Spatial changes and influencing factors of fine root carbon,nitrogen and phosphorus stoichiometry of plants in China

Aims Fine roots and leaves are important below- and above-ground functional organs. It is widely recognized that leaf nitrogen (N) and phosphorus (P) stoichiometry displays significant latitudinal variations, and two competing theories (i.e. Temperature-Plant Physiological Hypothesis and Growth Rate Hypothesis) have been proposed to explain this phenomenon. Although considerable efforts have been made to test these theories, comparatively few data have been reported for the plants in China to examine the latitudinal and longitudinal variations in fine root carbon (C), N and P stoichiometry. Accordingly, we compiled an extensive data set of root C, N and P stoichiometry, our objective was to address three main issues: (1) whether the C, N and P stoichiometric latitudinal patterns for roots conform to those reported for leaves, (2) how exactly does root C, N and P stoichiometry changes as a function of longitude, and (3) whether the Temperature-Plant Physiological Hypothesis or Growth Rate Hypothesis can account for the latitudinal patterns observed for fine root stoichiometry. Methods We compiled data on fine root C, N and P contents, climate, and geographic location, and analyzed the correlations among these variables. Important findings The N and P contents were higher in fine roots as opposed to coarse roots. The N and P contents in fine roots increased with increasing latitude. P content in fine roots declined with increasing longitude, whereas the N:P of fine roots increased with increasing longitude. The N and P contents in fine roots were negatively correlated with mean annual temperature and mean annual precipitation, but positively correlated with soil nutrient. Among the three abiotic factors (i.e. soil N and P contents, temperature and precipitation), soil N and P levels had the greatest effect on the N and P contents in fine roots . The variations observed in fine and coarse root C:P and N:P were inconsistent with the Growth Rate Hypothesis, whereas the positive correlations between root N and P contents and latitude were the same as those observed for leaves, which support Temperature-Plant Physiological Hypothesis, reflecting an adaptive strategy to environmental conditions.