Elevation effects on the carbon budget of tropical mountain forests (S Ecuador): the role of the belowground compartment

Carbon storage and sequestration in tropical mountain forests and their dependence on elevation and temperature are not well understood. In an altitudinal transect study in the South Ecuadorian Andes, we tested the hypotheses that (i) aboveground net primary production (ANPP) decreases continuously with elevation due to decreasing temperatures, whereas (ii) belowground productivity (BNPP) remains constant or even increases with elevation due to a shift from light to nutrient limitation of tree growth. In five tropical mountain forests between 1050 and 3060 m a.s.l., we investigated all major above‐ and belowground biomass and productivity components, and the stocks of soil organic carbon (SOC). Leaf biomass, stemwood mass and total aboveground biomass (AGB) decreased by 50% to 70%, ANPP by about 70% between 1050 and 3060 m, while stem wood production decreased 20‐fold. Coarse and large root biomass increased slightly, fine root biomass fourfold, while fine root production (minirhizotron study) roughly doubled between 1050 and 3060 m. The total tree biomass (above‐ and belowground) decreased from about 320 to 175 Mg dry mass ha^?1, total NPP from ca. 13.0 to 8.2 Mg ha^?1 yr^?1. The belowground/aboveground ratio of biomass and productivity increased with elevation indicating a shift from light to nutrient limitation of tree growth. We propose that, with increasing elevation, an increasing nitrogen limitation combined with decreasing temperatures causes a large reduction in stand leaf area resulting in a substantial reduction of canopy carbon gain toward the alpine tree line. We conclude that the marked decrease in tree height, AGB and ANPP with elevation in these mountain forests is caused by both a belowground shift of C allocation and a reduction in C source strength, while a temperature‐induced reduction in C sink strength (lowered meristematic activity) seems to be of secondary importance.     

Phosphate Relations of Acetabularia: Phosphate Pools, Adenylate Phosphates and 32P Influx Kinetics

Steady state phosphate relations are determined for the marinealga Acetabularia mediterranea with respect to cellular phosphatepools and phosphate transport. About 20% of the cellular acid-labilephosphate is found in the cell wall fraction (low speed sediment).By the use of cytoplasm-depleted cell segments, it isa establishedthat only about 10% of the total intracellular phosphate islocalized in the vacuole when cells are bathed in normal phosphateconcentration (<30 µM). Measurements of ATP, ADP, AMPand inorganic phosphate (Pj) in the entire cytoplasm and inisolated chloroplasts has enabled the calculation of the cytosolicadenylate energy charge (0.7–0.9) and phosphate potential(110–170 mV). Influx of ³²P, displays complex kinetics.Four components for uptake (approximate time constants: (A)1 s, (B) 20 s, (C) 300 s and (D) 3000 s) are tentatively identified.Focusing on the faster components, B and C, and possibly evenA, appear to be metabolically-linked, as judged by their sensitivityto temperature and to the inhibitor 2, 4-dinitrophenol. Thesethree components of influx are proportional to the externalP, concentration for values <30 µM, but B and C tendto saturate at higher concentrations. The results are discussedwith respect to the energetics of transport at the plasmalemmaof Acetabularia, especially the activity of the electrogenicCI-ATPase. Key words: Acetabularia, Energy charge, Phosphate pools, Phosphate potential, Phosphate uptake kinetics     

Mode of Action of the Crustacean Hyperglycemic Hormone

Glucose levels in crayfish hemolymph are enhanced by the crustaceanhyperglycemic hormone (CHH); at present there is some evidencethat this action is mediated by cyclic nucleotides. CHH is capableof stimulating adenylate cyclase in the abdominal muscle. Thereis an increase in cyclic AMP and cyclic GMP contents in hepatopancreasand abdominal muscle after CHH injection. Cyclic nucleotidesare able to evoke the same reaction as CHH in vivo and in vitro.Cyclic nucleotide-dependent protein kinases are activated bythe hormone, which leads to a phosphorylation and thereforeinhibition of glycogen synthase. So far, an effect of purifiedhormone on phosphorylase and phosphorylase kinase has not beendemonstrated in the abdominal muscle.