Spatial and temporal effects of nitrogen addition on root morphology and growth in a boreal forest

Abstract

The production and turnover of fine roots play a critical role in regulating underground carbon (C) cycling of terrestrial ecosystems, which are a biological feature in regulating the capacity of plant to capture soil nutrients. Although the importance of fine root production (FRP) and turnover (FRT) to whole-plant and ecosystem C cycling is increasingly recognized, their response to nitrogen (N) deposition remains unclear. To understand how N addition affects the FRP and FRT of fine roots, a field experiment was conducted with four N treatment levels (0, 2.5, 5.0, and 7.5gNm−2yr−1) to quantify the effects of N deposition on fine root dynamics and vertical allocation in a boreal forest using the minirhizotron technique. Our results showed that N deposition significantly decreased total number of live and dead fine roots and total surface area of live fine roots in topsoil layers (0–20cm soil depth), while increased in subsoil layers (20–40cm soil depth) during 2015–2016. Average diameter of fine root was increased by N addition particularly in subsoil layers. The FRP rate was reduced by N addition in the topsoil, but increased in the subsoil layers, whereas patterns of their seasonal changes were not affected in both soil layers. The FRT rate tended to decrease under N addition compared with control in both soil layers during the observation years, potentially indicating a slower underground C cycle with N addition. Moreover, fine roots distributed more deeply in the soil due to N addition, indicating fine roots may through self-regulation and change of growth strategy to face environment stressor.