Effects of elevated O 3 and N deposition on biodiversity and N pools of a subalpine grassland

Transcription

1 Federal Department of Economic Affairs, Education and Research EAER Agroscope Reckenholz-Tänikon Research Station ART Effects of elevated and N deposition on biodiversity and N pools of a subalpine grassland Seraina Bassin, Matthias Volk, Jürg Fuhrer 8 th April 214

2 Alp Flix Experiment (24-21) Ozone Nitrogen 9 fumigation rings 2 monoliths per fumigation ring control = ambient conc. N4 = ambient deposition + = 1.2 x a.c. N9 = + 5 kg N ha -1 yr = 1.6 x a.c. N14 = +1 kg N ha -1 yr -1 N29 = +25 kg N ha -1 yr -1 N54 = +5 kg N ha -1 yr -1 ambient concentration N ambient deposition ppb < 5 kg N ha -1 yr -1 and N effects on subalpine grassland 2

3 Species composition of the monoliths Geo-Montani-Nardetum, 17 vascular plant species Dominant species: Festuca rubra 12% Carex sempervirens 8% Nardus stricta 11% O3 and N effects on subalpine grassland 3

4 Nitrogen effect on productivity Biomass (g m -2 ) Grasses Forbs Sedges Legumes Nitrogen load (kg ha -1 yr -1 ) No effect on aboveground productivity Volk et al. 214 O3 and N effects on subalpine grassland 4

5 Proportion ( ) N effect: functional group composition.7.6 Grasses.4 Forbs.5.3 Proportion [ ] Sedges Year N4 N9 N14 N29 N Legumes Year Year Year Bassin et al. 213 and N effects on subalpine grassland Sign. effect with +5 kg N ha -1 yr -1 5

6 Proportion ( ) effect: functional group composition.7.6 Grasses.4 Forbs.5.3 Proportion [ ] control no sign. effect.4 Sedges.8 Legumes Year and N effects on subalpine grassland 6

7 Sedges Forbs Grasses Sign. effects on species abundance Species N N x time Agrostis capillaris Anthoxanthum alpinum Briza media Festuca spp. Helictotrichon versicolor Nardus stricta Arnica montana Gentiana acaulis Homogyne alpina Leontodon helveticus Ligusticum mutellina Plantago alpina Potentilla aurea Ranunculus villarsii Carex sempervirens Carex ornithopoda Trifolium alpinum Bassin et al

8 N effect on diversity and nutrient value 2.8 Shannon Index 2.3 Nutrient value Shannon diversity ( ) N4 N9 N14 N29 N54 Year But: N-induced reduction of species number: max 4% weak competition for light in open canopies (LAI <2.5) No N effect on nutrient value: small spectrum of nutrient values among present species (Sedges nitrophilous species) Nutrient value ( ) Year O3 and N effects on subalpine grassland 8

9 Conclusions species composition No effect Strong N induced increase of sedges - responsible for the strong biomass increase - similar response at 1 different subalpine sites (differing in ph) - slow growing, stress-tolerant species (oligotrophic) - successful due to its high phosphorous efficiency No N-induced shift in nutrient value Common principle of functional traits and indicator values do not hold in ecosystems that are limited by several abiotic factors But these are often the most species-rich habitats O3 and N effects on subalpine grassland 9

10 Soil N pools O3 and N effects on subalpine grassland 1

11 Soil cores and fractionation Treatments control +N N54 Green biomass Necromass Litter Roots 1 cm Microbial biomass Soluble N 6 cm Extractable N 11

12 Lignin content (mg kg -1 ) Soil N pools Hypotheses (speculative) N pool (g m -2 ) N effect effect x N effect Immobilized soil N Reduced Extractable decomposition soil N of N-rich SOM Soluble due to lower soil Ninput of labile C (-8% GPP, Microbial Volk biomass et al. 211) N Roots x N Litter effect N accumulation Necromassin recalcitrant SOM is weaker Green in phytomass + +N54 than in + due to altered root litter quality 32 O3c_N4 O3++_N4O3c_N54O3++_N54 control +N N54 Lignin content (g kg -1 dry matter) Roots Roots O3c_N4 control O3c_N54 +N54 O3++_N4 +O O3++_N N54 12

13 Conclusions N pools 7 years of increased N deposition - strongly increased plant N pools and was immobilized in soil 7 years of increased deposition - only marginally affected plant N pools - but strongly increased immobilized soil N (reduced decomposition due to lower input of labile C?) x N interactive effects - weaker N accumulation in +N54 (due to reduced lignin content in roots?) 13

14 Thanks! Robin Giger Anne-Lena Wahl Ulrike Zell Alain Valsangiacomo Hansruedi Oberholzer Jochen Mayer 14

15 C:N ratio O3 and N effects on subalpine grassland 15

16 N pool (g m -2 ) N pool (g m -2 ) N pool (g m -2 ) N and effect on ecosystem N pools N effect effect Green phytomass snow melt harvest N4 N Microbial biomass N4 N Green phytomass control Microbial biomass control ++ N pool (g m -2 ) May July Aug Necromass May July Aug Soluble N N pool (g m -2 ) May July Aug Necromass May July Aug Soluble N N 3 May July Aug Roots. 3 May July Aug Extractable NN 3 May July Aug Roots. 3 May July Aug Extractable N N May July Aug May July Aug May July Aug May July Aug 16

17 Immobilized soil N N pool (g m -2 ) N pool (g m -2 ) N effect effect Immobilized soil N N4 N Immobilized soil N control ++ Npool (g N m -2 ) N pool (g N m -2 ) May July Aug 3 May July Aug Hypothesis Altered litter quality (e.g. Nardus) Reduced decomposition SOM accumulation 17

18 effect: proportion of dead leaves.1 Dead plant material Proportion [ ] control + ++ Year and N effects on subalpine grassland 18

19 No of PQ hits [ ] N effect on species abundance 1 Festuca spp. Nardus stricta Carex sempervirens Agrostis capillaris Briza media Carex ornithopoda No PQ hits [ ] Plantago alpina Potentilla aurea O3 and N effects on subalpine grassland. Year Trifolium alpinum N4 N9 N14 N29 N54 19

20 No of PQ hits [ ] effect on species abundance 3. Anthoxanthum alpinum Briza media Carex ornithopoda 3. Potentilla aurea Leontodon helveticus Plantago alpina Nardus stricta and N effects on subalpine grassland Year control + ++ Plausible effect: - Strong effect (+4%) - Dose related - Increased over time 2

21 Change in soil %C of soil fractions 17 < Strong general increase in %C, increased by but more strongly in N4 12 Lignin content (g kg -1 dry matter) 22 Lignin content of roots O3c_N4 O3c_N54 O3++_N4 O3++_N54 Soil C content (% 23 relative to 21) < > Ozone treatment 1 2 Ozone treatment Weak general increase in %C, more increased by ++_N4 Weak general decrease in %C, decreased by N and, effect is stronger in N > Ozone treatment General decrease in %C, More strongly decreased by, effect only apparent in N Ozone treatment While light fractions are enriched with %C; more strongly in ++_N4 (higher lignin content?), the heavy fractions are C depleted; more stronly in ++_N4 (shift in substrate use?). 21