Photosynthetic traits of tree species in response to leaf nutrient content in the central Amazon

Abstract

Rainforest tree species are often found on poor soils where essential nutrients may be in low concentrations. Here, we determine the effect of nutrients (N, P, Ca, Mg and K) in photosynthetic traits in five rainforest tree species from central Amazonia. Gas exchange parameters were measured with an infrared gas analyzer in four saplings (1-3 m tall) per species using two leaves per plant. Data on gas exchange and leaf nutrient content (N, P, K, Ca and Mg) were collected between August and November, 2010. Specific leaf area (SLA) and leaf thickness (L T ) were also determined. Potential photosynthesis per unit mass (A pot-mass ), maximum carboxylation velocity of Rubisco (V c-max ) and electron transport rate (J max ) were responsive to variation in leaf nutrient content per unit mass. On a mass basis, P content was positively correlated with N, Mg, and K content; Mg content was positively correlated with K content. However, no correlation was found between the content of P, Mg, K and Ca, or between Ca, Mg, K and N. SLA and L T were strongly related to A pot-area , V c-max and J max (per unit area). Our study shows in situ evidence on the effect of leaf nutrients on A pot-mass , V c-max and J max (per unit mass) of tree saplings in the central Amazon. The magnitude of changes in photosynthetic capacity of juvenile trees in the forest understory depends not only on N and P use efficiency, but also on the availability of K, Mg and Ca, in decreasing order.

Juvenile tree growth correlates with photosynthesis and leaf phosphorus content in central Amazonia

“…Leaf nutrient contents found in this study are similar to those reported by Mendes & Marenco (2015). Except for leaf P concentration, the mean values of leaf nutrient content for N, K, Ca and Mg found in this study resemble those reported by Fyllas et al (2009) for tropical trees.…”

“…Therefore, data collected over seasons were combined for data analysis. In comparison with L T , SLA varied only within a narrow range, from 14.3 to 20.5 m 2 kg -1 (Table 2), which is within the range observed in other tree species in the same region (Marenco & Vieira, 2005, Mendes & Marenco, 2015. There was no difference among species on AIH, AID or ∆B ( Table 2), indicating that differences on growth rates across microsites were related to environmental factors rather than differences on the genetic make-up of the species.…”

“…Fyllas et al (2009) also found similar values for the N/K, K/Ca and the K/Mg ratios. On the other hand, because of low leaf P concentrations, the N/P and K/P ratios reported in this study are almost twice the values reported by Fyllas et al (2009) and Mendes & Marenco (2015). There is a gap in the information regarding critical levels for most Amazonian tree species.…”

“…The positive effect of leaf K, Ca and Mg content on photosynthetic parameters exemplifies the complexity of interactions between carbon gain and mineral nutrition of tropical rainforest, as suggested by Townsend et al (2011). Mendes & Marenco (2015) also found significant correlations between K, Ca and Mg and photosynthetic parameters (electron transport and CO 2 carboxylation rates). The reduction in either PNUE (as a function of leaf N) or PNUE with respect to leaf P content concurs with the results reported by Reich & Schoettle (1988) and Mendes & Marenco (2015).…”

“…Mendes & Marenco (2015) also found significant correlations between K, Ca and Mg and photosynthetic parameters (electron transport and CO 2 carboxylation rates). The reduction in either PNUE (as a function of leaf N) or PNUE with respect to leaf P content concurs with the results reported by Reich & Schoettle (1988) and Mendes & Marenco (2015). The positive correlation between photosynthesis and RGR is consistent with the results of Kruger & Volin (2006) and supports the hypothesis that in the study area, both A pot and plant growth are responsive to variation in leaf P concentration.…”