Latitudinal patterns of soil extracellular enzyme activities and their controlling factors in Pinus massoniana plantations in subtropical China

Abstract

Soil extracellular enzyme activities (EEAs) and enzymatic acquisition ratios are significantly affected by both abiotic and biotic factors across various scales and ecosystems. However, what determines the soil EEAs and their acquisition ratios in planted forests remains poorly understood. In this study, we measured the activities of β-1,4-glucosidase (BG), β-1,4-N-acetylglucosaminidase (NAG) and acid phosphatase (AP) and explored their key controlling factors in Pinus massoniana plantations along a 1100 km latitudinal gradient in subtropical China. The three enzyme activities increased with an increase in latitude and were significantly and negatively affected by mean annual temperature (MAT) and mean annual precipitation (MAP), but were positively correlated with soil available P content. From south to north, the enzymatic C:N (ln(BG):ln(NAG)) acquisition ratio decreased significantly, while the enzymatic C:P (ln(BG):ln(AP)) and N:P (ln(NAG):ln(AP)) acquisition ratios increased significantly. The latitudinal patterns of the enzymatic C:P and N:P acquisition ratios were significantly and negatively affected by MAT and MAP, but were positively affected by soil available P content. In total, climatic factors (e.g., MAT and MAP) accounted for more (14.2% and 25.5%, respectively) of the latitudinal variations in soil EEAs and their acquisition ratios than soil (e.g., available P) and stand (e.g., diameter at breast height). Therefore, these results illustrate that planted forests are susceptible to variations in soil EEAs and their acquisition ratios along a latitudinal gradient and that such changes are mainly driven by climate. Moreover, the similar average enzymatic C:P and N:P acquisition ratios in this pine plantation with the literature values reported for tropical and subtropical natural forests indicate that the pine plantations in subtropical China may be strongly P limited.