Graphical partitioning of seedling phenotypic plasticity of seven cool-season grass species subjected to two watering frequencies

Abstract

Successful seedling establishment requires the ability to adapt to changes in soil moisture, and this ability may be related to phenotypic plasticity. As a case-study of plasticity to water availability, we measured the seedling root and shoot dry-mass of 45-d-old seedlings of seven cool-season grass species grown under two watering-frequency (WF) regimes in a glasshouse. To depict species plasticity, we developed a graphical method with three salient features. First, we partitioned plasticity into two components, 1) 1:1 growth plasticity and 2) plasticity for root:shoot allocation. Second, we calculated 1) total dry-mass to measure growth plasticity and 2) root mass fraction (RMF) to measure allocation plasticity. Third, we plotted each species’ plastic response to WF on a graph with four axes: 1) shoot dry-mass, 2) root dry-mass, 3) total dry-mass, and 4) RMF. Three species displayed predominately growth plasticity, and four species displayed only allocation plasticity. In response to low WF, three growth-plasticity species decreased total dry-mass but did not change RMF, while four allocation-plasticity species did not change total dry-mass but increased RMF. Growth-plasticity species are opportunistic and can capitalize on additional water to increase growth, while allocation-plasticity species may increase survivorship by tailoring RMF to reflect current soil-moisture status.