Plant nitrogen and phosphorus utilization under invasive pressure in a montane ecosystem of tropical China

Abstract

Exotic plant invasion has been changing the vegetation composition and function of terrestrial ecosystems. Nitrogen (N) and phosphorus (P) are often the limiting nutrients for terrestrial plants. However, under invasive pressure, in situ plant N and P usage mechanisms remain poorly understood but are pivotal for a better understanding of plant invasion and coexistence in invaded ecosystems. Nitrogen and P concentrations, natural 15N abundance (δ15N values) were investigated in leaves and soils under different invasive pressures (here expressed as the biomass percentages of invasive plants in each plot) for two invasive species (Chromolaena odorata and Ageratina adenophora) in Xishuangbanna in tropical China. Soil N and P concentrations revealed the relatively N‐rich but P‐poor status of our study site. Under invasion, soil inorganic N (dominated by ammonium) and available P did not increase significantly. The leaf N and P of invasive plants increased, while leaf N increased but P decreased for native species. Natural δ15N mass balance between leaves and soil inorganic N sources revealed that ammonium dominated N utilization in both natives and invaders. Invasive plants showed ammonium utilization with increasing leaf N levels, while native plants under no invasion showed nitrate utilization with increasing leaf N levels. Synthesis. Increased soil ammonium availability contributed to preferential ammonium utilization by invasive plants and elevated ammonium utilization in natives, but the P competition of natives decreased in invaded ecosystems. These novel insights into nutrient dynamics in invaded ecosystems enhance our understanding of plant invasion and coexistence mechanisms.

Spartina alterniflora Leaf and Soil Eco-Stoichiometry in the Yancheng Coastal Wetland

“…The invasion of alien plants impacts the environment, economy, society, and functioning of ecosystems and is one of the most important threats facing the global ecosystem [ 14 ]. The successful invasion of alien plants involves many factors, including their own biological characteristics and non-biological environmental factors [ 15 , 16 , 17 ]. In the competition for habitat resources, invasive species often have better resource acquisition strategies than local plants.…”

Relationships between leaf δ15N and leaf metallic nutrients

“…Leaf δ 15 N values are primarily determined by the δ 15 N signatures of the plant N sources 7,28 . NO 3 − and NH 4 + are the most common sources of N in plants 28–30 . The δ 15 N values are often lower in soil NO 3 − than in soil NH 4 + due to the large isotopic fractionation of the nitrification process; leaf δ 15 N values usually decrease with an increases in plant NO 3 − uptake 29,30 .…”

“…NO 3 − and NH 4 + are the most common sources of N in plants 28–30 . The δ 15 N values are often lower in soil NO 3 − than in soil NH 4 + due to the large isotopic fractionation of the nitrification process; leaf δ 15 N values usually decrease with an increases in plant NO 3 − uptake 29,30 . Therefore, the variations in leaf δ 15 N values could be used to indicate the changes in plant N sources 7 .…”

Ecological stoichiometry and invasive strategies of two alien species (Bidens pilosa and Mikania micrantha) in subtropical China

“…For example, lower tissue N:P and C:P ratios are linked to higher whole‐organism P content, which helps drive protein synthesis and leads to higher growth rates and/or reproductive output (Elser., ), In contrast, a higher C:N ratio reflects higher carbon assimilation efficiency, but lower growth rates, also lower nutrient requirements (González et al, ). The C:N:P ratios play a key role in the growth and competition among plants (González et al, ; Hu et al, ; Sterner & Elser, ), therefore the ecological stoichiometry of populations allows us to explore the reasons for the success or otherwise of invasions.…”