Soil heterogeneity is common in natural habitats. It may trigger foraging responses (placing more ramets and/or roots in nutrient-rich patches than in nutrient-poor patches) and further affect the growth of plants. However, the impact of soil heterogeneity on competitive interactions has been little tested. We conducted a greenhouse experiment to investigate the effects of soil heterogeneity on intraspecific competition with a stoloniferous herb Hydrocotyle vulgaris. We grew one (without competition) or nine ramets (with competition) of H. vulgaris under a homogeneous environment and two heterogeneous environments differing in patch size (large or small patches). In the heterogeneous treatment, the soil consisted of the same number of nutrient-rich and nutrient-poor patches arranged in a chessboard manner, and in the homogeneous treatment, the soil was an even mixture of the same amount of the nutrient-rich and the nutrient-poor soil. Irrespective of intraspecific competition, H. vulgaris showed foraging responses to soil heterogeneity in the large patch treatment, e.g. it produced significantly more biomass, ramets, aboveground mass and root mass in the nutrient-rich patches than in the nutrient-poor patches. In the small patch treatment, foraging responses were observed when intraspecific competition was present, but responses were not observed when there was no competition. However, we find a significant effect of soil heterogeneity on neither overall growth nor competitive intensity of H. vulgaris. Our results suggest that foraging responses to soil heterogeneity may not necessarily be adaptive and intraspecific competition may not be influenced by soil heterogeneity.

Plant invasion is one of the major threats to natural ecosystems. Phenotypic plasticity is considered to be important for promoting plant invasiveness. High tolerance of stress can also increase survival of invasive plants in adverse habitats. Limited growth and conservation of carbohydrate are considered to increase tolerance of flooding in plants. However, few studies have examined whether invasive species shows a higher phenotypic plasticity in response to waterlogging or a higher tolerance of waterlogging (lower plasticity) than native species. We conducted a greenhouse experiment to compare the growth and morphological and physiological responses to waterlogging of the invasive, clonal, wetland species Alternanthera philoxeroides with those of its co-occurring, native, congeneric, clonal species Alternanthera sessilis. Plants of A. philoxeroides and A. sessilis were subjected to three treatments (control, 0 and 60 cm waterlogging). Both A. philoxeroides and A. sessilis survived all treatments. Overall growth was lower in A. philoxeroides than in A. sessilis, but waterlogging negatively affected the growth of A. philoxeroides less strongly than that of A. sessilis. Alternanthera philoxeroides thus showed less sensitivity of growth traits (lower plasticity) and higher waterlogging tolerance. Moreover, the photosynthetic capacity of A. philoxeroides was higher than that of A. sessilis during waterlogging. Alternanthera philoxeroides also had higher total non-structural and non-soluble carbohydrate concentrations than A. sessilis at the end of treatments. Our results suggest that higher tolerance to waterlogging and higher photosynthetic capacity may partly explain the invasion success of A. philoxeroides in wetlands.

Spatial patchiness and temporal variability in water availability are common in nature under global climate change, which can remarkably influence adaptive responses of clonal plants, i.e. clonal integration (translocating resources between connected ramets). However, little is known about the effects of spatial patchiness and temporal heterogeneity in water on growth and clonal integration between congeneric invasive and nativeHydrocotylespecies. In a greenhouse experiment, we subjected severed or no severed (intact) fragments ofHydrocotyle vulgaris, a highly invasive species in China, and its co-existing, native congenerH. sibthorpioidesto different spatial patchiness (homogeneous and patchy) and temporal interval (low and high interval) in water supply. Clonal integration had significant positive effects on growth of both species. In the homogeneous water conditions, clonal integration greatly improved the growth in fragments of both species under low interval in water. However, in the patchy water conditions, clonal integration significantly increased growth in both ramets and fragments ofH. vulgarisunder high interval in water. Therefore, spatial patchiness and temporal interval in water altered the effects of clonal integration of both species, especially forH. vulgaris. The adaptation ofH. vulgarismight lead to invasive growth and potential spread under the global water variability.

Background: Unvegetated tidal flats of mangrove ecosystems in estuarine and non-estuarine areas play a crucial role in the coastal blue carbon sinks and biogeochemical cycle. However, there is still a lack of comprehensive understanding of the differences in soil organic carbon (SOC) contents in mangrove tidal flats between estuarine and non-estuarine areas, as well as their influencing factors. Methods: In this study, soil samples were collected from estuarine and non-estuarine mangrove tidal flats in the Leizhou Peninsula. We compared the SOC and soil physicochemical properties between estuarine and non-estuarine mangrove tidal flats. The Random Forest algorithm was employed to identify the main influencing factors affecting SOC. The direct and indirect effects of the main influencing factors on SOC were studied using partial least squares structural equation modeling. Results: SOC, total nitrogen (TN), total phosphorus (TP), available potassium (AK), clay, silt, aluminum (Al), lithium (Li), boron (B), molybdenum (Mo), and cadmium (Cd) contents in the estuarine areas were significantly higher than those in the non-estuarine areas of the mangrove tidal flats. The soil particle size (clay, silt, and sand), soil nutrient (TN and TP), and soil metal elements (Al, Mo, and Cd) were the main influencing factors of the SOC contents in the estuarine and non-estuarine mangrove tidal flat areas. Soil particle size (clay, silt, and sand) indirectly positively influenced SOC contents by positively influencing soil nutrient (TN and TP). Conclusions: Our findings indicate that estuarine tidal flats have higher capacity of SOC sequestration compared with non-estuarine tidal flats. The main cause is that soil particle size has the potential to significantly increase SOC content by increasing soil nutrients, while metal elements have a direct influence on SOC content. The findings of the present study highlight an important mechanism that influences SOC contents in estuarine and non-estuarine mangrove tidal flats.

Interactions between alien plants and local enemies in introduced ranges may determine plant invasion success. However, little is known about whether herbivory-induced responses are transmitted across vegetative generations of plants and whether epigenetic changes are involved during this process. In a greenhouse experiment, we examined the effects of herbivory by the generalist herbivore Spodoptera litura on the growth, physiology, biomass allocation and DNA methylation level of the invasive plant Alternanthera philoxeroides in the first- (G1), second- (G2) and third-generation (G3). We also tested the effects of root fragments with different branching orders (i.e., the primary- or secondary-root fragments of taproots) of G1 on offspring performance. Our results showed that G1 herbivory promoted the growth of the plants in G2 that sprouted from the secondary-root fragments of G1 but had a neutral or negative effect on the growth of the plants in G2 from the primary-root fragments. The growth of plants in G3 was significantly reduced by G3 herbivory but not affected by G1 herbivory. Plants in G1 exhibited a higher level of DNA methylation when they were damaged by herbivores than when they were not, while neither plants in G2 nor G3 showed herbivory-induced changes in DNA methylation. Overall, the herbivory-induced growth response within one vegetative generation may represent the rapid acclimatization of A. philoxeroides to the unpredictable generalist herbivores in the introduced ranges. Herbivory-induced trans-generational effects may be transient for clonal offspring of A. philoxeroides, which can be influenced by the branching order of taproots, but be less characterized by DNA methylation.