4.3 Implication for fertilization management
Although numerous studies have found that N and P interact to control
plant growth, nutrient absorption, and reproductive allocation under
conditions of N and P addition (Li et al., 2017; Long et al., 2016; Zhao
et al., 2018b), the effect of multi-level N/P addition on plant
reproduction is still unclear, especially under various the other
nutrient addition levels. In our study, the effects of N addition upon
seed production did not differ significantly different under the low or
high P addition. A low P addition is sufficient to balance the increased
P demand of plant growth while a high P addition cannot be fully
utilized by plants, leading to a similar effect arising between these
two levels of P addition. The leaf N:P ratio tends to balance out at a
soil available N:P supply ratio of approximately 20 (Zhan et al., 2017).
Thus, our low rate of P addition (5 g m-2yr-1) may need 100 g N m-2yr-1 to balance the N demand from plant growth in this
temperate steppe.
Our study demonstrates the importance of N and P enrichment in
regulating the seed production of dominant species in a temperate
steppe. Seed production in response to changing available nutrients in
soil can profoundly determine plant community structure and dynamics
(Basto et al., 2015). Our findings of increased seed production of the
dominant species under both N and P addition treatments, coupled to
their additive effects, suggest that the S . krylovii will
become more dominant under accelerating N and P enrichment regimes.
Producing more seeds confers advantage in dispersal and fecundity,
resulting in higher probability of colonizing new favorable habitats.
Due to the higher reproductive growth of the dominant species, the
species would increase its capacity of dispersal capacity and occupy
more living space. More resources, such as light and water, would be
consumed by such dominant species, and this restricts the survival
spaces of other co-occurring species in the community, effectively
squeezing them out, over time leading to species losses in nutrient
amendment conditions. Nutrient enrichment has an obvious promoting
effect on the seed production of dominant species in natural ecosystems,
which provides new insight into the mechanisms of biodiversity loss in
the context of intensifying human activities in grasslands especially.