Light alters the impacts of nitrogen and foliar pathogens on the performance of early successional tree seedlings.
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ABSTRACT:
SUBMITTER: Brown A
PROVIDER: S-EPMC8272923 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Differences in photosynthetic capacity among tree species and tree functional types are currently assumed to be largely driven by variation in leaf nutrient content, particularly nitrogen (N). However, recent studies indicate that leaf N content is often a poor predictor of variation in photosynthetic capacity in tropical trees. In this study, we explored the relative importance of area-based total leaf N content (Ntot) and within-leaf N allocation to photosynthetic capacity versus light-harvesting in controlling the variation in photosynthetic capacity (i.e. V cmax, J max) among mature trees of 12 species belonging to either early (ES) or late successional (LS) groups growing in a tropical montane rainforest in Rwanda, Central Africa. Photosynthetic capacity at a common leaf temperature of 25˚C (i.e. maximum rates of Rubisco carboxylation, V cmax25 and of electron transport, J max25) was higher in ES than in LS species (+ 58% and 68% for V cmax25 and J max25, respectively). While Ntot did not significantly differ between successional groups, the photosynthetic dependency on Ntot was markedly different. In ES species, V cmax25 was strongly and positively related to Ntot but this was not the case in LS species. However, there was no significant trade-off between relative leaf N investments in compounds maximizing photosynthetic capacity versus compounds maximizing light harvesting. Both leaf dark respiration at 25˚C (+ 33%) and, more surprisingly, apparent photosynthetic quantum yield (+ 35%) was higher in ES than in LS species. Moreover, Rd25 was positively related to Ntot for both ES and LS species. Our results imply that efforts to quantify carbon fluxes of tropical montane rainforests would be improved if they considered contrasting within-leaf N allocation and photosynthetic Ntot dependencies between species with different successional strategies.
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Project description:Species of eucalypts are commonly cultivated for solid wood and pulp products. The expansion of commercially managed eucalypt plantations has chiefly been driven by their rapid growth and suitability for propagation across a very wide variety of sites and climatic conditions. Infection of foliar fungal pathogens of eucalypts is resulting in increasingly negative impacts on commercial forest industries globally. To assist in evaluating this threat, the present study provides a global perspective on foliar pathogens of eucalypts. We treat 110 different genera including species associated with foliar disease symptoms of these hosts. The vast majority of these fungi have been grown in axenic culture, and subjected to DNA sequence analysis, resolving their phylogeny. During the course of this study several new genera and species were encountered, and these are described. New genera include: Lembosiniella (L. eucalyptorum on E. dunnii, Australia), Neosonderhenia (N. eucalypti on E. costata, Australia), Neothyriopsis (N. sphaerospora on E. camaldulensis, South Africa), Neotrichosphaeria (N. eucalypticola on E. deglupta, Australia), Nothotrimmatostroma (N. bifarium on E. dalrympleana, Australia), Nowamyces (incl. Nowamycetaceae fam. nov., N. globulus on E. globulus, Australia), and Walkaminomyces (W. medusae on E. alba, Australia). New species include (all from Australia): Disculoides fraxinoides on E. fraxinoides, Elsinoe piperitae on E. piperita, Fusculina regnans on E. regnans, Marthamyces johnstonii on E. dunnii, Neofusicoccum corticosae on E. corticosa, Neotrimmatostroma dalrympleanae on E. dalrympleana, Nowamyces piperitae on E. piperita, Phaeothyriolum dunnii on E. dunnii, Pseudophloeospora eucalyptigena on E. obliqua, Pseudophloeospora jollyi on Eucalyptus sp., Quambalaria tasmaniae on Eucalyptus sp., Q. rugosae on E. rugosa, Sonderhenia radiata on E. radiata, Teratosphaeria pseudonubilosa on E. globulus and Thyrinula dunnii on E. dunnii. A new name is also proposed for Heteroconium eucalypti as Thyrinula uruguayensis on E. dunnii, Uruguay. Although many of these genera and species are commonly associated with disease problems, several appear to be opportunists developing on stressed or dying tissues. For the majority of these fungi, pathogenicity remains to be determined. This represents an important goal for forest pathologists and biologists in the future. Consequently, this study will promote renewed interest in foliar pathogens of eucalypts, leading to investigations that will provide an improved understanding of the biology of these fungi.
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Project description:Seedlings of co-occurring species vary in their response to resource availability and this has implications for the conservation and management of forests. Differential shade-tolerance is thought to influence seedling performance in mixed Nothofagus betuloides-Nothofagus pumilio forests of Patagonia. However, these species also vary in their soil nutrient requirements. To determine the effects of light and soil nutrient resources on small seedlings we examined responses to an experimental reduction in canopy tree root competition through root trenching and restricting soil nutrient depletion through the addition of fertilizer. To understand the effect of light these treatments were undertaken in small canopy gaps and nearby beneath undisturbed canopy with lower light levels. Seedling diameter growth was greater for N. pumilio and height growth was greater for N. betuloides. Overall, diameter and height growth were greater in canopy gaps than beneath undisturbed canopy. Such growths were also greater with fertilizer and root trenching treatments, even beneath undisturbed canopy. Seedling survival was lower under such treatments, potentially reflecting thinning facilitated by resource induced growth. Finally, above-ground biomass did not vary among species although the less shade tolerant N. pumilio had higher below-ground biomass and root to shoot biomass ratio than the more shade tolerant N. betuloides. Above- and below-ground biomass were higher in canopy gaps so that the root to shoot biomass ratio was similar to that beneath undisturbed canopy. Above-ground biomass was also higher with fertilizer and root trenching treatments and that lowered the root to shoot biomass ratio. Restricting soil nutrient depletion allowed seedlings of both species to focus their responses above-ground. Our results support a view that soil nutrient resources, as well as the more commonly studied light resources, are important to seedlings of Nothofagus species occurring on infertile soils.
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