Dynamics and Determinants of Maize Sap Flow Under Soil Compaction in the Black Soil Region of Northeast China

Soil compaction is considered as one of the main factors limiting plant growth. Understanding the variation in sap flow affected by soil compaction is of vital importance for precision agriculture. In this study, a two-year field experiment with three levels of soil compaction (i.e., NC, no compaction; MC, moderate compaction; and SC, severe compaction) was conducted in the black soil region of Northeast China. Results revealed that soil compaction had a significant impact on soil properties, soil water content, and plant growth parameters, which ultimately affected the sap flow rate of maize. The average daily sap flow rates of MC and SC decreased by 15.89% and 29.12% in comparison to those of NC in 2023, and decreased by 51.53% and 57.11% in comparison to those of NC in 2024, respectively. Net radiation and vapor pressure deficit were the two most important meteorological variables affecting sap flow rate. In addition, the relationship between sap flow rate and meteorological variables was independent of the level of soil compaction stress. Daily sap flow rate exhibited a strong linear relationship with leaf area index and stem diameter, but showed no significant correlation with plant height. Additionally, daily sap flow rate was well correlated with root length density in the 0–60 cm soil layer. Furthermore, daily sap flow rate was significantly affected by soil water content of the 0–60 cm soil layer, but there was no significant correlation between daily sap flow rate and penetration resistance. Moreover, cumulative sap flow rate was negatively correlated with soil bulk density in both the top layer (0–20 cm) and sub-layer (20–40 cm). Our results provide a scientific basis for understanding the relationship between maize sap flow and soil compaction. More precise and systematic characterization of soil compaction, especially in relation to root growth, is needed to explore the underlying mechanisms of soil compaction on plant sap flow in the future.