Canopy photosynthesis, canopy respiration and surplus production in a subtropical mangrove Kandelia candel forest, Okinawa Island, Japan

Abstract

The gross photosynthesis and respiration rates of leaves at different canopy depths in a Kandelia candel (L.) Druce stand were measured monthly over 2 yr. The maximum gross photosynthesis and dark respiration rates of the leaves existing at the top of the canopy were respectively 2 to 4 times and 2 to 7 times those of the bottom leaves throughout the year. The maximum gross photosynthesis and dark respiration rates showed positive correlations with leaf nitrogen content. Daily canopy gross photosynthesis and respiration showed apparent seasonal changes. The annual canopy gross photosynthesis, canopy respiration and surplus production were estimated as 102.9 ± 1.5, 44.0 ± 2.1 and 58.9 ± 0.6 (SE) t CO 2 ha -1 yr . The neglect of seasonal changes in the physiological traits of leaves resulted in estimates that were 65 to 125% of the annual surplus production. The relationship of gross primary production (GPP) to the product of LAI and warmth index (WI) was similar to those established for various types of terrestrial forests in perhumid climates.

The self-thinning process in mangrove Kandelia obovata stands

“…Although K. obovata was formerly recognized as K. candel (L.) Druce, it was split into two species, one of which is K. candel and the other is K. obovata, distributed in China and Japan (Sheue et al 2003). Intensive studies are now in progress in the mangrove K. obovata forest at Manko Wetland, Okinawa Island, Japan (Khan et al 2004(Khan et al , 2007Suwa et al 2006. However, there is no information about the self-thinning process of this mangrove forest.…”

How do tree competition and stand dynamics lead to spatial patterns in monospecific mangroves?

“…The negative spatial association between trees of different sizes (mutual inhibition of growth), as indicated by the negative values of k mm (r) within 2 m distance during the early stage and within 3 m distance after two decades of stand development, is an indication that small trees are associated with large neighbouring trees if competition suppresses growth (Law et al, 2009). The overall spatial randomness in tree locations for larger distances (> 2 m in young stage and > 3 m after two decades) might be related to a smaller tree crown in the K. obovata as a light-loving species (Khan et al, 2004;Suwa et al, 2006) and dwarf mangrove type (Lee, 1989), and the trees are not large enough to pose any shading threat to neighbours at large distances.…”

“…7) suggests a higher mortality of smaller trees in older stands due to intraspecific competition (Xue et al, 1999;Ogawa and Hagihara, 2003), which is supported by the earlier findings that K. obovata is intolerant to shade (Khan et al, 2004), and the trees strongly compete for light as is true for other heliophytes (Tüffers et al, 1999;Ball et al, 1988). In the case of a closed-canopy stand when larger trees obstruct light to smaller ones, the smaller trees are thinned out because of the shade of larger ones resulting in low photosynthetic production in the former, which still have a respiration cost (Weiner and Whigham, 1988;Suwa et al, 2006).…”

Canopy photosynthesis in a mangrove considering vertical changes in light-extinction coefficients for leaves and woody organs

“…All data were collected in a Kandelia obovata (S., L.) Yong stand at Manko Wetland, Okinawa Island, Japan (26°11 0 N, 127°40 0 E; Khan et al 2004;Suwa et al 2006). Based on 1992-2001 data obtained from the Okinawa Meteorological Observatory, the mean annual temperature was 23.2°C and the mean annual rainfall was 2086 mm year -1 .…”

“…The woody organs apparently have the potential to intercept the light in the forest canopy, and Yim et al (1969) incorporated the effect of woody organs in the light-penetration model. On the basis of the model developed by Yim et al (1969), Kurachi et al (1993) and Suwa et al (2006) estimated the canopy photosynthetic production of a plantation and a mangrove, respectively. Although Yim et al (1969) assumed that the cumulative woody silhouette area density C was proportional to F, according to the pipe model theory (Shinozaki et al 1964) the C/F ratio may increase with downward distance within a canopy, because the amounts of heart wood and dead branches increase.…”