Phenology of fine root and shoot using high frequency temporal resolution images in a temperate larch forest

Abstract

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. Here, we aimed to explore seasonal temperature patterns of daily-based root and shoot dynamics by capturing high frequency information of plant images in a larch forest. Additionally, we focused on seasonal changes in fine root color, which white roots absorb nutrients or water; brown roots undergo secondary structural development with transport resources. We monitored continuous images using an automated digital camera for shoot dynamics and a flatbed scanner for the fine root dynamics. 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. Larch shoot production had a single mountain-shaped peak, and there was a positive correlation between plant area index and air temperature. Fine root production had a bimodal root-growth pattern, with two peaks in early summer and late autumn. Soil temperature was positively correlated with white root proportion and negatively correlated with brown root proportion. We identified differences between shoots and roots regarding temperature relationships. In particular, the automated flatbed scanner method for root dynamics allowed the collection of detailed bimodal patterns of root production with a shift from whitening to browning color, which had previously been overlooked. Such high frequency temporal resolution analysis can illustrate the in-depth of mechanisms of fine-root and shoot phenology through different stages of plant development in terms of growth and senescence.