Photosynthesis and wood structure in Pinus radiata D. Don during dehydration and immediately after rewatering

Abstract. Experiments were carried out on Pinus radiata (D. Don) trees grown as cuttings from clonal parent stock. Some of these trees were about 0.4 m high while others were about 5 m high; all were grown in containers. The stem diameters at the tops and at the bottoms of the large trees, rates of photosynthesis, and needle water potentials were measured both when the trees were well watered and as they dehydrated after water was withheld. The water potentials of well-watered plants was highest in the small trees and lowest at the top of the large trees. When water was withheld, photosynthesis was in most cases unaffected by a small reduction in water potential, but the rate of photosynthesis fell as water potentials declined further. The stems of the large trees expanded at a constant rate when the trees were well watered and for part of the dehydration period, while subsequent stem shrinkage and the fall in photosynthesis both occurred at approximately the same time.
Water potentials increased little in the 24 h after rewatering, and significant rates of photosynthesis were not measured until 2 or 3 d later while renewed stem expansion was not measured until 2 d after rewatering.
Water deficits reduced the lumen diameter of newly matured stem tracheids, but increased the thickness of their walls. After 1 month of water potentials of about −2.4 MPa, tracheid lumen diameter and wall thickness were both much reduced, and this reduction continued in tracheids maturing shortly after rewatering.     

断根处理对银杏树体水力特征及生长的影响

以8年生银杏为试材,采用不同程度的断根处理,测定处理后树体超声（ultrasound acoustic emission,UAE）信号、枝条栓塞程度（percentage loss of hydraulic conductance,PLC）、树干液流通量、气孔导度、蒸腾速率以及叶片水势等生理指标,分析断根对银杏树体水力特征及生长状况的影响.结果表明:断根处理后,在短时间内有大量UAE信号产生,且随断根程度的加重而增大,在6 h出现最大值,随后逐渐降低;枝条的PLC在起初的12 h迅速增加,24 h后增速趋于停滞;银杏树干液流通量、叶片气孔导度、蒸腾速率和水势明显降低,各处理间差异显著.经统计分析,累积UAE（cumulative number of UAE, cUAE）信号量与PLC呈现显著的正相关关系,与液流通量和叶片水势呈负相关关系.次年的单叶面积、新生枝条长度显著下降,下降程度随断根处理的加重而加剧.断根处理在短时间内增加了银杏管胞气穴数量和木质部栓塞的程度,影响到水分输送和叶片蒸腾,最终对叶片和枝条的生长产生负面影响.     

The influence of CO2 enrichment, phosphorus deficiency and water stress on the growth, conductance and water use of Pinus radiata D. Don

Abstract. Seedlings of Pinus radiata D. Don were grown in growth chambers for 22 weeks with two levels of phosphorus, under either well-watered or water-stressed conditions at CO₂ concentrations of either 330 or 660mm³ dm^?3. Plant growth, water use efficiency and conductance were measured and the relationship between these and needle photosynthetic capacity, water use efficiency and conductance was determined by gas exchange at week 22. Phosphorus deficiency decreased growth and foliar surface area at both CO₂concentrations; however, it only reduced the maximum photosynthetic rates of the needles at 660 mm³ CO₂ dm^?3 (plants grown and measured at the same CO₂ concentration). Water stress reduced growth and foliar surface area at both CO₂ concentrations. Increases in needle photosynthetic rates appeared to be partly responsible for the increased growth at high CO₂ where phosphorus was adequate. This effect was amplified by accompanying increases in needle production. Phosphorus deficiency inhibited these responses because it severely impaired needle photosynthetic function. The relative increase in growth in response to high CO₂ was higher in the periodically water-stressed plants. This was not due to the maintenance of cell volume during drought. Plant water use efficiency was increased by CO₂ enrichment due to an increase in dry weight rather than a decrease in shoot conductance and, therefore, transpirational water loss. Changes in needle conductance and water use efficiency in response to high CO₂ were generally in the same direction as those at the whole plant level. If the atmospheric CO₂ level reaches the predicted concentration of 660 mm³ dm^?3 by the end of next Century, then the growth of P. radiata will only be increased in areas where phosphorus nutrition is adequate. Growth will be increased in drought-affected regions but total water use is unlikely to be reduced.     

豆科复叶和单叶树种的光合-水分关系分析

以豆科（Fabaceae）11个复叶树种和6个单叶树种为材料,测定他们的气孔导度、叶片水力导度、水势、相对含水量等指标,分析叶型对枝叶光合水分关系的影响。结果显示,复叶树种正午叶轴水势（-0.91 MPa）与单叶树种正午枝条水势（-0.88 MPa）间无显著差异,但正午枝条水势（-0.60 MPa）显著高于单叶树种。复叶树种正午气孔导度降低的百分比（55.3%）显著高于单叶树种（34.1%）。叶片、叶轴和枝条正午水势两两之间均显著正相关,但与正午气孔导度之间均不存在相关性。本研究中,17个树种的正午叶片水力导度与气孔导度间显著正相关（r=0.79,P<0.001）,但他们与气孔导度降低百分比间呈负相关（r=-0.81,P<0.001）,说明叶片导水率对日间气孔导度的维持具有重要作用。研究结果表明单叶和复叶树种在光合水分关系上存在明显差异,说明他们对环境条件具有不同的适应策略。     

Shoot hydraulic characteristics, plant water status and stomatal response in olive trees under different soil water conditions

Aims

To evaluate the impact of the amount and distribution of soil water on xylem anatomy and xylem hydraulics of current-year shoots, plant water status and stomatal conductance of mature ‘Manzanilla’ olive trees.

Methods

Measurements of water potential, stomatal conductance, hydraulic conductivity, vulnerability to embolism, vessel diameter distribution and vessel density were made in trees under full irrigation with non-limiting soil water conditions, localized irrigation, and rain-fed conditions.

Results

All trees showed lower stomatal conductance values in the afternoon than in the morning. The irrigated trees showed water potential values around ?1.4 and ?1.6 MPa whereas the rain-fed trees reached lower values. All trees showed similar specific hydraulic conductivity (K _s) and loss of conductivity values during the morning. In the afternoon, K _s of rain-fed trees tended to be lower than of irrigated trees. No differences in vulnerability to embolism, vessel-diameter distribution and vessel density were observed between treatments.

Conclusions

A tight control of stomatal conductance was observed in olive which allowed irrigated trees to avoid critical water potential values and keep them in a safe range to avoid embolism. The applied water treatments did not influence the xylem anatomy and vulnerability to embolism of current-year shoots of mature olive trees.     

Effect of nitrogen on growth and water relations of radiata pine families

The effect of nitrogen fertilisation on growth, foliar nutrients and water relations of four families of radiata pine (Pinus radiata, D. Don) currently in the Australian breeding program was examined from age six to 11 years. At this stage, the stand was ready for commercial thinning. The annual rainfall at the site varied from 563 to 733 mm.Application of nitrogen fertiliser resulted in stem wood volume at age nine years of 178 m³ ha^-1 in the controls, compared with 228 m³ ha^-1 in plots treated with 600 kg N ha^-1. Pre-dawn needle water potential () measured in three consecutive summers (when rainfall ranged from 53 to 106 mm) were consistently higher (less water stress) in nitrogen fertilised than in control trees. Similarly, the water stress integral (S) decreased consistently with increasing levels of nitrogen, although total water use in fertilised trees would have been substantially higher because fertiliser application increased the leaf area index. The relationship between S and basal area was strong and paralleled that of foliar nitrogen concentration and basal area growth. Therefore, nitrogen application increased growth rates of trees by improving the nutrient status of trees and lowering the water stress on trees in summer.Families showed markedly different responses of basal area growth to nitrogen, ranging from an increase of 9.4% over three years for the least responsive family to 99.0% for the most responsive. There was no nitrogen × family interaction on or S suggesting that the large genetic variation in the growth response to nitrogen is mediated by factors other than water relations. These results have implications for managing highly productive plantations grown in an environment where rainfall is low compared to potential evapotranspiration.     

Nutrient availability constrains the hydraulic architecture and water relations of savannah trees

Leaf and whole plant-level functional traits were studied in five dominant woody savannah species from Central Brazil (Cerrado) to determine whether reduction of nutrient limitations in oligotrophic Cerrado soils affects carbon allocation, water relations and hydraulic architecture. Four treatments were used: control, N additions, P additions and N plus P additions. Fertilizers were applied twice yearly, from October 1998 to March 2004. Sixty-three months after the first nutrient addition, the total leaf area increment was significantly greater across all species in the N- and the N + P-fertilized plots than in the control and in the P-fertilized plots. Nitrogen fertilization significantly altered several components of hydraulic architecture: specific conductivity of terminal stems increased with N additions, whereas leaf-specific conductivity and wood density decreased in most cases. Average daily sap flow per individual was consistently higher with N and N + P additions compared to the control, but its relative increase was not as great as that of leaf area. Long-term additions of N and N + P caused midday PsiL to decline significantly by a mean of 0.6 MPa across all species because N-induced relative reductions in soil-to-leaf hydraulic conductance were greater than those of stomatal conductance and transpiration on a leaf area basis. Phosphorus-fertilized trees did not exhibit significant changes in midday PsiL. Analysis of xylem vulnerability curves indicated that N-fertilized trees were significantly less vulnerable to embolism than trees in control and P-fertilized plots. Thus, N-induced decreases in midday PsiL appeared to be almost entirely compensated by increases in resistance to embolism. Leaf tissue water relations characteristics also changed as a result of N-induced declines in minimum PsiL: osmotic potential at full turgor decreased and symplastic solute content on a dry matter basis increased linearly with declining midday PsiL across species and treatments. Despite being adapted to chronic nutrient limitations, Cerrado woody species apparently have the capacity to exploit increases in nutrient availability by allocating resources to maximize carbon gain and enhance growth. The cost of increased allocation to leaf area relative to water transport capacity involved increased total water loss per plant and a decrease in minimum leaf water potentials. However, the risk of increased embolism and turgor loss was relatively low as xylem vulnerability to embolism and leaf osmotic characteristics changed in parallel with changes in plant water status induced by N fertilization.     

Water relations of citrus exocortis viroid-infected grapefruit trees in the field

Citrus viroids (CVds) were used to limit citrus tree size ('dwarfing'). It is hypothesized that changes also occur in the hydraulic properties of the conducting system, thereby affecting water relations. Grapefruit trees (var. Star Ruby on Troyer Citrange rootstock) in northern Israel were infected with citrus exocortis viroid (CEVd). The orchard was drip irrigated. The infected (I) and apparently healthy (H) control plots were subdivided into wet (W) and dry (D) irrigation treatments receiving 100% and 70% of the recommended irrigation quantity for the region. Soil water content, soil temperature, water uptake, leaf and stem water potential, and leaf conductance were measured in addition to climatic variables. Water uptake response to increasing spring-time soil temperatures was greater in healthy than in infected trees. Leaf conductance in the infected trees was lower than the non-infected trees only in the sixth year after inoculation. Stem water potential was significantly lower in the CEVd-infected trees than in the control trees. Water uptake was lower and hydraulic resistance higher in infected than in healthy trees. It was concluded that CEVd causes a reduction in the water uptake ability of the root and canopy system. Possible mechanisms for this are discussed.     

Stomatal conductance in relation to xylem sap abscisic acid concentrations in two tropical trees, Acacia confusa and Litsea glutinosa

Two tropical trees, Acacia confusa and Litsea glutinosa, were grown under controlled conditions with their roots subjected to soil drying and soil compaction treatments. In both species, a decline in stomatal conductance resulting from soil drying took place much earlier than the decline of leaf water potential. Soil compaction treatment also resulted in a substantial decrease in stomatal conductance but had little effect on leaf water potential. A rapid and substantial increase in xylem abscisic acid (ABA) concenation ([ABA]), rather than hulk leaf ABA, was closely related to soil drying and soil compaction. A significant relationship between stomatal conductance (g_s) and xylem [ABA] was observed in both species. Artificially feeding ABA solutions to excised leaves of both species showed that the relationship bet ween g_s and [ABA] was very similar to that obtained from the whole plant, i.e. the relationship between g_s and xylem [ABA]. These results suggest that xylem ABA may act as a stress signal in the control of stomatal conductance.     

Salinity tolerance of 'Valencia' orange trees on rootstocks with contrasting salt tolerance is not improved by moderate shade

The effects of shading in combination with salinity treatments were studied in citrus trees on two rootstocks with contrasting salt tolerance to determine if shading could reduce the negative effects of salinity stress. Well-nourished 2-year-old 'Valencia' orange trees grafted on Cleopatra mandarin (Cleo, relatively salt tolerant) or Carrizo citrange (Carr, relatively salt sensitive), were grown either under a 50% shade cloth or left unshaded in full sunlight. Half the trees received no salinity treatment and half were salinized with 50 mM Cl- during two 9 week salinity periods in the spring and autumn interrupted by an 11 week rainy period. The shade treatment reduced midday leaf temperature and leaf-to-air vapour pressure deficit regardless of salinity treatments. In non-salinized trees, shade increased midday CO2 assimilation rate (A(CO2)) and stomatal conductance, but had no effect on leaf transpiration (E(lf)). Shade also increased leaf chlorophyll and photosynthetic water use efficiency (A(CO2)/E(lf)) in leaves on both rootstocks and increased total plant dry weight in Cleo. The salinity treatment reduced leaf growth and leaf gas exchange parameters. Shade decreased Cl- concentrations in leaves of salinized Carr trees, but had no effect on leaf or root Cl- of trees on Cleo. There were no significant differences in leaf gas exchange parameters of shaded and unshaded salinized plants but the growth reduction from salinity stress was actually greater for shaded than for unshaded trees. Shaded trees on both rootstocks had higher leaf Na+ than unshaded trees after the first salinity period, and this shade-induced elevated leaf Na+ persisted after the second salinity period in trees on Carr. Thus, shading did not alleviate the negative effects of salinity on growth and Na+ accumulation.     

根系分区交替灌溉不同交替周期对苹果树

以11~12年生苹果树为研究对象,于2006~2007年在烟台市农科院果树研究所试验果园进行了根系分区交替灌溉（APRI）试验,研究了APRI灌溉模式下不同交替灌溉周期对苹果树生长、产量、品质及水分利用效率的影响。结果表明,APRI处理的苹果树湿润一侧土壤含水量随深度增加而减少,并出现明显拐点,交替周期愈短拐点愈接近地表,干旱一侧则随深度增加而增大,二者含水量最大差值出现在土壤表层0~10 cm。每2周交替灌溉1次的APRI1处理的叶水势、净光合速率、蒸腾速率和气孔导度稍有降低,但与对照均没有明显差异,而每4周交替灌溉1次的APRI2和APRI3处理的上述指标则显著低于对照（P < 0.05）。APRI处理显著抑制植株的新梢生长,但对果实直径没有显著影响。APRI1和APRI2处理的苹果产量比对照和APRI3下降了11.1 %~14.8 %,但供水量减少了50 %,水分利用效率提高了71 %~80 %,而且显著提高了可溶性固形物含量和果实干物质含量,使果实含酸量降低,果实硬度增加,果实品质明显改善。由此可以推断采用根系分区交替灌溉并进行适宜的交替周期处理（如本试验中的APRI1）可以达到大量节水、提高苹果品质而不明显降低产量的目的,是苹果生产中一种切实可行的灌溉方式,值得旱地苹果园大力推广。     

Maize stomatal conductance in the field: its relationship with soil and plant water potentials, mechanical constraints and ABA concentration in the xylem sap

Abstract. Stomatal conductance, leaf water potential, soil water potential and concentration of abscisic acid (ABA) in the xylem sap were measured on maize plants growing in the field, in two treatments with contrasting soil structures. Soil compaction affected the stomatal conductance, but this effect was no longer observed if the soil water potential was increased by irrigation. Differences in leaf water potential did not account for the differences in conductance between treatments. Conversely, the relationship between stomatal conductance and concentration of ABA in the xylem sap was consistent during the experiment. The proposed interpretation is that stomatal conductance was controlled by the root water potential via an ABA message. Control of the stomatal conductance by the leaf water potential or by an effect of mechanical stress on the roots is unlikely.     

Stomatal control of water use in olive tree leaves

Little is known about the strategies used by olive trees to overcome the long dry periods typical of the areas where they are cropped. This makes it difficult to optimize the water supply in orchards. To study the control of water consumption by olive trees, measurements of leaf water potential () and stomatal conductance to H₂O (g) were made on 26-year-old t Manzanillo olive trees under three irrigation treatments. The first treatment provided enough water to cover the crop water demand, the next treatment supplied one third of that rate, and the final treatment was no irrigation at all, typical of dry-farming conditions. Under conditions of high vapour pressure deficit of the air (D_a), the olive trees prevented excessive water loss by closing their stomata. Leaves of the current year showed better stomatal control than did the 1-year-old leaves. The upper-bound functional relationships between t g and t D_a and photon flux density (I_P) were obtained by boundary-line analysis, based on a technique of non-linear least squares. Maximum values of t g were observed at relatively low levels of t I_P, from about 500 mol m^-2 s^-1, and a proportional decrease in t g with increasing t D_a was also found, at least for values of up to approximately 3.5 kPa. Higher values of t g were observed in the morning than in the afternoon, for similar levels of t I_P and t D_a. Unirrigated olive trees recovered quickly after the dry season, showing values of and t g similar to those of irrigated trees after just two days.     

Leaf water potential and leaf conductance during the growing season in almond trees under different irrigation regimes

Seasonal changes in leaf water potential (Φ) and leaf conductance (g₁) were determined in almond trees under different irrigation regimes. The development of water stress in the rainfed treatment induced a specific seasonal dynamics of Φ values and an important reduction in g₁ values. A decrease in g₁ values occurred independently of the irrigation treatment through the growing season. No statistically significant differences were obtained in g₁ values within the drip irrigated treatments.     

Hydraulic Conductance and Stomatal Sensitivity to Changes of Leaf Water Status in Six Deciduous Tree Species

The relationship between shoot hydraulic conductance (L) and stomatal sensitivity to changes in leaf water status was studied in the saplings of six deciduous tree species. L increased significantly in sequence: Acer platanoides < Tilia Cordata < Padus avium = Quercus robur < Salix caprea = Populus tremula. L was higher in the trees grown in soil with a higher nitrogen content and lower in the trees grown under mild water stress or kept in darkness for several days. L was higher in July than in September in all the species. L correlated positively with maximum photosynthesis, stomatal conductance and stomatal sensitivity to an increase in leaf water potential, but negatively with stomatal sensitivity to a decrease in leaf water potential. The correlations between L and any other parameter were approximated by three different curves: data for water-stressed plants fit to the first, data for plants kept in darkness fit to the second and all the other data fit to the third curve. The reasons of the differences of shoot hydraulic conductance in the different experimental sets and the mechanisms which may cause the correlation between L and the other characteristics are discussed.     

Environmental Effects on Transpiration and Leaf Water Potential in Avocado

A field study was conducted to determine how atmospheric and edaphic conditions influenced the water relations of avocado trees (Persea americana Mill. cv. Bacon). With high and low levels of incident photosynthetically active radiation (PAR, 400–700 nm wave length), and either wet or dry soil, leaf conductance decreased as the absolute humidity difference from leaf to air increased. For any water stress treatment, conductance was higher at high PAR than at low PAR. Both conductance and transpiration were higher in well-watered trees than in stressed trees, and in prestressed trees levels were intermediate to unstressed and stressed trees. A model for water flux through the soil-plant-atmosphere continuum was used to examine the relationship of leaf xylem pressure potential to transpiration in well-watered trees and in trees stressed by dry soil. There was a close linkage between leaf xylem pressure potential and transpiration in unstressed and previously stressed trees with high or low PAR, i.e. similar potentials occurred with equivalent transpiration regardless of previous treatment or time of day. In stressed trees, xylem pressure potential was lower than in unstressed trees both during the day and night, and at a given transpiration rate the potential was lower after 1400 h than before that time. The model indicated that in stressed trees xylem pressure potential was uncoupled from transpiration, presumably because of altered resistance in the soil-root portion of the transport system.     

Water relations in Norway spruce trees growing at ambient and elevated CO2 concentrations

Water relations were studied in Norway spruce [Picea abies (L.) Karst.] trees grown at ambient (AC, 350 μmol mol⁻¹) and elevated (EC, 700 μmol mol⁻¹) CO₂ concentrations under temperate water stress. The results suggested that both crown position and variability in atmospheric CO₂ concentration are responsible for different patterns of crown water relations. Mean hourly sap flux density (FSA) showed higher values in upper crown position in comparison with the whole crown in both AC and EC treatments. Mean soil-to-leaf hydraulic conductance (G_Tsa) was 1.4 times higher for the upper crown than that calculated across the whole crown for the trees in AC. However, G_Tsa did not vary significantly with crown position in EC trees, suggesting that elevated CO₂ may mitigate differences in hydraulic supply for different canopy layers. The trees in EC treatment exhibited significantly higher values of F_SA measured on the whole crown level and slightly higher soil water content compared to AC treatment, suggesting more economical use of soil water and therefore an advantage under water-limited conditions.     

疏叶骆驼刺母株与子株间的水分整合

在未灌溉的土地上, 疏叶骆驼刺(Alhagi sparsifolia)通常不能进行有性繁殖, 克隆繁殖是其种群维持和延续的唯一方式。因此, 克隆性及其相关克隆性状(如水分整合)在疏叶骆驼刺自然种群的维持过程中可能扮演了极其重要的角色。该文通过疏叶骆驼刺母株和子株之间的间隔子切断和给母株补充水分的方法, 研究了母株和子株在各处理下的水势、叶形态和植株生长变化情况。结果表明: (1)间隔子切断后, 疏叶骆驼刺母株和子株正午水势均明显增大(p < 0.01), 说明间隔子切断使得母株和子株水分亏缺值都增大。(2)给母株补水后, 间隔子切断组和间隔子相连组中的母株水势均有明显增加, 同时间隔子相连组的子株水势明显增加(p < 0.01), 而间隔子切断组子株水势没有明显变化(p > 0.05)。(3)间隔子切断组的子株叶片含水率明显低于间隔子相连组子株, 而其株高、冠幅、分枝数和基径的增长量都明显小于间隔子相连组的子株(p < 0.01)。疏叶骆驼刺母株和子株间存在水分整合, 母株会通过根系向子株传输水分。研究成果对塔克拉玛干沙漠南缘的植被恢复以及水资源的合理利用有着重要的意义。     

锐齿栎水力结构和生长对降雨减少的响应

为探究气候变化背景下降雨减少对森林的影响,2013年在宝天曼锐齿栎天然次生林原位建立了3块降水减少(截雨)样地,研究降雨减少对锐齿栎水碳关系和生长的影响。结果表明:降雨减少后锐齿栎枝条水势显著低于对照,最低水势为(-1.36±0.11)MPa,但锐齿栎木质部栓塞88%的水势值为-3.19MPa,叶片气孔关闭时的水势值为-2.5MPa,故降雨减少在这一地区没有对锐齿栎水力结构造成严重的干扰。降雨减少后,锐齿栎的叶片、韧皮部和木质部的总非结构性碳浓度与对照没有显著差异。木质部导管密度和叶片气孔密度变大,而导管直径和气孔长度变小。在天气较为干旱时,降雨减少处理的锐齿栎气孔导度日变化呈"双峰"曲线,而在湿润天气时呈"单峰"曲线且中午峰值显著大于对照。降雨减少处理的锐齿栎木材密度、Huber值、比叶面积和胸径生长与对照没有显著差异。降雨减少后锐齿栎树木没有遭受水力失衡或碳饥饿的危害,生长也没有受到显著影响,但是水力输导系统发生了适应性调节。     

Growth and water relations of Liquidambar styraciflua L. in an urban park and plaza

Summary Growth and water relations of 10-year-old sweet gum (Liquidambar styraciflua L.) street trees were studied in sites with low and high potential evapotranspiration to determine how these differences are integrated by growth and water relations over time. The trees were located in the parking strip between the curb and sidewalk at a partially vegetated urban park and an urban plaza in Seattle, Washington. Crown size, and seasonal and diurnal stomatal conductance and water potential, as well as diurnal air temperature and humidity, were measured over 2 growing seasons. Yearly trunk growth since transplanting was measured from increment cores. Vapor pressure deficits and air temperatures averaged 18% greater at the plaza, but whole-tree water loss appeared to be much lower than the park trees due to more restricted stomatal conductance and crown size. In addition, yearly diameter increment declined progressively once the plaza trees were established in the existing soil several years after transplanting. Lower water potential in the plaza trees indicated greater internal moisture deficits than the park trees, and tissue analysis revealed lower nutritional status, particularly nitrogen. A manipulative study of water and fertilizer to several additional plaza trees showed an interaction between water and nutrient deficiencies in the coarse and shallow soil that apparently limited growth. Furthermore, soil limitations probably interacted with paved surface conditions over time by reducing nutrient recycling from leaf litter, and generating higher vapor pressure deficits that would contribute to prolonged stomatal closure. Restricted growth and water relations status of the plaza trees represented an equilibrium between chronic high-resource demand above ground and limited below ground.