Rising CO2 concentrations reduce nitrogen availability in alpine grasslands

Alpine grasslands, local biodiversity hotspots with very high nature conservation and cultural value, belong to one of the most affected ecosystems by global change. Yet, the potential effects of others than global warming factors on alpine plant functioning are poorly understood. To address this ga...

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Autores principales:	Sergey Rosbakh, Karl Auerswald, Peter Poschlod
Formato:	article
Lenguaje:	EN
Publicado:	Elsevier 2021
Materias:	CO2 fertilization Eutrophication Mountains Natural history collection Nitrogen Rubisco Ecology QH540-549.5
Acceso en línea:	https://doaj.org/article/2379d2d0c7a54983b91709f46ce2c09e
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spelling	oai:doaj.org-article:2379d2d0c7a54983b91709f46ce2c09e2021-12-01T04:57:31ZRising CO2 concentrations reduce nitrogen availability in alpine grasslands1470-160X10.1016/j.ecolind.2021.107990https://doaj.org/article/2379d2d0c7a54983b91709f46ce2c09e2021-10-01T00:00:00Zhttp://www.sciencedirect.com/science/article/pii/S1470160X21006555https://doaj.org/toc/1470-160XAlpine grasslands, local biodiversity hotspots with very high nature conservation and cultural value, belong to one of the most affected ecosystems by global change. Yet, the potential effects of others than global warming factors on alpine plant functioning are poorly understood. To address this gap, we made use of 359 herbarium specimens from nine vascular plant species collected in the Bavarian Alps, Germany, extending back 200 years (1807–2018) to reconstruct historical changes in foliar N content and stable isotope composition (δ15N), indicators of plant response to long-term N atmospheric deposition and rising atmospheric CO2 concentrations ([CO2]). These changes were interpreted in terms of three competing hypotheses (eutrophication, oligotrophication and photorespiration), representing alternative explanations for the response of plants to changes of N and CO2 availability.Foliar δ15N decreased significantly over time but an explanation by an increased input of reactive N from long-distance transport ('eutrophication' hypothesis) was unlikely because foliar N contents decreased significantly as well. An increased carbon gain due to increasing [CO2] (‘oligotrophication’) also was unlikely because instantaneous water use efficiency remained unchanged and indicated no increase in C gain. The detected patterns agreed well with the ‘photorespiration’ hypothesis that biochemically links N assimilation and C assimilation. Increasing concentration of ambient CO2 that decreases photorespiration explained decreasing δ15N values (R2 = 0.84, p < 0.001) and decreasing N contents (R2 = 0.40, p < 0.036).Our results suggest that increasing [CO2] by suppressing photorespiration reduces N availability to alpine plants. These findings contradict the generally accepted assumption of negative effects of eutrophication on alpine grasslands caused by air-borne N deposition. We conclude that increasing [CO2] should be considered as an alternative driver of long-term changes in alpine ecosystems, as it affects directly the plant C:N stoichiometry, a key plant trait determining several important ecosystem processes.Sergey RosbakhKarl AuerswaldPeter PoschlodElsevierarticleCO2 fertilizationEutrophicationMountainsNatural history collectionNitrogenRubiscoEcologyQH540-549.5ENEcological Indicators, Vol 129, Iss , Pp 107990- (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	CO2 fertilization Eutrophication Mountains Natural history collection Nitrogen Rubisco Ecology QH540-549.5
spellingShingle	CO2 fertilization Eutrophication Mountains Natural history collection Nitrogen Rubisco Ecology QH540-549.5 Sergey Rosbakh Karl Auerswald Peter Poschlod Rising CO2 concentrations reduce nitrogen availability in alpine grasslands
description	Alpine grasslands, local biodiversity hotspots with very high nature conservation and cultural value, belong to one of the most affected ecosystems by global change. Yet, the potential effects of others than global warming factors on alpine plant functioning are poorly understood. To address this gap, we made use of 359 herbarium specimens from nine vascular plant species collected in the Bavarian Alps, Germany, extending back 200 years (1807–2018) to reconstruct historical changes in foliar N content and stable isotope composition (δ15N), indicators of plant response to long-term N atmospheric deposition and rising atmospheric CO2 concentrations ([CO2]). These changes were interpreted in terms of three competing hypotheses (eutrophication, oligotrophication and photorespiration), representing alternative explanations for the response of plants to changes of N and CO2 availability.Foliar δ15N decreased significantly over time but an explanation by an increased input of reactive N from long-distance transport ('eutrophication' hypothesis) was unlikely because foliar N contents decreased significantly as well. An increased carbon gain due to increasing [CO2] (‘oligotrophication’) also was unlikely because instantaneous water use efficiency remained unchanged and indicated no increase in C gain. The detected patterns agreed well with the ‘photorespiration’ hypothesis that biochemically links N assimilation and C assimilation. Increasing concentration of ambient CO2 that decreases photorespiration explained decreasing δ15N values (R2 = 0.84, p < 0.001) and decreasing N contents (R2 = 0.40, p < 0.036).Our results suggest that increasing [CO2] by suppressing photorespiration reduces N availability to alpine plants. These findings contradict the generally accepted assumption of negative effects of eutrophication on alpine grasslands caused by air-borne N deposition. We conclude that increasing [CO2] should be considered as an alternative driver of long-term changes in alpine ecosystems, as it affects directly the plant C:N stoichiometry, a key plant trait determining several important ecosystem processes.
format	article
author	Sergey Rosbakh Karl Auerswald Peter Poschlod
author_facet	Sergey Rosbakh Karl Auerswald Peter Poschlod
author_sort	Sergey Rosbakh
title	Rising CO2 concentrations reduce nitrogen availability in alpine grasslands
title_short	Rising CO2 concentrations reduce nitrogen availability in alpine grasslands
title_full	Rising CO2 concentrations reduce nitrogen availability in alpine grasslands
title_fullStr	Rising CO2 concentrations reduce nitrogen availability in alpine grasslands
title_full_unstemmed	Rising CO2 concentrations reduce nitrogen availability in alpine grasslands
title_sort	rising co2 concentrations reduce nitrogen availability in alpine grasslands
publisher	Elsevier
publishDate	2021
url	https://doaj.org/article/2379d2d0c7a54983b91709f46ce2c09e
work_keys_str_mv	AT sergeyrosbakh risingco2concentrationsreducenitrogenavailabilityinalpinegrasslands AT karlauerswald risingco2concentrationsreducenitrogenavailabilityinalpinegrasslands AT peterposchlod risingco2concentrationsreducenitrogenavailabilityinalpinegrasslands
_version_	1718405650153734144

Rising CO2 concentrations reduce nitrogen availability in alpine grasslands

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