The effect of land-use change on fungal productivity; implications for decomposition and carbon cycling in tropical forests

Project Number 185 Back to projects

Start date

2018-02-12

End date

2018-05-01

Research areas

Biogeochemistry

Data use

Masters Project

Rationale

The focal point of this project is to quantify the effect of land-use change on fungal productivity and therefore assess the impact of habitat degradation on decomposition, a major ecosystem function. Tropical forests are being rapidly converted to agricultural land, resulting in increased amounts of deadwood debris. By understanding the dynamics of deadwood decomposition and how the process behaves under disturbance, we can more accurately estimate carbon fluxes and therefore implement suitable management practices and make better-informed policy decisions. This is important in the mitigation of global climate change. Fungi are the primary decomposers of deadwood due to their ability to metabolise cellulose and lignin. It is relatively well understood that optimum conditions for fungal respiration are warm temperatures and moist conditions, with moisture often more limiting than temperature, yet to my knowledge no studies exist that apply this concept to tropical forest degradation. Logging results in a hotter, drier environment as solar radiation can easily penetrate the understory. The hypothesis is therefore that productivity will be reduced in degraded versus primary forest, due to an altered microclimate that deviates from fungal optima. Fungi use the sugars derived during decay to grow, hence productivity should be a good indicator of decomposition ability. This will be tested with a combination of field observation and experimental treatments. In the field productivity will be measured across a land-use gradient by inserting microscope slides into deadwood pieces, allowing colonisation by fungal hyphae. From this productivity will be quantified and compared to both microclimate data and carbon efflux from deadwood pieces. Additionally, the assumption that moisture limits fungal growth in logged forest will be tested with a series of controlled desiccation experiments.

Methods

The study site is in Sabah, Malaysia, split between the SAFE (Stability of Altered Forest Ecosystems) Project and Maliau Basin Conservation Area. In each plot deadwood has been selected to represent 3 decay stages (2, 3, 4) and 6 diameter classes. Stage 1 has been omitted as a pilot study in the UK revealed difficulty in inserting microscope slides into wood that has not yet lost its rigidity. Stage 5 has been omitted as my research is part of the larger NERC grant “Decomposition of deadwood debris left over from tropical rainforest logging operations” (PI Dr Robert Ewers), a study ongoing for 2 years, by which time decay class 5 will have completely decomposed.

Taking inspiration from the Rossi-Cholodny method used in soil (Kaspari et al., 2014), slides will be inserted into each deadwood piece; to my knowledge this has not been done before. A sterilised saw will be used to make all incisions. Slides will be inserted at 3 points along the deadwood, with 4 slides at each point in a radial distribution, to account for surface variance. This experiment will run for 1 month, with slides replaced at 2-week intervals. Once removed slides will be heat fixed and stained with lactophenol blue to allow visualisation of transparent hyphae, so percentage cover of each slide can be estimated. I will take a photo of all slides as a record. Throughout the experiment microclimatic conditions will be recorded in each plot by a data logger. Soil moisture and carbon efflux from deadwood will also be measured in 2-week intervals at the time of slide replacement/collection.

For the controlled treatments desiccation chambers will be built from plastic boxes, with adequate drainage and ventilation to prevent anoxic conditions from inhibiting fungal respiration. Silica gel will be used to prevent moisture loss/gain through the air holes. Moisture will be controlled with regular misting/watering and there will be a data logger in each chamber to enable the maintenance of desired conditions. Blocks will be cut in the field from deadwood in decay class 3 to ensure fungal diversity is well-established. There will be 10 blocks in total, 5 from primary and 5 from logged forest; this is to observe whether the fungal communities react differently to changing moisture, perhaps indicating adaptation. Each wood block will then be split into 3 pieces that receive different treatments. This is an attempt to control for factors that differ between blocks (e.g. tree species, wood density, fungal community composition etc.). The treatments will represent conditions experienced in the field (‘dry’ = moisture in oil palm, ‘intermediate’ = logged forest and ‘wet’ = primary forest). 4 slides will be inserted into each wood block in a radial distribution, congruent with the field experiment. Similarly, this experiment will also run for 1 month, with slides replaced at 2-week intervals.

All data will be analysed using a mixed effects model to account for interaction between fixed variables and the influence of random variables like plot (field study), chamber and wood block (treatments).
Project members
ResearcherProject roleProject contact
Amber SawyerLead Researcher