Plant restoration leads to divergent sequestration of soil carbon and nitrogen in different fractions in an arid desert region

The Tibetan Plateau, a vulnerable eco-region undergoing global change, is hard to revegetate where land has become desertified due to the harsh habitat conditions. Sophora moorcroftiana shrubs, which are widely distributed in the middle reaches of the Yarlung Zangbo River basin of Tibet, China, have been naturally restored on desertified land during the last few decades. However, the influences of microtopography on the distribution and structure of the S. moorcroftiana population have been rarely reported. Here, we first describe the spatial variation of S. moorcroftiana population on a restored alluvial fan, and then explore the effects of microtopography on the restored S. moorcroftiana population, through a series of field surveys combined with the data collected by terrestrial laser scanning. The results indicate that the dominant age structure was adult shrubs (30-60 cm). Although the topographic effect had no significant impacts on soil organic matter and some other structural traits, which remained stable on the restored alluvial fan, it changed population density, plant growth, and distribution. The habitat conditions on the southwest aspect wapproximately 20-25 slope with altitudes ranging between 3,593-3,643 m, conditions that mostly favouring the distribution of the shrub population. The micro-topography played an important role in species distribution and growth of the S. moorcroftiana population. Our findings could help to understand the effect of micro-topography on plant population structure and distribution for ecological restoration of desertified land in the Southern Tibetan Plateau.

Section: Slopementioning

confidence: 81%

Section: Discussionmentioning

confidence: 99%

Stability and micro‐topographic effects of Sophora moorcroftiana population on a restored alluvial fan, Southern Tibetan Plateau

Liao

et al. 2021

“…In the subtropical red soil region, vegetation restoration created a more stable habitat by slowing down runoff activity. Less disturbance was conducive to the agglomeration of soil aggregates (Jia et al, 2019; Ma et al, 2019). Increasing amounts of residue tend to promote aggregate formation (De Gryze et al, 2005).…”

Section: Discussionmentioning

confidence: 99%

Aggregate‐associated soil organic carbon fractions in subtropical soil undergoing vegetative restoration

Liu

Zhang

et al. 2023

Precise assessment of soil organic carbon (SOC) storage requires understanding how vegetation and soil physico‐chemical properties differ in SOC fractions. Therefore, we aimed to analyze the dynamics of aggregate‐associated, labile organic carbon (LOC) fractions corresponding to depth to clarify the effect of vegetation and soil properties on water stable aggregate (WSA) mineral adsorption in subtropical, red soil with five vegetation restoration regimes. The results showed that the large macro‐aggregate fraction dominated the degraded red soil, which had the highest content of dissolved organic carbon (DOC). WSA‐associated, easily oxidized organic carbon (EOC) varied from 6.26 to 20.02 g/kg and was not affected by vegetation types. Schima superba pure forest significantly increased DOC (0.38 g/kg on average) and particulate organic carbon (POC, 7.92 g/kg on average), which had the highest biomass. Along with soil depth, WSA‐associated POC declined, while exhibiting a growth trend with decreasing particle size, for example, the highest POC was found in <0.053 mm aggregates. The redundancy analysis ordination indicated that soil porosity and total nitrogen (TN) were the main soil parameters that explained the most variance. Meanwhile, the vegetation biomass, except for litter, were all significantly positively correlated with <0.053 mm aggregates. Leaf biomass played the most important role on DOC in macro‐aggregates with a 53.42% contribution. For aggregate‐related POC, the largest contribution was from the interactions between branch biomass and pH (47.78%) followed by TN (35.1%) of micro‐aggregate‐related POC. Leaf biomass, <0.053 mm aggregates, and TN can be used as indicators to evaluate the impact of vegetation restoration on WSA‐associated SOC fractions. Broad‐leaved forest or in combination with indigenous coniferous species was a better choice for SOC sequestration improvement in the study area for managing C supply, process, and flux in subtropical terrestrial ecosystems.

“…With increasing land degradation, clay and silt particles are continuously eroded, and sand particles are retained and accumulated (Cheng et al, 2022; Feng et al, 2019). Desertification also increases soil sand content, and thus suppresses the mechanical protection from clay and silt for soil fertility (Jia et al, 2019; Qiu et al, 2021). However, it is unclear whether the decreases in soil fertility (C, N, and P) show nonlinear and threshold patterns (i.e., abrupt changes) as degradation intensifies in drylands across the Tibetan Plateau.…”

Section: Introductionmentioning

confidence: 99%

Soil fertility thresholds driven by sand content indicate drylands degradation phases on the Tibetan Plateau

Cai

Wang

et al. 2023

Understanding the process of dryland degradation is crucial to combating desertification and maintaining land sustainability. To identify important indicators of dryland degradation, we conducted a field survey of 46 drylands spanning an aridity gradient across the Tibetan Plateau. Our random forest model suggested that soil sand content was the most important predictor of variation in soil fertility (carbon, nitrogen, and phosphorus). Most soil fertility showed a nonlinear and abrupt decline with increasing soil sand content, and displayed three sequential thresholds. First, soil organic carbon sharply decreased beyond a soil sand content threshold of 47%. Second, exceeding a subsequent threshold of 70%, the total nitrogen and light fraction carbon declined dramatically with increasing soil sand content. Finally, soil heavy fraction carbon, inorganic carbon, and total carbon were drastically reduced when the soil sand content exceeded 80%. The three soil fertility thresholds along the gradient of the soil sand content indicated a sequence of dryland degradation phases. Our findings provide an approach for detecting the severity of dryland degradation and suggest vulnerable areas of degradation on the Tibetan Plateau.