mortiz085

Earthworms are thought to be the most ancient soil animals having started colonizing terrestrial environments about 600 million years ago (Spain and Lavelle 2001). They are the most predominant soil fauna except in dry and cold climates. Earthworms are semiaquatic animals which extract water continuously from the surrounding soil inorder to maintain their cuticle in a moist state to facilitate gas exchange. Thus moisture status is a major limitation to earthworm activities and distribution. Spain and Lavelle (2001) reported that since earthworms live in direct and continuous contact with the soil matrix and the soil solution, their presistence, propagation and activity are greatly affected by the chemical (pH, dissolved ions) characteristics of the soil. Based on their sensitivity to soil pH, earthworms are grouped into acidophilic species (able to thrive below pH 6 such as in organic forest litter), neutrophilic species (they prefer soil pH 6 to 7) and basophi lic species (prefer b...

Lantana camara Linn, locally called Utot-utot , Koronitas or Kantotoy in the Philippines, is a shrub which originated from tropical America. It is considered as one of the worst invasive plant species and is a noxious weed in many parts of the world. The plant is known to suppress the regeneration of neighboring plants through allelopathic effects (by releasing volatile and non-volatile chemicals from its tissues and residues). The spread of Lantana is aided by the characteristic of its leaves which is somewhat poisonous to animals while its fruit is a delicacy for many birds which distribute the seeds (Wikipedia). In a recent study published in Geoderma journal, Ling Fan and co-workers evaluated the chemical and microbiological properties of the soil underneath the canopy of Lantana camara as well as the soil away from it. They also investigated the effect of Lantana on the growth of three neighboring plant species (ryegrass, mungbean, and radish). Results revealed that the soils ...

Contributed by Juvia P. Sueta, University of Göttingen, Germany There is growing interest in the use of indigenous tree species in reforestation programs at present. Thought to be well adapted to their native areas, indigenous tree species are able to survive well and strongly influence the soil. However, the lack of published data on their performance often limits their full use and casts uncertainties on whether they have beneficial or negative impacts on the soil. To better understand the role of trees in improving soil quality, an understanding of how nutrient availability changes with time is important (Kelly and Mays, 1999). In this study which we conducted at the VSU-GTZ reforestation project site (see photo) in Mt. Pangasugan, Leyte, Philippines, we looked at the influence of two native tree species- Parashorea plicata and Dipterocarpus warburgii - on the nature and rate of changes on the chemical properties of a highly weathered soil following a change in land use from Impera...

Decomposition of organic materials on the forest floor is a vital link between the various components of the forest ecosystem. Through this process, mineral nutrients bound to the biomass are released into the soil and then subject to uptake by plants, fixation by soil components, and losses through leaching and erosion. Decomposition can have considerable influence on the biological and chemical properties of the forest soil depending on the kind of organic material, soil properties, climate, and the availability of decomposers (e.g. Gartner and Cardon, 2004). Exotic tree species are introduced species from other regions. They are widespread in tropical and subtropical countries since they are popular as reforestation species even in harsh environments (Nyland, 1996) due to their ability to adapt easily to variable site conditions (Weidelt, 1976). Many are considered economically viable because of their fast growth characteristic. Farmers value exotic species more than t...

Scientists predict that tropical regions will receive the most dramatic increase in nitrogen (N) deposition over the next decades. This is due to increased fertilizer use, legume cultivation, fossil fuel consumption and biomass burning. There is thus a need for a better understanding of N cycling in tropical forest ecosystems. In a recent study by Arnold et al. (2009) across an Andosol (young volcanic ash soil) toposequence in Ecuador (Equitorial South America), it was revealed that gross rates of N transformations, microbial N turnover time, and δ 15 N signatures in soil and leaf litter decreased with increasing elevation, indicating a decreasing N availability across the toposequence. Accompanying the above-mentioned trend was a decreasing degree of soil development with increasing elevation as indicated by declining clay content, total C, total N, effective cation exchange capacity and increasing base saturation. The study also revealed that soil N-cycling rates and δ 15 N signatu...

Soil fertility in terrestrial ecosystems has received increased attention from ecologists since it is now widely recognized that nutrient availability drives ecosystem functioning and processes (Wardle and Zackrisson, 2005). N and P are believed to be the most limiting nutrients in many terrestrial ecosystems particularly forests. Availability of N and P vary considerably during soil development as P is lost through leaching and fixation while N accumulates through biological N fixation (Walker and Syers, 1976; Crews et al., 1995). Thus, young soils have the tendency to be N limited while old soils are P limited. Ecosystem studies have confirmed this relationship of N and P indicated by the N:P ratio. It has been found that the leaf N:P ratio can detect nutrient limitation for wetland terrestrial ecosystem. An N:P ratio >16 indicates P limitation which is in clear agreement with the Redfield ratio (Redfield, 1958) for marine ecosystems. An N:P ratio indicates N limitation and bet...

The global distribution of soils is a function of climate and thus is related to latitude. Consequently, soil processes are known to vary with latitude. But a recent study by Jones et al. (2009) which used soils collected from 40 latitudinal points from the Arctic through to Antarctica, showed that this is not the case for key soil processes like the turnover of amino acids (amino acids represent a key pool of carbon and nitrogen in soil and their availability to plants and microorganisms is considered a major driver in regulating ecosystem functioning). They found that “soil solution amino acid concentrations were relatively similar between sites and not strongly related to latitude. In addition, when constraints of temperature and moisture were removed, they demonstrated that soils worldwide possess a similar innate capacity to rapidly mineralize amino acids. Similarly, they showed that the internal partitioning of amino acid-C into catabolic and anabolic processes is conservative in...

If you collect leaf litter from a Mahogany plantation and put it beaneath Gmelina trees or vice versa, the rate of litter decomposition will not be the same. According to a recent paper by Ayers et al. (2009), leaf litter decomposition is faster beneath the plant species from which the litter had been derived than beneath a different plant species. This is called home-field advantage. The authors observed that home-field advantage is widespread in forest ecosystems and hypothesized that this is due to the specialization of the soil organisms in decomposing litter derived from the plant above it. In other words, soil organisms living beneath the Mahogany trees are specialized in decomposing the leaf litter from this tree species. Reference: Ayers E et al. (2009). Home-field advantage accelerates leaf litter decomposition in forests. Soil Biology and Biochemistry 41: 606-610.