Water Use of Kiwifruit Vines and Apple Trees by the Heat-Pulse Technique

Green, S. R. and Clothier, B. E. 1988. Water use of kiwifruitvines and apple trees by the heat-pulse technique.–J.exp. Bot. 39: 115–123. The compensation heat-pulse method has been used to measuresap velocities in the stem of kiwifruit vines (Actinidia deliciosa)and apple trees (Malus sylvestris x Red Delicious). Becauseof the high flow rates typical in kiwifruit vines, we were unableto measure heat-pulse velocity using standard probe spacings.We increased the spacing between sensors with the downstreamsensor 20 mm and the upstream sensor 5-0 mm respectively fromthe heater probe. Corrections for flow blockage by the probeswere re-calculated at this new spacing for our 2-0 mm-diameterheater and teflon temperature probes following the procedureof Swanson and Whitfield (1981) Sap flux through the stem was found from heat-pulse velocitiesat four radial depths in the stem. Fluxes measured using theheat-pulse technique were compared with water uptake from appletrees and kiwifruit vines that had been cut-off at the baseand the butt placed in a container of water. Heat-pulse measurementswere also compared with known flow rates through stem-sectionsof kiwifruit vine in the laboratory. In apple the heat-pulsemeasurements agreed with independent flux measurements in excisionexperiments. In kiwifruit the independently measured fluxeswere consistently 1.6 times larger than the fluxes measuredwith the heat-pulse method. Possible reasons for this anomalousresult in kiwifruit vines are discussed     

The Effect of Drought and Vapour Pressure Deficit on Gas Exchange of Young Kiwifruit (Actinidia deliciosavar.deliciosa) Vines

To evaluate the effect of drought and vapour pressure deficit (VPD) on stomatal behaviour and gas exchange parameters, young kiwifruit vines (Actinidia deliciosavar.deliciosacv. Hayward) were exposed to alternating periods of drought and drought-relief over two growing seasons. Vines were grown either in the field or in containers. Stomatal conductance of fully-expanded leaves rapidly decreased as pre-dawn leaf water potential was reduced below a threshold value of -0.3MPa. Stomatal conductance reached minimum values of 10–20mmol m^-2s^-1. Transpiration rate was similarly sensitive to changes in leaf water status, whereas more severe drought levels were necessary to affect photosynthesis significantly. Net daily carbon gains were estimated at 4.7 and 2.7gm^-2for irrigated and droughted vines, respectively. Gas exchange parameters recovered to values of irrigated vines within a few hours after relief of stress. Rate of recovery depended on the level of stress reached during the previous drought period. There was a steady decline in stomatal conductance when VPD was increased from 0.8 to 2.5kPa in both irrigated and droughted vines. The VPD at which stomatal conductance reached 50% of maximum values was 2.1–2.2kPa for both treatments. We conclude that stomata were highly sensitive to changes in soil water status and that midday depression of photosynthesis measured in kiwifruit vines was related to water deficits arising in the leaf because of both transpirational losses and to the direct effect of increasing VPD.     

Root water uptake by kiwifruit vines following partial wetting of the root zone

Rates of sap flow and root-water uptake by two 7-year old kiwifruit vines (Acinidia deliciosa) were studied in an orchard with the aim of determining the ability of the vines to alter their spatial pattern of root-water uptake following differential wetting of the root zone. Time-domain reflectometry (TDR) was used to monitor changes in the soil's volumetric water content, . The heat-pulse technique was used to monitor sap flow not only in the stem but also in several large roots to see how root flow responded with local changes in soil water availability. Prior to irrigation there was a broad correspondence between the pattern of water uptake and the distribution of root-length density. However, following irrigation, we observed a preferential uptake of water from the wetter parts of the soil and a corresponding decline in water uptake from the drier parts of the soil. Observations of root uptake by TDR following irrigation also revealed the inordinate activity of near-surface roots. The vine would preferentially draw upon near-surface water if it were available. Kiwifruit vines are able to shift rapidly their pattern of uptake, in a matter of days, away from drier parts of the root zone and begin to extract water preferentially from those regions where it is more freely available. Upon full wetting of the root zone, previously inactive roots in the dry soil of the root zone were quickly able to recover their activity. Indeed their activity following rewatering was found to be greater than it had been prior to the period of soil dryness. A rapid flush of new root growth is considered to be the mechanism that leads to this enhanced activity.     

Root foraging in response to heterogeneous soil moisture in two grapevines that differ in potential growth rate

* Linkages between plant growth rate and root responses to soil moisture heterogeneity were investigated. * Root dynamics were studied using genetically identical shoots (Vitis vinifera cv. Merlot) with genetically distinct root systems that promote higher (HSV) and lower (LSV) shoot growth rates (1103P and 101-14 Mgt, respectively). Three quantities of irrigation replenished different amounts of evapotranspiration (0, 40 and 100%ET(c)) in a California vineyard. * Roots of HSV vines exhibited more plasticity, as indicated by greater preferential growth in irrigated soil during the summer, and a larger shift in root diameter with a change in soil moisture than LSV vines. Higher tolerance of low soil moisture was not observed in LSV roots--root survivorship was similar for the two rootstocks. LSV vines produced a large fraction of its roots during the winter months and increased root density over the study, while HSV vines produced roots mainly in summer and only exhibited a high initial peak in root biomass in the first year. * These results demonstrated that a plant of higher vigor has greater morphological plasticity in response to lateral heterogeneity in soil moisture but similar tolerance to moisture stress as indicated by root survivorship in dry soil.     

Root demography in kiwifruit (Actinidia deliciosa)

A rhizotron was used to study fine-root demography in mature vines of kiwifruit (Actinidia deliciosa). The vines were grown in a deep, well drained, silt loam and received normal orchard management. Roots were measured from 10 to 160cm depth at biweekly intervals for 2 years. After an initial phase of rapid colonisation of the repacked soil behind the rhizotron windows, the total length of visible roots per vine remained quite steady. This apparent stability of the total belied fast and sustained localized turnover of the fine roots at all soil depths. Fifty-one per cent of the roots survived ≤28d, 69% died at an age ≤56d and only 8% survived >252d. For each year, the cumulative length of roots grown was equivalent to about 2·75 times the maximum net length of roots visible. These may be the largest annual rates of root turnover yet reported. This has important ramifications for the carbon balance, mineral nutrition and water relations of the plant.     

Effects of Mesocriconema xenoplax on Vitis vinifera and Associated Mycorrhizal Fungi

Previous surveys of vineyards had indicated that Mesocriconema xenoplax was present in 85% of vineyards in western Oregon, but yields were not depressed in established vines. Microplot studies were initiated in 1997 in a Willamette Valley vineyard to determine the impact of M. xenoplax on vine establishment. Plots were infested with 0.03, 0.6, and 3.0 M. xenoplax g^-1 soil and planted with self-rooted Chardonnay and Pinot Noir vines. In November 2000, four growing seasons after planting, pruning weights, fine root weights, and fruit yield of vines planted in infested soil were reduced by 58%, 75%, and 33%, respectively, relative to control vines (planted in noninfested soil). In 1998 with ca 2000 degree-day base 9 °C accumulation, population densities increased 32-fold and 44-fold on 1-year-old Chardonnay and Pinot Noir vines, respectively. Nematode population dynamics and pruning data suggested that the carrying capacity of vines in microplots was 5 to 8 M. xenoplax g^-1 soil. In November 2000, more than 80% of the fine root length was colonized by arbuscular mycorrhizal fungi in all treatments. The frequency of fine roots containing arbuscules (the site of nutrient transfer between plant and fungus), however, was depressed from 5% to 65% in plants infested initially with M. xenoplax as compared to controls. Competition for photosynthate within the root system is proposed as a possible mechanism by which nematodes suppressed arbuscule frequency.     

A comparison of minirhizotron techniques for estimating root length density in soils of different bulk densities

Flexible- and rigid-walled minirhizotron techniques were compared for estimating root length density of 14- to 28-day-old Pinto bean (Phaseolus vulgaris L.) and spring whet (Triticum aestivum L.) plants in soil boxes under controlled environment conditions at three soil bulk densities (1.3, 1.5 and 1.7 g cm^–3). The flexible-tube system consisted of bicycle inner tubes inflated inside augered access holes and removed only when measurements were taken. Rigid tubes were constructed of extruded polybutyrate plastic. In both cases tubes were oriented horizontally. Despite similar root densities for wheat and beans based on measurements obtained from soil cores, root densities estimated from both types of minirhizotron were higher in bean than in wheat in uncompacted soil. Estimates of root density by the flexible tube minirhizotron were more closely correlated with soil core image analysis estimates than were those by the rigid minirhizotron system. At high soil bulk density, rigid tube measurements consistently overestimated actual rooting density of both wheat and bean. The relationship between estimated and actual rooting densities in the case of flexible tube measurements was not significantly influenced by soil bulk density. These findings were consistent with the theory that preferential root growth is induced by gaps at the soil-observation tube interface, inherent in the rigid tube technique, and was accentuated under conditions of high soil strength.     

用地统计学方法对落叶松人工纯林表层细根生物量的估计

 采用地统计学的变异函数分析方法定量研究了落叶松（Larix olgensis）纯林表层（0～10 cm）细根的空 间异质性特征,利用地统计学的克里格内插法结合定积分,对落叶松纯林表层细根（<2 mm）的生物量进 行了估测。结果表明：1）6种林龄（14～40 年）的落叶松人工纯林表层细根的变异函数曲线理论模型均 为球状模型,空间变异主要是由结构性因素引起,且空间自相关程度均属中等以上（空间结构比>25%）。 14、19、22、26、32、40年生的落叶松纯林表层细根的空间变异尺度分别为1.76、3.40、1.02、4.12、 3.37和5.58 m。在所研究的林龄范围内,随林龄的增长,落叶松纯林表层细根的空间变异尺度近似呈直线 增长（p =0.074 4）。2）非参数统计的成对样本符号检验结果表明,变异函数分析结果基础上的克里格 内插法适用于落叶松纯林表层细根生物量的估计。利用此估计值,拟合其与位置坐标值之间的多元回归关 系均为二元十次余弦级数多项式。利用此多项式,通过定积分的方法（积分区间为整块样地的大小）,估 计出14、19、22、26、32、40年生的落叶松纯林表层细根生物量分别为1.097 3、1.434 0、1.185 4、 0.974 3、1.682 6、1.255 6 Mg• hm-2。3）在本次调查的林龄范围内（14～40年）,落叶松纯林表层细 根的现存量近似相等（α=0.037 3）,土壤表层单株细根生物量与林龄之间呈极显著的指数增长关系（α =0.002）。4）采用地统计学的克里格空间插值,结合多元回归和定积分的方法,可以实现落叶松人工林 表层细根生物量的准确估计。     

Amendment with biocontrol strains increases Trichoderma numbers in mature kiwifruit (Actinidia chinensis) orchard soils for up to six months after application

A Trichoderma mixture was applied to kiwifruit plants in a pot experiment and to mature orchard vines to determine its effect on numbers of root-associated fungi and compare application methods into kiwifruit orchards in New Zealand. Trichoderma and other fungal numbers were recorded using a root plating technique. In the pot experiment, a significantly greater number of Trichoderma was isolated from treated compared to untreated plants 6 and 10 weeks after inoculation. Six months after application, greater numbers of Trichoderma were recovered in the orchards from Trichoderma treated vines and the increase was comparable for all application methods with over 50% of isolated fungi identified as Trichoderma compared to 33% in the water-only control. Different viable methods are available that can easily be integrated into everyday orchard management in order to introduce Trichoderma into mature kiwifruit stands. A six-monthly or more frequent application schedule seems advisable.     

Transitory effects of elevated atmospheric CO₂ on fine root dynamics in an arid ecosystem do not increase long-term soil carbon input from fine root litter

Experimental increases in atmospheric CO? often increase root production over time, potentially increasing soil carbon (C) sequestration. Effects of elevated atmospheric CO? on fine root dynamics in a Mojave desert ecosystem were examined for the last 4.5 yr of a long-term (10-yr) free air CO? enrichment (FACE) study at the Nevada desert FACE facility (NDFF). Sets of minirhizotron tubes were installed at the beginning of the NDFF experiment to characterize rooting dynamics of the dominant shrub Larrea tridentata, the codominant shrub Ambrosia dumosa and the plant community as a whole. Although significant treatment effects occurred sporadically for some fine root measurements, differences were transitory and often in opposite directions during other time-periods. Nonetheless, earlier root growth under elevated CO? helped sustain increased assimilation and shoot growth. Overall CO? treatment effects on fine root standing crop, production, loss, turnover, persistence and depth distribution were not significant for all sampling locations. These results were similar to those that occurred near the beginning of the NDFF experiment but unlike those in other ecosystems. Thus, increased C input into soils is unlikely to occur from fine root litter under elevated atmospheric CO? in this arid ecosystem.     

Predation of diaspidid scale insects on kiwifruit vines by European earwigs, <Emphasis Type="Italic">Forficula auricularia</Emphasis>, and steel-blue ladybirds, <Emphasis Type="Italic">Halmus chalybeus</Emphasis>

Significant predation of diaspidid scale insects occurs in unsprayed kiwifruit crops. Two predators, Forficula auricularia L. (Dermaptera: Forficulidae) and Halmus chalybeus (Boisduval) (Coleoptera: Coccinellidae) are likely to be important. Most F. auricularia were found as late instars or adults in the canopy of kiwifruit vines in late spring and early summer. Adults of H. chalybeus were present throughout the year but at lower densities on kiwifruit vines than on other host plants. In the field predation of scale insects occurred mainly at night and preferentially on late-instar scale insects consistent with the feeding behaviour of F. auricularia, not H.chalybeus. The latter mainly fed on early instar insects during the day. Numbers of scale insect crawlers were not correlated with numbers of F. auricularia or of H. chalybeus in kiwifruit vine canopies.     

Shade mitigates photoinhibition and enhances water use efficiency in kiwifruit under drought

We tested the hypotheses that a reduction of incident light of 50 % over sun-acclimated leaves of water stressed kiwifruit (Actinidia deliciosa var. deliciosa) would (1) reduce stomatal limitations to carbon supply and (2) mitigate the inactivation of the primary photochemistry associated with photosystem (PS) II, thereby this increases carbon gain and water-use efficiency (WUE). Groups of field-grown vines were either shaded or left naturally exposed and subjected to progressive water stress in order to study moderately and severely droughted vines, while other groups were well irrigated. Daily variations in leaf gas exchange and midday chlorophyll (Chl) a fluorescence were determined once plants had −0.6 MPa (moderate stress) and −1.0 MPa pre-down leaf water potential (severe stress). Variations in Chl pigment content and specific leaf area (SLA) are also discussed. Results reveal that 50 % shade application maintained efficiency of PSII close to 0.8 even under severe drought so that to prevent its large decline (0.65) recorded in sunlit leaves. Under moderate stress level stomata behaviour dominated upon metabolic impairments of PSII. Reduction of irradiance increased WUE (15–20 %) in droughted vines, representing a valuable intervention to save photosynthetic apparatus and improve WUE in vines experiencing typical Mediterranean summer stresses.     

Sugar accumulation in roots of two grape varieties with contrasting response to water stress

Root sugar accumulation was studied in two grapevine varieties contrasting in tolerance to water stress. During a 10‐day water withholding treatment, the drought‐tolerant variety, Grenache, sustained less negative predawn and midday leaf water potentials as well as root water potential compared with the sensitive variety, Semillon. Grenache vines also maintained lower stomatal conductance and transpiration than Semillon vines throughout the drying period. In both varieties there was accumulation of sucrose in the roots and concentrations were inversely correlated to leaf and root water status. In both Grenache and Semillon, elevated root osmolality was associated with decreased soil moisture indicating that sugar accumulation may play a role in osmotic protection. Petiole xylem sap abscisic acid (ABA) concentrations increased with water deficit in both varieties and were highest for vines with the most negative root and predawn leaf water potentials. Furthermore, root sucrose concentrations were positively correlated with leaf xylem sap ABA concentrations, indicative of integration between carbohydrate metabolism and the ABA signalling system. Similar root sugar accumulation patterns between the two varieties, however, demonstrate that other factors are likely influencing the ability of the drought‐tolerant variety to remain hydrated.     

Quantifying the impact of soil compaction on root system architecture in tomato (Solanum lycopersicum) by X-ray micro-computed tomography

Background and Aims

We sought to explore the interactions between roots and soil without disturbance and in four dimensions (i.e. 3-D plus time) using X-ray micro-computed tomography.

Methods

The roots of tomato Solanum lycopersicum ‘Ailsa Craig’ plants were visualized in undisturbed soil columns for 10 consecutive days to measure the effect of soil compaction on selected root traits including elongation rate. Treatments included bulk density (1·2 vs. 1·6 g cm⁻³) and soil type (loamy sand vs. clay loam).

Key Results

Plants grown at the higher soil bulk density exploited smaller soil volumes (P < 0·05) and exhibited reductions in root surface area (P < 0·001), total root volume (P < 0·001) and total root length (P < 0·05), but had a greater mean root diameter (P < 0·05) than at low soil bulk density. Swelling of the root tip area was observed in compacted soil (P < 0·05) and the tortuosity of the root path was also greater (P < 0·01). Root elongation rates varied greatly during the 10-d observation period (P < 0·001), increasing to a maximum at day 2 before decreasing to a minimum at day 4. The emergence of lateral roots occurred later in plants grown in compacted soil (P < 0·01). Novel rooting characteristics (convex hull volume, centroid and maximum width), measured by image analysis, were successfully employed to discriminate treatment effects. The root systems of plants grown in compacted soil had smaller convex hull volumes (P < 0·05), a higher centre of mass (P < 0·05) and a smaller maximum width than roots grown in uncompacted soil.

Conclusions

Soil compaction adversely affects root system architecture, influencing resource capture by limiting the volume of soil explored. Lateral roots formed later in plants grown in compacted soil and total root length and surface area were reduced. Root diameter was increased and swelling of the root tip occurred in compacted soil.     

In vitro breeding – shortcut to Pseudomonas syringae pv. actinidiae (Psa) tolerant kiwifruit

Pseudomonas syringae pv. actinidiae (Psa) causes the bacterial canker disease on kiwifruit vines. The disease outbreak has been reported in several countries worldwide, including New Zealand. Here, we briefly reviewed the current situation of Psa infection of kiwifruit vines in New Zealand, the effects of Psa on the New Zealand’s kiwifruit industry, and the disease control and breeding programmes undertaken in response to the outbreak of Psa in New Zealand. Then the methodology of an alternative breeding approach or in vitro breeding, which is a non-GM approach to obtain useful plant tissue culture-derived genetic variation in crop plants, was discussed. As a specific example of potential application of in vitro breeding, a novel plant breeding project idea based on the elemental defence mechanism is to generate Cu/Zn tolerant kiwifruit varieties that exhibit improved Psa tolerance.     

Net CO(2) Assimilation and Carbohydrate Partitioning of Grapevine Leaves in Response to Trunk Girdling and Gibberellic Acid Application

Leaf net CO₂ assimilation rate (A), stomatal conductance (g_s), carboxylation efficiency, and foliar nonstructural carbohydrates were measured on mature, field-grown Vitis vinifera L. (cv Thompson Seedless) vines that had been trunk girdled, sprayed with gibberellic acid, or both, shortly after anthesis. Girdling reduced A, g_s, and carboxylation efficiency when measured 2 weeks after imposition of the treatments. Diurnal measurements indicated that A of girdled vines was less than that of control vines between 1000 and 1800 hours. Gibberellic acid mitigated the depressing effect of girdling on g_s during the same diurnal measurements. The concentrations of foliar carbohydrates were greatest for the girdled vines, followed by the combination treatment and were lowest for the control vines. Foliar carbohydrates were greater for girdled vines 4 weeks after the treatments were imposed, however, by this time there was no significant difference in A between the control and girdled vines. Two and 4 weeks after the experiment was initiated root carbohydrate concentrations were less for the girdled vines when compared to the control vines. The data indicate that the reduction in A of girdled grapevines is not associated with the accumulation of leaf nonstructural carbohydrates following the girdling treatment.     

Nitrogen and phosphorus cycling in relation to stand age of Ecucalyptus regnans F. Muell

Water movement between a root and the soil depends on the hydraulic conductances of the soil, the root, and the intervening root-soil air gap (L_gap) created as roots shrink during soil drying. To measure L_gap, segments of young cylindrical roots of Agave deserti about 3 mm in diameter were placed concentrically or eccentrically within tubes of moistened filter paper at a known water potential. As the width of the air gap between the filter paper and a concentrically located root was made smaller, measured L_gap increased less than did predicted L_gap based on isothermal conditions. For gaps of the size expected in the soil during water loss from roots (e.g., 10% of the root radius), the underprediction was about 70% and was primarily caused by a lowering of the root surface temperature accompanying water evaporation. As a root segment was eccentrically moved toward the filter paper, the measured L_gap increased. For the most eccentric case of touching the filter paper, the measured L_gap was 2.4-fold greater than for the concentric case, compared with an infinite L_gap predicted if the water potential were constant around the root surface. When a root touched soil with a water potential of -1.0MPa, L_gap estimated using a graphical method increased about 2.3-fold and the overall conductance of the root-soil system increased by 31% compared with the concentric case. For markedly eccentric locations of roots in air gaps, L_gap, which can be the principal conductance initially limiting water loss from roots to a drying soil, can be about 60% of the value predicted for the concentric isothermal case.     

Greenhouse and field evaluations of potassium phosphonate: the control of Phytophthora foot rot of black pepper in Vietnam

Phytophthora foot rot of black pepper caused by Phytophthora capsici is a major disease of black pepper throughout production areas in Vietnam. The disease causes collar, foot and tap root rots and eventual death of the infected vine. Potassium phosphonate was evaluated for the control of this disease in greenhouse and field trials. In greenhouse trials three-month-old vines treated with phosphonate by soil drenching (10–20 g a.i./l) and then inoculated with P. capsici mycelium (2% v/v soil) had significantly less foot rot compared to vines grown in non-treated soil. In field trials mature vines were treated with phosphonate at 50–100 g a.i/pole soil drenching or 10 g a.i./l by root infusion. After 10 days root, stem and leaf specimens were removed for bioassay by inoculation with 5 ml of P. capsici zoospores suspension (10⁶–10⁸ spores/ml). Soil drenching with phosphonate inhibited the colonisation of pathogen on excised leaf, stem and root tissues, significantly more than phosphonate root infusion. Our study provides further evidence supporting the efficacy of potassium phosphonate in the management of black pepper foot rot caused by P. capsici. The excised leaf and stem bioassay used in this study is a rapid and useful technique for testing the efficacy of systemic fungicides in controlling this disease.     

Occurrence of Phytophthora Root and Stem Rot of Kiwifruit in Turkey

Vine decline of kiwifruit was observed in an orchard in Bart?n province of Turkey. Affected vines exhibited poor terminal growth, leaf discoloration and various degrees of dieback, including complete vine death. Symptoms were observed in the field on roots, crowns and stems. Two Phytophthora species were isolated from decayed cortical roots and lower stems of kiwifruits. They were identified as Phytophthora cryptogea and Phytophthora megasperma by their morphological characteristics and the analysis of sequences of the internal transcribed spacer (ITS) region of the rDNA. Pathogenicity of the isolates was tested by stem inoculation on kiwifruit seedlings. After 4 weeks, cankers developed in the plants inoculated with P. cryptogea, while no cankers formed in those inoculated with P. megasperma and in control plants. This is the first report of P. cryptogea causing root and stem rot of kiwifruit in Turkey.