Respiratory temperature responses of tropical conifers differ with leaf morphology

Abstract

Photosynthetic traits suggest that shade tolerance may explain the contrasting success of two conifer taxa, Podocarpaceae and Pinaceae, in tropical forests. Needle‐leaved species from Pinus (Pinaceae) are generally absent from tropical forests, whereas Pinus krempfii, a flat‐leaved pine, and numerous flat‐leaved Podocarpaceae are abundant. Respiration (R) traits may provide additional insight into the drivers of the contrasting success of needle‐ and flat‐leaved conifers in tropical forests. We measured the short‐term respiratory temperature (RT) response between 10 and 50°C and foliar morphological traits of three needle‐ and seven flat‐leaved conifer species coexisting in a tropical montane forest in the Central Highlands of Vietnam containing notable conifer diversity. We fit a lognormal polynomial model to each RT curve and extracted the following three parameters: a (basal R), and b and c (together describing the shape of the response). Needle‐leaved species (Pinus kesiya, Pinus dalatensis and Dacrydium elatum) had higher rates of area‐based R at 25°C (R25‐area) as well as higher area‐based modelled basal respiration (a) than flat‐leaved species (P. krempfii, Podocarpus neriifolius, Dacrycarpus imbricatus, Nageia nana, Taxus wallichiana, Keteeleria evelyniana and Fokienia hodginsii). No significant differences were found between needle‐ and flat‐leaved species in mass‐based R25 (R25‐mass) or in the shape of the RT response (b and c); however, interspecific differences in R25‐mass, R at nighttime temperature extremes (R4.1 and R20.6) and leaf traits were apparent. Differences in R25‐area and a suggest that needle‐leaved foliage may be more energetically costly to maintain than flat‐leaved foliage, providing new insight and additional support for the hypothesis that shade tolerance is an important driver of Podocarpaceae success and Pinaceae absence in the majority of tropical forests. Interspecific differences in R25‐mass and leaf traits highlight that varying ecological strategies are employed by conifers to coexist and survive in the Central Highlands of Vietnam. Ultimately, these data further our understanding of current conifer biogeographical distributions and underscore the need for additional studies to elucidate the effects of extreme temperature events on the continued survival of conifers in this unique forest. A free Plain Language Summary can be found within the Supporting Information of this article.

Variation in White spruce needle respiration at the species range limits: A potential impediment to Northern expansion

“…Leaves remained in the dark for a minimum of 1 h before the initiation of the respiration measurements. The mesh bag containing the leaves was placed inside a custom‐made cuvette (Figure , Patterson et al, 2018; Li et al, 2019; Schmiege et al, 2021) with computer‐controlled thermoelectrical cooling (CP‐121 Thermoelectric Peltier Cooling Unit; TE Technology). The custom cuvette was interfaced with a portable photosynthesis system (Li‐6400XT; LiCor Lincoln) which recorded all gas exchange and environmental parameters every 20 s. The infrared gas analyzers were ‘matched’ before the start of each temperature response curve and checked again at the end of the curve.…”

“…After equilibrating the system to 5°C, the mesh bag holding the leaves was sealed inside. Once stability was reached the instrument was zeroed and the response curve was measured as described in Heskel et al (2016), O'Sullivan et al (2013) and Schmiege et al (2021). During measurements the flow rate through the cuvette was set to 500 mmol s −1 and the CO 2 concentration to 400 ppm.…”

High Leaf Respiration Rates May Limit the Success of White Spruce Saplings growing in The Kampfzone at the Arctic Treeline

“…These needles were weighed to determine the initial fresh mass (g) and then placed in a fine nylon mesh bag, allowing for easy air flow through the bag while keeping the leaves from entering the optical bench of the infrared gas analyzer or becoming lost in the leaf cuvette. The mesh bag containing the leaves was placed inside a custom-made cuvette milled from a solid block of aluminum with a plexiglass lid sealed with a Viton gasket (Patterson et al, 2018;Li et al, 2019;Schmiege et al 2021)). The cuvette contained a mixing fan and two fine wire thermocouples to measure leaf and air temperatures.…”

“…The mesh bag holding the leaves was then sealed inside the cuvette and the system was again equilibrated to 5°C. Once stability was reached, the response curve was measured as described in previous studies (O'Sullivan et al, 2013;Heskel et al, 2016;Schmiege et al 2021). Conditions during the measurements included a flow rate of 500 ml min -1 through the cuvette, and a reference CO2 concentration of 400 ppm.…”

High Leaf Respiration Rates May Limit the Success of White Spruce Saplings Growing in the Kampfzone at the Arctic Treeline

“…The mesh bag holding the leaves was then sealed inside the cuvette and the system was again equilibrated to 5°C. Once stability was reached, the temperature response curve was measured as described in previous studies ( O’Sullivan et al, 2013 ; Heskel et al, 2016 ; Schmiege et al, 2021 ). Conditions during the measurements included a flow rate of 500mlmin −1 through the cuvette, and a reference CO 2 concentration of 400ppm.…”