CATENA | 红壤区土壤C、N、P储量及其化学计量与土地利用类型和侵蚀条件的关系

Soil C, N, P stocks and stoichiometry as related to land use types and erosion conditions in lateritic red soil region, south China

Ying Lu

1 Corresponding author at: No 483, Wushan Rd. South China Agricultural University, Guangzhou, Guangdong 510642, PR China.

2 College of Natural Resources and Environment, South China Agricultural University, Guangzhou 510642, PR China

Irrational land-use can accelerate soil erosion by deteriorating soil structure and depleting soil nutrients, especially profoundly alter soil organic carbon (C), total nitrogen (N), total phosphorus (P) contents and stocks. 不合理的土地利用通过破坏土壤结构和消耗土壤养分，特别是深刻改变土壤有机碳(C)、全氮(N)、全磷(P)含量和储量，加速土壤侵蚀。However, it remains unknown how soil C, N, P stoichiometry patterns are affected by land-use type and soil erosion. This study was carried out to examine the soil C:N:P stoichiometry patterns in woodland (WL), upland (UL), and paddy (PD) at soil depths of 0–10, 10–20, and 20–30 cm under collapsed gully erosion (CGE) and sheet erosion (SE) conditions in lateritic red soil region. 然而，土壤C、N、P化学计量特征如何受土地利用类型和土壤侵蚀的影响尚不清楚。本研究以红壤性红壤区崩沟侵蚀和片滩侵蚀为研究对象，研究了0 ~ 10、10 ~ 20、20 ~ 30 cm土层下林地（WL）、旱地（UL）和稻田（PD）土壤C:N:P化学计量特征。Compared to WL, C content and stock decreased by 19.1–31.9 g kg⁻¹ and 12.8–31.7 Mg ha⁻¹, but P content and stock increased by 4.9–7.4 g kg⁻¹ and 6.7–9.9 Mg ha⁻¹ in UL soil at 0–30 cm, resulting in a decrease in C:N, C:P and N:P ratios by 8.6–14.8, 23.0–28.6 and 0.7–1.0, respectively. In addition, N, P contents and stocks increased by −0.04–1.8 g kg⁻¹, 4.1–10.5 g kg⁻¹ and 1.8–1.1 Mg ha⁻¹, 7.0–8.2 Mg ha⁻¹ in PD soil at 0–30 cm, resulting in a decrease in the ratio of C:N, C:P and N:P by 8.1–10.6, 20.7–26.0 and 0.6–0.8, respectively. Furthermore, C, N, P contents, stocks and C:N ratio in UL and PD soils were more significant under SE than CGE condition with, while it was opposite trend in WL at 0–30 cm depth. Soil C, N, P contents and stocks significantly decreased with soil depth, while no significant changes were detected on their stoichiometric ratio. Soil porosity and texture had significant contribution to C, N and P stoichiometry by PCA and RDA analysis. Our results demonstrate that the intensive agricultural practices changing soil porosity and texture under SE condition led to more pronounced differences of soil C, N, P and their stoichiometric ratios in lateritic red soil region. 土壤C、N、P含量和储量均随土层深度的增加而显著降低，但其化学计量比变化不显著。通过PCA和RDA分析，土壤孔隙度和质地对C、N、P化学计量的贡献显著。说明SE条件下，集约化农作改变了土壤孔隙度和质地，导致红壤区土壤C、N、P及其化学计量比的差异更明显。

Fig. 1.Distribution of soil C (a), N (b) and P (c) contents in different land-use types under two erosion conditions. WL, woodland; UL, upland; PD, paddy; SOC, soil organic carbon; TN, soil total nitrogen; TP, soil total phosphorus. Bars represent the standard error of the mean (n = 3). Different capital letters in the same erosion condition indicate a significant difference among land-use types at P < 0.05 level; Different lower-case letters in the same land-use type indicate a significant difference among erosion conditions at P < 0.05 level. NS marker above the bars indicate non-significant differences among soil depths at P > 0.05; Different * marker above the bars indicate significant differences among soil depths at P < 0.05.

Fig. 2.Distribution of soil Cs (a), Ns (b) and Ps (c) in different land-use types under two erosion conditions. Bars represent the standard error of the mean (n = 3). WL, woodland; UL, upland; PD, paddy; SOC, soil organic carbon; TN, soil total nitrogen; TP, soil total phosphorus; Cs, SOC stocks; Ns, TN stocks; Ps, TP stocks. Different capital letters in the same erosion types indicate a significant difference among land use types at P < 0.05 level, and different lower-case letters in the same land use type indicate a significant difference among erosion types at P < 0.05 level. NS marker above the bars indicate non-significant differences among soil depths at P > 0.05; Different * marker above the bars indicate significant differences among soil depths at P < 0.05.

Fig. 3.Soil C, N and P stoichiometric ratios in different land-use types under two erosion conditions. Bars represent the standard error of the mean (n = 3). WL, woodland; UL, upland; PD, paddy; SOC, soil organic carbon; TN, soil total nitrogen; TP, soil total phosphorus; C:N, the ratio of SOC:TN; C:P, the ratio of SOC:TP; N:P, the ratio of TN:TP. Different capital letters in the same erosion types indicate a significant difference among land use types at P < 0.05 level, and different lower-case letters in the same land use type indicate a significant difference among erosion types at P < 0.05 level. NS marker above the bars indicate non-significant differences among soil depths at P > 0.05; Different * marker above the bars indicate significant differences among soil depths at P < 0.05.

Fig. 4.Linear relationships between soil C, N, P stocks and C, N, P stoichiometric ratio in the two erosion types with three land use types. SOC, soil organic carbon; TN, soil total nitrogen; TP, soil total phosphorus; C:N, the ratio of SOC:TN; C:P, the ratio of SOC:TP; N:P, the ratio of TN:TP; Cs, SOC stocks; Ns, TN stocks; Ps, TP stocks.

Fig. 5.Correlation analysis between C, N, P stoichiometric ratio, stocks and soil characteristics (*P < 0.05; **P < 0.01). BD: soil bulk density; CP: capillary porosity; NP: non-capillary porosity; Fe_d: free iron; SOC: soil organic carbon; TN: total nitrogen; TP: total phosphorus; C:N: the ratio of SOC and TN; C:P: the ratio of SOC and TP; N:P: the ratio of TN and TP; Cs: SOC stock; Ns: TN stock; Ps: TP stock. The numbers represent the correlation coefficients. Blue and red denote positive and negative correlations, respectively. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 6.Biplot of the first two components from the principal component analysis (PCA) under different land use and erosion types. BD: soil bulk density; CP: capillary porosity; NP: non-capillary porosity; Fef: free iron; SOC: soil organic carbon; TN: total nitrogen; TP: total phosphorus; C:N, the ratio of SOC and TN; C:P, the ratio of SOC and TP; N:P, the ratio of TN and TP; Cs, SOC stock; Ns, TN stock; Ps, TP stock. Black, red and green solid circles represent 95% confidence for paddy (PD), upland (UL) and woodland (WL) in the collapsed gully and sheet erosion regions, respectively. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 7.Two-dimensional sequence diagram of redundancy analysis (RDA) between soil properties and C, N and P stoichiometry in different land use soils with two soil erosion regions, respectively. BD, soil bulk density; CP, capillary porosity; NP, non-capillary porosity; Fef, free iron; C, soil organic carbon; N, total nitrogen; P, total phosphorus; C:N, the ratio of SOC and TN; C:P, the ratio of SOC and TP; N:P, the ratio of TN and TP; Cs, SOC stock; Ns, TN stock; Ps, TP stock.

本研究通过田间调查和室内试验相结合的方法，研究了土地利用类型和土壤侵蚀对农田土壤C:N:P化学计量的影响。UL土壤碳含量和碳储量低于WL，可能是由于农业耕作造成的碳损失和较少的植物残体投入量造成的;而PD土壤碳含量与UL相似，但由于施肥和淹水条件造成的土壤N含量和储量较高，导致UL和PD土壤的C∶N比值较低。人为磷肥的施用也显著提高了磷素含量和储量，降低了C∶P和N∶P比值。C、N、P含量和储量随土层深度的增加而降低，其化学计量比则相反，在0 ~ 10 cm处显著升高，表明表层土壤对土地利用和侵蚀更为敏感。土壤孔隙度、黏粒、粉粒和C、N、P含量的变化可能是土壤C、N、P化学计量比变化的主要原因。本研究提供了长期精耕细作条件下典型侵蚀条件下土壤C、N、P含量、储量和化学计量比变化的可比数据，对优化农业管理具有重要意义。