Soil salinity regulates spatial-temporal heterogeneity of seed germination and seedbank persistence of an annual diaspore-trimorphic halophyte in northern China

Abstract

Background and aims: Seed heteromorphism is a plant strategy that an individual plant produces two or more distinct types of diaspores, which have diverse morphology, dispersal ability, ecological functions and different effects on plant life history traits. The aim of this study was to test the effects of seasonal soil salinity and burial depth on the dynamics of dormancy/germination and persistence/depletion of buried trimorphic diaspores of a desert annual halophyte Atriplex centralasiatica.

Methods: We investigated the effects of salinity and seasonal fluctuations of temperature on germination, recovery of germination and mortality of types A, B, C diaspores of A. centralasiatica in the laboratory and buried diaspores in situ at four soil salinities and three depths. Diaspores were collected monthly from the seedbank from December 2016 to November 2018, and the number of viable diaspores remaining (not depleted) and their germinability were determined.

Results: Non-dormant type A diaspores were depleted in the low salinity "window" in the first year. Dormant diaspore types B and C germinated to high percentages at 0.3 and 0.1 mol L^-1 soil salinity, respectively. High salinity and shallow burial delayed depletion of diaspore types B and C. High salinity delayed depletion time of the three diaspore types and delayed dormancy release of types B and C diaspores from autumn to spring. Soil salinity modified the response of diaspores in the seedbank by delaying seed dormancy release in autum and winter and by providing a low-salt concentration window for germination of non-dormant diaspores in spring and early summer.

Conclusions: Buried trimorphic diaspores of annual desert halophyte A. centralasiatica exhibited diverse dormancy/germination behavior in respond to seasonal soil salinity fluctuation. Prolonging persistence of the seedbank and delaying depletion of diaspores under salt stress in situ primarily is due to inhibition of dormancy-break. The differences in dormancy/germination and seed persistence in the soil seedbank may be a bet-hadging strategy adapted to stressful temporal and spatial heterogeneity, and allows A. centralasiatica to persist in the unpredictable cold desert enevironment.

Keywords: Atriplex Centralasiatica; Environmental heterogeneity; Seed burial depth; Seed dormancy/Germination; Seed heteromorphism; Soil salinity; Soil seedbank.

Fig. 1

Experimental design for effects of soil salinity and burial depth on germination responses and persistance in the seedbank of the three diaspore types of Atriplex centralasiatica. L

Fig. 2

Sizes (mean ± SE) of in situ soil seedbank of the trimorphic diaspores of Atriplex centralasiatica on 30 September, 1 April and 20 August, which are the end of the life cycle, beginning of seedling establishment season and end of the growing season but prior to time for diaspore dispersal, respectively

Fig. 3

Mean percentage germination, germination recovery, dormancy and nonviable freshly matured A (a), B (b) and C (d) diaspores and dormancy-released B (c) and C (e) diaspores of Atriplex centralasiatica incubated in various concentrations of NaCl at 5/15°C. Germination recovery is quiescent diaspores that did not germinate after 30 days of incubation in the NaCl solutions but did germinate when moved from salt solutions to distilled water

Fig. 4

Mean monthly germination percentages (Mean ± SE) of Atriplex centralasiatica type A diaspores at four soil salt concentrations and three burial depths in the 2-year soil seedbank experiment. Four temperatures were used. The differents among each temperature was very small (almost all germinated to 100%). Thus, the line looks like only one temperature was used

Fig. 5

Mean monthly germination percentages (Mean ± SE) of Atriplex centralasiatica type B diaspores at four soil salt concentrations and three burial depths in the 2-year soil seedbank experiment

Fig. 6

Mean monthly germination percentages (Mean ± SE) of Atriplex centralasiatica type C diaspores at four soil salt concentrations and three burial depths in the 2-year soil seedbank experiment

Fig. 7

Effects of soil salinity, buried depth, incubation temperature and year of collection on germination of diaspore types A, B and C of Atriplex centialasiatica in the 2-year soil seedbank experiment. (a) Mean monthly germination percentages of type A, type B and type C at different concentrations of soil salinity. (b) Mean monthly germination of type A, type B and type C at different burial depths. (c) Mean monthly germination percentages of type A, type B and type C at different incubation temperatures. (d) Mean monthly germination percentages of type B and type C diaspores collected in 2017 and 2018. Different uppercase letters indicate significant differences in germination percentage among different diaspore types at the same salinity (a), burial depth (b), incubation temperature (c) and collection year (d) and different lowercase letters significant differences in germination among different salinity (a), burial depth (b), incubation temperature (c) and collection year (d) for the same diaspore type (P < 0.05)

Fig. 8

Mean number of types A, B and C diaspores of Atriplex centralasiatica remaining after various periods of burial at soil dpeths of 0 cm, 2 cm and 5 cm. Diaspores were buried in December 2016 and their presence/absence monitored until November 2018