T. S. Grove

The ability of 16 ectomycorrhizal fungi to increase growth and phosphorus uptake of Eucalyptus globulus Labill. and E. diversicolor F. Muell.

The effectiveness of 16 fungal isolates in forming ectomycorrhizas and increasing the growth and phosphorus uptake of Eucalyptus globulus Labill. and E. diversicolor F. Muell. seedlings was examined in the glasshouse. Seedlings were grown in yellow sand at 2 phosphorus levels (4 and 12 mg P kg-1 sand). At the time of harvest (100 days), the non-inoculated seedlings and seedlings inoculated with Paxillus muelleri (Berk.) Sacc. and Cortinarius globuliformis Bougher had a low level of contamination from an unknown mycorrhizal fungi. Seedlings inoculated with Thaxterogaster sp. nov. and Hysterangium inflatum Rodway had developed mycorrhizas of the superficial type whereas Hydnangium carneum Wallr. in Dietr., Hymenogaster viscidus Massee & Rodway, Hymenogaster zeylanicus Petch, Setchelliogaster sp. nov., Laccaria laccata (Scop. ex. Fr.) Berk., Scleroderma verrucosum (Vaillant) Pers., Amanita xanthocephala (Berk.) Reid & Hilton, Descolea maculata Bougher and Malajczuk and Pisolithus tinctorius (Pers.) Coker & Couch formed typical pyramidal ectomycorrhizas. The dry weight of non-inoculated and inoculated E. globulus seedlings at 12 mg P kg-1 sand did not differ, whereas several isolates caused growth depression of E. diversicolor. By contrast, at 4 mg P kg-1 sand growth increases ranged from 0–13 times above that of non-inoculated seedlings. P. tinctorius produced the largest growth increase on both eucalypt species. In general, isolates which developed more extensive mycorrhizas on roots produced the largest growth responses to inoculation. Isolates which increased plant growth also increased phosphorus uptake by the plant. Seedlings inoculated with L. laccata and S. verrucosum retained more phosphorus in their roots than plants inoculated with the other fungal isolates.

Nitrogen release from eucalypt leaves and legume residues as influenced by their biochemical quality and degree of contact with soil

Large areas of short-rotation eucalypt plantations are being established in south-western Australia on land previously used for agriculture. Options for maintaining soil N supply include retention of harvest residues and legume inter-cropping. We evaluated the effects of adding the residues of five legume species and Eucalyptus globulusleaves on inorganic N dynamics in two soils (a Rhodic Ferralsol or red earth and a Haplic Podzol or grey sand) using two modes of residue application in a laboratory incubation experiment (519 days). The time course of net N immobilisation and mineralisation in both soils was strongly influenced by the type and mode of application. Eucalypt leaves caused strong N immobilisation (−7 mg N g−1 residue-C) over the entire 519-day incubation, whereas for the legume species, N that was eventually immobilised at the start of the incubation, remineralised later to different degrees. Amongst the legumes, largest amounts of N were released from lupin residues (18 mg N g−1 residue-C) and lowest amounts from field pea (2 mg N g−1 residue-C). However, initial residue quality parameters were not significantly (P > 0.05) correlated with N release from the residues. Grinding and incorporating of the residues caused a much greater immobilisation of N than when residues were cut and surface applied. When ground residues were incorporated, immobilisation of N was more severe and endured for longer in the finer textured red earth than in the coarse textured grey sand. Where residues were surface applied, N dynamics were similar for both soil types. The results of this study suggest that legumes used as a mulch in eucalypt plantations are a readily available source of N for trees, and that the benefits from retention of harvest residues are more likely in maintaining soil N fertility on the long-term.

Change in soil carbon after land clearing or afforestation in highly weathered lateritic and sandy soils of south-western Australia

Soil organic carbon (SOC) is a significant component of the worlds terrestrial carbon stocks, and changes in land-use have potential to change pools of soil C. Land-use change is occurring over large areas of the world, so soil has potential to be a large source or sink for atmospheric C. Changes in amounts of soil C (0–1 m) were examined after clearing of native vegetation for pasture (20–71 years prior to study), and after establishment of Eucalyptus globulusplantations on ex-pasture sites (7–10 years prior to study). A suite of 10 sites in south western Australia were used in a three-way comparison between native vegetation, pasture and plantation. Soil types across the 10 sites included Acrisols, Arenosols, and a Ferrosol. Soil C was measured in the fine earth ( <2 mm), the 2–5 mm soil fraction, in charcoal and roots retained on a 5 mm screen, and in surface litter. Differences in soil bulk density between land-uses were accounted for by calculating depths for equivalent weights of soil. Despite large increases in soil fertility with conversion to pasture, amounts of soil C changed little. The amount of C in the 5–20 cm increment was significantly greater under pasture than native vegetation (mean of 8.4 Mg ha −1 , <5 mm), but in surface soil (0–5 cm) and <20 cm, there were no significant differences in soil C content between land-uses. Less C in soil at 5–20 cm under native vegetation was offset by significantly more C in coarse roots (average of 5 Mg ha −1 higher to 1 m depth), surface soil (2–5 mm fraction, 2 Mg ha −1 ), and in standing pools of surface litter (9.8 Mg ha −1 ). Amounts of soil C under plantation were not significantly different from pasture 7–10 years after plantation establishment. However, plantation soils had an average of 3.1 Mg ha −1 more C in coarse roots than pasture, and significant quantities of C in surface litter (average of 7.9 Mg ha −1 ). Overall, soil C content in the sites of this study was relatively stable and the effect of land-use change was limited.

Changes in soil N status and N supply rates in agricultural land afforested with eucalypts in south-western Australia

In south-western Australia, plantations of Eucalyptus globulus are being established on land that has previously been used for conventional agriculture. Sustaining the productivity of these tree plantations in second and subsequent rotations will depend partly on maintenance of soil fertility, especially soil nitrogen (N) supply rates. We compared soil N status and supply rates between adjacent pasture and 6–11 year old first-rotation eucalypt plantations at 31 paired sites in south-western Australia. Total soil N varied widely among sites (0.07–0.68% in the fraction <2 mm of the 0–10 cm soil layer), but concentrations averaged over all sites did not differ between land-use types. However, measurements of the indices of mineralization (mineral N produced during incubation of intact cores), potentially available N (from short-term anaerobic incubation) and model-predicted mineralization rates during 28-day aerobic incubations were generally lower in afforested soils than in pasture soils. This finding was supported by in situ field estimates of N mineralization over a full year at two contrasting paired pasture-plantation sites. At each site there was a marked reduction (2–3-fold) in net annual mineral N flux rates in soils under eucalypt plantations. Reduced N mineralization associated with tree plantations was due to both changes in soil organic matter quality and the generally lower soil moisture content under trees in comparison with pasture. These results suggest that N supply rates of pasture soils are likely to decline when the land is planted to successive crops of eucalypts. Eucalypt plantation managers will need to take account of this and implement management strategies to maintain adequate N nutrition to sustain tree growth in future rotations.

Nutrient accumulation by trees and understorey shrubs in an age-series of Eucalyptus diversicolor F. Muell. stands

Abstract Nutrient composition of aboveground components of overstorey trees and understorey shrubs were measured in four even-aged stands of E. diversicolor (4-, 8-, 11- and 36-years-old) and in a mature stand. The even-aged stands had regenerated from seed after cleafelling and slash-burning of native forest, and understories in the younger stands were the same age as trees. However in the 36-year-old and mature stands understories had regenerated from seed after prescribed burning and were 9 and 14 years of age, respectively. Trymalium spathulatum and the legume Bossiaea laidlawiana were the dominant understorey species in all stands. Aboveground nutrient pools varied less than biomass with stand age. This is because much of the increase in biomass as stands develop is due to production of heartwood, in which concentrations of nutrients are low. Understories contained a large proportion of the nutrients in all stands. In the 8- and 11-year-old stands about 46% of the aboveground biomass was understorey and this contained 49–56% of the N and S. In the 36-year-old stand, understorey contained 35% of the N and S although it was only 10% of the aboveground biomass. There was relatively more of the nutrient elements other than N and S in E. diversicolor than in understorey species in the 4-, 8-, and 11-year-old stands. In all five stands B. laidlawiana was an important component of the understorey, amounting to 51–93% of the biomass and containing 72–97% of the N. The leaves of B. laidlawiana contained about 40% of the P, and 31–36% of the N, S, Mg, Zn and Mn but comprised only 6–8% of the aboveground weight. Average rates of nutrient accumulation in aboveground biomass decreased with increasing stand age. This decrease was generally balanced by an increase in the amount of nutrients in litterfall so that, with the exception of mobile nutrients, the annual uptake of nutrients (accumulation plus litterfall) by vegetation was similar for each of the even-aged stands. Understorey accounted for a large proportion of the nutrients accumulating in aboveground biomass, particularly in the 36-year-old stand, where N, K, S, Zn and Cu accumulated more rapidly in understorey shrubs than in trees. The study suggests that the understorey plays a significant role in the nutrition of E. diversicolor stands.

Biomass production by trees and understorey shrubs in an age-series of Eucalyptus diversicolor F. Muell. stands

Abstract Aboveground biomass of trees and understorey species, and the biomass of fine roots and understorey roots, were estimated in E. diversicolor stands aged 4, 8, 11 and 36 years, and in a mature stand with trees probably several hundred years old. In the three youngest stands (4, 8 and 11 years) understorey age was the same as overstorey; understorey age was 9 years in the 36-years-old forest and 14 years in the mature stand. Sites were chosen in pure stands of E. diversicolor with understories dominated by Trymalium spathulatum and the legume Bossiaea laidlawiana. Highest stem densities were found in the youngest stands and there was a large variation in stem sizes for the major species in older stands. In stands aged 4–36 years, total aboveground biomass ranged from 31 t/ha for the 4-year-old stand to 249 t/ha for the 36-year-old stand. Understorey represented approximately 50% of aboveground biomass in the 8- and 11-year-old stands, and 10% of biomass in the 4- and 36-year-old stands. B. laidlawiana made up between 50 and 94% of understorey aboveground biomass in all stands, with leaves representing 6–8% of plant top weight. Biomass of large roots of understorey species was low (0.3–5.0 t/ha) compared with aboveground understorey biomass. It was estimated that biomass of fine roots of all species was about 3 t/ha in the older stands in late summer. Although there were large differences in biomass between stands, average rates of accumulation of organic matter were similar for the 4–36-year-old stands. Comparison of average rates of biomass accumulation for trees and understorey shrubs indicated that a large proportion of annual aboveground organic matter production in E. diversicolor forest was associated with the understorey. Periodic fuel reduction burning in E. diversicolor forest results in regular regeneration of the understorey and may explain the high rates of understorey biomass accumulation compared with other eucalypt forests in which fire is excluded.

Diagnosis of nitrogen deficiency and toxicity of Eucalyptus globulus seedlings by foliar analysis

The relationship between shoot growth and foliar nitrogen (N) in E. globulus seedlings was studied in the glasshouse to determine standard values for N deficiency and toxicity diagnosis. Seedlings were grown for 9 weeks in yellow sand, at 10 rates of N, applied as ammonium sulphate, calcium nitrate or ammonium nitrate. Shoot dry weight (DW) increased linearly with N rate for all forms of N in the deficiency range. Seedlings continued to respond to higher rates of ammonium and ammonium nitrate than to nitrate. Maximum shoot DW for nitrate fed plants and ammonium nitrate fed plants were 51% and 84% respectively of ammonium fed plants. Total N concentration in the youngest fully expanded leaf (YFEL) ranged from 1.0% to 3.3% in deficient and adequate plants. The critical N concentration for deficiency diagnosis (corresponding to 90% maximum yield) in the YFEL, determined from these growth response curves averaged over all N forms, was 2.6% N. For ammonium nitrate fed plants, total N concentration in the YFEL for the severely deficient, deficient, adequate, and toxic ranges were <1.4%, 1.4–2.5%, 2.6–3.5%, > 4.3%. High total N concentrations were associated with growth depression and toxicity symptoms, which differed with N form. For nitrate fed plants, a total N concentration above 3.3% in the YFEL was associated with severe growth depression, and leaf tip necrosis. The adequate concentration range for ammonium nitrate was similar to values found on a field trial with 7 month old E. globulus trees grown on an exforest site.

Improving the colonization capacity and effectiveness of ectomycorrhizal fungal cultures by association with a host plant and re-isolation

The ability of an ectomycorrhizal fungus to colonize plant roots (colonization capacity) and to increase plant growth at a deficient supply of P (effectiveness) declines after repeated subculture on agar media. We attempted to revitalize selected isolates of ectomycorrhizal fungi by inoculating them onto a compatible host (Eucalyptus globulus) and reisolating them from ectomycorrhizas and basidiomes. The growth on agar of the reisolated fungal cultures and the original fungal cultures was measured over 14 d. Seedlings of E. globulus were also inoculated with either the original fungal isolates or their reisolates and were grown in pots containing a P-deficient sand, in a temperature-controlled glasshouse. Seedlings were harvested 49 and 93 d after planting and were assessed for mycorrhizal colonization, dry weights and P concentrations. The reisolates generally grew at a faster rate on agar, and colonized plant roots more quickly, than the original isolates. Plants inoculated with the reisolates also had increased dry weights by day 93, which could be attributed to increased P uptake by the plant. We concluded that reisolating ectomycorrhizal fungi from mycorrhizas and basidiomes can increase the colonization capacity and effectiveness of isolates which have been grown on agar media for extended periods. This result, and the high cost of maintaining cultures emphasizes the need to examine alternative methods of storage of fungal isolates.

Growth responses of trees and understorey to applied nitrogen and phosphorus in karri (Eucalyptus diversicolor) forest

Abstract Two experiments were conducted to establish whether the growth of karri ( Eucalyptus diversicolor F. Muell.) and its associated understorey species were limited by the supply of nitrogen and phosphorus, and to determine the effects of adding these nutrients on species composition. In the first experiment, N and P treatments were applied to an 18-month-oldstand of karri regrowth and the above-ground biomass of tree and understorey species was estimated annually over a 4-year period. In a second experiment the biomass of understorey species was measured over the same period following application of P treatments in an old mixed eucalypt stand. In the regrowth stand, adding N increased karri growth by 12–26%. Addition of P increased mean tree weight but decreased tree density (number m −2 ) and thus did not increase karri biomass per unit area. The effect of P was greater where N was also added. Five years after treatments were applied, mean tree weights on plots with the highest levels of added N (200 kg N ha −1 ) and P (200 kg P ha −1 ) were about double those where N and P had not been applied. The high density of karri in the regrowth stand markedly suppressed understorey growth. Although there were no significant effects of treatments on total understorey biomass, the application of N depressed growth of the major legume, Bossiaea laidlawiana Tovey and Morris, and stimulated the growth of non-legume species. In the second experiment, adding P increased the growth of B. laidlawiana , particularly on a per-plant basis as the addition of P increased the rate of mortality of suppressed plants. In contrast to legume biomass, the biomass of non-legumes decreased with increasing P application. The results show that the supply of N and P can be limiting to growth of karri and understorey species on the soils of these forests. Increased supplies of N and P can accelerate the establishment of dominance and increase mortality and hence can stimulate the growth of larger trees. The response of understorey species indicate that N and P levels in soils can markedly influence the composition of the understorey stratum.

The survival and development of inoculant ectomycorrhizal fungi on roots of outplanted Eucalyptus globulus Labill.

The survival and development of two inoculant ectomycorrhizal fungi (Hebeloma westraliense Bough. Tom. and Mal. and Setchelliogaster sp. nov.) on roots of outplanted Eucalyptus globulus Labill. was examined at two expasture field sites in the south-west of Western Australia. Site 1 was a gravelly yellow duplex soil, and Site 2 was a yellow sandy earth. Plants were grown in steamed or unsteamed soil, in root bags designed as field containers for young growing trees. Three, 6 and 12 months after outplanting, plants were removed from these bags and assessed for dry weights of shoots and ectomycorrhizal colonization of roots.The inoculant ectomycorrhizal fungi (identified on the basis of the colour and morphology of their mycorrhizas) survived on roots of E. globulus for at least 12 months after outplanting at both field sites. At Site 1, however, colonization of new fine roots by the inoculant fungi was low (less than 20% of fine root length). Inoculation had no effect on the growth of E. globulus at this site. In contrast, at Site 2 the inoculant ectomycorrhizal fungi colonized up to 30–50% of new fine root length during the first 6 months after outplanting. There was a corresponding growth response to ectomycorrhizal inoculation at this site, with a close relationship (r2=0.82**) between plant growth at 12 months and root colonization at 3 months. Plant growth at 12 months was related less closely with root colonization at 6 or 12 months. Root colonization by ‘resident’ ectomycorrhizal fungi increased with time at both field sites. At Site 2, this increase appeared to be at the expense of colonization by the inoculant fungi, which was reduced to less than 10% of fine root length at 12 months. Steaming the soil had little effect on colonization by the inoculant ectomycorrhizal fungi at either field site, but decreased colonization by the resident ectomycorrhizal fungi.