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Table 2 Comparison of acid-base, systemic and respiratory variables among the different acclimation groups.

From: Physiological responses of Daphnia pulex to acid stress

Physiological Variable pH 7.8 acclimation pH 6.0 acclimation pH 5.5 acclimation Significant difference among acclimation groups
pH 8.334 ± 0.006 8.177 ± 0.025 8.104 ± 0.008# ***
(kPa) 0.56 ± 0.02 0.56 ± 0.02 0.33 ± 0.04# ***
(mM) 20.9 ± 0.7 14.6 ± 0.5# 7.2 ± 0.9# ***
(mM) 0.153 ± 0.005 0.074 ± 0.003 0.031 ± 0.007 ***
βA (meq L-1 pH-1) 2.0 5.1 2.2 not tested
βB (meq L-1 pH-1) 48.1 33.5 16.6 not tested
βC (meq L-1 pH-1) 0.70 0.34 0.14 not tested
βT (meq L-1 pH-1) 51.5 39.4 19.1 not tested
fH (min-1) 205 ± 10 246 ± 18 299 ± 12# **
fA (min-1) 374 ± 32 427 ± 58 500 ± 6# *
(nmol h-1 mm-3) 1.53 ± 0.09 1.95 ± 0.07†# 1.41 ± 0.14 **
  1. PCO2, CO2 partial pressure; βA, buffer value of the non-bicarbonate buffer; βB and βC, bicarbonate and carbonate buffer value; βT, total buffer value (= βA + βB + 2βC); fH, heart rate; fA, appendage beating rate; , specific oxygen consumption rate (per cubic body length). Data are expressed as means ± standard error, except for the buffer values which are given as means. The number of independent determinations (N) is 3, if not otherwise indicated. The PCO2 was calculated from the mean pH value and the three corresponding buffer curves (Table 1). Asterisks indicate significant differences among the acclimation groups (*P < 0.05, **P < 0.01, ***P < 0.001). #significant difference between an acid-stress (pH 6.0 or pH 5.5) group and the control (pH 7.8) group. N = 4.