Tree Water Deficit Research Articles

A 3-Year Study of Water Relations of Urban Street Trees

1. A 3-year field study of the water relations of street trees in New York City was undertaken with the following objectives: (i) to ascertain whether there was empirical evidence for water deficits; (ii) if water deficits occur, to correlate these events with prevailing weather conditions; (iii) to determine whether tree water relations varied systematically with street exposure; (iv) to compare street microclimate with that of a nearby park; (v) to compare water relations of two common street tree species; (vi) to evaluate the effectiveness of a minimum irrigation programme. 2. Water deficits in trees, as evidenced by midday stomatal closure, occurred but with lower frequency than is commonly expected. Average predicted frequency during the summer was 13% over a 21-year period. When deficits occurred, they were demand driven rather than supply limited. Deficit periods were characterized by maximum air temperatures on the street >41 0C and a maximum atmospheric vapour pressure deficit of 75 kPa. Official weather station data collected in a nearby park indicated far milder conditions, with a maximum air temperature and vapour pressure deficit of 32 'C and 2*5 kPa, respectively. Over the midday period, the mixing ratio, a conservative measure of atmospheric water content, was 84 g kg-' lower on Columbus Avenue than in the park, indicating that the street microclimate was far drier. 3. The west side of the street received more solar radiation than the east and was usually slightly hotter than either the east or the park. Yet, trees on the west side of the street were not more water stressed. Though Fraxinus pennsylvanica transpired at higher rates and sustained more negative water potentials than Tilia cordata these differences were variable and could not be separated statistically. Similarly, Fraxinus pennsylvanica showed small but statistically non-significant responses to minimal weekly irrigation while Tilia cordata was unresponsive.

Mechanism of cavitation development in the pine wilt disease

AbstractVolatile terpenes increase in xylem tissue after infection of Pinus thunbergii with the pine wood nematode (Bursaphelenchus xylophilus). The role of these terpenes in traeheid cavitation, which blocks xylem‐sap ascent and leads to water deficit in pine trees, was assessed. Volatile terpene concentration increased long before initiation of tracheid cavitation. After the volatile terpenes reached the highest concentration, severe cavitation developed. Direct injection of α‐pinene into healthy pine trunks formed artificial cavitation in xylem. These observations support the hypothesis that excessively produced volatiles, which are hydrophobic and have lower surface tension than water can promote tracheid cavitation in pine wilt disease.

INFLUENCE OF PREHARVEST IRRIGATION CUTOFF DURATION AND POSTHARVEST WATER DEPRIVATION IN ALMOND

Previously well irrigated mature `Nonpareil' almond trees (Prunus dulcis) were subjected to varying periods of water deprivation prior to harvest and then to either full or no postharvest irrigation. Eight preharvest water deprivation (PWD) lengths ranging from 14 to 63 days were evaluated on a sandy loam soil with a rooting depth of about 1.5 m.Development of tree water deficits occurred rapidly following PWD. Predawn leaf water potential decreased to about -1.8 and -3.1 MPa after 10 and 20 days, respectively. Defoliation began about 30 days after PWD and trees subjected to more than 50 days completely defoliated. The rate of hull split was directly related to the PWD duration. With early cutoffs, the size of the hull split-arrested nuts at harvest was large compared with the same nut type in later cutoffs suggesting that as nuts develop, large nuts are preferential sinks for assimilates. Kernel size was only mildly reduced by PWD during the first study year. There was a trend toward lower total kernel yield with longer PWD as a result of smaller kernel girth but yield differences were not significant. The number of nuts remaining in the tree after shaking was not related to PWD. Bark strength increased after PWD with 10 to 14 days required to prevent shaker damage. Postharvest irrigation resulted in late season defoliation but no rebloom. Bloom density reductions in 1990 were related more to the lack of 1989 postharvest irrigation than to early PWD.

Physiological response of large Douglas-fir to natural and induced soil water deficits

The effect of soil water deficits on net photosynthesis, transpiration, stomatal activity, twig xylem pressure potentials, and cambial growth were studied in large, field-grown Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco). Abnormally high soil and tree water deficits were periodically induced during the summer by withholding supplementary irrigation water from a 28-m Douglas-fir contained in a weighing lysimeter. This eventually promoted persistent stomatal closure which limited gas exchange rates. At such times, net photosynthesis was confined to early morning daylight hours and daily totals were reduced by about 70% compared with the well-watered condition; xylem pressure potentials decreased only about 0.6 MPa during the day from a predawn level of −1.6 MPa. After irrigation or major rainfall, predawn xylem pressure potentials increased to −0.4 MPa and the tree stem abruptly increased in size; both indicated the hydraulic recharge of internal tree tissues depleted during the induced drought. Stomata then responded primarily to light, even though midday xylem pressure potentials remained near −2.2 MPa. These data are compared with those obtained from a nearby tree which was responding to natural fluctuations in soil moisture content.

Phenology and Ecophysiology of Tropical Trees: Erythrina Poeppigiana O. F. Cook

Under the climatic conditions of San Jose, Costa Rica, leaf fall, flowering, and shoot emergence of Erythrina poeppigiana O. F. Cook were markedly asynchronous among trees of the same population, suggesting strong endogenous control of the tree's development. During 1 yr, trees passed through two cycles of leaf shedding and shoot emergence. The endogenous periodicity of leaf shedding appeared to be primarily the result of leaf senescence. During the dry season, leaf senescence and hence leaf shedding were enhanced by tree water deficits. As a consequence of leaf shedding, water stress was alleviated and shoot emergence occurred, even under continued drought. The degree of water stress, reflected in stem shrinkage, was affected by tree size, soil moisture availability, and seasonal changes in evapotranspiration. Large trees at dry sites water deficits and hence passed through leaf change early in the dry season, while smaller trees and trees at humid sites did so up to 3 mo later. The phenology of Erythrina along an altitudinal gradient of increasing atmospheric water stress showed a transition from an evergreen to a deciduous habit. At permanently humid sites, all phenological phases occurred simultaneously on the same tree. With increasing drought, consecutive developmental stages tended to be more separate in time and more synchronized. In humid tropical climates, characterized by the absence of significant environmental stress, the periodic development of Erythrina is thus primarily determined by variables such as leaf age and tree size, which affect the tree's internal functional balance. Increasing environmental stress, in tropical environments most likely drought, may secondly synchronize certain phases of the basic endogenous rhythmicity with seasonal climatic changes.

Water Relations: Soil Fertility, and Plant Nutrient Composition of a Pygmy Oak Ecosystem

The water and nutrient relations of Buzzard's Roost, an unusual pygmy oak ecosystem in southwest Missouri, USA, were studied in 1976 and 1977 in an attempt both to characterize the ecophysiology of the individuals's and find the causative agents for the existence of the pygmy forest. The stunted trees were mostly blackjack oak (Quercus marilandica) with some northern red oak (Q. rubra) and a few black oak (Q. velutina.?). In addition to being stunted, the trees were gnarled and twisted and had miniature leaves and acorns. Results of soil analysis showed the pygmy forest soil to be very acidic (pHw = 4.6), with very low levels of Ca and Mg (0.25 and 0.12 meq/100g, respectively) and very high levels of Al (600 ppm). Adjacent non—pygmy forest soils did not display these characteristics. Foliar analysis of blackjack, northern red, and black oak showed Ca and Mg to be much lower in pygmy foliage than in non—pygmy foliage, at three times during the growing season. Diurnal and seasonal pattern of xylen pressure potential, leaf conductance, and soil moisture content illustrated the development of very severe tree water deficits at Buzzard's Roost. Predawn and midday xylem pressure potentials declined to as low as —3610 and —4200kPa, respectively, accompanied by complete daytime stomatal closure. However, water stresses in nearby non—pygmy oaks sites, implying that water stress was not the major factor or causative agent in the stunting process. The evidence suggests that the very low nutrient levels in the soil, especially of Ca and Mg, plus the very high levels of Al, may be deficient (and/or toxic) for normal tree growth and development, and possibly responsible for the existence of the pygmy oak forest. Also, the xeric site characteristics add another severe stress to this ecosystem.

Water deficits in timberline trees in the Snowy Mountains of South-Eastern Australia.

Leaf water potential (Ψ), leaf diffusion resistance (r 1) and net photosynthesis of leaves of Eucalyptus pauciflora Sieb at timberline (2,040 m) were measured in winter and spring in the Snowy Mountains area of southeastern Australia. Four treatments were established in a 2×2 factorial design involving exposure to direct sunlight, screening to reduce solar radiation by approximately 50%, exposure to direct radiant cooling at night, and screening to reduce radiant cooling. A less comprehensive set of measurements was also made in summer.No significant water deficits developed in any of the treatments, water potentials remaining above Ψ=-14 bars in winter, and above Ψ=-10 bars in spring, well above the levels needed to cause tissue damage in this species. These results contrast with the extreme desiccation reported in trees at timberline in other regions and suggest that winter dehydration is not an important factor in limiting tree distribution in the Snowy Mountains.Tissue damage was observed in all treatments and was most pronounced in those exposed to natural radiation frosts, in which shoot die-back occurred. Although factors other than frost incidence may have been influenced by the treatments, the results suggest that low temperatures, possibly associated with periods of clear weather and cold nights in the spring, when the tissue was no longer winter-hardy, may have been the main factors responsible.

Studies on the water balance in Satsuma orange trees. III

The experiments were carried out during 1962-1965, to clarify the daily and seasonal changes of the water saturation deficit (W. S. D.) of leaves, as an index of the degree of water deficit in Satsuma orange trees. And further observations were made on the relationship between W. S. D. of leaves, climatic factors and soil moisture. The results obtained were summarized as follows:1. Daily changes of W.S.D. of leaves in summer were rose in a steady curve with sunrise, and maximum value was found to occur around noon, thereafter, values were gradually descended, and minimum value was observed around 6.00P.M. each day. On the other hand, its changes in winter were smaller than that in summer, although, the tendency was almost similar to that observed in summer.2. On the seasonal changes of W.S.D. of leaves, during the period from early to late February, its values were definitely ascended, and it might be mainly due to the low temperature and cold wind. And its values in early February were found to have the highest in winter period, but thereafter to late March, W.S.D. of leaves were gradually descended. In early May, however, W.S.D. of leaves were ascended rapidly and formed a peak, it seemed to be closely related to the drought of spring and sprouting a current shoots, but thereafter to late June, its values were slightly descended. During the period from early July to late August, under the condition of high temperature and drought, W.S.D. of leaves were notably ascended, and the trend was most remarkable in early August, its values in this period were the highest one. W.S.D. of leaves in September were considerably high compared with that in October, thereafter from early October its values were descended.3. In the winter half (Nov.-Apr.), W.S.D. of leaves had the high negative correlations with the air temperature, soil temperature, precipitation and saturation deficit of water vapour pressure. On the contrary, W.S.D. of leaves in the summer half (May-Oct.) had the high positive correlations with the air temperature, soil temperature and saturation deficit of water vapour pressure.4. W.S.D. of leaves in autumn and winter were ascended with the increasing of cold wind velocity, also, its values were ascended with the increasing of hours of exposed to the cold wind. Further, velocity of transpiration stream in shoot was increased by the exposed to the cold wind, and its velocity was diminished with the decreasing of soil moisture.5. W.S.D. of leaves in summer had a very high negative correlation with the soil moisture, therefore, by the use of curved regression equation, it was possible that the soil moisture is presumed with the W.S.D. of leaves. When the soil moisture was between field capacity and moisture equivalent, changes of W.S.D. of leaves were very small, and then W.S.D. of leaves were slowly ascended with the decreasing of soil moisture in less than moisture equivalent. Thereafter, its values were extremely ascended, being accompanied with a marked decreased of soil moisture to the wilting point. In addition, when the W.S.D. of leaves were reached 8.0 per cent, the trees showed visible symptoms of wilting in leaves, and its values reached 10.0 per cent, showed visible symptoms of wilting in fruits.In the winter period, however, no correlation could be found between W.S.D. of leaves and soil moisture, accordingly, the ascension of W.S.D. of leaves in winter were might be mainly due to the climatic factors.

The measurement of water deficits in broadleaf plants

A review of past work and a comparison of the well-known disk technique with Stocker's whole leaf method for determining water deficit of some hardwood trees reveals confusion in existing terms and methods. The water relations of leaf disks cut from broadleaf trees cannot be assumed to be the same as whole leaves, since the excised disk usually requires more water per unit weight to saturate. Stocker's term wasser defizit (WD) and the whole leaf method, when modified to allow shorter equilibration schedules, remain the best way to express and measure water deficits in forest trees.