Response of mycorrhizal western red cedar to organic phosphorus sources and benomyl

Abstract

In some British Columbia forests, western red cedar (Thuja plicntn Donn ex D. Don) grows well in soils with phosphorus (P) mainly in organic form and shows less response to P fertilization than other conifers. It was hypothesized that cedar or their associate arbuscular mycorrhizae could mineralize organic P. In a year-long greenhouse study, 2-year-old cedar trees in Turface were fed every 9 days with one of 1 1 P treatments (in Long Ashton solution): no P; high and low phytic acid (for all treatments, high is 50 mg P . L-', and low is 10 mg P . L-'); high and low ATP; high and low glycerophosphate; high and low pyrophosphate; high and low orthophosphate. Ten mycorrhizal trees were used per treatment; of these, five trees per treatment were treated with the fungicide benomyl, which significantly reduced colonization in only two treatments. Growth was good with high rates of glycerophosphate, ATP, and pyrophosphate; low rates of these compounds resulted in P deficiencies. The trees grew poorly with phytic acid, which may have been adsorbed to the Turface, and which may have cornplexed Ca, Zn, and Cu from the nutrient solution, inducing deficiencies. The P source influenced the activities of rhizosphere acid and alkaline phosphatase, but had no significant effect on phosphodiesterase or pyrophosphatase activity. Use of the fungicide benomyl caused a significant increase in foliar N, either directly from the fungicide or indirectly from effects on N cycling.Resume : Dans certaines for&ts de la Colombie Britannique, le thuya gCant (Thujn plicata Donn ex D. Don) pousse bien dans des sols oh le phosphore (P) prevaut sous forme organique, et rCagit moins bien B la fertilisation P que les autres coniEres. Les auteurs ont formu16 l'hypothkse que le thuya ou ses rnycorhizes arbusculaires (AM) associCes pourraient mineraliser le P organique. Les auteurs ont conduit une expCrience en serre qui a durC une annCe en appliquant les traitements suivants : des thuyas 2gCs de 2 ans ont Ct C cultivCs dans du Turface et nourris tous les 9 jours avec 1 des 11 traitenlents P (en solution de Long Ashton) : sans P; acide phytique ClevC et faible (pour tous les traitenlents, haut signifie 50 mg PIL; faible signifie 10 mg PIL); ATP ClevC et faible; glycerophosphate ClevC et faible; pyrophosphate ClevC et faible; orthophosphate ClevC et faible. Pour chaque traitement elles ont utilisC 10 plants dont 5 plants pour chaque traitement ont requ du fongicide bCnomyl, qui n'a rCduit significativement la mycorhization que dans deux traitements. La croissance a Ct C bonne avec des apports ClevCs en glycCrophosphate, ATP et pyrophosphate; les apports faibles en ces composCs ont entrain6 des dCficiences en P. La croissance a Ct C mediocre en presence d'acide phytique, lequel aurait pu Ctre adsorb6 par le Turface, et avoir complex6 le Ca, le Zn et le Cu de la solution nutritive, conduisant ainsi aux dtficiences. La source de P a influencC les activitCs des phosphatases acides et alcalines de la rhizosphkre, mais est demeurCe sans effet sur les activitC...

How does light and phosphorus fertilisation affect the growth and ectomycorrhizal community of two contrasting dipterocarp species?

“…Table 4 Foliar and root nutrient concentrations of (a) Hopea nervosa and (b) Shorea leprosula seedlings following growth for 10 months under moderate and high-light conditions and four levels of P fertilisation (all values are mean ± SE) Light P Leaves Roots N (mg g À1 ) P (mg g À1 ) N (mg g À1 ) P (mg g À1 ) The total % EcM colonisation was not reduced following the addition of P in this study, as had previously been observed in many studies with both arbuscular mycorrhizal (Cade-Menun and Berch 1997;Ingleby et al 2001) and EcM (Beckjord et al 1985;Bougher et al 1990;Jones et al 1990;Baum and Makeschin 2000) tree species. Given the number of previous studies that had observed a reduction in mycorrhizal colonisation following P fertilisation, our results emphasise the obligate nature of the EcM symbiosis for dipterocarp seedlings.…”

Morphological responses of plant roots to heterogeneity of soil resources

“…Several authors studied the influence of benomyl on other soil microorganisms and some metabolic processes. In addition to the suppression of nonmycorrhizal fungi (Carey et al, 1992;West et al, 1993), interference with the nitrogen cycle was found (Chen et al, 1995;Cademenun & Berch, 1997). Neither nor Merryweather and Fitter (1996) found any substantial increase in soil phosphate concentration as a consequence of benomyl application.…”

Contribution of arbuscular mycorrhizal fungi to utilization of organic sources of phosphorus by red clover in a calcareous soil

“…This enhancement effect could be due to both an increase in surface area and phosphatase activity of the extraradical hyphae (Li et al, 1997a;Tarafdar and Marschner, 1994). It is well established that arbuscular mycorrhiza can increase the P uptake of plants through the extraradical hyphae under certain conditions, but most research has dealt with inorganic P and few investigations have considered the utilization of organic P compounds by AM plants (Jayachandran et al, 1992;Joner and Jakobsen, 1994;Cade-Menun and Berch, 1997).…”