Explaining forest productivity using tree functional traits and phylogenetic information: two sides of the same coin over evolutionary scale?

Given evidences that diverse ecosystems provide more services than depauperate ones, much attention has now turned toward finding meaningful and operational diversity indices. We ask two questions: (1) Does phylogenetic diversity contain additional information not explained by functional traits? And (2) What are the strength and nature of the correlation between phylogeny and functional traits according to the evolutionary scale considered? We used data from permanent forest plots of northeastern Canada for which these links have been demonstrated and important functional traits identified. We show that the nature of the relationship between traits and phylogeny varies dramatically among traits, but also according to the evolutionary distance considered. The demonstration that different characters show phylogenetic autocorrelation at different evolutionary depths suggests that phylogenetic content of traits may be too crude to determine whether phylogenies contain relevant information. However, our study provides support for the use of phylogenies to assess ecosystem functioning when key functional traits are unavailable. We also highlight a potentially important contribution of phylogenetics for conservation and the study of the impact of biodiversity loss on ecosystem functioning and the provision of services, given the accumulating evidence that mechanisms promoting diversity effects shift over time to involve different traits.

Advancing biodiversity-ecosystem functioning science using high-density tree-based experiments over functional diversity gradients

Increasing concern about loss of biodiversity and its effects on ecosystem functioning has triggered a series of manipulative experiments worldwide, which have demonstrated a general trend for ecosystem functioning to increase with diversity. General mechanisms proposed to explain diversity effects include complementary resource use and invoke a key role for species' functional traits. The actual mechanisms by which complementary resource use occurs remain, however, poorly understood, as well as whether they apply to tree-dominated ecosystems. Here we present an experimental approach offering multiple innovative aspects to the field of biodiversity-ecosystem functioning (BEF) research. The International Diversity Experiment Network with Trees (IDENT) allows research to be conducted at several hierarchical levels within individuals, neighborhoods, and communities. The network investigates questions related to intraspecific trait variation, complementarity, and environmental stress. The goal of IDENT is to identify some of the mechanisms through which individuals and species interact to promote coexistence and the complementary use of resources. IDENT includes several implemented and planned sites in North America and Europe, and uses a replicated design of high-density tree plots of fixed species-richness levels varying in functional diversity (FD). The design reduces the space and time needed for trees to interact allowing a thorough set of mixtures varying over different diversity gradients (specific, functional, phylogenetic) and environmental conditions (e.g., water stress) to be tested in the field. The intention of this paper is to share the experience in designing FD-focused BEF experiments with trees, to favor collaborations and expand the network to different conditions.

Interspecific coordination and intraspecific plasticity of fine root traits in North American temperate tree species

Fine roots play an important role in nutrient and water absorption and hence overall tree performance. However, current understanding of the ecological role of belowground traits lags considerably behind those of aboveground traits. In this study, we used data on specific root length (SRL), fine root diameter (D) and branching intensity (BI) of two datasets to examine interspecific trait coordination as well as intraspecific trait variation across ontogenetic stage and soil conditions (i.e., plasticity). The first dataset included saplings of 12 North American temperate tree species grown in monocultures in a common garden experiment to examine interspecific trait coordination. The second dataset included adult and juvenile individuals of four species (present in both datasets) co-occurring in natural forests on contrasting soils (i.e., humid organic, mesic, and xeric podzolic).The three fine root traits investigated were strongly coordinated, with high SRL being related to low D and high BI. Fine root traits and aboveground life-strategies (i.e., relative growth rate) were weakly coordinated and never significant. Intraspecific responses to changes in ontogenetic stage or soil conditions were trait dependent. SRL was significantly higher in juveniles compared to adults for Abies balsamea and Acer rubrum, but did not vary with soil condition. BI did not vary significantly with either ontogeny or soil conditions, while D was generally significantly lower in juveniles and higher in humid organic soils. D also had the least total variability most of which was due to changes in the environment (plasticity). This study brings support for the emerging evidence for interspecific root trait coordination in trees. It also indicates that intraspecific responses to both ontogeny and soil conditions are trait dependent and less concerted. D appears to be a better indicator of environmental change than SRL and BI.

Norway maple displays greater seasonal growth and phenotypic plasticity to light than native sugar maple

Norway maple (Acer platanoides L), which is among the most invasive tree species in forests of eastern North America, is associated with reduced regeneration of the related native species, sugar maple (Acer saccharum Marsh) and other native flora. To identify traits conferring an advantage to Norway maple, we grew both species through an entire growing season under simulated light regimes mimicking a closed forest understorey vs. a canopy disturbance (gap). Dynamic shade-houses providing a succession of high-intensity direct-light events between longer periods of low, diffuse light were used to simulate the light regimes. We assessed seedling height growth three times in the season, as well as stem diameter, maximum photosynthetic capacity, biomass allocation above- and below-ground, seasonal phenology and phenotypic plasticity. Given the north European provenance of Norway maple, we also investigated the possibility that its growth in North America might be increased by delayed fall senescence. We found that Norway maple had significantly greater photosynthetic capacity in both light regimes and grew larger in stem diameter than sugar maple. The differences in below- and above-ground biomass, stem diameter, height and maximum photosynthesis were especially important in the simulated gap where Norway maple continued extension growth during the late fall. In the gap regime sugar maple had a significantly higher root : shoot ratio that could confer an advantage in the deepest shade of closed understorey and under water stress or browsing pressure. Norway maple is especially invasive following canopy disturbance where the opposite (low root : shoot ratio) could confer a competitive advantage. Considering the effects of global change in extending the potential growing season, we anticipate that the invasiveness of Norway maple will increase in the future.

Fatty acid oxidation is decreased in the liver of ovariectomized rats

Estrogen-deficient states are associated with hepatic steatosis. Based on previous findings obtained at the molecular and enzymatic levels, it has been suggested that estradiol exerts its lipid-lowering effects in liver through partitioning of triacylglycerols into oxidative pathways. However, information on relevant physiological response was lacking. Therefore, the purpose of the present study was to assess fatty acid oxidation rate in the liver of intact and ovariectomized rats. Tritiated water released from liver slices incubated with 9,10-[ (3)H]palmitate was measured as a reflection of in vivo fatty acid metabolism. Fatty acid oxidation rate was lowered by 34% (p<0.05), associated with 114% higher (p<0.01) hepatic triacylgylcerol content in the liver of ovariectomized as compared to intact rats. Estrogen replacement prevented all of these changes. Fatty liver has been linked with hepatic leptin resistance in obese male rats. Since leptin stimulates fatty acid oxidation in liver, we hypothesized that increased liver triacylglycerol content and decreased fatty acid oxidation might be associated with leptin resistance in ovariectomized rats. To this end, acute leptin delivery was performed. The 120-min intravenous leptin infusion increases fatty acid oxidation by 23% in the liver of ovariectomized rats, which was coupled with 24% lower hepatic triacylglycerol content. We conclude that fatty acid oxidation is decreased in the liver of ovariectomized rats, which is likely to contribute to hepatic steatosis development. Furthermore, our results suggest that leptin sensitivity is not completely lost in the liver of rats ovariectomized for 5 weeks.

Substituting food restriction by resistance training prevents liver and body fat regain in ovariectomized rats

OBJECTIVE

Fat mass gain and regain following weight loss are major concerns and may be even more critical after menopause. The present study was undertaken to evaluate the effect of a resistance training protocol on body weight and fat mass in ovariectomized Sprague-Dawley rats following diet-induced weight loss.

DESIGN

Rats were randomly divided into ovariectomized (Ovx) and sham-operated (Sham) groups. Five weeks after ovariectomy, Ovx rats were subjected to a 26% food restriction (OvxFR) for 8 weeks. Following this period, OvxFR rats went back to a normal ad libitum feeding and were divided into two groups: either sedentary or undergoing a resistance training program for an additional 5 weeks, which consisted of climbing a 6-m vertical grill, 20-40 times, with progressively increasing load four times/week.

RESULTS

The food restriction program decreased (p < 0.01) body mass, fat pad weight (intra-abdominal and subcutaneous), and liver triacylglycerol (TAG) levels as compared to normally fed Ovx rats. Stopping the food restriction program over a 5-week period resulted in a partial regain in body weight and intra-abdominal fat pad weight (p < 0.05), and in an almost complete regain in liver TAG compared to normally fed Ovx rats. On the other hand, no significant increases in these variables were noted when the food restriction was replaced by resistance training over the same 5-week period.

CONCLUSION

These results indicate that a resistance training program could be useful in preventing body weight as well as adipose tissue and liver fat regain in Ovx rats, following diet-induced weight loss. It is suggested that changing from a food restriction regimen to a resistance training program can be an interesting strategy to promote successful long-term weight reduction in postmenopausal women.

Pax genes and neural tube defects in the mouse

The Pax genes encode a family of transcription factors that are expressed in restricted regions of the developing embryo. Several Pax genes are expressed in the developing nervous system where they are believed to regulate the morphogenesis of neural structures. Loss-of-function mutations in the Pax-3 gene have been identified in a number of alleles of the mouse mutant splotch. In homozygous splotch embryos closure of the neural tube is defective with embryos exhibiting spina bifida and/or exencephaly. Other structures in which Pax-3 is expressed are also affected, most notably those tissues derived from the neural crest and somites.

Survival and growth of under-planted trees: a meta-analysis across four biomes

The transformation of natural forest regeneration processes by human activities has created the need to develop and implement new models of forest management. Alternative silvicultural systems such as variable retention harvest, partial and patch cuts, and older forest management practices such as under-planting, are used in many forests around the world, particularly in North American oak stands, the boreal and coastal temperate rain forests of Canada and the United States, and in many degraded tropical regions of Asia and the Americas. Specific objectives are pursued in each of these biomes, but some are common to most regions, such as preservation of cover and structure and their associated benefits for natural or artificial regeneration due to moderation of the microclimate, development of optimal light and competition conditions, and reduced predation by herbivores. Shelterwoods are often presented as an alternative to clear-cutting to improve the survival of planted trees. A meta-analysis of published results with randomization tests was performed to test the relationship between overstory density and planted seedling growth and survival. Multiple comparisons were also used to reveal optimal levels of overstory density, if they exist. A majority of studies show that survival and growth improve as stand density decreases to an intermediate level, below which they either drop or stabilize. This level seems optimal in most conditions, as it is also more apt to fulfill other objectives imposed on today's forest activities, such as the conservation of forest processes and structures, and the reconstruction of degraded stands through the accelerated return of mid- to late-successional species.