Drought is a major stress impacting forest ecosystems worldwide. We utilized quantitative trait loci (QTL) analysis to study the genetic basis of variation in (a) drought resistance and recovery and (b) candidate traits that may be associated with this variation in the forest tree Eucalyptus globulus. QTL analysis was performed using a large outcrossed F2 mapping population from which 300 trees were phenotyped based on the mean performance of their open‐pollinated F3 progeny. Progenies were grown in a glasshouse in a randomized complete block design. A subset of seedlings was subjected to a drought treatment after which they were rewatered and scored for damage and growth postdrought. Nondroughted seedlings were assessed for growth traits as well as lignotuber size and resprouting following severe damage to the main stem. QTL were detected for most traits. Importantly, independent QTL were detected for (a) drought damage and plant size, (b) drought damage and growth recovery, and (c) lignotuber size and resprouting capacity. Such independence argues that trade‐offs are unlikely to be a major limitation to the response to selection and at the early life history stage studied; there are opportunities to improve resilience to drought without adverse effects on productivity.
Understanding the effects of logging and fire on forest soil communities is integral to our knowledge of forest ecology and effective resource management. The resulting changes in soil biota have substantial impacts on forest succession and associated ecosystem processes. We quantified bacterial and fungal abundance, diversity and community composition across a logging and burn severity gradient, approximately one month after fire, in temperate wet eucalypt forests in Tasmania, Australia. Using amplicon sequencing and real‐time quantitative PCR of the bacterial 16S rRNA gene and fungal ITS1 region, we demonstrate that (i) burn severity is a strong driver of soil microbial community composition, (ii) logging and high severity burning substantially reduce the biomass and diversity of soil bacteria and fungi, and (iii) the impacts of logging and burning on soil microbial communities are largely restricted to the top 10 cm of soil, with weak impacts on the subsoil. The impacts of disturbance on microbial community composition are greater than the effects of site‐to‐site edaphic differences. Fire also drives more divergence in community composition than logging alone. Key microbial taxa driving differences in severely burnt soils include bacterial genera implicated in plant‐growth promotion and producing antifungal compounds as well as saprotrophic fungi that are also capable of forming ectomycorrhizal associations. Our research suggests that low‐moderate severity burns are important for maintaining diversity and biomass in soil microbial communities but having a range of burn severities across a site contributes to the overall diversity of habitat conditions providing for both microbial and plant diversity.
Intumescence is a nonpathogenic physiological disorder characterized by leaf blistering. This disorder can affect growth and development in glasshouses and growth chambers and may be confused with pathogenic diseases. We used quantitative trait loci (QTL) analysis to examine the genetic basis of variation in intumescence severity in Eucalyptus globulus, and test for colocation with previously detected QTLs for pathogen susceptibility. QTL analysis used the phenotype means of open-pollinated (OP) families of an outcrossed F2 mapping family (OP F3; n = 300) of E. globulus and the linkage map constructed in the F2. We validate this phenotyping approach for QTL analysis by assessing a trait previously used for QTL discovery in the F2 and showing the same major QTL was detected with the OP F3. For intumescence severity, five putative QTLs were detected across four linkage groups. Four of these did not colocate with previously reported QTLs for fungal pathogen susceptibility in Eucalyptus, suggesting the mechanisms underlying susceptibility to intumescence and to the two fungal pathogens are largely independent. This study demonstrates there is a genetic basis for variation in intumescence severity, reports the first QTL for intumescence severity in plants, and provides a robust framework for investigating the potential mechanisms involved.
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