Soil phosphorus accumulation changes with decreasing temperature along a 2300 m altitude gradient

Understanding the abundance of organic P in soil is a prerequisite for predicting the effects of climate change on P dynamics and availability in cold alpine regions. We sampled plant roots (up to 40 cm depth) and soils (100 cm depth) in grasslands along a 2300 m altitude gradient (1286–3589 m above sea level, mean annual temperature (MAT) from 9 to 0.3 °C) between alpine steppes on the Loess Plateau and alpine meadows on the Tibetan Plateau. A modified Hedley P fractionation in combination with root and microbial P, alongside phosphatase activity, was used to characterize P transformations depending on climate. Both the roots and microorganisms stored more P and produced higher phosphatase activity in cold meadow than in warm steppe soils. Total inorganic P (Pi) content decreased in cold meadow (MAT < 3 °C) compared with warm steppe soils because of the decrease of moderately labile Pi (extracted with diluted HCl) in cold meadow soils. Available P (NaHCO3) and labile Pi (NaOH) contents increased upslope, whereas the recalcitrant Pi (concentrated HCl) contents remained stable at all sites down to 100 cm soil depth. Labile (NaHCO3), moderately labile (NaOH) and recalcitrant (concentrated HCl) organic P (Po) contents sharply increased in cold meadow compared with warm steppe soils. The residue P in the 0–100 cm along the temperature gradient was similar to that of all Po fractions. The Po proportion in the total P was less than 10 % at sites with a MAT above 3 °C, but sharply increased up to 50 % at sites with a MAT below 0.7 °C. The greater root and microbial P uptake versus slower Po mineralization in cold meadows than in warm steppes increase the incorporation of Pi into organic pools in cold alpine areas. This accumulation of Po forms is a mechanism to prevent P losses by leaching as inorganic forms. The increased plant available P in cold meadows was associated with the increased phosphatase activity and Po contents compared with warm steppe soils. We conclude that the on-going climate warming could stimulate P cycling more in cold meadows than in warm steppe regions because Po dominated the total soil P in cold areas. © 2020 Elsevier B.V

Pharmacological analysis of G-protein activation mediated by guinea-pig recombinant 5-HT(1B) receptors in C6-glial cells: similarities with the human 5-HT(1B) receptor

1. The guinea-pig recombinant 5-hydroxytryptamine(1B) (gp 5-HT(1B)) receptor stably transfected in rat C6-glial cells was characterized by monitoring G-protein activation in a membrane preparation with agonist-stimulated [(35)S]-GTPγS binding. The intrinsic activity of 5-HT receptor ligands was compared with that determined previously at the human recombinant 5-HT(1B) (h 5-HT(1B)) receptor under similar experimental conditions. 2. Membrane preparations of C6-glial/gp 5-HT(1B) cells exhibited [(3)H]-5-carboxamidotryptamine (5-CT) and [(3)H] - N- [4-methoxy-3,4 - methylpiperazin-1-yl) phenyl] -3 - methyl - 4-(4 - pyridinyl)benzamide (GR 125743) binding sites with a pK(d) of 9.62 to 9.85 and a B(max) between 2.1 to 6.4 fmol mg(−1) protein. The binding affinities of a series of 5-HT receptor ligands determined with [(3)H]-5-CT and [(3)H]-GR 125743 were similar. Ligand affinities were comparable to and correlated (r(2): 0.74, P<0.001) with those determined at the recombinant h 5-HT(1B) receptor. 3. [(35)S]-GTPγS binding to membrane preparations of C6-glial/gp 5-HT(1B) cells was stimulated by the 5-HT receptor agonists that were being investigated. The maximal responses of naratriptan, zolmitriptan, sumatriptan, N-methyl-3-[pyrrolidin-2(R)-ylmethyl]-1H-indol-5-ylmethylsulphonamide (CP122638), rizatriptan and dihydroergotamine were between 0.76 and 0.85 compared to 5-HT. The potency of these agonists showed a positive correlation (r(2): 0.72, P=0.015) with their potency at the recombinant h 5-HT(1B) receptor. 1-naphthylpiperazine, (±)-cyanopindolol and (2′-methyl-4′-(5-methyl[1,2,4] oxadiazole-3-yl)biphenyl-4-carboxylic acid [4-methoxy-3-(4-methylpiperazin-1-yl)phenyl]amide (GR 127935) elicited an even smaller response (E(max): 0.32 to 0.63). 4. The ligands 1′-methyl-5-(2′-methyl-4′-(5-methyl-1,2,4-oxadiazole-3-yl) biphenyl-4-carbonyl)-2,3,6,7-tetrahydrospiro [furo[2,3-f]indole-3-spiro-4′-piperidine] (SB224289), methiothepin and ritanserin displayed inhibition of basal [(35)S]-GTPγS binding at concentrations relevant to their binding affinity for the gp 5-HT(1B) receptor. Methiothepin and SB224289 behaved as competitive antagonists at gp 5-HT(1B) receptors; pA(2) values were 9.74 and 8.73, respectively when 5-HT was used as an agonist. These estimates accorded with the potencies measured in antagonism of zolmitriptan-mediated inhibition of forskolin-stimulated cyclic AMP formation. Ketanserin acted as a weak antagonist (pK(B): 5.87) at gp 5-HT(1B) receptors. 5. In conclusion, the recombinant gp 5-HT(1B) receptor shares important pharmacological similarities with the recombinant h 5-HT(1B) receptor. The finding that negative activity occurs at these receptors further suggests that SB224289, methiothepin and ritanserin are likely to be inverse agonists