Irrigation regime affects water and aeration conditions in peat growth medium and the growth of containerized Scots pine seedings

Containerized Scots pine seedlings growing in light Sphagnum peat growth medium in a greenhouse were subjected to three irrigation treatments. The seedlings were irrigated by saturating the growth medium with a nutrient solution (i) daily or when (ii) –5 or (iii) –10 kPa medium matric potential was achieved. In general, the nutrient concentrations in the foliage of the seedlings were rather similar for all irrigation treatments. In the wet (daily) irrigation treatment, however, the foliar concentration of N was lower and the foliar concentrations of P, Ca, S, Mn and Na were higher than in the other two treatments. In the wet irrigation treatment, height growth was lower than that in the other treatments. In this treatment the shoot to root ratio and several other morphological characteristics were also reduced, while the number of root lenticels and seedling mortality were increased compared to the other treatments. Rapid growth was obtained by irrigating at –5 to –10 kPa matric potential. In the wet irrigation treatment, the median matric potential and air-filled porosity of the peat medium were –0.4 kPa and 11%, respectively, which indicated waterlogging and very suboptimal aeration to the seedlings. The respective values for the irrigations at –5 and –10 kPa were –2.7 to –3.3 kPa and 39 to 43%, which were considered to cover the range from optimum to slightly suboptimum for average water availability and aeration.     

Dry-matter partitioning in loblolly and slash pine: Effects of fertilization and irrigation

The effects of fertilization and irrigation, singly and in combination, on growth and dry-matter allocation in seedlings of Pinus taeda and P. elliottii were investigated under field conditions. Trickle irrigation was regulated to maintain soil water potential above −10 kPa and 111 g of fertilizer (N:P:K 10:10:10 plus micronutrients) were banded around each seedling on three occasions. Treatments were initiated at the beginning of the second growing-season in the field, the same year sampling was conducted. Sampling consisted of complete excavation of 15 seedlings per treatment per species beginning in early April and continued every 6 weeks through mid-November, 1986. Each seedling was measured for height, root-collar diameter, foliage, stem and root dry-matter, and total needle surface-area. Allometric growth-analysis was used to determine dry-matter partitioning among the various tree components.

The cultural treatments affected the two species differently. Loblolly pine responded to treatments by shifting dry-matter allocation from roots to shoots, with the greatest increase observed in the fertilization treatment. Slash pine showed a similar response to irrigation and to irrigation plus fertilization, but increased allocation to roots under the fertilization treatment. Allocation to stems was greater than to foliage in both species and treatments except the control loblolly pine.     

Effects of nitrogen on the growth and competition between seedlings of two temperate forest tree species

To understand how coexisting temperate tree species react to nitrogen (N) addition, seedlings of two coexisting species, Phellodendron amurense Rupr. and Fraxinus mandshurica Rupr. were transplanted to a controlled environment. Seedlings were then planted in two competition scenarios, control and mixed, and then subjected to four N addition treatments. The seedling growth parameters and competition effect were monitored and analyzed. The height and stem-base diameter showed a positive response to the N addition in all competition scenarios except for mixed P. amurense, which responded negatively. Chlorophyll content of the seedlings showed a positive relationship to N addition while the chlorophyll a/b showed a complex trend. The addition of N showed a positive relationship to the competition effect of diameter growth in both species and height growth in P. amurense. These results indicate that F. mandshurica may be more sensitive to N addition and could benefit more from N addition than P. amurense. With an increasing N input from the atmosphere, forests may be more suitable for F. mandshurica reducing the abundance of P. amurense.     

桢楠幼苗对模拟氮沉降的生长响应

为了解桢楠(Phoebe zhennan)幼苗的生长对模拟氮沉降的响应,以1年生桢楠幼苗为材料,设置5个氮水平CK(0)、N1(5.7 g·m-2·a-1)、N2(11.4 g·m-2·a-1)、N3(19.0 g·m-2·a-1)和N4(38.0 g·m-2·a-1),对不同施氮水平下幼苗的株高、地径、生物量和根系指标进行研究。结果表明,不同施氮处理均促进了株高、地径和叶面积的增长,株高增长率、地径增长率和叶面积均以N3处理最高,分别为CK的3.93、1.51和1.33倍;不同施氮处理均提高了幼苗的生物量,各施氮处理下整株鲜重分别较CK提高了22.15%、31.53%、96.45%和45.82%,以N3处理最高;随着施氮量的增加,幼苗的总根长、根直径、根表面积、根体积和根尖数均先升高后降低;隶属函数分析结果显示N3处理的桢楠幼苗质量最佳,说明适度氮沉降能促进幼苗生长,但更高水平的氮沉降可能会产生一定抑制作用。     

Soil phosphorus and water effects on growth,nutrient and carbohydrate concentrations, δ<Superscript>13</Superscript>C,and nodulation of mimosa (<Emphasis Type="Italic">Albizia julibrissin</Emphasis> Durz.) on a highly weathered soil

Growth and physiological performance of multipurpose tree species can be severely constrained by low phosphorus (P) availability in highly weathered soils. Limitations to plant growth are accentuated by seasonal dry periods. The overall objective of this study was to examine P fertilization and irrigation effects on survival, growth, biomass partitioning, foliar nutrients, intrinsic water-use efficiency (WUE) indexed by δ¹³C, Rhizobium nodulation, and carbohydrate content as an indicator of resprouting potential, of mimosa (Albizia julibrissin Durz.), a N₂-fixing tree species being tested for browse in agroforestry practices in south-central USA. In a field experiment carried out during two growing seasons near Booneville, Arkansas, USA, mimosa had a strong growth response to irrigation. The trial was arranged in a split plot design with three replications with irrigation as main plot treatment and P as sub-plot treatment. Mean total plant aboveground biomass at the end of the second growing season was 9.8 and 44.1 g plant⁻¹ for the rainfed treatment without and with 300 mm of irrigation water, respectively. Placed P fertilization increased mean total aboveground biomass from 19 g plant⁻¹ for the 0-P treatment to 69 g plant⁻¹ for the treatment with 90 kg P ha⁻¹ year⁻¹. Similarly, irrigation consistently increased stem basal diameter, total height, survival, root, stem, foliar and total aboveground biomass, and number of nodules per plant. Phosphorus fertilization increased basal diameter, and root and stem biomass in both irrigation treatments, survival and nodulation in the rainfed treatment, and foliar and total aboveground biomass in the rainfed +300 mm irrigation treatment. There was a decrease of foliar δ¹³C suggesting that WUE decreased with P fertilization. In a pot experiment, seedlings were subjected to a factorial combination of two irrigation treatments and six P levels in a randomized complete block design. Irrigation increased basal diameter, root, stem, foliar and total biomass, leaf area and nodulation, whereas P fertilization (i.e., levels from 0 to 3.68 g P kg⁻¹ soil) had similar effect in all the above variables except foliar biomass. Foliar P concentration to obtain 90% of the maximum total plant biomass (critical level) was estimated at 0.157%. Total nonstructural and water soluble carbohydrate, and starch concentrations increased non-linearly with irrigation and P addition suggesting impaired re-growth potential after defoliation of seedlings with reduced water supply and at low soil P availability. Results of this study indicated strong limitations for growth and regrowth potential of mimosa on a highly weathered soil with very low P availability and seasonal water content shortages. Placed (i.e., near the plant base) application of P appeared to be a good strategy to fertilize perennial woody plants.     

Autumn Fertilization in the Nursery Affects Growth of Picea abies Container Seedlings After Transplanting

Second-year Norway spruce seedlings [Picea abies (L.) Karst.] grown in containers were divided into three fertilization levels in August [5, 15 and 25 mg nitrogen (N) seedling^?1]. The resulting foliar concentrations of N were 11.0, 13.1 and 15.8 g kg^?1, respectively. Seedling height (mean 26.0 cm) did not differ among treatments. The next spring, the seedlings were tested in two experiments. (1) The seedlings were transplanted into pots containing sandy soil in the greenhouse, where they were fertilized with either pure water or nutrient solution (22 mg N l^?1). (2) The outplanting performance of the autumn-fertilized seedlings was tested on a sandy field. In the greenhouse experiment, the autumn fertilization level affected height growth and root egress of the seedlings significantly, but less than fertilization with a nutrient solution after planting. In the field experiment, during the first season after transplanting shoot growth of the seedlings increased with the level of autumn fertilization. After the second and third seasons, the seedling stem volume was highest with the highest level of autumn fertilization. These results suggest that, by improving the preplanting nutrient status of seedlings, the growth of shoot, stem diameter and root biomass can be enhanced after planting, especially on nutrient-poor soils. However, heavier autumn fertilization than that used here may yield a greater and more persistent increment in growth.     

N、P肥对湿加松幼苗生长效应的研究

通过盆栽试验,采用尿素、过磷酸钙各4个水平共8个处理,研究N、P肥对湿加松幼苗的生长效应.结果表明,尿素和过磷酸钙均对湿加松生长有显著影响;各处理对湿加松地径生长的影响在9-12月差异显著,N-1处理地径最大,P-2处理次之;各处理对冠幅生长的影响在7-11月有显著差异,7月以N-2处理冠幅最大,8-11月则以P-2处理最大;各处理对苗高生长的影响差异不显著.对湿加松苗木生物量和植株N、P含量的分析表明,施用一定量的尿素、过磷酸钙可改善植株的养分状况,过量施用则不利于N、P的正常吸收;湿加松苗木最佳施肥组合是每株施尿素6g＋过磷酸钙30 g＋氯化钾15 g.     

Frost hardiness, bud phenology and growth of containerized Picea mariana seedlings grown at three nitrogen levels and three temperature regimes

We studied the influence of temperature and near- and sub- optimal mineral nutrition of black spruce seedlings (Picea mariana [Mill.] B.S.P.) during their second growing period on bud set, bud development, growth, mineral content and cold tolerance. Bud break and growth after bud break were also studied. Seedlings were grown for 106 d in growth chambers under three temperature regimes in combination with three concentrations of a fertilizer. They were then cold hardened for 56 d and dehardened for 66 d.Under these near- and sub-optimal N levels, bud formation occurred during the growing season. Bud formation was accelerated with decreasing fertilization, but was not affected by temperature treatments. Needles from seedlings with 0.64% N (dry mass basis) before hardening did not harden. Those with 0.87% N showed a lesser degree of hardiness than those with 1.28% N. Stem diameter increased at the beginning of the hardening period. During this acclimation period, shoot dry mass decreased with time at a constant rate and at the same rate over time for all treatments whereas root dry mass was more variable. Total number of needle primordia was low and no difference was observed among growing conditions. Bud break was similar in all treatments. Following bud break, shoot height and stem diameter increases were small but their magnitude varied with the nutritional regimes applied during the previous growing period. During hardening, nitrogen concentration of shoot tissues first increased and then decreased; phosphorus concentration first increased and then remained stable; potassium concentration remained stable. Concentration of these three elements generally decreased in the roots during this hardening.     

Growth and nutrient dynamics of <Emphasis Type="Italic">Betula alnoides</Emphasis> seedlings under exponential fertilization

Betula alnoides is a fast-growing hardwood species grown in large plantations in Southeast Asia and South China. Nitrogen requirements for producing robust seedlings, growth and nutrient dynamics were investigated using exponential fertilization treatments. Root collar diameter, height, dry mass and nutrient contents of seedlings increased exponentially in all fertilization treatments as time progressed. Moreover, with water soluble fertilizer (Plant Products plus microelements N–P₂O₅–K₂O: 20–20–20), 300 mg N seedling^?1 was adequate. Vector analysis revealed that P was the most responsive nutrient element, followed by N and K. Dilutions of N and K were evident in the plants without N addition, which induced initial P sufficiency and then luxury consumption probably due to the antagonistic interaction between N and P. However, deficiencies of N, P and K were mostly observed in all exponential regimes during the experiment because seedling growth rate exceeded nutrient uptake rate, inferring that further study on improving the nutrient uptake efficiency is needed. Analysis of relationships among nutrient supply, dry mass, N content and N concentration demonstrated that 100–400 mg N seedling^?1 induced sufficiency to luxury consumption of nitrogen without significant change in dry mass, and 400 mg N seedling^?1 is recommended to apply for nutrient loading of seedlings before outplanting. The findings will help improve seedling quality and enhance the production of robust seedlings for plantation forestry of this species.     

Growth and Nutritional Responses of Juvenile Jeffrey Pine to Post-Planting Fertilization

Abstract

Broadcast fertilization of a three-year-old Jeffrey pine (Pinus jeffreyi Grev. & Balf.) plantation growing on an eroded Sierra Nevada site was examined for its capacity to enhance seedling growth. The amendments chosen for the study included controlled release and conventional soluble formulations that contained a variety of N forms, but all featured high N content along with other nutrients. Four application rates were used, and all amendments were distributed around the base of the seedlings as top dressing. Four seasons after treatment application, fertilized seedlings were 129% larger in height, 93% larger in diameter, and 865% greater in shoot volume than unfertilized seedlings overall. Seedling sizes generally increased with application rate, and by a small margin, the controlled release fertilizer outperformed the other formulations. Relative growth analysis suggested that stimulation by the amendments would continue beyond four seasons. Foliar analysis conducted early and again late during the study revealed that N and P concentrations were consistently raised by fertilization, which likely accounts for much of the accompanying growth gains, while Ca, Fe, Mn, B, and Al concentrations were consistently reduced. Either early or late, foliar K was also raised while Mg, S, Zn, and Cu were reduced. Collectively, these results indicate that fertilization with a variety of high N formulations can increase the availability and uptake of critical nutrients sufficiently to impart in Jeffrey pine on low quality sites a substantial growth advantage.     

不同施肥处理对3种海岛树种苗木生长及造林效果的影响

为了解不同施肥处理对普陀樟(Cinnamomum japonicum var.Chenii)、全缘冬青(Ilex integra Thunb.)、红楠(Machilus thunbergii Sieb.et Zucc)3种海岛树种苗木生长及造林效果的影响,设置了7个不同的施肥处理,即(1)N(对照),(2)N+P,(3)N+2P、(4)N+K、(5)N+2K、(6)N+1P+1K、(7)N+2P+2K,于2011年5月至2012年1月观测苗高和地径,并测定植物各部分的生物量。结果表明:3种苗木不同施肥处理下,通过测算苗木质量指数QI可知,在N+1K施肥组合下,全缘冬青的苗木质量最好,而红楠在N+2P+2K的施肥组合下苗木质量最高,普陀樟在N+1P+1K的施肥组合下,苗木质量要好于其他处理。     

Production and establishment techniques for the restoration of Nothofagus alessandrii,an endangered keystone species in a Mediterranean forest

Ruil (Nothofagus alessandrii) is an endangered keystone species from the Mediterranean climate zone of Chile. Ruil’s fragile state of conservation urges development of restoration programs, but specific protocols for nursery production and field establishment that ensure plant survival are largely unknown. Therefore, we examined the effect on nitrogen (N) fertilization and container size during nursery production in combination with the use of mesh shelters after outplanting on survival and growth during the first growing season in the field. First year outplanting survival of nursery-grown container seedlings was enhanced when seedlings were given nitrogen (N) during nursery production and deployed with mesh tree shelters in the field. The volume of the container had no effect on outplanting survival and growth. Increasing N from zero to 200 mg N L^?1 provided sufficient N levels, resulting in increased seedling height, root-collar diameter, shoot biomass, and total seedling N and phosphorous concentrations. Additional N provided by the 400 and 600 mg N L^?1 treatments underwent luxury consumption by the seedlings with no further benefits in field performance. Improved growth in the nursery, along with the use of mesh tree shelters after outplanting, especially during the typical summer drought, may be responsible for increased survival during the first growing season. Increasing the performance of nursery-grown ruil seedlings is essential to restoring this endangered, vulnerable, and foundation species within the highly biodiverse, yet seriously threatened endemic Maulino Costero Forest of the Mediterranean climate of central Chile.

     

Field Performance of Three Stock Sizes of Douglas-fir Container Seedlings Grown with Slow-release Fertilizer in the Nursery Growing Medium

Containerized coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were grown with conventional soluble fertilizer and supplemented with one of four slow-release fertilizers (SRF treatments) or unsupplemented (control treatment). Seedlings were outplanted to two sites in 1998. At the time of outplanting, SRF incorporated into the growing medium resulted in larger seedlings with higher foliar nutrient concentrations as compared to conventionally fertilized seedlings. After four growing seasons, SRF-amended seedlings at both sites had significantly greater height, basal stem diameter, and stem volume, with increases up to 19, 21, and 73%, respectively, as compared to conventionally fertilized seedlings. Additionally, three stock sizes were compared at one of the sites. Increasing stock size resulted in increased growth during the first two seasons, enabling larger stock to maintain their size advantage. Seedling responses to SRF are attributed to larger initial size, increased internal nutrient reserves at planting, and continued fertilization after planting.     

控释肥和灌溉方式对栓皮栎容器苗苗木质量及造林效果的影响

[目的]探讨控释肥和灌溉方式对栓皮栎(Quercus variabilis Bl.)容器苗生长、养分含量、基质电导率(EC)及2年造林效果的影响,为培育高质量苗木提供参考。[方法]以栓皮栎容器苗为研究对象,采用双因素完全随机试验设计,设置5个施肥水平(以N元素含量为基准,5个施肥水平分别为:25、75、125、175、225 mg·株~(-1))和2种灌溉方式(上方喷灌(O)、底部渗灌(S)),测定栓皮栎容器苗形态指标、养分含量、根系生长、基质EC值及连续2年造林效果。[结果]表明:(1)施肥量和灌溉方式二者对苗木形态指标影响存在交互效应,225-O处理的苗木地径、根生物量、单株生物量最大,但根生物量、单株生物量在225-O、125-S、175-O处理之间差异不显著。225-S处理的苗高、茎生物量、茎根比最大,茎生物量在225-S与225-O之间差异不显著。(2)苗木茎、根的氮磷钾浓度和含量随施肥量的增加而增大,施肥量125、175、225 mg·株~(-1)处理之间的根氮、磷含量及单株磷含量差异不显著。(3)增加施肥量促进苗木根系的生长,施肥量为125、175、225 mg·株~(-1)处理之间的根系表面积、体积差异不显著。(4)基质EC值随施肥量的增加而增大,底部渗灌显著提高了基质上层、下层的EC值,基质上层、下层的最大EC值分别为4. 69、0. 56d S·m-1,没有对苗木生长产生不利影响。(5)和上方喷灌相比,底部渗灌显著地促进造林第1年幼树的树高、地径生长;造林第1年、第2年的树高和地径均随施肥量的增加而增大,造林第2年,施肥量125、175、225 mg·株~(-1)处理之间的树高、地径差异不显著。[结论]底部渗灌提高了栓皮栎容器苗体内的养分含量,促进了造林第1年幼树树高、地径的生长。施加控释肥有利于苗期苗木质量的提高及造林后苗木的快速生长。综合考虑苗木质量、经济效益、环境利益,培育栓皮栎容器苗可选择底部渗灌和控释肥量为125 mg·株~(-1)的组合(以N元素含量为基准)。     

The effect of carbon and nutrient loading during nursery culture on the growth of black spruce seedlings: a six-year field study

We tested the effects of exponential nutrient loading and springtime carbon loading during nursery culture on the field performance of black spruce (Picea mariana (Mill.) B.S.P.). Seedlings were grown from seed with a conventional, fixed dose fertilizer (10 mg N seedling⁻¹) or an exponential nutrient loading regime (75 mg N seedling⁻¹). The following spring, seedlings were exposed for two weeks to either ambient (370 ppm) or elevated levels of CO₂ (800 ppm) and then planted in the field; seedling growth was followed for the next six years. Exponential nutrient loading increased seedling height, stem diameter and leader growth, with the largest increases in height and leader length occurring in the first three years after outplanting. Carbon loading increased seedling height and leader length, but only in seedlings that had been exponentially nutrient loaded. A combination of carbon and nutrient loading increased shoot height 26%, stem diameter 37% and leader length 40% over trees that received neither treatment. These results demonstrate that the growth enhancement seen under exponential nutrient loading is maintained under field conditions for at least six years. Carbon loading just before outplanting was a useful supplement to nutrient loading, but was ineffective in the absence of nutrient loading.     

Improving drought tolerance of <Emphasis Type="Italic">Casuarina equisetifolia</Emphasis> seedlings by arbuscular mycorrhizas under glasshouse conditions

Effects of mycorrhizal association on improving tolerance of host plant under stress environments have received attentions in recent years. In this paper, six isolates of AMF (arbuscular mycorrhizal fungus) were inoculated to Casuarina equisetifolia seedlings under glasshouse conditions to investigate the effects of AMF on growth and drought tolerance of host plants. All the six isolates which belong to Glomus showed high mycorrhizal colonization (88.5–96.0%) with C. equisetifolia seedlings. Seedlings were subjected to drought stress without watering for 7 days and survival of the seedlings inoculated with Glomus caledonium Gc90068, G. versiforme Gv9004 and G. caledonium Gc90036 increased by 36.6, 23.3 and 16.6%, respectively compared with uninoculated seedlings. Limited influence of AMF on seedling height growth was found, but the effects of AMF on total biomass increment were very significant; the increment ranged from 25.7 to 118.9% compared with uninoculated treatment, and it was noted that AMF exerted more influences on root biomass than shoot biomass. Based on the changes in physiological and biochemical parameters among different treatments caused by drought stress, it was concluded that AM (arbuscular mycorrhizal) associations improve the drought tolerance of C. equisetifolia seedlings by means of some physiological and biochemical responses, such as lowering permeability of plasma membrane and MDA (malondialdehyde) contents, enhancing concentrations of P nutrition, soluble sugar, soluble protein and activities of POX (Peroxidase) of C. equisetifolia seedlings.     

施肥对猴耳环幼苗生长的影响

The effects of applying N(urea, 46% N), P(phosphate, 12% P₂O₅) and K(potassium sulphate, 54% K₂O) fertilizers on the growth performance and biomass yield of 8-month-old Archidendron clypearia seedlings were examined by L9 orthogonal array with 3 replicates in the nursery of Zengcheng Forest Farm of Guangzhou, Guangdong Province. The test seedlings were potted with the subsoil of total N 0.0484%, total P 0.1518% and total K 1.2629%, and fertilized at the 2nd and 6th months with the application rates of 0, 10 and 20 mg of N, 0, 20 and 50 mg of P and 0, 10 and 20 mg of K per seedling. The results showed that the diameter at ground level(DGL), the height and the oven-dried weight biomass of 8-month-old seedlings differed significantly at P=0.05. The combined application dose of 20 mg N, 20 mg P and 0 mg K per seedling resulted in the best seedling growth and biomass yield. N fertilizer was a significant factor in the growth of DGL and height of A. clypearia seedlings. P fertilizer had no significant effects on both DGL and height, while K fertilizer only affected DGL significantly. Analysis of the leaf and root stoichiometry suggested that N may be the most single limiting nutrient, A. clypearia seedlings used N more efficiently than they used P.     

Growth and nutrient use efficiency of water tupelo seedlings in flooded and well-drained soil

Growth characteristics and nutrient utilization rate of Nyssa aquatica L. seedlings grown in pots containing flooded or well-drained soil were compared in a greenhouse study. For most of the growing season, relative height and diameter growth rates, and biomass accumulation rates were greater for seedlings in flooded soil than for seedlings in well-drained soil. The concentration of Fe in the roots of seedlings in flooded soil was almost tenfold greater than that of seedlings in well-drained soil. However, flooding had no effect on foliar Fe concentrations. The flooding treatment resulted in decreased concentrations of N in all component parts and increased concentrations of P in the roots and stem, but it had no effect on foliar P concentrations. In response to flooding, foliar K concentrations decreased, whereas the concentration of K in the roots increased. Flooding had no effect on the K concentration of the stem. Seedlings in flooded soil produced more total biomass per milligram of nutrient absorbed than seedlings in well-drained soil, suggesting that N. aquatica seedlings are more efficient at producing biomass and height growth under hydric conditions than under mesic conditions.     

Effects of sulphuric acid and heavy-metal deposition on frequency of asymptomatic infections of Gremmeniella abietina in Scots-pine seedlings

The isolation frequency of Gremmeniella abietina was measured from asymptomatic 4-year-old Scots-pine seedlings. The seedlings had been subjected to simulated sulphuric deposition (pH 3.1 or 4.1) or control treatments (irrigation with spring water (pH 6), or no irrigation) during the three previous growing seasons. The seedlings were planted in soil originating from two localities with different backround levels of copper (Cu) and nickel (Ni), and the soil was further amended with Cu (63.3 mg/1 of soil) and Ni (20.5 mg/1 of soil), or a combination of the two. The seedlings were inoculated with conidia of G. abietina during their third growing season in the field. Asymptomatic infections of G. abietina were recovered frequently from seedlings that had received water irrigation. The addition of sulphuric acid to the irrigation water, and/or the lowered pH (pH 3.1 and 4.1) resulting from this addition, mitigated the effect of water application. The effect of Ni-treatment on the recovery of G. abietina depended on the irrigation treatment; with no irrigation, Ni-treatment increased isolation frequency, but, in irrigated seedlings the response was the opposite. Only 10.6% of the seedlings had symptoms caused by G. abietina; most of the seedlings had become infected before the application of the various treatments.     

Auxin-impregnated hygroscopic gel: effects on ponderosa pine and common hackberry seedlings

Greenhouse and field studies were conducted to determine the effects of indole3-butyric acid (IBA) and 2,4-dichlorophenoxyacetic acid (2,4-D) on root development and survival of 3+0 bareroot Pinus ponderosa (Dougl. ex Laws.) and 2+0 bareroot Celtis occidentalis (L) seedlings. In the greenhouse, 100 and 200 ppm. IBA and 10 and 50 ppm 2,4-D were applied to seedlings through a root dip in an auxin hygroscopic gel mix. A randomized complete block analysis of variance indicated that IBA gel treatments increased root volume and root dry weight in hackberry and had no effect on ponderosa pine; 2,4-D gel treatments had detrimental effects on both species. In the field, IBA gel treated ponderosa pine seedlings exhibited improved height and survival relative to the non-treated control seedlings. There was no detectable improvement in survival in the field for hackberry. However, diameter and stem dry weight were lower for hackberry seedlings treated with the gel dip alone.