Impacts of experimentally imposed drought on leaf respiration and morphology in an Amazon rain forest

Abstract

Summary1. The Amazon region may experience increasing moisture limitation over this century. Leaf dark respiration (R) is a key component of the Amazon rain forest carbon (C) cycle, but relatively little is known about its sensitivity to drought. 2. Here, we present measurements of R standardized to 25°C and leaf morphology from different canopy heights over 5 years at a rain forest subject to a large-scale through-fall reduction (TFR) experiment, and nearby, unmodified Control forest, at the Caxiuana˜reserve in the eastern Amazon. 3. In all five post-treatment measurement campaigns, mean R at 25°C was elevated in the TFR forest compared to the Control forest experiencing normal rainfall. After 5 years of the TFR treatment, R per unit leaf area and mass had increased by 65% and 42%, respectively, relative to pre-treatment means. In contrast, leaf area index (L) in the TFR forest was consistently lower than the Control, falling by 23% compared to the pre-treatment mean, largely because of a decline in specific leaf area (S). 4. The consistent and significant effects of the TFR treatment on R, L and S suggest that severe drought events in the Amazon, of the kind that may occur more frequently in future, could cause a substantial increase in canopy carbon dioxide emissions from this ecosystem to the atmosphere.

Multiyear impacts of partial throughfall exclusion on Buxus sempervirens in a Mediterranean forest

“…, and/or by increasing leaf mass per unit area (Metcalfe et al, 2010), as well as cross-sectional sapwood area per supported leaf area (i.e. the Huber value; Cinnirella et al, 2002).…”

“…Overall, these changes promote xylem hydraulic safety. Leaf physiological traits may remain unchanged following long-term exposure to increased drought (Limousin et al, 2010a) or reach an altered state, due to parallel shifts in nitrogen concentration, leaf density and other anatomical and hydraulic traits (Ripullone et al, 2009;Metcalfe et al, 2010).…”

Characteristics of wood CO2 efflux in a Bornean tropical rainforest

“…For annual R foliage , seasonal variations in R foliage and LAI were not considered in the present study and the variations may lead to under-or overestimation although R foliage at the ecosystem scale did not vary seasonally in Peru (Malhi et al, 2014) and Brazil (Metcalfe et al, 2010). In the present study, R foliage at 25 • C was estimated using Q 10 of 2.3 reported in Costa Rica.…”

“…Thus, to accommodate light inhibition of R foliage , daytime R foliage was calculated as 67% of night time R foliage according to previous studies (Malhi et al, 2009(Malhi et al, , 2014da Costa et al, 2013;Doughty et al, 2013). Annual R foliage at the ecosystem scale (annual-R foliage , MgC ha −1 year −1 ) was estimated assuming 12 h of daytime and nighttime and a constant temperature of 25 • C each day throughout the year, and the error in annual R foliage represents spatial variation according to a previous study (Metcalfe et al, 2010). ANPP (6.76 ± 0.57 MgC ha −1 year −1 ) and TBCF (19.63 ± 6.37 MgC ha −1 year −1 ) were previously estimated in this study site (Katayama et al, 2013).…”

Why Do Some Evergreen Species Keep Their Leaves for a Second Winter, While Others Lose Them?

“…Indeed, there is mounting evidence of increases in respiration as a result of drought [38,39], so that the possibility of negative net assimilation during dry periods has to be taken seriously. It may also be of value to a tree to reduce its leaf mass in such a way that it is easier to maintain a favourable water status (and, as a result, a favourable carbon balance) in the remaining leaves.…”