Seed germinations react to their local growing conditions, but the impacts of soil heterogeneity on seed germinations are not well known.

Effects of three-dimensional soil heterogeneity on seed germinations of grasses species were explored, where two levels of such soil heterogeneity were created via alternatively filling nutrient-poor and nutrient-rich substrate in pot in all directions. Patch sizes of the two heterogeneity levels are around 7.5 and 15 cm, respectively. Fifty seeds of each of the grasses species (Lolium perenne and Elymus nutans) were set either in these heterogeneous soils or in petri dishes with distilled water. Seed germinations of these species were daily recorded.

We found that pots with smaller patches had relatively lower germination rate, which is consistent with our expectation that shorter distance between nutrient-rich and nutrient-poor patches in pots with smaller patches allows plants to reduce their germination rates and delay their germination, in order to reduce the negative impacts of the strong variation of soil resources in these pots. Our results also revealed that pots with smaller patches yielded more heterogeneous seed germination, i.e. seed germinations highly diverged among these pots. These findings highlight that the realistic three-dimensional design can improve our understanding of seed germination as driven by soil spatial heterogeneity.

Prediction of changes in ecosystem gross primary productivity (GPP) in response to climatic variability is a core mission in the field of global change ecology. However, it remains a big challenge for the model community to reproduce the interannual variation (IAV) of GPP in arid ecosystems. Accurate estimates of soil water content (SWC) and GPP sensitivity to SWC are the two most critical aspects for predicting the IAV of GPP in arid ecosystems.

We took a widely used model Biome-BGC as an example, to improve the model performances in a temperate grassland ecosystem. Firstly, we updated the estimation of SWC by modifying modules of evapotranspiration, SWC vertical profile and field capacity. Secondly, we modified the function of controlling water–nitrogen relation, which regulates the GPP–SWC sensitivity.

The original Biome-BGC overestimated the SWC and underestimated the IAV of GPP sensitivity, resulting in lower IAV of GPP than the observations, e.g. it largely underestimated the reduction of GPP in drought years. In comparison, the modified model accurately reproduced the observed seasonal and IAVs in SWC, especially in the surface layer. Simulated GPP–SWC sensitivity was also enhanced and became closer to the observations by optimizing parameter controlling nitrogen mineralization. Consequently, the model’s capability of reproducing IAV of GPP has been largely improved by the modifications. Our results demonstrate that SWC in the surface layer and the consequent effects on nitrogen availability should be among the first considerations for accurate modeling IAV of GPP in arid ecosystems.

In a large dam-regulated reservoir with regular hydrological pattern and strong flooding gradients across shore elevations, plants inhabiting in different shore elevations have to confront long-lasting flooding of differential intensities every year. Such persistent stress may lead to intraspecific differentiation of flooding tolerance in seeds. Echinochloa crusgalli var. zelayensis is a dominant annual plant in the shores of the Three Gorges Reservoir (TGR), which plays an important role in the shore vegetation. The objective of this study is to check whether intraspecific differentiation of seed flooding tolerance has occurred among E. crusgalli var. zelayensis populations in the TGR shores and whether such differentiation is associated with weak seed dispersal.

We collected seeds of E. crusgalli var. zelayensis from different populations in the TGR shores, and then placed them at four elevations in the shores flooded by reservoir impoundment. Parameters reflecting seed flooding tolerance including post-flooding percentage of intact seeds, seed germinability and seedling emergence rate were investigated for the seeds from different populations and undergoing flooding of different intensities. Floating time of seeds and speed of water level rise during impoundment were examined, and used to quantify dispersal potential of seeds in the shores of the TGR when flooded.

Both intact seed percentage and final seedling emergence rate after flooding significantly declined with increasing shore elevations where the seeds were collected, indicating that intraspecific differentiation in seed flooding tolerance has occurred among E. crusgalli var. zelayensis populations in the TGR shores after 7-year operation of the reservoir. The distance of seeds transported by rising water during reservoir impoundment was limited due to short-floating time of the seeds and relatively low speed of water level rise in the reservoir. This would be favourable to the development of intraspecific differentiation in seed flooding tolerance.