Elemental stoichiometry (C, N, P) of soil in the Yellow River Delta nature reserve: Understanding N and P status of soil in the coastal estuary

Abstract

The Yellow River Delta Nature Reserve (YNR), which includes two separated regions: part of the old Yellow River Delta (OYD) and part of the current Yellow River Delta (CYD), was established to protect coastal wetlands in the coastal estuary. A total of 120 plots were sampled in the YNR in April 2016, and the spatial patterns of soil C, N and P contents and their stoichiometric ratios (C:N (RCN), C:P (RCP) and N:P (RNP)) were studied and interpolated using the Ordinary Kriging method. Results indicated that the soil elemental contents and stoichiometric ratios showed high spatial heterogeneity and large variations. The mean C:N:P ratio (RCNP) was ~ 64.7:2.3:1 in OYD, and ~ 64.5:2.0:1 in CYD, respectively, and a well-constrained RCP ratio ~ 65:1 was found in the 0–50 cm soil depth within the YNR. N showed greater variation than C and P. Furthermore, N contents in the 0–5 cm soil layer of OYD were significantly higher than that of CYD (F = 4.79, p = 0.03); RCN in 0–5 cm, 5–10 cm layers of OYD was significantly lower than those in the same layers of CYD (F = 4.75, p = 0.03; F = 5.18, p = 0.02, respectively). RNP in 0–5 cm soil layer of OYD was notably higher than that of CYD (F = 4.88, p = 0.03). These results were due to the combined actions of sedimentation, reclamation and fertilization. Finally, we concluded that a longer reclamation and fertilization history led to decreased RCN in coastal estuary soils, confirmed that the soil of the YNR exhibits N limitation, and suggested that the soil RCN and RNP could be good indicators of the anthropogenic improvement status during soil development in this coastal estuary.