CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; and N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O fluxes along an altitudinal gradient in the northern Ecuadorean Andes: N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O consumption at higher altitudes