Stress driver analysis of annual wild soybean (Glycine soja) population decline and implications for the protection of wild soybean populations in China

Wild soybeans, the ancestors of soybeans, are important genetic resources.
Unfortunately, some natural populations of them are declining
inexplicably. This study revealed the drivers behind this decline to
inform conservation strategies. Conducted in the northeastern Inner
Mongolia, China, the study analyzed 12
community characteristics across 20 herbaceous communities to gain
insights into the causes and mechanisms of the decline. The wild soybean
populations face at least three stress factors: external
environments, internal community structures, and the
planting industry, and these factors
exhibit distinct stress mechanisms. The results mainly
included that: 1. Two correlations as regulatory factors
involved in maintaining community stabilizing, i.e., the
CNDP effect (conspecific negative density-plant weight correlation,
density effect) between density and single-plant
weight of wild soybeans in the populations, and the HDC effect
(heterospecific density complementary relation) between densities
of both wild soybeans and other companion plants in the communities.
2. Shading stress reduced companion
plant density but increased wild soybean density via the HDC
effect and CNDP effect. 3. Stressed
habitats favored perennial plants, significantly
outnumbering annual ones. 4. Our results demonstrated that
perennial herb density increases with latitude, while herbaceous
communities exhibited a latitudinal diversity gradient (LDG),
gradually decreasing in diversity with increasing latitude. 5.
The intra-community structures with high perennial ratios threatened wild
soybeans by favoring perennial dominance. 6. The wild soybean
populations near cropland experienced a severe decline compared
to those far from the cropland. Practical implication: This study
demonstrates that community environments, high perennial species
ratios, and the
planting industry affect the survival of
natural wild soybeans in agroecosystems. The high perennial species
ratio serves as an important intra-community biological
stressor, threatening annual wild soybeans, while herbicide spraying on
croplands would reduce the individual density of natural wild soybean
populations near croplands. The research results can be
used to guide the protection of wild soybeans in the field and
suggest that if wild soybean populations are to be maintained, then
artificial intervention is necessary to control community
succession of in-situ wild soybean nature reserves to
prevent any plant from gaining ecological advantages for
stable coexistence.