Plants take up nutrients from the soil and atmosphere as they grow, but then release them again when they die and decompose. Many people get excited in investigating only living plants. However, I get double excitement on linking the living plants to dead plants. My research is related to biodiversity, forest ecosystem functioning, plant afterlife functional traits effect on carbon and nutrient cycling, carbon sequestration. I am also interested in assessing CO2 efflux from woody debris (WD) through a disturbance gradient and its relation to tree species composition. I am also looking at the factors influencing WD decomposition in tropical environments. Additionally, I examine the role of wood traits and phylogeny in WD decomposition. I aim ultimately to improve the parameterization of the respiration rate of WD in order to accurately incorporate it into the global models of carbon cycle. For long, nutrient cycling in tropical biomes was thought to be controlled only by abiotic factors and much less by biotic factors such as fungi, termites and other arthropods However, I am convinced these biota are a critical yet overlooked contributor to nutrient cycling from woody debris in these biomes. Hence, I am well interested in linking biotic, especially arthropods, fungal diversity to decomposition rates in tropical biomes.
Past projects and achievements
In my past projects my research has focused on examining the way disturbance, either natural or anthropogenic, shapes forest composition, structure and functioning. For example, I questioned how plant diversity changes along an altitudinal gradient on a volcano mountain (Dossa et al. 2013; details in my cv). Another aspect was to investigate the effects of disturbance on nutrient cycling by examining decomposition of litters (leaf, woody debris and bark) (Dossa et al. 2016). Beside conventional methods in studying wood decomposition, I proposed and revived new methods in the field by borrowing from a sister field (soil biology), to foster our understanding on CO2 efflux from decomposing woody debris. For doing so, I corrected calculations on CO2 efflux from woody debris, and laid down the methodological framework of using a non-dispersive infrared gas analyzer to study woody debris decomposition (Dossa et al. 2015). Recently, I introduced a new and unconventional factor influencing wood decomposition, wood bark. This study establishes the importance of interspecific bark traits in determining variations in wood decomposition. Therefore, incorporating these effects into biogeochemical and climate-change models should help make them more accurate. One other area, I examined in the past is forest productivity through litter fall (Paudel, Dossa et al. 2015).
Current projects
My current projects continue to examine the biodiversity-nutrient cycling nexus. More specifically, I am interested in further understanding what drives nutrient cycling/release from woody debris to soil and/or atmosphere (Fig. 2). My research ultimately seeks to mechanistically predict the fate of organic matter whether from leaf litter or woody debris, with particular focus on the important but - unconventional and neglected role of bark in the decomposition of wood. More importantly, my objective is to extend and test the hypothesis of afterlife effects/legacy of plant traits and specifically how traits how C return to soil or atmosphere of a particular organ (e.g. wood) could be influenced or dictated by the traits of another, unrelated organ with a different function (e.g. bark)? The following five projects summarize my current research focus:
Project 1: Quantifying the factors affecting wood decomposition across a forest disturbance gradient
Woody debris represents a substantial reservoir of carbon in forests and thus the rate at which the sequestrated carbon is released into the atmosphere through decomposition is an important topic. To date, studies have examined several different aspects of woody debris decomposition, although the time-frame for measurements may vary from seconds to century. Forest degradation and deforestation in this century have had a substantial impact on biodiversity, and hence on biodiversity dependent ecosystem functions such as organic matter decomposition. Nonetheless, the effects of forest disturbance on wood decomposition remain poorly understood. In this project, I study the effects of forest disturbance on wood decomposition. I aimed to test the following hypotheses: i) wood decomposition rate decreases from open land > young forest > old forest due the changes in light availability (as a consequence of decomposition by photo degradation, (ii) the lower part of a woody debris in direct contact with soil decomposes faster than the upper part which is not in direct contact with soil. Then in order to disentangle the respective effect of variables confounded in the degradation categories, I constructed a shadehouse through a full factorial experiment with soil translocation and litter bed construction. However, I mimicked canopy openness by experimentally imposing different shade levels (full, half, no shade).
Project 2: The cover uncovered: bark control over wood decomposition
Studies of woody debris decomposition have usually considered wood and bark as a single plant organ. While this approach has enhanced our general knowledge concerning the overall rate of decomposition for woody debris, it has not provided the mechanistic understanding needed to make predictions for this important ecological process. In particular, studies on the decomposition of woody debris have revealed a strong species effect, even when controlling for critical traits such as wood density or diameter, but our understanding on what drives this species effect has been held back by the lack of distinction between wood and bark. In my recent and current project, I set out to investigate the role of bark on the decomposition of the wood inside it. Preliminary results indeed showed that bark does play an important role in wood decomposition and such role is species specific (Dossa et al. 2016). Follow up work suggests a size specific effect (Dossa et al.2018). All together, these results suggest that incorporating the effect of bark in wood decomposition will lead to a more realistic proxy to parameterize the decomposition process in global climate models.
Project 3: Biodiversity effects on woody debris decomposition: The role of microorganisms in wood decomposition
Given the high rates of global biodiversity loss, the relationship between diversity and ecosystem functioning is of critical concern and an important aspect of forest ecology. Wood decomposition is predominantly mediated by fungi, and the rate of decomposition is influenced by climate, substrate quality, and the responses of the decomposer community to these factors. Hence, diversity may affect wood decomposition through (i) habitat structure and its effect on microclimatic conditions on the ground, (ii) the chemical and physical properties of the wood, and (iii) the composition of the decomposer community. Moreover, the decomposition of woody debris is a successional process with different species performing distinct roles in the decomposition of substrates. However, most studies on the microorganism diversity and ecosystem functioning relationship are under environmental control with contradicting findings. Moreover, studies that attempt to investigate this relationship in the field have been confined to temperate and boreal forest, neglecting tropical forests. I use both traditional methods for measurement of microbial biomass through bio-marking phospholipid fatty acids (PLFA) and next generation sequencing to understand the relationship between microorganisms and wood decomposition rate as a basis for testing theoretical relationships.
Future project
Tropical forests constitute the world’s largest vegetation and soil carbon pools and shelter some of the most important global reservoirs of biodiversity, yet they face an increasing array of anthropogenic activities which threaten to degrade and destroy forest ecosystems. Increasing evidence suggests that forest disturbance and climate change are both resulting in increased liana abundance and biomass in tropical forests. The proliferation of lianas may have negative effects on forests ecosystems services; however, these effects are poorly understood. For example, organic matter decomposition, which consists of the degradation, break-down and redistribution of carbon and nutrients into the atmosphere and soil, has for the past focused on only the organs (wood, leaves, reproductive parts) of self-standing trees. There is an urgent need to evaluate how liana proliferation may affect local and regional carbon and nutrient cycles. To address this gap in our knowledge, my future research will evaluate liana decomposition and its contribution to forest biogeochemistry. The project will cover nutrient cycling in the canopy with investigation of the contribution from canopy dwellers arthropods. The project will focus on: (i) a phylogenetic perspective on liana wood decomposition, (ii) checking the resource complementarity hypothesis, which will evaluate the possibility that liana leaves enhance forest leaf litter quality and (iii) direct comparison of liana and self-standing tree organs (wood and leaves).