Summary: Leaf dark respiration (R_dark) is an important yet poorly quantified component of the global carbon cycle. Given this, we analyzed a new global database of R_dark and associated leaf traits. Data for 899 species were compiled from 100 sites (from the Arctic to the tropics). Several woody and nonwoody plant functional types (PFTs) were represented. Mixed‐effects models were used to disentangle sources of variation in R_dark. Area‐based R_dark at the prevailing average daily growth temperature (T) of each site increased only twofold from the Arctic to the tropics, despite a 20°C increase in growing T (8–28°C). By contrast, R_dark at a standard T (25°C, R_dark²⁵) was threefold higher in the Arctic than in the tropics, and twofold higher at arid than at mesic sites. Species and PFTs at cold sites exhibited higher R_dark²⁵ at a given photosynthetic capacity (V_cmax²⁵) or leaf nitrogen concentration ([N]) than species at warmer sites. R_dark²⁵ values at any given V_cmax²⁵ or [N] were higher in herbs than in woody plants. The results highlight variation in R_dark among species and across global gradients in T and aridity. In addition to their ecological significance, the results provide a framework for improving representation of R_dark in terrestrial biosphere models (TBMs) and associated land‐surface components of Earth system models (ESMs).

Summary: We examined whether variations in photosynthetic capacity are linked to variations in the environment and/or associated leaf traits for tropical moist forests (TMFs) in the Andes/western Amazon regions of Peru. We compared photosynthetic capacity (maximal rate of carboxylation of Rubisco (V_cmax), and the maximum rate of electron transport (J_max)), leaf mass, nitrogen (N) and phosphorus (P) per unit leaf area (M_a, N_a and P_a, respectively), and chlorophyll from 210 species at 18 field sites along a 3300‐m elevation gradient. Western blots were used to quantify the abundance of the CO₂‐fixing enzyme Rubisco. Area‐ and N‐based rates of photosynthetic capacity at 25°C were higher in upland than lowland TMFs, underpinned by greater investment of N in photosynthesis in high‐elevation trees. Soil [P] and leaf P_a were key explanatory factors for models of area‐based V_cmax and J_max but did not account for variations in photosynthetic N‐use efficiency. At any given N_a and P_a, the fraction of N allocated to photosynthesis was higher in upland than lowland species. For a small subset of lowland TMF trees examined, a substantial fraction of Rubisco was inactive. These results highlight the importance of soil‐ and leaf‐P in defining the photosynthetic capacity of TMFs, with variations in N allocation and Rubisco activation state further influencing photosynthetic rates and N‐use efficiency of these critically important forests.

We have recently reported the existence of binding sites in soybean membranes for a β‐glucan fraction derived from the fungal pathogen Phytophthora megasperma f. sp. glycinea, which may play a role in the elicitor‐mediated phytoalexin response of this plant [Schmidt, W. E. & Ebel, J. (1987) Proc. Natl Acad. Sci. USA 84, 4117–4121]. The specificity of β‐glucan binding to soybean membranes has now been investigated using a variety of competing polyglucans and oligoglucans of fungal origin. P. megaspermaβ‐glucan binding showed high apparent affinity for branched glucans with degrees of polymerization greater than 12. Binding affinity showed good correlation with elicitor activity as measured in a soybean cotyledon bioassay. Modification of the glucans at the reducing end with phenylalkylamine reagents had no effect on binding affinity. This characteristic was used to synthesize an oligoglucosyl tyramine derivative suitable for radioiodination. The ²⁵¹I‐glucan (15–30 Ci/mmol) provided higher sensitivity and lower detection limits for the binding assays while behaving in a manner identical to the [³H]glucan used previously. More accurate determinations of the K_d value for glucan binding indicated a higher affinity than previously shown (37 nM versus 200 nM). The ²⁵¹I‐glucan was used to provide the first reported evidence of specific binding of a fungal β‐glucan fraction in vivo to soybean protoplasts. The binding affinity to protoplasts proved identical to that found in microsomal fractions.