Climate change 2014 - Synthesis Report

Mangroves are woody plants that grow at the interface between land and sea in tropical and sub-tropical latitudes where they exist in conditions of high salinity, extreme tides, strong winds, high temperatures and muddy, anaerobic soils. There may be no other group of plants with such highly developed morphological and physiological adaptations to extreme conditions.

Because of their environment, mangroves are necessarily tolerant of high salt levels and have mechanisms to take up water despite strong osmotic potentials. Some also take up salts, but excrete them through specialized glands in the leaves. Others transfer salts into senescent leaves or store them in the bark or the wood. Still others simply become increasingly conservative in their water use as water salinity increases Morphological specializations include profuse lateral roots that anchor the trees in the loose sediments, exposed aerial roots for gas exchange and viviparous waterdispersed propagules.

Mangroves create unique ecological environments that host rich assemblages of species. The muddy or sandy sediments of the mangal are home to a variety of epibenthic, infaunal, and meiofaunal invertebrates Channels within the mangal support communities of phytoplankton, zooplankton and fish. The mangal may play a special role as nursery habitat for juveniles of fish whose adults occupy other habitats (e.g. coral reefs and seagrass beds).

Because they are surrounded by loose sediments, the submerged mangroves' roots, trunks and branches are islands of habitat that may attract rich epifaunal communities including bacteria, fungi, macroalgae and invertebrates. The aerial roots, trunks, leaves and branches host other groups of organisms. A number of crab species live among the roots, on the trunks or even forage in the canopy. Insects, reptiles, amphibians, birds and mammals thrive in the habitat and contribute to its unique character.

Living at the interface between land and sea, mangroves are well adapted to deal with natural stressors (e.g. temperature, salinity, anoxia, UV). However, because they live close to their tolerance limits, they may be particularly sensitive to disturbances like those created by human activities. Because of their proximity to population centers, mangals have historically been favored sites for sewage disposal. Industrial effluents have contributed to heavy metal contamination in the sediments. Oil from spills and from petroleum production has flowed into many mangals. These insults have had significant negative effects on the mangroves.

Habitat destruction through human encroachment has been the primary cause of mangrove loss. Diversion of freshwater for irrigation and land reclamation has destroyed extensive mangrove forests. In the past several decades, numerous tracts of mangrove have been converted for aquaculture, fundamentally altering the nature of the habitat. Measurements reveal alarming levels of mangrove destruction. Some estimates put global loss rates at one million ha y−1, with mangroves in some regions in danger of complete collapse. Heavy historical exploitation of mangroves has left many remaining habitats severely damaged.

These impacts are likely to continue, and worsen, as human populations expand further into the mangals. In regions where mangrove removal has produced significant environmental problems, efforts are underway to launch mangrove agroforestry and agriculture projects. Mangrove systems require intensive care to save threatened areas. So far, conservation and management efforts lag behind the destruction; there is still much to learn about proper management and sustainable harvesting of mangrove forests.

Mangroves have enormous ecological value. They protect and stabilize coastlines, enrich coastal waters, yield commercial forest products and support coastal fisheries. Mangrove forests are among the world's most productive ecosystems, producing organic carbon well in excess of the ecosystem requirements and contributing significantly to the global carbon cycle. Extracts from mangroves and mangrove-dependent species have proven activity against human, animal and plant pathogens. Mangroves may be further developed as sources of high-value commercial products and fishery resources and as sites for a burgeoning ecotourism industry. Their unique features also make them ideal sites for experimental studies of biodiversity and ecosystem function. Where degraded areas are being revegetated, continued monitoring and thorough assessment must be done to help understand the recovery process. This knowledge will help develop strategies to promote better rehabilitation of degraded mangrove habitats the world over and ensure that these unique ecosystems survive and flourish.

Biology of mangroves and mangrove Ecosystems

Tree Rings And Climate

The temperature sensitivity of litter decomposition will influence the rates of ecosystem carbon sequestration in a warmer world. A number of studies have shown that the temperature sensitivity of litter decomposition can vary depending on litter type and extent of decomposition. However, the underlying causes of this variation are not well understood. According to fundamental principles of enzyme kinetics, the temperature sen- sitivity of microbial decomposition should be inversely related to litter carbon quality. We tested the accuracy of this hypothesis by adding ground plant shoot and root material to soils incubated under controlled conditions and measuring the temperature sensitivities of decomposition at three time points throughout a 53-d incubation. As the overall quality of the litter organic C declined, litter decomposition became more sensitive to temperature. This was true regardless of whether differences in C quality were due to inherent differences in litter chemistry or due to differences in the extent of decomposition. The same pattern was observed when specific C compounds of varying quality were added to soil, suggesting that substrate C quality has a significant and predictable influence on the temperature sensitivity of microbial decomposition.

/pdf/litter-quality-and-the-temperature-sensitivity-of-1ljha34faw.pdf

Litter quality and the temperature sensitivity of decomposition

Farmers are facing serious plant protection issues and phytosanitary risks, in particular in the tropics. Such issues are food insecurity, lower income in traditional low- input agroecosystems, adverse effects of pesticide use on human health and on the environment in intensive systems and export restrictions due to strict regulations on quarantine pests and limits on pesticide residues. To provide more and better food to populations in both the southern and northern hemispheres in a sustainable manner, there is a need for a drastic reduction in pesticide use while keeping crop pest and disease damage under control. This can be achieved by breaking with industrial agriculture and using an agro- ecological approach, whose main pillar is the conserva- tion or introduction of plant diversity in agroecosystems. Earlier literature suggest that increasing vegetational biodiversity in agroecosystems can reduce the impact of pests and diseases by the following mechanisms: (1) resource dilution and stimulo-deterrent diversion, (2)

https://link.springer.com/content/pdf/10.1007%2Fs13593-011-0022-4.pdf

Plant species diversity for sustainable management of crop pests and diseases in agroecosystems: a review

The comparative decomposition of tropical leaf litters (e.g. Andropogon gayanus, Casuarina equisetifolia, Faidherbia albida) of different qualities was investigated under laboratory conditions during a 60-day incubation period conducted with a typical oxisol. Total CO2-C, soil inorganic N, microbial biomass (fumigation-extraction), β-glucosidase and dehydrogenase activities were determined over the incubation to assess how they responded to the addition of inorganic N (+N). Cumulative CO2-C evolved from the litter-amended soils was higher than that recorded for the unamended control soil. For the unfertilized treatment (0 N), correlation coefficients calculated between initial chemical data and CO2 flux during the first day of incubation were r =0.963 for water soluble-C and 0.869 for soluble carbohydrates (P <0.05). At the end of the incubation, the amounts of CO2-C in the F. albida- and A. gayanus-amended soils were higher than that in the C. equisetifolia-amended treatment. Cumulative net N immobilization increased during the first 30 days of incubation, the amounts being similar for A. gayanus- and C. equisetifolia-amended soil and higher than that recorded in the F. albida-amended treatment. Soil microbial biomass and enzyme activities increased in the litter-amended soils during the first 15 days of incubation and decreased (except for the dehydrogenase activity) thereafter. The addition of inorganic N modified the patterns of CO2-C respiration and net N immobilization. The magnitude of these modifications varied according to the litter quality. The use of an accurate indicator based on several litter components to predict the amplitude of organic material decomposition is discussed.

Microbial activities during the early stage of laboratory decomposition of tropical leaf litters: the effect of interactions between litter quality and exogenous inorganic nitrogen

The water, soil and vegetation characteristics are presented of themangroves of the Saloum River estuary, Senegal, in 1995 and 1996. Themangroves have changed markedly due to decreasing rainfall and increasingevaporation rates, particularly in the 1980s, as well as new oceanographicconditions resulting from the breaching of a protective sand dune. Thehealth of the remaining mangrove communities depends on the localhydrological and hydrodynamic conditions, the microtopography, the humanexploitation of the forest and the clay-sand composition of the soils.

Recent changes of the mangroves of the Saloum River Estuary, Senegal

Disturbance induced by two contrasting irrigation regimes (groundwater versus urban wastewater) was evaluated on a sandy agricultural soil through chemical and microbial analyses Contrary to wastewater, groundwater displayed very high nitrate contents but small amounts of ammonium and organic matter Despite these strong compositional shifts, soil organic carbon and nitrogen, nitrate and ammonium contents were not significantly different in both types of irrigated plot Moreover, neither microbial biomass nor its activity, determined as fluorescein diacetate hydrolysis activity, was influenced by irrigation regimes Bacterial community structure, assessed by denaturing gradient gel electrophoresis (DGGE) of 16S ribosomal DNA fragments, was also weakly impacted as molecular fingerprints shared an overall similarity of 85% Ammonia-oxidizing bacterial community (AOB) was monitored by DGGE of the functional molecular marker amoA gene (alpha subunit of the ammonia monooxygenase) Surprisingly, no amoA signals were obtained from plots irrigated with groundwater, whereas signal intensities were high in all plots under wastewater Among the last, compositional shifts of the AOB community were weak Overall, impact of irrigation water quality on soil chemistry could not be evidenced, whereas effects were low on the total bacterial compartment but marked on the AOB community

Impact of irrigation water quality on soil nitrifying and total bacterial communities

Adaptation to low water and soil P availability has been related to root properties. Two experiments were conducted in a greenhouse. Under hydroponics conditions, plants of the Souna 3 cultivar were grown for 30 d with three levels of P (P0 = 0.0 mol L -1 , PI = 0.073 10 -3 mol L -1 , and P2 = 1.65 10 -3 mol L -1 ). In the pot experiment, two cultivars (Souna 3 and IBMV8402) were planted in pots filled with 19 kg of P-deficient and sandy soil and subjected to two watering regimes: well watered and water stressed at the vegetative phase from 23 d after sowing (DAS) to 30 DAS. Phosphorus treatment consisted of two levels: application of phosphate fertilizer (P 2 O 5 ) at the rate of 649 mg per pot (34 mg P 2 O 5 kg -1 soil), referred to as Fl, and no phosphate application, referred to as F0. The results showed that under P deficiency, pearl millet [Pennisetum glaucum (L.) R. Br.| presented an alteration of root parameters, particularly root volume, by the formation of root hair. Under non-water-limited conditions as well as in high or low P, IBMV8402 showed a better root and shoot growth. However, under drought conditions, the leaf water potential (Ψ f ) of IBMV8402 (Ψ f = -5 MPa) decreased more than that of Souna 3 (Ψ f = -3 MPa). In spite of this, P supply improved the root and shoot growth of IBMV8402. Finally, except for the condition of water stress and without P supply, P utilization efficiency exhibited by IBMV8402 was 20 to 50% higher than that of Souna 3 on the basis of shoot biomass production.

Characterizing Root Responses to Low Phosphorus in Pearl Millet [Pennisetum glaucum (L.) R. Br.]

Mangroves are the dominant vegetation of over 70% of tropical and sub-tropical coastlines around the world (Fig 21) Mangrove ecosystems are estimated to cover 150 000 km2 world-wide, of which Africa has about 35 000 km2 (Diop 1992, 1993) They constitute complex forests with high wood biomass and structural complexity A significant feature of mangroves is their ability to develop morphological, physiological and reproductive adaptations, which enable them to colonise salty, waterlogged and erratic soil conditions The mangroves are characterised by high primary production and play vital roles in the transfer of nutrients (Fig 22), especially of carbon from the land to the sea, and serve either as sources or sinks in the global cycle of such substances (Lacerda and Novelli 1992) They are found in all countries along the western coast of the African continent, from Mauritania in the north, (Iles Tidra 19°50′ N) to Angola in the south (Angola estuary of the Rio Longo, 10°18′ S (Spalding et al 1997)

Aliou Guisse

Papers

Microbial activities during the early stage of laboratory decomposition of tropical leaf litters: the effect of interactions between litter quality and exogenous inorganic nitrogen

Recent changes of the mangroves of the Saloum River Estuary, Senegal

Impact of irrigation water quality on soil nitrifying and total bacterial communities

Characterizing Root Responses to Low Phosphorus in Pearl Millet [Pennisetum glaucum (L.) R. Br.]

Mangroves of Africa