Is there coordination of leaf and fine root traits at local scales? A test in temperate forest swamps

Abstract

Examining the coordination of leaf and fine root traits not only aids a better understanding of plant ecological strategies from a whole‐plant perspective, but also helps improve the prediction of belowground properties from aboveground traits. The relationships between leaf and fine root traits have been extensively explored at global and regional scales, but remain unclear at local scales. Here, we measured six pairs of analogous leaf and fine root traits related to resource economy and organ size for coexisting dominant and subordinate vascular plants at three successional stages of temperate forest swamps in Lingfeng National Nature Reserve in the Greater Hinggan Mountains, NE China. Leaf and fine root traits related to resource acquisition (e.g., specific leaf area [SLA], leaf N, leaf P, root water content, and root P) decreased with succession. Overall, we found strong linear relationships between leaf dry matter content (LDMC) and root water content, and between leaf and root C, N, and P concentrations, but only weak correlations were observed between leaf area and root diameter, and between SLA and specific root length (SRL). The strong relationships between LDMC and root water content and between leaf and root C, N, and P held at the early and late stages, but disappeared at the middle stage. Besides, C and P of leaves were significantly correlated with those of roots for woody plants, while strong linkages existed between LDMC and root water content and between leaf N and root N for herbaceous species. These results provided evidence for the existence of strong coordination between leaf and root traits at the local scale. Meanwhile, the leaf–root trait relationships could be modulated by successional stage and growth form, indicating the complexity of coordination of aboveground and belowground traits at the local scale.

Above- and Belowground Plant Functional Composition Show Similar Changes During Temperate Forest Swamp Succession

“…The main drivers of forest swamp succession are the expansion of Sphagnum , decreases in soil pH and nutrient availability and changes in water supply ( Rydin and Jeglum, 2013 ). The early successional stage (present day) was characterized by minerotrophic soils with a high soil pH and water-table level and dominant species such as Larix gmelini , Betula platyphylla , and Carex schmidtii ( Hu et al, 2019a ). The middle successional stage (hundreds of years) had intermediate soil nutrient availability and pH with a moderate water table level and an abundance of L. gmelini , Vaccinium spp., and mosses.…”

“…The three forest swamps we chose to represent succession across the riparian zone were located close to one another (<5 km apart). As described in section "Study Region, " there was a significant decrease in soil pH and nutrient availability along the successional gradient (Supplementary Figure 2; Rydin and Jeglum, 2013;Hu et al, 2019a). To determine the species composition, we randomly located five replicated plots (10 × 10 m) within each type of forest swamp (Supplementary Figure 1).…”

“…However, our understanding of functional diversity of fine roots lags that of leaves, mainly because fine roots are more difficult to collect and measure ( Pérez-Harguindeguy et al, 2013 ). A number of studies have reported strong coordination between leaf and root traits ( Freschet et al, 2010 ; Liu et al, 2010 ; Valverde-Barrantes et al, 2017 ; Hu et al, 2019a ) where patterns of means and diversity of functional root traits were thought to be similar to those of leaf traits. However, some studies have reported instances where leaf and root traits were weakly correlated ( Geng et al, 2014 ; Marañón et al, 2020 ), such that root traits were considered more than just analogs of leaf traits ( Bergmann et al, 2017 ; De Long et al, 2019 ).…”

“…Such chronosequences occur in forest swamps, which, however, have been largely overlooked from a functional trait perspective. Primary succession of temperate forest swamps is different from that of other ecosystems and the major drivers of successional changes are the overgrowth of moss and decrease in soil pH, which lower the soil nutrient availability ( van der Valk, 2006 ; Rydin and Jeglum, 2013 ; Hu et al, 2019a ). Furthermore, forest swamps are located in many parts of the boreal and temperate zones, and are vulnerable to environmental changes ( Erwin, 2009 ).…”

“…As the succession of temperate forest swamps was mainly characterized by the obvious changes in understory plants, here we only focused on the understory community. Forest swamps tend to shift from nutrient-rich to nutrient-poor conditions as succession progresses ( Hu et al, 2019a ), and plant functional strategies have been reported to be closely related to soil nutrients ( Ordoñez et al, 2009 ; Zemunik et al, 2015 ). Thus, we first hypothesized that abundance-weighted resource-acquisitive plant functional traits would decrease with succession, while resource-conservative plant traits would increase regardless of whether they are leaf or root traits.…”