Which processes drive fine root elongation in a natural mountain forest ecosystem?

Abstract

Background: Quantifying the dynamics of root growth is vital when characterising the role of vegetation in carbon cycling. Aims: We examined the temporal dynamics of root growth and responses to spatial (altitude, forest patchiness and soil depth) and biological factors (root diameter and root topology) in mid-montane and upper montane coniferous forest ecosystems. Methods: Using rhizotrons, two indicators were investigated: occurrence, i.e. the proportion of roots which had elongated since the previous measurement of root elongation (%), and daily root elongation speed (mm d?1) once the elongation occurred. Results: Spatial factors had a limited effect on root growth. Roots in the same diameter class possessed different elongation speeds and this was related to topological ranking, reflecting a disparity in physiological activity. Temporally, the occurrence of root elongation reached a peak in May-October (up to 90%) and sharply dropped after October 2010. The maximum root elongation speed (mean: 3.0 mm d?1) was measured in July-August. Root growth was the most inactive in February 2011 but some roots still exhibited positive elongation speeds (mean: 0.5 mm d?1). Occurrence and speed of elongation reacted differently with regard to environmental and biological factors. Conclusions: Temporal and biological factors contributed more towards explaining the variability of root growth than spatial factors. In future studies, both occurrence and speed of elongation should be used to characterise root growth. (Résumé d'auteur

Does mycorrhizal inoculation improve plant survival, aggregate stability, and fine root development on a coarse‐grained soil in an alpine eco‐engineering field experiment?

“…This assumption is supported by field measurements, showing low soil temperatures and more dry soil conditions during the dormant period 2010/2011 (Figure ). Comparable relations between root growth/development and (soil) climate were discussed in several studies [e.g., Pregitzer et al ., ; Alvarez‐Uria and Körner , ; Mao et al ., , ]. Both the coherent decrease of ASC and RLD (Figures a and b) and the significant relationship between ASC and RLD suggest (Figure a) that RLD is crucial for the formation of water‐stable aggregates in our experiment.…”

“…Even fine roots can store starch as well as nutrients, and the bigger the diameter, the more important this function is [ Danjon et al ., ]. When the photosynthesis rate is not sufficient, the stored starch can be used for root growth in times of low supplies, like early spring or winter season [ Danjon et al ., ; Mao et al ., , ].…”

Fine Root Abundance and Dynamics of Stone Pine (Pinus cembra) at the Alpine Treeline Is Not Impaired by Self-shading

“…Furthermore, several authors detected no root productivity differences, or even higher fine root growth rates, at the treeline compared to stands at lower elevation (Graefe et al, 2008; Hertel and Schöling, 2011b; Mao et al, 2013). This apparent contradiction calls for a detailed study of root zone temperatures and tree root growth at the alpine treeline.…”

Tree root dynamics in montane and sub-alpine mixed forest patches

“…Responses of root elongation and longevity to climatic variations have usually been studied at the species level (Barlow and Rathfelder, 1985), or artificially in growth chambers (Lahti et al, 2005;Alvarez-Uria and Körner, 2007), which do not reflect the true conditions found in natural or mixed forests (Kubisch et al, 2017). Tree roots in heterogeneous temperate forest ecosystems can initiate and elongate during the winter, even when mean daily air temperatures are below freezing, as long as the soil temperature does not drop below 0 °C (Mao et al, 2013a;Radville et al, 2016). Optimal soil temperatures for conifer root growth vary from 6 to 15 °C [Picea abies (L.) Karst] and from 10 to 20 °C (Abies sp.)…”

“…Optimal soil temperatures for conifer root growth vary from 6 to 15 °C [Picea abies (L.) Karst] and from 10 to 20 °C (Abies sp.) (Lopushinsky and Ma, 1990;Lyr, 1996;Alvarez-Uria and Körner, 2007;Nagelmüller et al, 2016), but periods of low or zero activity occur throughout the year (Mao et al, 2013a;Wang et al, 2018). However, few studies have characterized and quantified root active and dormant periods in the field, partially because of the relatively short duration of experimental studies on root growth and the assumption that root dormancy is synchronous with that of shoot dormancy (Eissenstat et al, 2005;Graefe et al, 2008;Abramoff and Finzi, 2015;Radville et al, 2016).…”