Fertilization reduced stomatal conductance but not photosynthesis of Pinus taeda which compensated for lower water availability in regards to growth

• Published in: Forest ecology and management 2016-12, Vol.381, p.37-47
• Main Authors: Maggard, Adam O., Will, Rodney E., Wilson, Duncan S., Meek, Cassandra R., Vogel, Jason G.
• Format: Article
• Language: English
• Subjects: Fertilization; Leaf gas exchange; Loblolly pine; Pinus taeda; Throughfall reduction
• ISSN: 0378-1127; 1872-7042
• DOI: 10.1016/j.foreco.2016.08.046

•Throughfall reduction reduces leaf gas exchange and slows growth.•Fertilization did not exacerbate the effects of throughfall reduction.•Fertilization reduced leaf-level conductance and increased water use efficiency.•Fertilization can benefit loblolly pine under reduced water availability. Loblolly pine (Pinus taeda L.) is the most commercially important tree species in the southeastern USA. Projected increases in regional temperature and drought severity likely will cause reductions in productivity, in particular for the western edge of the loblolly pine range. To determine the effects of nutrient availability and reduced water availability on leaf gas exchange, leaf area index (LAI), and tree growth, we examined the interactive effects of fertilization (one time application of 224kgNha−1, 28kgPha−1, 56kgKha−1 and micronutrients) and reduced throughfall (approximate 30% reduction) over growing seasons 5–7 for a loblolly pine plantation in southeastern Oklahoma. Throughfall reduction reduced volumetric soil water content from 11.3% to 8.8% and fertilization increased foliar nitrogen concentration from 1.13 to 1.27mgg−1. Fertilization increased LAI (10%) and subsequently tree growth while reducing stomatal conductance (7%) but caused less negative (3%) midday leaf water potential. Throughfall reduction reduced stomatal conductance (12%) and net photosynthesis (9%) and these responses were related to more negative midday leaf water potentials (11%). These results indicate that fertilization increased water use efficiency in that fertilized treatments maintained similar net photosynthetic rates as nonfertilized treatments even though stomatal conductance was lower. The net effect was that fertilization increased growth of throughfall reduction treatments such that productivity was similar to ambient throughfall treatments not receiving fertilization.