Plant uptake of nitrogen and phosphorus among grassland species affected by drought along a soil available phosphorus gradient
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.
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.
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.
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.
KeywordsGrassland species Nutrient homeostasis Nutrient limitation Nutrient stoichiometry Plant nutrient uptake Stable isotope labelling Water stress
This study was supported by an Australian Institute of Nuclear Science and Engineering Research Award (ALNGRA15209) awarded to FAD in 2015. PM was funded by the Swiss National Science Foundation (n°P300P3_154648).
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