RT Journal Article
SR Electronic
A1 Nascimento, H. C. S.
A1 Marenco, R. A.
T1 Mesophyll conductance variations in response to diurnal environmental factors in Myrcia paivae and Minquartia guianensis in Central Amazonia
JF Photosynthetica
YR 2013
VO 51
IS 3
SP 457
OP 464
DO 10.1007/s11099-013-0046-x
UL https://ps.ueb.cas.cz/artkey/phs-201303-0016.php
AB Mesophyll conductance (g &lt;sub&gt;m&lt;/sub&gt;) is essential to determine accurate physiological parameters used to model photosynthesis in forest ecosystems. This study aimed to determine the effects of time of day on photosynthetic parameters, and to assess the effect of using either intercellular CO&lt;sub&gt;2&lt;/sub&gt; concentration (C &lt;sub&gt;i&lt;/sub&gt;) or chloroplast CO&lt;sub&gt;2&lt;/sub&gt; concentration (C &lt;sub&gt;c&lt;/sub&gt;), on maximum carboxylation velocity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), V &lt;sub&gt;cmax&lt;/sub&gt;. We used Amazonian saplings of Myrcia paivae and Minquartia guianensis. Photosynthetic parameters were measured using an infrared gas analyzer (IRGA); g &lt;sub&gt;m&lt;/sub&gt; was determined using both gas exchange and chlorophyll (Chl) a fluorescence and gas-exchange data alone. Leaf thickness (L &lt;sub&gt;T&lt;/sub&gt;) and specific leaf area (SLA) were also measured. Air temperature, relative humidity or understory light did not correlate with g &lt;sub&gt;m&lt;/sub&gt; and on average daily IRGA-fluorometer-determined g &lt;sub&gt;m&lt;/sub&gt; was 0.04 mol(CO&lt;sub&gt;2&lt;/sub&gt;) m&lt;sup&gt;-2&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt; for M. paivae and 0.05 mol(CO&lt;sub&gt;2&lt;/sub&gt;) m&lt;sup&gt;-2&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt; for M. guianensis. Stomatal conductance (g &lt;sub&gt;s&lt;/sub&gt;), g &lt;sub&gt;m&lt;/sub&gt;, electron transport rate (J &lt;sub&gt;F&lt;/sub&gt;), and light-saturated net photosynthetic rate (P &lt;sub&gt;Nmax&lt;/sub&gt;) were lower in the afternoon than in the morning. However, no effect of time of day was observed on V &lt;sub&gt;cmax&lt;/sub&gt;. L &lt;sub&gt;T&lt;/sub&gt; and SLA did not affect any of the examined parameters. IRGA-determined g &lt;sub&gt;m&lt;/sub&gt; was almost the double of the value obtained using the IRGA-fluorescence method. V &lt;sub&gt;cmax&lt;/sub&gt; values determined using C &lt;sub&gt;c&lt;/sub&gt; were about 25% higher than those obtained using C &lt;sub&gt;i&lt;/sub&gt;, which highlighted the importance of using C &lt;sub&gt;c&lt;/sub&gt; in V &lt;sub&gt;cmax&lt;/sub&gt; calculation. Decline in P &lt;sub&gt;Nmax&lt;/sub&gt; at the end of the afternoon reflected variations in g &lt;sub&gt;s&lt;/sub&gt; and g &lt;sub&gt;m&lt;/sub&gt; rather than changes in V &lt;sub&gt;cmax&lt;/sub&gt;. Diurnal variation in g &lt;sub&gt;m&lt;/sub&gt; appeared to be associated more with endogenous than with atmospheric factors.