Changes in mass allocation play a more prominent role than morphology in resource acquisition of the rhizomatous Leymus chinensis under drought stress

Abstract

Background and aims: Plants can respond to drought by changing their relative investments in the biomass and morphology of each organ. The aims of this study were to quantify the relative contribution of changes in morphology vs. allocation and determine how they affect each other. These results should help us understand the mechanisms that plants use to respond to drought events.

Methods: In a glasshouse experiment, we applied a drought treatment (well-watered vs. drought) at early and late stages of plant growth, leading to four treatment combinations (well-watered in both early and late periods, WW; drought in the early period and well-watered in the late period, DW; well-watered in the early period and drought in the late period, WD; drought in both early and late periods, DD). We used the variance partitioning method to compare the contribution of organ (leaf and root) biomass allocation and morphology to the leaf area ratio, root length ratio and root area ratio, for the rhizomatous grass Leymus chinensis (Trin.) Tzvelev.

Key results: Compared with the continuously well-watered treatment, the leaf area ratio, root length ratio and root area ratio showed increasing trends under various drought treatments. The contribution of leaf mass allocation to leaf area ratio differed among the drought treatments and was 2.1- to 5.3-fold greater than leaf morphology, and the contribution of root mass allocation to root length ratio was ~2-fold greater than that of root morphology. In contrast, root morphology contributed more to the root area ratio than biomass allocation under drought in both the early and late periods. There was a negative correlation between the ratio of leaf mass fraction to root mass fraction and the ratio of specific leaf area to specific root length (or specific root area).

Conclusions: This study suggested that organ biomass allocation drove a larger proportion of variation than morphological traits for the absorption of resources in this rhizomatous grass. These findings should help us understand the adaptive mechanisms of plants when they are confronted with drought stress.

Keywords: Rhizomatous grass; biomass allocation; drought stress; drought timing; plant functional trait.

Fig. 1.

General morphology of Leymus chinensis (Zhang et al., 2009) and its phenological stages (Shi et al., 2017).

Fig. 2.

Schematic illustration of the overall experimental design, including the timing of treatment and harvest throughout the whole experiment (W, well-watered; D, drought). The four treatments included: WW, plants were well-watered in both the early and late periods; DW, plants experienced drought in the early period and were well-watered in the late period; WD, plants were well-watered in the early period and experienced drought in the late period; and DD, plants were drought affected in both the early and late periods.

Fig. 3.

Violin plots of leaf and root biomass allocation and morphology measured under drought treatment. (A) Specific leaf area, SLA; (B) specific root length, SRL; (C) specific root area, SRA; (D) leaf mass fraction, LMF; (E) root mass fraction, RMF; (F) leaf area ratio, LAR; (G) root length ratio, RLR; (H) root area ratio, RAR. Different capital letters denote a P < 0.05 difference based on a Tukey’s post-hoc test among treatments (WW: plants were well-watered in both the early and late periods, DW: plants experienced drought in the early period and were well-watered in the late period, WD: plants were well-watered in the early period and experienced drought in the late period, and DD: plants experienced drought in both the early and late periods).

Fig. 4.

Relative contribution of leaf and root biomass allocation (leaf mass fraction: LMF, or root mass fraction: RMF, light grey bars) and morphology (specific leaf area: SLA, specific root length: SRL, or specific root area: SRA, dark grey bars) to the total variation in leaf area ratio (LAR), root length ratio (RLR) and root area ratio (RAR).

Fig. 5.

Standardized major axis (SMA) regressions between (A) the leaf to root mass ratio and the specific leaf area to specific root length (SLA:SRL) ratio under the WW (blue), DW (black), WD (purple) and DD (red) treatments. SMA regressions between (B) the leaf to root mass ratio and the specific leaf area to specific root area (SLA:SRA) ratio. Significant relationships are indicated by solid lines and non-significant relationships are indicated by dashed lines.