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1.  Multi-stemmed trees of Nothofagus pumilio second-growth forest in Patagonia are formed by highly related individuals 
Annals of Botany  2012;110(4):905-913.
Background and Aims
Multi-stemmed trees (tree clusters) in Nothofagus pumilio, a dominant tree species in Patagonia, are very uncommon and are restricted to the edge of second-growth forests following human-provoked fires. No vegetative reproduction has been reported so far. The genetic structure of multi-stemmed trees of this species was investigated and it was hypothesized that genets within a cluster were more closely related than average in the population.
Methods
Fifteen clusters (composed of at least three purported stems) and 15 single trees were sampled at the edge of a second-growth forest and genotyped using two amplified fragment length polymorphism (AFLP) primer pairs. We obtained 119 polymorphic markers that allowed clonality to be determined, together with sibship structure and relatedness among samples.
Key Results
Clonality was detected in seven clusters but all clusters had at least two different genotypes. Full sibs were found exclusively within clusters and in all clusters. Within a cluster, stems that were not identified as full sibs were often half sibs. Relatedness values for the full sibs and half sibs were higher than the theoretical values of 0·5 and 0·25 but the relatedness between clusters was very low.
Conclusions
Tree clusters that are merged at the edge of the second-growth forest of N. pumilio are composed of stems of the same genotype and of other genotypes that are highly related (but not always). It is suggested that this peculiar genetic structure results from a combination of several causes, including selection for merging of related individuals.
doi:10.1093/aob/mcs146
PMCID: PMC3423804  PMID: 22782238
AFLP; multi-stemmed trees; Patagonia; post-fire regeneration; sibship structure
2.  No evidence of carbon limitation with tree age and height in Nothofagus pumilio under Mediterranean and temperate climate conditions 
Annals of Botany  2011;108(5):907-917.
Background and Aims
Trees universally decrease their growth with age. Most explanations for this trend so far support the hypothesis that carbon (C) gain becomes limited with age; though very few studies have directly assessed the relative reductions of C gain and C demand with tree age. It has also been suggested that drought enhances the effect of C gain limitation in trees. Here tests were carried out to determine whether C gain limitation is causing the growth decay with tree age, and whether drought accentuates its effect.
Methods
The balance between C gain and C demand across tree age and height ranges was estimated. For this, the concentration of non-structural carbohydrates (NSCs) in stems and roots of trees of different ages and heights was measured in the deciduous temperate species Nothofagus pumilio. An ontogenetic decrease in NSCs indicates support for C limitation. Furthermore, the importance of drought in altering the C balance with ontogeny was assessed by sampling the same species in Mediterranean and humid climate locations in the southern Andes of Chile. Wood density (WD) and stable carbon isotope ratios (δ13C) were also determined to examine drought constraints on C gain.
Key Results
At both locations, it was effectively found that tree growth ultimately decreased with tree age and height. It was found, however, that NSC concentrations did not decrease with tree age or height when WD was considered, suggesting that C limitation is not the ultimate mechanism causing the age/height-related declining tree growth. δ13C decreased with tree age/height at the Mediterranean site only; drought effect increased with tree age/height, but this pattern was not mirrored by the levels of NSCs.
Conclusions
The results indicate that concentrations of C storage in N. pumilio trees do not decrease with tree age or height, and that reduced C assimilation due to summer drought does not alter this pattern.
doi:10.1093/aob/mcr195
PMCID: PMC3177673  PMID: 21852277
Carbon isotope composition; drought; hydraulic limitation hypothesis; Mediterranean climate; non-structural carbohydrates; Nothofagus pumilio; ontogeny; Patagonia

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