Microclimatic Influences on Soil Nitrogen Dynamics and Plant Diversity Across Rocky Desertification Gradients in Southwest China

Abstract

Soil active nitrogen (N) fractions are essential for plant growth and nutrient cycling in terrestrial ecosystems. While previous studies have primarily focused on the impact of vegetation restoration on soil active nitrogen in karst ecosystems, the role of microclimate variation in rocky desertification areas has not been well explored. This study investigates soil active nitrogen fractions and key biotic and abiotic factors across four grades of rocky desertification-non-rocky desertification (NRD), light rocky desertification (LRD), moderate rocky desertification (MRD), and intense rocky desertification (IRD)-within two distinct microclimates: a dry-hot valley and a humid monsoon zone in the karst region of Guizhou Province, China. We evaluate soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), soil nitrate nitrogen (NO₃^--N), ammonium nitrogen (NH₄⁺-N), microbial biomass nitrogen (MBN), soluble organic nitrogen (SON), and plant diversity. Results showed that SOC, TN, and TP were significantly higher in IRD areas. Soil NO₃^--N, MBN, and SON initially decreased before increasing, with consistent MBN growth in the dry-hot valley. NH₄⁺-N did not differ significantly under NRD but was higher in the dry-hot valley under LRD, MRD, and IRD. The dry-hot valley had higher MBN and SON across most desertification grades. Microclimate significantly influenced soil active N, with higher levels in the dry-hot valley under LRD and MRD conditions. Plant diversity and regeneration varied markedly between the microclimates. In the dry-hot valley, Artemisia dominated herbaceous regeneration, especially in MRD areas. Conversely, the humid monsoon zone showed more diverse regeneration, with Artemisia and Bidens prevalent in MRD and NRD grades. Despite declining plant diversity with desertification, the humid monsoon zone displayed greater resilience. These findings highlight the role of microclimate in influencing soil nitrogen dynamics and plant regeneration across rocky desertification gradients, offering insights for restoration strategies in karst ecosystems.

Keywords: biodiversity; karst ecosystem; microclimate types; rocky desertification; soil active nitrogen.

Figure 1

Characteristics of soil active nitrogen in the dry-hot valley climate zone, with NH₄⁺-N concentration (a), NO₃-N concentration (b), MBN concentration (c) and SON concentration (d). Capital letters (A, B, C) indicate significant differences among the four grades of rocky desertification, while lowercase letters (a, b, c) indicate significant differences within the soil layers (A, B, and C). The figure shows soil NH₄⁺-N and NH₃-N concentrations, microbial biomass nitrogen (MBN), and soil organic nitrogen (SON) across three soil layers in four grades of rocky desertification; non-rocky desertification (NRD), light rocky desertification (LRD), moderate rocky desertification (MRD), and intense rocky desertification (IRD).

Figure 2

Characteristics of soil active nitrogen in the humid monsoon climate zone, with NH₄⁺-N concentration (a), NO₃-N concentration (b), MBN concentration (c) and SON concentration (d). Capital letters (A, B, C) indicate significant differences among the four grades of rocky desertification, while lowercase letters (a, b, c) indicate significant differences within the soil layers (A, B, and C). Figure shows soil ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NH₃-N) concentrations, soil microbial biomass nitrogen (MBN), and soil organic nitrogen (SON) across three soil layers in humid monsoon climate zones among the four grades of desertification; non-rocky desertification (NRD), light rocky desertification (LRD), moderate rocky desertification (MRD), and intense rocky desertification (IRD). Capital letters (A, B, C) indicate significant differences among the four levels of rocky desertification, while lower-case letters (a, b, c) indicate significant differences within the soil layers (A, B, and C).

Figure 3

Relationships between soil physicochemical properties and active nitrogen fractions in the two regions. The dry-hot valley climate zone (a) and the humid monsoon climate zone (b). Statistical significance is indicated as follows: *** p < 0.001, ** p < 0.01, and * p < 0.05.

Figure 4

The comparative analysis of soil active nitrogen fractions across different rocky desertification grades in the humid monsoon climate and the dry-hot valley climate region, with NH₄⁺-N concentration in NRD (a), LRD (b), MRD (c) and IRD (d), NO₃-N concentration in NRD (e), LRD (f), MRD (g) and IRD (h), MBN concentration in NRD (i), LRD (j), MRD (k) and IRD (l) and SON concentration in NRD (m), LRD (n), MRD (o) and IRD (p). Values with p ≤ 0.05 indicate significant difference, while NS indicates no significant difference (Wilcoxon signed-rank). DHV and HMC represent the dry-hot valley climate region and the humid monsoon climate region, respectively.