In this study, we addressed how interannual rainfall determines belowground productivity through a multi-year manipulation experiment in the Jornada Experimental Range LTER site in the Northern Chihuahuan Desert in New Mexico. Through a factorial, ecosystem scale experiment containing drought (-80% and -50% below the ambient precipitation) and irrigated treatments (+80% and +50% above the ambient precipitation) we have controlled the quantity of rainfall reaching 132 plots over the course of three years. The goal of this study was to detect whether a relationship existed between belowground net primary production (BNPP) and rainfall in the present year, rainfall in the prior two-years, and an interaction of current and past rainfall, during the third year of manipulations. Our approach for attaining an estimate of BNPP consisted of constructing and harvesting 4 replicate, 30-cm deep, 5-cm diameter ingrowth cores that had been in the field for one growing season, and additionally, using belowground images of roots to provide a secondary indicator of BNPP’s response to the rainfall treatments.
Results/Conclusions:
The ingrowth core results showed a BNPP range of 0.04 - 22.1 g m-2 year-1. BNPP increased with current year precipitation in the enhanced precipitation treatment (r2 = 0.21, P < 0.05, n=39). Past rainfall and the interaction of past and present rainfall, in contrast, showed no significant effects upon BNPP. The difference in root surface area gauged by minirhizotron images before and after the growing season revealed no relationship between BNPP and current rainfall, past rainfall, or an interaction of the two. That we detected treatment effects with ingrowth cores and not with minirhizotron images underscores the importance of using multiple independent methods to assess belowground productivity. With a better understanding of the relationship between precipitation and belowground production in arid and semi-arid ecosystems we expect to improve our ability to predict ecosystem response to changes in pattern and amount of rainfall with climate change.
