Global responses of fine root biomass and traits to plant species mixtures in terrestrial ecosystems

Abstract

Aim Fine root traits underpin terrestrial ecosystem functioning. Despite ongoing plant diversity loss due to anthropogenic activities, our understanding of the effects of plant diversity on fine root traits remains elusive. We addressed: (a) Do fine roots modify their traits in response to species mixtures? (b) Do these responses change with the species richness in mixtures, stand age, and soil depth? (c) Do plant‐mixture induced responses of root traits differ across terrestrial ecosystems? Location Global. Time period Publication years: 1985–2019. Major taxa studied Plants. Methods We conducted a global meta‐analysis of 852 paired observations from 103 published studies to assess the effects of species mixtures on fine root biomass and traits (including root/shoot ratio, community‐weighted mean rooting depth, root length density, specific root length, mean root diameter and root nitrogen content). Results We found that the effects of species mixtures were highly dependent on species richness in mixtures, stand age, and soil depth. The positive effects of species mixtures on root biomass increased with species richness, soil depth, and mean annual temperature. Species mixture effects on root length density shifted from negative to positive with increasing stand age and soil depth and with decreased temperatures. The effects of species mixtures on specific root length shifted from positive to negative with increasing species richness and soil depth, and from negative to positive with increasing stand age. Main conclusions Our meta‐analysis highlights that the community‐level consequences of changes in plant diversity on fine root traits are not consistent, and that predicting these consequences requires taking into account the extent of changes in plant species richness, stand age, soil depth investigated, background climates, and importantly, particular fine root traits.

Tree species mixing reduces biomass but increases length of absorptive fine roots in European forests

“…Yet, our results show underyielding of FRB (Figures 1a and 2a) and no overall changes in RLD (Figures 1b and 2b) across all four forest types. These results contrast with several previous studies in mature (semi‐)natural forests where either a higher FRB in mixtures or no differences across richness levels have been observed (Brassard et al., 2013; Finér et al., 2017; Meinen et al., 2009a; Peng & Chen, 2020).…”

“…Error bars represent one standard error of the mean. Asterisks indicate significant differences between monospecific and mixed stands for the entire soil profile (**p < 0.01, ns p > 0.1) previous studies in mature (semi-)natural forests where either a higher FRB in mixtures or no differences across richness levels have been observed (Brassard et al, 2013;Finér et al, 2017;Meinen et al, 2009a;Peng & Chen, 2020).…”

“…Brassard et al., 2013; Sun et al., 2017; Valverde‐Barrantes et al., 2015; Zeng et al., 2020) or lower biomass (Archambault et al., 2019; Bolte & Villanueva, 2006), or no changes in mixtures compared to pure stands (e.g. Bauhus et al., 2000; Finér et al., 2017; Ma & Chen, 2016; Peng & Chen, 2020). These inconsistencies may have occurred for a number of reasons.…”

Talking with Strangers: Improving Serianthes Transplant Quality with Interspecific Companions

“…Such biodiversity effects in modern cropping systems are supported by ancient origins and contemporary ecological research [6]. Other experimental and observational studies have advanced our understanding of how such root behavior contributes to the over-yielding that often accompanies biodiversity [4,[7][8][9][10][11]. Some of these studies indicate mechanisms other than nutrient enrichment.…”

Assembly history modulates vertical root distribution in a grassland experiment

“…However, the effect of plant diversity on the vertical distribution of roots has not been as clear, with most of the roots accumulating at the top of the soil (Mommer et al, 2010;de Kroon et al, 2012;Luo et al, 2021). Recently, two meta-analyses showed that increasing plant species richness does not seem to affect the rooting depth of plant communities (Barry et al, 2020;Peng and Chen, 2021). With the exception of one study that reported that high diversity plots in a grassland field experiment had a higher proportion of root biomass allocated to deeper soil layers (Mueller et al, 2013), there is little evidence supporting an increase in vertical root niche differentiation with increased plant diversity in either grasslands (Mommer et al, 2010;Ravenek et al, 2014;Oram et al, 2018) or forests (Valverde-Barrantes et al, 2015;Luo et al, 2021;Zeng et al, 2021).…”