Elucidating the response of soil nutrients to long-term drought can better predict the impact of climate change on the ecosystem of moso bamboo (Phyllostachys edulis）forest in the future, and can guide the production and management practice of bamboo forest.

This study measured and analyzed the response of soil organic carbon, total nitrogen, total phosphorus content and storage, as well as their stoichiometric characteristics, to no throughfall exclusion (CK) and long-term throughfall exclusion (DR) in bamboo forests using the “ceiling method” for rain interception.

The results showed that the average value of available phosphorus content, hydrolytic nitrogen and organic carbon content, as well as the average soil C/N and C/P values in the 0-50 cm soil layer of drought soil were significantly lower than those in the control soil (P<0.05). The total phosphorus content and average pH value of drought soil were slightly lower than those in the control, while the total nitrogen content and N/P value of soil were higher than those in the control. There was no significant difference in soil nutrient content between drought and control treatments in each soil layer of 0-10 cm, 10-30 cm, and 30-50 cm. The soil pH values in all drought soil layers were lower than those in the control, with the pH value in the 10-50 cm range being significantly lower than that of the control (P<0.05). The C/P value in the 10-30 cm drought soil layer and the C/N value in the 10-50 cm drought soil layer were significantly lower than those in the control (P<0.05), while the N/P value in the 30-50 cm soil layer was significantly higher than that in the control (P<0.05). Drought has increased the “surface aggregation” phenomenon of soil nutrient content and the chemical stoichiometry. The organic carbon storage and total phosphorus storage in the 0-50 cm soil layer under drought were lower than the control, while the total nitrogen storage in the soil was higher than the control. Relevant analysis shows that the pH value of the control soil is significantly positively correlated with organic carbon, total nitrogen, and total phosphorus storage (P<0.01), while the pH value of soil under drought stress is only significantly negatively correlated with C/N and significantly positively correlated with N/P. The total nitrogen, total phosphorus, and organic carbon content in soil under drought are significantly or extremely significantly positively correlated with N/P (P<0.05 or P<0.01), while the total phosphorus content is significantly negatively correlated with C/N (P<0.05).

The soil pH value, total phosphorus, and available phosphorus content are the main influencing factors of nitrogen and phosphorus balance in soils under drought.

This study aimed to investigate the temporal dynamics of biogenic volatile organic compounds (BVOCs) in four typical subtropical forest types, and to provide theoretical support for the development of forest therapy resources.

Mixed broadleaved forest, Phoebe forest, Chinese fir plantation, and Moso bamboo plantation were selected as study objects, and the composition and relative mass concentrations of major BVOCs were analyzed in May, August, and October, and their correlations with temperature, relative humidity, and air negative ions were examined.

The results showed that BVOCs exhibited the highest diversity in mixed broadleaved forest (79 species), compared to 69 species in other forest types. All four forest types released similar BVOCs components, predominantly alkanes, terpenes, and aldehydes (11-19 species each), with aromatic hydrocarbons and aldehydes being the most abundant (15%-35% of total emissions). Among the 19 terpenoid compounds detected, α-pinene was the dominant component. The mixed broadleaved forest showed significantly higher relative mass concentrations of terpenes than other forests, peaking in May. Both BVOCs diversity and relative mass concentrations displayed distinct seasonal patterns: the mixed broadleaved forest, Phoebe forest, and Chinese fir plantation showed maximum component richness in May and minimum in August, while the opposite trend was observed in moso bamboo plantation. Peak relative mass concentrations occurred in May and October for mixed broadleaved forest and Phoebe forest, but in August and October for Chinese fir plantation and moso bamboo plantation. Additionally, BVOCs emissions were primarily negatively correlated with temperature, relative humidity, and air negative ions.

Among the four subtropical forest types, the mixed broadleaved forest had the richest BVOCs composition and the highest relative concentrations of health-beneficial terpenes, particularly peaking in May. Therefore, forest therapy activities during this period may yield optimal therapeutic effects.

Solar radiation (SR) plays critical roles in plant physiological processes and ecosystems functions. However, the exploration of SR influences on the biogeochemical cycles of forest ecosystems is still in a slow progress, and has important implications for the understanding of plant adaption strategy under future environmental changes. Herein, this research was aimed to explore the influences of SR on plant nutrient characteristics, and provided theoretical basis for introducing SR into the establishment of biochemical models of forest ecosystems in the future researches.

We measured leaf nitrogen (N) and phosphorus (P) stoichiometry in 19 Chinese fir plantations across subtropical China by a field investigation. The direct and indirect effects of SR, including global radiation (Global R), direct radiation (Direct R) and diffuse radiation (Diffuse R) on the leaf N and P stoichiometry were investigated.

The linear regression analysis showed that leaf N concentration had no association with SR, while leaf P concentration and N: P ratio were negatively and positively related to SR, respectively. Partial least squares path model (PLS-PM) demonstrated that SR (e.g. Direct R and Diffuse R), as a latent variable, exhibited direct correlations with leaf N and P stoichiometry as well as the indirect correlation mediated by soil P content. The direct associations (path coefficient=−0.518) were markedly greater than indirect associations (path coefficient=−0.087). The covariance-based structural equation modeling (CB-SEM) indicated that SR had direct effects on leaf P concentration (path coefficient=−0.481), and weak effects on leaf N concentration. The high SR level elevated two temperature indexes (mean annual temperature, MAT; ≥ 10℃ annual accumulated temperature, ≥ 10℃ AAT) and one hydrological index (mean annual evapotranspiration, MAE), but lowered the soil P content. MAT, MAE and soil P content could affect the leaf P concentration, which cause the indirect effect of SR on leaf P concentration (path coefficient=0.004). Soil N content had positive effect on the leaf N concentration, which was positively and negatively regulated by MAP and≥10℃ AAT, respectively.

These results confirmed that SR had negatively direct and indirect impacts on plant nutrient status of Chinese fir based on a regional investigation, and the direct associations were greater than the indirect associations. Such findings shed light on the guideline of taking SR into account for the establishment of global biogeochemical models of forest ecosystems in the future studies.