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Invasive plants are a major threat to biodiversity and may adversely affect food security. Clonal integration enables the sharing of resources between connected ramets and can enhance plant performance in many invasive species. However, few studies have examined the role of clonal integration when weeds are exposed to plant growth regulators (PGRs). PGRs are used extensively in agriculture and may affect nearby weeds through soil leaching, erosion and runoff. Our aim was to investigate the effects of clonal integration on growth in a noxious weed, Alternanthera philoxeroides (alligator weed), in response to two PGRs frequently used in agriculture, gibberellins (GAs) and paclobutrazol (PAC). Ramets of A. philoxeroides were propagated in the greenhouse, and treated with PGRs. PGRs were applied to the older ramets (i.e. ‘basal’ part), with half of the plants having the stems between the apical (younger) and basal parts left connected, while the remaining plants had the stems between the two parts severed. Following the growing period, plants were measured for growth traits. We found that GA and PAC had contrasting effects on plant growth. GA significantly promoted above-ground growth of the apical ramets via clonal integration. Alternatively, PAC inhibited above-ground growth in the basal and apical parts, and enhanced below-ground growth of the basal and apical ramets through clonal integration. Our results highlight how clonal integration can promote growth in A. philoxeroides following the application of PGRs, which is likely an important mechanism for this species to invade new environments.

Aims Projections of invasive species expansion under a warmer world often do not explicitly consider the concurring nitrogen (N) deposition. It remains largely unknown how the convoluted effect of climate warming and N deposition will shift the native and invasive species dynamics. Here, we hypothesize that the concurring increases in N and temperature would promote growth of invasive species greater than that of native species. Methods A controlled greenhouse experiment was conducted to quantify the growth response of an invasive species (Solidago canadensis L.) and a co-existing native species (Artemisia argyi Levl. et Van) under the effects of climate warming, N deposition and their interactions. Important Findings Due to the strong positive effect of N addition, the interactive effect of temperature increase and N addition resulted in an overall significant increase in growth of both invasive and native species, demonstrating that these manipulations may make microhabitats more favorable to plant growth. However, the relative increases in biomass, height and diameter of invasive S. canadensis were significantly lower than those of native A. argyi. This suggests that the vegetative growth superiority of invasive S. canadensis over the native species A. argyi is reduced by the enhanced N availability in the warmer world. Therefore, the inclusion of N deposition may mitigate the projection of invasive species S. canadensis expansion under climate warming.

AimsChange in nitrogen (N) availability regulates phosphorus (P) acquisition and potentially alters the competition among native species and invasive weeds. This study determines how current and projected N deposition affect the growth, the intraspecific and interspecific competitive ability of native and invasive plants in calcareous soils with low P availability.MethodsA controlled greenhouse experiment was conducted using sparingly soluble hydroxyapatite (HAP) to simulate the calcareous soils with low P availability. The growth and competitive intensity between an invasive weed (Solidago canadensis) and a native weed (Pterocypsela laciniata) exposed to two levels of N addition representative of current and future N deposition in China were experimentally determined.Important FindingsP acquisition and the growth of both S. canadensis and P. laciniata growing alone significantly increased with increasing N level. However, the effect of N addition was reduced when intraspecific or interspecific competition existed. N addition altered the competitive relationship between S. canadensis and P. laciniata allowing S. canadensis to out-compete P. laciniata due to variation in P acquisition from HAP. Elevated N deposition might assist the invasion of S. canadensis in the widely distributed calcareous soils under environmental changes.