Soil respiration plays a critical role in driving soil carbon (C) cycling in terrestrial forest ecosystems. However, evidence to demonstrate the response of roots, mycorrhizal hyphae, and soil free-living microbes of soil respiration and their temperature sensitivity (Q10) remains lacking. Here, we used a root exclusion method to assess the contribution and response of root respiration (Rroot), mycorrhizal respiration (Rmyc), and (soil organic matter) SOM respiration (Rsom) to soil temperature in a larch forest. During the growing period, the contributions of Rroot, Rmyc, and Rsom to soil respiration were 42%, 6%, and 52%, respectively. The respiration rates of all components increased exponentially with increasing temperature. Based on these constitutive respiration rates with soil temperature, the Q10 values for Rroot, Rmyc, and Rsom were 3.84, 5.18, and 1.86, respectively. The results showed that the response to temperature change was different among roots, mycorrhizal hyphae, and microbes in the soil, while the temperature sensitivity of autotrophic respiration was higher than that of heterotrophic respiration. Importantly, the Rmyc at this site was extremely sensitive to temperature, although its overall emission was small. Mycorrhizal associations were identified as the key drivers of soil respiration and temperature sensitivity. A good understanding of the different soil CO2 efflux components will provide useful information for determining soil C fluxes and predicting soil C dynamics under changing environments.
Purpose
Understanding tree phenology reveals the underlying mechanisms through plant functional and productive activities and carbon sinks in forest ecosystems. However, previous research on tree phenology has focused on shoot dynamics rather than tree root dynamics. We aimed to explore seasonal temperature patterns of daily-based root and shoot dynamics by capturing high frequency plant images in a larch forest.
Methods
We monitored continuous images using an automated digital camera for shoot dynamics and a flatbed scanner for the fine root dynamics in the larch. Using the images, we analyzed the relationship between temperature and plant area index as shoot growth status and total root-area proportion of white and brown roots.
Results
Larch shoot production had a single mountain-shaped peak with a positive correlation between plant area index and air temperature. Fine root production had two peaks in the bimodal root-growth pattern in early summer and late autumn. Soil temperature was positively correlated with white root proportion and negatively correlated with brown root proportion.
Conclusion
We found differences between shoots and roots regarding temperature relationships. In particular, the automated flatbed scanner method for the root dynamics allowed the collection of detailed bimodal patterns of root production with shift from whitening to browning color, which had been previously overlooked. Such high frequency temporal resolution analysis can provide an in-depth of mechanisms of fine-root and shoot phenology through different stages of plant development in terms of growth and senescence.
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