Relationship of water status to vegetative growth and leaf gas exchange of peach (Prunus persica) trees on different rootstocks

We investigated relationships between tree water status, vegetative growth and leaf gas exchange of peach trees growing on different rootstocks under field conditions. Tree water status was manipulated by partially covering (0, approximately 30 and approximately 60%) the tree canopies on individual days and then evaluating the effects of tree water status on vegetative growth and leaf gas exchange. Early morning stem water potentials were approximately -0.4 MPa for trees in all treatments, but mean midday values ranged from -1.1 to -1.7 MPa depending on rootstock and canopy coverage treatment. Relative shoot extension growth rate, leaf conductance, transpiration rate and net CO2 exchange rate differed significantly among trees in the different rootstocks and canopy coverage treatments. Shoot extension growth rate, leaf conductance, leaf transpiration rate and leaf net CO2 exchange rate were linearly correlated with midday stem water potential. These relationships were independent of the rootstock and canopy coverage treatments, indicating that tree water relations are probably directly involved in the mechanism that imparts vegetative growth control by selected peach rootstocks.     

Influence of controlled water supply on shoot and root development of young peach trees

Three controlled water supply treatments were applied to 1-year-old peach trees grown in root observation boxes. The treatments were: I(0), growth medium maintained at 50% field capacity; I(1), water supplied when daily net tree stem diameter change was negative or zero for 1 day; I(3) as for I(1) except that water was applied after net daily stem diameter change was negative or zero for 3 consecutive days. Trees in treatment I(0) had the greatest mean daily first-order shoot growth rates, and trees in treatment I(3) had the lowest shoot growth rates. Because leaf production rate (apparent plastochron) of first-order shoots was unaffected by treatment, differences in shoot length were due to differences in internode extension and not to the number of internodes. Trees in treatment I(0) had a greater number of second-order shoot axes than trees in treatment I(1) or I(3). Furthermore, an increase in the rate of growth of the first-order shoot axis was associated with an increased tendency for branching (i.e., the development of sylleptic second-order shoots). Increased leaf length was also associated with more frequent watering. Trees in treatment I(0) had the greatest root lengths and dry weights, and this was attributed to a greater number of first-and second-order (lateral) root axes compared with trees in the I(1) and I(3) treatments. The extension rate and apical diameter of first-order roots were reduced by the I(3) treatment. The density of second-order roots along primary root axes was not affected by any of the treatments.     

Hydraulic conductance characteristics of peach (Prunus persica) trees on different rootstocks are related to biomass production and distribution

We investigated hydraulic conductance characteristics and associated dry matter production and distribution of peach trees grafted on different rootstocks growing in the field. A single scion genotype was grown on a low ('K146-43'), an intermediate ('Hiawatha') and a high ('Nemaguard') vigor rootstock. 'K146-43' and 'Hiawatha' rootstocks had 27 and 52% lower mean leaf-specific hydraulic conductances, respectively, than the more vigorous 'Nemaguard' rootstock. Tree growth rates and patterns of biomass distribution varied significantly among rootstocks. Mean dry mass relative growth rates of trees on 'K146-43' and 'Nemaguard' were 66 and 75%, respectively, of the rates of trees on 'Nemaguard', and the scion to rootstock dry mass ratios of trees on 'K146-43' and 'Hiawatha' were 63 and 82%, respectively, of the ratio of trees on 'Nemaguard'. Thus, differences in dry matter distribution between the scion and rootstock, which may be a compensatory response to the differences in leaf specific hydraulic conductance among rootstocks, appeared to be related to differences in growth rates. Correspondingly, there was a positive linear relationship between the scion to rootstock dry mass ratio and the rootstock to scion hydraulic conductance ratio when conductance was normalized for dry mass. This study confirms that rootstock effects on tree water relations and vegetative growth potential result, at least in part, from differences in tree hydraulic conductance associated with specific peach rootstocks.     

Crop load and water stress effects on daily stem growth in peach (Prunus persica)

We investigated crop load and water stress effects on diurnal stem extension growth of field-grown peach (Prunus persica (L.) Batsch) trees. Neither the presence of fruit nor reduced irrigation significantly altered the timing of diurnal fluctuations in stem growth rate. Stems with subtending fruit had significantly reduced growth compared to stems with no subtending fruit. Crop load had no significant effect on relative stem extension rates and the majority of the reduction in absolute growth was the result of a smaller zone of elongation in fruit-bearing stems than in stems with no subtending fruit. Fruit removal did not increase growth rates within 24 h. When irrigation was reduced, the length of the stem elongation zone and total daily stem growth were significantly decreased relative to well-irrigated controls and the decreases were highly correlated with stem water potential. Compared with well-irrigated controls, relative stem extension rates of water-stressed trees were reduced at several times during the 24-h period, but the degree of reduction was not proportional to the difference in stem water potentials between the treatments.     

Growth strategy of trees related to successional status I. Architecture and extension growth

The architecture and growth pattern of early (Alnus nepalensis and Schima khasiana) and late (Machilus kingii, Quercus dealbata and Q. griffithii) successional tree species in a sub-tropical montane, humid, evergreen forest at Upper Shillong (1900 m) in north-east India were analyzed and related to their ecological strategy for niche occupancy in the forest ecosystem. In the early successional species the architectural development pattern and growth design are geared to maximize production under high light environments. These trees have an indeterminate pattern of shoot growth, a prolonged growth period with greater extension growth and rhythmicity (except for A. nepalensis with continuous growth) and branch mainly by syllepsis. These species emphasize vertical growth at the expense of lateral spread. In contrast, the late successional species make modest growth under a determinate scheme, the growth being confined to preformed bud primordia for a brief period of the growing season. There is less rhythmicity in growth and branch productin is by prolepsis. These species emphasize lateral spread, as an adaptation to highly competitive environments. In forest situations these species have one determinate flush of shoot growth only but in open situations there were two such flushes. Bifurcation ratio values are found to vary in forest and open situations, suggesting the capacity of the species to adjust their architecture to changed light conditions.     

Tree water storage and its diurnal dynamics related to sap flow and changes in stem volume in old-growth Douglas-fir trees

Diurnal and seasonal tree water storage was studied in three large Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) trees at the Wind River Canopy Crane Research site. Changes in water storage were based on measurements of sap flow and changes in stem volume and tissue water content at different heights in the stem and branches. We measured sap flow by two variants of the heat balance method (with internal heating in stems and external heating in branches), stem volume with electronic dendrometers, and tissue water content gravimetrically. Water storage was calculated from the differences in diurnal courses of sap flow at different heights and their integration. Old-growth Douglas-fir trees contained large amounts of free water: stem sapwood was the most important storage site, followed by stem phloem, branch sapwood, branch phloem and needles. There were significant time shifts (minutes to hours) between sap flow measured at different positions within the transport system (i.e., stem base to shoot tip), suggesting a highly elastic transport system. On selected fine days between late July and early October, when daily transpiration ranged from 150 to 300 liters, the quantity of stored water used daily ranged from 25 to 55 liters, i.e., about 20% of daily total sap flow. The greatest amount of this stored water came from the lower stem; however, proportionally more water was removed from the upper parts of the tree relative to their water storage capacity. In addition to lags in sap flow from one point in the hydrolic pathway to another, the withdrawal and replacement of stored water was reflected in changes in stem volume. When point-to-point lags in sap flow (minutes to hours near the top and stem base, respectively) were considered, there was a strong linear relationship between stem volume changes and transpiration. Volume changes of the whole tree were small (equivalent to 14% of the total daily use of stored water) indicating that most stored water came from the stem and from its inelastic (sapwood) tissues. Whole tree transpiration can be maintained with stored water for about a week, but it can be maintained with stored water from the upper crown alone for no more than a few hours.     

The influence of severe shoot pruning on growth,carbon and nitrogen status in young peach trees (Prunus persica)

One-year-old peach trees (Prunus persica (L.) Batsch) were severely pruned in July by removing 60% of the shoots. Tree responses were analyzed in terms of architecture and nutritional status. Tree growth was recorded from July to September by nondestructive (leaf production, thickening and branching of the remaining secondary axes) and destructive measurements (biomass partitioning and concentrations of total nitrogen (N) and nonstructural carbohydrates (NC) in specific tissues). The dry weights of pruned trees were lower than those of control trees at the end of the growing season (i.e., 2.5 months after pruning), whereas shoot:root ratios were restored to the initial values. Tree response occurred in two stages. During the first 24 days following pruning, the growth components of the remaining secondary axes were similar to the control, and new secondary axes were produced. During the next 17 days, increases in both diameter and branching of secondary axes contributed to the maintenance of pruned tree growth rate (similar to that of control trees) and restoration of initial shoot:root ratios. No significant effect of pruning was observed on NC concentrations, whereas N concentrations increased in several organs of the pruned trees during the first growth period. The transient increase in internal N availability contributed to the initiation of new axes and the restoration of a more functional biomass partitioning between shoots and roots.     

不同立地、土壤类型对土壤含水量和苹果新梢生长的影响

为了给苹果园土壤水分管理提供依据,以‘长富2’苹果为试材,选取粘壤土平地、粘壤土梯田、壤土平地、壤土梯田、沙土平地、沙土梯田、上层壤土、下层尾矿砂平地7种不同立地、土壤类型苹果园,研究其对土壤含水量及苹果新梢生长的影响。结果表明:不同时期粘壤土平地的土壤含水量均极显著高于沙土平地、沙土梯田、上层壤土下层尾矿砂平地的土壤含水量,沙土平地、沙土梯田的土壤含水量均极显著低于其他立地、土壤类型。各立地、土壤类型长、中、短新梢均只有一次生长,迅速生长期基本一致,在4月初到5月底;除沙土平地和沙土梯田类型外,其他5种立地、土壤类型徒长新梢均出现了二次生长,第1次迅速生长期与其他新梢一致,第2次生长期在7月至8月。不同立地、土壤类型土壤含水量与苹果各类新梢长度均呈正相关,达到显著相关水平的时期多出现在新梢生长高峰期,其中,4月22日至5月13日,壤土梯田、沙土平地的土壤含水量与长梢长度的相关系数分别为0.968、0.966,5月14日至5月31日,壤土梯田的土壤含水量与徒长新梢长度的相关系数为0.986,壤土平地的土壤含水量与长梢长度的相关系数为0.980。     

The dwarfing mechanism of citrus rootstocks F&A 418 and #23 is related to competition between vegetative and reproductive growth

The annual development of Navelina (Citrus sinensis (L.) Osbeck) trees budded on three hybrid citrus rootstocks was studied. Two rootstocks, named #23 and #24, were obtained from the cross of Troyer citrange (C. sinensis x Poncirus trifoliata (L.) Raf.) x Cleopatra mandarin (C. reshni Hort. ex Tan.). The third rootstock, named F&A 418, came from a cross of Troyer citrange x common mandarin (C. deliciosa Ten.). Rootstocks #23 and F&A 418 are dwarfing rootstocks and reduce the size of the scion by about 75%. Rootstock #24 yields a standard size scion. Major growth differences that influenced tree size were apparent during the first summer after grafting and appeared to be related to fruit productivity, because defruiting the dwarfed scions caused a significant increase in vegetative shoot development, including summer sprouting. The reduced growth of the dwarfed scions was not restored by hormone application, indicating that a hormonal deficiency is unlikely to be the primary reason for scion dwarfing, although differences in gibberellin concentrations were found in actively growing shoots. Leaf photosynthesis was similar in scions on all three rootstocks, but the carbohydrate accumulation in fruits and fibrous roots during the summer sprouting period was significantly greater in the dwarfed trees than in the standard trees. Our results suggest that the dwarfing mechanism induced by the F&A 418 and #23 rootstocks is mediated by enhanced reproductive development and fruit growth, resulting in reduced vegetative development in the summer. Thus, a change in the pattern of assimilate distribution appears to be one of the main components of the dwarfing mechanism.     

The interplay between leaf water potential and osmotic adjustment on photosynthetic and growth parameters of tropical dry forest trees

Mimosa tenuiflora and Piptadenia stipulacea are commonly accepted as drought-tolerant species but little is known about their response to drought followed by rehydration.Therefore,the interplay between leaf water potential and osmotic adjustment on photo synthetic and growth parameters of these species was examined.A greenhouse study was conducted in a split-plot design with two water conditions in the main plots(control;drought followed by rehydration),and eight sampling times in the subplots(1...     

Vegetative propagation of Dalbergia sissoo: effect of growth regulators, length, position of shoot and type of cuttings on rooting potential in stem cuttings

The effect of auxins (IAA or IBA at 100,200,500 mg L 1) on rooting and sprouting parameters differed significantly (p < 0.05).Rooting and sprouting percentages were higher in some treatments while other parameters were significantly higher in other treatments.The results of the present study revealed that rooting was significantly (p < 0.05) affected by the length of cuttings,as well as the position of shoots and type of cuttings.On average,86.0 per cent rooting was observed in the 30-cm long cuttings compared to the other two lengths of cuttings,i.e.,20 and 25 cm,irrespective of any auxin treatment.In a control set,without any auxin treatment,a maximum of 60.0% rooting was recorded in the 30-cm long cuttings and a minimum of 40.0% of the cuttings rooted in the 20-cm long cuttings.Similarly,cuttings collected from the lower and upper portions of shoots resulted in 72.5 and 52.5 per cent rooting respectively,irrespective of auxin treatments.Maximum rooting was observed in the lower portion (40.0%) of cutting compared to the upper portion (30.0%) in the control set without auxin treatment.Leafless branches produced maximum (72.0%) rooting compared to the leafy cuttings (35.0%),irrespective of the auxin treatment.The leafy cuttings produces a minimum of 15.0% sprouting and rooting in the control set.     

Additive mixed models to study the effect of tree age and climatic factors on stem radial growth of Eucalyptus trees

The effect of tree age and climatic variables on stem radial growth of two hybrid clones of Eucalyptus was determined using longitudinal data from eastern South Africa.The stem radius of was measured weekly as the response variable.In addition to tree age,average weekly temperature,solar radiation,relative humidity and wind speed were simultaneously recorded with total rainfall at the site.An additive mixed effects model that incorporates a non-parametric smooth function was used.The results of the analysis indicate that the relationship between stem radius and each of the covariates can be explained by nonlinear functions.Models that account for the effect of clone and season together with their interaction in the parametric part of the additive mixed model were also fitted.The interaction between clone and season was not significant in all cases.For analyzing the joint effect all the covariates,additive mixed models that included two or more covariates were fitted.A significant effect of tree age was found in all cases.Although tree age was the key determinant of stem radial growth,weather variables also had a significant effect that was dependent on season.