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1.
Studies on the influence of seed-bed condition on the emergence and development of pepper seedlings (Capsicum frutescens L.) revealed that seed-bed compaction delayed and reduced seedling emergence. High nutrient and organic matter content accentuated the severity of soil compaction, regardless of whether the soil moisture was low or high. Influence of compaction was less on “dry” poor soil. Best seedling emergence was obtained from “moist” crumbly “rich” soil. However, “moist” crumbly “poor” soil, moist compacted poor soil, “dry” crumbly rich soil and “dry” crumbly poor soil also gave very high seedling emergence. The dry compacted rich soil gave the poorest cumulative emergence figures. High soil moisture regime and high nutrient content reduced the severity of soil compaction on seedling root and shoot development. Soil compaction also caused abnormal hypocotyl morphology in seedlings that germinated but failed to emerge.  相似文献   

2.
Urban trees are frequently exposed to unsuitable soil conditions that can hamper root system development, potentially affecting both tree health and stability. Engineered soil designs have been developed to increase soil volume for trees planted in confined spaces, and past research has shown that these designs improve growing conditions. However, tree stability in these engineered soils has received limited attention from researchers. In this study, we evaluated the stability of two tree species of contrasting soil quality tolerance (Prunus serrulata and Ulmus parvifolia) after 3 years growth in two skeletal soil mixes, in a suspended pavement design (uncompacted soil), and in a conventionally prepared soil pit. Tree stability was evaluated by measuring trunk resistance to a lateral deflecting force applied with a rope winch system under both ambient and near-saturated soil conditions. Although heavily irrigating the experimental soils had no effect on tree stability, species-specific responses to soil mixes were observed. P. serrulata grown in the gravel-based skeletal soil showed greater trunk deflection resistance than trees grown in the other soil treatments, yet the stability of U. parvifolia was unaffected by soil type. These species-specific responses were consistent with earlier observations of root development in which P. serrulata grew up to 60 times greater root length in gravel-based skeletal soil whereas U. parvifolia root growth was similar in all soil treatments. This research provides evidence that certain tree species planted in conventional tree pits may be more prone to uprooting due to poor root development and that root anchorage might be improved for these species by utilizing a skeletal soil mix.  相似文献   

3.
The interactive effects of rooting volume and nutrient availability in a skeletal soil medium designed to meet street tree and pavement needs were observed in a containerized experiment. Benjamin fig (Ficus benjamina L.) was grown in a stone-soil blended skeletal soil material (CU-Soil™) and compared to a loam soil. The same topsoil used as the soil component in the skeletal soil material was used as the sole component in the comparison soil-only treatment.Plants grown in the skeletal soil material had reduced leaf tissue N content and depressed growth compared with plants grown in non-diluted soil. No other mineral deficiencies were found. Leaf number, chlorophyll concentration, shoot weight, and root characteristics were all affected.Reduced growth from soil dilution could be offset by the provision of an enlarged rooting volume for root development. Large containers of skeletal soil were observed to have smaller root systems compared to equivalent net volumes of loam soil at the first two harvest dates of the study. By the end of the study, the large containers of skeletal soil were observed to have developed larger root systems compared to equivalent net volumes of loam soil; resulting in comparable leaf N levels and total plant dry matter. Plants in skeletal soil had lower shoot: root ratios at the end of the study. Investing resources to further root growth in times of nutrient shortages is a probable plant reaction as evidenced by differences in specific root length between treatments. The study allowed a method for directly partitioning the containerization effect by having equivalent amounts of soil over two volumes.  相似文献   

4.
设施砂壤土容重对番茄幼苗生长和根系构型的影响   总被引：1，自引：0，他引：1  
土壤紧实是设施蔬菜生产的土壤障碍因子之一。在塑料大棚砂壤土条件下,用人工土柱栽培法研究了土壤容重分别为1.20、1.35和1.58 g ? cm-3的土壤对番茄幼苗生长和根系构型的影响。结果表明,随容重增大,叶片伸长速度、株高、植株含水量、鲜质量、干质量、根冠比、根表面积、根长密度和根体积密度等都显著降低。随容重增大,根系干质量、根表面积、根长密度和根体积密度在垂直面上的分布显著降低,容重1.58 g ? cm-3处理的根系全部分布在0 ~ 6 cm土层内。高容重土壤使根毛区皮层产生形变,即细胞变长,皮层下陷,根表面凹凸不平,根圆度变差,偏心率增大,降低根毛区的吸收能力。  相似文献   

5.
Citizen science has been gaining popularity in ecological research and resource management in general and in urban forestry specifically. As municipalities and nonprofits engage volunteers in tree data collection, it is critical to understand data quality. We investigated observation error by comparing street tree data collected by experts to data collected by less experienced field crews in Lombard, IL; Grand Rapids, MI; Philadelphia, PA; and Malmö, Sweden. Participants occasionally missed trees (1.2%) or counted extra trees (1.0%). Participants were approximately 90% consistent with experts for site type, land use, dieback, and genus identification. Within correct genera, participants recorded species consistent with experts for 84.8% of trees. Mortality status was highly consistent (99.8% of live trees correctly reported as such), however, there were few standing dead trees overall to evaluate this issue. Crown transparency and wood condition had the poorest performance and participants expressed concerns with these variables; we conclude that these variables should be dropped from future citizen science projects. In measuring diameter at breast height (DBH), participants had challenges with multi-stemmed trees. For single-stem trees, DBH measured by participants matched expert values exactly for 20.2% of trees, within 0.254 cm for 54.4%, and within 2.54 cm for 93.3%. Participants’ DBH values were slightly larger than expert DBH on average (+0.33 cm), indicating systematic bias. Volunteer data collection may be a viable option for some urban forest management and research needs, particularly if genus-level identification and DBH at coarse precision are acceptable. To promote greater consistency among field crews, we suggest techniques to encourage consistent population counts, using simpler methods for multi-stemmed trees, providing more resources for species identification, and more photo examples for other variables. Citizen science urban forest inventory and monitoring projects should use data validation and quality assurance procedures to enhance and document data quality.  相似文献   

6.
不同土壤紧实度对平邑甜茶根系特征及氮代谢的影响   总被引：3，自引：0，他引：3  
以盆栽平邑甜茶为试材,研究了不同土壤紧实度对其幼苗根系特征和氮代谢的影响。结果表明,土壤紧实度增加显著抑制平邑甜茶地下部分的生长,表现为根系长度、侧根数量以及延长根和黄褐色须根的质量、总表面积和总长度均随着土壤容重的增加而降低,根系活力也随土壤容重的增加显著降低,叶片和根系硝态氮质量分数则随土壤容重的增加而增加;叶片和根系中铵态氮质量分数的变化趋势一致,均是容重为1.3g·cm-3处理的最高,1.5g·cm-3处理次之,而紧实度小的1.1g·cm-3处理最低;叶片硝酸还原酶活性随着土壤容重的增加而降低,而根系硝酸还原酶活性和叶片谷氨酰胺合酶活性以中等紧实度的1.3g·cm-3处理最高,1.5g·cm-3处理显著低于其他处理,根系谷氨酰胺合酶活性则随着容重增加而升高。结果说明土壤紧实度能直接影响平邑甜茶植株的氮代谢活动,进而影响植株对养分的吸收和利用。  相似文献   

7.
《Scientia Horticulturae》2004,101(3):291-303
The relationships between tree vigour and soil and landscape properties of a rainfed olive orchard located on a marly slope of southern Spain were studied. The different properties and thickness of three soil layers (viz. the secondary carbonate-free layer, the solum, and the layer penetrated by roots), and the properties of the 0–30 cm layer, were used as soil variables. Olive tree vigour and soil properties were found to be strongly correlated. Much of the variability in tree vigour was related to soil morphology. The thickness of the root zone and the average CaCO3 content in the secondary carbonate-free layer and the upper 30 cm of soil accounted for ∼58 and ∼68%, respectively, of the variance in canopy volume. Tree vigour was related to some properties of the root zone, such as clay content and cation exchange capacity, expressed on a surface basis. Topographic properties such as distance to summit, slope gradient and profile curvature were also found to be significantly correlated with tree vigour, but had less influence than intrinsic soil properties.  相似文献   

8.
This case study describes a method for utilizing leaf-off airborne laser scanning (ALS) data for mapping characteristics of urban trees. ALS data were utilized to detect and update all street trees in the tree inventory of the City of Helsinki, Finland. The inventory consists of roughly 20,000 street trees with mean diameter at breast height (DBH) of 24 cm and mean height of 10.6 m. The large number of trees makes the manual updating process very laborious. The automatic mapping procedure presented in this paper detected 88.8% of all trees in the inventory. Tree height was predicted with root mean square error (RMSE) of 1.27 meters and tree DBH with RMSE of 6.9 cm. The presented method provides a practical and cost–effective tool for the mapping of urban tree characteristics. The cost–efficiency was further enhanced because the used ALS data were originally collected for other urban planning purposes.  相似文献   

9.
Trials with the fungicides Cuprozin WP (active ingredient copper hydroxide), Malvin WG (captan), Switch (cyprodinil and fludioxonil) and Signum (pyraclostrobin and boscalid) were conducted in two young blueberry orchards (variety ‘Duke’) severely affected by twig dieback. Treatments were sprayed twice during leaf fall in autumn 2011 or once during budding in spring 2012. No treatment had any effect against twig dieback. This result confirms earlier indications of winter frost damage of xylem tissue as the primary cause of these symptoms in Northern Germany. A colonisation of dead twigs by Godronia cassandrae was therefore probably the consequence, rather than cause, of dieback.  相似文献   

10.
Summary

Passionfruit are grown in the tropics and subtropics where mean monthly soil temperatures at 15 cm range from about 10° to 30°C. The choice of rootstock can also influence production with most industries exploiting either the purple (Passiflora edulis f. edulis) or golden passionfruit (P. edulis tflavicarpa). We examined the relationship between shoot and root growth in purple x golden hybrid E-23 grafted onto golden passionfruit seedlings. Growth was manipulated by varying the volume of the soil available to the roots or temperature of the root zone. Shoot and root growth increased as root zone volume increased from 0.3, 1.4, 4, 12 to 24 1. Shoot weight (Ws) was correlated with root weight (WR):WS = 12.697 + 5.272 WR + 0.195 WR2 (r2 = 91%, P<0.001), with the plants allocating a smaller proportion of dry matter to the roots as root weight increased. Differences in shoot growth with pot volume were not due to changes in water or nutrient status. In the temperature experiment, the two critical root zone temperatures at 90% of maximum growth were about 20° and 35° C for vine extension, leaf area, node and leaf production, and 20° and 30°C for flower production. Leaf and stem dry weight were optimal between about 18° and 34°C, while maximum root growth occurred at 38°C. There was a weak relationship between shoot (Ws) and root dry weight (WR): Ws = ?19.346 + 24.500 WR ?1.046 WR2 (r2 = 53%, .P<0.001). Apparently, variations in shoot growth at different soil temperatures cannot be explained solely by differences in root growth. Reduced growth at 10°C was associated with lower chlorophyll concentration, stomatal conductance and net CO2 assimilation, but not lower leaf water potential. The concentration of most nutrients were lower at 10°C than at higher temperatures, but none was outside the range which would be expected to restrict growth. There appears to be a co-ordination of shoot and root growth as the soil volume available for root growth increases, whereas root temperature affects the roots and tops differently. The results of the pot volume experiment demonstrate the importance of rootstock vigour in passionfruit breeding. Productivity would be affected in cool subtropical areas with soil <20°C and in tropical areas with soil >30°C.  相似文献   

11.
The effects of soil management practice on sward composition, the levels of available nutrients in the soil and leaf nutrient content of 11-year-old ‘Golden Delicious’ apple trees were examined over a 3-year period. The treatments consisted of: (a) grass sward mown at either 9 cm or 18 cm high, or controlled with the use of grass suppressant maleic hydrazide; (b) total herbicide coverage using simazine/paraquat or terbacil; (c) clean cultivation.Within the tree rows, beneath the tree canopies, the sward was composed of a higher percentage of weeds and grass and a lower percentage of clover than the sward in the alleys. In both areas, the magnitude of the clover component in the sward was in the order: grass suppressant > short grass > long grass. Over the 3 years, the mean dry-matter yield of herbage clippings returned was 11 938 kg ha?1 year?1 in the long-grass treatment, and 9089 kg ha?1 year?1 in the short-grass treatment. This was reflected in the higher amounts of mineral nutrients returned in the herbage clippings from the former treatment.In general, the surface soil (0–10 cm) from grassed plots contained more exchangeable Ca and Mg and less NO3-N than that from the non-grassed plots. Available P accumulated in the surface layer of the herbicide-treated plots. No significant differences in available nutrients were detected below 10 cm soil depth. Over the 3 years, soil management practice had no measurable effect on tree growth or crop yield. However, in the second and third seasons, trees from grassed plots tended to have lower leaf total N contents than those from non-grassed treatments, while trees from cultivated plots tended to have lower leaf K levels than trees from other plots.  相似文献   

12.
This study was conducted to compare two water-saving practices, deficit irrigation (DI) and partial rootzone drying (PRD), and examine how they affected soil water distribution, water use, growth and yield of greenhouse grown hot pepper compared to commercial irrigation (CI). Control (CI) in which irrigation water was applied to both sides of the system when soil water content was lower by 80% of field capacity; deficit irrigation (DI50, DI75) in which 50% and 75% irrigation water of CI supplied to both sides of the root system; 1PRD with half of the root system exposed to soil drying and other half kept well-watered with 50% irrigation water of CI, and 2PRD with 50% irrigation water of CI supplied, half to fixed side of the root system. The results showed mean soil volumetric water content of DI75, DI50, 1PRD and 2PRD were lower by 21.06%, 28.32%, 24.48% and 34.76%, respectively than that of CI after starting the experiment. Water consumption showed some significant effect of irrigation treatments during the growing period of drought stress application, and therefore decreased in DI75, DI50, 1PRD and 2PRD to a level around 75% and 50% of CI. All the DI and PRD treatments resulted in a reduction of total dry mass of 7.29–44.10%, shoot biomass of 24.97–47.72% compared to CI, but an increase in the root–shoot ratio of 12.50–35.42% compared to the control and with significant differences between 2PRD, 1PRD, DI50 and CI. The yield of 1PRD was significantly reduced by 23.98% compared to CI (19,566 kg hm−2) over a period of 109 days after transplanting. However, the 1PRD treatment had 17.21% and 24.54% additional yield over the DI50 and 2PRD treatments and had 52.05% higher irrigation water use efficiency (IWUE) than CI treatment. At harvest, although there was a significant difference recorded as single fruit weight and single fruit volume were reduced under the DI and PRD treatments, total soluble solids concentration of fruit harvested under the water-deficit treatments were higher compared to CI. Stomatal conductance measured in fresh leaf was the lowest under 1PRD treatment relative to CI and other treatments. The low stomatal conductance of fresh-leaf issue observed in the work supported the root signaling mechanism reported earlier in plants having undergone partial root drying cycles.  相似文献   

13.
We conducted two experiments to evaluate the impact of cultural treatments on growth and establishment of container-grown London planetrees (Platanus × acerifolia’ Bloodgood’). In both experiments, 48 trees grown in 100 l (#25) black plastic containers were assigned at random to one of three root-ball treatments prior to planting; no treatment (Control), outer 3 cm of roots removed around entire root-ball (Shave), or outer circling roots disentangled from the root-ball (Tease). In Experiment 1, half of the trees were fertilized with 400 g of controlled release fertilizer (15-9-12; N-P2O5-K2O) at planting and the remainder of the trees were not fertilized. In Experiment 2, half of the trees were mulched with an 8 cm deep × 2 m diameter ring of coarse ground pine bark at planting and the remainder of the trees were not mulched. In Experiment 1, fertilization at planting increased SPAD chlorophyll content on two of four measurement dates but did not affect cumulative height or caliper growth after two years. After two growing seasons, root-ball treatments (shaving or teasing) increased root growth outside the original root-ball compared to control trees. Both root-ball treatments also reduced circling roots. In Experiment 2, mulching at planting increased soil moisture and cumulative tree height and diameter growth. Shaving increased new root growth and both root-ball treatments improved root architecture and reduced circling roots. Overall, the study demonstrates that root-ball manipulations can stimulate new root growth and reduce circling roots. Mulch is a valuable aid to conserve soil moisture and increase tree growth. Fertilization at planting provided little benefit in this experiment, which may have been related to a high level of soil fertility at the site or nutrient loading of the trees from nursery culture prior to transplanting.  相似文献   

14.
土壤紧实度对玫瑰幼苗生长及根系氮代谢的影响   总被引：3，自引：0，他引：3  
孙曰波  赵兰勇  张玲 《园艺学报》2011,38(9):1775-1780
 以盆栽玫瑰（Rosa rugosa）‘珲春’实生苗为试材,研究土壤紧实度对其生长和根系氮代谢的影响。结果表明,玫瑰幼苗生长指标及生物量在不同土壤紧实度下的大小顺序为：1.30 g · cm-3处理 > 1.50 g · cm-3处理 > 1.10 g · cm-3处理;根冠比随土壤紧实度的增加而下降,1.50 g · cm-3处理下降显著。土壤紧实度的增加抑制了地下部的生长,表现为根系长度、侧根数量、主根直径等均随土壤紧实度的增加而降低,根系平均直径和总面积有所增加;根系活力以土壤紧实度为1.30 g · cm-3的处理最高,1.50 g · cm-3处理最低;根系中硝态氮、氨态氮含量和硝酸还原酶活性变化趋势一致,均是土壤紧实度为1.30 g · cm-3的处理最高,1.50 g · cm-3处理次之,1.10 g · cm-3处理最低;谷氨酰胺合成酶活性随着土壤紧实度的增加而升高。土壤紧实度显著影响玫瑰幼苗氮代谢活动,进而影响植株对养分的吸收和利用,1.30 g · cm-3的土壤紧实度较适宜于玫瑰的生长。  相似文献   

15.
Establishment of roadside plantings is often limited by adverse site conditions, particularly poor soil physical and chemical properties. We compared plant establishment of shrubs, herbaceous perennials, and grasses in response to addition of compost and/or tillage before planting in replicated plots at two locations along an interstate highway near Detroit, MI, USA. Plots at each location received one of four site preparation treatments: control (no treatment), compost only (top-dressed with 8 cm of municipal compost), tillage only (soil tilled to 20 cm) or compost + tillage (8 cm of compost added and tilled to 20 cm). Within each site preparation plot, we established sub-plots of 16 selections of shrubs, perennials, and ornamental grasses. Compost addition, plant selection, and location affected (P ≤ 0.05) plant survival, height growth, and % plant cover two years after planting. Tillage did not affect (P > 0.05) plant establishment. Similarly, the interaction of tillage × compost was not significant, indicating that surface application of compost was as effective as tilling compost into the soil. Improved plant establishment with the addition of compost was associated with improved soil and plant nutrition and reduced soil pH and soil bulk density. Within each plant group (i.e., shrubs, perennials, grasses) plant establishment varied widely. Overall, the results indicate that compost addition can improve establishment of diverse roadside plantings, which was associated with improved soil fertility. In contrast, tillage provided comparatively little benefit to plant performance in this trial.  相似文献   

16.
The influence of wood fiber substrates (WFS) and their volume weights (VW) on the growth of tomato transplants (Lycopersicon lycopersicum (L.) Karst. ex Farw.) were examined. No significant differences were observed for the absolute and relative growth rate of tomato transplants cultivated in WFS as compared to white peat (WP). Particularly in WFS plants showed a well developed root system. When the tomato transplants were cultivated in spring increases of VW led to a reduction of root growth, but no significant differences were observed for other plant parameters. In summer differences between weakly and strongly compacted substrate treatments for fresh mass of leaf and stem for both WFS were found. The coarse WFS also showed a significant difference in leaf area for these two treatments. Weakly compressed substrate had a faster decrease of matric potential in summer.WFS are suitable for cultivation of vegetable transplants and are a good alternative for peat-based substrates. When filling containers, moderate compression of WFS is recommended.  相似文献   

17.
A conversion period of at least two years is required for annual crops before produce may be certified as organically grown. There is a need for better understanding of the various management options for implementing from conventional to organic production. The purpose of this study was to evaluate the effects of three organic amendments on growth and yield of bell pepper (Capsicum annuum L.), the benefit:cost ratio, soil fertility and enzymatic activities during conversion to organic production. For that purpose six treatments were established: composted farmyard manure (FYMC, T1); vermicompost (VC, T2); poultry manure (PM, T3) along with biofertilizers (BF) [Azotobacter + phosphorus solubilizing bacteria (Pseudomonas striata)] and mix of three amendments (FYMC + PM + VC + BF, T4); integrated crop management (FYMC + NPK, T5) and unamended control (T6). The bell pepper yield under organic management was markedly lower (33–53% and 18–40% less in first and second year of conversion, respectively) than with the integrated crop management (FYMC 10 Mg ha−1 + NPK – 100:22:41.5 kg ha−1) treatment (T5). Combined application of three organic amendments (FYMC 10 Mg ha−1 + PM and VC each 1.5 Mg ha−1 + BF, T4) and T1 produced similar but significantly higher bell pepper yield (27.9 and 26.1 Mg ha−1, respectively) compared with other organic amendment treatments. Both T4 and T1 greatly lowered soil bulk density (1.15–1.17 Mg m−3), and enhanced soil pH (7.1) and oxidizable organic carbon (1.2–1.3%) compared with T5 and unamended control (T6) after a two-year transition period. However, the N, P and K levels were highest in the plots under integrated management. T1 plots showed higher dehydrogenase activity values. However, acid phosphatase and β-glucosidase activities were higher in T6 plots whereas urease activity was greater in T5 plots compared with other treatments. Among the treatments involving organic amendments alone, T1 gave a higher gross margin (US $ 8237.5 ha−1) than other treatments. We conclude that T1 was found more suitable for enhancing bell pepper growth and yield, through improved soil properties, during conversion to organic production.  相似文献   

18.
蚯蚓对苹果园土壤生物学特性及幼树生长的影响   总被引：2，自引：0，他引：2  
申为宝  杨洪强  乔海涛  申洁 《园艺学报》2009,36(10):1405-1410
 以果园褐土、潮土和棕壤以及2年生红富士苹果(Malus domestica Borkh. ) 幼树为试材, 在盆栽条件下, 通过向盆土埋放蚯蚓, 研究蚯蚓对土壤酶、土壤微生物量碳和氮以及苹果根系和新梢生长的影响。结果表明, 引入蚯蚓后, 3类土壤中脲酶、酸性磷酸酶和碱性磷酸酶活性以及微生物量氮均显著提高, 其中棕壤脲酶活性提高78.9% , 潮土碱性磷酸酶活性提高170.0% , 棕壤微生物量氮提高180.4%。蚯蚓处理也显著提高褐土和潮土微生物量碳, 其中潮土微生物量碳提高幅度最大, 达299.2%。3类土壤经蚯蚓处理后, 苹果幼树根系活力、根系和新梢生长量均显著提高, 其中, 棕壤中的幼树根系活力最高, 褐土中的幼树根系生长量最大, 潮土中的幼树新梢生长量最大。  相似文献   

19.
Soil properties vary according to the topography. They affect water uptake and root exploration in the soil. Consequently, they may also influence the spread of plant–parasitic nematodes. This study reports on the effect of toposequence-related variations in soil on banana yields, foliar nutrient status, and nematode impact. Twenty banana plots were visited within 6 hills/valleys at each of the three toposequence positions: valley bottom, mid-slope and crest. Important variability in plant growth, nutrition and soil properties was observed within the toposequence. Significantly better plant growth (height and girth) was observed in the valley bottoms, where banana bunch weight was 1.7–3.4 kg higher (although not significant) than at upper toposequence positions. Best plant growth was observed in valley bottoms in contrast to the highest N and K foliar deficiencies in this position. Plants in the valley bottoms had higher foliar Ca and Mg, and K compared to those in the crest. Plants in the mid-slope had greater percentage of dead roots (19.1%), compared to the plants in the valley bottoms (12.3%) and the crest (14.2%). Soils in the valley bottoms were deeper, sandier, with lower organic matter, lower N, and K compared to the soils at higher toposequence. Nematodes likely play a key role in banana root damage, however, their effect appear to be in relation to various soil factors at each position. The abundance of Pratylenchus goodeyi had generally limited impact on banana yields in fields having less than 5% slope (crest and valley bottom) where soil conditions were more optimal for root growth. However, in the presence of increased run-off on steeper middle slopes, root death was increased even under moderate pressure from P. goodeyi.  相似文献   

20.
《Scientia Horticulturae》2005,104(1):79-89
The seasonal effect of soil water availability on leaf gas exchange of plantain plants cv. Hartón growing on two different texture soils (loamy and clayey) were evaluated. Soil water deficits corresponded to 48, 24 and 4 days without precipitation. Daily measurements of leaf gas exchange and microclimatic conditions were carried out at 2 h intervals in a humid tropical environment south of Maracaibo Lake, Venezuela. The results show that cv. Hartón is sensitive to conditions of low water deficit on loamy and to a much greater degree on clayey soils. A marked reduction in leaf conductance (gs) was observed under severe as well as moderate deficit (below 50 mmol m−2 s−1) on clayey soils. Under low deficit gs increases to values between 60 and 100 mmol m−2 s−1. The same trend was observed in plants on loamy soils but higher gs for all conditions were obtained compared with plants on clayey soil. Stomatal closure produced a reduction of 85 and 55% of total assimilation (Atot) for severe and moderate deficit in plants on clayey soils, respectively. While plants on loamy soil exhibited a 65 and 35% reduction, respectively. Water use efficiency (WUE) consistently decreased as available soil water decreased on both soil types. Independently of soil water conditions, higher WUE were always obtained for loamy soils. This suggests that cv. Hartón does not have the ability to adjust the CO2 assimilation to transpiration ratio in order to optimize gas exchange. This evidences the importance of maintaining high conditions of available soil water in order to avoid lower assimilation rates that probably influence negatively on yield and fruit quality.  相似文献   

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