Leaf carbon isotope ratios and leaf mineral composition (Ca, K, Mg, Mn, N, and P) were measured on the dominant species along an irradiance cline in a subtropical monsoon forest of southern China. This irradiance cline resulted from disturbance caused by fuel-harvesting. Leaf carbon isotope ratios increased from undisturbed to disturbed sites for all species, indicating that leaf intercellular CO concentrations decreased and leaf water use efficiencies increased along this cline. Nitrogen and magnesium levels were lower in leaves of species on the disturbed sites, but there were no clear patterns for calcium, potassium, phosphorus or manganese.
Carbon isotope ratios were used to survey the distribution of photosynthetic pathways among taxa, the relationship between photosynthetic pathway and habitat light levels, and the relationship between intercellular CO levels of C plants and habitat light levels within a subtropical monsoon forest in southern China. Of 128 species, most (94) possessed the C photosynthetic pathway; 33 species possessed the C pathway and all of these were restricted to high light locations. There was one epiphytic CAM species. The C species were classified as occurring in open, intermediate, and closed canopy sites. Among C species, carbon isotope ratios tended to become more negative with decreasing light availability in the habitat.
Guzmania lingulata (L.) Mez. 'Cherry' were grown in coco chips and fertigated with half-strength Hoagland solution containing various concentrations of boric acid. Excessive boron induced changes in growth, relative chlorophyll content, and leaf anatomy were investigated. Plants treated with 5 mg·L -1 or higher boric acid concentration had reduced SPAD-502 readings and Fv/Fm values and increased leaf necrosis in the lower leaves. Boron was distributed unevenly within a leaf, with the maximum concentration in the leaf tip. Increased necrotic length and new leaves with necrosis were evident where average whole leaf boron concentration was higher than 170 µg·g -1 on dry weight basis. More leaf growth and higher transpiration or stomatal conductance were recorded in plants under 40% (average 676 µmol·m -2 ·s -1 PPF at noon) than 76% (average 270 µmol·m -2 ·s -1 PPF at noon) shade. Excessive boron was not found to affect epidermal cells or water storage tissue, but caused browning and shriveling of the chlorenchyma cells.
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