Late growing season carbon subsidy in native gymnosperms in a northern temperate forest

Abstract

Evergreen tree species that maintain positive carbon balance during the late growing season may subsidize extra carbon in a mixed forest. To test this concept of ‘carbon subsidy’, leaf gas exchange characteristics and related leaf traits were measured for three gymnosperm evergreen species (Chamaecyparis thyoides, Tsuga canadensis and Pinus strobus) native to the oak-hickory deciduous forest in northeast USA from March (early Spring) to October (late Autumn) in a single year. All three species were photosynthetically active in Autumn. During the Summer–Autumn transition, photosynthetic capacity (Amax) of T. canadensis and P. strobus increased (T-test, P < 0.001) and was maintained in C. thyoides (T-test, P = 0.49), while dark respiration at 20 °C (Rn) and its thermal sensitivity were generally unchanged for all species (one-way ANOVA, P > 0.05). In Autumn, reductions in mitochondrial respiration rate in the daylight (RL) and the ratio of RL to Rn (RL/Rn) were observed in P. strobus (46.3% and 44.0% compared to Summer, respectively). Collectively, these physiological adjustments resulted in higher ratios of photosynthesis to respiration (A/Rnand A/RL) in Autumn for all species. Across season, photosynthetic biochemistry and respiratory variables were not correlated with prevailing growth temperature. Physiological adjustments allowed all three gymnosperm species to maintain positive carbon balance into late Autumn, suggesting that gymnosperm evergreens may benefit from Autumn warming trends relative to deciduous trees that have already lost their leaves.

Precipitation alters the CO2 effect on water‐use efficiency of temperate forests

“…However, if A is RuBP regeneration‐limited, then photosynthesis acclimation is observed as trees reduce their investment in Rubisco. Our analysis (Figure S4) and recent empirical measurements (Li et al, 2019) suggest that the rate of photosynthesis in T. canadensis is commonly limited by RuBP regeneration. The modest rates of A increase observed after 1975 could also result from N or light limitation, or both.…”

“…To estimate A c and A j , we used 17.05 and 39.43 µmol m −2 s −1 as values for V cmax and J max , respectively. These values are from summer measurements (June–August) of T. canadensis in NE‐US (Li et al, 2019). R d was assumed to be 0.5 µmol m −2 s −1 , and Γ* and K m were calculated as temperature (JJA) and atmospheric pressure dependent using the R‐package rpmodel (Stocker et al, 2020).…”

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.…”

“…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 S2, 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;…”

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.…”