semi-arid coastal areas, benefiting from the advantages of earliness and closeness to the main markets. Planting of several cultivars in the same orchard requires accurate tuning of the irrigation regime based on water use efficiency (WUE) principles. The object of this study was to assess the behavior of these cultivars under a cultivation regime with high radiation and temperatures for a more accurate determination of irrigation needs in the orchard. The study was conducted in the area of Lushnja during 2011 in a commercial orchard of 2.5 ha, trained as central and being in its 6th year. Measurements included flow based at both branch and trunk level as well as trunk diameter variation (TDV) using dendrometers placed at the trunk and at the central leader. Gypsum block sensors were used to measure soil water potential at different depths while a portable meteorological station measured global radiation, temperature and relative humidity. Potential evapotranspiration (PET) and vapour pressure deficit (VPD) were calculated using a model implemented in Mini32 software. Trees were subjected to a gradually increasing water stress. Biometric measurements of canopy elements like vegetative versus reproductive shoot ratio, branch diameter and length, rootstock and trunk diameter, affinity index were also measured and analyzed. Maximum values of PET varied between 0,8-0,9 mm/h during the entire measurement period. Sap flow (SF) values changed significantly between cultivars and were strongly correlated with global radiation and VPD. The trunk sensor values integrated well the transpiration of the entire tree and were correlated with the values of shoots. Due to their vigorous growth, the cultivars Red Delicious and to some degree also Golden Delicious showed higher levels of transpiration. The comparison of SF values under low and high SWP showed that Pink Lady on M9 is more sensitive to soil water availability.

Usefulness of stem dendrometers as continuous indicator of loquat trees water status

Postharvest regulated deficit irrigation (RDI) is an effective strategy to hasten flowering and harvest in loquat (Eriobotrya japonica Lindl.) trees, which in the Mediterranean countries has been related to an increase in the economic return. The success of an RDI strategy, however, depends on the duration and severity of the water stress reached by the trees. When RDI is applied, then, it is important to regularly monitor the plant water status. The measurement of the trunk diameter variations by means of stem dendrometers, which can be automated to remotely determine the plant water status, is a proven method for many fruit trees. In loquat, however, its use has not been yet assessed. In this experiment performed in a loquat orchard planted with the cv. ‘Cardona’ during the summer of 2009, the suitability of using stem dendrometers to detect plant water stress was assessed by taking measurements in fully irrigated and trees subjected to a drought cycle of 47 days. Results showed that at the beginning of the drought cycle period there was an increase in the maximum daily trunk shrinkage (MDS) in non-irrigated trees even before that clear differences in stem water potential (Ψs) could be detected between treatments. However, when plant water stress became more severe (Ψs lower than −1.4MPa), MDS did not increase further. The maximum trunk diameter (MXTD) evolution in control trees showed a steadily increase in trunk growth during the whole experimental period. In non-irrigated trees, however, MXTD remained stable until the end of the treatment when irrigation was resumed. The Ψs was the most sensitive indicator to water stress due to its very low tree-to-tree variability in comparison with the other indicators. Overall results show that trunk diameter variations have some limitations to monitor plant water status in loquat RDI orchards and therefore new alternatives should be explored.

Sustainable management of limited water resources in a young orange orchard

In the study, deficit irrigation (DI) strategies were imposed on a young orange orchard in Sicily (Southern Italy) with the aim to monitor and analyze crop physiological features, first yield and fruit quality data for possible negative effects. The orchard includes trees irrigated with drip and sub-drip irrigation systems. Irrigation strategies, based on DI concepts, including regulated deficit irrigation (RDI) and partial root-zone drying (PRD), were adopted during the irrigation seasons 2011 and 2012, each supplying different percentages of the crop evapotranspiration (ETc). Several physiological indices indicative of plant water status were analyzed during the trial, including, stem water potential, stomatal conductance, canopy temperature, trunk diameter variations, leaf area index (LAI). The imposed DI strategies allowed maximum water saving of 41% (PRD treatment), without conditioning the first yield data. Fruit composition resulted positively affected by water restrictions. The impact of the imposed deficit on trees depends mainly on its degree of severity (i.e. lowering of stem water potential above the threshold of −1.3MPa for citrus orchards). A certain growth reduction was observed in DI treatments causing WUE (plant water use efficiency) increase, in terms of reducing competition between vegetative and reproductive growth. Subsurface drip irrigation system, designed for supplying 75% of ETc allowed plant water status, yield and quality data quite comparable with those obtained in the control treatment, supplying 100% of ETc by surface drip irrigation systems. Overall, the obtained results show that the studied DI strategies were successfully applied in a young orange orchard allowing water saving without significant detrimental effect on trees.

Combined effect of irrigation regime and fruit load on the patterns of trunk-diameter variation of ‘Hass’ avocado at different phenological periods

The objective was to investigate the combined effect of irrigation regime and fruit load on trunk-diameter variation patterns of ‘Hass’ avocado trees grown in lysimeters, at different phenological periods. Plant water uptake of both fruited and defruited trees was monitored at high temporal resolution during successive growth stages. The trunk growth rate (TGR) during all the experiments was not affected by the irrigation treatments, yet daily TGR fluctuated significantly during the season, probably in association with periodic changes in the priority of partitioning of carbohydrates between reproductive and vegetative plant organs, i.e., flushes of shoot or root growth. Fruit load clearly played a dominant role in determining TGR, very likely because of the dramatic effect of fruit load on stomatal conductance and leaf carbohydrate concentration and, therefore, on the overall availability of assimilates. Thus, analyses of trunk diameter variation (TDV) data that lead to evaluation of TGR and maximum trunk diameter variation (MTDV) reflect phenological stages and periodicity of shoot, fruit and root growth, and also may provide an integrative, “holistic viewpoint” of overall tree status.The observed high dependency between the MTDV and irrigation treatments may indicate that MTDV actually depends on water-stress history rather than on the actual plant-water status. Thus, MTDV cannot be used on an absolute basis for irrigation management control. On the other hand, it may be a very efficient aid to control irrigation when used on a relative basis, after identifying the impacts of local phenological and environmental factors on the MTDV. Furthermore, the immediate MTDV response to accidental faults may illustrate the advantages of using dendrometer devices for remotely controlling irrigation systems.

Influence of different cultivars–locations on maximum daily shrinkage indicators: Limits to the reference baseline approach

The use of biosensors for irrigation scheduling is an interesting way to improve water use efficiency. Trunk diameter variations (TDV) have been studied in several species as a biosensor capable of detecting water stress. The most frequently used parameter for this purpose from TDV is maximum daily shrinkage (MDS). In the present study, MDS was studied in olive trees in two locations in Spain (Badajoz and Ciudad Real), with different cultivars in each one (‘Morisca’ in Badajoz and ‘Cornicabra’ in Ciudad Real), for three years in one location and four years in the other. In order to establish a reference baseline for both locations the relationship between vapour pressure deficit (VPD) and MDS was calculated. Four irrigation treatments were used: one control, irrigated by the FAO method, two in relation to stem water potential threshold and one based on both the trunk growth and MDS from linear variable differential transducers (LVDT). Heteroscedasticity was found in MDS data, so the transformation of the square root (SQR) of the data was necessary be done. The reference baseline with SQR of MDS vs VPD was significantly different between varieties/locations. A local calculation is thus needed to obtain an accurate reference baseline. The relationship between SQR of MDS vs stem water potential (SWP) showed a lineal fit with values higher than −1.8MPa. In order to ensure that the relationship between SWP and MDS is not due to their relation to VPD, SWP and MDS were divided by their theoretical values in function of VPD. It was observed that the response of MDS to water stress is much weaker than SWP and in this range of SWP (higher of −1.8MPa) variations of MDS are only due to VPD. The number of sensors necessary for precise measurement of MDS was, on average, more than thirty.

SAP FLOW RESPONSE TO OLIVE WATER STRESS: A COMPARATIVE STUDY WITH TRUNK DIAMETER VARIATIONS AND LEAF TURGOR PRESSURE

11 pages, 3 figures, 19 references.-- VIII International Symposium on Sap Flow, celebrado del 8-12 de mayo 2011, en Volterra, Italia.

RELATIONSHIP BETWEEN SAP FLOW, MAXIMUM DAILY SHRINKAGE AND OTHER ECOPHYSIOLOGICAL PARAMETERS IN PRUNUS AVIUM SUBJECTED TO WATER STRESS

Daily sap flow and maximum daily shrinkage (MDS) are two parameters that can be used for irrigation decision-making. In this subchapter we try to understand the different behavior of the two parameters at different timescales. The data come from the anterior assay (Chapter 1A) An assay was raised under controlled conditions where drought was imposed by irrigation withdrawal in cherry plants to compare their response of MDS with that of other ecophysiological parameters commonly used in water relations studies. Results showed contrasting relationships between MDS and daily sap flow depending on the degree of water stress that could be due to stomatal regulation. At a daily timescale, trunk diameter variation and sap flow were related to each other via a loop that differs according to tree water status. MDS resulted more sensitive to drought than sap flow, but the simultaneous use of both indicators rendered complementary information sensitive to the water status of the plants.

Use of maximum trunk diameter measurements to detect water stress in mature ‘Arbequina’ olive trees under deficit irrigation

a b s t r a c t Olive is one of the fruit tree species for which measurements of the trunk diameter variation (TDV) has shown a lower potential both for monitoring water stress and for scheduling irrigation. This is particularly true in the case of old, big olive trees with heavy fruit load. Fernandez et al. (2011, J. Environ. Exp. Bot. 72, 330-338) observed that the daily difference for maximum trunk diameter between deficit irrigated 'Manzanilla' olive trees and control trees growing under non-limiting soil water conditions, termed DMXTD, is more sensitive and reliable for detecting the water stress of the trees than other widely used TDV- derived indices. However, they considered their results as preliminary because of the lack of replications. The aim of this work was to evaluate the usefulness of the DMXTD index for detecting plant water stress in an orchard with 12-year-old 'Arbequina' olive trees with heavy fruit load. The performance of DMXTD for detecting water stress of the trees was compared to that of the signal intensity for the maximum daily shrinkage (SI-MDS) derived from the same TDV records. Results showed that SI-MDS was not useful for indicating the water stress of the trees. On the other hand, the dynamics of DMXTD mimicked those of the soil and plant water status. Four instrumented trees per treatment (replicates) were enough to reduce the uncertainty of the TDV measurements to a reasonable level. Our results show that DMXTD is a useful index to detect the onset, and severity, of water stress in mature 'Arbequina' olive trees with heavy fruit load. They also suggest a potential of DMXTD for scheduling low frequency deficit irrigation strategies. © 2011 Elsevier B.V. All rights reserved.

Usefulness of trunk diameter variations as continuous water stress indicators of pomegranate (Punica granatum) trees

Abstract Pomegranate trees ( Punica granatum L.) is a deciduous fruit tree included in the so-called group of minor fruit tree species, not widely grown but of some importance in the south east of Spain. Pomegranate trees are considered as a culture tolerant to soil water deficit. However, very little is known about pomegranate orchard water management. The objective of this research was to asses the feasibility of using trunk diameter variation (TDV) indexes, obtained by means of LVDT sensors, as a plant water stress indicators for pomegranate trees. The experiment was carried out with mature trees grown in the field under three irrigation regimes: control well watered trees; trees continuously deficit irrigated at 50% of the control regime (SDI); and trees that had a summer water stress cycle being irrigated at 25% of the control rates only in July and August (RDI). The seasonal variations of maximum diurnal trunk shrinkage (MDS) and trunk growth rates (TGR) were compared with midday stem water potential (Ψstem) measurements. During the course of the entire season, control trees maintained lower MDS values than the SDI ones. In the RDI treatment, as water restrictions began, there was a slow increase in MDS, in correspondence with a decrease in Ψstem. When water was returned at full dosage, the RDI quickly recovered to MDS and Ψstem values similar to the control. However, lower MDS for a given Ψstem values were observed as the season advanced. The magnitude of differences between well watered and deficit irrigated trees was much larger in the case of MDS than for Ψstem. However, the tree-to-tree variability of the MDS readings was more than four times higher than for Ψstem; average coefficient of variation of 7.5 and 36% for Ψstem and MDS, respectively. On the other hand, TGR did not clearly reflect differences in tree water status. Overall, results reported indicated that MDS is a good indicator of pomegranate tree water status and it can be further used for managing irrigation. However, the seasonal changes in the MDS-Ψstem relationship should be taken into account when attempting to use threshold MDS values for scheduling irrigation.