Nutrient uptake in soil niches affected by plant species and drought stress

摘要

Benefits of grassland mixtures over monocultures are hypothesized to be based on niche complementarity among plant species. The objective of this experiment was to use tracer methods to assess the below-ground niche differentiation between deep and shallow rooting species under benign and drought conditions. A field experiment was established with plots containing monocultures and mixtures of Lolium perenne (Lp), Cichorium intybus (Ci), Trifolium repens (Tr) and Trifolium pratense (Tp) according to asimplex design. Using rainout shelters, half of the plots were subjected to a drought treatment of 10 weeks summer rain exclusion. During the drought period, a rubidium chloride solution was applied in 50x50 cm sub-plots at 5 and 35 cm depth and Rb concentrations and uptake in the individual plant species was measured. Results show that Rb uptake was much higher from 5 cm depth compared to 35 cm depth for all species. There was a relative shift of Rb uptake to the deeper soil layer under drought conditions for all species. The deep rooting species (Ci and Tp) were shown to have relatively higher Rb uptake at 35cm, and the shift to deeper root layers under drought conditions was larger.