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Cathaya argyrophylla is an ancient and threatened Pinaceae species endemic to China, but its eco-physiological traits are rarely reported. We hypothesized that Cathaya showed eco-physiological outliers to its Pinaceae relatives, which lead to its current endangered status. Here we collected the photosynthetic capacity (P n, maximum photosynthesis rate) and branchlet hydraulic safety (P 50, the water potential at which a 50% loss in conductivity occurs) of Pinaceae species globally, including our measurements on Cathaya. We applied the phylogenetic comparative methods to investigate: (i) the phylogenetic signal of the two key traits across Pinaceae species, and (ii) the trait–climate relationships and the photosynthesis–cavitation resistance relationship across Pinaceae species. We applied the polygenetic quantile regression (PQR) method to assess whether Cathaya showed eco-physiological outliers to its Pinaceae relatives in terms of cavitation resistance and photosynthetic capacity. It was found that P 50, and to a less extent, P n, had a strong phylogenetic signal consistent with niche conservation among Pinaceae species. Hydraulic safety largely determined non-threatened Pinaceae species' distribution across moisture gradients at the global scale. There was also an adaptive trade-off relationship between P n and P 50. Cathaya is a high cavitation resistant, low photosynthetic capacity species. It showed eco-physiological outliers to its Pinaceae relatives because it had lower P 50 and P n below the 10% quantile boundaries along moisture and/or temperature gradients; also, it was above the 90% quantile boundary of the P n and P 50 relationship across non-endangered Pinaceae species. The PQR output demonstrated that in the subtropical area of China characterized by abundant rainfall, Cathaya has extra high hydraulic safety, suggesting inefficiency of carbon economy associated with either competition or other life history strategies, which lead to its current endangered status. [ABSTRACT FROM AUTHOR]

To study the effects of elevated CO2 concentration ([CO2]) on relationships between nitrogen (N) nutrition and foliar gas exchange parameters, white birch (Betula papyrifera Marsh.) seedlings were exposed to one of five N-supply regimes (10, 80, 150, 220, 290 mg Nl-1) in either ambient [CO2] (360 µmol mol-1) or elevated [CO2] (720 µmol mol-1) in environment-controlled greenhouses. Foliar gas exchange and chlorophyll fluorescence were measured after 60 and 80 days of treatment. Photosynthesis showed a substantial down-regulation (up to 57%) in response to elevated [CO2] and the magnitude of the down-regulation generally decreased exponentially with increasing leaf N concentration. When measured at the growth [CO2], elevated [CO2] increased the overall rate of photosynthesis (Pn) and instantaneous water-use efficiency (IWUE) by up to 69 and 236%, respectively, but decreased transpiration (E) and stomatal conductance (gs) in all N treatments. However, the degree of stimulation of photosynthesis by elevated [CO2] decreased as photosynthetic down-regulation increased from 60 days to 80 days of treatment. Elevated [CO2] significantly increased total photosynthetic electron transport in all N treatments at 60 days of treatment, but the effect was insignificant after 80 days of treatment. Both Pn and IWUE generally increased with increasing leaf N concentration except at very high leaf N concentrations, where both Pn and IWUE declined. The relationships of Pn and IWUE with leaf N concentration were modeled with both a linear regression and a second-order polynomial function. Elevated [CO2] significantly and substantially increased the slope of the linear regression for IWUE, but had no significant effect on the slope for Pn. The optimal leaf N concentration for Pn and IWUE derived from the polynomial function did not differ between the CO2 treatments when leaf N was expressed on a leaf area basis. However, the mass-based optimal leaf N concentration for Pn was much lower in seedlings in elevated [CO2] than in ambient [CO2] (31.88 versus 37.00 mg g-1). Elevated [CO2] generally decreased mass-based leaf N concentration but had no significant effect on area-based leaf N concentration; however, maximum N concentration per unit leaf area was greater in elevated [CO2] than in ambient [CO2] (1.913 versus 1.547 g N m-2). [ABSTRACT FROM AUTHOR]

To investigate the interactive effects of atmospheric carbon dioxide concentration ([CO2]) and nutrition on photosynthesis and its acclimation to elevated [CO2], a two-way factorial experiment was carried out with two nutritional regimes (high- and low-nitrogen (N), phosphorus (P) and potassium (K)) and two CO2 concentrations (360 and 720 ppm) with white birch seedlings (Betula papyrifera Marsh.) grown for four months in environment-controlled greenhouses. Elevated [CO2] enhanced maximal carboxylation rate (Vcmax), photosynthetically active radiation-saturated electron transport rate (Jmax), actual photochemical efficiency of photosystem II (PSII) in the light (ΔF/Fm′) and photosynthetic linear electron transport to carboxylation (Jc) after 2.5 months of treatment, and it increased net photosynthetic rate (An), photosynthetic water-use efficiency (WUE), photosynthetic nitrogen-use efficiency (NUE) and photosynthetic phosphorus-use efficiency (PUE) after 2.5 and 3.5 months of treatment, but it reduced stomatal conductance (gs), transpiration rate (E) and the fraction of total photosynthetic linear electron transport partitioned to oxygenation (Jo/JT) after 2.5 and 3.5 months of treatment. Low nutrient availability decreased An, WUE, Vcmax, Jmax, triose phosphate utilization (TPU), (/Fm′ – F)//Fm′ and Jc, but increased Jo/JT and NUE. Generally, Vcmax was more sensitive to nutrient availability than Jmax. There were significant interactive effects of [CO2] and nutrition over time, e.g., the positive effects of high nutrition on An, Vcmax, Jmax, ΔF/Fm′ and Jc were significantly greater in elevated [CO2] than in ambient [CO2]. In contrast, the interactive effect of [CO2] and nutrition on NUE was significant after 2.5 months of treatment, but not after 3.5 months. High nutrient availability generally increased PUE after 3.5 months of treatment. There was evidence for photosynthetic up-regulation in response to elevated [CO2], particularly in seedlings receiving high nutrition. Photosynthetic depression in response to low nutrient availability was attributed to biochemical limitation (or increased mesophyll resistance) rather than stomatal limitation. Elevated [CO2] reduced leaf N concentration, particularly in seedlings receiving low nutrition, but had no significant effect on leaf P or K concentration. High nutrient availability generally increased area-based leaf N, P and K concentrations, but had negligible effects on K after 2.5 months of treatment. [ABSTRACT FROM AUTHOR]

One-year-old jack pine (Pinus banksiana Lamb.) and current-year white birch (Betula papyrifera Marsh.) seedlings were grown in ambient (360 ppm) or twice ambient (720 ppm) atmospheric CO2 concentration ([CO2]) and at three soil temperatures (Tsoil = 7, 17 and 27 °C initially, increased to 10, 20 and 30 °C two months later, respectively) in a greenhouse for 4 months. In situ foliar gas exchange, in vivo carboxylation characteristics and chlorophyll fluorescence were measured after 2.5 and 4 months of treatment. Low Tsoil suppressed net photosynthetic rate (Pn), stomatal conductance (gs) and transpiration rate (E) in jack pine in both CO2 treatments and gs and E in white birch in ambient [CO2], but enhanced instantaneous water-use efficiency (IWUE) in both species after 2.5 months of treatment. Treatment effects on gs and E remained significant throughout the 4-month study. Low Tsoil reduced maximal carboxylation rate (Vcmax) and PAR-saturated electron transport rate (Jmax) in jack pine in elevated [CO2] after 2.5 months of treatment, but not after 4 months of treatment. Low Tsoil increased actual photochemical efficiency of photosystem II (PSII) in the light (ΔF/Fm′) in jack pine, but decreased ΔF/Fm′ in white birch after 4 months of treatment. In response to low Tsoil, photosynthetic linear electron transport to carboxylation (Jc) decreased in jack pine after 2.5 months and in white birch after 4 months of treatment. Low Tsoil increased the ratio of the photosynthetic linear electron transport to oxygenation (Jo) to the total photosynthetic linear electron transport rate through PSII (Jo/JT) in both species after 2.5 months of treatment, but the effects became statistically insignificant in white birch after 4 months of treatment. High Tsoil decreased foliar N concentration in white birch. Elevated [CO2] increased Pn, IWUE and Jc but decreased Jo/JT in both species at both measurement times except Jc in white birch after 2.5 months of treatment. Elevated [CO2] also decreased gs and E in white birch at high Tsoil, Vcmax in both species and triose phosphate utilization in white birch at low Tsoil after 4 months of treatment, and ΔF/Fm′ in white birch after 2.5 months of treatment. Elevated [CO2] also increased foliar N concentration in both species. Low Tsoil caused no permanent damage to PSII in either species, but jack pine responded and acclimated to low Tsoil more quickly than white birch. Photosynthetic down-regulation and a decrease in photosynthetic electron transport to photorespiration occurred in both species in response to elevated [CO2]. [ABSTRACT FROM AUTHOR]