Reactive N additions and their effects in microbial activity and soil respiration under a Nothofagus glauca (Phil.) Krasser forest of Chile
Authors: Fuentes Juan-Pablo , Celedón Daniela , Bown Horacio , Martínez Amanda , Vega Marina 
Published: March 2020

&lt;p&gt;Increases in available soil N under forests can affect several ecosystem functions including soil CO&lt;sub&gt;2 &lt;/sub&gt;fluxes and microbial activity. Most of the studies, concerning reactive N deposition in natural ecosystems, are located in the northern hemisphere, meanwhile little is known in southern forest ecosystems, including deciduous &lt;em&gt;Nothofagus&lt;/em&gt; forests. We evaluated the effect of reactive N additions (N-NO&lt;sub&gt;3&lt;/sub&gt; broadcasted under 20 trees at a rate of 400 Kg ha&lt;sup&gt;-1 &lt;/sup&gt;yr&lt;sup&gt;-1&lt;/sup&gt;) in soil CO&lt;sub&gt;2&lt;/sub&gt; fluxes &lt;span&gt;&lt;span&gt;(&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;&lt;em&gt;Rs&lt;/em&gt;&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;, &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;&amp;#956;mol CO&lt;/span&gt;&lt;/span&gt;&lt;sub&gt;&lt;span&gt;&lt;span&gt;2&lt;/span&gt;&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;&lt;span&gt; m&lt;/span&gt;&lt;/span&gt;&lt;sup&gt;&lt;span&gt;&lt;span&gt;-2&lt;/span&gt;&lt;/span&gt;&lt;/sup&gt;&lt;span&gt;&lt;span&gt; s&lt;/span&gt;&lt;/span&gt;&lt;sup&gt;&lt;span&gt;&lt;span&gt;-1&lt;/span&gt;&lt;/span&gt;&lt;/sup&gt;&lt;span&gt;&lt;span&gt;)&lt;/span&gt;&lt;/span&gt;, &lt;span&gt;microbial biomass C (MBC), and related ecophysiological indexes, in the most septentrional &lt;/span&gt;&lt;span&gt;&lt;em&gt;N. glauca&lt;/em&gt;&lt;/span&gt;&lt;span&gt; forest of Chile &lt;/span&gt;&lt;span&gt;&lt;span&gt;(19S 310464 S, 6213139 &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;W&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;). &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;Twenty additional &lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;&lt;em&gt;N. glauca&lt;/em&gt;&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; trees,&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;with no N additions, were used as controls.&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; After seven months of N-application, soil respiration was significantly higher (p&lt;0.001) under the N-fertilized trees than in the control trees. &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;Soil MBC, the ratio &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;betwee&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;n &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;MBC and soil organic C (&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;&lt;em&gt;q&lt;/em&gt;&lt;/span&gt;&lt;/span&gt;&lt;sub&gt;&lt;span&gt;&lt;span&gt;&lt;em&gt;mic&lt;/em&gt;&lt;/span&gt;&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;&lt;span&gt;), and the ratio between cummulative basal respiration and SOC (&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;&lt;em&gt;q&lt;/em&gt;&lt;/span&gt;&lt;/span&gt;&lt;sub&gt;&lt;span&gt;&lt;span&gt;&lt;em&gt;min&lt;/em&gt;&lt;/span&gt;&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;&lt;span&gt;) &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;decreased significantly (p&lt;0.05) in the N-enriched trees, but only after two years of N application. Basal respiration and the metabolic quotient &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;&lt;em&gt;qCO&lt;/em&gt;&lt;/span&gt;&lt;/span&gt;&lt;sub&gt;&lt;span&gt;&lt;span&gt;&lt;em&gt;2&lt;/em&gt;&lt;/span&gt;&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;&lt;span&gt; were not affected by N &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;enrichment. &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;Even though soil respiration increased, &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;N enrichment inhibited microbial activity. Temporal variations in MBC, basal respiration, and &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;&lt;em&gt;q&lt;/em&gt;&lt;/span&gt;&lt;/span&gt;&lt;sub&gt;&lt;span&gt;&lt;span&gt;mic&lt;/span&gt;&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;&lt;span&gt; were also found and were associated to water availability.&lt;/span&gt;&lt;/span&gt;&lt;/p&gt;