Canopy Organic Matter Research Articles

Climate, as well as branch-level processes, drive canopy soil abundance and chemistry

Canopy soils can be important to forest nutrient cycling, hydrology, and biodiversity, but the factors determining their distribution and properties are largely unknown. We surveyed canopy soils across gradients of temperature and precipitation in six primary forests in Costa Rica. We used solid-state 13C nuclear magnetic resonance (NMR) and mass spectrometry (MS) to understand how the composition of canopy soil organic matter varies within and across sites. Climate, particularly fog, appears to drive canopy soil abundance across forests, while tree size determines canopy soil abundance within a forest. Canopy soil chemistry mostly varied within sites, though temperature was associated with the carbon (C) to nitrogen ratio, total dissolved nitrogen, and alkyl-C abundance, while fog explained some of the variation in dissolved organic carbon and O-alkyl C abundance. This study is the first-ever glimpse into large- and small-scale drivers of canopy soil abundance and biochemical composition. Our results highlight the importance of tree size and fog in determining the quantity and quality of canopy soil organic matter, suggesting that canopy soil stocks may be particularly vulnerable to climate and land use change. Identifying how multi-scale factors influence canopy organic matter processes will enhance our ability to identify and predict how environmental change might affect the abundance and chemistry of canopy soils and thus biodiversity that they support.

Myxomycetes associated with canopy organic matter in temperate rainforests of southern New Zealand

The dead plant material (canopy organic matter) associated with the mats of vascular plants and bryophytes found on tree branches in temperate rainforests along the southwestern coast of New Zealand was investigated for the presence of myxomycetes (plasmodial slime molds or myxogastrids). Samples of both the superficial litter layer (canopy litter) on the surface of the mat and the humus-like layer (canopy soil) beneath the mat were collected and used to prepare a series of moist chamber cultures. Canopy soil yielded more positive cultures (57%) but only three species of myxomycetes, whereas eight species were recovered from canopy litter (40% positive cultures). The higher percentage of positive cultures for canopy soil was the result of the appearance of plasmodia that could not be induced to form fruiting bodies. In contrast, fruiting bodies represented 67% of the positive cultures recorded from canopy litter.

The long way down--are carbon and oxygen isotope signals in the tree ring uncoupled from canopy physiological processes?

The carbon (δ(13)C) and oxygen (δ(18)O) stable isotope composition is widely used to obtain information on the linkages between environmental drivers and tree physiology over various time scales. The tree-ring archive can especially be exploited to reconstruct inter- and intra-annual variation of both climate and physiology. There is, however, a lack of information on the processes potentially affecting δ(13)C and δ(18)O on their way from assimilation in the leaf to the tree ring. As a consequence, the aim of this study was to trace the isotope signals in European beech (Fagus sylvatica L.) from leaf water (δ(18)O) and leaf assimilates (δ(13)C and δ(18)O) to tree-ring wood via phloem-transported compounds over a whole growing season. Phloem and leaf samples for δ(13)C and δ(18)O analyses as well as soil water, xylem water, leaf water and atmospheric water vapour samples for δ(18)O analysis were taken approximately every 2 weeks during the growing season of 2007. The δ(13)C and δ(18)O samples from the tree rings were dated intra-annually by monitoring the tree growth with dendrometers. δ(18)O in the phloem organic matter and tree-ring whole wood was not positively related to leaf water evaporative enrichment and δ(18)O of canopy organic matter pools. This finding implies a partial uncoupling of the tree-ring oxygen isotopic signal from canopy physiology. At the same time, internal carbon storage and remobilization physiology most likely prevented δ(13)C in tree-ring whole wood from being closely related to intra-annual variation in environmental drivers. Taking into account the post-photosynthetic isotope fractionation processes resulting in alterations of δ(13)C and δ(18)O not only in the tree ring but also in phloem carbohydrates, as well as the intra-annual timing of changes in the tree internal physiology, might help to better understand the meaning of the tree-ring isotope signal not only intra- but also inter-annually.

Comparison of arboreal and terrestrial soil characteristics in a lower montane forest, Monteverde, Costa Rica

Summary In many tropical and temperate forests, live and dead components of canopy-held organic matter (COM) form communities that are distinct from terrestrially rooted plant and forest floor soil communities, but that interact with whole-forest processes. We quantified some of the soil characteristics of dead organic matter held within the canopy of mature trees in a tropical lower montane forest of Monteverde, Costa Rica, and compared them to soils from the upper horizons on the ground. The concentration of canopy organic matter was significantly higher than terrestrial soil, but similar for P and Ca. Canopy humus had very low pH compared to terrestrial soils. The terrestrial soil had a tenfold greater amount of extractable cations, but the C/N ratios and cation exchange capacity of COM and the upper soil horizon did not differ significantly. Canopy organic matter has rarely been considered in forest ecosystem studies due to its inaccessibility, the lack of rigorous sampling and extrapolation methods, and because its mass is small relative to total forest soil mass. However, in habitats where COM is large, a canopy root-humus mat occurs on branch and trunk surfaces, similar to that which occurs on the forest floor. Organic matter in the forest canopy may thus have more ecological importance than its mass implies, as the nutrient-retaining capacity of the root-humus mat layer could play an important role in nutrient conservation for the individual trees and epiphytes whose roots are imbedded within the mats, and for the forest ecosystem as a whole.

Invertebrates in Canopy and Ground Organic Matter in a Neotropical Montane Forest, Costa Rica

In a neotropical cloud forest of Costa Rica, we compared the density and composition of macro- and mesoinvertebrates in organic matter found within the canopy to that found in the upper soil horizons on the forest floor. We used a Winkler sifting apparatus to extract invertebrates from accumulated litter and humus. The numerically dominant invertebrate groups in both canopy humus and forest floor leaf litter were mites, adult beetles, holometabolous insect larvae, ants, collembola, amphipods, and isopods. Relative abundances of these major taxa were the same in canopy and on the forest floor, indicating that canopy organic matter shares a fundamentally similar invertebrate community with forest floor. All of these groups except ants had significantly higher densities in the canopy, with a mean density 2.6 times greater on the ground than in the canopy. Ant density was similar in both microhabitats.

Microbial biomass and activity in canopy organic matter and the forest floor of a tropical cloud forest

In some tropical forests, organic matter derived from epiphytic plants accumulates as mats on tree branches. Microbial characteristics relating to the cycling of C and N were studied in this canopy organic matter (COM) and in the forest floor of a tropical montane forest in Costa Rica. COM was found to have high microbiat activity which was. in general, similar to the forest floor H (FF-H) horizon. The concentration of microbial biomass C was 2650, 2670 and 1950 μg g −1 soil in COM, FF-H and FF-Al, respectively. Biomass N, laboratory CO 2 evolution and laboratory N mineralization were also higher or similar for COM relative to the forest floor. In contrast to the H and Al horizons of the forest floor, nitrification was not detectable or only very low in COM during laboratory and field incubations. The potential for denitrification, as evidenced by the decline in added NO − 1 relative to NH + 4 during laboratory incubation, was higher in the forest floor than in the canopy. Microbial respiration and biomass in COM and the forest floor responded more to C (as glucose) than N (as NH 4NO 1) amendments. Microbial immobilization of added N appeared to be higher in the forest floor than in COM, although the microbial population in all materials readily immobilized inorganic N in the presence of glucose. The total pool of COM in this forest is estimated to be between 1000 and 2000 kg ha −1. From this, a preliminary estimate of 0.7 kg ha − of N immobilized in microbial tissue can be calculated. Because of their high biomass and activity, microorganisms in the canopy could be important in regulating N availability in this forest.