Variations and determinants of tissue carbon concentration of 32 sympatric temperate tree species

Plant carbon(C)concentration is a fundamental trait for estimating C storage and nutrient utilization.However,the mechanisms of C concentration variations among different tree tissues and across species remains poorly understood.In this study,we explored the variations and determinants of C concentration of nine tissues from 216 individuals of 32 tree species,with particular attention on the effect of wood porosity(i.e.,non-porous wood,diffuse-porous wood,and ring-porous wood).The inter-tissue pattern of C concentration diverged across the three porosity types;metabolically active tissues(foliage and fine roots,except for the foliage of ring-porous species)generally had higher C levels compared with inactive wood.The poor inter-correlations between tissue C concentrations indicated a necessity of measuring tissue-and specific-C concentrations.Carbon concentration for almost all tissues generally decreased from non-porous,to diffuse-porous and to ring-porous.Tissue C was often positively correlated with tissue(foliage and wood)density and tree size,while negatively correlated with growth rate,depending on wood porosity.Our results highlight the mediating effect of type of wood porosity on the variation in tissue C among temperate species.The variations among tissues were more important than that among species.These findings provided insights on tissue C concentration variability of temperate forest species.

Distribution of mechanical strain in equine distal metacarpal subchondral bone:A microCT-based finite element model

Microdamage accumulation and adaptation of subchondral bone subjected to intensive cyclic loading are important processes associated with catastrophic bone failure,and joint degeneration in athletic humans and racehorses.At the tissue-level,they lead to a spatial variation in bone tissue mineral density(TMD)which affects the response of the bone to mechanical load.Quantifying the spatial distribution of mechanical load within the subchondral bone is critical for understanding the mechanism of the joint failure.Previously,a gradient of TMD and mechanical properties has been reported under unconfined compression in osteochondral plugs.In the present study,we used micro computed tomography(μCT)-based finite element(FE)models of cartilage-bone to investigate the gradient of strain in the subchondral bone(SCB)from the third metacarpal(MC3)condyle of racehorses under simulated in situ compression.Non-destructive mechanical testing of specimens under high-rate compression provided the apparent-level modulus of SCB.FE models were analysed using unconfined and confined boundary conditions.Unconfined FE-predicted apparent-level gradient of modulus across the SCB thickness correlated well with the experimental results(R^(2)=0.72,p<0.05).The highest strain occurred in the most superficial SCB(0.5–2.5 mm deep to the cartilage-bone interface)under the simulated in-situ compression through articular cartilage.The findings of this study provide an estimation for the spatial distribution of mechanical strain within SCB in-situ in the presence of heterogeneous bone tissue which is commonly observed in joints subjected to intensive cyclic loading.