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<p class="MsoNormal"><span lang="EN-GB" style="font-family:&quot;Garamond Premr Pro&quot;">A pot experiment was made to study effects of ethylene glycol tetraacetic acid (EGTA, an inhibitor of Ca²⁺) and trifluoperazine (TFP, an inhibitor of calmodulin (CaM) on mycorrhizal colonization, growth performance, and chlorophyll, sucrose and glucose concentrations of four-month-old trifoliate orange (<i>Poncirus trifoliata</i>) seedlings under mycorrhization with <i>Rhizophagus intraradices</i>. Exogenous EGTA and TFP notably inhibited root mycorrhizal colonization, and the addition of EGTA also decreased soil hyphal length. In general, EGTA treatment decreased but TFP increased easily extractable glomalin-related soil protein (EE-GRSP) and total GRSP (T-GRSP) concentrations. In addition, EGTA and TFP applications generally significantly inhibited growth performance (height, stem diameter, leaf number, and shoot and root biomass), root traits (total length, surface area, volume, and number of 1^st, 2^nd and 3^rd order lateral root), and chlorophyll <i>a</i>,<i>b</i> and <i>a</i>+<i>b</i> concentrations, the mycorrhizal inoculation generally reversed the negative effects and markedly increased these variables, irrespective of whether the seedlings were applied by inhibitors or not. EGTA and TFP treatments generally inhibited sucrose and glucose levels of leaf and root, except that TFP application notably increased root glucose in AM and non-AM seedlings. AMF inoculation resulted in carbohydrate modification: decrease in leaf sucrose, increase in root sucrose and leaf glucose, as well increase in root glucose under no-inhibitor and EGTA conditions and decrease in root glucose under TFP. It suggests that Ca²⁺ and CaM were involved in mycorrhizal and root development in trifoliate orange.</span></p>