Factors involved in alleviating water stress by partial crop removal in pear trees

We studied the relief of water stress associated with fruit thinning in pear (Pyrus communis L.) trees during drought to determine what mechanisms, other than stomatal adjustment, were involved. Combinations of control irrigation (equal to crop water use less effective rainfall) and deficit irrigation (equal to 20% of control irrigation), fruit load (unthinned and thinned to 40 fruits per tree) and root pruning (pruned and unpruned) treatments were applied to pear (cv. 'Conference') trees during Stage II of fruit development. Daily patterns of midday stem water potential (Psi(stem)) and leaf conductance to water vapor (g(l)) of deficit-irrigated trees differed after fruit thinning. In response to fruit thinning, gl progressively declined with water stress until 30 days after fruit thinning and then leveled off, whereas the effects of decreased fruit load on Psi(stem) peaked 30-40 days after fruit thinning and then tended to decline. Soil water depletion was significantly correlated with fruit load during drought. Our results indicate that stomatal adjustment and the resulting soil water conservation were the factors determining the Psi(stem) response to fruit thinning. However, these factors could not explain differences in daily patterns between g(l) and Psi(stem) after fruit thinning. In all cases, effects of root pruning treatments on Psi(stem) in deficit-irrigated trees were transitory (Psi(stem) recovered from root pruning in less than 30 days), but the recovery of Psi(stem) after root pruning was faster in trees with low fruit loads. This behavior is compatible with the concept that the water balance (reflected by Psi(stem) values) was better in trees with low fruit loads compared with unthinned trees, perhaps because more carbon was available for root growth. Thus, a root growth component is hypothesized as a mechanism to explain the bimodal Psi(stem) response to fruit thinning during drought.     

Responses of apple fruit size to tree water status and crop load

The combined effects of irrigation rate and crop load on apple yield and fruit size were examined in two commercial apple orchards (cv. Golden Delicious) in a semi-arid zone. The irrigation rates applied were 1, 3 and 7 mm day(-1), and the two fruit thinning treatments involved adjusting crop load to 100 and 300 fruits per tree at Ortal and 50 and 150 fruits per tree at Matityahu. Unthinned trees served as the control. The fruit from each tree was picked separately, and fruit size distribution was determined with a commercial grading machine. Midday stem water potentials varied from -0.9 to -2.8 MPa, crop load varied from 80,000 to 1,900,000 fruit ha(-1) and crop yield varied from 10 to 144 Mg ha(-1). Midday stem water potential decreased with increasing crop load in all irrigation treatments at Matityahu, but only in the 1 mm day(-1) treatment at Ortal. The extent of the lowering of midday stem water potential by crop load decreased with increasing soil water availability. At both orchards, a similar response of total crop yield to crop load on a per hectare basis was observed. Mean fruit mass and relative yield of fruit > 70 mm in diameter increased with midday stem water potential, with the low crop loads having similar but steeper slopes than the high crop load. The responses of mean fruit mass and relative yield of fruit > 70 mm in diameter to midday stem water potential were similar at both orchards, perhaps indicating that thresholds for irrigation scheduling are transferable to other orchards within a region. Factors that may limit the transferability of these thresholds are discussed.     

Effect of crop load on fruiting and leaf photosynthesis of 'Braeburn'/M.26 apple trees

Four-year-old apple (Malus x domestica Borkh.) trees cv. 'Braeburn' on M.26 rootstock were thinned at full bloom to establish six crop loads ranging from a heavy crop to a deflowered treatment. At harvest, mean yield per tree varied from 0 to 38 kg and mean fruit weight ranged from 225 g in the heaviest cropping treatment to 385 g in the lightest cropping treatment. Light cropping resulted in a significant advance in fruit maturity as indicated by background color, starch/iodine score and soluble solids. There were small differences in leaf photosynthetic rate among the treatments when shoot growth was active. However, in early January, coincident with cessation of shoot growth and maximum rate of accumulation of fruit weight, leaf assimilation rate was reduced by as much as 65% on the deflowered trees compared to the trees carrying the heaviest crop. Leaf assimilation rate showed a curvilinear response to crop load at this time, with little increase in leaf assimilation when crop load exceeded 12 fruit m(-2) leaf area.     

经济林树种在园林绿化中的应用

许多经济林树种具有良好的观赏价值和适应性，是园林绿化的好树种。园林绿化效果的体现，很大程度上取决于植物材料的应用，各种植物材料通过科学搭配，遵循生态学基本原理，因地制宜，适地适树，充分利用土地、空间，这不仅能满足人们的审美要求，也能使绿地充分发挥其生态功能。章分析了经济林树种在园林中应用的意义，并简要介绍了部分适于绿化的经济林树种，如花楸树、柿树、紫红叶榛子、曲茎榛子、红苞日本栗、垂枝毛樱桃、枸杞、核桃楸、银杏、垂枝杏、斑叶杏、山楂、金手指葡萄、软枣称狠桃等。     

Mist, substrate water potential and cutting water potential influence rooting of stem cuttings of loblolly pine

We investigated the influence of cutting water potential (Psicut) on rooting of juvenile hardwood (dormant) and softwood (succulent) stem cuttings of loblolly pine (Pinus taeda L.) propagated under varying substrate water potentials (Psisub) and volumes of mist application. Mist treatment and Psisub contributed to the Psicut of unrooted stem cuttings. When Psisub was held constant across mist treatments, mist treatment contributed strongly to Psicut. Substrate water potential affected rooting percentage when mist treatment was sub-optimal or excessive, otherwise mist treatment had a stronger effect than Psisub on rooting percentage. Cuttings rooted best when subjected to moderate cutting water potentials (-0.5 to -1.2 MPa) during the initial 4 or 5 weeks of the rooting period. Cuttings experiencing either severe water deficit or no water deficit rooted poorly. We conclude that the rooting environment should impose a moderate water stress on loblolly pine stem cuttings to achieve optimum rooting.     

Daily shoot extension growth of peach trees growing on rootstocks that reduce scion growth is related to daily dynamics of stem water potential

We studied relationships between diurnal patterns of stem water potential (PsiSTEM) and stem extension growth of the same scion cultivar growing on three rootstocks with differing size-controlling potentials. The peach trees (Prunus persica (L.) Batsch) used in this field experiment consisted of an early-maturing freestone cultivar, 'Flavorcrest,' grafted onto three different rootstocks: Nemaguard (a vigorous seed-propagated control, P. persica x P. davidiana hybrid), Hiawatha (an intermediate vigor rootstock, derived from an open pollinated seedling of a P. besseyi x P. salicina hybrid) and K-146-43 (a semi-dwarfing rootstock, P. salicina x P. persica hybrid). Diurnal patterns of PsiSTEM and stem extension growth were measured on six dates (March 29, April 12, April 26, May 10, May 24 and June 18) during the primary period of peach shoot extension growth. Rootstocks clearly affected diurnal patterns of PsiSTEM and stem extension growth. Trees on K-146-43 had the lowest midday PsiSTEM and stem extension growth. Differences among rootstocks in the amount of diurnal oscillation in PsiSTEM explained stem extension rate differences induced by the three rootstocks. The sensitivity of shoot extension growth to tree water relations tended to decrease as the season progressed and was not apparent by mid-June. The results of the study indicate that water relations may play an important role in the dwarfing mechanism induced by size-controlling peach rootstocks.     

Effect of trees on the yield of wheat crop

A study was conducted at the National Agricultural Research Center (NARC) of Pakistan Agricultural Research Council (PARC) by planting trees of four different species: Eucalyptus camaldulensis, Albizia procera, Morus alba and Leucaena leucocephala along the boundary of wheat fields in a randomized complete block design. Data on crop yield for each tree species and control (no trees) at different distances viz 2, 4, 6, 8, 10 and 12 meter (m) from the tree bases and control were collected and analyzed. The statistical analysis did not show any significant difference in the wheat yield among different tree species. However, the wheat yield was numerically lowest at 2 m distance in case of all the four tree species and control. In case of mulberry, it was lowest statistically also from other distances. Numerically higher wheat yield values were noted at later distances (8, 10 and 12 m) in case of all tree species including control except for siris where numerically highest value was found at 6 m distance. Therefore, it can be generalized that tree's impact on wheat yield can be experienced up to 2 m distance, there is little, if any, impact up to 6 m distance and almost no impact at 8, 10 and 12 m distances.     

Effects of varying crop load on photosynthesis, dry matter production and partitioning of Crispin/M.27 apple trees

Fruit load was altered by flower thinning on three- and four-year-old, field-grown apple trees. Increasing fruit load led to increases in dry matter production per unit leaf area and partitioning to fruit and to decreases in fruit size, percentage fruit dry matter, dry matter partitioning to new shoot growth, thickening of existing woody tissue and root growth. Flower bud production for the following spring was also negatively affected by an increase in fruit load. Leaf photosynthesis was increased in cropping trees in July and August at the time of maximum fruit dry weight increase. Calculated light interception was linearly related to leaf area. The efficiency of conversion of intercepted photosynthetic active radiation to dry matter energy equivalents was 3.3% in heavily cropping trees and 1.8% in non-cropping trees. Total dry matter production was linearly related to both leaf area and light interception, but the variance accounted for by the regression was more than doubled if fruit dry matter or fruit number was included in the regression.     

利用相对电导率和茎尖水势预报落叶松苗木生活力的研究

本文对落叶松在不同晾晒时间中茎尖水势，相对电导率及苗木生活力的动态变化过程进行了测定。结果表明：茎尖水势，相对电导率确实能反映苗木遇到逆境后对其生活力的影响，用于预报造林成活率和初期生长量具有极强的可靠性。     

Estimating stem and root-anchorage flexibility in trees

This paper describes a nondestructive method for distinguishing root flexibility from stem flexibility in living trees. It is used here for Sitka spruce (Picea sitchensis (Bong.) Carrière.), but is applicable to any species where the main stem is normally straight and near-vertical. Well-known engineering equations permit the calculation of deflected shape for a vertical cantilever with arbitrary distribution of mass and bending stiffness, when infjected to a lateral force. The equations are used to calculate stem deflections of four Sitka spruce trees for which the stem and branch mass distribution and stem taper have been measured. Free parameters in the mathematical model are a nominal value of Young's Modulus E (assumed uniform and isotropic over the cross section and height of the tree stem) and a root-anchorage stiffness k. The former allows the stem to curve, whereas the latter represents the flexibility of the roots and allows the stem to tilt elastically at ground level. For each of the four trees, the calculated deflection curve is compared with actual deflections measured when the living tree is pulled by a rope at a specified point. By adjusting both E and k, iteratively, a best fit solution is obtained. This provides a simple and effective way to determine both stem stiffness and root hinge stiffness from a single experiment on a living tree.     

Vitality characterization of stressed trees based on non-destructive and real-time monitoring of stem water content

The detection of stem water content is necessary as it is an important indicator for measuring woody plant vitality. However, the relationship between stem water content, determined by non-destructive, real-time, and long-term monitoring, and woody plant vitality remains undefined. In this study, the response of woody plant vitality to stem water content under different stress (freeze–thaw, pest, or drought) was analysed by mining the dynamic characteristics of the stem water content in different woody plants at the temporal scales of year, month, and day. Compared with unstressed trees, stressed trees had contrasting diurnal patterns. The stem water content in Populus koreana Rehd. during the freeze period was much lower than that during the thaw period, and opposite diurnal variation trends were observed during the freeze and thaw periods. The stem water content in infected Lagerstroemia indica was lower than that in uninfected L. indica, and the amplitude of the diurnal variation curve was lower in infected than in uninfected L. indica. Under drought stress, the more severe the water shortage, the lower the stem water content in Malus micromalus. When it was below a certain threshold, the diurnal variation trend was opposite to that without water shortage. In conclusion, stem water content dynamics can be used to evaluate the cold, pest, and drought response of trees, which could monitor tree health and guide forest assessment.     

Temporal dynamics of stem expansion and contraction in savanna trees: withdrawal and recharge of stored water

Relationships between diel changes in stem expansion and contraction and discharge and refilling of stem water storage tissues were studied in six dominant Neotropical savanna (cerrado) tree species from central Brazil. Two stem tissues were studied, the active xylem or sapwood and the living tissues located between the cambium and the cork, made up predominantly of parenchyma cells (outer parenchyma). Outer parenchyma and sapwood density ranged from 320 to 410 kg m(-3) and from 420 to 620 kg m(-3), respectively, depending on the species. The denser sapwood tissues exhibited smaller relative changes in cross-sectional area per unit change in water potential compared with the outer parenchyma. Despite undergoing smaller relative changes in cross-sectional area, the sapwood released about 3.5 times as much stored water for a given change in area as the outer parenchyma. Cross-sectional area decreased earlier in the morning in the outer parenchyma than in the sapwood with lag times up to 30 min for most species. The relatively small lag time between dimensional changes of the two tissues suggested that they were hydraulically well connected. The initial morning increase in basal sap flow lagged about 10 to 130 min behind that of branch sap flow. Species-specific lag times between morning declines in branch and main stem cross-sectional area were a function of relative stem water storage capacity, which ranged from 16 to 31% of total diurnal water loss. Reliance on stored water to temporarily replace transpirational losses is one of the homeostatic mechanisms that constrain the magnitude of leaf water deficits in cerrado trees.     

Roots under the load of heavy machinery in spruce trees

The effects of the passage of forwarders on soil and damage to spruce root systems along an experimental trail were studied. The site was characterized by medium-textured soil of the pseudogley type under favorable moisture conditions. Due to the passages, the soil was compacted down to a depth of 20 cm, soil porosity was decreased by 5% (volume) and soil aeration was decreased by more than 5%. Substantially higher values of mechanical soil resistance occurred (estimated by penetrometric measurements) in a soil pit situated in a rut after passages. Pressure measured by sensors placed at a depth of 10 cm below the soil surface reached values ranging from 0.09 to 0.11 MPa in plots uncovered with slash and 0.03–0.07 MPa in plots covered with slash after two to four passages, and 0.06–0.07 after six to ten passages. Soil surface deformations occurred in the upper soil layers through tire impression. This resulted in the origin of ruts, whose depth and width was dependent on the type of tires, their load, surface conditions, type and texture of soil, soil moisture and number of passages. Pressure in the soil layers imposed by the tire of a given type, inflation and load changed in relation to depth, ground cover, soil properties and reinforcing components on the soil surface. Sap flow in coarse roots actually treated by a moving heavy load clearly and immediately responded with a sharp increase followed by a similar decrease (peak flow) after several minutes. On average, the flow rate decreased by about 8% after the first treatment compared to the untreated state, and remained the same after passing the peak during the second pass when the maximum load was applied. However, this decrease amounted to about 40%, when compared to the “relative zero flow” after root severing. This indicates serious local damage to the conducting system. Even when loading directly damaged rather small fractions of the total root systems, it opened tree tissues to subsequent fungal infection, whose impact could be very serious in future years. Flow in stem sections oriented in the opposite direction to the trail and the flow in stem sections and root buttresses oriented toward the trail (but where roots were not actually growing below the trail or grew deeper in the soil), neither responded to the treatment or responded insignificantly. Sap flow responded only in surface roots below trails, occurring down to a depth of about 10 cm below the original soil (litter) surface. This occurred only when a significant part of the roots (with the total projected area of treated root branches more then 500 cm²) were under the tires. This indicates the protective ability of soils and also, a possible method of artificial root protection.     

Phenotypic plasticity and climatic adaptation in an Atlantic maritime pine breeding population

Context

Pinus pinaster Ait. is found in the Iberian Peninsula under Mediterranean and Atlantic conditions. Both climates encounter each other in Galicia (NW Spain), where two bioclimatic regions can be differentiated: coastal and inland. A breeding program was launched in the coastal area, with two breeding and deployment areas delimited.

Aims

We analyse plasticity patterns across regions in a coastal breeding population to assess the suitability of current breeding areas and how genetic material will likely respond to future climate.

Methods

Total height at ages 3 and 8?years was assessed in 16 trials established along the coast and in inner Galicia. Clustering of environments with similar genotypic performance, family sensitivities to climatic factors and stability analyses were performed.

Results

Sizeable genetic variation in plasticity was found among families, and crossover genotype-by-environment interactions were detected within and between regions. It was unfeasible to regionalize Galicia into alternative areas of stable genotypic performance. Only the cold regime was found to noticeably underlie the array of phenotypic responses to changing environmental conditions.

Conclusions

Results suggest that previous delimitation in two breeding areas is pointless and indicate reduced effects of a changing climate towards Mediterranean conditions on decreasing population fitness.     

Effects of trees on the yield of irrigated wheat crop in semi-arid regions

A study was conducted in the semi-arid regions of Haryana, in Northern India, to see the effect of Azadirachta indica, Prosopis cineraria, Dalbergia sissoo and Acacia nilotica on the yield of irrigated wheat crop. Data on crop yield for each tree species at different distances (1, 3, 5 and 7 m) and four directions (east, west, north and south) from the tree bases and control (no trees) were collected. Results indicate that A. indica and P. cineraria did not show any significant difference in the wheat yield while the other two species (D. sissoo and A. nilotica) showed a reduction in wheat yield. A. nilotica had the most significant and prominent effect, and a reduction of nearly 40 to 60% wheat yield was observed. The effect of this tree species was observed even beyond the spread of the crown. D. sissoo reduced yield by 4 to 30% but the reduction was only up to a distance of 3 m. In general, the impact of trees on wheat yield was observed up to 3 m distance and there is little, if any, impact up to 5 m distance and almost no impact at 7 m distance. In all the tree species, the wheat yield was reduced to a maximum on the north side of the trees and had almost no effect in the southern direction. Crop maturity was observed to be delayed by three weeks under A. nilotica, by 9–10 days under D. sissoo, and only by 6–7 days under P. cineraria and A. indica.     

Biomass production potential of three short rotation woody crop species under varying nitrogen and water availability

A study was conducted in an agricultural field to examine the biomass production of three fast-growing short rotation woody crop (SRWC) species, Populus deltoides, Quercus pagoda, and Platanus occidentalis using fertilization and irrigation (fertigation). The study included a randomized complete block (RCB) with five treatments; control, irrigated, and irrigated with 56, 112, and 224 kg nitrogen (N) ha⁻¹ year⁻¹. We quantified survival, basal area, standing biomass, aboveground net primary productivity (ANPP), leaf area index (LAI), and growth efficiency (GE) for each species along the soil nitrogen and water gradient. P. deltoides had low rates of survival (83, 82, and 77% years six, seven, and eight, respectively), but had production values greater than Q. pagoda and P. occidentalis. Standing biomass reached its peak for P. deltoides and P. occidentalis (17.56 and 10.36 Mg ha¹, respectively) in the irrigation treatment, and in the 112 kg N treatment for Q. pagoda (5.42 Mg ha⁻¹). P. deltoides and P. occidentalis ANPP peaked in the irrigation treatment (6.66 and 6.31 Mg ha⁻¹ year⁻¹, respectively) and in the 112 kg N (4.43 Mg ha⁻¹ year⁻¹) for Q. pagoda. ANPP was correlated with LAI; however, the relationship was species specific. Maximum ANPP was reached below the maximum LAI for Q. pagoda and P. occidentalis. P. deltoides ANPP was highest at the maximum LAI, which was achieved with IRR. These results suggest that species-specific cultural practices producing optimum LAI and maximum ANPP should be identified before fertigation techniques are adopted widely for SRWC production on agricultural fields.     

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.     

Diurnal and seasonal changes in stem increment and water use by yellow poplar trees in response to environmental stress

To evaluate indicators of whole-tree physiological responses to climate stress, we determined seasonal, daily and diurnal patterns of growth and water use in 10 yellow poplar (Liriodendron tulipifera L.) trees in a stand recently released from competition. Precise measurements of stem increment and sap flow made with automated electronic dendrometers and thermal dissipation probes, respectively, indicated close temporal linkages between water use and patterns of stem shrinkage and swelling during daily cycles of water depletion and recharge of extensible outer-stem tissues. These cycles also determined net daily basal area increment. Multivariate regression models based on a 123-day data series showed that daily diameter increments were related negatively to vapor pressure deficit (VPD), but positively to precipitation and temperature. The same model form with slight changes in coefficients yielded coefficients of determination of about 0.62 (0.57-0.66) across data subsets that included widely variable growth rates and VPDs. Model R2 was improved to 0.75 by using 3-day running mean daily growth data. Rapid recovery of stem diameter growth following short-term, diurnal reductions in VPD indicated that water stored in extensible stem tissues was part of a fast recharge system that limited hydration changes in the cambial zone during periods of water stress. There were substantial differences in the seasonal dynamics of growth among individual trees, and analyses indicated that faster-growing trees were more positively affected by precipitation, solar irradiance and temperature and more negatively affected by high VPD than slower-growing trees. There were no negative effects of ozone on daily growth rates in a year of low ozone concentrations.     

Crop load affects maximum daily trunk shrinkage of plum trees

We studied the effects of low fruit load (3-4 fruits cm(-2) of trunk cross-sectional area (TCSA), and high fruit load (6-7 fruits cm(-2) TCSA) on maximum daily trunk shrinkage (MDS) and trunk growth rates (TGR) over two seasons in plum (Prunus salicina Lindell) trees receiving full irrigation or deficit irrigation. Seasonal changes in MDS and TGR were compared with those in midday stem water potential (Psi(s)) and leaf stomatal conductance (g (s)). Crop load increased g (s) in fully irrigated trees approaching harvest. Although crop load did not affect plant water status in either watering regime, there were considerable differences in both MDS and TGR as a function of crop load. Compared with low-cropping [corrected] trees, MDS was 34% higher and TGR was 48% lower in high-cropping [corrected] trees. The differential responses of MDS and Psi(s) to crop load were a consequence of a higher MDS for a given Psi(s) in the high-cropping trees compared with the low-cropping trees. There was a linear increase in MDS with crop load, with a slope of 15.2 microm MPa(-1) per unit increment of crop load. In the fully irrigated trees, day-to-day variations in MDS were related to evaporative demand; however, the slope of the relationship between MDS and evaporative demand increased with crop load, indicating that different reference equations must be used to adjust for tree crop load when using MDS to determine plant water status and irrigation requirements.