Regulated deficit irrigation (RDI) strategies, often applied in tree crops, require precise monitoring methods of water stress. Crop water stress index (CWSI), based on canopy temperature ...measurements, has shown to be a good indicator of water deficits in field crops but has seldom been used in trees. CWSI was measured on a continuous basis in a Central California mature pistachio orchard, under full and deficit irrigation. Two treatments--control, returning the full evapotranspiration (ETc) and RDI--irrigated with 40% ETc during stage 2 of fruit grow (shell hardening). During stage 2, the canopy temperature--measured continuously with infrared thermometers (IRT)--of the RDI treatment was consistently higher than the control during the hours of active transpiration; the difference decreasing after irrigation. The non-water-stressed baseline (NWSB), obtained from clear-sky days canopy-air temperature differential and vapour pressure deficit (VPD) in the control treatment, showed a marked diurnal variation in the intercept, mainly explained by the variation in solar radiation. In contrast, the NWSB slope remained practically constant along the day. Diurnal evolution of calculated CWSI was stable and near zero in the control, but showed a clear rising diurnal trend in the RDI treatment, increasing as water stress increased around midday. The seasonal evolution of the CWSI detected large treatment differences throughout the RDI stress period. While the CWSI in the well-irrigated treatment rarely exceeded 0.2 throughout the season, RDI reached values of 0.8-0.9 near the end of the stress period. The CWSI responded to irrigation events along the whole season, and clearly detected mild water stress, suggesting extreme sensitivity to variations in tree water status. It correlated well with midday leaf water potential (LWP), but was more sensitive than LWP at mild stress levels. We conclude that the CWSI, obtained from continuous nadir-view measurements with IRTs, is a good and very sensitive indicator of water stress in pistachio. We recommend the use of canopy temperature measurements taken from 1200 to 1500 h, together with the following equation for the NWSB: (T c - T a) = -1.33·VPD + 2.44. Measurements of canopy temperature with VPD < 2 kPa are likely to generate significant errors in the CWSI calculation and should be avoided.
This work advances the evaluation and interpretation of the Photochemical Reflectance Index (PRI) as an indicator of water stress, over a range of canopy structures and pigment content levels. Very ...high resolution (VHR) narrow-band multispectral (10cm) and thermal (20cm) imagery was acquired diurnally, in four airborne campaigns conducted over an experimental vineyard site undergoing three different irrigation treatments. Field measurements of leaf stomatal conductance (Gs) and leaf water potential (Ψleaf) were acquired concurrently with the airborne campaigns and compared against the Crop Water Stress Index (CWSI), a widely accepted, thermal-based indicator of water stress, and against narrow-band multispectral indices calculated from pure-vegetation pixels. The study proposes a new formulation, a normalized PRI (PRInorm), in which the standard PRI index is normalized by an index that is sensitive to canopy structure (Renormalized Difference Vegetation Index, RDVI) and by a red edge index that is sensitive to chlorophyll content (R700/R670). The hypothesis investigated is that the new index, calculated as PRInorm=PRI/RDVI·R700/R670, not only detects xanthophyll pigment changes as a function of water stress, but also normalizes for the chlorophyll content level and canopy leaf area reduction induced by stress. Results demonstrated that when comparing PRInorm against stomatal conductance (r2=0.79; p<0.001) and leaf water potential (r2=0.77; p<0.001) measured at midday, the new index performed better than the standard PRI (r2=0.52 and 0.49, respectively). Further, when using the four flights conducted during the diurnal experiment, the relationships with stomatal conductance also showed the superior performance of PRInorm (r2=0.68) as opposed to PRI (r2=0.4). The proposed normalized PRI was highly related (r2=0.75; p<0.001) to the thermal indicator of water stress, CWSI, which was used here as a benchmark. In comparison, the standard PRI index was found to be significantly related to CWSI (p<0.001), although the relationship was weaker (r2=0.58) than that obtained for PRInorm. In summary, this study demonstrates that PRInorm isolated better than PRI the physiological changes against a changing background of altered pigments and structure, tracking more precisely the diurnal dynamics of the stomatal aperture. Simulations conducted, using leaf and canopy radiative transfer models to elucidate these results, showed that PRInorm is more linearly related to canopy pigment content than the standard PRI, and was more capable of differentiating between stress levels, providing better insight into the results of this diurnal study.
•PRI normalized by structure and chlorophyll improved sensitivity to conductance.•The new PRInorm index is calculated as PRI / RDVI · R700/R670.•PRInorm was superior than PRI in a diurnal airborne experiment against Gs and Ψleaf.•PRInorm obtained comparable results to thermal water stress CWSI and Tc-Ta indices.•Simulations showed that PRInorm saturates less on high pigments and LAI.
► The intra-crown variability of canopy temperature was assessed in two almond cvs. ► 8 pressure chambers were assembled enabling the measurement of 240 trees per flight. ► The frequency distribution ...of canopy temperature varied according to water status. ► Standard deviation of crown temperature may be an indicator of tree water stress. ► The factors controlling the source of variation of canopy temperature are discussed.
Tree water status is often characterized by measuring a few leaves and it is not known to what extent such measurements represent the tree as a whole. We present an assessment of the intra-crown temperature variability and its relationship with water status in two almond cultivars. High-resolution imagery was acquired on 30 June 2009 at 11:30, 14:30, and 16:30
h (solar time) with a thermal camera on-board an aircraft over an almond orchard in Kern County, CA, USA. Ten irrigation levels were applied, ensuring a wide variability in water status, and each was replicated eight times. Stem water potential and stomatal conductance were measured on trees of various irrigation regimes at each flight. Significant variation in canopy temperature was found within each crown, probably reflecting differences in stomatal conductance in different parts of the tree crown. The intra-crown standard deviation of canopy temperature (intra-crown
σT
c) increased from fully irrigated trees to intermediate irrigation levels, diminishing afterwards in the most stressed treatments. Mean canopy temperature was well correlated with stomatal conductance and stem water potential (
R
2 above 0.65). In trees that had similar mean canopy temperature, intra-crown
σT
c correlated well with tree water status. Our results quantified in detail the spatial variability in surface temperatures that exists within almond tree crowns and suggest that the intra-crown temperature variation may be a useful indicator of the onset of tree water stress.
A study was conducted in a large pistachio farm in Madera County, California, to assess the spatial variability in water status and irrigation needs by using high-resolution thermal imagery acquired ...by an unmanned aerial system. We determined the Crop Water Stress Index (CWSI) of two fields, 130Â ha each, based on canopy temperature measurements of individual tree crowns, thus assessing the spatial variations in tree water status within each field. The CWSI of each potential management unit (sectors encompassing about 175 trees) was then calculated and related to the days since last irrigation (DSLI) in F1 and F2. The relationship between CWSI and DSLI was established to calculate the average CWSI corresponding to the whole area that was irrigated on the same day. This value was afterward compared with the actual CWSI value of each management unit as a proxy of the spatial variability in CWSI. This information was used to calculate the deviation of each irrigation unit from the fixed irrigation schedule for the whole fields. Our results show that it is feasible to use high-resolution thermal imagery for integrating the crop response in irrigation performance assessment and for providing recommendations at the farm scale.
The use of plant indicators may be the ideal method for irrigation scheduling but it is hampered by the dynamic nature of plant water status and by the lack of suitable indicators, relative to ...established scheduling methods based on atmospheric and soil observations. A study was conducted in an almond orchard located in the San Joaquin Valley of California during the 2001 season using trunk diameter variations as the only indicator for determining the amount of irrigation. The ratio of the maximum daily shrinkage (MDS) of tree trunks relative to a reference MDS, calculated from a relationship between MDS of fully irrigated trees and atmospheric vapor pressure deficit, was used as a signal for modifying the amount of applied irrigation water. Applied water was increased by 10% each time the MDS signal exceeded the prescribed threshold. When the MDS signal went below the threshold, applied water was reduced by 10% in an interactive manner. Two schedules were tested with signal thresholds of 1.75 and 2.75, which generated mild and moderate water stress, respectively, as indicated by their stem water potential (SWP) values. The two irrigation treatments had SWP that varied over the season from around -0.7 to -1.1 MPa and -0.8 to -1.7 MPa, respectively. The two schedules resulted in seasonal water applications of 860 mm for the 1.75 and 525 mm for the 2.75 signal threshold treatments. The grower/cooperator, who based his schedule primarily on SWP measurements but also considered the water balance, applied 900 mm. Estimated crop evapotranspiration was 1,030 mm. The mean coefficients of variation for the two irrigation treatments during the monitoring period were 0.115 and 0.031 for the MDS and SWP measurements, respectively. The stress produced by the irrigation treatments hastened fruit maturation, as evidenced by accelerated hull splitting. This resulted in lower fruit hydration just prior to harvest; 17.3% and 8.0% for the two irrigation schedules, respectively, compared with 27.3% for the grower/cooperator. Based on harvesting selected trees with the same nut load, fresh and dry nut weights in the 2.75 threshold treatment were 9.0% and 10.7% less than those of the 1.75 threshold, which were not significantly different from the results for the grower cooperator. Our results demonstrate that it is feasible to develop an irrigation schedule for almond trees based solely on MDS signals, which may be tailored to any desired stress pattern and be operated in full automation with appropriate software development.PUBLICATION ABSTRACT
The reduction in agricultural water use in areas of scarce supplies can release significant amounts of water for other uses. As improvements in irrigation systems and management have been widely ...adopted by fruit tree growers already, there is a need to explore the potential for reducing irrigation requirements via deficit irrigation (DI). It is also important to quantify to what extent the reduction in applied water through DI is translated into net water savings via tree evapotranspiration (ET) reduction. An experiment was conducted in a commercial pistachio orchard in Madera, CA, where a regulated deficit irrigation (RDI) program was applied to a 32.3-ha block, while another block of the same size was fully irrigated (FI). Four trees were instrumented with six neutron probe access tubes each, in the two treatments and the soil water balance method was used to determine tree ET. Seasonal irrigation water in FI, applied through a full-coverage microsprinkler system, amounted to 842
mm, while only 669
mm were applied in RDI. Seasonal ET in FI was 1024
mm, of which 308
mm were computed as evaporation from soil (
E
s). In RDI, seasonal ET was reduced to 784
mm with 288
mm as
Es. The reduction in applied water during the deficit period amounted to 147
mm. The ET of RDI during the deficit period was also reduced relative to that of FI by 133
mm, which represented 33% of the ET of FI during the deficit irrigation period. There was an additional ET reduction in RDI of about 100
mm that occurred in the post-deficit period.
Among the factors influencing the decision-making process in irrigation, the threshold level of available soil water content (AWC) is critical for irrigation timing. An experiment was conducted with ...mature peach trees (
Prunus persica L. Bastch) using a large weighing lysimeter to establish the threshold levels of AWC for evapotranspiration (ET), leaf conductance and photosynthesis during a deficit irrigation period. Three approaches were used to determine the AWC in the lysimeter and it was found, via continuous monitoring of soil water content with capacitance sensors, that the trees had not fully explored the soil in the lysimeter. The threshold level for the onset of ET decline was 60 and 53% of AWC when AWC was calculated as the difference between the field capacity and the wilting point of the soil layer explored by roots (90
cm) and as the total water extracted by the tree from the lysimeter, respectively. When the whole soil depth of the lysimeter (160
cm) was considered as a reservoir for water uptake, the threshold level for ET decline started at 94% of AWC; a value so high as to suggest erroneous assumptions. Similar threshold values were found for the reduction of leaf conductance and photosynthesis. Soil water monitoring in the lysimeter gave diurnal patterns of water extraction that lagged behind the transpiration of the lysimeter for about 2
h in the morning and ended earlier in the afternoon. Also, measured peak extraction rates near the emitters were several times higher than those representing tree transpiration from lysimeter weight loss. Soil water extraction patterns in trees outside the lysimeter that were watered with the same deficit irrigation regime differed from those in the lysimeter in that considerable extraction occurred from 90 to 180
cm. The different tree responses to deficit irrigation in and outside the lysimeter demonstrate the importance of considering wetting patterns, soil depth, and root exploration in high frequency irrigation management.
The inherited motor neuron disease spinal muscular atrophy (SMA) is caused by deficient expression of survival motor neuron (SMN) protein and results in severe muscle weakness. In SMA mice, synaptic ...dysfunction of both neuromuscular junctions (NMJs) and central sensorimotor synapses precedes motor neuron cell death. To address whether this synaptic dysfunction is due to SMN deficiency in motor neurons, muscle, or both, we generated three lines of conditional SMA mice with tissue-specific increases in SMN expression. All three lines of mice showed increased survival, weights, and improved motor behavior. While increased SMN expression in motor neurons prevented synaptic dysfunction at the NMJ and restored motor neuron somal synapses, increased SMN expression in muscle did not affect synaptic function although it did improve myofiber size. Together these data indicate that both peripheral and central synaptic integrity are dependent on motor neurons in SMA, but SMN may have variable roles in the maintenance of these different synapses. At the NMJ, it functions at the presynaptic terminal in a cell-autonomous fashion, but may be necessary for retrograde trophic signaling to presynaptic inputs onto motor neurons. Importantly, SMN also appears to function in muscle growth and/or maintenance independent of motor neurons. Our data suggest that SMN plays distinct roles in muscle, NMJs, and motor neuron somal synapses and that restored function of SMN at all three sites will be necessary for full recovery of muscle power.
Transgenic analyses have defined two transcriptional enhancers that regulate
MyoD expression in mammals, the core enhancer and distal regulatory region; these enhancers exhibit complementary ...activities and together are sufficient to recapitulate
MyoD expression in developing and mature skeletal muscle. The core enhancer is activated in presumptive muscle cells and determined myoblasts, suggesting an important role in initiating
MyoD expression. Here, targeted mutagenesis in the mouse is used to identify necessary and redundant core enhancer functions. The core enhancer is essential for the timely initiation of
MyoD expression in limb buds and branchial arches, as enhancer deletion delayed
MyoD activation by 1 to 2 days in these muscle lineages. Functionally, this delay in
MyoD transcription delayed the onset of muscle differentiation, as assayed by expression of the gene encoding for the early differentiation marker, Myogenin. In addition to these lineage-specific defects, a generalized, modest reduction in
MyoD expression was observed in all muscle lineages and at all embryonic stages examined. Interestingly, however, a specific defect was not observed in the nascent myocytes at the medial and lateral aspects of the myotome, suggesting the existence of at least one other enhancer with this specificity. The core enhancer was also dispensable for Myf-5- and Pax-3-dependent regulation of
MyoD transcription. These data demonstrate a differential requirement for core enhancer activity in muscle lineages derived from migratory precursors and suggest redundancy in
cis regulatory mechanisms controlling myotomal
MyoD expression.
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