Gas exchange and water balance of a mistletoe species and its mangrove hosts

Summary The gas exchange and water relations of the hemiparasite Pthirusa maritima and two its mangrove host species, Conocarpus erectus and Coccoloba uvifera, were studied in an intertidal zone of the Venezuelan coast. Carbon uptake and transpiration, leaf osmotic and total water potential, as well as nutrient content in the xylem sap and leaves of mistletoes and hosts were followed through the dry and wet season. In addition, carbon isotope ratios of leaf tissue were measured to further evaluate water use efficiency. Under similar light and humidity conditions, mistletoes had higher transpiration rates, lower leaf water potentials, and lower water use efficiencies than their hosts. Potassium content was much higher in mistletoes than in host leaves, but mineral nutrient content in the xylem sap of mistletoes was relatively low. The resistance of the liquid pathway from the soil to the leaf surface of mistletoes was larger than the total liquid flow resistance of host plants. Differences in the daily cycles of osmotic potential of the xylem sap also indicate the existence of a high resistance pathway along the vascular connection between the parasite pathway along the vascular connection between the parasite and its host. P. maritima mistletoes adjust to the different physiological characteristics of the host species which it parasitizes, thus ensuring an adequate water and carbon balance.     

Are mangroves in the tropical Atlantic ripe for invasion? Exotic mangrove trees in the forests of South Florida

Two species of mangrove trees of Indo-Pacific origin have naturalized in tropical Atlantic mangrove forests in South Florida after they were planted and nurtured in botanic gardens. Two Bruguiera gymnorrhiza trees that were planted in the intertidal zone in 1940 have given rise to a population of at least 86 trees growing interspersed with native mangrove species Rhizophora mangle, Avicennia germinans and Laguncularia racemosa along 100 m of shoreline; the population is expanding at a rate of 5.6% year⁻¹. Molecular genetic analyses confirm very low genetic diversity, as expected from a population founded by two individuals. The maximum number of alleles at any locus was three, and we measured reduced heterozygosity compared to native-range populations. Lumnitzera racemosa was introduced multiple times during the 1960s and 1970s, it has spread rapidly into a forest composed of native R. mangle, A. germinans, Laguncularia racemosa and Conocarpus erectus and now occupies 60,500 m² of mangrove forest with stem densities of 24,735 ha⁻¹. We estimate the population growth rate of Lumnitzera racemosa to be between 17 and 23% year⁻¹. Populations of both species of naturalized mangroves are dominated by young individuals. Given the long life and water-dispersed nature of propagules of the two exotic species, it is likely that they have spread beyond our survey area. We argue that the species-depauperate nature of tropical Atlantic mangrove forests and close taxonomic relatives in the more species-rich Indo-Pacific region result in the susceptibility of tropical Atlantic mangrove forests to invasion by Indo-Pacific mangrove species.     

Diet and feeding patterns in the kipunji (<Emphasis Type="Italic">Rungwecebus kipunji</Emphasis>) in Tanzania’s Southern Highlands: a first analysis

The diet and feeding behaviour of the kipunji (Rungwecebus kipunji) was studied over 45 months, the first dietary analysis for this species. During 9498 h of direct observation of 34 kipunji groups, a list of 122 identified foodplants was recorded. The list represents 60 families, including 64 trees, 30 herbs, 9 climbers, 7 shrubs, 6 lianas, 3 grasses and 3 ferns. Kipunji were observed eating bark, young and mature leaves, ripe and unripe fruits, flowers, pith, seed pods, rhizomes, tubers, shoots and stalks. Invertebrates, fungi, moss, lichen, and soil were also eaten. Macaranga capensis var. capensis, an early successional tree, was the most commonly consumed species, with leaves, leaf stalks, pith, flowers and bark all eaten. We demonstrate that the kipunji is an omnivorous dietary generalist, favouring mature and immature leaves, ripe and unripe fruits and bark in similar proportions, with an almost comparable fondness for leaf stalks and flowers. Kipunji appear to be adaptable foragers able to modify their diet seasonally, being more folivorous in the dry season and more frugivorous in the wet. Whereas more ripe fruit is eaten in the wet season, the proportion of unripe fruit remains similar across the year. The proportion of mature leaves and pith increases throughout the dry season at the expense of ripe fruits and bark, and this may compensate nutritionally for the lack of available dry-season ripe fruits. Relatively more pith is eaten in the dry season, more stalks at the end of the dry and beginning of the wet seasons, and bark consumption increases as the rainfall rises.     

Standing crop and aboveground biomass partitioning of a dwarf mangrove forest in Taylor River Slough,Florida

The structure and standing crop biomass of a dwarf mangrove forest, located in the salinity transition zone ofTaylor River Slough in the Everglades National Park, were studied. Although the four mangrove species reported for Florida occurred at the study site, dwarf Rhizophora mangle trees dominated the forest. The structural characteristics of the mangrove forest were relatively simple: tree height varied from 0.9 to 1.2 meters, and tree density ranged from 7062 to 23 778 stems ha^–1. An allometric relationship was developed to estimate leaf, branch, prop root, and total aboveground biomass of dwarf Rhizophora mangle trees. Total aboveground biomass and their components were best estimated as a power function of the crown area times number of prop roots as an independent variable (Y = B × X^–0.5083). The allometric equation for each tree component was highly significant (p<0.0001), with all r² values greater than 0.90. The allometric relationship was used to estimate total aboveground biomass that ranged from 7.9 to 23.2 ton ha^–1. Rhizophora mangle contributed 85% of total standing crop biomass. Conocarpus erectus, Laguncularia racemosa, and Avicennia germinans contributed the remaining biomass. Average aboveground biomass allocation was 69% for prop roots, 25% for stem and branches, and 6% for leaves. This aboveground biomass partitioning pattern, which gives a major role to prop roots that have the potential to produce an extensive root system, may be an important biological strategy in response to low phosphorus availability and relatively reduced soils that characterize mangrove forests in South Florida.     

Plant-animal interactions and the structure and function of mangrove forest ecosystems*

Trophic interactions involving plants and animals in tropical mangrove forests have important controlling influences on several population, community and ecosystem-level processes. Insect herbivores remove up to 35% of leaf area from some mangrove tree species and can cause the death of seedlings. Leaf chemistry and toughness and soil nutrient status all appear to be important in explaining the between- and among-species variance in leaf damage. Insects also attack and damage, mainly by boring, a large proportion of mangrove seeds. Shadehouse experiments have shown that such post-dispersal predation can have a significant effect on seedling survival, growth and biomass allocation to leaves, stems and roots. Sesarmid crabs are also responsible for severe post-dispersal seed predation. In field trials, crabs consumed more than 70% of the seeds of five tree species. For four of these five species there was an inverse relationship between seed predation rate and the dominance of conspecific adult trees, while the within-site distribution pattern of one tree species appears to be partially controlled by crabs. The same crab species also consume 30–80% (depending on forest type and intertidal elevation), of the annual litter fall in mangrove forests and, thus, have an important role in controlling the rate of remineralization of detritus within forests and the export of particulate matter from the forests to other nearshore habitats. The other major component of litter in the forests is wood, which is broken down relatively rapidly by teredinid molluscs (shipworms). More than 90% of the weight loss from decomposing trunks of Rhizophora species during the first four years of decay is through ingestion by teredinids. The annual turnover of dead wood mass in Rhizophora forests is equivalent to that of the processing of leaf detritus by crabs. Because of the relatively low species richness of trees and consumers in tropical mangrove forests, they are likely to serve as productive sites for further investigations of the influence of plant-animal interactions on the dynamics of tropical forests.     

Tannin Dynamics of Propagules and Leaves of Kandelia candel and Bruguiera gymnorrhiza in the Jiulong River Estuary, Fujian, China

Changes in the total phenolics, condensed tannins (CT), protein-precipitable phenolics content and protein precipitation capacity were determined on a series of mangrove leaves from two true viviparous mangrove species (Kandelia candel and Bruguiera gymnorrhiza) at various stages of development and decomposition in the Jiulong River Estuary, Fujian, China. Similar measurements were also done for the propagules at different developmental stages. The results showed that the total phenolics, extractable condensed tannins, total condensed tannins, protein-precipitable phenolics content and protein precipitation capacity in young leaves were higher than those in mature and senescent leaves. Tannin dynamics during leaf decomposition varied with species, and the rapid loss of phenolics observed during decomposition can be ascribed to leaching and degradation. Protein-bound CT and fibre-bound CT tended to increase with leaf decomposition, with CT binding more strongly to protein than to fibre. Protein-bound CT was higher than fibre-bound CT with the exception of mature leaves. Total phenolics, extractable CT and protein-precipitable phenolics contents in flower tissues were relatively lower than those in hypocotyls at different developmental stages. Protein precipitation capacity fluctuated with the development of propagules. Increases in nitrogen in decaying litter, and declines in contents of total phenolics and total condensed tannins of detritus support the general conclusion that decomposing mangrove detritus can be a more palatable heterotrophic substrate than living leaves.     

Mangrove leaf litter decomposition under mangrove forest stands with different levels of pollution in the Niger River Delta,Nigeria

Nutrient cycling often moves between litter fall and decomposition. It is hypothesized that hydrocarbon pollution will slow down mangrove litter decomposition because of the reduction in microbial activities. We studied decomposition rates at different levels of pollution (i.e. high and low) and amongst different mangrove species (i.e. red, white and black). For the first experiment, fresh leaves of Rhizophora racemosa were collected, sealed in a litter bag and placed on the mangrove floor for 1.24 years at which all the leaves had completely decomposed to humus and were oven‐dried and weighed to calculate the decomposition rate constant (k) of mass loss. Although there was no significant difference in the rate of decomposition (P > 0.05), leaves at the highly polluted plot had lower rate of decomposition (6.58 × 10^?4) when compared to leaves at the lowly polluted plot (1.75 × 10^?3). In the second experiment, there was a significant difference in decomposition rates amongst species (P < 0.05). Red mangrove leaves (0.41) decomposed more than white (0.28) and black (0.28) mangrove leaves. This implies that hydrocarbon pollution slowed, but did not stop the decomposition of mangrove leaves.     

Leaf Litter Decomposition and Monodominance in the Peltogyne Forest of Marací Island, Brazil1

The forest type dominated by Peltogyne gracilipes (Caesalpiniaceae) on the riverine Marací Island is the least speciesrich of any recorded for Brazilian Amazonia. Because the forest has high soil and foliar Mg concentrations, and Mg is known to be toxic to plant growth at high concentrations, this study tested the hypothesis that dominance by Peltogyne is related to Mg leaf litter amounts and decomposition. We predicted that decomposition of Peltogyne leaves would differ from that of other species, and that their decomposition would result in a pulse of Mg release. Three plots (50 × 50 m) were established in each of three forest types: Peltogyne‐rich forest (PRF; dominated by P. gracilipes),Peltogyne‐poor forest (PPF), and forest without Peltogyne (FWP). Three leaf litter decomposition experiments tested if decomposition of mixed leaf litter in coarse‐ mesh (CM) litterbags differed among forests (experiment 1); whether or not decomposition and nutrient release of Ecclinusa guianensis, Lueheopsis duckeana, and Peltogyne in CM litterbags differed among forests and species (experiment 2); and using fine‐mesh (FM) litterbags, investigated the differences in the influence of fauna! activity on Ecclinusa and Peltogyne decomposition (experiment 3). Decomposition was independent of the presence and dominance of Peltogyne, since decomposition rates in both PRF and FWP were in general lower than in PPF. These differences appeared to be related to fauna] activity. The decomposition of Peltogyne leaves was lower than that of the other species tested and was more affected by microbial and physical action. It is possible that the monodominance of Peltogyne is related to its deciduousness and faster decomposition in the dry season, which coincides with a large leaf fall. Magnesium was lost quickly from the Peltogyne leaves and the resultant pulses of Mg into the soil during the heavy rains at the beginning of the wet season may be deleterious for other species that are not adapted to high solution Mg concentrations. Results obtained were consistent with the hypothesis that Peltogyne dominance is related to the pattern of its leaf decomposition and the seasonal pulses of toxic Mg.     

Frost damage and its cascading negative effects on <Emphasis Type="Italic">Aesculus</Emphasis><Emphasis Type="Italic">glabra</Emphasis>

Frost damage and re-foliation are seldom quantified for forest species, but are of ecological and evolutionary importance. This study of Aesculus glabra (Ohio buckeye) in a deciduous forest remnant in Illinois, USA, quantified frost damage to leaves and flowers after sub-freezing temperatures in April 2007. It also documented re-foliation and later growth, reproduction, and survival in 2007–2009 for the 355 study individuals of four life stages growing 0–200 m from the forest edge. Life stages differed in % leaf damage because of differences in phenology during the frost. Large saplings with fully expanded, immature leaves had higher % damage and lower % canopy fullness after re-foliation than smaller saplings with partially or fully mature leaves and canopy trees undergoing shoot expansion with folded leaflets. Percent damage increased for saplings closer to edges. Large saplings with heavier frost damage to leaves had partial re-foliation in deep shade, lower % canopy fullness, earlier senescence, a shorter growing season, and greater death of next year’s buds. By 2008, large saplings with greater damage in 2007 had more dead branches and lower % canopy fullness. By 2009, 11% of large saplings had died. In 2007, frost damaged no flowers, but final fruit crop size was negatively related to % leaf damage. Edge trees with total leaf damage aborted all fruits. The frost event differentially affected individuals in their length and time of growing season, energy budget, and, ultimately, reproduction, and survival. The population’s local-scale demography and spatial pattern also changed as large saplings died.     

Effects of experimental sedimentation on the phenological dynamics and leaf traits of replanted mangroves at Gazi bay,Kenya

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Phenology of the red mangrove, Rhizophora mangle L., in the Caeté Estuary,Pará, equatorial Brazil

The current study presents phenology data for Rhizophora mangle from two equatorial mangrove stands with different salinity regimes in Brazil. Observations based on litter fall and individual shoot development were compared and related to environmental factors. Patterns observed in litter fall were consistent with results of direct monitoring. While both reproductive organs and leaves were produced throughout the year, rates of formation followed seasonal trends. Distinct differences in propagule production between low and high salinity sites and between years of observation were detected; main propagule release was, however, restricted to the wet season which offers enhanced conditions for propagule establishment. Emergence of flowers was linked to leaf production. While there was no obvious single peak in leaf production, it was reduced towards the end of the dry season at both high and low salinity sites. Time series analysis revealed an independent pattern of leaf development superimposed on this annual seasonal trend, indicating slower development of leaf primordia during periods of low light availability in the wet season. No significant difference in age structure was detected between sun and shade leaves; maximum leaf life-time was approximately 1 year.     

Mangrove Tree Specificity and Conservation Implications of the Arboreal Crab <Emphasis Type="Italic">Parasesarma leptosoma</Emphasis> at Mngazana,a Mangrove Estuary in the Eastern Cape,South Africa

The arboreal crab Parasesarma leptosoma has been recently discovered at Mngazana, a southerly mangrove system in southern Africa, where crab tree preferences were studied using an indirect (browse leaf damage) and a direct (tree traps) method. The extent of crab induced leaf damage was compared for three mangrove species at two sites, one next to a tidal creek and one away from the creek. Using ANOVA, significant differences were found between tree species (P < 0.001) at different distances from the creek (P < 0.022). Crabs were found to occur on Rhizophora mucronata and Brugueira gymnorrhiza, but not on Avicennia marina. This reflected a gradient in browsing, from well-browsed R. mucronata (100% near the creek and 25.7% away from the creek), to medium browsing of B. gymnorrhiza (51.5% near and 0% away) and no browsing on A. marina (near or away). These differences could be explained in terms of palatability, as both R. mucronata and B. gymnorrhiza are salt excluders, while A. marina secretes salt from its leaves. Leaf consumption levels averaged between 1.73% and 2.6% of leaf area for R. mucronata and 0–1.76% for B. gymnorrhiza. For both R. mucronata and B. gymnorrhiza there was a significant correlation between the number of crabs caught directly and the amount of browse leaf damage (P < 0.01). Crab number was also significantly correlated with tree circumference for R. mucronata (r ² = 0.67) and B. gymnorrhiza (r ² = 0.76, P < 0.05), with crabs more prevalent on the former tree species and no crabs trapped on A. marina (91.7%, 38.3% and 0% catches, respectively), thus reflecting the results obtained by the indirect method. Total Nitrogen and Phosphate were measured for both sediment and leaves of the three mangrove species at the two sites. Leaf comparisons showed significant differences (P < 0.01) for both Total Nitrogen and Phosphate with R. mucronata having the highest values, followed by A. marina and lastly B. gymnorrhiza. Total Nitrogen was significantly higher for both B. gymnorrhiza and R. mucronata compared with A. marina, while leaf phosphate was significantly lower for B. gymnorrhiza when compared with both R. mucronata and A. marina. No significant differences were found for leaf nutrients between sites, with the exception of A. marina and R. mucronata Total Nitrogen, which was significantly higher at the near creek sites (P < 0.05). Sediment analysis showed no significant differences (P > 0.05) in either nutrients or median particle size. Thus, R. mucronata, especially near the creek, had higher nutrient value and was probably more palatable and could explain observed differences in crab distribution. Very little browse damage was encountered in saplings below 10 cm. Most poles chopped by the local communities are R. mucronata in the 15–20 cm category, which coincides with peak crab frequencies in the 15–25 cm size classes for R. mucronata and B. gymnorrhiza, so that this selective harvesting is affecting this crab population maximally. Predictions were made as to the effect of crab loss, tree replacement rate and alternatives to chopping, which would boost community socio-economic levels and reduce the anthropogenic pressure on this biodiverse southerly mangrove system.     

Provenance effect on carbon assimilation,photochemistry and leaf morphology in Mediterranean Cistus species under chilling stress

• The potential resilience of shrub species to environmental change deserves attention in those areas threatened by climate change, such as the Mediterranean Basin. We asked if leaves produced under different climate conditions through the winter season to spring can highlight the leaf traits involved in determining potential resilience of three Cistus spp. to changing environmental conditions and to what extent intraspecific differences affect such a response.
• We analysed carbon assimilation, maximum quantum efficiency of PSII photochemistry (F_v/F_m) and leaf morphological control of the photosynthetic process in leaves formed through the winter season into spring in C. creticus subsp. eriocephalus (CE), C. salvifolius (CS) and C. monspeliensis (CM) grown from seed of different provenances under common garden conditions.
• Intraspecific differences were found in F_v/F_m for CE and CS. Carbon assimilation‐related parameters were not affected by provenance. Moreover, our analysis highlighted that the functional relationships investigated can follow seasonal changes and revealed patterns originating from species‐specific differences in LMA arising during the favourable period.
• Cistus spp. have great ability to modify the structure and function of their leaves in the mid‐term in order to cope with changing environmental conditions. The F_v/F_m response to chilling reveals that susceptibility to photoinhibition is a trait under selection in Cistus species. Concerning carbon assimilation, differing ability to control stomatal opening was highlighted between species. Moreover, seasonal changes of the functional relationships investigated can have predictable consequences on species leaf turnover strategies.

     

Reproductive phenology of a northeast Brazilian mangrove community: Environmental and biotic constraints

Brazil has the third largest area of mangrove in the world, which is widely threatened by anthropogenic pressures. We carried out the first long-term phenological study investigating whether environment and competition for pollinators shape the reproduction of a western mangrove community in Brazil, and provide new information for mangrove conservation. We monitored monthly the flowering and fruiting of Avicennia schaueriana, Conocarpus erectus, Laguncularia racemosa and Rhizophora mangle, the only species composing this mangrove community. We applied circular statistics to detect seasonal trends, null models to test for aggregated, staggered or random flowering patterns, performed correlations between phenophases and climate, and calculated intra-specific phenological synchrony. Each species presented a different flowering pattern, from brief annual to continuous and from regular to irregular, resulting in a bimodal pattern at community level. Fruiting was annual or continuous and seasonally unimodal at community level. Precipitation showed the strongest correlation with reproduction for all species, except L. racemosa. Flowering was randomly distributed among species sharing pollinators and each species presented high intra-specific synchrony. The studied mangrove showed a diversity of flowering patterns despite the low number of species. Annual to sub-annual sequential flowering were prevalent, sustaining the pollinators of species all the year long, while the wind-pollinated species flowered continuously. We provide strong evidence that daylength, rainfall and temperature are driving the flowering and fruiting rhythm of these mangrove species.     

Nutrient relations of dwarf <Emphasis Type="Italic">Rhizophora mangle</Emphasis> L. mangroves on peat in eastern Puerto Rico

Dwarf mangroves on peat substrate growing in eastern Puerto Rico (Los Machos, Ceiba State Forest) were analyzed for element concentration, leaf sap osmolality, and isotopic signatures of C and N in leaves and substrate. Mangrove communities behind the fringe presented poor structural development with maximum height below 1.5 m, lacked a main stem, and produced horizontal stems from which rhizophores developed. This growth form departs from other dwarf mangrove sites in Belize, Panama, and Florida. The dwarf mangroves were not stressed by salinity but by the low P availability reflected in low P concentrations in adult and senescent leaves. Low P availability was associated with reduced remobilization of N and accumulation of K in senescent leaves, contrasting with the behavior of this cation in terrestrial plants. Remobilization of N and P before leaf abscission on a weight basis indicated complete resorption of these nutrients. On an area basis, resorption was complete for P but not for N. Sulfur accumulated markedly with leaf age, reaching values up to 400%, compared with relatively modest accumulation of Na (40%) in the same leaves. This suggests a more effective rejection of Na than sulfate at the root level. Dwarf mangrove leaves had more positive δ¹³C values, which were not related to salinity, but possibly to drought during the dry season due to reduced flooding, and/or reduced hydraulic conductance under P limitation. Negative leaf δ¹⁵N values were associated with low leaf P concentrations. Comparison with other R. mangle communities showed that P concentration in adult leaves below 13 mmol kg⁻¹ is associated with negative δ¹⁵N values, whereas leaves with P concentrations above 30 mmol kg⁻¹ in non-polluted environments had positive δ¹⁵N values.     

Mound-building behaviour of a keystone bioturbator alters rates of leaf litter decomposition and movement in urban reserves

Bioturbation, the disturbance of soil and litter by digging animals plays an important role for a variety of species and ecological processes in many ecosystems. The majority of studies globally on the ecosystem engineering effects of digging vertebrates have focussed on mammals, with birds, reptiles and amphibians remaining comparatively understudied. The loss of ecosystem engineers is a key conservation challenge, and the return of these species is increasingly seen as a priority for habitat restoration; yet this concept is highly novel when we consider urban ecosystems. The Australian brush-turkey (Alectura lathami), historically a rainforest bird and now common in urban ecosystems, displaces significant quantities of soil and leaf litter through its foraging and nest-building behaviour and has previously been described as an ecosystem engineer. Here, we tested the effect of brush-turkey nest building on the decomposition rate of leaf litter, an important ecosystem process. We placed mesh bags of dried Angophora costata and Lantana camara leaves at increasing distances from brush-turkey incubation mounds. We predicted that leaf litter closer to the nest would break down faster during the brush-turkey breeding season due to increased turnover associated with nest mound maintenance. We found slower leaf litter decomposition in the breeding than the non-breeding season, but a relatively greater rate of decomposition closer to the mound in the breeding season. Our results show a seasonal difference in the spatial pattern of leaf litter decomposition and movement; we interpret that brush-turkey mound-building behaviour was the key driver. The ecosystem services provided by brush-turkeys are of particular interest for future research as this species is naturally recolonizing areas where it has been absent for decades, including urban areas. The effect of this species on ecosystem processes including nutrient cycling, seedbank stimulation and reduced fuel loads warrants further investigation.     

Volatiles from different organs of Unxia camphorata L. f. growing wild in the Amazon

The essential oils obtained from fresh leaves, flowers, roots and stems of Unxia camphorata collected in the rainy and dry seasons in the state of Pará, were examined by GC and GC/MS. The highest oil yields were observed from the samples collected at the dry season (flowers: 0.6%, leaves: 0.6%, stems: 0.3%, roots: 0.4%). All parts of the plant were rich in α-phellandrene, with non-significant changes during the rainy and dry seasons (flowers: 61.9–53.7%, leaves: 18.3–17.4%, stems: 68.3–72.8%, roots: 51.9–48.3%). In the leaf oil, the monoterpenoid camphor was the largest component (rainy season: 28.5%, dry season: 28.8%). In the leaf oil, the high amount of α-phellandrene was followed by methylthymol (rainy season: 14.1%, dry season: 13.1%). Depending on the plant part studied, these oils can be characterized by α-phellandrene, camphor/α-phellandrene/camphene, or α-phellandrene/methylthymol type.     

Leaf Longevity,Construction, and Maintenance Costs of Three Mangrove Species Under Field Conditions

This study assessed the effect of leaf age on construction cost (CC) in the mangrove species Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle growing in their natural habitat. Leaf osmolality values were species-specific, the highest in A. germinans (1 693 mmol kg^–1) and the lowest in L. racemosa (1 270 mmol kg^–1). In the three species, contents of chlorophyll (a+b) (Chl_a+b) and nitrogen (N) per unit of leaf area were maximal in adult leaves and tended to decline with age. Leaf mass to leaf area ratio (LMA) and ash content increased during leaf ageing. Similarly, as leaves aged, a significant increase in leaf construction cost per leaf area (CC_a) was observed, while per leaf mass (CC_m) it remained almost constant, suggesting a sustained production of leaf compounds as leaves became older. CC was positively correlated with LMA and heat of combustion (Hc) per leaf area, suggesting differences among species in the quantity and composition of expensive compounds. Leaf half lifetime (t_0.5) showed contrasting values in the three mangrove species (60, 111, and 160 d in L. racemosa, R. mangle, and A. germinans, respectively). Overall, L. racemosa was the species with less expensive leaves to construct while leaves of A. germinans and R. mangle had the highest CC_m and CC_a, respectively. Leaf longevity was positively correlated with the ratio between CC and maximum photosynthetic rate (P _max), clearly showing the existence of a balance between leaf costs and benefits.     

Litter Decomposition and Nutrient Release in a Tropical Seasonal Rain Forest of Xishuangbanna,Southwest China1

We studied litter decomposition and nutrient release in a tropical seasonal rain forest of Xishuangbanna, Southwest China. The monthly decay rates (k) of leaf litter ranged from 0.02 to 0.21/mo, and correlated with rainfall and soil moisture. Annual k values for leaf litter (1.79/yr) averaged 4.2 times of those for coarse wood (2.5–3.5 cm in diameter). The turnover coefficients of forest floor mass (annual litterfall input/mean floor mass) were: 4.11/yr for flowers and fruits, 2.07/yr for leaves, and 1.17/yr for fine wood (≤2 cm in diameter), with resident time decreasing from fine woods (0.85 yr) to leaves (0.48 yr) and to flower and fruits (0.24 yr). Nutrient residence times in the forest floor mass were ranked as: Ca (1.0 yr) > P (0.92 yr) > Mg (0.64 yr) > N (0.36 yr) > K (0.31 yr). Our data suggest that rates of litter decomposition and nutrient release in the seasonal rain forest of Xishuangbanna are slower than those in typical lowland rain forests, but similar to those in tropical semideciduous forests.