Nitrogen and phosphorus addition differentially enhance seed production
of dominant species in a temperate steppe
Abstract
Previous studies have demonstrated changes in plant growth and
reproduction in response to nutrient availability, but how
investigations of such responses to multiple levels of nutrient
enrichment remains unclear. In this study, we manipulated nitrogen (N)
and phosphorus (P) availability to examine seed production responses to
three levels each of N and P addition in a factorial experiment: no N
addition (0 g N m-2 yr-1), low N addition (10 g N m-2 yr-1), high N
addition (40 g N m-2 yr-1), and no P addition (0 g P m-2 yr-1), low P
addition (5 g P m-2 yr-1), high P addition (10 g P m-2 yr-1). Low N
addition enhanced seed production by 814%, 1371%, and 1321% under
ambient, low, and high P addition levels, respectively. High N addition
increased seed production by 2136%, 3560%, and 3550% under ambient,
low, and high P addition levels, respectively. However, P addition did
not affect seed production in the absence of N addition, but it did
enhance it under N addition. Furthermore, N addition enhanced seed
production mainly by increasing the tiller number and inflorescence
abundance per plant, whereas P addition stimulated it by decreasing the
plant density yet stimulating height of plants and their seed number per
inflorescence. Our results indicate seed production is limited not by P
but rather by N in the temperate steppe, whereas seed production will be
increased by P addition when N availability is improved. These findings
enable a better understanding of plant reproduction dynamics of steppe
ecosystems under intensified nutrient enrichment and can inform their
improved management in the future.