Ecosystem Productivity and Evapotranspiration Are Tightly Coupled in Loblolly Pine (Pinus taeda L.) Plantations along the Coastal Plain of the Southeastern U.S.

Abstract

Forest water use efficiency (WUE), the ratio of gross primary productivity (GPP) to evapotranspiration (ET), is an important variable to understand the coupling between water and carbon cycles, and to assess resource use, ecosystem resilience, and commodity production. Here, we determined WUE for managed loblolly pine plantations over the course of a rotation on the coastal plain of North Carolina in the eastern U.S. We found that the forest annual GPP, ET, and WUE increased until age ten, which stabilized thereafter. WUE varied annually (2–44%), being higher at young plantation (YP, 3.12 ± 1.20 g C kg−1 H2O d−1) compared to a mature plantation (MP, 2.92 ± 0.45 g C kg−1 H2O d−1), with no distinct seasonal patterns. Stand age was strongly correlated with ET (R2 = 0.71) and GPP (R2 = 0.64). ET and GPP were tightly coupled (R2 = 0.86). Radiation and air temperature significantly affected GPP and ET (R2 = 0.71 − R2 = 0.82) at a monthly scale, but not WUE. Drought affected WUE (R2 = 0.35) more than ET (R2 = 0.25) or GPP (R2 = 0.07). A drought enhanced GPP in MP (19%) and YP (11%), but reduced ET 7% and 19% in MP and YP, respectively, resulting in a higher WUE (27–32%). Minor seasonal and interannual variation in forest WUE of MP (age > 10) suggested that forest functioning became stable as stands matured. We conclude that carbon and water cycles in loblolly pine plantations are tightly coupled, with different characteristics in different ages and hydrologic regimes. A stable WUE suggests that the pine ecosystem productivity can be readily predicted from ET and vice versa. The tradeoffs between water and carbon cycling should be recognized in forest management to achieve multiple ecosystem services (i.e., water supply and carbon sequestration).

Responses in the Coupling of Carbon and Water Vapor Exchanges of Irrigated and Rainfed Andean Potato (<i>Solanum Tuberosum</i> Subsp. Andigenum) Agroecosystems

“…At the well-watered conditions of the FI site, the diurnal cycles of ET and GPP were proportional and largely synchronized, which is consistent with other studies (Aguilos et al, 2021;Beer et al, 2009;Nelson et al, 2018b). The higher coupling indicates that the amount of carbon that enters the canopy is proportional to water that leaves, and at noon, when the stomata begin to close, carbon and water fluxes decrease by a similar percentage (Gentine et al, 2019;Mallick et al, 2016;Nelson et al, 2018b;van Dijke et al, 2020a).…”

“…From equation 6, there is a linear relationship between GPP and ET, adjusted by VPD. To quantify the degree of carbon-water coupling for an individual day, the linear correlation coefficient ET vs GPP*VPD was computed using the half-hourly data (Aguilos et al, 2021;Nelson et al, 2018a;Zhou et al, 2014). The correlation coefficients were determined on both, the daily scale during all crop growth for each site, and the average half-hour for each growth stage "vegetative", "tuberization" and "tuber bulking" for each site.…”

“…To know whether effectively water and carbon signals were coupled or decoupled under the water availability conditions of the measurement sites, we quantified ET-GPP coupling through the daily correlation coefficients for GPP*VPD vs ET using half-hourly data, and by computing daily 𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼 = 𝐺𝐺𝐺𝐺𝐺𝐺 * 𝑉𝑉𝑉𝑉𝑉𝑉 𝐸𝐸𝐸𝐸 from the total daily sums of GP and ET, and average VPD. IWUE has been widely used in numerous studies as a measure of carbon and water coupling (Battipaglia et al, 2013b;Beer et al, 2009;Grossiord et al, 2014;Leonardi et al, 2012;Loader et al, 2011;Zhou et al, 2015Zhou et al, , 2014, and since it shows an improved linear relationship among GPP, ET, and VPD the daily correlation coefficient (r) of GPP*VPD vs ET has been used as an indicator for quantify the coupling/decoupling degree between water and carbon fluxes (Aguilos et al, 2021;Beer et al, 2009;Nelson et al, 2018b;Zhou et al, 2015Zhou et al, , 2014. However, numerous environmental factors and non-stomatal limitations to carbon assimilation control the photosynthesis/transpiration balance and could affect carbon and water fluxes, causing a carbon-water decoupling (Nelson et al, 2018b;Zhou et al, 2015).…”

Detecting Coastal Wetland Degradation by Combining Remote Sensing and Hydrologic Modeling

“…Fish & Wildlife Service, Washington, DC, USA, https://www.fws.gov/refuge/Alligator_River/ (accessed on 5 April 2021)). Mean annual precipitation of the study area was 1366 ± 57 mm (1971-2018) and mean annual temperature from 1971 to 2000 was about 16.9 • C, with the highest and lowest temperature of 26.5 • C and 6.8 • C in July and January, respectively [9,50,51]. The ARNWR has been experiencing rapid SLR in recent decades.…”

Environmental and Plant-Derived Controls on the Seasonality and Partitioning of Soil Respiration in an American Sycamore (Platanus occidentalis) Bioenergy Plantation Grown at Different Planting Densities

“…Soil respiration can be also related to photosynthetic activity, and respiratory activity and plant productivity have been shown to be coupled [52,53]. Root-derived carbon respiration and leaf area index (LAI) can be used as predictive parameters to determine this coupling [54].…”