Browsing by Author "He, MZ"

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    Plant and microbial uptake of nitrogen and phosphorus affected by drought using 15N and 32P tracers
    (Elsevier, 2015-03) Dijkstra, FA; He, MZ; Johansen, MP; Harrison, JJ; Keitel, C
    Competition for nutrients between plants and microbes is an important determinant for plant growth, biodiversity and carbon cycling. Perturbations such as drought affect the availability of nitrogen (N) and phosphorus (P), and may cause shifts in uptake of N and P between plants and microbes. Competitiveness for these nutrients may depend on how flexible plants and microbes are in taking up N and P. We used a novel dual isotope labelling technique (15N and 32P) to assess short-term uptake of N and P by plants and microbes affected by drought in two different plant–soil systems. Mesocosms were extracted from two grassland sites differing in soil nutrient availability and plant species. Half of the mesocosms were subjected to drought one week prior to injection of 15N (as KNO3) and 32P (as H3PO4) tracers. Uptake rates of NO3- and P in plants and microbes were estimated based on average source pool enrichment during the labelling period and on plant and microbial recovery of 15N and 32P measured after 4 days of labelling. Overall competition for N and P was reduced with drought as less NO3- and P was taken up in plants and microbes. However, plant NO3-uptake of was more sensitive to drought than microbial NO3- uptake, while microbial P uptake was more sensitive than plant P uptake. These different sensitivities to drought by plants and microbes may decouple the N and P cycle with increased drought conditions. © 2015 Elsevier Ltd
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    Plant-microbe competition for nitrogen and phosphorous affected by drought
    (The University of Western Australia, 2014-08-05) Dijkstra, FA; He, MZ; Johansen, MP; Harrison, JJ; Keitel, C
    Competition for nutrients between plants and microbes is an important determinant for plant growth, biodiversity and carbon cycling. Perturbations such as drought affect plant-microbe competition for nitrogen (N) and phosphorus (P). Despite the importance of these nutrients in most ecosystems, plant-microbe competition for N and P remains poorly understood. We used a novel dual isotope labelling technique (15N and 32P) to assess plant-microbe competition for N and P affected by drought in two different plant-soil systems. Mesocosms were extracted from a grassland site where plants were strongly limited by N (N-limiting system) and from a grassland site that showed strong soil P adsorption (P-adsorbing system). Half of the mesocosms were subjected to drought one week prior to injection of the tracers. Stable 15N (as KNO3) and radio-labelled 32P (as H3PO4) were injected, and measured in the plant and microbial biomass 72 hrs later. Microbial uptake of 32P was strongly reduced by drought (on average by 89%), while microbial 15N uptake was not. In contrast, drought reduced plant uptake of 15N (by 28%), but not of 32P. Microbial 15N uptake was much larger in the N-limiting system than in the P-adsorbing system (by 491%), while plant 32P uptake was much larger in the P-adsorbing system than in the Nlimiting system (by 703%). Both plants and microbes showed large flexibility in taking up 15N and 32P with the largest uptake of the nutrient that was in greatest demand. Our results suggest that under drought conditions, plants lose in terms of N uptake, but win in terms of P uptake when competing for these nutrients with microbes. These different sensitivities to drought by plants and microbes may enhance decoupling of the N and P cycle with increased drought conditions, depending on if plants and microbes are N or P limited.