Estimating net photosynthesis and productivity of a loblolly pine forest grown with carbon dioxide enrichment

I examined the long-term effects of elevated CO2 on the leaf chemistry and photosynthesis of four species growing in the understory and two species growing in the overstory at the Duke Forest FACE experiment. I then used these measurements to parameterize a process based forest productivity model, PnET-II, in order to model the net primary productivity of the portions of the forest growing under ambient and elevated CO2. Finally, I performed a greenhouse study that examined the effects of elevated CO 2 and water availability on the growth and biomass allocation of loblolly pine seedlings from four distinct geographic locations. At the Duke FACE experiment I found a continued stimulation of photosynthesis with elevated CO2 in each species I measured. However the effect of elevated CO2 on photosynthesis of these species did depend on canopy position, season, and year. I observed no CO2-induced changes in leaf chemistry or morphology. Modeled estimates of net primary productivity of the Duke Forest were in good agreement with those measured at the Duke FACE experiment. Estimates of net primary productivity of the portions of the forest grown under elevated CO2 were much greater than the estimates of the portions of the forest grown under ambient CO2. I also found that future climatic conditions expected in North Carolina, USA should alter forest net primary productivity overall but would not alter the response of forest productivity to elevated CO2. In the study of the response of loblolly pine seedlings from different geographic locations to elevated CO2, I found significantly higher biomass in elevated CO2-grown seedlings but I found no evidence of provenance specificity in the growth response to elevated CO2. Decreased water availability did decrease the plant growth and alter biomass allocation irrespective of geographic location and growth CO2 concentration. However, I also concluded that a more detailed analysis is needed with respect to provenance specific responses of loblolly pine to variables of climate change such as CO2 and water availability. Overall my studies revealed that the stimulation of photosynthesis and productivity at the Duke Forest FACE experiment has persisted into the latter years of the experiment and, with no changes in leaf chemistry, no loss of stimulation is expected

Determination of freedom-from-rabies for small Indian mongoose populations in the United States Virgin Islands, 2019–2020

Mongooses, a nonnative species, are a known reservoir of rabies virus in the Caribbean region. A cross-sectional study of mongooses at 41 field sites on the US Virgin Islands of St. Croix, St. John, and St. Thomas captured 312 mongooses (32% capture rate). We determined the absence of rabies virus by antigen testing and rabies virus exposure by antibody testing in mongoose populations on all three islands. USVI is the first Caribbean state to determine freedom-from-rabies for its mongoose populations with a scientifically-led robust cross-sectional study. Ongoing surveillance activities will determine if other domestic and wildlife populations in USVI are rabies-free

Rapid report Elevated CO 2 influences the expression of floral-initiation genes in Arabidopsis thaliana

Summary • Atmospheric CO 2 concentration ([CO 2 ]) is rising on a global scale and is known to affect flowering time. Elevated [CO 2 ] may be as influential as temperature in determining future changes in plant developmental timing, but little is known about the molecular mechanisms that control altered flowering times at elevated [CO 2 ]. • Using Arabidopsis thaliana, the expression patterns were compared of floralinitiation genes between a genotype that was selected for high fitness at elevated [CO 2 ] and a nonselected control genotype. The selected genotype exhibits pronounced delays in flowering time when grown at elevated [CO 2 ], whereas the control genotype is unaffected by elevated [CO 2 ]. Thus, this comparison provides an evolutionarily relevant system for gaining insight into the responses of plants to future increases in [CO 2 ]. • Evidence is provided that elevated [CO 2 ] influences the expression of floral-initiation genes. In addition, it is shown that delayed flowering at elevated [CO 2 ] is associated with sustained expression of the floral repressor gene, FLOWERING LOCUS C (FLC), in an elevated CO 2 -adapted genotype. • Understanding the mechanisms that account for changes in plant developmental timing at elevated [CO 2 ] is critical for predicting the responses of plants to a high-CO 2 world of the near future

The changing role of forests in the global carbon cycle: Responding to elevated carbon dioxide in the atmosphere

Worldwide, forests have an enormous impact on the global C cycle. Of the 760 gigatons (1015 g, Gt) of C in the atmosphere, photosynthesis by terrestrial vegetation removes approximately 120 Gt, almost 16% of the atmospheric pool each year, and about half of this amount (56 Gt) is returned annually by plant respiration (Figure 8.1). The difference between gross canopy photosynthesis and plant respiration (see below) is defined as net primary production (NPP), and represents the annual production of organic matter that is available to consumers. Although estimates vary considerably, forests make up almost half of the global NPP, and approximately 80% of the terrestrial NPP (Figure 8.2). Thus, small changes in the capacity of forests to remove C from the atmosphere by photosynthesis, or return it to the atmosphere by respiration, or store it in wood and soils greatly affect the distribution of C between the terrestrial and atmospheric pool. Because trees use the C3 pathway of photosynthesis, they are very responsive to increases in atmospheric CO2, and it has been hypothesized that a stimulation of photosynthesis and growth of trees may reduce the rate of accumulation of C in the atmosphere derived from fossil fuels. Mounting evidence suggests that a significant portion of the imbalance in the global C cycle, the 2.8 Gt year-1 that is unaccounted for when all known sinks are subtracted from known sources (Figure 8.1), may be explained by additional C uptake in temperate forests (Fan et al., 1998; Pacala et al., 2001; Janssens et al., 2003). How much of this sink is derived from land use change vs. growth enhancement of trees by elevated CO2, nitrogen deposition, and changes in climate remains uncertain

Identification of a major QTL that alters flowering time at elevated [CO(2)] in Arabidopsis thaliana.

The transition from vegetative to reproductive stages marks a major milestone in plant development. It is clear that global change factors (e.g., increasing [CO(2)] and temperature) have already had and will continue to have a large impact on plant flowering times in the future. Increasing atmospheric [CO(2)] has recently been shown to affect flowering time, and may produce even greater responses than increasing temperature. Much is known about the genes influencing flowering time, although their relevance to changing [CO(2)] is not well understood. Thus, we present the first study to identify QTL (Quantitative Trait Loci) that affect flowering time at elevated [CO(2)] in Arabidopsis thaliana.We developed our mapping population by crossing a genotype previously selected for high fitness at elevated [CO(2)] (SG, Selection Genotype) to a Cape Verde genotype (Cvi-0). SG exhibits delayed flowering at elevated [CO(2)], whereas Cvi-0 is non-responsive to elevated [CO(2)] for flowering time. We mapped one major QTL to the upper portion of chromosome 1 that explains 1/3 of the difference in flowering time between current and elevated [CO(2)] between the SG and Cvi-0 parents. This QTL also alters the stage at which flowering occurs, as determined from higher rosette leaf number at flowering in RILs (Recombinant Inbred Lines) harboring the SG allele. A follow-up study using Arabidopsis mutants for flowering time genes within the significant QTL suggests MOTHER OF FT AND TFL1 (MFT) as a potential candidate gene for altered flowering time at elevated [CO(2)].This work sheds light on the underlying genetic architecture that controls flowering time at elevated [CO(2)]. Prior to this work, very little to nothing was known about these mechanisms at the genomic level. Such a broader understanding will be key for better predicting shifts in plant phenology and for developing successful crops for future environments

Response of the MFT knock-out mutant and wild-type (WT), which is Columbia (Col-0) to current (380 ppm) and elevated (700 ppm) CO₂.

<p>Symbols are means ± 1 standard error.</p

Frequency distribution of RIL responses for flowering time.

<p>The x-axis was calculated as days to flower at 700 ppm [CO₂] minus days to flower 380 ppm [CO₂]. Thus, positive values represent delays in flowering at elevated [CO₂] and negative values represent more rapid flowering (with 0 being no change in flowering time due to [CO₂]). Differences for parental Cvi-0 and SG are shown with arrows.</p