Identification of environmental indices that influence SOC
plasticity
To define the environmental factors influencing SOC, we examined the
general trends of three key climate conditions during the growth season:
temperature, precipitation, and solar radiation. Among the three
experimental sites, Hefei (HF) exhibits the lowest cumulative
growing-degree day (GDD) values, while Chengdu (CD) has the least amount
of cumulative precipitation (Fig. 1b; Fig. S3). For solar radiation,
Wuhan (WH) has higher levels of ultraviolet B (UV-B) irradiation during
the leaf stage than the other sites. However, this trend diminishes and
eventually reverses as the plants progress to inflorescence emergence
and later stages (Fig. S4). In addition, variations in environmental
conditions between different years at the same site also contributed to
SOC plasticity (Fig. 1b, Fig. S3, S4). We identified days of cold stress
(below -3.0°C) as a significant
variable, with a noticeable disparity between years, with 33 days in
HF2018 and 17 days in HF2017, suggesting that low temperature should be
considered when assessing SOC differences (Fig. S3). These climate
conditions are likely to be pivotal factors influencing SOC plasticity,
but further investigation is needed to determine the key phases that
affect SOC performance more explicitly.
To identify the explicit environmental indices that contribute to SOC
plasticity, we used the CERIS package, a tool designed for analyzing
phenotypic plasticity (Fig. S5). Through the exploration of various
combinations of environmental parameters and growth windows, CERIS
identified three factors: DTR183–192,
PR166–195, and UVB144–186, showing
strong correlation with environmental means, thus determining SOC
plasticity in eight different environments (Fig. 2).
DTR183–192 represents the average diurnal temperature
range within the window of 183–192 days after planting. This window
falls within the pod-filling stage, highlighting plant sensitivity to
temperature changes during this stage. PR166–195 and
UVB144–186 represent the average precipitation (PR) and
average UV-B irradiation (UVB) in the windows of 166–195 and 144–186
days after planting, respectively. These two windows coincide with the
flowering and pod-filling stages. To quantify the influence of these
environmental indices on SOC, we conducted separate regressions of the
environmental mean for SOC with each factor, revealing a 0.78% decrease
in SOC for every 1-unit increment in DTR183–192, a
1.55% increase in PR166–195, and a 1.9% decrease in
UVB144–186 (Fig. S6). These findings establish a
quantitative link between environmental indices, growth stages, and SOC
plasticity, thereby enhancing our understanding of the environmental
basis of SOC plasticity.