N, P and O 3 -responses of subalpine plants and their

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Reginald Sharp
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mycorrhiza Verena Blanke, Matthias Volk, Seraina Bassin, Jürg Fuhrer

1 Federal Department of Economic Affairs FDEA Agroscope Reckenholz-Tänikon Research Station ART N, P and O 3 -responses of subalpine plants and their mycorrhiza Verena Blanke, Matthias Volk, Seraina Bassin, Jürg Fuhrer February 3 rd 2010, 23 rd Task Force Meeting of the UNECE ICP Vegetation, Tervuren, Belgium

2 arbuscular mycorrhiza (AM) mycorrhiza = "fungusroot" AM most common mycorrhiza type c. 80 % of vascular plant species, mostly herbs (in temperate zones) Glomeromycetes nutrients carbon Brundrett et al. 1996, modified 2

3 arbuscular mycorrhiza ecology and function arbuscular mycorrhizal fungi (AMF) are obligate symbionts, dependent on plant C main function: phosphorus nutrition of host plants at high P-availability plants stop C- allocation to fungi % of root length colonized (% RLC) by AMF is reduced further improved: e.g. uptake of nitrogen % RLC also reduced at high N- availability 3

4 arbuscular mycorrhiza ecology and function + AMF control 4

5 arbuscular mycorrhiza in plant communities plant species differ in their dependency on the mycorrhiza when AMF are present, more dependent species are superior competitors for nutrients when few or no AMF are present, less dependent or nonmycorrhizal species have an advantage influence coexistence, composition of plant communities Brundrett et al. 1996, modified 5

6 Alp Flix N x P experiment fertilization effect depends on nature of nutrient limitation N-input in non N-limited system may increase limitation by another nutrient aboveground productivity at Alp Flix co-limited by N and P? after +P: N:P-ratios indicate N-limitation; increase of plant P-concentrations after +N: grasses (most abundant functional group) maybe P-limited 9/10 x 4 treatments: control + 50 kg N ha -1 year kg P ha -1 year -1 + N + P 6

7 N x P experiment AM background mycorrhizal growth depends on availability of N and P relative to each other (N:P-ratio) t colonization by AMF root low P high P low N high N at high P-availability, N-addition leads to a reduction of N-limitation and less plants' C-investement in fungi at low P-availabillity, N-addition leads to an amplification of P-limitation and more plants' C-investment in fungi? 7

µm allows hyphal growth prevents root growth (Johnson et al.

8 N x P experiment phytometers plants in ingrowth cores (May - August 2008) treatment effects on shoot & root mass and % root length colonized by AMF Leontodon helveticus Trifolium alpinum Carex sempervirens Festuca violacea 15 cm x 2 cm PE mesh 40 µm allows hyphal growth prevents root growth (Johnson et al. 2001, modified) in half of the monoliths, cores rotated weekly disrupts external mycelium reduces nutrient transfer and % RLC N, P and O3-responses of subalpine plants and their mycorrhiza 8

9 N x P experiment 2008, results F. violacea means ± SD linear model (n = factor N-addition, p = factor P-addition, = factor rotation) significant effect, if p<0.05 biomass: n-effect, p-effect (same for shoot & root) shoot:root-ratio: n-effect biomass increased by +N and decreased by +P N-limitation? ( monolith data: grasses rather N+P co-limited) shoot:root-ratio increased by N-addition competition is shifting aboveground (light)? 9

10 N x P experiment 2008, results F. violacea means ± SD linear model (n = factor N-addition, p = factor P-addition, = factor rotation) significant effect, if p<0.05 biomass: n-effect, p-effect (same for shoot & root) shoot:root-ratio: n-effect % RLC: n-effect, p-effect, -effect % RLC reduced by +P and increased by +N P-limitation? ( plant data, P-status of grasses in monoliths) % RLC of phytometers rather mirror mycorrhizal status of whole vegetation or functional group? decreased % RLC by rotation did not affect biomass 10

11 N x P experiment synthesis Although aboveground productivity suggests co-limitation by N and P, only P-addition apparently reduces AMF abundance in roots (possibly following P- status of the vegetation). 11

12 N x P experiment synthesis Although aboveground productivity suggests co-limitation by N and P, only P-addition apparently reduces AMF abundance in roots (possibly following P- status of the vegetation). N-input of simulated 50 kg ha -1 yr -1 increased root colonization of Festuca violacea grasses become P-limited after N- fertilization and invest more C in fungi? 12

13 N x O 3 experiment phytometers ingrowth cores in N x O 3 -experiment (May - August 2009) in lowest and highest O 3 -treatment (control: ambient, c. 46 ppb; +O 3 : 2x ambient) L. helveticus T. alpinum Potentilla aurea Festuca rubra in lowest and highest N-treatment (control: background deposition, c. 4 kg N ha -1 year -1 ; +N: +50 kg N ha -1 year -1 ) 13

14 N x O 3 experiment AM background ozone damages reduce carbon allocation to roots and mycorrhizal hyphae (e.g. Andersen 2000) reduced mycorrhizal colonization (McCool & Menge 1983, Yoshida et al. 2001) high O 3 : greater leaf damages and even inferior growth of mycorrhizal plants fungus is a significant C drain for damaged plants (McCool & Menge 1984) but mycorrhiza also improves plant traits like nutrient status, photosynthesis... could as well lead to improved O 3 tolerance? 14

15 N x O 3 experiment AM background if high nutrient supply leads to stronger O 3 damages of plants (greater leaf area, stomatal conductance = increased O 3 uptake) if high nutrient supply leads to better O 3 tolerance (improved photosynthesis, carbohydrate/ energy availability) root colonization n by AMF low nutrient high nutrient root colonization n by AMF high nutrient low nutrient low O 3 high O 3 low O 3 high O 3 well supplied plants will have less carbohydrates left for fungi? poorly supplied plants will have less carbohydrates left for fungi? 15

16 N x O 3 experiment 2009, results F. rubra biomass means ± SD linear mixed effects model (ring = random, n = factor N-addition, o 3 = factor O 3 -fumigation, = factor rotation) significant effect, if p<0.05 total: n-effect, o 3-trend (0.058), n*o 3 -trend (0.085) shoot: n-effect root: trends for n (0.083), o 3 (0.054), n*o 3 (0.098) shoot:root-ratio: n-effect biomass and shoot:root-ratio increased by +N ( N x P-experiment) O 3 possibly has negative influence - but not on shoots at first, C-allocation belowground is affected? under O 3 -stress, plants cannot profit from added N? 16

17 N x O 3 experiment 2009, results F. rubra % RLC means ± SD linear mixed effects model (ring = random, n = factor N-addition, o 3 = factor O 3 -fumigation) significant effect, if p<0.05 n-effect, o 3 -trend (0.088), n*o 3 -trend (0.065) N-fertilization increase in % RLC P-limitation? ( N x P experiment) O 3 : possible reduction of C belowground reduction of % RLC? under O 3 -stress, plants cannot afford to invest more C in AMF after N-addition? 17

18 N x O 3 experiment, synthesis N-input (50 kg ha -1 yr -1 ) in subalpine pasture at Alp Flix P-limitation of grasses? increase in root colonization by arbuscular mycorrhizal fungi of most abundant grass Festuca rubra positive influence on overall AMF abundance, as grasses contribute most to total plant biomass would favour species more dependent on AM 18

19 N x O 3 experiment, synthesis N-input (50 kg ha -1 yr -1 ) in subalpine pasture at Alp Flix P-limitation of grasses? increase in root colonization by arbuscular mycorrhizal fungi of most abundant grass Festuca rubra positive influence on overall AMF abundance, as grasses contribute most to total plant biomass would favour species more dependent on AM elevated O 3 (c. 100 ppb) might reduce root, but not shoot mass of grasses reduction of belowground C-transfer? seems to reduce % RLC of grasses resulting decreased AMF abundance would favour species less dependent on AM 19

20 N x O 3 experiment, synthesis possible N x O 3 interaction N-addition only increases AMF abundance in low O 3 environment O 3 -stressed plant cannot "afford" to invest more C in AMF nutrient stress: stronger O 3 effect? 20

21 many thanks Federal Office for the Environment FOEN 21

22 N x P experiment 2008, vegetation monoliths aboveground biomass, means ± SD linear model (n = factor N-addition, p = factor P-addition) significant effect, if p<0.05 total: n-effect, p-effect grasses: n-effect, p-effect whole vegetation and grasses co-limited by N and by P? 22

23 N x P experiment 2008, vegetation monoliths N:P-ratio, means ± SD linear model (n = factor N-addition, p = factor P-addition) significant effect, if p<0.05 total: p-effect grasses: p-effect total N:P around 18 (control, +N) co- or P-limitation (Tessier & Raynal 2003, Güsewell 2004) P-addition N-limitation grasses reacted similarly (higher N:P closer to P-limitation?) 23

1 Towards Ecological Relevance Progress and Pitfalls in the Path Towards an Understanding of Mycorrhizal Functions in Nature... 3 D.J.

Contents Section A: Introduction 1 Towards Ecological Relevance Progress and Pitfalls in the Path Towards an Understanding of Mycorrhizal Functions in Nature... 3 D.J. Read 1.1 Summary.............................