Analysis of biological and meteorological controls of evapotranspiration in pristine forests and a pasture site in Amazonia

Abstract

This work studied the behavior and seasonality of evapotranspiration influenced by biotic and abiotic factors through analysis of diurnal variation of aerodynamic resistance (ra), stomatal resistance (rs) and decoupling factor (Ω). This index was proposed by Jarvis and McNaughton (1986) as an indicative of the control of these resistances on the evapotranspiration of vegetation. Selection of representative data from wet and dry seasons from a primary forest in Central Amazonia and a primary forest and a pasture sites in Southwestern Amazonia had shown that: (i) ra is about 20 s.m-1 in both forests in both seasons, and ranges from 70 to 100 s.m-1 in the pasture site; (ii) rs varies both throughout the day and seasonally, with medians increasing from 40 in the morning, to 150 s.m-1 in late afternoon, in the wet season in the forests and from 50 to 160 s.m-1 in the pasture. These values increase in the dry season, with the forests rs ranging from 50 up to 500 s.m-1 and pasture rs starting from 140 s.m‑1 and reaching up to more than 1800 s.m-1 in the dry afternoons; (iii) Ω ranges from 0.5 to 0.8 during the wet season, and reduces to values below 0.5 in the afternoons during the dry season, indicating that, although a strong influence of net radiation in the evaporative loss is present, to a large extent the evapotranspiration fluxes are coupled to the biotic control of stomatal closure in the vegetation, especially in the pasture and during dry periods.

Carbon and water vapor exchanges coupling in irrigated and rainfed Andean potato (Solanum tuberosum subsp. andigenum) agroecosystems

“…However, as discussed previously, this higher Rc may restrict photosynthesis more than it restricts ET (Jarvis 1985;Steduto and Hsiao 1998;Spinelli et al 2016Spinelli et al , 2018, and unbalance constraint occurs over GPP due to stomatal and non-stomatal limitations to photosynthesis. Other researchers have reported a decreasing trend of omega under water deficit caused by an increase in the canopy resistance and a decrease in aerodynamic resistance (Spinelli et al 2016;Paulino Junior and Silva von Randow 2017;Silva et al 2017;Ferreira 2017;de Kauwe et al 2017;Sutherlin et al 2019a) which agrees with the results presented in this study.…”

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

“…However, the higher Rc reducing evapotranspiration, may restrict photosynthesis more than it restricts ET (Jarvis, 1985;Spinelli et al, 2018bSpinelli et al, , 2016Steduto and Hsiao, 1998) as discussed previously. Other researchers have reported a decreasing trend of omega under water deficit caused by an increase in the canopy resistance and a decrease in aerodynamic resistance (de Kauwe et al, 2017;Ferreira, 2017;Paulino Junior and Silva von Randow, 2017;Silva et al, 2017;Spinelli et al, 2016;Sutherlin et al, 2019b) which agrees with the results presented in this work. Unlike FI and DI sites omega and r, have a similar trend of variation along crop growth.…”

“…In our results, at the FI site, higher values of daily ET occurred in lower Rc during all crop growth stages. This expected low canopy resistance under wellwatered conditions has been reported by other researchers (Aires et al, 2008;Kumagai et al, 2008;Paulino Junior and Silva von Randow, 2017;Souza et al, 2012). Unlike with López-Olivari et al (2022), we observed a larger aerodynamic resistance (generally higher than Rc) indicating more importance of Ra in total resistance to water vapor transport.…”

Analytical approach to relate evapotranspiration, canopyatmosphere coupling level, and water deficit sensitivity

“…The main driving force of the biophysical interaction between the biosphere and the atmosphere is the radiative energy from solar radiation. Although evapotranspiration is directly linked to this available energy (which is the primary driver of vapor transport), there is a considerable influence of the biotic factors (Nassif et al 2014, Paulino Junior et al 2017, Spinelli et al 2018. The decoupling factor was proposed by Jarvis and McNaughton (1986).…”