Assessing Cumulative Effects of Climate Change Manipulations on Phosphorus Limitation in a Californian Grassland

Abstract

Grasslands throughout the world are responding in diverse ways to changing climate and environmental conditions. In this study we analyze indicators of phosphorus limitation including phosphorus concentrations, phosphorus to nitrogen and carbon ratios as well as oxygen isotope ratios of phosphate in vegetation, and enzyme activity in soil. The study was conducted at the Jasper Ridge Global Change Experiment, (JRGCE) California where manipulations mimicking increases in temperature, water, nitrogen and carbon-dioxide have been maintained for over 15 years. A study documenting changes in net primary productivity (NPP) over time at the JRGCE could not identify a progressive effect of the manipulations on NPP. Here we shed light on the long term effects of the manipulations on phosphorus availability to vegetation. We compare our results to an earlier study conducted 3 years after the start of the experiment, in order to assess any change in the response of phosphorus over time. Our results suggest that a decade later the measured indicators show similar or only slightly stronger responses. Specifically, addition of nitrogen, the principle parameter controlling biomass growth, increased phosphorus demand but thresholds that suggest P limitation were not reached.