Response of carbon fluxes to drought in a coastal plain loblolly pine forest

Abstract

Full accounting of ecosystem carbon (C) pools and fluxes in coastal plain ecosystems remains less studied compared with upland systems, even though the C stocks in these systems may be up to an order of magnitude higher, making them a potentially important component in regional C cycle. Here, we report C pools and CO 2 exchange rates during three hydrologically contrasting years (i.e. 2005-2007) in a coastal plain loblolly pine plantation in North Carolina, USA. The daily temperatures were similar among the study years and to the long-term average, whereas the amount and timing of precipitation differed significantly. Precipitation was the largest in 2005 (147 mm above normal), intermediate in 2006 (48 mm below) and lowest in 2007 (486 mm below normal). The forest was a strong C sink during all years, sequestering 361 AE 67 (2005), 835 AE 55 (2006) and 724 AE 55 (2007) g C m À2 yr À1 according to eddy covariance measurements of net ecosystem CO 2 exchange (NEE). The interannual differences in NEE were traced to drought-induced declines in canopy and whole tree hydraulic conductances, which declined with growing precipitation deficit and decreasing soil volumetric water content (VWC). In contrast, the interannual differences were small in gross ecosystem productivity (GEP) and ecosystem respiration (ER), both seemingly insensitive to drought. However, the drought sensitivity of GEP was masked by higher leaf area index and higher photosynthetically active radiation during the dry year. Normalizing GEP by these factors enhanced interannual differences, but there were no signs of suppressed GEP at low VWC during any given year. Although ER was very consistent across the 3 years, and not suppressed by low VWC, the total respiratory cost as a fraction of net primary production increased with annual precipitation and the contribution of heterotrophic respiration (R h ) was significantly higher during the wettest year, exceeding new litter inputs by 58%. Although the difference was smaller during the other 2 years (R h : litterfall ratio was 1.05 in 2006 and 1.10 in 2007), the soils lost about 109 g C m À2 yr À1 , outlining their potential vulnerability to decomposition, and pointing to potential management considerations to protect existing soil C stocks.

A Comparison of Three Methods to Estimate Evapotranspiration in Two Contrasting Loblolly Pine Plantations: Age-Related Changes in Water Use and Drought Sensitivity of Evapotranspiration Components

“…More details on LAI measurements at this site are given in Domec et al (2009) and Noormets et al (2010). The optical method was not appropriate because of the open canopy at the early-rotation site, so minimum LAI (winter LAI) was measured destructively on 6 -10 trees harvested in late winter every year.…”

Leveraging 35 years of <i>Pinus taeda</i> research in the southeastern US to constrain forest carbon cycle predictions: regional data assimilation using ecosystem experiments

“…The US-DK3 site was located in the same forest as the Duke FACE site described above (Novick et al, 2015). The US-NC2 site was located in coastal North Carolina (Noormets et al, 2010). We used monthly gross ecosystem production (GEP; modeled gross primary productivity from net ecosystem exchange measured at an eddy-covariance tower) and evapotranspiration (ET) estimates from the sites.…”

“…Furthermore, many of these experiments are multi-factor with water exclusion by nutrient addition , water addition by nutrient addition (Albaugh et al, 2004;Allen et al, 2005;Samuelson et al, 2008), and CO 2 by nutrient addition treatments (McCarthy et al, 2010;Oren et al, 2001). Beyond experimental treatments, southeastern US loblolly pine ecosystems include at least two eddy-covariance sites with high-frequency measurements of C and water fluxes along with biometric observations over many years (Noormets et al, 2010;Novick et al, 2015) and sites with multiyear sap flow data Gonzalez-Benecke and Martin, 2010;Phillips and Oren, 2001). Finally, there are studies that include plots that span the regional environmental gradients and extend back to the 1980s (Burkhart et al, 1985).…”

Relationships between climate, radial growth and wood properties of mature loblolly pine in Hawaii and a northern and southern site in the southeastern United States

“…In the future, the duration and intensity of summer droughts may increase (Seager et al, 2009) and impact loblolly pine forest productivity (Schmidtling, 1994;Noormets et al, 2010). For example, simulations from a process based ecosystem model indicated reductions in net primary productivity as high as 40% in southern forests in response to drought over the period of 1895(Chen et al, 2012.…”