Nitrogen availability and forest productivity along a climosequence on Whiteface Mountain, New York

We studied broadleaf and needle-leaf forests along an elevation gradient (600–1200 m) at Whiteface Mountain, New York, to determine relationships among temperature, mineral N availability, and aboveground net primary productivity (ANPP) and controls on the latter two variables. We measured net N mineralization during the growing season, annual litterfall quantity and quality, aboveground woody biomass accumulation, and soil organic matter quality. Inorganic N deposition from cloudwater markedly increases mineral N availability above 1000 m in this region. Consequently, mineral N availability across the climosequence remains relatively constant because N mineralization decreases with increasing elevation. Across this climosequence, air temperature (as growing season degree-days) exerted the most control on ANPP. Nitrogen mineralization was most strongly related to soil growing season degree-days and less so to lignin to N ratios in litter. ANPP was correlated with N mineralization but not with mineral N availability. Combining our data with those from similar studies in other boreal and cool temperate forests shows that N mineralization and ANPP are correlated at local, regional, and interbiome scales. Regarding the persistent question concerning cause and effect in the N mineralization – forest productivity relationship, our data provide evidence that at least in this case, forest productivity is a control on N mineralization. Comments Copyright NRC Research Press. Published in Canadian Journal of Forest Research, Volume 33, Number 10, October 2003, pages 1880-1891. Publisher URL: http://pubs.nrc-cnrc.gc.ca This journal article is available at ScholarlyCommons: http://repository.upenn.edu/ees_papers/12 Nitrogen availability and forest productivity along a climosequence on Whiteface Mountain, New York Amishi B. Joshi, David R. Vann, Arthur H. Johnson, and Eric K. Miller Abstract: We studied broadleaf and needle-leaf forests along an elevation gradient (600–1200 m) at Whiteface MounWe studied broadleaf and needle-leaf forests along an elevation gradient (600–1200 m) at Whiteface Mountain, New York, to determine relationships among temperature, mineral N availability, and aboveground net primary productivity (ANPP) and controls on the latter two variables. We measured net N mineralization during the growing season, annual litterfall quantity and quality, aboveground woody biomass accumulation, and soil organic matter quality. Inorganic N deposition from cloudwater markedly increases mineral N availability above 1000 m in this region. Consequently, mineral N availability across the climosequence remains relatively constant because N mineralization decreases with increasing elevation. Across this climosequence, air temperature (as growing season degree-days) exerted the most control on ANPP. Nitrogen mineralization was most strongly related to soil growing season degree-days and less so to lignin to N ratios in litter. ANPP was correlated with N mineralization but not with mineral N availability. Combining our data with those from similar studies in other boreal and cool temperate forests shows that N mineralization and ANPP are correlated at local, regional, and interbiome scales. Regarding the persistent question concerning cause and effect in the N mineralization – forest productivity relationship, our data provide evidence that at least in this case, forest productivity is a control on N mineralization. Résumé : Nous avons étudié des forêts de feuillus et de résineux le long d’un gradient altitudinal (600–1200 m) à Whiteface Mountain dans l’État de New York pour déterminer les relations entre la température, la disponibilité en azote minéral, la productivité primaire nette aérienne (PPNA) et les facteurs contrôlant ces deux dernières variables. Nous avons mesuré la minéralisation nette de l’azote pendant la saison de croissance, la quantité annuelle de litière et sa qualité, le cumul de biomasse ligneuse aérienne et la qualité de matière organique du sol. Dans cette région, les dépôts d’azote inorganique provenant de l’eau des nuages augmentent de façon marquée la disponibilité en azote minéral au-dessus de 1000 m. De cette façon, la disponibilité en azote minéral dans la climoséquence reste relativement constante parce que la minéralisation de l’azote diminue avec l’altitude. Le long de cette climoséquence, la température de l’air (exprimée en degrés-jours pendant la saison de croissance) exerce le contrôle le plus important sur la PPNA. La minéralisation de l’azote est la plus fortement reliée aux degrés-jours dans le sol pendant la saison de croissance et moins au rapport lignine:azote dans la litière. La PPNA est corrélée avec la minéralisation de l’azote mais pas avec la disponibilité en azote minéral. La combinaison de nos données avec celles d’autres études semblables effectuées dans d’autres forêts boréales et tempérées froides montre que la minéralisation de l’azote et la PPNA sont corrélées aux échelles locales, régionale et entre les biomes. A propos de la question persistante concernant les liens de cause à effet entre la minéralisation de l’azote et la productivité forestière, nos données fournissent la preuve qu’au moins dans le cas présent la productivité forestière exerce un contrôle sur la minéralisation de l’azote. [Traduit par la Rédaction] Joshi et al. 1891