RESUMO
Potassium (K) is the second most abundant nutrient in plant leaves after nitrogen (N) and the most abundant cation in plant cells. It plays an important role in plant growth regulation, homeostasis maintenance, and stress response. Previous studies on the effects of N input on plant nutrient status mainly focus on N and phosphorus (P), but less on K and its stoichiometry. We examined the effects of N input and mowing on K content and N:K at both plant functional group and community levels. We analyzed the relative contribution of changes in functional groups and community composition to changes of community level nutrition status. The results showed that N input increased N content of each plant functional group and increased K content of rhizomatous grasses and legumes. Mowing reduced N content of rhizomatous grasses and bunchgrass, but did not affect K content and N:K of all functional groups. Nitrogen input significantly increased plant N and K contents at the community level, while mowing significantly increased plant N content. Both N input and mowing did not affect plant N:K at functional group and community levels. The contribution of nutritional changes in plant functional groups to the variation at the community level was greater than that of changes in community composition. For all the three examined nutritional traits, the contribution of nutrients at functional group level and that of community composition showed negative covariation. Our results indicated that plant N:K had high homeostasis in meadow steppe and that plants could regulate N and K balance, which was of great significance for maintaining N:K stoichiometry under the background of increasing N deposition.
Assuntos
Pradaria , Nitrogênio , China , Ecossistema , Nitrogênio/análise , Fósforo , Plantas , Poaceae , Potássio , SoloRESUMO
Long-term overuse of grasslands results in quantitative and qualitative decline of forage yield. Nutrient supplementation is a key strategy to improve forage yield. While mounting evidence showed that nitrogen (N) supplementation can increase forage yield, little is known about its impacts on forage quality. To understand the effects of N supplementation on forage quality at the community level, we carried out a field experiment in the meadow steppe of Hulunbuir. Our results showed that N supplementation significantly increased forage yield by 23%, which was mainly due to positive responses of perennial rhizomatous grass. The yield of other plant functional groups showed neutral response to N supplementation. The concentrations of crude protein, crude fat, and crude fiber varied significantly among different plant functional groups. Nitrogen supplementation significantly enhanced the concentration of crude protein in rhizomatous grass, bunchgrass, legume, and sedge. It enhanced the content of crude fat in rhizomatous grass but with no effect on other functional groups. Nitrogen supplementation had no effect on the concentration of crude fibre in all functional groups. At the community level, N supplementation significantly increased the concentrations of crude protein and crude fat. Our results are important for understanding the responses of forage production in meadow steppe under the scenarios of N enrichment.
Assuntos
Pradaria , Nitrogênio , Poaceae , China , FertilizantesRESUMO
Plant genome size (GS) varies greatly over 2400-fold in angiosperms. Genome sizes are closely related to plant traits from cellular to individual level, which would have far-reaching ecolo-gical implications. Genome size may shape the interspecific responses of plants to changes of resource availability in Inner Mongolia grassland which is co-limited by water and nitrogen availabi-lity. We tested the role of genome size in structuring plant community composition after single and combined water (W) amd nitrogen (N) addition in a typical grassland of Inner Mongolia. Plant genome sizes were estimated by flow cytometry. We found that the response of plant aboveground net primary production (ANPP) to change in water availability was significantly affected by genome size. Water and NW addition significantly increased ANPP of small GS plants, instead of large GS species. Nitrogen addition had no effects on ANPP of both small and large GS plants. We found no effects of all the treatments on plant species richness. Results showed that GS modulated the response of grassland plant species to changes in water rather than nitrogen availability in Inner Mongolia. Since GS is a relatively constant trait with substantial interspecific variation, the application of GS in ecological studies would be of great significance to better understanding of ecosystem structure and function under global change.