title: Photodegradation leads to increased carbon dioxide losses from terrestrial organic matter

authors: Rutledge, Susanna

subjects: abiotic decomposition

abstract: CO₂ production in terrestrial ecosystems is generally assumed to be solely biologically driven while the role of abiotic processes has been largely overlooked. In addition to microbial decomposition, photodegradation – the direct breakdown of organic matter (OM) by solar irradiance – has been found to contribute to litter mass loss in dry ecosystems. Previous small-scale studies have shown that litter degradation by irradiance is accompanied by emissions of CO₂. However, the contribution of photodegradation to total CO₂ losses at ecosystems scales is unknown. This study determined the proportion of the total CO₂ losses caused by photodegradation in two ecosystems: a bare peatland in New Zealand and a seasonally dry grassland in California. The direct effect of solar irradiance on CO₂  production was examined by comparing daytime CO₂  fluxes measured using eddy covariance (EC) systems with simultaneous measurements made using an opaque chamber and the soil CO₂ gradient technique, and with night-time EC measurements under the same soil temperature and moisture conditions. In addition, a transparent chamber was used to directly measure CO₂ fluxes from OM caused by solar irradiance. Photodegradation contributed 19% of the annual CO₂ flux from the peatland and almost 60% of the dry season CO₂ flux from the grassland, and up to 62% and 92% of the summer mid-day CO₂ fluxes, respectively. Our results suggest that photodegradation may be important in a wide range of ecosystems with exposed OM. Furthermore, the practice of partitioning daytime ecosystem CO₂ exchange into its gross components by assuming that total daytime CO₂ losses can be approximated using estimates of biological respiration alone may be in error. To obtain robust estimates of global ecosystem–atmosphere carbon transfers, the contribution of photodegradation to OM decomposition must be quantified for other ecosystems and the results incorporated into coupled carbon–climate models.

text: Photodegradation leads to increased carbon dioxide losses from terrestrial organic matter CO₂ production in terrestrial ecosystems is generally assumed to be solely biologically driven while the role of abiotic processes has been largely overlooked. In addition to microbial decomposition, photodegradation – the direct breakdown of organic matter (OM) by solar irradiance – has been found to contribute to litter mass loss in dry ecosystems. Previous small-scale studies have shown that litter degradation by irradiance is accompanied by emissions of CO₂. However, the contribution of photodegradation to total CO₂ losses at ecosystems scales is unknown. This study determined the proportion of the total CO₂ losses caused by photodegradation in two ecosystems: a bare peatland in New Zealand and a seasonally dry grassland in California. The direct effect of solar irradiance on CO₂  production was examined by comparing daytime CO₂  fluxes measured using eddy covariance (EC) systems with simultaneous measurements made using an opaque chamber and the soil CO₂ gradient technique, and with night-time EC measurements under the same soil temperature and moisture conditions. In addition, a transparent chamber was used to directly measure CO₂ fluxes from OM caused by solar irradiance. Photodegradation contributed 19% of the annual CO₂ flux from the peatland and almost 60% of the dry season CO₂ flux from the grassland, and up to 62% and 92% of the summer mid-day CO₂ fluxes, respectively. Our results suggest that photodegradation may be important in a wide range of ecosystems with exposed OM. Furthermore, the practice of partitioning daytime ecosystem CO₂ exchange into its gross components by assuming that total daytime CO₂ losses can be approximated using estimates of biological respiration alone may be in error. To obtain robust estimates of global ecosystem–atmosphere carbon transfers, the contribution of photodegradation to OM decomposition must be quantified for other ecosystems and the results incorporated into coupled carbon–climate models.

year: 2009

title: Psychological Time: The effect of task complexity upon the human estimation of duration.

authors: Webber, Simon

subjects: time

abstract: This thesis was designed to investigate the effect of task complexity upon how humans estimate duration.  Previous task complexity research suggests that duration is overestimated with simple tasks and underestimated with complex tasks.  One-hundred and forty-two first and second year university students participated.  Twelve experiments were conducted, which required participants to complete computer generated jigsaw puzzles and periodically estimate how long they thought they had been doing the puzzle.  In Experiment 1, participants were required to complete a jigsaw puzzle before making an estimate.  In the remaining eleven experiments, estimates were made throughout the session whilst participants worked on the jigsaw puzzle.  In the first four experiments, a task was complex if there were more puzzle pieces and simpler if there were fewer puzzle pieces.  There were no significant results obtained from the first four experiments.  Given the lack of effect from the first four experiments, the next two experiments partially replicated two task complexity studies to determine how task complexity can be used as an explanation for why estimations of duration differ.  Again, there were no significant results obtained from these two experiments.  The next four experiments tested whether people's estimates of duration were affected by the rate of reinforcement they receive (i.e., successfully moving a puzzle piece to a new location per unit time).  In the first of these two experiments (7 and 8) there was no effect of the manipulation, which consisted of decreasing the distance which a puzzle piece could be moved on the screen, relative to the distance the computer mouse was moved and fixing the speed at which a puzzle piece could be moved.  In Experiments 9 and 10, more discriminative stimuli were used to indicate to participants that a change in the reinforcement rate was occurring.  There was a significant result in Experiment 9 in one condition but this effect was not replicated in Experiment 10.  In Experiment 11, the reinforcement rate was reduced to zero and there was a significant effect on participants' estimates of duration.  However, these results suggested a confound between whether the reinforcement rate or not being able to access the jigsaw puzzle was affecting estimates of duration.  In Experiment 12, access to the jigsaw puzzle was limited, whilst simultaneously controlling the reinforcement rate and the results showed that not having access to the jigsaw puzzle affected how participants estimate duration.  These findings suggest that information can act as reinforcement, enabling a person to engage in private behaviour.  When there is no access to reinforcement, time 'drags' for humans.

text: Psychological Time: The effect of task complexity upon the human estimation of duration. This thesis was designed to investigate the effect of task complexity upon how humans estimate duration.  Previous task complexity research suggests that duration is overestimated with simple tasks and underestimated with complex tasks.  One-hundred and forty-two first and second year university students participated.  Twelve experiments were conducted, which required participants to complete computer generated jigsaw puzzles and periodically estimate how long they thought they had been doing the puzzle.  In Experiment 1, participants were required to complete a jigsaw puzzle before making an estimate.  In the remaining eleven experiments, estimates were made throughout the session whilst participants worked on the jigsaw puzzle.  In the first four experiments, a task was complex if there were more puzzle pieces and simpler if there were fewer puzzle pieces.  There were no significant results obtained from the first four experiments.  Given the lack of effect from the first four experiments, the next two experiments partially replicated two task complexity studies to determine how task complexity can be used as an explanation for why estimations of duration differ.  Again, there were no significant results obtained from these two experiments.  The next four experiments tested whether people's estimates of duration were affected by the rate of reinforcement they receive (i.e., successfully moving a puzzle piece to a new location per unit time).  In the first of these two experiments (7 and 8) there was no effect of the manipulation, which consisted of decreasing the distance which a puzzle piece could be moved on the screen, relative to the distance the computer mouse was moved and fixing the speed at which a puzzle piece could be moved.  In Experiments 9 and 10, more discriminative stimuli were used to indicate to participants that a change in the reinforcement rate was occurring.  There was a significant result in Experiment 9 in one condition but this effect was not replicated in Experiment 10.  In Experiment 11, the reinforcement rate was reduced to zero and there was a significant effect on participants' estimates of duration.  However, these results suggested a confound between whether the reinforcement rate or not being able to access the jigsaw puzzle was affecting estimates of duration.  In Experiment 12, access to the jigsaw puzzle was limited, whilst simultaneously controlling the reinforcement rate and the results showed that not having access to the jigsaw puzzle affected how participants estimate duration.  These findings suggest that information can act as reinforcement, enabling a person to engage in private behaviour.  When there is no access to reinforcement, time 'drags' for humans.

year: 2007

title: Telling “Us” in the “Days Destined to You: Response Life-Telling: Indigenous Oral Autobiography and the Performance of Relation

authors: Mahuika, Nepia

subjects: Arts & Humanities

abstract: This “tau-utuutu” (responsive) protocol feels familiar to me.² My turn to speak, to respond, to share in a conversation with Warren Cariou’s stimulating essay on “Life-Telling,” Indigenous autobiography, and Dovie Thomason. It reminds me of how life-telling, orality, and history, interweave and work in my tribal universe. At home, we take turns speaking. We inherit our words, we respond, carve, and weave new narratives—make them ours. Where I come from, lives are frequently “told,” sung, cried, carved, and performed, through tribal conversations, a chorus of textured tones, sometimes in a grand debate within which our personal and collective pasts, presents, and futures converge and diverge.³ I am glad, then, to be invited, to add my voice to this present discussion. It feels natural . . . normal . . . Native.

text: Telling “Us” in the “Days Destined to You: Response Life-Telling: Indigenous Oral Autobiography and the Performance of Relation This “tau-utuutu” (responsive) protocol feels familiar to me.² My turn to speak, to respond, to share in a conversation with Warren Cariou’s stimulating essay on “Life-Telling,” Indigenous autobiography, and Dovie Thomason. It reminds me of how life-telling, orality, and history, interweave and work in my tribal universe. At home, we take turns speaking. We inherit our words, we respond, carve, and weave new narratives—make them ours. Where I come from, lives are frequently “told,” sung, cried, carved, and performed, through tribal conversations, a chorus of textured tones, sometimes in a grand debate within which our personal and collective pasts, presents, and futures converge and diverge.³ I am glad, then, to be invited, to add my voice to this present discussion. It feels natural . . . normal . . . Native.

year: 2016