Abstract:

Despite the recognized importance of the fine roots in influencing tree growth and stand productivity, knowledge of fine roots is still limited, especially in adverse sites like saline-alkali land. In this paper, we applied sequential soil coring to assess the influence of stand age, soil depth and growth month on fine roots in 3, 16, 30 and 40-year old Robinia pseudoacacia stand in coastal saline-alkali land of the Yellow River Delta, China. Besides, the correlations between fine roots characteristics fine root biomass (FRB), fine root length (FRL), fine root surface area (FRSA), specific root length (SRL) and specific root surface area (SRA)) and abiotic factors (temperature, precipitation, soil water content (SWC), soil salt content (SSC) and soil nutrients) were discussed. In this paper, FRB, FRL, FRSA, SWC and soil nutrients increased, while SRL and SSC decreased with increasing stand age. Vertically, fine roots were concentrated in a 0-20 cm soil layer. SRL, SWC and SSC increased, while soil nutrients decreased with increasing soil depth. Temporally, FRB, FRL, FRSA, soil hydrolytic nitrogen and available potassium (AK) shared similar patterns and reached maximum in May or September. In July, SWC, SRL and SRA reached maximum while SSC reached the minimum. Soil total nitrogen (TN) and organic matter (OM) were highest in May or November. Correlation analysis showed that FRB, FRL and FRSA were negatively correlated with SWC and SSC, positively correlated with HN and AK. SRL was positively correlated with temperature, precipitation, SWC and SSC, while negatively correlated with TN. Among abiotic factors, temperature, precipitation and HN played key roles in the study area. This study improves our understanding of the fine roots and belowground ecology of R. pseudoacacia stands in coastal saline-alkali land of the Yellow River Delta.

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