Enzymatic stoichiometry in degraded soils after two decades of restoration in a Brazilian semiarid region

Abstract

Land degradation has emerged as a significantly pressing environmental concern, contributing to the decline of soil properties in both arid and semiarid regions. Despite this, there is limited understanding of how degradation and subsequent long-term restoration efforts impact enzymatic stoichiometry in soils of the Brazilian semiarid area. Therefore, our study aimed to quantify C-, N-, and P-acquiring enzymes in soil samples from the Caatinga, a Brazilian semiarid region. We compared three different conditions: (a) Native Caatinga vegetation, primarily dominated by Fabaceae species; (b) Restored land, resulting from two decades of grazing exclusion; and (c) Degraded land due to overgrazing, characterized by high-intensity grazing practices. A total of 54 soil samples were collected at depths of 0–10 cm during both dry and rainy seasons to evaluate the levels of C-, N-, and P-acquiring enzymes and their respective stoichiometries. Our findings revealed that, overall, C- and N-enzymes showed higher and similar levels between native and restored land, whereas these enzyme levels significantly decreased (approximately 60% for C-enzymes and 80% for N-enzymes) in degraded land. Moreover, P-acquiring enzymes exhibited a notable decrease (approximately 70%) in degraded land specifically during the dry season. The degraded land exhibited a higher C/N ratio (8.5) during the rainy season compared to native land (4.8). Conversely, higher values of C/P and N/P ratios (both during rainy seasons) were observed in native land (0.3 and 0.07, respectively). Redundancy analysis showed that native and restored lands clustered with all acquiring enzymes and were notably influenced by key soil properties such as organic C, microbial biomass C, and nutrients. In contrast, degraded land showed correlations with Al3+ and Na+. Our results provide substantial evidence that Caatinga soils affected by degradation may be microbially P-limited. This underscores the necessity of integrating P-enriched amendments or fertilizers and implementing long-term restoration practices.