Abstract
Light and soil water availability may limit carbon uptake of trees in tropical rainforests. The objective of this work was to determine how photosynthetic traits of juvenile trees respond to variations in rainfall seasonality, leaf nutrient content, and opening of the forest canopy. The correlation between leaf nutrient content and annual growth rate of saplings was also assessed. In a terra firme rainforest of the central Amazon, leaf nutrient content and gas exchange parameters were measured in five sapling tree species in the dry and rainy season of 2008. Sapling growth was measured in 2008 and 2009. Rainfall seasonality led to variations in soil water content, but it did not affect leaf gas exchange parameters. Subtle changes in the canopy opening affected CO2 saturated photosynthesis (A pot, p = 0.04). Although A pot was affected by leaf nutrient content (as follows: P > Mg > Ca > N > K), the relative growth rate of saplings correlated solely with leaf P content (r = 0.52, p = 0.003). At present, reduction in soil water content during the dry season does not seem to be strong enough to cause any effect on photosynthesis of saplings in central Amazonia. This study shows that leaf P content is positively correlated with sapling growth in the central Amazon. Therefore, the positive effect of atmospheric CO2 fertilization on long-term tree growth will depend on the ability of trees to absorb additional amount of P
Highlights
Growth rates of plants depend on several factors, including soil water content (Wagner et al, 2012) and availability of mineral nutrients (Wright et al, 2011; Santiago et al, 2012)
The mild dry period in central Amazonia is limited to only a few months; the magnitude of the effect of reduction in soil water content on tree growth during the dry season remains to be elucidated (Marenco et al, 2014a)
Based on soil characteristics of the central Amazon, in this study is hypothesized that in this region, variations in leaf P content affect photosynthetic traits, and that increases in photosynthesis result in faster growth rates of saplings
Summary
Growth rates of plants depend on several factors, including soil water content (Wagner et al, 2012) and availability of mineral nutrients (Wright et al, 2011; Santiago et al, 2012). In addition to light and nutrient availability, soil water content is another factor that influences photosynthesis and plant growth, and over a wide range of plant species and growth conditions, there seems to be a positive correlation between plant growth and photosynthetic rates (Kruger & Volin, 2006). Based on soil characteristics of the central Amazon, in this study is hypothesized that in this region, variations in leaf P content affect photosynthetic traits, and that increases in photosynthesis result in faster growth rates of saplings. The objective of this work was to determine how photosynthetic traits of juvenile trees respond to variations in soil water content, leaf nutrient content, and forest canopy opening in central Amazonia. The correlation between leaf nutrient content and annual growth rate of saplings was assessed
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