Identify the Path Structure and Quantify Direct and Indirect Effects in an Above-below-ground System under Warming
Date Issued
2014
Date
2014
Author(s)
Tseng, Tzu-Jung
Abstract
Climate warming could affect the interactions between above- and below- ground biota and change the strength of direct or indirect effects, but relevant studies are sparse. To better understand above-below-ground interactions under warming, this study examined a system including the plant Commelina diffusa, the aphid Aphis gossypii, and the earthworm Amynthas corticis under 2 scenarios: (1) normal (day and night temperature at 22.5 and 18.5oC, respectively) and (2) warming (a 4 oC increase in day and night temperature). Each scenario included four treatments: a) control treatment (plants only), b) earthworm treatment (plants, earthworms), c) aphid treatment (plants, aphids), and d) earthworm–aphid treatment (plants, aphids, earthworms). To qualify and quantify the direct and indirect effects in this system, I measured the traits of plants, earthworms, aphids, litter, and soil. Data analyses were conducted by (1) redundancy analysis for exploring the general patterns of plant traits in response to the treatment factors (earthworm, aphid, and warming); (2) Bayesian hierarchical modelling to quantify the direct effects in the system; (3) d-sep test and mediation analysis for identifying and quantifying the indirect effects. The results showed that (1) the effect sizes of earthworm and aphid treatments on plants were similar but different in direction, and showed a non-contingent response to warming; (2) the effect of warming treatment on plants was strong but decreased linearly with time; (3) there were no interactions among aphid, earthworm, and warming treatments in this system; thus, the effects of these 3 factors were additive. In addition, I found 2 indirect effects in this system, suggesting plant nitrogen content and soil physical property as mediators in above-below-ground interactions: (1) earthworm treatment increased aphid population by increasing plant nitrogen content, and (2) warming and earthworm treatments increased plant growth (i.e. plant node number) by modifying soil physical property. Overall, this study reveals that warming can affect an above-below-ground system via direct and indirect pathways.
Subjects
地上部地下部交互作用
暖化
蚯蚓
蚜蟲
中介分析
SDGs
Type
thesis
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