Plant uptake of nitrogen and phosphorus among grassland species affected by drought along a soil available phosphorus gradient

Abstract

Aims: Here we assessed N and P uptake of four grassland species grown together in response to a short-term drought event along a soil P gradient. Methods: We used 15N and 32P tracers to examine uptake of N and P by the grasses Bothriochloa macra, Themeda triandra, Lolium perenne and Microlaena stipoides grown together in pots with initial available P levels of 3, 8, 12, 20 mg P kg−1 soil. Soil moisture in half the pots was reduced from 60 to 30% water holding capacity during a 7-day period to simulate drought. Results: Plant P uptake was strongly reduced by drought in all species across all P levels, much more so than N uptake, indicating decoupling in N and P uptake. Soil available P (Bray method) was not affected by drought, suggesting that the reduced P uptake with drought was due to reduced soil P mobility. Plant competition for N and P changed with drought and soil P levels, where relatively more N and P was taken up with drought by M. stipoides at the lowest soil P level. Conclusions: We showed that greater reductions in P than in N uptake and shifts in N and P uptake among species caused by a short-term drought have strong consequences for plant growth.