Growth rate, root development and nutrient uptake of 55 plant species from the Great Plains Grasslands, USA

Empirical and theoretical studies have highlighted that plant competition and species diversity are substantially affected by interactions among plant growth and nutrient uptake rates, root lateral spread, root plasticity, and small scale soil nutrient heterogeneity. This study was designed to (a) experimentally estimate parameters regarding root scaling patterns, root biomass allocation, growth rates, nutrient productivity, and root nutrient influx rates of 55 plant species common to Great Plains grasslands; and (b) determine if grasses and forbs can be classified into statistically distinct groups based on these characteristics. We found that: (1) In all species root lateral spread, root length, and root surface area had significant allometric scaling relationships with root biomass, but that the relationships were unaffected by N availability. (2) Reductions in the supply of N increased the root: shoot ratio in 62% of the species. (3) The frequency distribution and mean values of maximum relative growth rates were very similar for grasses and forbs/shrubs, but mid successional grasses had a higher relative growth rate than late successional ones. (4) In 78% of the species tested, N productivity was increased by reductions in the N supply. (5) When subjected to a high N supply, the N and P productivity of grasses was, on average, higher than that of forbs/shrubs, and the N and P productivity of C-4 grasses was, on average, higher than that of C-3 grasses. No differences were found under a low N supply. (6) No differences on the average maximum N and P influx rates per unit of root surface area were found between grasses and forbs or between C-3 and C-4 grasses, but both were correlated with maximum relative growth rate. (7) The set of parameters we measured were able to separate grasses and forbs/shrubs into statistically distinct groups that tend to follow in broad terms the "coarse" vs. "fine" scale foraging strategies hypothesis.