Growth, water relations and solute accumulation in osmotically stressed seedlings of the tropical tree Colophospermum mopane

Root and hypocotyl elongation, water status and solute accumulation were studied in osmotically stressed seedlings of the tropical tree, Colophospermum mopane (Kirk ex Benth.) Kirk ex J. Léonard, which grows in hot arid areas of southern and central Africa. Seeds were imbibed for 24 h and then subjected to a polyethylene-glycol-generated osmotic stress of -0.03 (control), -0.2, -0.8, -1.6 or -2.0 MPa for 60 h. Seedlings subjected to moderate water stress (-0.2 MPa) had higher root growth rates (2.41 +/- 0.24 mm h(-1)), greater final root lengths (111 +/- 3.8 mm) and longer cells immediately behind the root elongation zone than control seedlings (1.70 +/- 0.15 mm h(-1) and 93 +/- 3.9 mm, respectively). Root lengths of seedlings in the -0.8 and -1.6 MPa treatments were similar to those of control seedlings, whereas the -2.0 MPa seedlings had significantly shorter roots. Both root and hypocotyl tissues exhibited considerable osmotic adjustment to the external water potential treatments. Seedlings in the -0.03, -0.2, and -0.8 MPa treatments had similar cell turgor pressures (0.69 +/- 0.10, 0.68 +/- 0.07 and 0.57 +/- 0.04 MPa, respectively), whereas the -2.0 MPa treatment lowered cell turgor pressure to 0.17 +/- 0.04 MPa. Root vacuolar osmotic pressures were generally similar to sap osmotic pressures, indicating that the increased root elongation observed in moderately water-stressed seedlings was not caused by increased turgor pressure difference. Neutral-fraction solute concentrations, including the osmoticum pinitol, increased approximately two-fold in root sap in response to a low external water potential. In hypocotyl sap of seedlings in the -2.0 MPa treatment, pinitol more than doubled, sucrose increased from about 2 to 75 mol m(-3) but glucose and fructose remained unchanged and, as a result, total sugars increased only slightly. The benefits of rapid early root elongation and osmoticum accumulation under conditions of water stress are discussed in relation to seedling establishment.     

Relationships between the root system size and its hydraulic properties in white spruce seedlings

Seedlings grown under different N supply were examined for relationships between root system size attributes and its hydraulic properties. These relationships were also studied on seedlings of different stock types (grown in different container types). Measurements with root pressure probes were taken at various times after germination, under applied hydrostatic pressure and non-limiting soil moisture. Different N-treatments and stock types were used solely to produce seedling of different sizes, especially root system sizes. Specific root hydraulic conductivity (Lp_r) typically declined with an increasing root system size and correlations between Lp_r and the root system size attributes were often negative. The flow of water through the root system correlated well with root system size attributes only in young (3–4 month old) seedlings but the correlations were inconsistent among different N treatments and stock types. Neither the root system surface area nor dry weight reliably reflected its ability to absorb and conduct water. Generally, the amount of water delivered through the root system and available for transpiration per unit or leaf surface area or unit of leaf dry weight correlated poorly or negatively with the root system size. Practical and scientific implications of the findings are discussed. *Paper presented at Forest Seedling Root Development Conference: From the Nursery to the Field, Eugene, Oregon, May 12–13, 2004.     

Importance of root growth in overcoming planting stress

Root growth is critical to the establishment of planted seedlings. Seedlings can undergo stress just after planting if root growth is not sufficient to couple the seedling to available soil water. Stress occurs when a newly planted seedling’s root system can not supply enough water to transpiring needles to maintain a proper water balance and ensure survival. Thus, a newly planted seedling’s ability to overcome planting stress is affected by its root system size and distribution, root–soil contact, and root hydraulic conductivity. This paper describes how factors of root growth and water status of newly planted seedlings are important in overcoming the phenomenon of planting stress which then allows a newly planted seedling to enter the establishment phase of development.     

Transpiration sensitivity of urban trees in a semi-arid climate is constrained by xylem vulnerability to cavitation

Establishing quantitative links between plant hydraulic properties and the response of transpiration to environmental factors such as atmospheric vapor pressure deficit (D) is essential for improving our ability to understand plant water relations across a wide range of species and environmental conditions. We studied stomatal responses to D in irrigated trees in the urban landscape of Los Angeles, California. We found a strong linear relationship between the sensitivity of tree-level transpiration estimated from sap flux (m(T); slope of the relationship between tree transpiration and ln D) and transpiration at D=1 kPa (E(Tref)) that was similar to previous surveys of stomatal behavior in natural environments. In addition, m(T) was significantly related to vulnerability to cavitation of branches (P(50)). While m(T) did not appear to differ between ring- and diffuse-porous species, the relationship between m(T) and P(50) was distinct by wood anatomy. Therefore, our study confirms systematic differences in water relations in ring- versus diffuse-porous species, but these differences appear to be more strongly related to the relationship between stomatal sensitivity to D and vulnerability to cavitation rather than to stomatal sensitivity per se.     

Comparison of drought resistance among Prunus species from divergent habitats

Root and shoot characteristics related to drought resistance were compared among cultivated peach (Prunus persica (L.) Batsch.), P. andersonii (Nevada Desert almond), P. besseyi (western sand cherry), P. maritima (beach plum), P. subcordata (Sierra or Pacific plum), and P. tomentosa (Nanking cherry). In all species, shoot characteristics were more closely associated with drought adaptation than root characteristics. The most xeric species, P. andersonii, had the lowest specific leaf area, smallest leaves, highest stomatal conductance (before stress), highest rate of carbon assimilation (A), high root length/leaf area and root weight/leaf area ratios, and the highest leaf nitrogen content on an area basis. Root hydraulic conductivity was similar for all species, indicating a lack of importance of this parameter for drought resistance. During a 5-7 day drought, water use efficiency (WUE) increased as shoot water potentials (Psi) declined to -3.0 to -4.0 MPa for the xeric P. andersonii and P. subcordata, whereas after an initial increase, WUE decreased with declining Psi in the -1.5 to -3.0 MPa range for the more mesic P. maritima, P. persica and P. tomentosa as a result of non-stomatal limitations to A. Carbon assimilation rate decreased linearly with Psi during drought in all species, but the Psi at which A reached zero was not associated with drought adaptation. We conclude that the variation in leaf characteristics among Prunus species could be exploited to improve the drought resistance of commercial cultivars.     

Effects of hypoxia and elevated carbon dioxide concentration on water flux through Populus roots

Restricted gas exchange between the rhizosphere and aerial environment reduces the concentration of oxygen (O(2)) and elevates the concentration of carbon dioxide (CO(2)) in the root zone, thereby leading to increased resistance to root water uptake. In this study, the effects of hypoxia and 20% CO(2) on water flux (J(v)) through roots of hybrid poplar (Populus trichocarpa Torr. & A. Gray x P. deltoides Bartr. ex Marsh) were measured in detached root systems under pressure in solution culture. Because stomata closed and there was no change in foliar water potential in hypoxic plants, root resistance was measured in detached systems as opposed to using whole plant measurements. However, under aerated conditions root resistance values were similar in intact plants and excised roots. Water fluxes through pressurized root systems treated with nitrogen and low oxygen (< 2% O(2)), elevated CO(2) (20% CO(2)), and low O(2) with elevated CO(2) concentrations were reduced to 40, 51 and 58%, respectively, of J(v) of plants aerated with ambient air. Reductions in J(v) occurred more rapidly in response to elevated CO(2) than to low O(2) concentrations. The effects of low O(2) and elevated CO(2) were not additive. Changes in pH that resulted from elevated CO(2) concentrations did not account for the reduction in J(v). When root systems of intact plants were pretreated for 24 or 48 h with low O(2) concentration, J(v) measured on pressurization was reduced by 33 and 48%, respectively, compared to aerated roots. Stomatal conductance was also reduced, however, so leaf water potential of plants with hypoxic roots were similar to those of aerated controls.     

Effects of xylem cavitation and freezing injury on dieback of yellow birch (Betula alleghaniensis) in relation to a simulated winter thaw

Shoot dieback, shoot growth, stem xylem cavitation, stem and root freezing injury, and root pressure were measured in 2-year-old, cold-hardened, potted yellow birch (Betula alleghaniensis Britt.) seedlings that had been subjected to a simulated winter thaw for 0, 5, 10, 19 or 27 days followed by 10 weeks at -10 degrees C. Stem xylem cavitation was determined as percent loss of hydraulic conductivity. Stem freezing injury was measured as electrolyte leakage (EL). Root freezing injury was determined by EL and by triphenyl tetrazolium chloride (TTC) reduction. Thaw duration was significantly correlated with dieback, new shoot growth, stem xylem cavitation, stem and root freezing damage, and root pressure (P < 0.05). In particular, shoot dieback was positively correlated with stem xylem cavitation (P < 0.001), residual stem xylem cavitation (P < 0.01) and root freezing injury (P < 0.010), but only weakly correlated with stem freezing damage (P < 0.05). In roots, freezing damage was negatively correlated with root pressure (P < 0.05), which, in turn, was negatively correlated with residual stem xylem cavitation after root pressure development. In stems, there was no correlation between freezing damage and xylem cavitation. We conclude that long periods of winter thaw followed by freezing resulted in freezing injury to roots concomitant with a reduction in root pressures, leading to poor recovery from freezing-induced xylem embolism.     

川楝苗木失水处理对其活力及造林效果的影响

通过对金沙江干热河谷上段乡土树种川楝1年生苗木进行5种晾晒处理试验,测定不同晾晒处理后根系的相对含水率、相对电导率、根系活力和移植后的成活率,分析探讨川楝苗木水分与苗木活力的关系.结果表明:川楝苗木活力与其苗木水分密切相关,在晾晒的过程中苗木失水使相对含水量下降,相对电导率增加,根系活力下降,最终导致苗木成活率降低和影响幼林生长情况.在川楝造林时,要做好起苗后的苗木保护工作,尤其是根系的保护,这对于维持苗木活力,提高造林成活率和保存率有重要的意义.     

云杉幼树根系分泌物对2种草本植物种子萌发和幼苗生长的影响

【目的】探究西南亚高山人工针叶林主要造林树种粗枝云杉根系分泌物输入对林下草本植物种子萌发和幼苗生长的影响,揭示根系分泌物对林下植被更新和群落多样性的潜在生态效应。【方法】通过前期在野外原位收集根系分泌物,后期在实验室人工添加的方式,从种子萌发、幼苗生物量、幼苗形态3个方面来探究根系分泌物对西南亚高山人工云杉林生境内的2种草本植物白车轴草[JP2]和紫花苜蓿的影响。【结果】1)在种子萌发方面,根系分泌物添加降低了2种草本植物的种子发芽率、发芽势和发芽指数,且紫花苜蓿种子在处理间差异显著。2)在幼苗生物量方面,2种草本植物幼苗鲜质量、干质量在根系分泌物处理下均呈下降趋势,而且紫花苜蓿幼苗处理间差异显著。3)在幼苗形态特征方面,根系分泌物添加降低了2种草本植物的总长度、总表面积、总体积,且幼苗总长度处理间存在显著差异。4)根系分泌物处理下,2种草本植物的各项化感效应指数(RI值)均小于0,而且根系分泌物处理造成的2种植物化感效应综合指数(SE值)小于0,表明根系分泌物添加对2种草本植物种子萌发和幼苗生长均具有抑制作用,且对紫花苜蓿种子的抑制作用更强。5)UPLC-MS分析表明,云杉幼树根系分泌物中检测出多种酚酸类物质。【结论】云杉幼树根系分泌物输入对林下草本植物种子萌发及幼苗生长均产生了抑制效应。根系分泌物中的酚酸类物质可能是导致根系分泌物处理下草本植物种子萌发和幼苗生长受到抑制的内在驱动机制。     

Water availability and branch length determine delta(13)C in foliage of Pinus pinaster

The stable carbon isotope composition (delta(13)C) of foliage integrates signals resulting from environmental and hydraulic constraints on water movement and photosynthesis. We used branch length as a simple predictor of hydraulic constraints to water fluxes and determined the response of delta(13)C to varying water availability. Foliage up to 6 years old was taken from Pinus pinaster Ait. trees growing at four sites differing in precipitation (P; 414-984 mm year(-1)) and potential evaporation (ET; 1091-1750 mm year(-1)). Branch length was the principal determinant of temporal trends in delta(13)C. The strong relationship between delta(13)C and branch length was a function of hydraulic conductance, which was negatively correlated with branch length (r(2) = 0.84). Variation in P and ET among sites was reflected in delta(13)C, which was negatively correlated with P/ET (r(2) = 0.66). However, this analysis was confounded by differences in branch length. If the effects of branch length on delta(13)C were first removed, then the 'residual' delta(13)C was more closely related to P/ET (r(2) = 0.99), highlighting the importance of accounting for variation in hydraulic constraints to water flux between sites and years. For plant species that exhibit considerable phenotypic plasticity in response to changes in environment (e.g., variation in leaf area, branch length and number, or stem form), the environmental effects on delta(13)C in foliage can only be reliably assessed if deconvoluted from hydraulic constraints.     

Root growth and hydraulic conductivity of southern pine seedlings in response to soil temperature and water availability after planting

Comparison of the root system growth and water transport of southern pine species after planting in different root-zone environments is needed to guide decisions regarding when, and what species to plant. Evaluation of how seed source affects root system responses to soil conditions will allow seed sources to be matched to planting conditions. The root growth and hydraulic conductivity of three sources each of shortleaf, loblolly and longleaf pine seedlings were evaluated for 28 days in a seedling growth system that simulated the planting environment. Across species, an increase in root-zone temperature alleviated limitations to root growth caused by water stress. In the coldest temperature, longleaf pine maintained a higher hydraulic conductivity compared to shortleaf and loblolly pine. Without water limitation, the root growth and hydraulic conductivity of shortleaf and loblolly pine were superior to that of longleaf pine, but as water availability decreased, the root growth of longleaf pine surpassed that of loblolly pine. Hydraulic conductivities of the seed sources differed, and differences were attributed to either new root growth, or an increase in the efficiency of the root system to transport water.     

Physiological responses of radiata pine roots to soil strength and soil water deficit

We investigated physiological responses of radiata pine (Pinus radiata D. Don) roots to soil strength and soil water deficit by measuring the osmotic potential (Psi(pi)) and yield turgor (Y) in the elongation zone of root segments of seedlings growing (i) in polyethylene glycol 4000-containing rooting solution of different water potentials (Psi(s)) and (ii) in soil of different soil strengths (Q) at the same soil matric potential (Psi(m)). Root elongation rate (Deltal/Deltat) decreased progressively with decreasing Psi(s) and was associated with decreased Psi(pi) and decreased turgor pressure (P). Osmotic adjustment occurred at Psi(s) < -0.2 MPa. Over a range in Psi(s) of -0.01 to -1.0 MPa, Psi(pi) fell 0.3 MPa whereas P fell 0.7 MPa. Mean Psi in the solution experiment was 0.37 MPa and did not differ significantly with Psi(s) (P = 0.10). Root elongation rate decreased exponentially as Q increased from 0 to 3.0 MPa, and was associated with an increase in P of 0.11 MPa as a consequence of Psi(pi) decreasing by the same amount. Mean Y in the soil experiment was 0.49 MPa and did not change significantly with Q (P = 0.87).     

Tracheid diameter is the key trait determining the extent of freezing-induced embolism in conifers

We tested the hypotheses that freezing-induced embolism is related to conduit diameter, and that conifers and angiosperms with conduits of equivalent diameter will exhibit similar losses of hydraulic conductivity in response to freezing. We surveyed the freeze-thaw response of conifers with a broad range of tracheid diameters by subjecting wood segments (root, stem and trunk wood) to a freeze-thaw cycle at -0.5 MPa in a centrifuge. Embolism increased as mean tracheid diameter exceeded 30 microm. Tracheids with a critical diameter greater than 43 microm were calculated to embolize in response to freezing and thawing at a xylem pressure of -0.5 MPa. To confirm that freezing-induced embolism is a function of conduit air content, we air-saturated stems of Abies lasiocarpa (Hook.) Nutt. (mean conduit diameter 13.7 +/- 0.7 microm) by pressurizing them 1 to 60 times above atmospheric pressure, prior to freezing and thawing. The air saturation method simulated the effect of increased tracheid size because the degree of super-saturation is proportional to a tracheid volume holding an equivalent amount of dissolved air at ambient pressure. Embolism increased when the dissolved air content was equivalent to a mean tracheid diameter of 30 microm at ambient air pressure. Our centrifuge and air-saturation data show that conifers are as vulnerable to freeze-thaw embolism as angiosperms with equal conduit diameter. We suggest that the hydraulic conductivity of conifer wood is maximized by increasing tracheid diameters in locations where freezing is rare. Conversely, the narrowing of tracheid diameters protects against freezing-induced embolism in cold climates.     

两种叶面肥对马尾松苗期生长的影响研究

为了解叶面肥种类对马尾松(Pinus massonianna)苗期生长质量的影响,对马尾松苗分别喷施质量浓度为1g.L-1的特多收和0.125 g·L-1喷施宝叶面肥,结果表明:2种叶面肥处理3个月后马尾松苗高、地径、根系生长以及苗木质量较清水处理均有所提高,特多收叶面肥处理各生长指标均显著高于清水处理(P＜0.05),特多收叶面肥处理较喷施宝叶面肥处理的苗高、地径、主根长、须根数、总须根长、鲜质量和Ⅰ级苗比例分别增加0.7％、3.1％、17.6％、29.5％、21.4％、1.6％和1.5％,施肥效果优于喷施宝(P＜0.05).     

Photosynthesis and light-use efficiency by plants in a Canadian boreal forest ecosystem

Measurements of the photosynthetic response to midsummer irradiance were made for 11 species representing the dominant trees, understory shrubs, herbaceous plants and moss species in an old black spruce (Picea mariana (Mill.) B.S.P.) boreal forest ecosystem. Maximum rates of photosynthesis per unit foliage area at saturating irradiance, A(max), were highest for aspen (Populus tremuloides Michx.), reaching 16 micromol m(-2) s(-1). For tamarack (Larix laricina (Du Roi) K. Kock) and P. mariana, Amax was only 2.6 and 1.8 micromol m(-2) s(-1), respectively. Values of A(max) for understory shrubs and herbaceous plants were clustered between 9 and 11 micromol m(-2) s(-1), whereas A(max) of feather moss (Pleurozium schreberi (Brid.) Mitt.) reached only 1.9 micromol m(-2) s(-1). No corrections were made for differences in shoot structure, but values of photosynthetic light-use efficiency were similar for most species (70-80 mmol CO2 mol(-1)); however, they were much lower for L. laricina and P. mariana (15 mmol CO2 mol(-1)) and much higher for P. schreberi (102 m;mol CO2 mol(-1)). There was a linear relationship between Amax and foliage nitrogen concentration on an area basis for the broad-leaved species in the canopy and understory, but the data for P. mariana, L. laricina and P. schreberi fell well below this line. We conclude that it is not possible to scale photosynthesis from leaves to the canopy in this ecosystem based on a single relationship between photosynthetic rate and foliage nitrogen concentration.     

杉木起苗后不同处理方法对根生长势的影响

苗木品质的好坏直接影响到造林的成败。在起苗到造林的过程中 ,由于对苗木处理不当 ,苗木地上或地下部分常易遭受损伤 ,或丧失水分 ,从而影响苗木的生活力 ,甚至导致造林失败。研究上述不良现象对苗木品质的影响 ,为起苗到造林过程中的苗木保护提供依据具有重要意义[1] 。1　材料与方法1.1　材料杉木 [Cunninghamia lanceolata( Lamb.) Hook.]1年生播种苗于 1999年 3月 2 0日随机起自安徽省宣州市敬亭山绿化管理处苗圃。起苗后立即按国标 [2 ] 的要求测定苗高、地径、长度≥ 5 cm侧根数等形态指标。测定时 ,发现 3级以下的苗木随时剔除。…     

间作绿豆对核桃苗光合特性及根系导水力的作用

[目的]为研究间作绿豆对核桃苗根系生长、根系水分运输和光合特性的影响,[方法]采用砂培方法,在温室内将1年生核桃嫁接苗和绿豆进行间作。[结果]显示:间作绿豆增加了土壤全氮含量(0.014%0.021%),不添加氮素间作绿豆,核桃苗根系总表面积、根系总长度、根系直径和根系总体积均显著增加,而正常供应氮素间作绿豆,核桃苗根系生长降低。核桃苗根系单位面积的导水率与土壤氮素含量显著相关,添加氮素与否间作绿豆后,根系单位面积导水率分别升高0.102×10^-5 mL·cm^-1·min^-1·MPa^-1和0.057 ×10^-5 mL·cm^-1·min^-1·MPa^-1;而不添加氮素间作绿豆整株根系导水率增加0.043 mL·cm^-1·min^-1·MPa^-1,正常供应氮素间作绿豆后,核桃苗整株根系导水率反而降低0.034 mL·cm^-1·min^-1·MPa^-1;核桃苗气孔导度对各处理响应和根系整株导水力有相同趋势,不添加氮素间作绿豆核桃光合能力升高至对照水平,光饱和点达1 567.17 μmol·m^-2·s^-1,最大净光合速率达12.84 μmol·m^-2·s^-1,光补偿点和暗呼吸速率降低;而正常供应氮素间作绿豆核桃苗光合能力降低。[结论]间作绿豆改善了核桃苗的生长环境,有益于增加核桃苗的根系吸收面积、水分运输以及光合代谢;但在氮素充足的土壤中,间作绿豆非但无益于核桃苗,反而降低核桃苗的水分供应,影响其气体交换和光合能力。     

Field determination of unsaturated hydraulic conductivity of forest soils

This study introduces a field method to determine unsaturated hydraulic conductivity which is applicable to sloping terrain with a limited water supply. A single steel ring infiltrometer and an artificial rainfall simulator are used in this method to reduce the amount of water required to attain a steady-state flux condition. Six tensiometers and a time domain reflectometry (TDR) are employed as the soil capillary pressure head and the volumetric soil water content measurement devices, respectively. Water contents measured by the TDR are corrected using a simple calibration method suggested by Hook and Livingston (1996). Unsaturated hydraulic conductivities are computed based on the instantaneous profile method using capillary pressure head and water content changes measured during a drainage process. The proposed method was applied to a forest soil profile in Rokko Mountain range. Results showed that the relationships between the unsaturated hydraulic conductivity and capillary pressure head developed by the proposed method coincide well with those measured by the conventional steady-state laboratory experiment. The proposedin-situ method is the effective simple means to determine unsaturated hydraulic conductivities of forest soils, since this method is enough accurate and consuming less amount of water and time. This research was partly supported by a Grant-in-Aid for Scientific Research (No. 08760149) from the Ministry of Education, Science, Sports, and Culture, Japan.     

Stomatal conductance, growth and root signaling in young oak seedlings subjected to partial soil drying

Leaf conductance, water relations, growth, and abscisic acid (ABA) concentrations in xylem sap, root apices and leaves were assessed in oak seedlings (Quercus robur L.) grown with a root system divided between two compartments and subjected to one of four treatments: (a) well watered, WW; (b) half of root system exposed to soil drying and half kept well watered, WD; (c) whole root system exposed to drought, DD; and (d) half of root system severed, RE. Sharp decreases in plant stomatal conductance, leaf water potential, hydraulic conductance and leaf growth were observed during DD treatment. No significant differences in plant leaf water potential and stomatal conductance were detected between the WW and WD treatments. Nevertheless, the WD treatment resulted in inhibition of leaf expansion and stimulation of root elongation only in the well-watered compartment. Abscisic acid concentrations did not change in leaves, root tips, or xylem sap of WD- compared to WW-treated plants. Increased concentrations of ABA were observed in xylem sap from DD-treated plant roots, but the total flux of ABA to shoots was reduced compared to that in WW-treated plants, because of decreases in transpiration flux. Similar plant responses to the WD and RE treatments indicate that the responses observed in the WD-treated plants were probably not triggered by a positive signal originating from drying roots.     

Fertilizer-induced Changes in Rhizosphere Electrical Conductivity: Relation to Forest Tree Seedling Root System Growth and Function

Fertilization is standard practice in forest tree seedling nursery culture. Additionally, fertilization at outplanting has potential to facilitate nutrient uptake and reduce transplant shock. Fertilization, however, may dramatically alter rhizosphere chemical properties such as pH, ion availability, and electrical conductivity (EC). These changes may inhibit root system growth and function by reducing soil osmotic potential and creating specific ion toxicities. The risk of root damage associated with high EC levels appears to be dependent on species, age of root system, and soil moisture availability. Root inhibition in container nursery culture of conifers is likely to occur above 2.5 dS m⁻¹, though threshold EC levels for bareroot culture and field plantings are largely unavailable. Fertilization at outplanting has the added risk that drought conditions may prevent leaching of excess fertilizer salts, which can increase rhizosphere EC beyond safe levels and ultimately impair root uptake of water or nutrients. For fertilization programs to be successful, a critical threshold balance must be maintained between optimizing seedling nutrient availability in the rhizosphere, while minimizing potential for root damage. Future research is needed to identify optimal EC levels for a range of species across all stages of the reforestation process, from nursery culture through plantation establishment.