Soil enzyme activity and stoichiometry along a gradient of vegetation restoration at the Karst Critical Zone Observatory in Southwest China

Abstract

The “Grain for Green Programme” was implemented in the 1990s as a solution to the extreme degradation of karst landscapes that cover one‐third of China, largely caused by decades of poorly managed intensive agriculture. The recovery of soil functions is key to the success of ecosystem regeneration of abandoned croplands where the carbon (C) and nutrient cycles have been severely perturbed by cultivation. However, an ecological ‘tipping point’ beyond which soil functions are unrecoverable in manageable timescales may have been passed in the fragile, subtropical karst ecosystem. The aim of this study was to use the activity of key enzymes for C, nitrogen (N), and phosphorus (P) acquisition in the soil as a proxy for the biological response to vegetation restoration after agricultural abandonment in a severely degraded karst catchment at the Karst Critical Zone Observatory in Guizhou Province. In 2016, a space‐for‐time approach was used to establish a chronosequence of vegetation recovery: sloping cropland < recently abandoned sloping cropland < shrubland < secondary (regenerated) forest < primary (natural) forest. Soils were sampled from the surface to the bedrock (up to 80‐cm depth) in each recovery phase. The activity of all enzymes in the top 0 to 30‐cm depth increased after abandonment and was positively correlated with soil nutrient and water contents. Nitrogen deficiencies were indicated by the reduced ratios of C‐ relative to N‐hydrolase activity and the increased ratios of N‐ relative to P‐hydrolase activity in the abandoned croplands and shrublands. Phosphorus deficiencies were indicated by the reduced ratios of N‐ relative to P‐hydrolase activity and C‐ relative to P‐hydrolase activity in the soils of the shrubland and secondary forest compared with the primary forest. Our results revealed that near‐to‐natural biological soil function was recoverable as vegetation naturally restored and suggested that the rate of recovery may be accelerated by managed nutrient amendments during the early stages after abandonment. This new information may help to inform the managed regeneration of degraded agricultural land in nutrient‐poor, subtropical environments.

Effects of vegetation restoration on soil quality in fragile karst ecosystems of southwest China

“…The effects of vegetation restoration on soil quality in degraded lands remain controversial. Some studies reported that vegetation restoration could improve soil physicochemical properties in karst cropland, such as increasing soil nutrients like SOC, N concentration ( Chen et al, 2019 ; Liu et al, 2019 ; Zhang et al, 2019a ); others supported that most of the restoration projects were failed or get limited success ( Asmelash, Bekele & Birhane, 2016 ), especially in the fragile karst ecosystem southwest China, where an ecological ‘tipping point’ may have been passed, beyond which soil properties are unrecoverable in manageable timescales ( Guo et al, 2019 ). In our study, none of the vegetation restoration types decreased soil quality significantly, with VSQI between −0.03 and 0.17, SQI values in natural shrubland, Toona sinensis - Pennisetum purpureum and Zenia insignis in total soil depth (0–30 cm) were significantly higher than that in the corresponding controls ( Table 8 ).…”

“…To address these problems, several national-scale ecological restoration projects have been carried out in karst areas, including the Grain for Green Program, the Rocky Desertification Control Project and the Natural Forest Protection Project ( Zhang et al, 2016 , 2018b ). The recovery of soil functions is vital to ecosystem regeneration of degraded croplands ( Guo et al, 2019 ), many scholars have evaluated the impacts of different vegetation restoration strategies on soil quality, which has been widely used to determine how soil responds to various management practices ( Raiesi & Kabiri, 2016 ; Guo et al, 2018 ; Vincent et al, 2018 ). However, most of these studies compared the soil quality of different vegetation restoration types without considering their original ecosystem conditions, and judged each type based only on the status quo ( Yang et al, 2017 ; Li et al, 2018a ; Zhang et al, 2019a ).…”

Soil nitrogen‐hydrolyzing enzyme activity and stoichiometry following a subtropical land use change

“…Soil extracellular enzyme stoichiometry (EES) reflects the energy and nutrient limitations on microbial metabolism, indicating how shifts in substance and energy allocation alter them according nutrient demand (Cui et al, 2018; Guo et al, 2019; Sinsabaugh & Follstad, 2012). It has been suggested that ecosystem C:N: phosphorus (P) enzyme stoichiometry greatly varies with land‐use types (Li et al, 2012).…”

Peer Review #1 of "Effects of vegetation restoration on soil quality in fragile karst ecosystems of southwest China (v0.1)"

“…Some studies reported that vegetation restoration could improve soil physicochemical properties in karst cropland, such as increasing soil nutrients like SOC, N concentration (Chen et al 2019;Zhang et al 2019a); others supported that most of the restoration projects were failed or get limited success (Asmelash et al 2016), especially in the fragile karst ecosystem southwest China, where an ecological 'tipping point' may have been passed, beyond which soil properties are unrecoverable in manageable timescales (Guo et al 2019). In our study, none of the Manuscript to be reviewed vegetation restoration types decreased soil quality significantly, with VSQI between 0.03 and 0.17, SQI values in natural shrubland, Toona sinensis-Pennisetum purpureum and Zenia insignis in total soil depth (0-30 cm) were significantly higher than that in the corresponding controls (Table 8).…”

“…The recovery of soil functions is vital to ecosystem regeneration of degraded croplands (Guo et al 2019), many scholars have evaluated the impacts of different vegetation restoration strategies on soil quality, which has been widely used to determine how soil responds to various management practices (Raiesi & Kabiri 2016;Guo et al 2018;Vincent et al 2018). However, most of these studies compared the soil quality of different vegetation restoration types without considering their original ecosystem conditions, and judged each type based only on the status quo (Yang et al 2017;Li et al 2018a;Zhang et al 2019a).…”