Spectral characteristics and quantities of dissolved organic matter released from leaves with competitive and stress-tolerant ecological strategies in a subtropical region
Plants have different ecological strategies in response to environmental stress under global climate change, and the spectral characteristics and quantities of dissolved organic matter (DOM) leaching from leaves depend on the plant's ecological strategy. DOM leaching due to different strategies will influence soil nutrient cycling. The objective of this study was to investigate the differences in the spectral characteristics and quantities of DOM derived from leaves of plants (Dendropanax dentίger,Machilus grίjsii,Symplocos cochinchinensis (Lour.),Altingia gracilipes, Castanopsis fargesii,and Castanopsis faberi) with different ecological strategies in a subtropical region. In this study, we sampled fresh leaves from 6 kinds of plants,including 3 competitive-type plants (C-strategy) and 3 stress-tolerant-type plants (S-strategy). We examined dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) to determine the quantities of DOM,and employed Special Ultraviolet-Visible Absorption (SUVA ) , Humification Index (HIX ) and Fourier-Transform Infrared (FTIR) to analyze the spectral characteristics of DOM. The results showed that there were no significant differences in the DOC concentrations between C-type and S-type plants. However, DON was higher in C-type plants compared to S-type plants. In addition, we examined the structural characteristics of DOM between the C- and S-strategies using SUVA, fluorescence, and FTIR absorption spectrometry. The aromatic index and HIX were in the order: S > C. In addition, the synchronous fluorescence spectra were stronger in C-type compared to S-type plants,which suggests that DOM leaching from the leaves of a C-type plant was greater. The degree of humification was lower in the labile materials,while it was higher in the S-type plants. FTIR spectroscopy indicated that DOM from different types of leaves exhibited similar absorption peaks, with the strongest absorption arising from the prolonged vibration of H-bonding hydroxyl groups in all cases. This result shows that DOM from C-type plants has a simple structure that is in accord with fluorescence spectra. Overall,DOM from S-type plants was richer in nutrient composition and had a more complex structure compared to that from C-type plants. Our results suggested that S-type plants have better adaption under environment stress. Owing to the complex structure of DOM from S-type plants, it would reduce soil carbon turnover after leaching into the soil. Therefore, S-type plants are more effective in the formation of soil carbon sink under climate change.