comLinking flowering and reproductive allocation in response to nitrogen addition in an alpine meadow

Aims Plants can change in phenology and biomass allocation in response to environmental change.It has been demonstrated that nitrogen is the most limiting resource for plants in many terrestrial ecosystems.Previous studies have usually focused on either flowering phenology or biomass allocation of plants in response to nitrogen addition;how-ever,attempts to link flowering phenology and biomass allocation are still rare.In this study,we tested the effects of nitrogen addition on both flowering phenology and reproductive allocation in 34 common species.We also examined the potential linkage between flowering time and reproductive allocation in response to nitrogen addition.Methods We conducted a 3-year nitrogen addition experiment in Tibetan alpine meadow.We measured first flowering date and the repro-ductive allocation for 34 common plant species in control,low and high nitrogen added plots,respectively.one-way analysis of variance was used to examine differences of first flowering date and reproductive allocation among treatments.The relationships between the change in species first flowering date and change in reproductive allocation in response to nitrogen addition were examined by calculating Pearson correlation coefficients.Important Findings For most species,both first flowering date and reproductive alloca-tion significantly responded to nitrogen addition.Nitrogen addition significantly delayed the first flowering date and reduced the repro-ductive allocation for all graminoid species,but accelerated flower-ing and increased reproductive allocation for most forb species.We found that changes in first flowering date significantly negatively correlated with the changes in reproductive allocation over spe-cies in response to nitrogen,which indicated a positive relationship between flowering response and plant performance in reproductive allocation.species that advanced their flowering time with nitrogen addition increased their reproductive allocation,whereas those that delayed flowering time tended to decline in reproductive allocation with nitrogen addition.our results suggest that species-specific switch from vegetative growth to reproductive growth could influence species performance.

Reproductive Allocation Patterns in Different Density Populations of Spring Wheat

The effects of increased intraspecific competition on size hierarchies （size inequality） and reproductive allocation were investigated in populations of the annual plant, spring wheat （Triticurn aestivurn）. A series of densities （100, 300, 1 000, 3 000 and 10 000 plants/m^2） along a gradient of competition intensity were designed in this experiment. The results showed that average shoot biomass decreased with increased density. Reproductive allocation was negatively correlated to Gini coefficient （R^2 = 0.927）, which suggested that reproductive allocation is inclined to decrease as size inequality increases. These results suggest that both vegetative and reproductive structures were significantly affected by intensive competition. However, results also indicated that there were different relationships between plant size and reproductive allocation pattern in different densities. In the lowest density population, lacking competition （100 plants/m^2）, individual reproductive allocation was size independent but, in high density populations （300, 1 000, 3 000 and 10 000 plants/m^2）, where competition occurred, individual reproductive allocation was size dependent： the small proportion of larger individuals were winners in competition and got higher reproductive allocation （lower marginal reproductive allocation; MRA）, and the larger proportion of smaller individuals were suppressed and got lower reproductive allocation （higher MRA）. In conclusion, our results support the prediction that elevated intraspecific competition would result in higher levels of size inequality and decreased reproductive allocation （with a negative relationship between them）. However, deeper analysis indicated that these frequency- and size-dependent reproductive strategies were not evolutionarily stable strategies.

Different Responses of Sexual and Asexual Reproduction of Arundinella hirta to Flooding

The sexual and asexual reproductive features of the graminoid species Arundinella hirta growing at riversides of the Jialing River were analyzed.It was found that the total seed mass,seed number per plant,and sexual reproductive allocation of A.hirta decreased with decreasing bank elevation,and plants growing at the lowest elevations of banks subjected to intense flooding did not show sexual reproduction.The total plant biomass and the number of ramifications per plant increased with flooding intensity,which implies that,contrary to sexual reproduction,asexual reproduction of A.hirta was enhanced by flooding.