Effects of flooding depth on growth,morphology and photosynthesis in <Emphasis Type="Italic">Alnus japonica</Emphasis> species

The present study deals with effects of flooding depth on growth, morphology and photosynthesis in Alnus japonica species thorough one field study and two controlled experiments. In the field study performed in Kushiro Mire, Hokkaido Island, Japan, tree heights and stem diameters decreased with an increase in water depth accompanied with the reduction of soil redox potential. In contrast, the rate of multiple stems per individual tree increased. In the controlled experiments for seedlings flooding suppressed the shoot elongation and biomass increment in roots. However, diameter increment around water levels, epicormic shoot development and adventitious root formation were enhanced in flooded seedlings. The photosynthetic rate and stomatal conductance of flooded seedlings also were lowered with an increase in flooding depth. The recovery of the reduced photosynthetic rate and stomatal conductance occurred simultaneously with the advancement of adventitious root formation in the flooded seedlings. These results indicate the importance of a series of morphological changes occurring on stems around water levels in flood tolerance in A. japonica species.     

落叶松水浸液对胡桃楸幼苗生长的影响

A study was conducted to detect the effect of water extracts from different parts such as root, bark, branch and leaf, of adult larch, Larix gmelini, trees on growth of Manchurian walnut, Juglans mandshudca, seedlings and the allelopathy between the two tree species. Four concentrations （100 g. kg i, 50 g. kg^-1, 25 g. kg^-1 and 12.5 g. kg^-1） were prepared for each kind of extracts. Result showed that the water extracts with low and moderate concentrations accelerated the growth of collar diameter and increased biomass and root/shoot ratio of walnut seedlings. The water extracts from branches and barks with low and moderate concentrations accelerated the height growth of the seedlings, while those from leaves and roots slightly decreased the height growth of seedlings. The fact that application of water extracts of larch improved the growth of Manchurian walnut attributes possibly to the allelopathy between the two tree species.     

Inhibiting factors of symptom development in several Japanese red pine (<Emphasis Type="Italic">Pinus densiflora</Emphasis>) families selected as resistant to pine wilt

Pinus densiflora and P. thunbergii, native to Japan, are highly susceptible to pine wilt disease caused by infection with a pine wood nematode (Bursaphelenchus xylophilus). Trees of these susceptible species have occasionally been found surviving in forests that are extensively damaged by this disease. Seedlings from a part of surviving trees that were selected as resistant families indicate lower mortality rates after the infection. The factors that prevent the symptoms from developing in resistant families of a susceptible species, P. densiflora, as based on the analysis of the pathogens behavior in the tree tissue and the anatomy of the resistant families, are presented in this paper. Nematode populations remained lower in the stems of seedlings from resistant families of P. densiflora than in the stems of non-resistant families. Areas dysfunctional in water transport developed in the stems of resistant families, but did not reach a size large enough to seriously block the ascent of sap. These results suggest that there are systems within the seedlings that prevent nematode migration and reproduction. The 2-year-old seedlings from resistant families of P. densiflora, however, did not suppress the pathogen activity. Numerous branches are a visible characteristic in the seedlings of some resistant families. The arrangement of the resin canals, the only channels in the tree to the pathogen migration, was disoriented at the joints between the branches and the main stem. Such a structure may be effective as a barrier to nematode dispersal.     

Effects of brassinolide on the survival,growth and drought resistance of <Emphasis Type="Italic">Robinia pseudoacacia</Emphasis> seedlings under water-stress

We conducted field and pot experiments to investigate the effects of brassinolide on 1-year-old Robinia pseudoacacia L. seedlings. In the field experiment, seedling roots were soaked in brassinolide solutions containing 0–0.4 mg/l pure brassinolide before planting. Survival and growth of the seedlings were determined 8 months later. The results showed that soaking roots in brassinolide prior to planting significantly increased the survival and growth of seedlings. The best results were in the 0.2 mg/l brassinolide treatment. In the pot experiment, roots were soaked in 0–0.4 mg/l brassinolide before planting followed by a foliar application of brassinolide when the seedlings leafed out. After the seedlings were established, the soil water content in the pots was regulated to simulate drought conditions and various physiological parameters were measured. The results showed that treatment with 0.2 mg/l brassinolide decreased the transpiration rate, stomatal conductance and malondialdehyde (MDA) content of seedlings growing under moderate or severe water stress compared to untreated seedlings. Leaf water content, predawn water potential, soluble sugar content, free proline content, and superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities were all greater in water-stressed seedlings in the 0.2 mg/l brassinolide treatment compared to the control. The results indicate that the application of brassinolide can ameliorate the effects of water stress and enhance drought resistance of Robinia seedlings. Treatment of seedlings with brassinolide may be a useful management tool for afforestation projects in arid and semiarid areas.     

Development of Leptographium wageneri on root surfaces and other substrata

Conidia of Leptographium wageneri var. ponderosum, Leptographium wageneri var. pseudotsugae and Leptographium wageneri var. wageneri germinated on wounded roots of ponderosa pine (Pinus ponderosa), Douglas fir (Pseudotsuga menziesii), and pinyon (Pinus edulis), but not on unwounded roots. On wounds, germination occurred regardless of the combination of pathogen variety and plant species. When wounded roots of ponderosa pine and Douglas fir seedlings were inoculated with conidia of L. w. var. ponderosum and L. w. var. pseudotsugae, respectively, 87-100% of the seedlings became infected. When unwounded roots were inoculated with wooden blocks colonized with L. wageneri, 60-66% of the seedlings became infected. The development of L. w. var. ponderosum and L. w. var. pseudotsugae on agar was compared with their development on agar overlaid with either cellophane or Nucleopore membranes. Undulating hyphae were found commonly in and on the agar, but less frequently on the membranes. On both membranes, mycelia formed mats which were tightly appressed to the surface; mats were not formed on the agar. On both agar and the membranes, two or more hyphae often formed a strand. When L. w. var. ponderosum mycelia were allowed to colonize the surface of an unwounded pine root, strands, undulating hyphae and poorly formed mats were seen.     

First hybrid plane trees to show resistance against canker stain (Ceratocystis fimbriata f. sp. platani)

Canker stain, caused by the ascomycete Ceratocystis fimbriata f. sp. platani, is a major threat to plane trees in Europe. The American plane tree (Platanus occidentalis) carries some genetic resistance, but this species is not adapted to the climatic conditions in Europe. Therefore, hybrids between susceptible oriental plane trees (Platanus orientalis) and resistant P. occidendalis were screened for disease resistance in France. Among 960 hybrids, we found 18 individuals which survived two successive inoculations. These putatively resistant trees were cut back and, after 18 months, on each tree 12 of the newly produced shoots as well as two roots, were inoculated again. From these trees, only one showed complete and another one partial resistance. This selection process resulting in the resistant clone ‘Vallis clausa’ is described in detail.     

Traumatic resin canals as markers of infection events in Douglas‐fir roots infected with Armillaria root disease

In response to an infection, traumatic resin canals (TRCs) are formed in the roots of many conifers, which may be used to determine the timing and sequence of infection events essential for epidemiological studies of root diseases. Juvenile Douglas‐fir (Pseudotsuga menziesii) tree roots at coastal and interior sites in British Columbia were wounded at various times of the year or were inoculated with an isolate of Armillaria ostoyae, and root sections were taken to determine the timing and extent of TRC formation. Naturally infected Douglas‐fir were also examined to determine the extent of the TRCs in infected and uninfected roots on infected trees and in the lower stem. Wounds made in March and October had poor or no TRC formation while the summer wounds responded strongly and were associated with resin soaking. Roots wounded in October did not respond until the following year in all trees except one. Trees produced TRCs and resin soaked tracheids at all times in response to the fungal inoculations. The most striking difference between wounding or fungal inoculation was the multiple bands of TRCs produced in response to the fungus. TRCs at natural A. ostoyae infections were found 92% of time in roots at the stem junction and 74% of the time in the stem at soil line. TRCs were produced in uninfected roots on infected trees but disappeared with increasing distance from the initiating lesion. TRCs can be used to time yearly and seasonal root infections when they can be traced from an identified lesion.     

Statistical interferometric investigation of nano-scale root growth: effects of short-term ozone exposure on ectomycorrhizal pine (<Emphasis Type="Italic">Pinus densiflora</Emphasis>) seedlings

This study presents the effects of short-term ozone exposure on the nano-scale growth behavior of the fine roots of Pinus densiflora (Japanese red pine) seedlings. Root elongation measurements were obtained in nanometers for very short (sub-second) time intervals by using the optical interference method called statistical interferometry, developed by the authors. Three categories of P. densiflora seedlings were investigated; two categories were infected with ectomycorrhiza of Pisolithus sp. (Ps) and Cenococcum geophilum (Cg), while the third was without any fungal infection. In experiments, two points on a root with a separation of 3 mm were illuminated by laser beams and the elongation was measured continuously by analyzing speckle patterns successively taken by a CCD camera. The ectomycorrhizal fungi-infected and uninfected seedlings were exposed to ozone at concentrations of 120 and 240 ppb for periods of 1, 3, or 5 h in separate treatments. The root elongations of P. densiflora seedlings were measured before and immediately after the each ozone treatment and then the root elongation rates (RER) were determined for growth-measurement periods of 5.5 s and 9.5 min. From the measurements obtained for 9.5 min, we found that the RERs of uninfected and Cg-infected seedlings were reduced by 42 and 18%, respectively, after 5 h of exposure to 120 ppb ozone compared with that before exposure, while the reduction in RER of Ps-infected seedlings was not significant. When the concentration of ozone was increased to 240 ppb, the RERs of Ps-infected and Cg-infected seedlings were reduced by 32 and 44%, respectively, after exposure for 5 h, while the reduction in RER of uninfected seedlings was 59%. These observations prove that the non-mycorrhizal seedling roots are more sensitive to ozone stress. From this study, we found that the RERs of both mycorrhizal and non-mycorrhizal seedlings apparently fluctuated throughout the measurements, even within a few minutes.     

Growth,morphology and photosynthetic activity in flooded <Emphasis Type="Italic">Alnus japonica</Emphasis> seedlings

This study was conducted on Alnus japonica seedlings subjected to flooding for 2, 4, and 6 weeks to examine responses in growth, morphology, and photosynthesis to different periods of flooding. Seedlings subjected to flooding for 2 and 4 weeks were drained after flooding then watered daily. Increases in biomass of leaves, roots, and whole plants were less for 6-week-flooded seedlings. Rate of photosynthesis and stomatal conductance of flooded seedlings decreased within 2 weeks. For 2-week-flooded seedlings recovery from reduced stomatal conductance and recovery of photosynthetic activity occurred after drainage. For the 6-week-flooded seedlings stomatal conductance recovered by the end of the experiment. Adventitious root formation by the 4 and 6-week-flooded seedlings was observed from the third week of flooding. These results suggest that recovery of reduced function in leaves may progress with development of adventitious roots during the period of flooding.     

Early root morphology of jack pine seedlings grown in different types of container

Abstract

This study compared the effects of container type on early root system morphology of jack pine (Pinus banksiana Lamb.) seedlings to determine impacts of container type on root characteristics that may be important for tree stability. Seedlings were grown for one season in Multipots®, Ventblocks®, Copperblocks®, Starpots® and Jiffy® pellets, and for a second season in sand culture in pots. After the first growing season, roots that had grown between Jiffy plugs were cut using a knife, either “early”, in September, or “late”, in November. Seedlings produced in non-pruning containers, Multipots and Ventblocks, had more vertical structural roots, less even root distribution and high shoot:root mass after a second season. Seedlings grown in pruning containers, Copperblocks, Starpots and Jiffy pellets, had more horizontal structural roots and more evenly distributed roots. Jiffy seedlings had high shoot:root mass after pruning, but ratios decreased to low levels similar to Starpots and Copperblocks after a second season in pots. Early pruning of Jiffy seedlings removed less root mass than late pruning, but total live root mass of early and late pruned seedlings was similar after the potting trial. Pruning containers thus produced structural root forms with more desirable characteristics for tree stability. These characteristics were evident after the first season and persisted after the second season in the potting trial.     

Effects of nickel and copper on growth and mycorrhiza of Scots pine seedlings inoculated with Gremmeniella abietina

Scots pine (Pinus sylvestris) seedlings were planted in soil originating from two localities with different background levels of nickel and copper. In addition, some of the seedlings were exposed to additional nickel (20.5 mg Ni/l of soil) or copper (63.5 mg Cu/l of soil), or a combination of both Ni and Cu, via soil without direct shoot exposure during their second growing period. The seedlings were either irrigated with spring water (pH 6) or got only natural rain during the whole field experiment. All seedlings were inoculated with conidia of a shoot‐pathogen Gremmeniella abietina during their third growing season, and harvested the following spring. Lengths of shoots of different year‐classes were used as growth estimates. In roots, the proportion of fungal (assumedly mycorrhizal) biomass was estimated by measuring ergosterol concentration. Guajacol peroxidase activity was measured. Short roots were classified into two groups according to their condition and the composition of the mycorrhizal community was expressed as a proportion of morphotypes in the roots. The seedlings exposed to additional Ni had higher shoot growth than the seedlings in the other treatments. The mean Ni concentration in the roots of seedlings exposed to additional Ni was 79 p.p.m. and in other seedlings 16 p.p.m. Additional Ni also decreased the frequency of clearly senescent short roots and the proportion of the mycorrhizal morphotype with the thinnest mantle. These results indicate that the Ni exposure levels used in this experiment had some positive effects on the seedlings. The relative fungal biomass was about 6% lower (p = 0.0981) in the fine roots of seedlings treated with additional Cu. The mean Cu concentration in the roots of seedlings exposed to additional Cu was 256 p.p.m. and in other seedlings 29 p.p.m. Peroxidase activity, which was used as a general stress indicator in this study, was not affected by any of the treatments. The shoot growth and the relative biomass of fungi in the fine roots were positively correlated in all seedlings, and this correlation was stronger in seedlings exposed to additional Ni that were not irrigated compared with seedlings not exposed to additional Ni that were irrigated. The frequency of asymptomatic infections of G. abietina was positively correlated with the proportion of senescent short roots in the irrigated seedlings but not in not‐irrigated seedlings. The general condition of seedlings may be an important factor for infection by G. abietina when moisture is high enough for the fungi to infect seedlings by conidia.     

Pathogenicity of Spanish isolates of Heterobasidion annosum s. s. in Pinus pinaster seedlings

The aim of this study was to test the pathogenicity of two Spanish isolates of Heterobasidion annosum sensu stricto in 2‐year‐old Pinus pinaster seedlings. Two types of inocula (woodchips and sawdust) were used to infect the seedlings by two different routes (stem inoculation and soil infestation). The mortality rates of the stem‐inoculated seedlings differed significantly from controls, but those of the seedlings infected via soil infestation did not differ. For both types of inoculation, the lesions were longer, and wilting symptoms were more severe in the seedlings inoculated with H. annosum than in control seedlings. For stem inoculation, biomass allocation did not differ significantly between the infected and control seedlings. However, the percentage of fine roots was lower in seedlings infected via soil infestation than in the control seedlings. To our knowledge, this is the first pathogenicity test with H. annosum isolates and P. pinaster.     

Microbial communities in roots of Pinus sylvestris seedlings with damping‐off symptoms in two forest nurseries as determined by ITS1/2 rDNA sequencing

A methodological molecular procedure, which included extraction and cloning of the ITS1/2 rDNA of root‐associated organisms with subsequent transformation and sequencing of representative clones, was effective for detection, discrimination and determination of the frequency of the main damping‐off pathogens in roots of Pinus sylvestris seedlings growing in different forest‐tree nursery soils and exhibiting different rates of disease progress. Roots exhibiting slower damping‐off progression were colonized by Fusarium oxysporum, Neonectria radicicola (Ascomycota) and Pythium spp. (Oomycota), which comprised 50% of the microbial community. Roots exhibiting faster damping‐off progression were dominated by Thanatephorus cucumeris (Basidiomycota), which comprised 80% of the microbial community. The microbial community was more diverse in roots with slower damping‐off progression (14 species) than in roots with faster disease progression (seven species).     

The contribution of root respiration of<Emphasis Type="Italic">Pinus koraiensis</Emphasis> seedlings to total soil respiration under elevated CO<Subscript>2</Subscript> concentrations

The impacts of elevated atmospheric CO₂ concentrations (500 μmol·mol⁻¹ and 700 μmol·mol⁻¹) on total soil respiration and the contribution of root respiration ofPinus koraiensis seedlings were investigated from May to October in 2003 at the Research Station of Changbai Mountain Forest Ecosystems, Chinese Academy of Sciences, Jilin Province, China. After four growing seasons in top-open chambers exposed to elevated CO₂, the total soil respiration and roots respiration ofPinus koraiensis seedlings were measured by a Li-6400-09 soil CO₂ flux chamber. Three PVC cylinders in each chamber were inserted about 30 cm into the soil instantaneously to terminate the supply of current photosynthates from the tree canopy to roots for separating the root respiration from total soil respiration. Soil respirations both inside and outside of the cylinders were measured on June 16, August 20 and October 8, respectively. The results indicated that: there was a marked diurnal change in air temperature and soil temperature at depth of 5 cm on June 16, the maximum of soil temperature at depth of 5 cm lagged behind that of air temperature, no differences in temperature between treatments were found (P>0.05). The total soil respiration and soil respiration with roots severed showed strong diurnal and seasonal patterns. There was marked difference in total soil respiration and soil respiration with roots severed between treatments (P<0.01); Mean total soil respiration and contribution of root under different treatments were 3.26, 4.78 and 1.47 μmol·m⁻²·s⁻¹, 11.5%, 43.1% and 27.9% on June 16, August 20 and October 8, respectively. Foundation item: This study was supported by the Knowledge Innovation Project of the Chinese Academy of Sciences (KZCX1-SW-01) and the National Natural Science Foundation of China (30070158). Biography: LIU Ying (1976-), female, Ph. D. Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, P. R. China. Responsible editor: Song Funan     

Detection of nitrogen transfer from N<Subscript>2</Subscript>-fixing shade trees to cacao saplings in <Superscript>15</Superscript>N labelled soil: ecological and experimental considerations

Theobroma cacao seedlings were grown alone (TCA) or associated with saplings of N₂-fixing shade trees Gliricidia sepium and Inga edulis in 200 l of ¹⁵N labelled soil within a physical root barrier for studying direct nitrogen transfer between the trees and cacao. Root:shoot partitioning ratio for sapling total N was lower than biomass root:shoot ratio in all species. Sapling total ¹⁵N was partitioned between root and shoot in about the same ratio as total N in cacao and inga but in gliricidia much higher proportion of ¹⁵N than total N was found in roots. Thus, whole plant harvesting should be used in ¹⁵N studies whenever possible. Average percentage of fixed N out of total tree N was 74 and 81% for inga estimated by a yield-independent and yield-dependent method, respectively, and 85% for gliricidia independently of estimation method. Strong isotopic evidence on direct N transfer from trees to cacao was observed in two cases out of ten with both tree species. Direct N transfer was not correlated with mycorrhizal colonisation of either donor or receiver plant roots. Direct N transfer from inga and gliricidia to cacao is conceivable but its prevalence and the transfer pathway via mycorrhizal connections or via reabsorption of N-rich legume root exudates by cacao require further study. Competition in the restricted soil space may also have limited the apparent transfer in this study because the trees accumulated more soil-derived N than cacao in spite of active N₂ fixation.     

Effects of water stress on growth,dry matter allocation and water-use efficiency of a leguminous species, <Emphasis Type="Italic">Sophora davidii</Emphasis>

The adaptation responses to different water conditions and the drought tolerance of Sophora davidii seedlings were assessed in a greenhouse experiment. Two-month-old seedlings were subjected to the following water supplies for 95 days: 100, 80, 60, 40 and 20% of field water capacity. The seedlings at 100% FC had the greatest productivity, height, basal diameter, branch number, leaf number and leaf area. Water supply <80% FC was the threshold of drought-initiated negative effects on seedling growth, yield and physiological processes; these parameters were severely reduced at 20% FC, however, there was no plant death during the experiment. Moreover, water stress decreased leaf relative water content, specific leaf area, leaf area ratio, and water-use efficiency (WUE), whereas it increased the biomass allocation to roots, which resulted in a higher root:stem mass ratio under drought. The S. davidii seedlings tolerated drought by maintaining high leaf relative water content and by reducing branching and leaf expansion. However, low productivity and WUE at 20% FC suggested that seedlings did not produce high biomass under severe drought. Therefore, prior to introducing S. davidii in forestation efforts, a water supply >40% FC is recommended for seedlings to maintain growth and productivity. These results provide insights into limitations and opportunities for establishment of S. davidii in arid regions.     

Tamarack and Black Spruce Growth on a Boreal Fen in Central Alberta 9 Years after Drainage

Tree growth was measured before, and 9 years after draining a boreal fen that supported a 50- to 60-year-old stand of tamarack (Larix laricina (Du Roi) K. Koch) and black spruce (Picea mariana (Mill.) B.S.P.). Treatments consisted of a series of ditches spaced 30, 40 or 50 m apart, and an undrained control. Nine years after drainage, the diameter, height, basal area, and volume growth of tamarack had increased by 2–5 times that on the control site. Black spruce growth on the drained site was 1.6–5 times that on the control. Tamarack average volume growth (1.20 m³ ha⁻¹ year⁻¹) on the drained site was superior to that of black spruce (0.21 m³ ha⁻¹ year⁻¹). In general for both species, there were no significant differences in growth between trees on the different ditch spacings. This result was attributed to the water table being low enough that adequate aeration zones existed across the strips between ditches on all spacings. Regeneration after treatment was greater on the drained than on the control plots, particularly in the disturbed areas near the ditches where new tamarack seedlings reached densities between 9400 and 12,000 stems ha⁻¹. There was no relationship between increased tree growth and tree distance from the ditches for both species, probably because the water table had been lowered sufficiently so that inadequate substrate aeration was no longer a limiting factor.     

The effects of the degree of soil cover with an impervious sheet on the establishment of tree seedlings in an arid environment

Low precipitation and high evaporation rates hinder the establishment of tree seedlings in arid environments. The objective of this study was to assess the effect of covering different fractions (0, 30, 70 and 100%) of the wetted area surrounding seedlings of Acacia saligna (Labill.) H.L. Wendl. with a black polyethylene sheet on the seedlings development and water use. The cover treatments were applied to plots with and without Acacia seedlings. Within the mulched areas at all depths, soil temperatures close to the edges were lower than at the corresponding depth close to the center, but still higher than in the non-mulched plots. In plots with Acacia seedlings, the total soil water losses were similar among treatments. However, the cumulative evaporative losses near the soil surface were lower with larger mulched areas. During early growth stages, roots grew deeper in the 30% mulch treatment and more laterally in the other mulched treatments. The non-mulched treatment produced the smallest root system. Larger canopies developed in the mulched treatments and the gross water use efficiency increased with the increasing fraction of the mulched area. Optimum utilization of stored soil water and seedling development were attained with the 70% mulch treatment.     

Dynamics of non-structural carbohydrate reserves in pruned <Emphasis Type="Italic">Erythrina poeppigiana</Emphasis> and <Emphasis Type="Italic">Gliricidia sepium</Emphasis> trees

In alley cropping systems, fast growing leguminous trees are pruned to reduce competition with crops for light and to provide organic inputs for crop nutrition. Tree regrowth depends on non-structural carbohydrate reserves in the remaining tree parts. In this study, the dynamics of starch and soluble carbohydrates in roots and stems of completely pruned (all shoots removed), partially pruned (one branch retained on the pruned stump) and unpruned Erythrina poeppigiana (Walp.) O.F. Cook and Gliricidia sepium (Jacq.) Kunth ex Walp. trees were studied under humid tropical conditions in Turrialba, Costa Rica. Measurements on starch and soluble carbohydrates in roots and stems were made at 0, 2, 6 and 12 weeks after pruning during both a “rainy” and a “dry” season. In general, the dynamics of non-structural carbohydrates in roots and stems of pruned E. poeppigiana and G. sepium trees were similar. Starch concentration was highest in unpruned trees and higher in roots than in stems of pruned trees. The effect of pruning intensity was first observed in stems, and starch reserves were more depleted in stems than in roots, an effect more evident during the “dry” season. The critical tree regrowth stage for starch mobilisation was that of vigorous sprout development at six or four weeks after pruning particularly in completely pruned trees. At this time, fine root biomass and length and nodule biomass in pruned trees decreased. Survival of fine roots and nodules was greater in partially pruned than in completely pruned trees. Starch accumulation in roots recommenced at 12 weeks after pruning in G. sepium, and later than 12 weeks after pruning in E. poeppigiana roots. This study showed that E. poeppigiana responded better to pruning regimes than G. sepium. Recovery of trees after pruning is better when trees are partially pruned than when completely pruned.     

Response of <Emphasis Type="Italic">Theobroma cacao</Emphasis> and <Emphasis Type="Italic">Inga edulis</Emphasis> seedlings to cross-inoculated populations of arbuscular mycorrhizal fungi

Response of Theobroma cacao L. (cacao) and the shade tree Inga edulis Mart. (inga) seedlings from an organically-grown cacao plantation to inoculation with native arbuscular mycorrhizae forming fungi (AMF) was studied in a cross-inoculation assay under greenhouse conditions. Seedlings of inga and cacao were grown in pots filled with heat-treated soil from the plantation. Control was heat-treated soil without inoculum and roots of cacao and inga from the plantation were applied as AMF inocula. Undisturbed soil blocks were used as a “positive control” of the inoculation potential of untreated soil and roots combined. No AMF structures were observed in the roots of either species in the heat-treated control. All inocula were infective in both hosts and the differences in the total AMF colonization percentage between the hosts were not significant but inga had significantly higher colonization by hyphal coils and arbuscules. Cacao roots but neither inga roots nor soil block inocula stimulated cacao growth. All inocula significantly increased growth of inga, which had higher relative mycorrhizal responsiveness than cacao. Thus, in spite of the strong infectivity of the inocula in both hosts, cacao and inga responded differently to the same AMF populations. The strong conspecific preference of cacao suggests that attention must be paid to the AMF inoculum used for this species. However, the strong response of inga to cacao root inoculum indicates that the two species may share same AMF symbionts, thus enabling positive interactions between them, including formation of common mycelial networks.