Effects of Soil Fertility and Atmospheric CO_2 Enrichment on Leaf, Stem and Root Dark Respiration of Populus tremuloides

An open-top chamber experiment was conducted at the University of Michigan Biological Station near Pellston, Michigan, USA, to study the effects of soil fertility and CO2 on leaf, stem and root dark respiration (Rd) of Populus tremuloides. Overall, area-based day-time leaf Rd (Rda) was significantly greater at elevated than at ambient CO2 in high-fertility soil, but not in low-fertility soil. Mass-based leaf Rd (Rdm) was overall greater for high- than for low-fertility soil grown trees at elected, but not at ambient CO2. Nighttime leaf Rd. and Rdm were unthected by soil fertility or CO2, nor was stem Rda, which ranged from 1.0 to 1.4 μmol m-2 s-1 in the spring and 3.5 to 4.5 μmol m-2 s-1 in the summer. Root Rda. was significantly higher in high- than in low-fertility soil, but was unaffected by CO2. Since biomass production of P. tremuloides will be significantly greater at elevated CO2 while specific Rd will either increase or remain unchanged, we predict that carbon loss to the atmosphere through respiration from this ecologically important species would increase at higher CO2. Soil fertility would also interact with elevated CO2 in affecting the carbon flow in the plant-soil-air system.

Leaf Gas Exchange,Photon Capture and Light Harvest in Aldina heterophylla along a Vegetation Gradient in the Amazon Rainforest

Adaptation along environmental gradients is presumed to induce physiological and biochemical leaf changes in plant species. In this paper, we report how leaf gas exchange, photon capture and light harvest for photosynthesis in Aldina heterophylla change along a vegetation gradient from low stature open vegetation on extremely nutrient-poor white sand (Campina, CP), through inter-mediate closet type (Campinarana, CR) to tall closed rain forest (RF). The pigment concentrations did not differ between the CP, CR and RF habitats. The performance index for the photosynthesis (PIABS) of individuals in RF and CP was approximately 30% higher than that in CR individuals. This species showed similar potential rates of photosynthesis in the different vegetation types;however, the dark respiration rates were higher in CP. Our results indicate that the differences in the leaves and soil nitrogen concentrations are not enough to change the levels of gas exchange. Other environmental features may be driving the observed morphological features in this gradient, in particular, the tree height.

Thermal acclimation of leaf respiration varies between legume and non-legume herbaceous

Aims Ubiquitous thermal acclimation of leaf respiration could mitigate the respiration increase.However,whether species of different plant functional groups showing distinct or similar acclimation justifies the simple prediction of respiratory carbon(C)loss to a warming climate.Methods In this study,leaf dark respiration(Rd)of illinois bundleflower(IB,legume),stiff goldenrod(GR,C_(3) forbs),indian grass,little bluestem and king ranch bluestem(IG,LB and KB,C_(4) grass)were measured with detached leaves sampled in a 17-year warming experiment.Important Findings The results showed that Rd at 20℃ and 22℃(R_(20) and R_(22))were significantly lower in the warming treatment for all the five species.Lower R_(22) in warmed than R_(20) in control in GR,KB,LB and IG imply acclimation homeostasis,but not in IB.The significant decline in temperature sensitivity of respiration(Q_(10))of GR resulted in the marginal reduction of Q_(10) across species.No significant changes in Q_(10) of C_(4) grasses suggest different acclimation types for C_(3) forbs and C_(4) grass.The magnitude of acclimation positively correlated with leaf C/N.Our results suggest that non-legume species had a rela-tive high acclimation,although the acclimation type was different between C_(3) forbs and C_(4) grasses,and the legume species displayed no acclimation in Rd.Thus,the plant functional types should be taken into account in the grassland ecosystem C models.