Phosphorus addition increased carbon partitioning to autotrophic respiration but not to biomass production in an experiment with Zea mays

Plant carbon (C) partitioning—the relative use of photosynthates for biomass production, respiration, and other plant functions—is a key but poorly understood ecosystem process. In an experiment with Zea mays, with or without arbuscular mycorrhizal fungi (AMF), we investigated the effect of phosphorus (P) fertilization and AMF on plant C partitioning. Based on earlier studies, we expected C partitioning to biomass production (i.e., biomass production efficiency; BPE) to increase with increasing P addition due to reduced C partitioning to AMF. However, although plant growth was clearly stimulated by P addition, BPE did not increase. Instead, C partitioning to autotrophic respiration increased. These results contrasted with our expectations and with a previous experiment in the same set-up where P addition increased BPE while no effect on autotropic respiration was found. The comparison of both experiments suggests a key role for AMF in explaining these contrasts. Whereas in the previous experiment substantial C partitioning to AMF reduced BPE under low P, in the current experiment, C partitioning to AMF was too low to directly influence BPE. Our results illustrate the complex influence of nutrient availability and mycorrhizal symbiosis on plant C partitioning.     

Ectomycorrhiza and nitrogen effects on root IAA: results contrary to current theory

Summary Indole-3-acetic acid (IAA) concentrations of mycorrhizal and non-mycorrhizal Scots pine roots under moderate and high-nitrogen nutrition were assayed using mass spectrometry with an internal standard. Contrary to current theory, IAA was lower in mycorrhizal roots than in the controls, and higher during highnitrogen nutrition.     

Use of strontium isotopes and foliar K content to estimate weathering of biotite induced by pine seedlings colonised by ectomycorrhizal fungi from two different soils

Pinus sylvestris seedlings, colonised by ectomycorrhizal (EM) fungi from either of two different soils (untreated forest soil and a limed soil from a clear cut area), were grown with or without biotite as a source of K. The biotite was naturally enriched in ⁸⁷Sr and the ratio of ⁸⁷Sr/ ⁸⁶Sr in the plant biomass was estimated and used as a marker for biotite weathering and compared to estimates of weathering based on foliar content of K. Different nutrient regimes were used to expose the seedlings to deficiencies of K with and without an application of nitrogen (NH₄NO₃) in excess of seedling demand. The seedlings were grown for 220 days and the elemental composition of the shoots were analysed at harvest. The EM colonisation was followed by analysing the concentration of ergosterol in the roots and the soils. Bacterial activity of the soil was estimated by the thymidine incorporation technique. The concentration of organic acids in the soil solution was measured in the soil in which seedlings colonised by EM fungi from the untreated forest soil were grown. It was found that seedlings colonised by EM fungi from untreated forest soil had taken up more K in treatments with biotite addition compared to seedlings colonised by EM fungi from the limed forest soil (p<0.05). Seedlings from untreated forest soil had larger shoots and contained more K when grown with biotite compared to KCl as K source, indicating that biotite had a stimulatory effect on the growth of these seedlings which was not related to K uptake. Seedlings from the limed soil, on the other hand, had similar foliar K content when grown with either biotite or KCl as K source. The larger uptake of K in seedlings from untreated forest soil was not an effect of a more developed EM colonisation of the roots since seedlings from the limed soil had a higher ergosterol concentration both in the soil and in the roots. Nutrient regimes had no significant influence on the total uptake of K but the ⁸⁷Sr/ ⁸⁶Sr isotope ratio in the plant biomass indicated that seedlings grown with excess nitrogen supply had taken up proportionally less Sr from the biotite (1.8% of total Sr content) compared to seedlings grown with a moderate nitrogen supply (5.0%). Furthermore, seedlings grown with excess nitrogen supply had a reduced fungal colonisation of roots and soil and bacterial activity was lower in these soils. The ⁸⁷Sr/ ⁸⁶Sr ratio in the plant biomass was positively correlated with fungal colonisation of the roots (r ²=0.98), which may indicate that the fungus was involved in releasing Sr from the biotite. Uptake of K from biotite was not related to the amount of organic acids in the soil solution. Oxalic acid was positively related to the amount of ergosterol in the root, suggesting that oxalic acid in the soil solution originates from the EM symbionts. The accuracy of the estimations of biotite weathering based on K uptake by the seedlings in comparison with the ⁸⁷Sr/⁸⁶Sr isotope ratio measured in the shoots is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ectomycorrhizal mycelial species composition in apatite amended and non-amended mesh bags buried in a phosphorus-poor spruce forest

We studied the effect of apatite amendment on ectomycorrhizal (EM) mycelial biomass production and species composition in a phosphorus-poor spruce forest using sand-filled mesh bags. Control and apatite-amended bags were buried in pairs in the lower part of the organic horizon for one growth season. DNA extraction, PCR of the ITS region, cloning and random sequencing were used to examine the fungal species composition in each bag. Sequences were identified by comparison with the UNITE database and GenBank. Our study confirmed previous results that the major fungal ingrowth in mesh bags was of EM origin. On average 13 species were detected in each bag. Tylospora fibrillosa, Amphinema sp., Tomentellopsis submollis, and Xerocomus badius made up almost 80 % of the EM sequences. High biomass was related to increased dominance of specific species. There were no statistically significant differences in biomass production estimated from PLFA 18:2ω6, 9, or between fungal communities of apatite-amended and control bags estimated from DNA after one growth season. The potential of the mesh bag method in studies of functional diversity of EM mycelia in the field is discussed.     

Chemotaxonomy of the Oleaceae: iridoids as taxonomic markers

The distribution and biosynthesis of iridoid glucosides in the Oleaceae is reviewed and five distinct biosynthetic pathways to iridoids have been identified in the family, deoxyloganic acid apparently being a common intermediate. Likewise, the distributions of caffeoyl phenylethanoid glycosides (CPGs), i.e. verbascoside and its analogues, as well as cornoside are listed. Iridoid glucoside data exist for 17 genera of Oleaceae and the occurrence of iridoids from the different biosynthetic pathways correlate extremely well with the phylogenetic classification inferred from recent chloroplast DNA sequence data. Thus the tribe Fontanesieae (Fontanesia) contains "normal" secoiridoids, Forsythieae (Abeliophyllum, Forsythia) contains cornoside and/or iridoids from the forsythide pathway, Myxopyreae (Myxopyrum, Nyctanthes) have iridoids from the myxopyroside pathway, and finally, the two tribes Jasmineae and Oleeae (the remaining genera) both contain iridoids from the oleoside pathway. Within Jasmineae, one group of Jasminum sp. is characterized by the presence of jasminin or similar compounds, while another group of Jasminum species and Menodora display derivatives of 10-hydroxyoleoside, compounds not present in the other group. CPGs are reported from about half of the species investigated. With regard to taxonomy at the order level, the chemical data might support a position within or close to Lamiales due to the common presence of CPGs, the iridoids being of less significance since they are of a type that are barely found elsewhere.     

Phylogeny and classification of Oleaceae based on rps16 and trnL-F sequence data

Phylogenetic relationships among 76 species of Oleaceae, representing all 25 recognized genera of the family, were assessed by a cladistic analysis of DNA sequences from two noncoding chloroplast loci, the rps16 intron and the trnL-F region. Consensus trees from separate and combined analyses are congruent and agree well with nonmolecular data (chromosome numbers, fruit and wood anatomy, leaf glycosides, and iridoids). The two debated genera Dimetra and Nyctanthes, previously suggested to belong to Verbenaceae (sensu lato) or Nyctanthaceae, are shown to belong to Oleaceae, sister to the hitherto genus incertae sedis Myxopyrum. This clade is also supported by anatomical and chemical data. The subfamily Jasminoideae is paraphyletic, and a new classification is presented. The subfamily level is abandoned, and the former Jasminoideae is split into four tribes: Myxopyreae (Myxopyrum, Nyctanthes, and Dimetra), Fontanesieae (Fontanesia), Forsythieae (Abeliophyllum and Forsythia), and Jasmineae (Jasminum and Menodora). The tribe Oleeae (previous subfamily Oleoideae) is clearly monophyletic, comprising the subtribes Ligustrinae (Syringa and Ligustrum), Schreberinae status novus (Schrebera and Comoranthus), Fraxininae status novus (Fraxinus), and Oleinae (12 drupaceous genera). An rps16 sequence obtained from Hesperelaea, known only from the type specimen collected in 1875, confirmed the placement of this extinct taxon in the subtribe Oleinae.     

Reproductive tactics of the ringed plover Charadrius hiaticula

Reproductive tactics of ringed plovers Charadrius hiaticula were studied at three localities in SW Sweden during five seasons. The usual clutch size is four, but removal experiments showed that females can produce five eggs in succession, with similar intervals between all eggs. High predation made mean breeding success per clutch low, 6.3% of eggs resulting in fledged young. Replacement clutches were common, and many pairs laid again after rearing their first brood to fledging. Egg laying spanned three months, much longer than for other waders in this region. Between years, reproductive success varied unpredictably with time of the season, but averaged over several years, the expected success was low and similar for the different parts of the breeding season. Chicks from late clutches had similar survival and recruitment as others. Because of the long breeding season and high rate of nest failure a female may produce up to five clutches of four eggs per season, containing in total about 3.7 times her own mass. Yearly local survival of adult females and males was estimated to 84.6 and 88.6%, respectively. Ability to produce many clutches with similar expected success throughout the season favours a long reproductive period, sometimes leading to double-brooding. Possible life-history trade-offs are discussed.