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Spatial patterns of leaf angle distribution covary with canopy fluorescence yield, reflectance indices, and leaf chlorophyll content, in a mixed temperate forest
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Summary Nonstructural carbohydrate (NSC) concentrations might reflect the strategies described in the leaf economic spectrum (LES) due to their dependence on photosynthesis and respiration.We examined if NSC concentrations correlate with leaf structure, chemistry, and physiology traits for 114 species from 19 sites and 5 biomes around the globe.Total leaf NSC concentrations varied greatly from 16 to 199 mg g−1dry mass and were mostly independent of leaf gas exchange and the LES traits. By contrast, leaf NSC residence time was shorter in species with higher rates of photosynthesis, following the fast‐slow strategies in the LES. An average leaf held an amount of NSCs that could sustain one night of leaf respiration and could be replenished in just a few hours of photosynthesis under saturating light, indicating that most daily carbon gain is exported.Our results suggest that NSC export is clearly linked to the economics of return on resource investment.more » « less
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Abstract Background and AimsLeaf abscission is the process whereby plants actively shed leaves through physical detachment at the abscission zone (AZ). Leaf abscission is generally preceded by senescence, during which there is an active reclamation of leaf nutrients. The physiological regulation of leaf abscission remains poorly studied in trees, with a suite of environmental and endogenous signals believed to regulate the process. Here, we sought to characterize the role of water status, leaf gas exchange, senescence and the phytohormone abscisic acid (ABA) in regulating leaf abscission in temperate trees. MethodsWe developed a novel method to quantify AZ competency (AZC) and simultaneously measured leaf gas exchange, chlorophyll content, water potential, AZC and ABA levels from late summer until leaf death in four temperate tree species representing deciduous, brevi-deciduous, and marcescent leaf habits. We tested for associations between changes in key physiological traits and AZC in all species. Key ResultsThe two deciduous species showed contrasting physiological patterns leading to leaf abscission: one species degraded chlorophyll and ceased photosynthesis before complete AZC, while the other retained chlorophyll and continued photosynthesis until complete AZC. The brevi-deciduous species degraded most chlorophyll but developed AZC gradually over a longer period. The marcescent species’ leaves fully senesced but did not develop AZC. ConclusionsThese findings demonstrate that leaf senescence and abscission are distinct and variably timed processes across temperate tree species. These results have implications for predicting future leaf lifespan as the climate changes, with the characterization of physiological diversity in the regulation of leaf abscission profoundly understudied.more » « less
