Responses of absorptive root and mycorrhizal colonization of Chinese fir (Cunninghamia lanceolata) to varied environmental conditions

Root branching and mycorrhizal symbioses are two major mechanisms for soil resource acquisition by trees. Understanding the relationship between these two mechanisms and their responses to varied environmental conditions is crucial for predicting the responses of foraging strategies of roots to environmental changes. This study was conducted in 11 Chinese fir (Cunninghamia lanceolata) plantations distributed in different environmental conditions in Subtropical China to assess the relationship between root tip traits related to nutrient foraging (branching ratio of 1st-order roots to 2nd-order roots, arbuscular mycorrhizal (AM) colonization) and their environmental variables, including mean annual precipitation (MAP), mean annual temperature (MAT), soil C, soil N, soil P, and soil pH. Root branching was more sensitive to environmental conditions than mycorrhizal symbioses. The branching ratio and AM colonization of Chinese fir were significantly related to several environmental variables. The branching ratios were positively correlated with MAT, but negatively correlated with soil C, soil N, and soil pH (P < 0.05), suggesting that harsh environmental conditions can promote absorptive root branching. To our surprise, the AM colonization of absorptive roots was not as sensitive to environmental factors as branching ratio. However, the AM colonization of absorptive roots was positively correlated with soil pH (P < 0.1), indicating that soil acidity controls mycorrhizal symbioses. Moreover, the branching ratio was significantly negatively correlated with AM colonization (P < 0.05). Our results confirmed that environmental conditions significantly regulate fine root branching and its mycorrhizal symbioses, but with different controlling variables. The negatively correlated relationship of branching ratio and AM colonization shows that environmental factors regulate absorptive root traits in different ways.

Automated summary

This study investigated the relationship between root tip traits and environmental variables in Chinese fir plantations in Subtropical China. The results showed that root branching is more sensitive to environmental conditions than mycorrhizal symbioses. The branching ratio of Chinese fir was positively correlated with mean annual temperature, but negatively correlated with soil carbon, soil nitrogen, and soil pH. Surprisingly, the AM colonization of absorptive roots was not as sensitive to environmental factors as branching ratio, but it was positively correlated with soil pH. The study confirmed that environmental conditions significantly regulate fine root branching and its mycorrhizal symbioses, but with different controlling variables.